The properties of ultrathin polymer films are often different from their bulk counterparts. We use spin casting, Langmuir-Blodgett deposition, and surface grafting to fabricate ultrathin films in the range of 100 to 1000 Angstroms thick. Macromolecular amphiphiles are examined at the air-water interface by surface pressure, Brewster angle microscopy, and interfacial shear measurements and on solid substrates by atomic force microscopy, FTIR, and ellipsometry. A vapor-deposition-polymerization process has been developed for covalent grafting of poly(amino acids) from solid substrates. FTIR measurements permit study of secondary structures (right and left-handed alpha helices, parallel and anti-parallel beta sheets) as a function of temperature and environment.

A broadly interdisciplinary collaboration has been established with the Department of Ophthalmology in the Stanford School of Medicine. We have designed and synthesized a fully interpenetrating network of two different hydrogel materials that have properties consistent with application as a substitute for the human cornea: high water swellability up to 85%,tensile strength comparable to the cornea, high glucose permeability comparable to the cornea, and sufficient tear strength to permit suturing. We have developed a technique for surface modification with adhesion peptides that allows binding of collagen and subsequent growth of epithelial cells. Broad questions on the relationships among molecular structure, processing protocol, and biomedical device application are being pursued.

Academic Appointments

Honors & Awards

  • Principal Investigator, National Science Foundation
  • CMA Stine Award, American Institute of Chemical Engineers
  • Fellow, American Physical Society

Professional Education

  • PhD, University of Illinois (1972)

2014-15 Courses

All Publications

  • Scientific Delirium Madness LEONARDO Knight, M. H., Jacobs, C. D., Frank, C. W., Sternberg, D., Petrenko, S., Tromble, M., Sumner, D., Sundaralingam, P. 2015; 48 (3): 219-225
  • Tunable mesoscale-structured self-assembled hydrogels synthesized by organocatalytic ring-opening polymerization POLYMER Fox, C. H., Engler, A. C., Toney, M. F., Hedrick, J. L., Frank, C. W. 2015; 65: 93-104
  • A Semi-Interpenetrating Network Approach for Dimensionally Stabilizing Highly-Charged Anion Exchange Membranes for Alkaline Fuel Cells CHEMSUSCHEM He, S. S., Strickler, A. L., Frank, C. W. 2015; 8 (8): 1472-1483


    There is a delicate balance between ion exchange capacity (IEC), conductivity, and dimensional stability in anion exchange membranes as higher charge content can lead to increased water uptake, causing excessive swelling and charge dilution. Using highly-charged benzyltrimethylammonium polysulfone (IEC=2.99 mEq g(-1) ) as a benchmark (which ruptured in water even at room temperature), we report the ability to dramatically decrease water uptake using a semi-interpenetrating network wherein we reinforced the linear polyelectrolyte with a crosslinked poly(styrene-co-divinylbenzene) network. These membranes show enhanced dimensional stability as a result of lower water uptake (75 % vs. 301 % at 25 °C) while maintaining excellent hydroxide conductivity (up to 50 mS cm(-1) at 25 °C). These improvements produced an enhanced alkaline fuel cell capable of generating 236 mW cm(-2) peak power density at 80 °C. This method is easily adaptable and can be a viable strategy for stabilizing existing systems.

    View details for DOI 10.1002/cssc.201500133

    View details for Web of Science ID 000353511400020

    View details for PubMedID 25820199

  • Effects of Aromatic Regularity on the Structure and Conductivity of Polyimide-Poly(ethylene glycol) Materials Doped with Ionic Liquid JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS Coletta, E., Toney, M. F., Frank, C. W. 2015; 53 (7): 509-521

    View details for DOI 10.1002/polb.23664

    View details for Web of Science ID 000351092000006

  • Organocatalytic Ring-Opening Polymerization of Trimethylene Carbonate To Yield a Biodegradable Polycarbonate JOURNAL OF CHEMICAL EDUCATION Chan, J. M., Zhang, X., Brennan, M. K., Sardon, H., Engler, A. C., Fox, C. H., Frank, C. W., Waymouth, R. M., Hedrick, J. L. 2015; 92 (4): 708-713

    View details for DOI 10.1021/ed500595k

    View details for Web of Science ID 000353368000023

  • Influences of liquid electrolyte and polyimide identity on the structure and conductivity of polyimide-poly(ethylene glycol) materials JOURNAL OF APPLIED POLYMER SCIENCE Coletta, E., Toney, M. F., Frank, C. W. 2015; 132 (12)

    View details for DOI 10.1002/app.41675

    View details for Web of Science ID 000346580600012

  • Phosphatidylinositol 4,5-Bisphosphate Is an HCV NS5A Ligand and Mediates Replication of the Viral Genome. Gastroenterology Cho, N., Lee, C., Pang, P. S., Pham, E. A., Fram, B., Nguyen, K., Xiong, A., Sklan, E. H., Elazar, M., Koytak, E. S., Kersten, C., Kanazawa, K. K., Frank, C. W., Glenn, J. S. 2015; 148 (3): 616-625


    Phosphoinositides (PIs) bind and regulate localization of proteins via a variety of structural motifs. PI 4,5-bisphosphate (PI[4,5]P2) interacts with and modulates the function of several proteins involved in intracellular vesicular membrane trafficking. We investigated interactions between PI(4,5)P2 and hepatitis C virus (HCV) nonstructural protein 5A (NS5A) and effects on the viral life cycle.We used a combination of quartz crystal microbalance, circular dichroism, molecular genetics, and immunofluorescence to study specific binding of PI(4,5)P2 by the HCV NS5A protein. We evaluated the effects of PI(4,5)P2 on the function of NS5A by expressing wild-type or mutant forms of Bart79I or FL-J6/JFH-5'C19Rluc2AUbi21 RNA in Huh7 cells. We also studied the effects of strategies designed to inhibit PI(4,5)P2 on HCV replication in these cells.The N-terminal amphipathic helix of NS5A bound specifically to PI(4,5)P2, inducing a conformational change that stabilized the interaction between NS5A and TBC1D20, which is required for HCV replication. A pair of positively charged residues within the amphipathic helix (the basic amino acid PI(4,5)P2 pincer domain) was required for PI(4,5)P2 binding and replication of the HCV-RNA genome. A similar motif was found to be conserved across all HCV isolates, as well as amphipathic helices of many pathogens and apolipoproteins.PI(4,5)P2 binds to HCV NS5A to promote replication of the viral RNA genome in hepatocytes. Strategies to disrupt this interaction might be developed to inhibit replication of HCV and other viruses.

    View details for DOI 10.1053/j.gastro.2014.11.043

    View details for PubMedID 25479136

  • A Simple Method for Encapsulating Single Cells in Alginate Microspheres Allows for Direct PCR and Whole Genome Amplification PLOS ONE Bigdeli, S., Dettloff, R. O., Frank, C. W., Davis, R. W., Crosby, L. D. 2015; 10 (2)


    Microdroplets are an effective platform for segregating individual cells and amplifying DNA. However, a key challenge is to recover the contents of individual droplets for downstream analysis. This paper offers a method for embedding cells in alginate microspheres and performing multiple serial operations on the isolated cells. Rhodobacter sphaeroides cells were diluted in alginate polymer and sprayed into microdroplets using a fingertip aerosol sprayer. The encapsulated cells were lysed and subjected either to conventional PCR, or whole genome amplification using either multiple displacement amplification (MDA) or a two-step PCR protocol. Microscopic examination after PCR showed that the lumen of the occupied microspheres contained fluorescently stained DNA product, but multiple displacement amplification with phi29 produced only a small number of polymerase colonies. The 2-step WGA protocol was successful in generating fluorescent material, and quantitative PCR from DNA extracted from aliquots of microspheres suggested that the copy number inside the microspheres was amplified up to 3 orders of magnitude. Microspheres containing fluorescent material were sorted by a dilution series and screened with a fluorescent plate reader to identify single microspheres. The DNA was extracted from individual isolates, re-amplified with full-length sequencing adapters, and then a single isolate was sequenced using the Illumina MiSeq platform. After filtering the reads, the only sequences that collectively matched a genome in the NCBI nucleotide database belonged to R. sphaeroides. This demonstrated that sequencing-ready DNA could be generated from the contents of a single microsphere without culturing. However, the 2-step WGA strategy showed limitations in terms of low genome coverage and an uneven frequency distribution of reads across the genome. This paper offers a simple method for embedding cells in alginate microspheres and performing PCR on isolated cells in common bulk reactions, although further work must be done to improve the amplification coverage of single genomes.

    View details for DOI 10.1371/journal.pone.0117738

    View details for Web of Science ID 000350322700069

    View details for PubMedID 25689864

  • Interpenetrating polymer network hydrogel scaffolds for artificial cornea periphery. Journal of materials science. Materials in medicine Parke-Houben, R., Fox, C. H., Zheng, L. L., Waters, D. J., Cochran, J. R., Ta, C. N., Frank, C. W. 2015; 26 (2): 5442-?


    Three-dimensional scaffolds based on inverted colloidal crystals (ICCs) were fabricated from sequentially polymerized interpenetrating polymer network (IPN) hydrogels of poly(ethyleneglycol) and poly(acrylic acid). This high-strength, high-water-content IPN hydrogel may be suitable for use in an artificial cornea application. Development of a highly porous, biointegrable region at the periphery of the artificial cornea device is critical to long-term retention of the implant. The ICC fabrication technique produced scaffolds with well-controlled, tunable pore and channel dimensions. When surface functionalized with extracellular matrix proteins, corneal fibroblasts were successfully cultured on IPN hydrogel scaffolds, demonstrating the feasibility of these gels as materials for the artificial cornea porous periphery. Porous hydrogels with and without cells were visualized non-invasively in the hydrated state using variable-pressure scanning electron microscopy.

    View details for DOI 10.1007/s10856-015-5442-2

    View details for PubMedID 25665845

  • Supramolecular motifs in dynamic covalent PEG-hemiaminal organogels. Nature communications Fox, C. H., Ter Hurrne, G. M., Wojtecki, R. J., Jones, G. O., Horn, H. W., Meijer, E. W., Frank, C. W., Hedrick, J. L., García, J. M. 2015; 6: 7417-?


    Dynamic covalent materials are stable materials that possess reversible behaviour triggered by stimuli such as light, redox conditions or temperature; whereas supramolecular crosslinks depend on the equilibrium constant and relative concentrations of crosslinks as a function of temperature. The combination of these two reversible chemistries can allow access to materials with unique properties. Here, we show that this combination of dynamic covalent and supramolecular chemistry can be used to prepare organogels comprising distinct networks. Two materials containing hemiaminal crosslink junctions were synthesized; one material is comprised of dynamic covalent junctions and the other contains hydrogen-bonding bis-hemiaminal moieties. Under specific network synthesis conditions, these materials exhibited self-healing behaviour. This work reports on both the molecular-level detail of hemiaminal crosslink junction formation as well as the macroscopic behaviour of hemiaminal dynamic covalent network (HDCN) elastomeric organogels. These materials have potential applications as elastomeric components in printable materials, cargo carriers and adhesives.

    View details for DOI 10.1038/ncomms8417

    View details for PubMedID 26174864

  • Impacts of polymer-polymer interactions and interfaces on the structure and conductivity of PEG-containing polyimides doped with ionic liquid POLYMER Coletta, E., Toney, M. Y., Frank, C. W. 2014; 55 (26): 6883-6895
  • Increasing Cell Homogeneity of Semicrystalline, Biodegradable Polymer Foams With a Narrow Processing Window via Rapid Quenching POLYMER ENGINEERING AND SCIENCE Wright, Z. C., Frank, C. W. 2014; 54 (12): 2877-2886

    View details for DOI 10.1002/pen.23847

    View details for Web of Science ID 000344594300021

  • Comparison of anhydrous and monohydrated forms of orotic acid as crystal nucleating agents for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) POLYMER Tsui, A., Frank, C. W. 2014; 55 (24): 6364-6372
  • Prediction of Gas Solubility in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Melt to Inform Process Design and Resulting Foam Microstructure POLYMER ENGINEERING AND SCIENCE Tsui, A., Wright, Z., Frank, C. W. 2014; 54 (11): 2683-2695

    View details for DOI 10.1002/pen.23822

    View details for Web of Science ID 000343798500027

  • Facilitating hydroxide transport in anion exchange membranes via hydrophilic grafts JOURNAL OF MATERIALS CHEMISTRY A He, S. S., Frank, C. W. 2014; 2 (39): 16489-16497

    View details for DOI 10.1039/c4ta02942a

    View details for Web of Science ID 000342880200022

  • Impact of Processing Temperature and Composition on Foaming of Biodegradable Poly(hydroxyalkanoate) Blends INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH Tsui, A., Frank, C. W. 2014; 53 (41): 15896-15908

    View details for DOI 10.1021/ie5021766

    View details for Web of Science ID 000343277100013

  • Directed Axonal Outgrowth Using a Propagating Gradient of IGF-1. Advanced materials Lee, W., Frank, C. W., Park, J. 2014; 26 (29): 4936-4940


    The temporospatial regulation of axon outgrowth is useful for guiding de novo connectivity or re-connectivity of neurons in neurological injury or disease. Here we report the successful construction of a biocompatible guidance device, in which a linear propagation of IGF-1 gradient sequentially directs axon outgrowth. We observe the extensive in vitro axonal extension over 5 mm with a desired growth rate of ∼1 mm/day.

    View details for DOI 10.1002/adma.201305995

    View details for PubMedID 24664530

  • Vesicle Adhesion and Rupture on Silicon Oxide: Influence of Freeze-Thaw Pretreatment LANGMUIR Jackman, J. A., Zhao, Z., Zhdanov, V. P., Frank, C. W., Cho, N. 2014; 30 (8): 2152-2160


    We have investigated the effect of freeze-thaw (FT) pretreatment on the adhesion and rupture of extruded vesicles over a wide range of vesicle sizes. To characterize the size distributions of vesicles obtained with and without FT pretreatment, dynamic light scattering (DLS) experiments were performed. The interaction between extruded vesicles and a silicon oxide substrate was investigated by quartz crystal microbalance with dissipation (QCM-D) monitoring, with a focus on comparative analysis of similar-sized vesicles with and without FT pretreatment. Under this condition, there was a smaller mass load at the critical coverage associated with untreated vesicles, as compared to vesicles which had been subjected to FT pretreatment. In addition, the rupture of treated vesicles generally resulted in formation of a complete planar bilayer, while the adlayer was more heterogeneous when employing untreated vesicles. Combined with kinetic analysis and extended-DLVO model calculations, the experimental evidence suggests that the differences arising from FT pretreatment are due to characteristics of the vesicle size distribution and also multilamellarity of an appreciable fraction of untreated vesicles. Taken together, our findings clarify the influence of FT pretreatment on model membrane fabrication on solid supports.

    View details for DOI 10.1021/la404582n

    View details for Web of Science ID 000332494000029

    View details for PubMedID 24512463

  • Grafting of Cross-Linked Hydrogel Networks to Titanium Surfaces ACS APPLIED MATERIALS & INTERFACES Muir, B. V., Myung, D., Knoll, W., Frank, C. W. 2014; 6 (2): 958-966


    The performance of medical implants and devices is dependent on the biocompatibility of the interfacial region between tissue and the implant material. Polymeric hydrogels are attractive materials for use as biocompatible surface coatings for metal implants. In such systems, a factor that is critically important for the longevity of an implant is the formation of a robust bond between the hydrogel layer and the implant metal surface and the ability for this assembly to withstand physiological conditions. Here, we describe the grafting of cross-linked hydrogel networks to titanium surfaces using grit-blasting and subsequent chemical functionalization using a silane-based adhesion promoter. Metal surface characterization was carried out using profilometry, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analysis. Hydrogel layers composed of poly(ethylene glycol)-dimethacrylate (PEG-DMA), poly(2-hydroxyethylmethacrylate) (PHEMA), or poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) semi-interpenetrating polymer networks (semi-IPNs) have been prepared. The mechanical properties of these hydrogel-metal assemblies have been characterized using lap-shear measurements, and the surface morphology was studied by SEM and EDX. We have shown that both high surface roughness and chemical functionalization are critical for adhesion of the hydrogel layer to the titanium substrate.

    View details for DOI 10.1021/am404361v

    View details for Web of Science ID 000330201900031

    View details for PubMedID 24364560

  • Enhanced particle removal using viscoelastic fluids JOURNAL OF RHEOLOGY Walker, T. W., Hsu, T. T., FitzGibbon, S., Frank, C. W., Mui, D. S., Zhu, J., Mendiratta, A., Fuller, G. G. 2014; 58 (1): 63-88

    View details for DOI 10.1122/1.4832637

    View details for Web of Science ID 000329357400003

  • Instabilities and elastic recoil of the two-fluid circular hydraulic jump EXPERIMENTS IN FLUIDS Hsu, T. T., Walker, T. W., Frank, C. W., Fuller, G. G. 2014; 55 (1)
  • A Renewable Lignin-Lactide Copolymer and Application in Biobased Composites ACS SUSTAINABLE CHEMISTRY & ENGINEERING Chung, Y., Olsson, J. V., Li, R. J., Frank, C. W., Waymouth, R. M., Billington, S. L., Sattely, E. S. 2013; 1 (10): 1231-1238

    View details for DOI 10.1021/sc4000835

    View details for Web of Science ID 000325512000004

  • Comparison of Extruded and Sonicated Vesicles for Planar Bilayer Self-Assembly MATERIALS Cho, N., Hwang, L. Y., Solandt, J. J., Frank, C. W. 2013; 6 (8): 3294-3308

    View details for DOI 10.3390/ma6083294

    View details for Web of Science ID 000330293100017

  • Antibody conjugated supported lipid bilayer for capturing and purification of viable tumor cells in blood for subsequent cell culture BIOMATERIALS Wu, J., Tseng, P., Tsai, W., Liao, M., Lu, S., Frank, C. W., Chen, J., Wu, H., Chang, Y. 2013; 34 (21): 5191-5199


    Interest in the identification and isolation of circulating tumor cells (CTCs) has been growing since the introduction of CTCs as an alternative to the tumor tissue biopsy, which can potentially be important indices for prognosis and cancer treatment. However, the contamination of non-specific binding of normal hematologic cells makes high purity CTCs detection problematic. Furthermore, preserving the viability of CTCs remains a challenge. In this study, we proposed to construct an anti-EpCAM functionalized supported lipid bilayer (SLB), a biomimetic and non-fouling membrane coating, for CTCs capturing, purification and maintaining the viability. Healthy human blood spiked with pre-stained colorectal cancer cell lines, HCT116 and colo205, were used to investigate interaction of cells with the anti-EpCAM functionalized SLB surfaces. Over 97% of HCT116, and 72% of colo205 were captured and adhered by the surface anti-EpCAM; conversely, the majority of blood cells were easily removed by gentle buffer exchange, with the overall purity of cancer cells exceeding 95%. The bound cancer cells were subsequently detached for cell culture. Both HCT116 and colo205 continued to proliferate over 2-week observation period, indicating that the anti-EpCAM functionalized SLB platform providing a simple strategy for capturing, purifying, and releasing viable targeted rare cells.

    View details for DOI 10.1016/j.biomaterials.2013.03.096

    View details for Web of Science ID 000319630000028

    View details for PubMedID 23615560

  • In vivo biocompatibility of two PEG/PAA interpenetrating polymer networks as corneal inlays following deep stromal pocket implantation JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE Tan, X. W., Hartman, L., Tan, K. P., Poh, R., Myung, D., Zheng, L. L., Waters, D., Noolandi, J., Beuerman, R. W., Frank, C. W., Ta, C. N., Tan, D. T., Mehta, J. S. 2013; 24 (4): 967-977


    This study compared the effects of implanting two interpenetrating polymer networks (IPNs) into rabbit corneas. The first (Implant 1) was based on PEG-diacrylate, the second (Implant 2) was based on PEG-diacrylamide. There were inserted into deep stromal pockets created using a manual surgical technique for either 3 or 6 months. The implanted corneas were compared with normal and sham-operated corneas through slit lamp observation, anterior segment optical coherence tomography, in vivo confocal scanning and histological examination. Corneas with Implant 1 (based on PEG-diacrylate) developed diffuse haze, ulcers and opacities within 3 months, while corneas with Implant 2 (based on PEG-diacrylamide) remained clear at 6 months. They also exhibited normal numbers of epithelial cell layers, without any immune cell infiltration, inflammation, oedema or neovascularisation at post-operative 6 month. Morphological studies showed transient epithelial layer thinning over the hydrogel inserted area and elevated keratocyte activity at 3 months; however, the epithelium thickness and keratocyte morphology were improved at 6 months. Implant 2 exhibited superior in vivo biocompatibility and higher optical clarity than Implant 1. PEG-diacrylamide-based IPN hydrogel is therefore a potential candidate for corneal inlays to correct refractive error.

    View details for DOI 10.1007/s10856-012-4848-3

    View details for Web of Science ID 000318509100013

    View details for PubMedID 23354737

  • Biodegradable Polyesters from Renewable Resources ANNUAL REVIEW OF CHEMICAL AND BIOMOLECULAR ENGINEERING, VOL 4 Tsui, A., Wright, Z. C., Frank, C. W. 2013; 4: 143-?


    Environmental concerns have led to the development of biorenewable polymers with the ambition to utilize them at an industrial scale. Poly(lactic acid) and poly(hydroxyalkanoates) are semicrystalline, biorenewable polymers that have been identified as the most promising alternatives to conventional plastics. However, both are inherently susceptible to brittleness and degradation during thermal processing; we discuss several approaches to overcome these problems to create a balance between durability and biodegradability. For example, copolymers and blends can increase ductility and the thermal-processing window. Furthermore, chain modifications (e.g., branching/crosslinking), processing techniques (fiber drawing/annealing), or additives (plasticizers/nucleating agents) can improve mechanical properties and prevent thermal degradation during processing. Finally, we examine the impacts of morphology on end-of-life degradation to complete the picture for the most common renewable polymers.

    View details for DOI 10.1146/annurev-chembioeng-061312-103323

    View details for Web of Science ID 000321740100008

    View details for PubMedID 23540287

  • Biodegradable Films and Foam of Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate) Blended with Silk Fibroin GREEN POLYMER CHEMISTRY: BIOCATALYSIS AND MATERIALS II Tsui, A., Hu, X., Kaplan, D. L., Frank, C. W. 2013; 1144: 251-279
  • Characterizing the effects of ambient aging on the mechanical and physical properties of two commercially available bacterial thermoplastics Srubar, W. V., Wright, Z. C., Tsui, A., Michel, A. T., Billington, S. L., Frank, C. W. ELSEVIER SCI LTD. 2012: 1922-1929
  • Role of shear-thinning on the dynamics of rinsing flow by an impinging jet PHYSICS OF FLUIDS Walker, T. W., Hsu, T. T., Frank, C. W., Fuller, G. G. 2012; 24 (9)

    View details for DOI 10.1063/1.4752765

    View details for Web of Science ID 000309425800022

  • Extruded foams from microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and its blends with cellulose acetate butyrate POLYMER ENGINEERING AND SCIENCE Liao, Q., Tsui, A., Billington, S., Frank, C. W. 2012; 52 (7): 1495-1508

    View details for DOI 10.1002/pen.23087

    View details for Web of Science ID 000305473100012

  • Modeling the kinetics of water transport and hydroexpansion in a lignocellulose-reinforced bacterial copolyester POLYMER Srubar, W. V., Frank, C. W., Billington, S. L. 2012; 53 (11): 2152-2161
  • Mechanisms and impact of fiber-matrix compatibilization techniques on the material characterization of PHBV/oak wood flour engineered biobased composites COMPOSITES SCIENCE AND TECHNOLOGY Srubar, W. V., Pilla, S., Wright, Z. C., Ryan, C. A., Greene, J. P., Frank, C. W., Billington, S. L. 2012; 72 (6): 708-715
  • Antibody Adsorption and Orientation on Hydrophobic Surfaces LANGMUIR Wiseman, M. E., Frank, C. W. 2012; 28 (3): 1765-1774


    The orientation of a monoclonal, anti-streptavidin human IgG1 antibody on a model hydrophobic, CH(3)-terminated surface (1-dodecanethiol self-assembled monolayer on gold) was studied by monitoring the mechanical coupling between the adsorbed layer and the surface as well as the binding of molecular probes to the antibodies. In this study, the streptavidin antigen was used as a probe for the Fab portions of the antibody, while bacteria-derived Protein G' was used as a probe for the Fc region. Bovine serum albumin (BSA) acted as a blocking protein. Monolayer coverage occurred around 468 ng/cm(2). Below 100 ng/cm(2), antibodies were found to adsorb flat-on, tightly coupled to the surface and unable to capture their antigen, whereas the Fc region was able to bind Protein G'. At half-monolayer coverage, there was a transition in the mechanism of adsorption to allow for vertically oriented antibodies, as evidenced by the binding of both Protein G' and streptavidin as well as looser mechanical coupling with the surface. Monolayer coverage was characterized by a reduced level in probe binding per antibody and an even less rigid coupling to the surface.

    View details for DOI 10.1021/la203095p

    View details for Web of Science ID 000299366500015

    View details for PubMedID 22181558

  • Meso-ordered soft hydrogels SOFT MATTER Claesson, M., Engberg, K., Frank, C. W., Andersson, M. 2012; 8 (31): 8149-8156

    View details for DOI 10.1039/c2sm26226f

    View details for Web of Science ID 000306527800018

  • Competitive swelling forces and interpolymer complexation in pH- and temperature-sensitive interpenetrating network hydrogels SOFT MATTER Kelmanovich, S. G., Parke-Houben, R., Frank, C. W. 2012; 8 (31): 8137-8148

    View details for DOI 10.1039/c2sm25389e

    View details for Web of Science ID 000306527800017

  • Diffusion of Protein through the Human Cornea OPHTHALMIC RESEARCH Charalel, R. A., Engberg, K., Noolandi, J., Cochran, J. R., Frank, C., Ta, C. N. 2012; 48 (1): 50-55


    To determine the rate of diffusion of myoglobin and bovine serum albumin (BSA) through the human cornea. These small proteins have hydrodynamic diameters of approximately 4.4 and 7.2 nm, and molecular weights of 16.7 and 66 kDa, for myoglobin and BSA, respectively.Diffusion coefficients were measured using a diffusion chamber where the protein of interest and balanced salt solution were in different chambers separated by an ex vivo human cornea. Protein concentrations in the balanced salt solution chamber were measured over time. Diffusion coefficients were calculated using equations derived from Fick's law and conservation of mass in a closed system.Our experiments demonstrate that the diffusion coefficient of myoglobin is 5.5 ± 0.9 × 10(-8) cm(2)/s (n = 8; SD = 1.3 × 10(-8) cm(2)/s; 95% CI: 4.6 × 10(-8) to 6.4 × 10(-8) cm(2)/s) and the diffusion coefficient of BSA is 3.1 ± 1.0 × 10(-8) cm(2)/s (n = 8; SD = 1.4 × 10(-8) cm(2)/s; 95% CI: 2.1 × 10(-8) to 4.1 × 10(-8) cm(2)/s).Our study suggests that molecules as large as 7.2 nm may be able to passively diffuse through the human cornea. With applications in pharmacotherapy and the development of an artificial cornea, further experiments are warranted to fully understand the limits of human corneal diffusion and its clinical relevance.

    View details for DOI 10.1159/000329794

    View details for Web of Science ID 000305551100009

    View details for PubMedID 22398578

  • Star polymers with random number of temperature sensitive arms and crosslinked poly(EGDMA)-core and their application to drug delivery REACTIVE & FUNCTIONAL POLYMERS Alvarez-Sanchez, J., Licea-Claverie, A., Cornejo-Bravo, J. M., Frank, C. W. 2011; 71 (11): 1077-1088
  • Protein diffusion in photopolymerized poly(ethylene glycol) hydrogel networks BIOMEDICAL MATERIALS Engberg, K., Frank, C. W. 2011; 6 (5)


    In this study, protein diffusion through swollen hydrogel networks prepared from end-linked poly(ethylene glycol)-diacrylate (PEG-DA) was investigated. Hydrogels were prepared via photopolymerization from PEG-DA macromonomer solutions of two molecular weights, 4600 Da and 8000 Da, with three initial solid contents: 20, 33 and 50 wt/wt% PEG. Diffusion coefficients for myoglobin traveling across the hydrogel membrane were determined for all PEG network compositions. The diffusion coefficient depended on PEG molecular weight and initial solid content, with the slowest diffusion occurring through lower molecular weight, high-solid-content networks (D(gel) = 0.16 ± 0.02 × 10(-8) cm(2) s(-1)) and the fastest diffusion occurring through higher molecular weight, low-solid-content networks (D(gel) = 11.05 ± 0.43 × 10(-8) cm(2) s(-1)). Myoglobin diffusion coefficients increased linearly with the increase of water content within the hydrogels. The permeability of three larger model proteins (horseradish peroxidase, bovine serum albumin and immunoglobulin G) through PEG(8000) hydrogel membranes was also examined, with the observation that globular molecules as large as 10.7 nm in hydrodynamic diameter can diffuse through the PEG network. Protein diffusion coefficients within the PEG hydrogels ranged from one to two orders of magnitude lower than the diffusion coefficients in free water. Network defects were determined to be a significant contributing factor to the observed protein diffusion.

    View details for DOI 10.1088/1748-6041/6/5/055006

    View details for Web of Science ID 000295035500006

    View details for PubMedID 21873762

  • Structure and Mechanism of Strength Enhancement in Interpenetrating Polymer Network Hydrogels MACROMOLECULES Waters, D. J., Engberg, K., Parke-Houben, R., Ta, C. N., Jackson, A. J., Toney, M. F., Frank, C. W. 2011; 44 (14): 5776-5787

    View details for DOI 10.1021/ma200693e

    View details for Web of Science ID 000292850100030

  • Toward the development of an artificial cornea: improved stability of interpenetrating polymer networks. Journal of biomedical materials research. Part B, Applied biomaterials Hartmann, L., Watanabe, K., Zheng, L. L., Kim, C., Beck, S. E., Huie, P., Noolandi, J., Cochran, J. R., Ta, C. N., Frank, C. W. 2011; 98 (1): 8-17


    A novel interpenetrating network (IPN) based on poly(ethylene glycol) (PEG) and poly(acrylic acid) was developed and its use as an artificial cornea was evaluated in vivo. The in vivo results of a first set of corneal inlays based on PEG-diacrylate precursor showed inflammation of the treated eyes and haze in the corneas. The insufficient biocompatibility could be correlated to poor long-term stability of the implant caused by hydrolytic degradation over time. Adapting the hydrogel chemistry by replacing hydrolysable acrylate functionalities with stable acrylamide functionalities was shown to increase the long-term stability of the resulting IPNs under hydrolytic conditions. This new set of hydrogel implants now shows increased biocompatibility in vivo. Rabbits with corneal inlay implants are healthy and have clear cornea and non-inflamed eyes for up to 6 months after implantation.

    View details for DOI 10.1002/jbm.b.31806

    View details for PubMedID 21504051

  • pH-Driven Assembly of Various Supported Lipid Platforms: A Comparative Study on Silicon Oxide and Titanium Oxide LANGMUIR Cho, N., Jackman, J. A., Liu, M., Frank, C. W. 2011; 27 (7): 3739-3748


    Supported lipid platforms are versatile cell membrane mimics whose structural properties can be tailored to suit the application of interest. By identifying parameters that control the self-assembly of these platforms, there is potential to develop advanced biomimetic systems that overcome the surface specificity of lipid vesicle interactions under physiological conditions. In this work, we investigated the adsorption kinetics of vesicles onto silicon and titanium oxides as a function of pH. On each substrate, a planar bilayer and a layer of intact vesicles could be self-assembled in a pH-dependent manner, demonstrating the role of surface charge density in the self-assembly process. Under acidic pH conditions where both zwitterionic lipid vesicles and the oxide films possess near-neutral electric surface charges, vesicle rupture could occur, demonstrating that the process is driven by nonelectrostatic interactions. However, we observed that the initial rupturing process is insufficient for propagating bilayer formation. The role of electrostatic interactions for propagating bilayer formation differs for the two substrates; electrostatic attraction between vesicles and the substrate is necessary for complete bilayer formation on titanium oxide but is not necessary on silicon oxide. Conversely, in the high pH regime, repulsive electrostatic interactions can result in the irreversible adsorption of intact vesicles on silicon oxide and even a reversibly adsorbed vesicle layer on titanium oxide. Together, the results show that pH is an effective tool to modulate vesicle-substrate interactions in order to create various self-assembled lipid platforms on hydrophilic substrates.

    View details for DOI 10.1021/la104348f

    View details for Web of Science ID 000288970900068

    View details for PubMedID 21366275

  • Role of fluid elasticity on the dynamics of rinsing flow by an impinging jet PHYSICS OF FLUIDS Hsu, T. T., Walker, T. W., Frank, C. W., Fuller, G. G. 2011; 23 (3)

    View details for DOI 10.1063/1.3567215

    View details for Web of Science ID 000289153000015

  • Anaerobic biodegradation of the microbial copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate): Effects of comonomer content, processing history, and semi-crystalline morphology POLYMER Morse, M., Liao, Q., Criddle, C. S., Frank, C. W. 2011; 52 (2): 547-556
  • Interfacial Biocatalysis on Charged and Immobilized Substrates: The Roles of Enzyme and Substrate Surface Charge LANGMUIR Feller, B. E., Kellis, J. T., Cascao-Pereira, L. G., Robertson, C. R., Frank, C. W. 2011; 27 (1): 250-263


    An enzyme charge ladder was used to examine the role of electrostatic interactions involved in biocatalysis at the solid-liquid interface. The reactive substrate consisted of an immobilized bovine serum albumin (BSA) multilayer prepared using a layer-by-layer technique. The zeta potential of the BSA substrate and each enzyme variant was measured to determine the absolute charge in solution. Enzyme adsorption and the rate of substrate surface hydrolysis were monitored for the enzyme charge ladder series to provide information regarding the strength of the enzyme-substrate interaction and the rate of interfacial biocatalysis. First, each variant of the charge ladder was examined at pH 8 for various solution ionic strengths. We found that for positively charged variants the adsorption increased with the magnitude of the charge until the surface became saturated. For higher ionic strength solutions, a greater positive enzyme charge was required to induce adsorption. Interestingly, the maximum catalytic rate was not achieved at enzyme saturation but at an invariable intermediate level of adsorption for each ionic strength value. Furthermore, the maximum achievable reaction rate for the charge ladder was larger for higher ionic strength values. We propose that diffusion plays an important role in interfacial biocatalysis, and for strong enzyme-substrate interaction, the rate of diffusion is reduced, leading to a decrease in the overall reaction rate. We investigated the effect of substrate charge by varying the solution pH from 6.1 to 8.7 and by examining multiple ionic strength values for each pH. The same intermediate level of adsorption was found to maximize the overall reaction rate. However, the ionic strength response of the maximum achievable rate was clearly dependent on the pH of the experiment. We propose that this observation is not a direct effect of pH but is caused by the change in substrate surface charge induced by changing the pH. To prove this hypothesis, BSA substrates were chemically modified to reduce the magnitude of the negative charge at pH 8. Chemical modification was accomplished by the amidation of aspartic and glutamic acids to asparagine and glutamine. The ionic strength response of the chemically modified substrate was considerably different than that for the native BSA substrate at an identical pH, consistent with the trend based on substrate surface charge. Consequently, for substrates with a low net surface charge, the maximum achievable catalytic rate of the charge ladder was relatively independent of the solution ionic strength over the range examined; however, at high net substrate surface charge, the maximum rate showed a considerable ionic strength dependence.

    View details for DOI 10.1021/la103079t

    View details for Web of Science ID 000285560400034

    View details for PubMedID 21128607

  • The Role of Electrostatic Interactions in Protease Surface Diffusion and the Consequence for Interfacial Biocatalysis LANGMUIR Feller, B. E., Kellis, J. T., Cascao-Pereira, L. G., Robertson, C. R., Frank, C. W. 2010; 26 (24): 18916-18925


    This study examines the influence of electrostatic interactions on enzyme surface diffusion and the contribution of diffusion to interfacial biocatalysis. Surface diffusion, adsorption, and reaction were investigated on an immobilized bovine serum albumin (BSA) multilayer substrate over a range of solution ionic strength values. Interfacial charge of the enzyme and substrate surface was maintained by performing the measurements at a fixed pH; therefore, electrostatic interactions were manipulated by changing the ionic strength. The interfacial processes were investigated using a combination of techniques: fluorescence recovery after photobleaching, surface plasmon resonance, and surface plasmon fluorescence spectroscopy. We used an enzyme charge ladder with a net charge ranging from -2 to +4 with respect to the parent to systematically probe the contribution of electrostatics in interfacial enzyme biocatalysis on a charged substrate. The correlation between reaction rate and adsorption was determined for each charge variant within the ladder, each of which displayed a maximum rate at an intermediate surface concentration. Both the maximum reaction rate and adsorption value at which this maximum rate occurs increased in magnitude for the more positive variants. In addition, the specific enzyme activity increased as the level of adsorption decreased, and for the lowest adsorption values, the specific enzyme activity was enhanced compared to the trend at higher surface concentrations. At a fixed level of adsorption, the specific enzyme activity increased with positive enzyme charge; however, this effect offers diminishing returns as the enzyme becomes more highly charged. We examined the effect of electrostatic interactions on surface diffusion. As the binding affinity was reduced by increasing the solution ionic strength, thus weakening electrostatic interaction, the rate of surface diffusion increased considerably. The enhancement in specific activity achieved at the lowest adsorption values is explained by the substantial rise in surface diffusion at high ionic strength due to decreased interactions with the surface. Overall, knowledge of the electrostatic interactions can be used to control surface parameters such as surface concentration and surface diffusion, which intimately correlate with surface biocatalysis. We propose that the maximum reaction rate results from a balance between adsorption and surface diffusion. The above finding suggests enzyme engineering and process design strategies for improving interfacial biocatalysis in industrial, pharmaceutical, and food applications.

    View details for DOI 10.1021/la103080a

    View details for Web of Science ID 000285217700047

    View details for PubMedID 21080656

  • Targeting of Cancer Cells Using Quantum Dot-Polypeptide Hybrid Assemblies That Function as Molecular Imaging Agents and Carrier Systems ADVANCED FUNCTIONAL MATERIALS Atmaja, B., Lui, B. H., Hu, Y., Beck, S. E., Frank, C. W., Cochran, J. R. 2010; 20 (23): 4091-4097
  • Hydrophobic nanoparticles improve permeability of cell-encapsulating poly(ethylene glycol) hydrogels while maintaining patternability PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Lee, W., Cho, N., Xiong, A., Glenn, J. S., Frank, C. W. 2010; 107 (48): 20709-20714


    Cell encapsulating poly(ethylene glycol) hydrogels represent a promising approach for constructing 3D cultures designed to more closely approximate in vivo tissue environment. Improved strategies are needed, however, to optimally balance hydrogel permeability to support metabolic activities of encapsulated cells, while maintaining patternability to restore key aspects of tissue architecture. Herein, we have developed one such strategy incorporating hydrophobic nanoparticles to partially induce looser cross-linking density at the particle-hydrogel interface. Strikingly, our network design significantly increased hydrogel permeability, while only minimally affecting the matrix mechanical strength or prepolymer viscosity. This structural advantage improved viability and functions of encapsulated cells and permitted micron-scale structures to control over spatial distribution of incorporated cells. We expect that this design strategy holds promise for the development of more advanced artificial tissues that can promote high levels of cell metabolic activity and recapitulate key architectural features.

    View details for DOI 10.1073/pnas.1005211107

    View details for Web of Science ID 000284762400026

    View details for PubMedID 21071674

  • Vesicle Adsorption on Mesoporous Silica and Titania LANGMUIR Claesson, M., Cho, N., Frank, C. W., Andersson, M. 2010; 26 (22): 16630-16633


    Lipid bilayer formation via vesicle fusion on mesoporous silica and mesoporous titania was investigated using quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescent recovery after photobleaching (FRAP). Results showed that lipid bilayers were formed on mesoporous silica and that intact vesicle adsorption was obtained on mesoporous titania. From the FRAP results, it could be concluded that the lipid bilayer was fluid; however, it had a smaller diffusivity constant compared to bilayers supported on a nonporous silica.

    View details for DOI 10.1021/la102719w

    View details for Web of Science ID 000283837800002

    View details for PubMedID 20932045

  • Fabrication of a Planar Zwitterionic Lipid Bilayer on Titanium Oxide LANGMUIR Cho, N., Frank, C. W. 2010; 26 (20): 15706-15710


    There is great demand to fabricate planar phospholipid bilayers on biocompatible materials. The preferred method of forming bilayers on these substrates is the spontaneous adsorption and rupture of phospholipid vesicles. However, in the case of titanium oxide, model vesicles composed solely of zwitterionic phospholipids do not follow this self-assembly pathway under physiological conditions, prompting the use of complex bilayer materials and less-facile methods. Herein, we report a novel pH-based strategy for fabricating zwitterionic bilayers on titanium oxide in a simple and robust manner. Depending on the pH conditions under which lipid vesicles adsorb onto titanium oxide, quartz crystal microbalance-dissipation (QCM-D) monitoring demonstrated that the self-assembly pathway can in fact result in planar bilayer formation. The pH of the solution could then be adjusted to physiological levels with no effect on the mass and viscoelastic properties of the bilayer. Moreover, fluorescence recovery after photobleaching (FRAP) measurements indicated a high degree of lateral lipid diffusivity within the bilayer at physiological pH, commensurate with its role as a cell membrane mimic. Compared to existing protocols, this strategy permits the fabrication of a more diverse array of planar bilayers on titanium oxide by tuning the self-assembly pathway of lipid vesicle adsorption onto solid substrates.

    View details for DOI 10.1021/1a101523f

    View details for Web of Science ID 000282936700002

    View details for PubMedID 20857902

  • Morphology of Photopolymerized End-Linked Poly(ethylene glycol) Hydrogels by Small-Angle X-ray Scattering MACROMOLECULES Waters, D. J., Engberg, K., Parke-Houben, R., Hartmann, L., Ta, C. N., Toney, M. F., Frank, C. W. 2010; 43 (16): 6861-6870


    Due to the biocompatibility of poly(ethylene glycol) (PEG), PEG-based hydrogels have attracted considerable interest for use as biomaterials in tissue engineering applications. In this work, we show that PEG-based hydrogels prepared by photopolymerization of PEG macromonomers functionalized with either acrylate or acrylamide end-groups generate networks with crosslink junctions of high functionality. Although the crosslink functionality is not well controlled, the resultant networks are sufficiently well ordered to generate a distinct correlation peak in the small angle x-ray scattering (SAXS) related to the distance between crosslink junctions within the PEG network. The crosslink spacing is a useful probe of the PEG chain conformation within the hydrogel and ranges from approximately 6 to 16 nm, dependent upon both the volume fraction of polymer and the molecular weight of the PEG macromonomers. The presence of a peak in the scattering of photopolymerized PEG networks is also correlated with an enhanced compressive modulus in comparison to PEG networks reported in the literature with much lower crosslink functionality that exhibit no scattering peak. This comparison demonstrates that the method used to link together PEG macromonomers has a critical impact on both the nanoscale structure and the macroscopic properties of the resultant hydrogel network.

    View details for DOI 10.1021/ma101070s

    View details for Web of Science ID 000280855000042

    View details for PubMedID 21403767

  • Type I Collagen-Functionalized Supported Lipid Bilayer as a Cell Culture Platform BIOMACROMOLECULES Huang, C., Cho, N., Hsu, C., Tseng, P., Frank, C. W., Chang, Y. 2010; 11 (5): 1231-1240


    The supported phospholipid bilayer serves as an important biomimetic model for the cell membrane in both basic and applied scientific research. We have constructed a biomimetic platform based on a supported phospholipid bilayer that is functionalized with type I collagen to serve as a substrate for cell culture. To create the type I collagen-functionalized lipid bilayer assembly, a simple chemical approach was employed: lipid vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(glutaryl) (DP-NGPE), a carboxylic acid-functionalized phospholipid, were prepared and then fused onto an SiO(2) substrate to form a supported lipid bilayer. Subsequently, type I collagen molecules were introduced to form stable collagen-lipid conjugates via amide linkages with activated DP-NGPE lipids. The binding kinetics of the conjugation process and the resultant changes in film thickness and viscoelasticity were followed using the quartz crystal microbalance with dissipation (QCM-D) monitoring. The morphology of the conjugated collagen adlayer was investigated with atomic force microscopy (AFM). We observed that the adsorbed collagen molecules tended to self-assemble into fibrillar structures. Fluorescence recovery after photobleaching (FRAP) was utilized to estimate lateral lipid mobility, which was reduced by up to 20% after the coupling of type I collagen to the underlying lipid bilayer. As a cell culture platform, the collagen-conjugated supported lipid bilayer showed promising results. Smooth muscle cells (A10) retained normal growth behavior on the collagen-functionalized platform, unlike the bare POPC lipid bilayer and the POPC/DG-NGPE bilayer without collagen. The biomimetic functionalized lipid system presented here is a simple, yet effective approach for constructing a cell culture platform to explore the interactions between extracellular matrix components and cells.

    View details for DOI 10.1021/bm901445r

    View details for Web of Science ID 000277355800013

    View details for PubMedID 20361729

  • Silica xerogel/aerogel-supported lipid bilayers: Consequences of surface corrugation BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES Goksu, E. I., Hoopes, M. I., Nellis, B. A., Xing, C., Faller, R., Frank, C. W., Risbud, S. H., Satcher, J. H., Longo, M. L. 2010; 1798 (4): 719-729


    The objective of this paper was to review our recent investigations of silica xerogel and aerogel-supported lipid bilayers. These systems provide a format to observe relationships between substrate curvature and supported lipid bilayer formation, lipid dynamics, and lipid mixtures phase behavior and partitioning. Sensitive surface techniques such as quartz crystal microbalance and atomic force microscopy are readily applied to these systems. To inform current and future investigations, we review the experimental literature involving the impact of curvature on lipid dynamics, lipid and phase-separated lipid domain localization, and membrane-substrate conformations and we review our molecular dynamics simulations of supported lipid bilayers with the atomistic and molecular information they provide.

    View details for DOI 10.1016/j.bbamem.2009.09.007

    View details for Web of Science ID 000275998300003

    View details for PubMedID 19766590

  • Surface-Initiated Vapor Deposition Polymerization of Poly (gamma-benzyl-L-glutamate): Optimization and Mechanistic Studies LANGMUIR Zheng, W., Frank, C. W. 2010; 26 (6): 3929-3941


    Surface-initiated vapor deposition polymerization (SI-VDP) is a very effective approach to synthesize grafted poly(amino acids). In this study, we developed an SI-VDP system with pressure and temperature control and demonstrated highly efficient surface-grafting of poly(gamma-benzyl-L-glutamate) (PBLG) on a silicon wafer at pressure 1000 times larger than those in prior reports. More importantly, we developed new methods to quantitatively investigate mechanistic details of the SI-VDP process. First, we monitored the amount of vaporized monomer and developed a VDP reaction profile (VDPRP) method to study the major monomer reservoir processes. Next, we developed a quantitative Fourier transform infrared analysis of both as-deposited PBLG and chemisorbed PBLG films in addition to ellipsometric data to evaluate the major substrate surface processes. We observed two classes of characteristic features (pulses or two peaks) of VDPRPs, which depended upon the monomer temperature, and proposed possible mechanisms. We also found that the two peaks of VDPRPs can selectively track different reservoir processes in real time. For surface processes, we proposed possible mechanisms to obtain the surface-grafted PBLG that are expected to have either high packing density with mostly alpha-helix segments or low packing density with both random coil and alpha-helix segments.

    View details for DOI 10.1021/la9032628

    View details for Web of Science ID 000275226700029

    View details for PubMedID 19961195

  • Interfacial Binding Dynamics of Bee Venom Phospholipase A(2) Investigated by Dynamic Light Scattering and Quartz Crystal Microbalance LANGMUIR Jackman, J. A., Cho, N., Duran, R. S., Frank, C. W. 2010; 26 (6): 4103-4112


    Bee venom phospholipase A(2) (bvPLA(2)) is part of the secretory phospholipase A(2) (sPLA(2)) family whose members are active in biological processes such as signal transduction and lipid metabolism. While controlling sPLA(2) activity is of pharmaceutical interest, the relationship between their mechanistic actions and physiological functions is not well understood. Therefore, we investigated the interfacial binding process of bvPLA(2) to characterize its biophysical properties and gain insight into how membrane binding affects interfacial activation. Attention was focused on the role of membrane electrostatics in the binding process. Although dynamic light scattering experiments indicated that bvPLA(2) does not lyse lipid vesicles, a novel, nonhydrolytic activity was discovered. We employed a supported lipid bilayer platform on the quartz crystal microbalance with dissipation sensor to characterize this bilayer-disrupting behavior and determined that membrane electrostatics influence this activity. The data suggest that (1) adsorption of bvPLA(2) to model membranes is not primarily driven by electrostatic interactions; (2) lipid desorption can follow bvPLA(2) adsorption, resulting in nonhydrolytic bilayer-disruption; and (3) this desorption is driven by electrostatic interactions. Taken together, these findings provide evidence that interfacial binding of bvPLA(2) is a dynamic process, shedding light on how membrane electrostatics can modulate interfacial activation.

    View details for DOI 10.1021/la903117x

    View details for Web of Science ID 000275226700051

    View details for PubMedID 20020725

  • Identification of a Class of HCV Inhibitors Directed Against the Nonstructural Protein NS4B SCIENCE TRANSLATIONAL MEDICINE Cho, N., Dvory-Sobol, H., Lee, C., Cho, S., Bryson, P., Masek, M., Elazar, M., Frank, C. W., Glenn, J. S. 2010; 2 (15)


    New classes of drugs are needed to combat hepatitis C virus (HCV), an important worldwide cause of liver disease. We describe an activity of a key domain, an amphipathic helix we termed 4BAH2, within a specific HCV nonstructural protein, NS4B. In addition to its proposed role in viral replication, we validate 4BAH2 as essential for HCV genome replication and identify first-generation small-molecule inhibitors of 4BAH2 that specifically prevent HCV replication within cells. Mechanistic studies reveal that the inhibitors target 4BAH2 function by preventing either 4BAH2 oligomerization or 4BAH2 membrane association. 4BAH2 inhibitors represent an additional class of compounds with potential to effectively treat HCV.

    View details for DOI 10.1126/scitranslmed.3000331

    View details for Web of Science ID 000277264100002

    View details for PubMedID 20371471

  • Exploring the versatility of hydrogels derived from living organocatalytic ring-opening polymerization SOFT MATTER Nederberg, F., Trang, V., Pratt, R. C., Kim, S., Colson, J., Nelson, A., Frank, C. W., Hedrick, J. L., Dubois, P., Mespouille, L. 2010; 6 (9): 2006-2012

    View details for DOI 10.1039/b920216a

    View details for Web of Science ID 000277031300023

  • Polymer-Tethered Bimolecular Lipid Membranes POLYMER MEMBRANES/BIOMEMBRANES Knoll, W., Bender, K., Foerch, R., Frank, C., Goetz, H., Heibel, C., Jenkins, T., Jonas, U., Kibrom, A., Kuegler, R., Naumann, C., Naumann, R., Reisinger, A., Ruehe, J., Schiller, S., Sinner, E. 2010; 224: 87-111

    View details for DOI 10.1007/12_2009_27

    View details for Web of Science ID 000274503000003

  • Quartz crystal microbalance with dissipation monitoring of supported lipid bilayers on various substrates NATURE PROTOCOLS Cho, N., Frank, C. W., Kasemo, B., Hook, F. 2010; 5 (6): 1096-1106


    Supported lipid bilayers (SLBs) mimic biological membranes and are a versatile platform for a wide range of biophysical research fields including lipid-protein interactions, protein-protein interactions and membrane-based biosensors. The quartz crystal microbalance with dissipation monitoring (QCM-D) has had a pivotal role in understanding SLB formation on various substrates. As shown by its real-time kinetic monitoring of SLB formation, QCM-D can probe the dynamics of biomacromolecular interactions. We present a protocol for constructing zwitterionic SLBs supported on silicon oxide and titanium oxide, and discuss technical issues that need to be considered when working with charged lipid compositions. Furthermore, we explain a recently developed strategy that uses an amphipathic, alpha-helical (AH) peptide to form SLBs on gold and titanium oxide substrates. The protocols can be completed in less than 3 h.

    View details for DOI 10.1038/nprot.2010.65

    View details for Web of Science ID 000278354700012

    View details for PubMedID 20539285

  • Hindered diffusion of oligosaccharides in high strength poly(ethylene glycol)/poly(acrylic acid) interpenetrating network hydrogels: Hydrodynamic vs. obstruction models POLYMER Waters, D. J., Frank, C. W. 2009; 50 (26): 6331-6339


    Diffusion coefficients of small oligosaccharides within high strength poly(ethylene glycol)/poly(acrylic acid) interpenetrating network (PEG/PAA IPN) hydrogels were measured by diffusion through hydrogel slabs. The ability of hindered diffusion models previously presented in the literature to fit the experimental data is examined. A model based solely on effects due to hydrodynamics is compared to a model based solely on solute obstruction. To examine the effect of polymer volume fraction on the observed diffusion coefficients, the equilibrium volume fraction of polymer in PEG/PAA IPNs was systematically varied by changing the initial PEG polymer concentration in hydrogel precursor solutions from 20 to 50 wt./wt.%. To examine the effect of solute radius on the observed diffusion coefficients, solute radii were varied from 3.3 to 5.1 Å by measuring diffusion coefficients of glucose, a monosaccharide; maltose, a disaccharide; and maltotriose, a trisaccharide. Both the hydrodynamic and obstruction models rely on scaling relationships to predict diffusion coefficients. The proper scaling relationship for each of the hindered diffusion models is evaluated based on fits to experimental data. The scaling relationship employed is found to have a greater significance for the hydrodynamic model than the obstruction model. Regardless of the scaling relationship employed, the obstruction model provides a better fit to our experimental data than the hydrodynamic model.

    View details for DOI 10.1016/j.polymer.2009.05.034

    View details for Web of Science ID 000272654100019

    View details for PubMedID 20514136

  • The reliable targeting of specific drug release profiles by integrating arrays of different albumin-encapsulated microsphere types BIOMATERIALS Lee, W., Wiseman, M. E., Cho, N., Glenn, J. S., Frank, C. W. 2009; 30 (34): 6648-6654


    Biodegradable polymer microspheres have been successfully utilized as a medium for controlled protein or peptide-based drug release. Because the release kinetics has been typically controlled by modulating physical or chemical properties of the medium, these parameters must be optimized to obtain a specific release profile. However, due to the complexity of the release mechanism and the complicated interplay between various design parameters of the release medium, detailed prediction of the resulting release profile is a challenge. Herein we suggest a simple method to target specific release profiles more efficiently by integrating release profiles for an array of different microsphere types. This scheme is based on our observation that the resulting release profile from a mixture of different samples can be predicted as the linear summation of the individually measured release profiles of each sample. Hence, by employing a linear equation at each time point and formulating them as a matrix equation, we could determine how much of each microsphere type to include in a mixture in order to have a specific release profile. In accordance with this method, several targeted release profiles were successfully obtained. We expect that the proposed method will allow us to overcome limitations in controlling complicated release mechanisms so that drug delivery systems can be reliably designed to satisfy clinical demands.

    View details for DOI 10.1016/j.biomaterials.2009.08.035

    View details for Web of Science ID 000271347900010

    View details for PubMedID 19775742

  • Mechanism of an Amphipathic alpha-Helical Peptide's Antiviral Activity Involves Size-Dependent Virus Particle Lysis ACS CHEMICAL BIOLOGY Cho, N., Dvory-Sobol, H., Xiong, A., Cho, S., Frank, C. W., Glenn, J. S. 2009; 4 (12): 1061-1067


    The N-terminal region of the hepatitis C virus (HCV) nonstructural protein NS5A contains an amphipathic alpha-helix that is necessary and sufficient for NS5A membrane association. A synthetic peptide (AH) comprising this amphipathic helix is able to lyse lipid vesicles that serve as a model system for virus particles. Based on quartz crystal microbalance-dissipation (QCM-D) experiments, the degree of vesicle rupturing was found to be inversely related to vesicle size, with maximal activity in the size range of several medically important viruses. In order to confirm and further study vesicle rupture, dynamic light scattering (DLS) and atomic force microscopy (AFM) experiments were also performed. The size dependence of vesicle rupturing helps explain the peptide's observed effect on the infectivity of a wide range of viruses. Further, in vitro studies demonstrated that AH peptide treatment significantly decreased the infectivity of HCV particles. Thus, the AH peptide might be used to rupture HCV particles extra-corporally (for HCV prevention) and within infected individuals (for HCV therapy).

    View details for DOI 10.1021/cb900149b

    View details for Web of Science ID 000272845900010

    View details for PubMedID 19928982

  • Biocompatibility of poly(ethylene glycol)/poly(acrylic acid) interpenetrating polymer network hydrogel particles in RAW 264.7 macrophage and MG-63 osteoblast cell lines JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A Yim, E. S., Zhao, B., Myung, D., Kourtis, L. C., Frank, C. W., Carter, D., Smith, R. L., Goodman, S. B. 2009; 91A (3): 894-902


    Hydrogel polymers comprise a novel category of synthetic materials being investigated for use in cartilage replacement. One candidate compound, a poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) interpenetrating polymer network (IPN), was developed for use in corneal prostheses and was recently engineered for potential orthopedic use. The current study examined the effects of particles of this compound on two cell lines (MG-63 osteoblast-like cells and RAW 264.7 macrophages) over a 48-h time course. To mimic the effects of wear debris, particles of the compound were generated and introduced to the cells. In the MG-63 cell line, the particles had no significant effect on cell viability measured by PicoGreen assay and trypan blue exclusion. In contrast, a significant decrease in cell viability was detected in the Raw 264.7 macrophage cells at the final timepoint with the highest concentration of hydrogel (3.0% v:v). A concentration- and time-dependent increase in TNF-alpha release characteristic of other known biocompatible materials was also detected in RAW 264.7 cells, but nitric oxide and interleukin (IL)-1beta showed no response. In addition, the MG-63 cell line demonstrated no IL-6 response. Particles of the PEG/PAA IPN thus seem to stimulate biological responses similar to those in other biocompatible materials.

    View details for DOI 10.1002/jbm.a.32311

    View details for Web of Science ID 000271588800027

  • Melt viscoelasticity of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymers POLYMER Liao, Q., Noda, I., Frank, C. W. 2009; 50 (25): 6139-6148
  • Antibody Binding to a Tethered Vesicle Assembly Using QCM-D ANALYTICAL CHEMISTRY Patel, A. R., Kanazawa, K. K., Frank, C. W. 2009; 81 (15): 6021-6029


    The bilayer-tethered vesicle assembly has recently been proposed as a biomimetic model membrane platform for the analysis of integral membrane proteins. Here, we explore the binding of antibodies to membrane components of the vesicle assembly through the use of quartz crystal microbalance with dissipation monitoring (QCM-D). The technique provides a quantitative, label-free avenue to study binding processes at membrane surfaces. However, converting the signal generated upon binding to the actual amount of antibody bound has been a challenge for a viscoelastic system such as the tethered vesicle assembly. In this work, we first established an empirical relationship between the amount of bound antibody and the corresponding QCM-D response. Then, the results were examined in the context of an existing model describing the QCM-D response under a variety of theoretical loading conditions. As a model system, we investigated the binding of monoclonal antidinitrophenyl (DNP) IgG(1) to tethered vesicles displaying DNP hapten groups. The measured frequency and dissipation responses upon binding were compared to an independent measure of the amount of bound antibody obtained through the use of an in situ ELISA assay. At saturation, the surface mass density of bound antibody was approximately 900 ng/cm(2). Further, through the application of QCM-D models that describe the response of the quartz when loaded by either a single homogeneous viscoelastic film or by a two-layered viscoelastic film, we found that a homogeneous, one-layer model accurately predicts the amount of antibody bound to the tethered vesicles near antibody surface saturation, but a two-layer model must be invoked to accurately describe the kinetic response of the dissipation factor, which suggests that the binding of the antibody results in a stiffening of the top layer of the film.

    View details for DOI 10.1021/ac802756v

    View details for Web of Science ID 000268455600011

    View details for PubMedID 19580260

  • Bioactive interpenetrating polymer network hydrogels that support corneal epithelial wound healing JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A Myung, D., Farooqui, N., Zheng, L. L., Koh, W., Gupta, S., Bakri, A., Noolandi, J., Cochran, J. R., Frank, C. W., Ta, C. N. 2009; 90A (1): 70-81


    The development and characterization of collagen-coupled poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) interpenetrating polymer network hydrogels is described. Quantitative amino acid analysis and FITC-labeling of collagen were used to determine the amount and distribution of collagen on the surface of the hydrogels. The bioactivity of the coupled collagen was detected by a conformation-specific antibody and was found to vary with the concentration of collagen reacted to the photochemically functionalized hydrogel surfaces. A wound healing assay based on an organ culture model demonstrated that this bioactive surface supports epithelial wound closure over the hydrogel but at a decreased rate relative to sham wounds. Implantation of the hydrogel into the corneas of live rabbits demonstrated that epithelial cell migration is supported by the material, although the rate of migration and morphology of the epithelium were not normal. The results from the study will be used as a guide toward the optimization of bioactive hydrogels with promise in corneal implant applications such as a corneal onlay and an artificial cornea.

    View details for DOI 10.1002/jbm.a.32056

    View details for Web of Science ID 000266648700007

  • Alpha-Helical Peptide-Induced Vesicle Rupture Revealing New Insight into the Vesicle Fusion Process As Monitored in Situ by Quartz Crystal Microbalance-Dissipation and Reflectometry ANALYTICAL CHEMISTRY Cho, N., Wang, G., Edvardsson, M., Glenn, J. S., Hook, F., Frank, C. W. 2009; 81 (12): 4752-4761


    We have used simultaneous quartz crystal microbalance-dissipation (QCM-D) monitoring and four-detector optical reflectometry to monitor in situ the structural transformation of intact vesicles to a lipid bilayer on a gold surface. The structural transformation of lipid vesicles to a bilayer was achieved by introducing a particular amphipathic, alpha-helical (AH) peptide. The combined experimental apparatus allows us to simultaneously follow the acoustic and optical property changes of the vesicle rupturing process upon interaction with AH peptides. While QCM-D and reflectometry have similar sensitivities in terms of mass and thickness resolution, there are unique advantages in operating these techniques simultaneously on the same substrate. These advantages permit us to (1) follow the complex interaction between AH peptides and intact vesicles with both acoustic and optical mass measurements, (2) calculate the amount of dynamically coupled water during the interaction between AH peptides and intact vesicles, (3) demonstrate that the unexpectedly large increase of both adsorbed mass and the film's energy dissipation is mainly caused by swelling of the vesicles during the binding interaction with AH peptides, and (4) permit us to understand the structural transformation from intact vesicles to a bilayer via the AH peptide interaction by monitoring viscoelastic properties, acoustic mass, optical mass, and thickness changes of both the binding and destabilization processes. From the deduced "hydration signature" we followed the complex transformation of lipid assemblies. On the basis of this information, a mechanism of this structural transformation is proposed that provides new insight into the process of vesicle fusion on solid substrates.

    View details for DOI 10.1021/ac900242s

    View details for Web of Science ID 000266969700012

    View details for PubMedID 19459601

  • Defect Generation Surrounding Nanoparticles in a Cross-Linked Hydrogel Network LANGMUIR Yanagioka, M., Frank, C. W. 2009; 25 (10): 5927-5939


    A detailed understanding of polymer-nanoparticle interactions is a key element in demystifying the reinforcement mechanism for nanocomposites. To decouple the effects of the polymer-nanoparticle interactions from the particle distribution, we utilized polymerized crystalline colloidal arrays based on a thermosensitive hydrogel, poly(N-isopropylacrylamide) (pNIPAAm). First, the hydrogel network structure in the vicinity of the nanoparticles was investigated by the deswelling behavior of particle-filled hydrogels. The addition of nanoparticles led to an increased rate of deswelling when the particle-filled hydrogel was heated beyond the lower critical solution temperature (32 degrees C). To interpret this observation, we have suggested that the polymer network has a significant increase in defects (e.g., dangling chain ends) in the vicinity of the nanoparticles. The apparent percolation threshold associated with the interaction of the nanoparticles was about 20 times smaller than the theoretical percolation threshold of spherical particles. As a consequence, we have determined the thickness of this defect zone to be about 85 nm. This is much larger than the size of the unperturbed linear pNIPAAm chains, suggesting that the polymers that play a role in the adsorption are not constrained segments of polymers bound between cross-link junctions but relatively free chains. This finding enabled us to emulate the adsorption behavior of pNIPAAm hydrogels on the particles by simply adding linear pNIPAAm chains to the particle suspensions. We then prepared silica and polystyrene suspensions with free pNIPAAm chains at a concentration much lower than the overlap concentration c*. A rheological study was conducted to determine the adsorption thickness of linear polymer chains on both silica and polystyrene nanoparticles. No significant adsorption was observed on silica, whereas the resultant thickness of the polymer was 8 nm on polystyrene.

    View details for DOI 10.1021/la804130m

    View details for Web of Science ID 000266081000069

    View details for PubMedID 19371046

  • Influence of Interfacial Layer Between Nanoparticles and Polymeric Matrix on Viscoelastic Properties of Hydrogel Nanocomposites MACROMOLECULES Yanagioka, M., Toney, M. F., Frank, C. W. 2009; 42 (4): 1331-1343

    View details for DOI 10.1021/ma802152s

    View details for Web of Science ID 000263429700062

  • Viral infection of human progenitor and liver-derived cells encapsulated in three-dimensional PEG-based hydrogel BIOMEDICAL MATERIALS Cho, N., Elazar, M., Xiong, A., Lee, W., Chiao, E., Baker, J., Frank, C. W., Glenn, J. S. 2009; 4 (1)


    We have studied the encapsulation of human progenitor cells into 3D PEG hydrogels. Replication-incompetent lentivirus promoter reporter vectors were found to efficiently detect the in vivo expression of human hepatic genes in hydrogel-encapsulated liver progenitor cells. Similarly, hydrogel-encapsulated cells could be efficiently infected with hepatitis C virus, and progeny infectious virus could be recovered from the media supernatants of the hydrogels. Provocatively, the diameters of these virus particles range from approximately 50 to 100 nm, while the calculated mesh size of the 8 k hydrogel is 44.6 +/- 1.7 A. To reconcile how viral particles can penetrate the hydrogels to infect the encapsulated cells, we propose that microfractures/defects of the hydrogel result in a functional pore size of up to 20 fold greater than predicted by theoretical mesh calculations. These results suggest a new model of hydrogel structure, and have exciting implications for tissue engineering and hepatitis virus studies.

    View details for DOI 10.1088/1748-6041/4/1/011001

    View details for Web of Science ID 000263071200001

    View details for PubMedID 18981544

  • Supramolecular Assembly of Block Copolypeptides with Semiconductor Nanocrystals LANGMUIR Atmaja, B., Cha, J. N., Marshall, A., Frank, C. W. 2009; 25 (2): 707-715


    We report the analogy between the self-assembly properties of amphiphilic phospholipids and the similar behavior observed for quantum dot (CdSe/CdS)-diblock copolypeptide hybrid systems, and the effect of the self-assembly on secondary structures of the polypeptides. At neutral pH, the diblock copolypeptide, poly(diethyleneglycol-l-lysine)-poly(l-lysine), comprises a positively charged poly-l-lysine (PLL) block and a hydrophilic and uncharged poly(diethyleneglycol-l-lysine) (PEGLL) block. By itself, the copolypeptide is not amphiphilic. However, when the polymers are mixed with water-soluble, negatively charged, citrate-functionalized quantum dots (QDs) in water, shell-like structures or dense aggregates are spontaneously formed. Electrostatic and hydrogen-bonding interactions between the positively charged PLL residues and the negatively charged ligands on the QDs lead to charge neutralization of the PLL block, while the PEGLL block remains hydrophilic. As a result, a pseudo "amphiphilic" molecular unit is formed in which the "hydrophobic" and hydrophilic sections constitute the charge-neutralized PLL residues together with the associating QD and the remaining polypeptide residues that are not neutralized, respectively. The generation of these "amphiphilic" molecular units in turn drives the formation of the QD-polypeptide assemblies. Support for this analogy comes from the observed transition in the shape of the assembly from a shell-like structure to a dense aggregate that is very much analogous to the vesicle-to-micelle transition observed in lipid systems. Furthermore, this shape transition can be explained qualitatively using a concept that is analogous to the surfactant number (N = a(hc)/a(hg)), which has been applied extensively in amphiphilic lipid systems. Specifically, as the ratio of the "hydrophobic" area (a(hc)) to the hydrophilic area (a(hg)) decreases, a shape transition from the shell-like structure to the dense aggregate occurs. In addition, the size of the shell-like structure changes as a function of the dimensions of the "amphiphilic" molecular unit in a manner that is similar to how the size of the lipid vesicle changes with the dimensions of the lipid molecule. Circular dichroism (CD) measurements have shown that the PEGLL-PLL molecule has a well-defined secondary structure (alpha-helical PEGLL block and random coil PLL block) that remains virtually unchanged after reacting with the QDs. This finding is consistent with the hypothesis that it is the electrostatic interaction between the amines on the PLL block and the citrate ligands on the QDs that drives the self-assembly.

    View details for DOI 10.1021/la801848d

    View details for Web of Science ID 000262431100013

    View details for PubMedID 19072205

  • Adsorbed alpha-Helical Diblock Copolypeptides: Molecular Organization, Structural Properties, and Interactions LANGMUIR Atmaja, B., Cha, J. N., Frank, C. W. 2009; 25 (2): 865-872


    In this work, we have developed 11-mercaptoundecanoic acid (MUA)-polypeptide "bilayer" systems by adsorbing poly(diethylene glycol-l-lysine)-poly(l-lysine) (PEGLL-PLL) diblock copolypeptide molecules of various architectures onto MUA-functionalized gold substrates. An objective of our present work is to use the PEGLL-PLL/MUA bilayer as a model system for studying the interfacial phenomena that occur when PEGLL-PLL molecules interact with carboxylic acid (COOH) moieties of nanoparticle ligands. Specifically, we have elucidated the nature of the interactions between the PEGLL-PLL and COOH moieties as well as the resulting polypeptide conformation and organization, using a combination of surface techniques-grazing-incidence IR spectroscopy, ellipsometry, and contact angle. We have also thoroughly characterized other film properties such as the packing and graft density of the polypeptide molecules as a function of the PEGLL-PLL architecture. From the IR data, the adsorption process occurs primarily by means of electrostatic interaction between the protonated PLL residues (pKa approximately 10.6) and carboxylate moieties of the MUA self-assembled monolayer (SAM) (pKa approximately 6) that is enhanced by H-bonding. The PLL block is thought to adopt a random-coil (extended) conformation, while the PEGLL block that is not interacting with the MUA molecules is found to adopt an alpha-helical conformation with an average tilt angle of -60 degrees. The PEGLL-PLL molecules have also been deduced to form a heterogeneous film and adopt liquidlike/disordered packing on the surface. The average contact angle of the MUA-polypeptide bilayer systems is -40 degrees, which implies that the diethylene glycol (EG2) side chains of the PEGLL residues may be oriented somewhat toward the surface normal. From ellipsometry measurements, it is found that PEGLLx-PLLy molecules with a longer alpha-helical block are associated with a lower graft density on the MUA surface compared to those with a shorter alpha-helical block. This observation may be attributed to the greater repulsion-steric and H-bonding effects-that is imposed by the EG2 side chains found on and projected area occupied by the longer PEGLL block. The bilayer systems have been found to be extremely stable over a 2-week period with no changes in the contact angle, thickness, polypeptide tilt angle, or conformation. Beyond that, there is a gradual decrease in the thickness and increase in the contact angle of the bilayer that could be attributed to the oxidation of the MUA SAM molecules.

    View details for DOI 10.1021/la801973x

    View details for Web of Science ID 000262431100033

    View details for PubMedID 19177647

  • The Use of the RAFT-Technique for the Preparation of Temperature/pH Sensitive Polymers in Different Architectures Licea-Claverie, A., Alvarez-Sanchez, J., Picos-Corrales, L. A., Obeso-Vera, C., Flores, M. C., Munuel Cornejo-Bravo, J., Hawker, C. J., Frank, C. W. WILEY-V C H VERLAG GMBH. 2009: 56-66
  • Biomimetic Lipoglycopolymer Membranes: Photochemical Surface Attachment of Supramolecular Architectures with Defined Orientation ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Schiller, S. M., Reisinger-Friebis, A., Goetz, H., Hawker, C. J., Frank, C. W., Naumann, R., Knoll, W. 2009; 48 (37): 6896-6899

    View details for DOI 10.1002/anie.200901544

    View details for Web of Science ID 000269937200027

    View details for PubMedID 19688795

  • Preparation and Characterization of Glycoacrylate-Based Polymer-Tethered Lipid Bilayers on Benzophenone-Modified Substrates LANGMUIR Hwang, L. Y., Goetz, H., Knoll, W., Hawker, C. J., Frank, C. W. 2008; 24 (24): 14088-14098


    Polymer-tethered lipid bilayers are promising models for biological membranes as they may provide a soft, lubricating environment with sufficient spacing between the substrate and bilayer for incorporating transmembrane proteins. We present such a system that uses a glycoacrylate-based telechelic lipopolymer in combination with a lipid analogue. Characterization of the mixed monolayers of lipopolymers and free lipids at the air-water interface is used to examine the molecular organization that dictates the final assembly properties. Isotherms indicate that the source of the dominating interactions, whether polymer interactions in the subphase or alkyl chain interactions, depends on both the tethering density and area per molecule. Moreover, a critical composition exists at which the alkyl chain interactions dominate the monolayer behavior regardless of the area per molecule. Isobaric creep and hysteresis experiments suggest that permanent states due to irreversible polymer-polymer interactions are not created as the monolayer is compressed. These data, combined with theoretical polymer predictions, are used to understand the organization of the monolayers at the air-water interface and, hence, the separation distance between the bottom of the bilayer and substrate in the water-swollen state of the final bilayer assembly. Atomic force microscopy is used to confirm that the measured separation distance of 11.2 nm is on the order of what would be predicted using a theoretical analysis for a representative 5 mol % lipopolymer-tethered bilayer. Next, the homogeneity of the final bilayer is probed at multiple scales. Fluorescence microscopy is used to demonstrate that homogeneous and continuous bilayers can be formed (within the optical resolution limit of 500 nm) with all polymer tethering densities used in this study. Atomic force microscopy studies demonstrate that homogeneity comparable to that of a solid-supported lipid bilayer can be achieved for a representative 5 mol % lipopolymer-tethered bilayer. Langmuir-Blodgett transfer conditions for depositing monolayers that can be used to create homogeneous, fluid bilayers are also discussed. Finally, the distal leaflet lateral mobility is measured using fluorescence recovery after photobleaching experiments and shown to be a function of the tethering density. A possible model for the mobility data is developed in which the tethered lipids in the proximal leaflet act as immobile lipid obstacles that couple to distal leaflet lipids.

    View details for DOI 10.1021/la8022997

    View details for Web of Science ID 000261631700040

    View details for PubMedID 19360958

  • Enzymatic Proteolysis of a Surface-Bound alpha-Helical Polypeptide LANGMUIR Hardesty, J. O., Cascao-Pereira, L., Kellis, J. T., Robertson, C. R., Frank, C. W. 2008; 24 (24): 13944-13956


    In this work, we studied the interactions of enzymes with model substrate surfaces using label-free techniques. Our model system was based on serine proteases (a class of enzymes that digests proteins) and surface-bound polypeptide substrates. While previous studies have focused on bulk media factors such as pH, ionic strength, and surfactants, this study focuses on the role of the surface-bound substrate itself. In particular, we assess how the substrate density of a polypeptide with an alpha-helical secondary structure influences surface reactivity. An alpha-helical secondary structure was chosen based on literature indicating that stable alpha-helices can resist enzymatic digestion. To investigate the protease resistance of a surface-bound a-helix, we designed an a-helical polypeptide (SS-polypeptide, where SS = disulfide), used it to form films of varying surface coverage and then measured responses of the films to enzymatic exposure. Using quartz-crystal microbalance with dissipation (QCM-D), angle-resolved X-ray photoelectron spectroscopy (AR-XPS), grazing-angle infrared spectroscopy (GAIRS), and other techniques, we characterized the degradation of films to determine how the lateral packing density of the surface-bound SS-polypeptide substrate affected surface proteolysis. Characterization of pure SS-polypeptide films indicated dense packing of helices that maintained their helical structure and were generally oriented normal to the surface. We found that films of pure SS-polypeptide significantly resisted enzymatic digestion, while incorporation of very minor amounts of a diluent in such films resulted in rapid digestion. In part, this may be due to the need for the enzyme to bind several peptides along the peptide substrate within the cleft for digestion to occur. Only SS-polypeptide films that were densely packed and did not permit catalytic access to multiple peptides (e.g., terminal peptides only) were resistant to enzymatic proteolysis.

    View details for DOI 10.1021/la8020386

    View details for Web of Science ID 000261631700022

    View details for PubMedID 19360953

  • Fluorescence Quantification for Surface Plasmon Excitation LANGMUIR Feller, B. E., Kellis, J. T., Cascao-Pereira, L. G., Knoll, W., Robertson, C. R., Frank, C. W. 2008; 24 (21): 12303-12311


    Surface plasmon resonance and surface plasmon fluorescence spectroscopy in combination have the potential to distinguish multicomponent surface processes. However, surface intensity variations from resonance angle shifts lead to a nonlinear response in the fluorescence intensity. We report a method to account for surface intensity variations using the experimentally measured relationship between fluorescence and reflectivity. We apply this method to monitor protease adsorption and proteolytic substrate degradation simultaneously. Multilayer protein substrates are prepared for these degradation studies using a layer-by-layer technique.

    View details for Web of Science ID 000260508800034

    View details for PubMedID 18844383

  • Structure, stability and applications of colloidal crystals Yanagioka, M., Frank, C. W. KOREAN SOC RHEOLOGY. 2008: 97-107
  • Effect of particle distribution on morphological and mechanical properties of filled hydrogel composites MACROMOLECULES Yanagioka, M., Frank, C. W. 2008; 41 (14): 5441-5450

    View details for DOI 10.1021/ma8003778

    View details for Web of Science ID 000257665900050

  • Progress in the development of interpenetrating polymer network hydrogels POLYMERS FOR ADVANCED TECHNOLOGIES Myung, D., Waters, D., Wiseman, M., Duhamel, P., Noolandi, J., Ta, C. N., Frank, C. W. 2008; 19 (6): 647-657


    Interpenetrating polymer networks (IPNs) have been the subject of extensive study since their advent in the 1960s. Hydrogel IPN systems have garnered significant attention in the last two decades due to their usefulness in biomedical applications. Of particular interest are the mechanical enhancements observed in "double network" IPN systems which exhibit nonlinear increases in fracture properties despite being composed of otherwise weak polymers. We have built upon pioneering work in this field as well as in responsive IPN systems to develop an IPN system based on end-linked poly-(ethylene glycol) (PEG) and loosely crosslinked poly(acrylic acid) (PAA) with hydrogen bond-reinforced strain-hardening behavior in water and high initial Young's moduli under physiologic buffer conditions through osmotically induced pre-stress. Uniaxial tensile tests and equilibrium swelling measurements were used to study PEG/PAA IPN hydrogels having second networks prepared with varying crosslinking and photoinitiator content, pH, solids content, and comonomers. Studies involving the addition of non-ionic comonomers and neutralization of the second network showed that template polymerization appears to be important in the formation of mechanically enhanced IPNs.

    View details for DOI 10.1002/pat.1134

    View details for Web of Science ID 000257014100025

    View details for PubMedID 19763189

  • Development of hydrogel-based keratoprostheses: A materials perspective BIOTECHNOLOGY PROGRESS Myung, D., Duhamel, P., Cochran, J. R., Noolandi, J., Ta, C. N., Frank, C. W. 2008; 24 (3): 735-741


    Research and development of artificial corneas (keratoprostheses) in recent years have evolved from the use of rigid hydrophobic materials such as plastics and rubbers to hydrophilic, water-swollen hydrogels engineered to support not only peripheral tissue integration but also glucose diffusion and surface epithelialization. The advent of the AlphaCor core-and-skirt hydrogel keratoprosthesis has paved the way for a host of new approaches based on hydrogels and other soft materials that encompass a variety of materials preparation strategies, from synthetic homopolymers and copolymers to collagen-based bio-copolymers and, finally, interpenetrating polymer networks. Each approach represents a unique strategy toward the same goal: to develop a new hydrogel that mimics the important properties of natural donor corneas. We provide a critical review of these approaches from a materials perspective and discuss recent experimental results. While formidable technical hurdles still need to be overcome, the rapid progress that has been made by investigators with these approaches is indicative that a synthetic donor cornea capable of surface epithelialization is now closer to becoming a clinical reality.

    View details for DOI 10.1021/bp070476n

    View details for Web of Science ID 000256593300033

    View details for PubMedID 18422366

  • Glucose-permeable interpenetrating polymer network hydrogels for corneal implant applications: A pilot study CURRENT EYE RESEARCH Myung, D., Farooqui, N., Waters, D., Schaber, S., Koh, W., Carrasco, M., Noolandi, J., Frank, C. W., Ta, C. N. 2008; 33 (1): 29-43


    Epithelialization of a keratoprosthesis requires that the implant material be sufficiently permeable to glucose. We have developed a poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) interpenetrating polymer network (IPN) hydrogel that can provide adequate passage of glucose from the aqueous humor to the epithelium in vivo. A series of PEG/PAA IPNs with varying PEG macromonomer molecular weights were synthesized and evaluated through swelling studies to determine their water content and diffusion experiments to assess their permeability to glucose. One of the PEG/PAA hydrogels prepared in this study had a glucose diffusion coefficient nearly identical to that of the human cornea (approximately 2.5 x 10(-6) cm(2)/sec). When implanted intrastromally in rabbit corneas, this hydrogel was retained and well-tolerated in 9 out of 10 cases for a period of 14 days. The retained hydrogels stayed optically clear and the epithelium remained intact and multilayered, indicating that the material facilitated glucose transport from the aqueous humor to the anterior part of the eye. The results from these experiments indicate that PEG/PAA hydrogels are promising candidates for corneal implant applications such as keratoprostheses and intracorneal lenses, and that the PEG/PAA IPN system in general is useful for creating permeable substrates for ophthalmic and other biomedical applications.

    View details for DOI 10.1080/02713680701793930

    View details for Web of Science ID 000252582500005

    View details for PubMedID 18214741

  • Sum frequency vibrational spectroscopy: The molecular origins of the optical second-order nonlinearity of collagen BIOPHYSICAL JOURNAL Rocha-Mendoza, I., Yankelevich, D. R., Wang, M., Reiser, K. M., Frank, C. W., Knoesen, A. 2007; 93 (12): 4433-4444


    The molecular origins of second-order nonlinear effects in type I collagen fibrils have been identified with sum-frequency generation vibrational spectroscopy. The dominant contributing molecular groups are: 1), the methylene groups associated with a Fermi resonance between the fundamental symmetric stretch and the bending overtone of methylene; and 2), the carbonyl and peptide groups associated with the amide I band. The noncentrosymmetrically aligned methylene groups are characterized by a distinctive tilt relative to the axis perpendicular to the main axis of the collagen fiber, a conformation producing a strong achiral contribution to the second-order nonlinear effect. In contrast, the stretching vibration of the carbonyl groups associated with the amide I band results in a strong chiral contribution to the optical second-order nonlinear effect. The length scale of these chiral effects ranges from the molecular to the supramolecular.

    View details for DOI 10.1529/biophysj.107.111047

    View details for Web of Science ID 000251298100035

    View details for PubMedID 17766339

  • Design and fabrication of an artificial cornea based on a photolithographically patterned hydrogel construct BIOMEDICAL MICRODEVICES Myung, D., Koh, W., Bakri, A., Zhang, F., Marshall, A., Ko, J., Noolandi, J., Carrasco, M., Cochran, J. R., Frank, C. W., Ta, C. N. 2007; 9 (6): 911-922


    We describe the design and fabrication of an artificial cornea based on a photolithographically patterned hydrogel construct, and demonstrate the adhesion of corneal epithelial and fibroblast cells to its central and peripheral components, respectively. The design consists of a central "core" optical component and a peripheral tissue-integrable "skirt." The core is composed of a poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) double-network with high strength, high water content, and collagen type I tethered to its surface. Interpenetrating the periphery of the core is a microperforated, but resilient poly(hydroxyethyl acrylate) (PHEA) hydrogel skirt that is also surface-modified with collagen type I. The well-defined microperforations in the peripheral component were created by photolithography using a mask with radially arranged chrome discs. Surface modification of both the core and skirt elements was accomplished through the use of a photoreactive, heterobifunctional crosslinker. Primary corneal epithelial cells were cultured onto modified and unmodified PEG/PAA hydrogels to evaluate whether the central optic material could support epithelialization. Primary corneal fibroblasts were seeded onto the PHEA hydrogels to evaluate whether the peripheral skirt material could support the adhesion of corneal stromal cells. Cell growth in both cases was shown to be contingent on the covalent tethering of collagen. Successful demonstration of cell growth on the two engineered components was followed by fabrication of core-skirt constructs in which the central optic and peripheral skirt were synthesized in sequence and joined by an interpenetrating diffusion zone.

    View details for DOI 10.1007/s10544-006-9040-4

    View details for Web of Science ID 000250462200017

    View details for PubMedID 17237989

  • Enrichment of deuterium oxide at hydrophilic interfaces in aqueous solutions LANGMUIR Stalgren, J. J., Boschkova, K., Ericsson, J., Frank, C. W., Knoll, W., Satija, S., Toney, M. F. 2007; 23 (24): 11943-11946


    The structure of water at aqueous interfaces is of the utmost importance in biology, chemistry, and geology. We use neutron reflectivity and quartz crystal microbalance to probe an interface between hydrophilic quartz and bulk liquid solutions of H2O/D2O mixtures. We find that near the interface the neutron scattering length density is larger than in the bulk solution and there is an excess adsorbed mass. We interpret this as showing that there is a region adjacent to the quartz that is enriched in D2O and extends 5-10 nm into the solution. This suggests caution when interpreting results where D2O is substituted for H2O in aqueous interfacial chemistry.

    View details for DOI 10.1021/la700932s

    View details for Web of Science ID 000250976700001

    View details for PubMedID 17958382

  • Quartz resonator signatures under Newtonian liquid loading for initial instrument check JOURNAL OF COLLOID AND INTERFACE SCIENCE Cho, N., D'Amour, J. N., Stalgren, J., Knoll, W., Kanazawa, K., Frank, C. W. 2007; 315 (1): 248-254


    The quartz crystal microbalance (QCM) has been increasingly utilized in the monitoring of the deposition of thin macromolecular films. Studies in the deposition of polymers, biomaterials, and interfacial reactions under electrochemical environment are some of the conditions for the study of these material and deposition properties at a lipid interface. Numerous studies have shown the difficulties in configuring an experimental setup for the QCM such that the recorded data reflect only the behavior of the quartz crystal and its load, and not some artifact. Such artifacts for use in liquids include mounting stress, surface properties such as hydrophobicity, surface roughness coupling to loading liquids, influence of compressional waves, and even problems with the electronic circuitry including the neglect of the quartz capacitance and the hysteretic effects of electronic components. It is thought useful to obtain a simple test by which the user could make a quick initial assessment of the instrument's performance. When a smooth quartz crystal resonator is immersed from air into a Newtonian liquid, the resonance and loss characteristics of the QCM are changed. A minimum of two experimental parameters is needed to characterize these changes. One of the changes is that of the resonant frequency. The second is characterized by either a change in the equivalent circuit resistance (DeltaR) or a change in the resonance dissipation (DeltaD). Two combinations of these observables, in terms of either Deltaf and DeltaR or Deltaf and DeltaD, which we define as Newtonian signatures of S(1) and S(2), are calculated to have fixed values and to be independent of the harmonic and of the physical values of the Newtonian liquid. We have experimentally determined the values of S(1) and S(2) using three different QCM systems. These are the standard oscillator, the network analyzer, and the QCM dissipation instrument. To test the sensitivity of these signatures to surface roughness, which is potential experimental artifact, we determined the values of S(1) and S(2) for roughened crystals and found that these signatures do reflect that experimental condition. Moreover, these results were qualitatively in accord with the roughness scaling factor described by Martin.

    View details for DOI 10.1016/j.jcis.2007.06.020

    View details for Web of Science ID 000249989500032

    View details for PubMedID 17706241

  • New ground for organic catalysis: A ring-opening polymerization approach to hydrogels BIOMACROMOLECULES Nederberg, F., Trang, V., Pratt, R. C., Mason, A. F., Frank, C. W., Waymouth, R. M., Hedrick, J. L. 2007; 8 (11): 3294-3297


    Herein, we describe an organocatalytic living polymerization approach to network and subsequent hydrogel formation. Cyclic carbonate-functionalized macromolecules were ring-opened using an alcoholic initiator in the presence of an organic catalyst, amidine 1,8-diazabicyclo[5.4.0]undec-7-ene. A model reaction for the cross-linking identified monomer concentration-dependent reaction regimes, and enhanced kinetic control was demonstrated by introducing a co-monomer, trimethylene carbonate. The addition of the co-monomer facilitated near-quantitative conversion of monomer to polymer (>96%). Resulting poly(ethylene glycol) networks swell significantly in water, and an open co-continuous (water-gel) porous structure was observed by scanning electron microscopy. The organocatalytic ring-opening polymerization of cyclic carbonate functional macromonomers using alcoholic initiators provides a simple, efficient, and versatile approach to hydrogel networks.

    View details for DOI 10.1021/bm700895d

    View details for Web of Science ID 000250960300002

    View details for PubMedID 17994785

  • Creation of lipid partitions by deposition of amphipathic viral peptides LANGMUIR Cho, N., Cho, S., Hardesty, J. O., Glenn, J. S., Frank, C. W. 2007; 23 (21): 10855-10863


    Phospholipid vesicles exhibit a natural characteristic to fuse and reform into a continuous single bilayer membrane on hydrophilic solid substrates such as glass, mica, and silica. The resulting solid-supported bilayer mimics physiological tendencies such as lipid flip-flop and lateral mobility. The lateral mobility of fluorescently labeled lipids fused into solid-supported bilayers is found to change upon deposition on the membrane surface of an amphipathic alpha-helical peptide (AH) derived from the hepatitis C virus (HCV) NS5A protein. The binding of the AH peptide to a phospholipid bilayer, with the helical axis parallel to the bilayer, leads to immobilization of the bilayer. We used AFM to better understand the mechanistic details of this specific interaction, and determined that the diminished fluidity of the bilayer is due to membrane thinning. Utilizing this specific interaction between AH peptides and lipid molecules, we demonstrate a novel process for the creation of lipid partition by employing AH peptides as agents to immobilize lipid molecules, thus creating a patterned solid support with partition-defined areas of freely mobile lipid bilayers. This architecture could have a wide range of applications in novel sensing, biotechnology, high-throughput screening, and biomimetic strategies.

    View details for DOI 10.1021/1000640h

    View details for Web of Science ID 000249948700058

    View details for PubMedID 17803321

  • Employing two different quartz crystal microbalance models to study changes in viscoelastic behavior upon transformation of lipid vesicles to a bilayer on a gold surface ANALYTICAL CHEMISTRY Chot, N., Kanazawa, K. K., Glenn, J. S., Frank, C. W. 2007; 79 (18): 7027-7035


    By analyzing the viscoelastic properties of two distinct layers, a layer of "soft" vesicles and a "rigid" bilayer, we have created a model system to permit the study of film behavior in the region of nonlinear mass and frequency change (non-Sauerbrey). The structural transformation of lipid vesicles to a bilayer is shown to be accompanied by significant changes in their physical properties. After the adsorption and saturation of intact vesicles on gold surfaces, the adsorbed vesicle layer exhibits a soft, water-rich, viscoelastic state. The AH peptide, a vesicle-destabilizing agent, is then added to trigger the formation of a much thinner (approximately 5 nm), compact, and rigid bilayer. In this study, we used the quartz crystal microbalance with dissipation technique. Large non-Sauerbrey frequency and energy dissipation changes characterize the viscoelastic nature of adsorbed intact vesicle films thicker than approximately 10 nm. Once the transformation is complete, the frequency changes along with zero energy dissipation for sufficiently thin films (t approximately 5 nm) were effectively modeled with the Sauerbrey equation. Furthermore, we checked the validity of the Voigt-Voinova model in which the quartz substrate is treated as a Voigt element, which is beyond the Sauerbrey description. The calculations treating the film as having a constant viscosity agreed well with the Voigt-Voinova model. These results were compared to calculations done using the electromechanical (EM) model, which does not require a series expansion. The Voigt-Voinova results were in excellent agreement with the EM model, providing evidence that the expansion used in their study is quite accurate.

    View details for Web of Science ID 000249527700016

    View details for PubMedID 17685547

  • Kinetics of oligonucleotide hybridization to DNA probe Arrays on high-capacity porous silica substrates BIOPHYSICAL JOURNAL Glazer, M. I., Fidanza, J. A., McGall, G. H., Trulson, M. O., Forman, J. E., Frank, C. W. 2007; 93 (5): 1661-1676


    We have investigated the kinetics of DNA hybridization to oligonucleotide arrays on high-capacity porous silica films that were deposited by two techniques. Films created by spin coating pure colloidal silica suspensions onto a substrate had pores of approximately 23 nm, relatively low porosity (35%), and a surface area of 17 times flat glass (for a 0.3-microm film). In the second method, latex particles were codeposited with the silica by spin coating and then pyrolyzed, which resulted in larger pores (36 nm), higher porosity (65%), and higher surface area (26 times flat glass for a 0.3-microm film). As a result of these favorable properties, the templated silica hybridized more quickly and reached a higher adsorbed target density (11 vs. 8 times flat glass at 22 degrees C) than the pure silica. Adsorption of DNA onto the high-capacity films is controlled by traditional adsorption and desorption coefficients, as well as by morphology factors and transient binding interactions between the target and the probes. To describe these effects, we have developed a model based on the analogy to diffusion of a reactant in a porous catalyst. Adsorption values (k(a), k(d), and K) measured on planar arrays for the same probe/target system provide the parameters for the model and also provide an internally consistent comparison for the stability of the transient complexes. The interpretation of the model takes into account factors not previously considered for hybridization in three-dimensional films, including the potential effects of heterogeneous probe populations, partial probe/target complexes during diffusion, and non-1:1 binding structures. The transient complexes are much less stable than full duplexes (binding constants for full duplexes higher by three orders of magnitude or more), which may be a result of the unique probe density and distribution that is characteristic of the photolithographically patterned arrays. The behavior at 22 degrees C is described well by the predictive equations for morphology, whereas the behavior at 45 degrees C deviates from expectations and suggests that more complex phenomena may be occurring in that temperature regime.

    View details for DOI 10.1529/biophysj.106.103275

    View details for Web of Science ID 000248722200023

    View details for PubMedID 17496028

  • Histological processing of pH-sensitive hydrogels used in corneal implant applications JOURNAL OF HISTOTECHNOLOGY Farooqui, N., Myung, D., Koh, W., Masek, M., Dalal, R., Carrasco, M. R., Noolandi, J., Frank, C. W., Ta, C. N. 2007; 30 (3): 157-163
  • Biomimetic strain hardening in interpenetrating polymer network hydrogels POLYMER Myung, D., Koh, W., Ko, J., Hu, Y., Carrasco, M., Noolandi, J., Ta, C. N., Frank, C. W. 2007; 48 (18): 5376-5387
  • Employing an amphipathic viral peptide to create a lipid bilayer on Au and TiO2 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Cho, N., Cho, S., Cheong, K. H., Glenn, J. S., Frank, C. W. 2007; 129 (33): 10050-?

    View details for DOI 10.1021/ja0701412

    View details for Web of Science ID 000248896400003

    View details for PubMedID 17661464

  • Binding dynamics of hepatitis C virus' NS5A amphipathic peptide to cell and model membranes JOURNAL OF VIROLOGY Cho, N., Cheong, K. H., Lee, C., Frank, C. W., Glenn, J. S. 2007; 81 (12): 6682-6689


    Membrane association of the hepatitis C virus NS5A protein is required for viral replication. This association is dependent on an N-terminal amphipathic helix (AH) within NS5A and is restricted to a subset of host cell intracellular membranes. The mechanism underlying this specificity is not known, but it may suggest a novel strategy for developing specific antiviral therapy. Here we have probed the mechanistic details of NS5A AH-mediated binding to both cell-derived and model membranes by use of biochemical membrane flotation and quartz crystal microbalance (QCM) with dissipation. With both assays, we observed AH-mediated binding to model lipid bilayers. When cell-derived membranes were coated on the quartz nanosensor, however, significantly more binding was detected, and the QCM-derived kinetic measurements suggested the existence of an interacting receptor in the target membranes. Biochemical flotation assays performed with trypsin-treated cell-derived membranes exhibited reduced AH-mediated membrane binding, while membrane binding of control cytochrome b5 remained unaffected. Similarly, trypsin treatment of the nanosensor coated with cellular membranes abolished AH peptide binding to the cellular membranes but did not affect the binding of a control lipid-binding peptide. These results therefore suggest that a protein plays a critical role in mediating and stabilizing the binding of NS5A's AH to its target membrane. These results also demonstrate the successful development of a new nanosensor technology ideal both for studying the interaction between a protein and its target membrane and for developing inhibitors of that interaction.

    View details for DOI 10.1128/JVI.02783-06

    View details for Web of Science ID 000246987500050

    View details for PubMedID 17428867

  • Glyco-acrylate copolymers for bilayer tethering on benzophenone-modified substrates COLLOIDS AND SURFACES B-BIOINTERFACES Hwang, L. Y., Goetz, H., Hawker, C. J., Frank, C. W. 2007; 54 (2): 127-135


    Model biological membranes are becoming increasingly important for studying fundamental biophysical phenomena and developing membrane-based devices. To address the anticipated problem of non-physiological interactions between membrane proteins and substrates seen in "solid-supported lipid bilayers" that are formed directly on hydrophilic substrates, we have developed a polymer-tethered lipid bilayer system based on a random copolymer with multiple lipid analogue anchors and a glyco-acrylate backbone. This system is targeted at applications that, most importantly, require stability and robustness since each copolymer has multiple lipid analogues that insert into the bilayer. We have combined this copolymer with a flexible photochemical coupling scheme that covalently attaches the copolymer to the substrate. The Langmuir isotherms of mixed copolymer/free lipid monolayers measured at the air-water interface indicate that the alkyl chains of the copolymer lipid analogues and the free lipids dominate the film behavior. In addition, no significant phase transitions are seen in the isotherms, while hysteresis experiments confirm that no irreversible states are formed during the monolayer compression. Isobaric creep experiments at the air-water interface and AFM experiments of the transferred monolayer are used to guide processing parameters for creating a fluid, homogeneous bilayer. Bilayer homogeneity and fluidity are monitored using fluorescence microscopy. Continuous bilayers with lateral diffusion coefficients of 0.6 microm(2)/s for both leaflets of the bilayer are observed for a 5% copolymer system.

    View details for DOI 10.1016/j.colsurfb.2006.08.010

    View details for Web of Science ID 000244473900001

    View details for PubMedID 17207977

  • Kinetics of oligonucleotide hybridization to photolithographically patterned DNA arrays ANALYTICAL BIOCHEMISTRY Glazer, M., Fidanza, J. A., McGall, G. H., Trulson, M. O., Forman, J. E., Suseno, A., Frank, C. W. 2006; 358 (2): 225-238


    The hybridization kinetics of oligonucleotide targets to oligonucleotide probe arrays synthesized using photolithographic fabrication methods developed by Affymetrix have been measured. Values for the fundamental adsorption parameters, k(a), k(d), and K, were determined at both room temperature and 45 degrees C by monitoring the hybridization of fluorescently labeled targets to the array. The values for these parameters and the adsorbed target density (

    View details for DOI 10.1016/j.ab.2006.07.042

    View details for Web of Science ID 000241681000008

    View details for PubMedID 16982029

  • Bonding and molecular environment effects on near-infrared optical absorption behavior in nonlinear optical monoazo chromophore-polymer materials MACROMOLECULES Barto, R. R., Frank, C. W., Bedworth, P. V., Taylor, R. E., Anderson, W. W., Ermer, S., Jen, A. K., Luo, J. D., Ma, H., Tang, H., Lee, M., Ren, A. S. 2006; 39 (22): 7566-7577

    View details for DOI 10.1021/mo060033k

    View details for Web of Science ID 000241492700020

  • Quantitative analysis of tethered vesicle assemblies by quartz crystal microbalance with dissipation monitoring: Binding dynamics and bound water content LANGMUIR Patel, A. R., Frank, C. W. 2006; 22 (18): 7587-7599


    To implement the molecular recognition properties of membrane proteins for applications including biosensors and diagnostic arrays, the construction of a biomimetic platform capable of maintaining protein structure and function is required. In this paper, we describe a tethered phospholipid vesicle assembly that overcomes the major limitations of planar supported lipid bilayers and alternative biomimetic membrane platforms and characterize it using quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence microscopy. We provide evidence of a one-step mechanism for bilayer formation and monitor the subsequent adsorption and binding of streptavidin, vesicles, and streptavidin-coated microspheres. For all three species, we identify a critical surface density above which a significant amount of coupled interstitial water contributes to the response of the quartz resonator in a phenomenon similar to dynamic coupling due to surface roughness. A Sauerbrey-type analysis is sufficient to accurately interpret the QCM-D results for streptavidin binding if water is treated as an additional inertial mass, but viscoelastic models must be invoked for vesicle and microsphere binding. Additionally, we present evidence of vesicle flattening, possibly enhanced by a biotin-mediated membrane-membrane interaction.

    View details for DOI 10.1021/la0610452

    View details for Web of Science ID 000239921800020

    View details for PubMedID 16922537

  • Fluid supported lipid bilayers containing mono sialoganglioside GM1: A QCM-D and FRAP study COLLOIDS AND SURFACES B-BIOINTERFACES Weng, K. C., Kanter, J. L., Robinson, W. H., Frank, C. W. 2006; 50 (1): 76-84


    In an effort to use model fluid membranes for immunological studies, we compared the formation of planar phospholipid bilayers supported on silicon dioxide surfaces with and without incorporation of glycolipids as the antigen for in situ antibody binding. Dynamic light scattering measurements did not differentiate the hydrodynamic volumes of extruded small unilamellar vesicles (E-SUVs) containing physiologically relevant concentrations (0.5-5 mol%) of monosialoganglioside GM1 (GM1) from exclusive egg yolk L-alpha-phosphatidylcholine (egg PC) E-SUVs. However, quantifiable differences in deposition mass and dissipative energy loss emerged in the transformation of 5 mol% GM1/95 mol% egg PC E-SUVs to planar supported lipid bilayers (PSLBs) by vesicle fusion on thermally evaporated SiO2, as monitored by the quartz crystal microbalance with dissipation (QCM-D) technique. Compared to the 100 mol% egg PC bilayers on the same surface, E-SUVs containing 5 mol% GM1 reached a approximately 12% higher mass and a lower dissipative energy loss during bilayer transformation. PSLBs with 5 mol% GM1 are approximately 18% heavier than 100 mol% egg PC and approximately 11% smaller in projected area per lipid, indicating an increased rigidity and a tighter packing. Subsequent binding of polyclonal immunoglobulin G anti-GM1 to the PSLBs was performed in situ and showed specificity. The anti-GM1 to GM1 ratios at equilibrium were roughly proportional to the concentrations of anti-GM1 administered in the solution. Fluorescence recovery after photobleaching was utilized to verify the retained, albeit reduced lateral fluidity of the supported membranes. Five moles percentage of GM1 membranes (GM1 to PC ratio approximately 1:19) decorated with 1 mol% N-(Texas Red sulfonyl)-1,2-dihexadecanoyl-sn-glycerol-3-phosphoethanolamine (Texas Red DHPE) exhibited an approximately 16% lower diffusion coefficient of 1.32+/-0.06 microm2/s, compared to 1.58+/-0.04 microm2/s for egg PC membranes without GM1 (p<0.01). The changes in vesicle properties and membrane lateral fluidity are attributed to the interactions of GM1 with itself and GM1 with other membrane lipids. This system allows for molecules of interest such as GM1 to exist on a more biologically relevant surface than those used in conventional methods such as ELISA. Our analysis of rabbit serum antibodies binding to GM1 demonstrates this platform can be used to test for the presence of anti-lipid antibodies in serum.

    View details for DOI 10.1016/j.colsurfb.2006.03.010

    View details for Web of Science ID 000238515200012

    View details for PubMedID 16730958

  • Surface reorganization of an amphiphilic block copolymer film studied by NEXAFS spectroscopy MACROMOLECULES Theato, P., Brehmer, M., Conrad, L., Frank, C. W., Funk, L., Yoon, D. Y., Luning, J. 2006; 39 (7): 2592-2595

    View details for DOI 10.1021/ma0509964

    View details for Web of Science ID 000236574400026

  • Capillary aging of the contacts between glass spheres and a quartz resonator surface PHYSICAL REVIEW LETTERS D'Amour, J. N., Stalgren, J. J., Kanazawa, K. K., Frank, C. W., Rodahl, M., Johannsmann, D. 2006; 96 (5)


    The strength of the contacts between small glass spheres and the surface of a quartz crystal resonator has been probed based on the increase of resonance frequency induced upon sphere contact. The acoustic interaction between the sphere and the plate is modeled as a low-frequency coupled resonance; the dependence of the resonant parameters on overtone order lends support to this model. After exposing the sample to humid air and drying it again, the contact strength increases at least tenfold due to capillary forces--we observe a hysteretic form of the sand-castle effect. Repeated wet-dry cycles reveal logarithmic capillary aging with time. The experiments suggest that the drying of the liquid bridges leads to a contraction of small voids in the contact zone, subsequently increasing cohesion.

    View details for DOI 10.1103/PhysRevLett.96.058301

    View details for Web of Science ID 000235252200097

    View details for PubMedID 16487001

  • Synthesis of well-defined hydrogel networks using Click chemistry CHEMICAL COMMUNICATIONS Malkoch, M., Vestberg, R., Gupta, N., Mespouille, L., Dubois, P., Mason, A. F., Hedrick, J. L., Liao, Q., Frank, C. W., Kingsbury, K., Hawker, C. J. 2006: 2774-2776


    New PEG-based hydrogel materials have been synthesized by Click chemistry and shown to result in well-defined networks having significantly improved mechanical properties; the selectivity of the azide/acetylene coupling reaction also allows for the incorporation of various additives and functional groups leading to chemical tailoring of the hydrogels.

    View details for DOI 10.1039/b603438a

    View details for Web of Science ID 000238616900010

    View details for PubMedID 17009459

  • Probing interparticle adhesion of dry and wet granular materials with the quartz crystal microbalance PROCEEDINGS OF THE 2006 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM AND EXPOSITION, VOLS 1 AND 2 Johannsmann, D., d'Amour, N. J., Kanazawa, K. K., Stalgren, J. J., Frank, C. W., Rodahl, M. 2006: 550-553
  • The dramatic effect of architecture on the self-assembly of block copolymers at interfaces LANGMUIR Kim, Y., Pyun, J., Frechet, J. M., Hawker, C. J., Frank, C. W. 2005; 21 (23): 10444-10458


    Dramatic morphological changes are observed in the Langmuir-Blodgett (LB) film assemblies of poly(ethylene glycol)-b-(styrene-r-benzocyclobutene) block copolymer (PEG-b-(S-r-BCB)) after intramolecular cross-linking of the S-r-BCB block to form a linear-nanoparticle structure. To isolate architectural effects and allow direct comparison, the linear block copolymer precursor and the linear-nanoparticle block copolymer resulting from selective intramolecular cross-linking of the BCB units were designed to have exactly the same molecular weight and chemical composition but different architecture. It was found that the effect of architecture is pronounced with these macromolecular isomers, which self-assemble into dramatically different surface aggregates. The linear block copolymer forms disklike surface assemblies over the range of compression states, while the linear-nanoparticle block copolymer exhibits long (>10 microm) wormlike aggregates whose length increases as a function of increasing cross-linking density. It is shown that the driving force behind the morphological change is a combination of the altered molecular geometry and the restricted degree of stretching of the nanoparticle block because of the intramolecular cross-linking. A modified approach to interpret the pi-A isotherm, which includes presence of the block copolymer aggregates, is also presented, while the surface rheological properties of the block copolymers at the air-water interface provide in-situ evidence of the aggregates' presence at the air-water interface.

    View details for DOI 10.1021/la047122f

    View details for Web of Science ID 000233129500037

    View details for PubMedID 16262305

  • Near-infrared optical-absorption behavior in high-beta nonlinear optical chromophore-polymer guest-host materials. II. Dye spacer length effects in an amorphous polycarbonate copolymer host JOURNAL OF CHEMICAL PHYSICS Barto, R. R., Frank, C. W., BEDWORTH, P. V., Ermer, S., Taylor, R. E. 2005; 122 (23)


    In the second of a three-part series, spectral absorption behavior of nonlinear optical (NLO) dyes incorporated into amorphous polycarbonate, comprised of a homologous series of dialkyl spacer groups extending from the midsection of the dye molecule, is characterized by UV-Vis and photothermal deflection spectroscopy. The dyes are structural analogs of the NLO dye FTC [2-(3-cyano-4-{2-[5-(2-{4-[ethyl-(2-methoxyethyl)amino]phenyl}vinyl)-3,4-diethylthiophen-2-yl]vinyl}-5,5-dimethyl-5H-furan-2-ylidene)malononitrile]. Previous Monte Carlo calculations [B. H. Robinson and L. R. Dalton, J. Phys. Chem. A 104, 4785 (2000)] predict a strong dependence of the macroscopic nonlinear optical susceptibility on the chromophore waist: length aspect ratio in electric-field-poled films arising from interactions between chromophores. It is expected that these interactions will play a role in the absorption characteristics of unpoled films, as well. The spacer groups range in length from diethyl to dihexyl, and each dye is studied over a wide range of concentrations. Among the four dyes studied, a universal dependence of near-IR loss on inhomogeneous broadening of the dye main absorption peak is found. The inhomogeneous width and its concentration dependence are seen to vary with spacer length in a manner characteristic of the near-IR loss-concentration slope at transmission wavelengths of 1.06 and 1.3 mum, but not at 1.55 mum. The lower wavelength loss behavior is assigned to purely Gaussian broadening, and is described by classical mixing thermodynamic quantities based on the Marcus theory of inhomogeneous broadening [R. A. Marcus, J. Chem. Phys. 43, 1261 (1965)], modeled as a convolution of dye-dye dipole broadening and dye-polymer van der Waals broadening. The Gaussian dipole interactions follow a Loring dipole-broadening description [R. F. Loring, J. Phys. Chem. 94, 513 (1990)] dominated by the excited-state dipole moment, and have a correlated homogeneous broadening contribution. The long-wavelength loss behavior has a non-Gaussian dye-dye dipole contribution which follows Kador's broadening analysis [L. Kador, J. Chem. Phys. 95, 5574 (1991)], with a net broadening described by a convolution of this term with a Gaussian van der Waals interaction given by Obata et al. [M. Obata, S. Machida, and K. Horie, J. Polym. Sci. B 37, 2173 (1999)], with each term governed by the dye spacer length. A minimum in broadening and loss-concentration slope at a spacer length of four carbons per alkyl at all wavelengths has important consequences for practical waveguide devices, and is of higher aspect ratio than the spherical limit shown by Robinson and Dalton to minimize dipole interactions under a poling field.

    View details for DOI 10.1063/1.1929742

    View details for Web of Science ID 000230091400064

    View details for PubMedID 16008487

  • Phase separation behavior of poly(methyl methacrylate-co-dimethylaminoethyl methacrylate)/methyl silsesquioxane hybrid nanocomposites studied by dansyl fluorescence CHEMISTRY OF MATERIALS Huang, Q. R., Frank, C. W., Mecerreyes, D., Volksen, W., Miller, R. D. 2005; 17 (6): 1521-1528

    View details for DOI 10.1021/cm048774s

    View details for Web of Science ID 000227772100039

  • Surface characteristics of polyfluorene films studied by polarization-dependent NEXAFS spectroscopy MACROMOLECULES Jung, Y., Cho, T. Y., Yoon, D. Y., Frank, C. W., Luning, J. 2005; 38 (3): 867-872

    View details for DOI 10.1021/ma0483221

    View details for Web of Science ID 000226764500031

  • Vesicle adsorption and lipid bilayer formation on glass studied by atomic force microscopy LANGMUIR Schonherr, H., Johnson, J. M., Lenz, P., Frank, C. W., Boxer, S. G. 2004; 20 (26): 11600-11606


    The adsorption of phosphatidylcholine (PC) vesicles (30, 50, and 100 nm nominal diameters) and of dye-labeled PC vesicles (labeled with 6% Texas Red fluorophore (TR) and encapsulated carboxy fluorescein (CF)) to glass surfaces was studied by contact mode atomic force microscopy in aqueous buffer. These studies were performed in part to unravel details of the previously observed isolated rupture of dye-labeled PC vesicles on glass (Johnson, J. M.; Ha, T.; Chu, S.; Boxer, S. G. Biophys. J. 2002, 83, 3371-3379), specifically to differentiate partial rupture, that is, pore formation and leakage of entrapped dye, from full rupture to form bilayer disks. In addition, the adhesion potential of PC vesicles on glass was calculated based upon the adhesion-driven flattening of adsorbed vesicles and a newly developed theoretical model. The vesicles were found to flatten considerably upon adsorption to glass (width-to-height ratio of approximately 5), which leads to an estimate for the adhesion potential and for the critical rupture radius of 1.5 x 10(-4) J/m2 and 250 nm, respectively. Independent of vesicle size and loading with dye molecules, the adsorption of intact vesicles was observed at all concentrations below a threshold concentration, above which the formation of smooth lipid bilayers occurred. In conjunction with previous work (Johnson, J. M.; Ha, T.; Chu, S.; Boxer, S. G. Biophys. J. 2002, 83, 3371-3379), these data show that 6% TR 20 mM CF vesicles adsorb to the surface intact but undergo partial rupture in which they exchange content with the external buffer.

    View details for DOI 10.1021/la049302v

    View details for Web of Science ID 000225816800046

    View details for PubMedID 15595789

  • Planar bilayer lipid membranes supported on mesoporous aerogels, xerogels, and Vycor((R)) glass: an epifluorescence microscopy study Weng, K. C., Stalgren, J. J., Risbud, S. H., Frank, C. W. ELSEVIER SCIENCE BV. 2004: 46-53
  • In situ formation and characterization of poly(ethylene glycol)-supported lipid bilayers on gold surfaces LANGMUIR Munro, J. C., Frank, C. W. 2004; 20 (24): 10567-10575


    Inclusion of a polymer cushion between a lipid bilayer membrane and a solid surface has been suggested as a means to provide a soft, deformable layer that will allow for transmembrane protein insertion and mobility. In this study, mobile, tethered lipid bilayers were formed on a poly(ethylene glycol) (PEG) support via a two-step adsorption process. The PEG films were prepared by coadsorbing a heterofunctional, telechelic PEG lipopolymer (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-(pyridyldithio)propionate]) (DSPE-PEG-PDP) and a nonlipid functionalized PEG-PDP from an ethanol/water mixture, as described in a previous paper (Munro, J. C.; Frank, C. W. Langmuir 2004, 20, 3339-3349). Then a two-step lipid adsorption strategy was used. First, lipids were adsorbed onto the PEG support from a hexane solution. Second, vesicles were adsorbed and fused on the surface to create a bilayer in an aqueous environment. Fluorescence recovery after photobleaching experiments show that this process results in mobile bilayers with diffusion coefficients on the order of 2 microm2/s. The mobility of the bilayers is decreased slightly by increasing the density of tethered lipids. The formation of bilayers, and not multilayer structures, is also confirmed by surface plasmon resonance, which was used to determine in situ film thickness, and by fluorimetry, which was used to determine quantitatively the fluorescence intensity for each 18 by 18 mm sample. Unfortunately, fluorescence microscopy also shows that there are large defects on the samples, which limits the utility of this system.

    View details for DOI 10.1021/la048378o

    View details for Web of Science ID 000225207400029

    View details for PubMedID 15544386

  • Highly fluorinated and crosslinkable dendritic polymer for photonic applications MACROMOLECULAR RAPID COMMUNICATIONS Ma, H., Luo, J. D., Kang, S. H., Wong, S., Kang, J. W., Jen, A. K., Barto, R., Frank, C. W. 2004; 25 (19): 1667-1673
  • Sum-frequency spectroscopy and imaging of aligned helical polypeptides IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS Knoesen, A., Pakalnis, S., Wang, M., Wise, W. D., Lee, N., Frank, C. W. 2004; 10 (5): 1154-1163
  • Fluid biomembranes supported on nanoporous aerogel/xerogel substrates LANGMUIR Weng, K. C., Stalgren, J. J., Duval, D. J., Risbud, S. H., Frank, C. W. 2004; 20 (17): 7232-7239


    Planar supported lipid bilayers have attracted immense interest for their properties as model cell membranes and for potential applications in biosensors and lab-on-a-chip devices. We report the formation of fluid planar biomembranes on hydrophilic silica aerogels and xerogels. Scanning electron microscopy results showed the presence of interconnected silica beads of approximately 10-25 nm in diameter and nanoscale open pores of comparable size for the aerogel and grain size of approximately 36-104 nm with approximately 9-24 nm diameter pores for the xerogel. When the aerogel/xerogel was prehydrated and then allowed to incubate in l-alpha-phosphatidylcholine (egg yolk PC) unilamellar vesicle (approximately 30 nm diameter) solution, lipid bilayers were formed due to the favorable interaction of vesicles with the hydroxyl-abundant silica surface. Lateral mobility of labeled lipid N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine was retained in the membranes. A diffusion coefficient of 0.61 +/- 0.22 microm(2)/s was determined from fluorescence recovery after photobleaching analysis for membranes on aerogels, compared to 2.46 +/- 0.35 microm(2)/s on flat glass. Quartz crystal microbalance-dissipation was utilized to monitor the kinetics of the irreversible adsorption and fusion of vesicles into bilayers on xerogel thin films.

    View details for DOI 10.1021/la049940d

    View details for Web of Science ID 000223276400040

    View details for PubMedID 15301510

  • Perfluorocyclobutane-based polyester(arylene ether)s for applications in integrated optics MACROMOLECULES Wong, S., Ma, H., Jen, A. K., Barto, R., Frank, C. W. 2004; 37 (15): 5578-5585

    View details for DOI 10.1021/ma049783p

    View details for Web of Science ID 000222856000017

  • Langmuir and Langmuir-Blodgett films of amphiphilic bistable rotaxanes LANGMUIR Lee, I. C., Frank, C. W., Yamamoto, T., Tseng, H. R., Flood, A. H., Stoddart, J. F., Jeppesen, J. O. 2004; 20 (14): 5809-5828


    A series of amphiphilic bistable [2]rotaxanes--in which a ring-shaped component, the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), has been assembled around two recognition sites, a tetrathia-fulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) ring system, situated apart at different strategic locations within the central polyether section of an amphiphilic dumbbell component that is terminated by a hydrophobic tetraarylmethane-based stopper (near the TTF unit) at one end and by a hydrophilic tetraarylmethane-based stopper (near the DNP ring system) at the other end--has been designed and synthesized. The effects of systematic changes in the constitutions of the three ethylene glycol tails (diethylene or tetraethylene glycol) and end groups (hydroxyl or methoxyl functions) attached to the hydrophilic stoppers on Langmuir film balance and surface rheology experiments at 20 degreesC were examined to determine the monolayer stabilities and co-conformations of the [2] rotaxanes and their free dumbbell counterparts. These experiments allow us to propose a model for the rotaxane's structures at different surface pressures. All the [2]rotaxanes form stable Langmuir films. These films typically pass from a liquid-expanded region to a liquid-condensed region. The transition between the two regions was either directly observed or ascertained using film stability experiments. Film balance and surface rheology experiments showed that the addition of the tetracationic cyclophane component and hydroxyl end groups markedly increased the stabilities and viscoelasticity of the films.

    View details for DOI 10.1021/la0361518

    View details for Web of Science ID 000222429200027

    View details for PubMedID 16459596

  • Near-infrared optical absorption Behavior in high-beta nonlinear optical chromophore-polymer guest-host materials. 1. Continuum dielectric effects in polycarbonate hosts JOURNAL OF PHYSICAL CHEMISTRY B Barto, R. R., Frank, C. W., BEDWORTH, P. V., Ermer, S., Taylor, R. E. 2004; 108 (25): 8702-8715

    View details for DOI 10.1021/jp037239x

    View details for Web of Science ID 000222125900029

  • Influence of substrate chemistry on the properties of ultrathin polymer films D'Amour, J. N., Okoroanyanwu, U., Frank, C. W. ELSEVIER SCIENCE BV. 2004: 209-217
  • Interaction of poly(vinylidene fluoride) with graphite particles. 2. Effect of solvent evaporation kinetics and chemical properties of PVDF on the surface morphology of a composite film and its relation to electrochemical performance CHEMISTRY OF MATERIALS Yoo, M., Frank, C. W., Mori, S., Yamaguchi, S. 2004; 16 (10): 1945-1953
  • Adsorption of lipid-functionalized poly(ethylene glycol) to gold surfaces as a cushion for polymer-supported lipid bilayers LANGMUIR Munro, J. C., Frank, C. W. 2004; 20 (8): 3339-3349


    Inclusion of a polymer cushion between a lipid bilayer membrane and a solid surface has been suggested as a means to provide a soft, deformable layer that will allow for transmembrane protein insertion and mobility. In this study, the properties of a heterofunctional, telechelic PEG lipopolymer (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N- [3-(2-(pyridyldithio)propionate]) (DSPE-PEG-PDP) adsorbed from ethanol and water solutions onto gold surfaces were studied using a variety of surface-sensitive techniques. X-ray photoelectron spectroscopy showed that the PEG molecules are tethered to the gold surface via thiolate bonds. When adsorbed from water, ethanol, or their mixtures, reflection-absorption infrared spectroscopy showed that amorphous PEG layers with disordered DSPE alkyl chains were formed, independent of adsorption time or solution concentration. On the basis of advancing and receding water and hexadecane contact angles on the lipopolymer films, the DSPE lipid groups appear to segregate from the PEG layer and become exposed at the surface of the polymer films. Swelling observed in surface plasmon resonance experiments and the large contact angle hysteresis observed indicate that highly swellable, mobile films capable of molecular rearrangements are formed. The self-assembling and amorphous properties of these PEG layers make them ideal candidates as polymer cushions for polymer-supported lipid bilayers. The DSPE surface concentration can be controlled, to a limited degree, by varying the adsorption time of DSPE-PEG-PDP from ethanol. A more effective strategy is to coadsorb DSPE-PEG-PDP with a non-lipid-functionalized PEG-PDP from an ethanol/water mixture, which allows the PEG thickness and density to remain constant while decreasing the density of DSPE groups.

    View details for DOI 10.1021/la036062v

    View details for Web of Science ID 000220750300050

    View details for PubMedID 15875867

  • Polyacrylamide adsorption from aqueous solutions on gold and silver surfaces monitored by the quartz crystal microbalance MACROMOLECULES Munro, J. C., Frank, C. W. 2004; 37 (3): 925-938

    View details for DOI 10.1021/ma030297w

    View details for Web of Science ID 000188803000034

  • Nanoporous, low-dielectric constant organosilicate materials derived from inorganic polymer blends POLYMERS FOR MICROELECTRONICS AND NANOELECTRONICS Miller, R. D., Volksen, W., Lee, V. Y., Connor, E., Magbitang, T., Zafran, R., Sundberg, L., Hawker, C. J., HEDRICK, J. L., Huang, E., Toney, M., Huang, Q. R., Frank, C. W., Kim, H. C. 2004; 874: 144-160
  • Photo-cross-linkable PNIPAAm copolymers. 5. Mechanical properties of hydrogel layers LANGMUIR Harmon, M. E., Kucking, D., Frank, C. W. 2003; 19 (26): 10660-10665

    View details for DOI 10.1021/la030232m

    View details for Web of Science ID 000187507500007

  • Photo-cross-linkable PNIPAAm copolymers. 4. Effects of copolymerization and cross-linking on the volume-phase transition in constrained hydrogel layers LANGMUIR Harmon, M. E., Kuckling, D., Pareek, P., Frank, C. W. 2003; 19 (26): 10947-10956

    View details for DOI 10.1021/la030217h

    View details for Web of Science ID 000187507500044

  • Highly fluorinated trifluorovinyl aryl ether monomers and perfluorocyclobutane aromatic ether polymers for optical waveguide applications MACROMOLECULES Wong, S., Ma, H., Jen, A. K., Barto, R., Frank, C. W. 2003; 36 (21): 8001-8007

    View details for DOI 10.1021/ma034467g

    View details for Web of Science ID 000186058700018

  • Miscibility in organic/inorganic hybrid nanocomposites suitable for microelectronic applications: Comparison of modulated differential scanning calorimetry and fluorescence spectroscopy MACROMOLECULES Huang, Q. R., Kim, H. C., Huang, E., Mecerreyes, D., HEDRICK, J. L., Volksen, W., Frank, C. W., Miller, R. D. 2003; 36 (20): 7661-7671

    View details for DOI 10.1021/ma034034d

    View details for Web of Science ID 000185731100031

  • Fast-responsive semi-interpenetrating hydrogel networks imaged with confocal fluorescence microscopy POLYMER Harmon, M. E., Schrof, W., Frank, C. W. 2003; 44 (22): 6927-6936
  • Adsorption of disulfide-modified polyacrylamides to gold and silver surfaces as cushions for polymer-supported lipid bilayers POLYMER Munro, J. C., Frank, C. W. 2003; 44 (20): 6335-6344
  • Photolithographic polymerization of diacetylene-containing phospholipid bilayers studied by multimode atomic force microscopy LANGMUIR Morigaki, K., Schonherr, H., Frank, C. W., Knoll, W. 2003; 19 (17): 6994-7002

    View details for DOI 10.1021/la034078f

    View details for Web of Science ID 000184768600066

  • A microfluidic actuator based on thermoresponsive hydrogels POLYMER Harmon, M. E., Tang, M., Frank, C. W. 2003; 44 (16): 4547-4556
  • Effect of poly(vinylidene fluoride) binder crystallinity and graphite structure on the mechanical strength of the composite anode in a lithium ion battery POLYMER Yoo, M., Frank, C. W., Mori, S., Yamaguchi, S. 2003; 44 (15): 4197-4204
  • A hyperbranched aromatic fluoropolyester for photonic applications MACROMOLECULES Kang, S. H., Luo, J. D., Ma, H., Barto, R. R., Frank, C. W., Dalton, L. R., Jen, A. K. 2003; 36 (12): 4355-4359

    View details for DOI 10.1021/ma0217229

    View details for Web of Science ID 000183526900017

  • Morphology of vapor-deposited poly(alpha-amino acid) films LANGMUIR Lee, N. H., Christensen, L. M., Frank, C. W. 2003; 19 (8): 3525-3530

    View details for DOI 10.1021/la020788u

    View details for Web of Science ID 000182389100065

  • Nucleation and crystallization of low-crystallinity polypropylene followed in situ by hot stage atomic force microscopy MACROMOLECULES Schonherr, H., Waymouth, R. M., Frank, C. W. 2003; 36 (7): 2412-2418

    View details for DOI 10.1021/ma0208335

    View details for Web of Science ID 000182045800031

  • Ultrathin films of poly(ethylene oxides) on oxidized silicon. 1. Spectroscopic characterization of film structure and crystallization kinetics MACROMOLECULES Schonherr, H., Frank, C. W. 2003; 36 (4): 1188-1198

    View details for DOI 10.1021/ma020685i

    View details for Web of Science ID 000181117200033

  • Interaction of poly(vinylidene fluoride) with graphite particles. 1. Surface morphology of a composite film and its relation to processing parameters CHEMISTRY OF MATERIALS Yoo, M., Frank, C. W., Mori, S. 2003; 15 (4): 850-861

    View details for DOI 10.1021/cm0209970

    View details for Web of Science ID 000181120300007

  • Ultrathin films of poly(ethylene oxides) on oxidized silicon. 2. In situ study of crystallization and melting by hot stage AFM MACROMOLECULES Schonherr, H., Frank, C. W. 2003; 36 (4): 1199-1208

    View details for DOI 10.1021/ma020686a

    View details for Web of Science ID 000181117200034

  • Surface-initiated vapor polymerization of various alpha-amino acids LANGMUIR Lee, N. H., Frank, C. W. 2003; 19 (4): 1295-1303

    View details for DOI 10.1021/la020432i

    View details for Web of Science ID 000181017700047

  • Photophysical characterization of conformational rearrangements for amphiphilic 6-arm star block copolymers in selective solvent mixtures MACROMOLECULES Yoo, M., Heise, A., HEDRICK, J. L., Miller, R. D., Frank, C. W. 2003; 36 (1): 268-271

    View details for DOI 10.1021/ma0213394

    View details for Web of Science ID 000180364900035

  • Photo-cross-linkable PNIPAAm copolymers. 2. Effects of constraint on temperature and pH-responsive hydrogel layers MACROMOLECULES Harmon, M. E., Kuckling, D., Frank, C. W. 2003; 36 (1): 162-172

    View details for DOI 10.1021/ma021025g

    View details for Web of Science ID 000180364900024

  • Modifications to thermophysical behavior in ultrathin polymer films ADVANCES IN RESIST TECHNOLOGY AND PROCESSING XX, PTS 1 AND 2 D'Amour, J. N., Frank, C. W., Okoroanyanwu, U. 2003; 5039: 996-1007
  • Kinetics off the N-isopropyllacrylamide gel-volume phase transition in the presence off free polymer chains POLYMER GELS: FUNDAMENTALS AND APPLICATIONS Harmon, M. E., Frank, C. V. 2003; 833: 2-11
  • Nanoscale architectural control of organic functional materials for photonics NANOMATERIALS AND THEIR OPTICAL APPLICATIONS Luo, J. D., Kim, T. D., Ma, H., Liu, S., Kang, S. H., Wong, S., Haller, M., Jang, S. H., Li, H., Barto, R. R., Frank, C. W., Dalton, L. R., Jen, A. K. 2003; 5224: 104-112
  • Separation of chiral molecules using polypeptide-modified poly(vinylidene fluoride) membranes POLYMER Lee, N. H., Frank, C. W. 2002; 43 (23): 6255-?
  • Synthesis of lipo-glycopolymer amphiphiles by nitroxide-mediated living free-radical polymerization JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Gotz, H., Harth, E., Schiller, S. M., Frank, C. W., Knoll, W., Hawker, C. J. 2002; 40 (20): 3379-3391

    View details for DOI 10.1002/pola.10428

    View details for Web of Science ID 000178180400006

  • Structure and interaction of organic/inorganic hybrid nanocomposites for microelectronic applications. 1. MSSQ/P(MMA-co-DMAEMA) nanocomposites CHEMISTRY OF MATERIALS Huang, Q. R., Volksen, W., Huang, E., Toney, M., Frank, C. W., Miller, R. D. 2002; 14 (9): 3676-3685

    View details for DOI 10.1021/cm020014z

    View details for Web of Science ID 000178128900011

  • Photo-cross-linkable PNIPAAm copolymers. 1. Synthesis and characterization of constrained temperature-responsive hydrogel layers MACROMOLECULES Kuckling, D., Harmon, M. E., Frank, C. W. 2002; 35 (16): 6377-6383

    View details for DOI 10.1021/ma0203041

    View details for Web of Science ID 000177090400042

  • A surface plasmon resonance study of volume phase transitions in N-isopropylacrylamide gel films MACROMOLECULES Harmon, M. E., Jakob, T. A., Knoll, W., Frank, C. W. 2002; 35 (15): 5999-6004

    View details for DOI 10.1021/ma010985k

    View details for Web of Science ID 000176814600041

  • Unraveling the nanostructure of supramolecular assemblies of hydrogen-bonded rosettes on graphite: An atomic force microscopy study PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Schonherr, H., Paraschiv, V., Zapotoczny, S., Crego-Calama, M., Timmerman, P., Frank, C. W., Vancso, G. J., Reinhoudt, D. N. 2002; 99 (8): 5024-5027


    The self-organization of multicomponent tetrarosette assemblies into ordered nanostructures on graphite surfaces has been studied by atomic force microscopy (AFM). Real-space information on the level of individual molecules allowed us to analyze the underlying structure in unprecedented detail. In highly ordered nanorod domains, tetrarosettes 1(3) x (DEB)(12) arrange in the form of parallel rows with a spacing of 4.6 +/- 0.1 nm. High resolution AFM revealed the internal packing of the tetrarosette assemblies in these rows, which can be described by an oblique lattice with a = 2.5 +/- 0.3 nm, b = 5.0 +/- 0.1 nm, and gamma = 122 +/- 3 degrees. The results, together with recent improvements in synthetic approaches, contribute to the development of a general strategy to develop H-bonding-based nanostructures with molecular precision.

    View details for DOI 10.1073/pnas.072685399

    View details for Web of Science ID 000175087000056

    View details for PubMedID 11929980

  • Morphology of thermoplastic elastomers: Elastomeric polypropylene MACROMOLECULES Schonherr, H., Wiyatno, W., Pople, J., Frank, C. W., Fuller, G. G., Gast, A. P., Waymouth, R. M. 2002; 35 (7): 2654-2666

    View details for DOI 10.1021/ma010959m

    View details for Web of Science ID 000174559600037

  • Surface shear rheology of a polymerizable lipopolymer monolayer LANGMUIR Brooks, C. F., Thiele, J., Frank, C. W., O'Brien, D. F., Knoll, W., Fuller, G. G., Robertson, C. R. 2002; 18 (6): 2166-2173

    View details for DOI 10.1021/la0112312

    View details for Web of Science ID 000174403000032

  • Analyzing the surface temperature depression in hot stage atomic force microscopy with unheated cantilevers: Application to the crystallization of poly(ethylene oxide) LANGMUIR Schonherr, H., Bailey, L. E., Frank, C. W. 2002; 18 (2): 490-498

    View details for DOI 10.1021/la010977x

    View details for Web of Science ID 000173423700025

  • Using surface plasmon resonance and the quartz crystal microbalance to monitor in situ the interfacial behavior of thin organic films LANGMUIR Bailey, L. E., Kambhampati, D., Kanazawa, K. K., Knoll, W., Frank, C. W. 2002; 18 (2): 479-489

    View details for DOI 10.1021/la0112716

    View details for Web of Science ID 000173423700024

  • The polymer-supported phospholipid bilayer: Tethering as a new approach to substrate-membrane stabilization BIOMACROMOLECULES Naumann, C. A., Prucker, O., Lehmann, T., Ruhe, J., Knoll, W., Frank, C. W. 2002; 3 (1): 27-35


    We present a new molecular engineering approach in which a polymer-supported phospholipid bilayer is vertically stabilized by controlled covalent tethering at both the polymer-substrate and polymer-bilayer interfaces. This approach is based on lipopolymer molecules, which not only form a polymer cushion between the phospholipid bilayer and a solid glass substrate but also act as covalent connections (tethers) between the bilayer and cushion. Our approach involves Langmuir-Blodgett transfer of a phospholipid-lipopolymer monolayer followed by Schaefer transfer of a pure phospholipid monolayer and is capable of varying the tethering density between the polymer layer and the phospholipid bilayer in a very controlled manner. Further stabilization is achieved if the glass substrate is surface-functionalized with a benzophenone silane. In this case, a photocross-linking reaction between the polymer and benzophenone group allows for the covalent attachment of the polymer cushion to the glass substrate. This approach is similar to that recently reported by Wagner and Tamm in which double tethering is achieved via lipopolymer silanes (Wagner, M. L.; Tamm, L. K. Biophys. J. 2000, 79, 1400). To obtain a deeper understanding of how the covalent tethering affects the lateral mobility of the bilayer, we performed fluorescence recovery after photobleaching (FRAP) experiments on polymer-tethered bilayers at different tethering densities (lipopolymer/phospholipid molar ratios). The FRAP data clearly indicate that the hydrophobic lipopolymer moieties act as rather immobile obstacles within the phospholipid bilayer, thereby leading to hindered diffusion of phospholipids. Whereas the high lateral diffusion coefficient of D = 17.7 mum(2)/s measured at low tethering density (5 mol % lipopolymer) indicates rather unrestricted motion within the bilayer, corresponding values at moderate (10 mol % lipopolymer) and high (30 mol % lipopolymer) tethering densities of D = 9.7 mum(2)/s and D = 1.1 mum(2)/s, respectively, show significant hindered diffusion. These results are contrary to the recent findings on similar membrane systems reported by Wagner and Tamm in which no significant change in phospholipid diffusion was found between 0 and 10 mol % lipopolymer. Our experimental report leads to a deeper understanding of the complex problem of interlayer coupling and offers a path toward a compromise between stability of the whole system and lateral mobility within the bilayer. Furthermore, the FRAP measurements show that polymer-tethered membranes are very interesting model systems for studying problems of restricted diffusion within two-dimensional fluids.

    View details for DOI 10.1021/bm0100211

    View details for Web of Science ID 000174256500005

    View details for PubMedID 11866552

  • Interaction between poly(vinylidene fluoride) binder and graphite in the anode of lithium ion batteries: Rheological properties and surface chemistry MATERIALS FOR ENERGY STORAGE, GENERATION AND TRANSPORT Yoo, M. Y., Frank, C. W. 2002; 730: 167-172
  • Dendritic NLO chromophore with fluorinated dendrons for improving poling efficiency in electro-optic devices NANOSCALE OPTICS AND APPLICATIONS Jen, A. K., Luo, J. D., Ma, H., Haller, M., Barto, R. R., Frank, C. W. 2002; 4809: 79-85
  • Measuring thermophysical properties of ultrathin photoresist films ADVANCES IN RESIST TECHNOLOGY AND PROCESSING XIX, PTS 1 AND 2 D'Amour, J. N., Frank, C. W., Okoroanyanwa, U. 2002; 4690: 936-942
  • Pyrene fluorescence as a molecular probe of miscibility in organic/inorganic hybrid nanocomposites suitable for microelectronic applications ORGANIC/INORGANIC HYBRID MATERIALS-2002 Huang, Q. R., Mecerreyes, D., HEDRICK, J. L., Volksen, W., Frank, C. W., Miller, R. D. 2002; 726: 211-216
  • Polymer molecular environment effects on Disperse Red Vis-NIR absorption behavior PHOTONICS FOR SPACE ENVIRONMENTS VIII Barto, R., Frank, C. W., ERMER, S. P., Anderson, W. W., Sun, S., Maaref, S., Jen, A. K., Luo, J. D., Lee, M. 2002; 4823: 54-66
  • Photocrosslinking and SHG stability of PDRMA/PDRFC thin films LINEAR AND NONLINEAR OPTICS OF ORGANIC MATERIALS II Maaref, S., Roz, Z., Sun, S. S., Seo, K., Bonner, C. E., Barto, R., Frank, C. W. 2002; 4798: 203-211
  • Transient quartz crystal microbalance behaviors compared JOURNAL OF THE ELECTROCHEMICAL SOCIETY Geelhood, S. J., Frank, C. W., Kanazawa, K. 2002; 149 (1): H33-H38

    View details for DOI 10.1149/1.1427080

    View details for Web of Science ID 000172938900059

  • Multistep adsorption of perfluoropolyether hard-disk lubricants onto amorphous carbon substrates from solution LANGMUIR Bailey, L. E., Kanazawa, K. K., Bhatara, G., Tyndall, G. W., Kreiter, M., Knoll, W., Frank, C. W. 2001; 17 (26): 8145-8155

    View details for DOI 10.1021/la010374l

    View details for Web of Science ID 000172956200031

  • Colloidal silica films for high-capacity DNA probe arrays CHEMISTRY OF MATERIALS Glazer, M., Fidanza, J., McGall, G., Frank, C. 2001; 13 (12): 4773-4782

    View details for DOI 10.1021/cm010578n

    View details for Web of Science ID 000172889300058

  • Dendritic-linear A(x)B(x) block copolymers prepared via controlled ring-opening polymerization of lactones from orthogonally protected multifunctional initiators MACROMOLECULES Wursch, A., Moller, M., Glauser, T., Lim, L. S., Voytek, S. B., HEDRICK, J. L., Frank, C. W., Hilborn, J. G. 2001; 34 (19): 6601-6615

    View details for DOI 10.1021/ma0105035

    View details for Web of Science ID 000170853500018

  • Fluorescence studies of the hybrid composite of segmented-polyurethane and silica CHEMISTRY OF MATERIALS Goda, H., Frank, C. W. 2001; 13 (9): 2783-2787

    View details for DOI 10.1021/cm000711w

    View details for Web of Science ID 000171104200009

  • Investigation of the initiation behavior of a dendritic 12-arm initiator in atom transfer radical polymerization MACROMOLECULES Heise, A., Diamanti, S., HEDRICK, J. L., Frank, C. W., Miller, R. D. 2001; 34 (11): 3798-3801
  • Two-dimensional physical networks of lipopolymers at the air/water interface: Correlation of molecular structure and surface rheological behavior LANGMUIR Naumann, C. A., Brooks, C. F., Fuller, G. G., Lehmann, T., Ruhe, J., Knoll, W., Kuhn, P., Nuyken, O., Frank, C. W. 2001; 17 (9): 2801-2806

    View details for DOI 10.1021/la000778y

    View details for Web of Science ID 000168373000041

  • Star polymers with alternating,arms from miktofunctional mu-initiators using consecutive atom transfer radical polymerization and ring-opening polymerization MACROMOLECULES Heise, A., Trollsas, M., Magbitang, T., HEDRICK, J. L., Frank, C. W., Miller, R. D. 2001; 34 (9): 2798-2804
  • Rheological properties of lipopolymer-phospholipid mixtures at the air-water interface: A novel form of two-dimensional physical gelation MACROMOLECULES Naumann, C. A., Brooks, C. F., Wiyatno, W., Knoll, W., Fuller, G. G., Frank, C. W. 2001; 34 (9): 3024-3032

    View details for DOI 10.1021/ma0009810

    View details for Web of Science ID 000168236600041

  • Frictional properties of perfluoropolyether monolayers investigated with quartz resonators APPLIED PHYSICS LETTERS Laschitsch, A., Bailey, L. E., Tyndall, G. W., Frank, C. W., Johannsmann, D. 2001; 78 (17): 2601-2603
  • Polymer-supported lipid bilayers on benzophenone-modified substrates BIOMACROMOLECULES Shen, W. W., Boxer, S. G., Knoll, W., Frank, C. W. 2001; 2 (1): 70-79


    Solid-supported lipid membranes are important for their roles in fundamental biophysical research as well as in applications such as biosensors. In our study, lipopolymers containing alkyl side chains were synthesized and a mixture of the lipopolymer and free lipids was preorganized at the air-water interface and then transferred to a solid substrate using the Langmuir-Blodgett technique. A photochemical reaction between a substrate-functionalized benzophenone and C-H bonds on the lipopolymer was used to attach the lipopolymers to the substrate. The final assembly of the membrane was completed by vesicle fusion. Langmuir film experiments at the air-water interface indicate tighter molecular packing for the lipopolymers with 28 mol % alkyl side chains than for the ones with 22 mol %. Atomic force microscopy images point to phase separation of lipopolymers on the substrates due to their dewetting from hydrophobic surfaces. However, a mixture of lipopolymers and free lipids formed a smooth film on the same substrate. After the addition of the second lipid layer on the lipopolymer/free lipid layer, the fluorescence images of the polymer-supported bilayer suggested that the distal lipid layer is homogeneous on the micrometer scale. The relaxation of the fluorescent probe lipids was analyzed after application of an electric field to determine their diffusion coefficient; the distal lipid layer was mobile with an average diffusion coefficient of approximately 0.1 microm(2)/s. Moreover, the immobile fraction of the lipids in the distal layer was estimated to be around 15%.

    View details for DOI 10.1021/bm005581z

    View details for Web of Science ID 000168755800011

    View details for PubMedID 11749157

  • Two-dimensional physical networks of lipopolymers at the air/water interface Frank, C. W., Naumann, C. A., Knoll, W., Brooks, C. F., Fuller, G. G. WILEY-V C H VERLAG GMBH. 2001: 1-12
  • Hindered diffusion in polymer-tethered membranes: A monolayer study at the air-water interface BIOMACROMOLECULES Naumann, C. A., Knoll, W., Frank, C. W. 2001; 2 (4): 1097-1103


    Polymer-tethered phospholipid bilayers, which are based on a phospholipid-lipopolymer mixture, represent a very promising approach to stabilize complex biomimicking composite membranes. Furthermore, they are interesting model systems to study problems of hindered diffusion in two-dimensional liquids. Here, we present fluorescence recovery after photobleaching experiments (FRAP) on mixed phospholipid-lipopolymer monolayers of DMPC and DSPE-EO(45) at the air-water interface. In contrast to recent polymer-tethered bilayer experiments where the hydrophobic lipopolymer anchors behaved as immobile obstacles within the fluid phospholipid matrix,(1) this paper investigates the influence of mobile lipopolymer obstacles on the lateral diffusion of phospholipids. We found that the lateral diffusion of phospholipids with D = 7.1 +/- 0.5 microm(2)/s is independent of the lipopolymer obstacle concentration if adjacent polymer chains do not interact with each other. However, the diffusion coefficient of nontethered phospholipids gradually decreases from D = 7.1 +/- 0.5 microm(2)/s to D = 3.4 +/- 0.1 microm(2)/s in the case of increasing polymer-polymer interactions based on frictional coupling. This can be understood by a slowing down of the obstacle mobility. While phospholipids still show a significant lateral diffusion as long as the polymer moieties interact with each other only via frictional coupling, they become rather immobile (D = 0.9 +/- 0.1 microm(2)/s) if lipopolymers form a two-dimensional physical network.

    View details for DOI 10.1021/bm010022t

    View details for Web of Science ID 000174256400006

    View details for PubMedID 11777379

  • Sum-frequency spectroscopic investigation of the alignment of liquid crystals on self-assembled monolayers and Imaging of endgrafted alpha-helical polypeptide films LEOS 2001: 14TH ANNUAL MEETING OF THE IEEE LASERS & ELECTRO-OPTICS SOCIETY, VOLS 1 AND 2, PROCEEDINGS Knoesen, A., Pakalnis, S., Follonier, S., Miller, W., Abbott, N., Lee, N., Frank, C. 2001: 632-633
  • High capacity substrates as a platform for a DNA probe array genotyping assay Fidanza, J., Glazer, M., Mutnick, D., McGall, G., Frank, C. TAYLOR & FRANCIS INC. 2001: 533-538


    Colloidal silica particles were deposited on a glass substrate to produce high-capacity porous supports for high-density DNA probe arrays. Porous surfaces were used to increase the addressable surface area and number of probes available for hybridization. Surfaces derived from 70-100 nm size particles deposited in films from 0.15 to 2 microns thick exhibited excellent performance in light-directed oligonucleotide synthesis. Evaluation of these substrates in a genotyping assay is reported.

    View details for Web of Science ID 000170690500032

    View details for PubMedID 11563070

  • Starlike polymeric architectures by atom transfer radical polymerization: Templates for the production of low dielectric constant thin films MACROMOLECULES Heise, A., Nguyen, C., Malek, R., HEDRICK, J. L., Frank, C. W., Miller, R. D. 2000; 33 (7): 2346-2354
  • Interfacial interaction in polyimide/silica hybrid composites by fluorescence spectroscopy CHEMISTRY OF MATERIALS Ha, C. S., Park, H. D., Frank, C. W. 2000; 12 (3): 839-844
  • Viscoelastic properties of lipopolymers at the air-water interface: A combined interfacial stress rheometer and film balance study LANGMUIR Naumann, C. A., Brooks, C. F., Fuller, G. G., Knoll, W., Frank, C. W. 1999; 15 (22): 7752-7761
  • Polymer thin film properties as a function of temperature and pressure MACROMOLECULAR SYMPOSIA Kleideiter, G., Prucker, O., Bock, H., Frank, C. W., Lechner, M. D., Knoll, W. 1999; 145: 95-102
  • Quadrupolar and polar anisotropy in end-grafted alpha-helical poly(gamma-benzyl-L-glutamate) on solid substrates JOURNAL OF CHEMICAL PHYSICS Chang, Y. C., Frank, C. W., Forstmann, G. G., Johannsmann, D. 1999; 111 (13): 6136-6143
  • Photochemical attachment of polymer films to solid surfaces via monolayers of benzophenone derivatives JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Prucker, O., Naumann, C. A., Ruhe, J., Knoll, W., Frank, C. W. 1999; 121 (38): 8766-8770
  • Starlike block copolymers with amphiphilic arms as models for unimolecular micelles JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Heise, A., HEDRICK, J. L., Frank, C. W., Miller, R. D. 1999; 121 (37): 8647-8648
  • Discrimination of DNA hybridization using chemical force microscopy BIOPHYSICAL JOURNAL Mazzola, L. T., Frank, C. W., Fodor, S. P., Mosher, C., Lartius, R., Henderson, E. 1999; 76 (6): 2922-2933


    Atomic force microscopy (AFM) can be used to probe the mechanics of molecular recognition between surfaces. In the application known as "chemical force" microscopy (CFM), a chemically modified AFM tip probes a surface through chemical recognition. When modified with a biological ligand or receptor, the AFM tip can discriminate between its biological binding partner and other molecules on a heterogeneous substrate. The strength of the interaction between the modified tip and the substrate is governed by the molecular affinity. We have used CFM to probe the interactions between short segments of single-strand DNA (oligonucleotides). First, a latex microparticle was modified with the sequence 3'-CAGTTCTACGATGGCAAGTC and epoxied to a standard AFM cantilever. This DNA-modified probe was then used to scan substrates containing the complementary sequence 5'-GTCAAGATGCTACCGTTCAG. These substrates consisted of micron-scale, patterned arrays of one or more distinct oligonucleotides. A strong friction interaction was measured between the modified tip and both elements of surface-bound DNA. Complementary oligonucleotides exhibited a stronger friction than the noncomplementary sequences within the patterned array. The friction force correlated with the measured strength of adhesion (rupture force) for the tip- and array-bound oligonucleotides. This result is consistent with the formation of a greater number of hydrogen bonds for the complementary sequence, suggesting that the friction arises from a sequence-specific interaction (hybridization) of the tip and surface DNA.

    View details for Web of Science ID 000080556700006

    View details for PubMedID 10354420

  • An interfacial stress rheometer to study rheological transitions in monolayers at the air-water interface LANGMUIR Brooks, C. F., Fuller, G. G., Frank, C. W., Robertson, C. R. 1999; 15 (7): 2450-2459
  • Adaptation of bulk constitutive equations to insoluble monolayer collapse at the air-water interface SCIENCE Kampf, J. P., Frank, C. W., Malmstrom, E. E., Hawker, C. J. 1999; 283 (5408): 1730-1733


    A constitutive equation based on stress-strain models of bulk solids was adapted to relate the surface pressure, compression rate, and temperature of an insoluble monolayer of monodendrons during collapse at the air-water interface. A power law relation between compression rate and surface pressure and an Arrhenius temperature dependence of the steady-state creep rate were observed in data from compression rate and creep experiments in the collapse region. These relations were combined into a single constitutive equation to calculate the temperature dependence of the collapse pressure with a maximum error of 5 percent for temperatures ranging from 10 degrees to 25 degrees C.

    View details for Web of Science ID 000079102800050

    View details for PubMedID 10073937

  • Novel starlike poly(methyl methacrylate)s by controlled dendritic free radical initiation MACROMOLECULES Heise, A., HEDRICK, J. L., Trollsas, M., Miller, R. D., Frank, C. W. 1999; 32 (1): 231-234
  • Stability and molecular conformation of poly(benzyl ether) monodendrons with oligo(ethylene glycol) tails at the air-water interface LANGMUIR Kampf, J. P., Frank, C. W., Malmstrom, E. E., Hawker, C. J. 1999; 15 (1): 227-233
  • High surface area substrates for DNA arrays ORGANIC/INORGANIC HYBRID MATERIALS II Glazer, M., Frank, C., Vinci, R. P., McGall, G., Fidanza, J., Beecher, J. 1999; 576: 371-376
  • On the glass transition in ultrathin polymer films of different molecular architecture MACROMOLECULAR CHEMISTRY AND PHYSICS Prucker, O., Christian, S., Bock, H., Ruhe, J., Frank, C. W., Knoll, W. 1998; 199 (7): 1435-1444
  • Orientation in a fatty acid monolayer: Effect of flow type LANGMUIR Maruyama, T., Lauger, J., Fuller, G. G., Frank, C. W., Robertson, C. R. 1998; 14 (7): 1836-1845
  • Vapor deposition-polymerization of alpha-amino acid N-carboxy anhydride on the silicon(100) native oxide surface LANGMUIR Chang, Y. C., Frank, C. W. 1998; 14 (2): 326-334
  • Supramolecular Thin Film Architectures for Photonic Applications MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS Advincula, R., Frank, C. W., Roitman, D., Sheats, J., Moon, R., Knoll, W. 1998; 316: 103-112
  • End group effects on adhesion of perfluoropolyether lubricants to solid substrates JOURNAL OF ADHESION Xu, C. B., Frank, C. W., Tang, W. T., Terrill, C. 1998; 67 (1-4): 195-215
  • Glass transition in ultrathin polymer films ORGANIC THIN FILMS Prucker, O., Christian, S., Bock, H., Ruhe, J., Frank, C. W., Knoll, W. 1998; 695: 233-249
  • Langmuir and Langmuir-Blodgett-Kuhn films of poly(vinylidene fluoride) and poly(vinylidene fluoride-co-trifluoroethylene) alternated with poly(methyl methacrylate) or poly(octadecyl methacrylate) ORGANIC THIN FILMS Advincula, R. C., Knoll, W., Blinov, L., Frank, C. W. 1998; 695: 192-205
  • Pentaerythritol-based polyether dendrimers at the air-water interface ORGANIC THIN FILMS Kampf, J. P., Einloth, T. L., Frank, C. W., Li, Y. F., Oh, J. M., Moore, J. A. 1998; 695: 31-42
  • Flow-induced deformation and relaxation processes of polydomain structures in Langmuir monolayer ORGANIC THIN FILMS Yim, K. S., Brooks, C. F., Fuller, G. G., Frank, C. W., Robertson, C. R. 1998; 695: 43-56
  • Chemical grafting of poly(L-glutamate) gamma-esters on silicon (100) surfaces by vapor polymerization of N-carboxy anhydride monomers ORGANIC THIN FILMS Chang, Y. C., Frank, C. W. 1998; 695: 142-157
  • Exact linear analogs of dendritic polyether macromolecules: Design, synthesis, and unique properties JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Hawker, C. J., Malmstrom, E. E., Frank, C. W., Kampf, J. P. 1997; 119 (41): 9903-9904
  • Surface polymerization of poly(gamma-alkyl-L-glutamate) on solid substrates MACROMOLECULAR SYMPOSIA Chang, Y. C., Frank, C. W. 1997; 118: 641-646
  • Orientational dynamics of a two-dimensional polymer nematic. Fuller, G. G., Maruyama, T., Frank, C. W., Robertson, C. R. AMER CHEMICAL SOC. 1997: 521-POLY
  • Interfacial properties of polyimide Langmuir-Blodgett film Shin, D. M., Frank, C. W., Miller, R. D. AMER CHEMICAL SOC. 1997: 383-POLY
  • Grafting of poly(gamma-benzyl-L-glutamate) on chemically modified silicon oxide surfaces LANGMUIR Chang, Y. C., Frank, C. W. 1996; 12 (24): 5824-5829
  • Deformation and relaxation processes of mono- and bilayer domains of liquid crystalline Langmuir films on water LANGMUIR Lauger, J., Robertson, C. R., Frank, C. W., Fuller, G. G. 1996; 12 (23): 5630-5635
  • Flow-induced molecular orientation of a Langmuir film SCIENCE Maruyama, T., Fuller, G., Frank, C., Robertson, C. 1996; 274 (5285): 233-235
  • Polymer chain organization and orientation in ultrathin films: A spectroscopic investigation JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS DESPOTOPOULOU, M. M., Miller, R. D., Rabolt, J. F., Frank, C. W. 1996; 34 (14): 2335-2349
  • Kinetics of chain organization in ultrathin poly(di-n-hexylsilane) films MACROMOLECULES DESPOTOPOULOU, M. M., Frank, C. W., Miller, R. D., Rabolt, J. F. 1996; 29 (18): 5797-5804
  • Perfluoropolyether derivatives at the air-water and air-solid interfaces. Xu, C. B., Goedel, W. A., Tang, W. T., Frank, C. W. AMER CHEMICAL SOC. 1996: 328-POLY
  • Structure in thin and ultrathin spin-cast polymer films SCIENCE Frank, C. W., Rao, V., DESPOTOPOULOU, M. M., Pease, R. F., Hinsberg, W. D., Miller, R. D., Rabolt, J. F. 1996; 273 (5277): 912-915
  • Direct visualization of flow-induced anisotropy in a fatty acid monolayer LANGMUIR FRIEDENBERG, M. C., Fuller, G. G., Frank, C. W., Robertson, C. R. 1996; 12 (6): 1594-1599
  • In-situ studies of flow-induced phenomena in Langmuir monolayers Maruyama, T., Friedenberg, M., Fuller, G. G., Frank, C. W., Robertson, C. R., Ferencz, A., Wegner, G. ELSEVIER SCIENCE SA. 1996: 76-83
  • Structure in Thin and Ultrathin Spin-Cast Polymer Films Science (New York, N.Y.) Frank, C. W., Rao, V., Despotopoulou, M. M., Pease, R. F., Hinsberg, W. D., Miller, R. D., Rabolt, J. F. 1996; 273 (5277): 912-5


    The molecular organization in ultrathin polymer films (thicknesses less than 1000 angstroms) and thin polymer films (thicknesses between 1000 and 10,000 angstroms) may differ substantially from that of bulk polymers, which can lead to important differences in resulting thermophysical properties. Such constrained geometry films have been fabricated from amorphous poly(3-methyl-4-hydroxy styrene) (PMHS) and semicrystalline poly(di-n-hexyl silane) (PD6S) by means of spin-casting. The residual solvent content is substantially greater in ultrathin PMHS films, which suggests a higher glass transition temperature that results from a stronger hydrogen-bonded network as compared with that in thicker films. Crystallization of PD6S is substantially hindered in ultrathin films, in which a critical thickness of 150 angstroms is needed for crystalline morphology to exist and in which the rate of crystallization is initially slow but increases rapidly as the film approaches 500 angstroms in thickness.

    View details for PubMedID 8688068

  • Interfacial rheology of monolayers XIITH INTERNATIONAL CONGRESS ON RHEOLOGY, PROCEEDINGS Maruyama, T., Lauger, J., Maffettone, P. L., Fuller, G. G., Frank, C., Robertson, R. 1996: 163-164
  • MONOLAYERS OF PERFLUOROPOLYETHERS WITH A HYDROPHILIC HEAD GROUP LANGMUIR Goedel, W. A., Wu, H., FRIEDENBERG, M. C., Fuller, G. G., Foster, M., Frank, C. W. 1994; 10 (11): 4209-4218
  • Diazonaphthoquinone-novolac resist dissolution in composite Langmuir-Blodgett and spin-cast films IRRADIATION OF POLYMERIC MATERIALS Kosbar, L. L., Frank, C. W., Pease, R. F., Hutchinson, J. 1993; 527: 245-265
  • CONTIN ANALYSIS OF COLLOIDAL AGGREGATES LANGMUIR Ju, R. T., Frank, C. W., Gast, A. P. 1992; 8 (9): 2165-2171