Eric Appel

All Publications

• Delivery of CAR-T cells in a transient injectable stimulatory hydrogel niche improves treatment of solid tumors. Science advances Grosskopf, A. K., Labanieh, L., Klysz, D. D., Roth, G. A., Xu, P., Adebowale, O., Gale, E. C., Jons, C. K., Klich, J. H., Yan, J., Maikawa, C. L., Correa, S., Ou, B. S., d'Aquino, A. I., Cochran, J. R., Chaudhuri, O., Mackall, C. L., Appel, E. A. 2022; 8 (14): eabn8264

  Abstract

  Adoptive cell therapy (ACT) has proven to be highly effective in treating blood cancers, but traditional approaches to ACT are poorly effective in treating solid tumors observed clinically. Novel delivery methods for therapeutic cells have shown promise for treatment of solid tumors when compared with standard intravenous administration methods, but the few reported approaches leverage biomaterials that are complex to manufacture and have primarily demonstrated applicability following tumor resection or in immune-privileged tissues. Here, we engineer simple-to-implement injectable hydrogels for the controlled co-delivery of CAR-T cells and stimulatory cytokines that improve treatment of solid tumors. The unique architecture of this material simultaneously inhibits passive diffusion of entrapped cytokines and permits active motility of entrapped cells to enable long-term retention, viability, and activation of CAR-T cells. The generation of a transient inflammatory niche following administration affords sustained exposure of CAR-T cells, induces a tumor-reactive CAR-T phenotype, and improves efficacy of treatment.

  View details for DOI 10.1126/sciadv.abn8264

  View details for PubMedID 35394838

• Hydrogel-Based Slow Release of a Receptor-Binding Domain Subunit Vaccine Elicits Neutralizing Antibody Responses Against SARS-CoV-2. Advanced materials (Deerfield Beach, Fla.) Gale, E. C., Powell, A. E., Roth, G. A., Meany, E. L., Yan, J., Ou, B. S., Grosskopf, A. K., Adamska, J., Picece, V. C., d'Aquino, A. I., Pulendran, B., Kim, P. S., Appel, E. A. 2021: e2104362

  Abstract

  The development of effective vaccines that can be rapidly manufactured and distributed worldwide is necessary to mitigate the devastating health and economic impacts of pandemics like COVID-19. The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein, which mediates host cell entry of the virus, is an appealing antigen for subunit vaccines because it is efficient to manufacture, highly stable, and a target for neutralizing antibodies. Unfortunately, RBD is poorly immunogenic. While most subunit vaccines are commonly formulated with adjuvants to enhance their immunogenicity, clinically-relevant adjuvants Alum, AddaVax, and CpG/Alum are found unable to elicit neutralizing responses following a prime-boost immunization. Here, it has been shown that sustained delivery of an RBD subunit vaccine comprisingCpG/Alumadjuvant in an injectable polymer-nanoparticle (PNP) hydrogelelicited potentanti-RBD andanti-spikeantibody titers, providing broader protection against SARS-CoV-2 variants of concern compared to bolus administration of the same vaccine and vaccines comprising other clinically-relevant adjuvant systems. Notably, a SARS-CoV-2 spike-pseudotyped lentivirus neutralization assay revealed that hydrogel-based vaccines elicited potent neutralizing responses when bolus vaccines didnot. Together, these results suggest that slow delivery of RBD subunit vaccines with PNP hydrogels can significantly enhance the immunogenicity of RBD and induce neutralizing humoral immunity.

  View details for DOI 10.1002/adma.202104362

  View details for PubMedID 34651342

• Designing spatial and temporal control of vaccine responses. Nature reviews. Materials Roth, G. A., Picece, V. C., Ou, B. S., Luo, W., Pulendran, B., Appel, E. A. 2021: 1-22

  Abstract

  Vaccines are the key technology to combat existing and emerging infectious diseases. However, increasing the potency, quality and durability of the vaccine response remains a challenge. As our knowledge of the immune system deepens, it becomes clear that vaccine components must be in the right place at the right time to orchestrate a potent and durable response. Material platforms, such as nanoparticles, hydrogels and microneedles, can be engineered to spatially and temporally control the interactions of vaccine components with immune cells. Materials-based vaccination strategies can augment the immune response by improving innate immune cell activation, creating local inflammatory niches, targeting lymph node delivery and controlling the time frame of vaccine delivery, with the goal of inducing enhanced memory immunity to protect against future infections. In this Review, we highlight the biological mechanisms underlying strong humoral and cell-mediated immune responses and explore materials design strategies to manipulate and control these mechanisms.

  View details for DOI 10.1038/s41578-021-00372-2

  View details for PubMedID 34603749

• Physical networks from entropy-driven non-covalent interactions. Nature communications Yu, A. C., Lian, H., Kong, X., Lopez Hernandez, H., Qin, J., Appel, E. A. 2021; 12 (1): 746

  Abstract

  Physical networks typically employ enthalpy-dominated crosslinking interactions that become more dynamic at elevated temperatures, leading to network softening. Moreover, standard mathematical frameworks such as time-temperature superposition assume network softening and faster dynamics at elevated temperatures. Yet, deriving a mathematical framework connecting the crosslinking thermodynamics to the temperature-dependent viscoelasticity of physical networks suggests the possibility for entropy-driven crosslinking interactions to provide alternative temperature dependencies. This framework illustrates that temperature negligibly affects crosslink density in reported systems, but drastically influences crosslink dynamics. While the dissociation rate of enthalpy-driven crosslinks is accelerated at elevated temperatures, the dissociation rate of entropy-driven crosslinks is negligibly affected or even slowed under these conditions. Here we report an entropy-driven physical network based on polymer-nanoparticle interactions that exhibits mechanical properties that are invariant with temperature. These studies provide a foundation for designing and characterizing entropy-driven physical crosslinking motifs and demonstrate how these physical networks access thermal properties that are not observed in current physical networks.

  View details for DOI 10.1038/s41467-021-21024-7

  View details for PubMedID 33531475

• A Quantitative Description for Designing the Extrudability of Shear-Thinning Physical Hydrogels. Macromolecular bioscience Lopez Hernandez, H., Souza, J. W., Appel, E. A. 2020: e2000295

  Abstract

  Physically associated hydrogels (PHs) capable of reversible transitions between solid and liquid-like states have enabled novel strategies for 3D printing, therapeutic drug and cell delivery, and regenerative medicine. Among the many design criteria (e.g., viscoelasticity, cargo diffusivity, biocompatibility) for these applications, engineering PHs for extrudability is a necessary and critical design criterion for the successful application of these materials. As the development of many distinct PH material systems continues, a strategy to determine the extrudability of PHs a priori will be exceedingly useful for reducing costly and time-consuming trial-and-error experimentation. Here, a strategy to determine the property-function relationships for PHs in injectable drug delivery applications at clinically relevant flow rates is presented. This strategy-validated with two chemically and physically distinct PHs-reveals material design spaces in the form of Ashby-style plots that highlight acceptable, application-specific material properties. It is shown that the flow behavior of PHs does not obey a single shear-thinning power law and the implications for injectable drug delivery are discussed. This approach for generating design criteria has potential for streamlining the screening of PHs and their utility in applications with varying geometrical (i.e., needle diameter) and process (i.e., flow rate) constraints.

  View details for DOI 10.1002/mabi.202000295

  View details for PubMedID 33164332

• An ultrafast insulin formulation enabled by high-throughput screening of engineered polymeric excipients. Science translational medicine Mann, J. L., Maikawa, C. L., Smith, A. A., Grosskopf, A. K., Baker, S. W., Roth, G. A., Meis, C. M., Gale, E. C., Liong, C. S., Correa, S., Chan, D., Stapleton, L. M., Yu, A. C., Muir, B., Howard, S., Postma, A., Appel, E. A. 2020; 12 (550)

  Abstract

  Insulin has been used to treat diabetes for almost 100 years; yet, current rapid-acting insulin formulations do not have sufficiently fast pharmacokinetics to maintain tight glycemic control at mealtimes. Dissociation of the insulin hexamer, the primary association state of insulin in rapid-acting formulations, is the rate-limiting step that leads to delayed onset and extended duration of action. A formulation of insulin monomers would more closely mimic endogenous postprandial insulin secretion, but monomeric insulin is unstable in solution using present formulation strategies and rapidly aggregates into amyloid fibrils. Here, we implement high-throughput-controlled radical polymerization techniques to generate a large library of acrylamide carrier/dopant copolymer (AC/DC) excipients designed to reduce insulin aggregation. Our top-performing AC/DC excipient candidate enabled the development of an ultrafast-absorbing insulin lispro (UFAL) formulation, which remains stable under stressed aging conditions for 25 ± 1 hours compared to 5 ± 2 hours for commercial fast-acting insulin lispro formulations (Humalog). In a porcine model of insulin-deficient diabetes, UFAL exhibited peak action at 9 ± 4 min, whereas commercial Humalog exhibited peak action at 25 ± 10 min. These ultrafast kinetics make UFAL a promising candidate for improving glucose control and reducing burden for patients with diabetes.

  View details for DOI 10.1126/scitranslmed.aba6676

  View details for PubMedID 32611683

• Injectable Hydrogels for Sustained Codelivery of Subunit Vaccines Enhance Humoral Immunity. ACS central science Roth, G. A., Gale, E. C., Alcántara-Hernández, M. n., Luo, W. n., Axpe, E. n., Verma, R. n., Yin, Q. n., Yu, A. C., Lopez Hernandez, H. n., Maikawa, C. L., Smith, A. A., Davis, M. M., Pulendran, B. n., Idoyaga, J. n., Appel, E. A. 2020; 6 (10): 1800–1812

  Abstract

  Vaccines aim to elicit a robust, yet targeted, immune response. Failure of a vaccine to elicit such a response arises in part from inappropriate temporal control over antigen and adjuvant presentation to the immune system. In this work, we sought to exploit the immune system's natural response to extended pathogen exposure during infection by designing an easily administered slow-delivery vaccine platform. We utilized an injectable and self-healing polymer-nanoparticle (PNP) hydrogel platform to prolong the codelivery of vaccine components to the immune system. We demonstrated that these hydrogels exhibit unique delivery characteristics, whereby physicochemically distinct compounds (such as antigen and adjuvant) could be codelivered over the course of weeks. When administered in mice, hydrogel-based sustained vaccine exposure enhanced the magnitude, duration, and quality of the humoral immune response compared to standard PBS bolus administration of the same model vaccine. We report that the creation of a local inflammatory niche within the hydrogel, coupled with sustained exposure of vaccine cargo, enhanced the magnitude and duration of germinal center responses in the lymph nodes. This strengthened germinal center response promoted greater antibody affinity maturation, resulting in a more than 1000-fold increase in antigen-specific antibody affinity in comparison to bolus immunization. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of subunit vaccines.

  View details for DOI 10.1021/acscentsci.0c00732

  View details for PubMedID 33145416

  View details for PubMedCentralID PMC7596866

• A co-formulation of supramolecularly stabilized insulin and pramlintide enhances mealtime glucagon suppression in diabetic pigs. Nature biomedical engineering Maikawa, C. L., Smith, A. A., Zou, L. n., Roth, G. A., Gale, E. C., Stapleton, L. M., Baker, S. W., Mann, J. L., Yu, A. C., Correa, S. n., Grosskopf, A. K., Liong, C. S., Meis, C. M., Chan, D. n., Troxell, M. n., Maahs, D. M., Buckingham, B. A., Webber, M. J., Appel, E. A. 2020

  Abstract

  Treatment of patients with diabetes with insulin and pramlintide (an amylin analogue) is more effective than treatment with insulin only. However, because mixtures of insulin and pramlintide are unstable and have to be injected separately, amylin analogues are only used by 1.5% of people with diabetes needing rapid-acting insulin. Here, we show that the supramolecular modification of insulin and pramlintide with cucurbit[7]uril-conjugated polyethylene glycol improves the pharmacokinetics of the dual-hormone therapy and enhances postprandial glucagon suppression in diabetic pigs. The co-formulation is stable for over 100 h at 37 °C under continuous agitation, whereas commercial formulations of insulin analogues aggregate after 10 h under similar conditions. In diabetic rats, the administration of the stabilized co-formulation increased the area-of-overlap ratio of the pharmacokinetic curves of pramlintide and insulin from 0.4 ± 0.2 to 0.7 ± 0.1 (mean ± s.d.) for the separate administration of the hormones. The co-administration of supramolecularly stabilized insulin and pramlintide better mimics the endogenous kinetics of co-secreted insulin and amylin, and holds promise as a dual-hormone replacement therapy.

  View details for DOI 10.1038/s41551-020-0555-4

  View details for PubMedID 32393892

• Wildfire prevention through prophylactic treatment of high-risk landscapes using viscoelastic retardant fluids. Proceedings of the National Academy of Sciences of the United States of America Yu, A. C., Lopez Hernandez, H., Kim, A. H., Stapleton, L. M., Brand, R. J., Mellor, E. T., Bauer, C. P., McCurdy, G. D., Wolff, A. J., Chan, D., Criddle, C. S., Acosta, J. D., Appel, E. A. 2019

  Abstract

  Polyphosphate fire retardants are a critical tactical resource for fighting fires in the wildland and in the wildland-urban interface. Yet, application of these retardants is limited to emergency suppression strategies because current formulations cannot retain fire retardants on target vegetation for extended periods of time through environmental exposure and weathering. New retardant formulations with persistent retention to target vegetation throughout the peak fire season would enable methodical, prophylactic treatment strategies of landscapes at high risk of wildfires through prolonged prevention of ignition and continual impediment to active flaming fronts. Here we develop a sprayable, environmentally benign viscoelastic fluid comprising biopolymers and colloidal silica to enhance adherence and retention of polyphosphate retardants on common wildfire-prone vegetation. These viscoelastic fluids exhibit appropriate wetting and rheological responses to enable robust retardant adherence to vegetation following spray application. Further, laboratory and pilot-scale burn studies establish that these materials drastically reduce ignition probability before and after simulated weathering events. Overall, these studies demonstrate how these materials actualize opportunities to shift the approach of retardant-based wildfire management from reactive suppression to proactive prevention at the source of ignitions.

  View details for DOI 10.1073/pnas.1907855116

  View details for PubMedID 31570592

• A Multiscale Model for Solute Diffusion in Hydrogels. Macromolecules Axpe, E., Chan, D., Offeddu, G. S., Chang, Y., Merida, D., Hernandez, H. L., Appel, E. A. 2019; 52 (18): 6889–97

  Abstract

  The number of biomedical applications of hydrogels is increasing rapidly on account of their unique physical, structural, and mechanical properties. The utility of hydrogels as drug delivery systems or tissue engineering scaffolds critically depends on the control of diffusion of solutes through the hydrogel matrix. Predicting or even modeling this diffusion is challenging due to the complex structure of hydrogels. Currently, the diffusivity of solutes in hydrogels is typically modeled by one of three main theories proceeding from distinct diffusion mechanisms: (i) hydrodynamic, (ii) free volume, and (iii) obstruction theory. Yet, a comprehensive predictive model is lacking. Thus, time and capital-intensive trial-and-error procedures are used to test the viability of hydrogel applications. In this work, we have developed a model for the diffusivity of solutes in hydrogels combining the three main theoretical frameworks, which we call the multiscale diffusion model (MSDM). We verified the MSDM by analyzing the diffusivity of dextran of different sizes in a series of poly(ethylene glycol) (PEG) hydrogels with distinct mesh sizes. We measured the subnanoscopic free volume by positron annihilation lifetime spectroscopy (PALS) to characterize the physical hierarchy of these materials. In addition, we performed a meta-analysis of literature data from previous studies on the diffusion of solutes in hydrogels. The model presented outperforms traditional models in predicting solute diffusivity in hydrogels and provides a practical approach to predicting the transport properties of solutes such as drugs through hydrogels used in many biomedical applications.

  View details for DOI 10.1021/acs.macromol.9b00753

  View details for PubMedID 31579160

• Use of a supramolecular polymeric hydrogel as an effective post-operative pericardial adhesion barrier. Nature biomedical engineering Stapleton, L. M., Steele, A. N., Wang, H. n., Lopez Hernandez, H. n., Yu, A. C., Paulsen, M. J., Smith, A. A., Roth, G. A., Thakore, A. D., Lucian, H. J., Totherow, K. P., Baker, S. W., Tada, Y. n., Farry, J. M., Eskandari, A. n., Hironaka, C. E., Jaatinen, K. J., Williams, K. M., Bergamasco, H. n., Marschel, C. n., Chadwick, B. n., Grady, F. n., Ma, M. n., Appel, E. A., Woo, Y. J. 2019; 3 (8): 611–20

  Abstract

  Post-operative adhesions form as a result of normal wound healing processes following any type of surgery. In cardiac surgery, pericardial adhesions are particularly problematic during reoperations, as surgeons must release the adhesions from the surface of the heart before the intended procedure can begin, thereby substantially lengthening operation times and introducing risks of haemorrhage and injury to the heart and lungs during sternal re-entry and cardiac dissection. Here we show that a dynamically crosslinked supramolecular polymer-nanoparticle hydrogel, with viscoelastic and flow properties that enable spraying onto tissue as well as robust tissue adherence and local retention in vivo for two weeks, reduces the formation of pericardial adhesions. In a rat model of severe pericardial adhesions, the hydrogel markedly reduced the severity of the adhesions, whereas commercial adhesion barriers (including Seprafilm and Interceed) did not. The hydrogels also reduced the severity of cardiac adhesions (relative to untreated animals) in a clinically relevant cardiopulmonary-bypass model in sheep. This viscoelastic supramolecular polymeric hydrogel represents a promising clinical solution for the prevention of post-operative pericardial adhesions.

  View details for DOI 10.1038/s41551-019-0442-z

  View details for PubMedID 31391596

• A cGAMP-Containing Hydrogel for Prolonged SARS-CoV-2 Receptor-Binding Domain Subunit Vaccine Exposure Induces a Broad and Potent Humoral Response ADVANCED NANOBIOMED RESEARCH Bohnert, V., Gale, E. C., Lahey, L. J., Yan, J., Powell, A. E., Ou, B. S., Carozza, J. A., Li, L., Appel, E. A. 2024

  View details for DOI 10.1002/anbr.202400077

  View details for Web of Science ID 001364928000001

• Electrochemically mutable soft metasurfaces. Nature materials Doshi, S., Ji, A., Mahdi, A. I., Keene, S. T., Selvin, S. P., Lalanne, P., Appel, E. A., Melosh, N. A., Brongersma, M. L. 2024

  Abstract

  Active optical metasurfaces, capable of dynamically manipulating light in ultrathin form factors, enable novel interfaces between humans and technology. In such interfaces, soft materials bring many advantages based on their flexibility, compliance and large stimulus-driven responses. Here, we create electrochemically mutable, soft metasurfaces that capitalize on the swelling of soft conducting polymers to alter the shape and associated resonant response of metasurface elements. Such geometric tuning overcomes the typical trade-off between achieving substantial tuning and low optical loss that is intrinsic to dynamic metasurfaces relying on index tuning of materials. Using the commercial polymer PEDOT:PSS, we demonstrate dynamic, high-resolution colour tuning and high-diffraction-efficiency (>19%) beam-steering devices that operate at CMOS-compatible voltages (~1.5V). These results highlight how the deformability of soft materials can enable a class of high-performance metasurfaces that are suitable for body-worn technologies.

  View details for DOI 10.1038/s41563-024-02042-4

  View details for PubMedID 39537748

• Viral Vector Eluting Lenses for Single-Step Targeted Expression of Genetically-Encoded Activity Sensors for in Vivo Microendoscopic Calcium Imaging. Macromolecular bioscience Jons, C. K., Cheng, D., Dong, C., Meany, E. L., Nassi, J. J., Appel, E. A. 2024: e2400359

  Abstract

  Optical methods for studying the brain offer powerful approaches for understanding how neural activity underlies complex behavior. These methods typically rely on genetically encoded sensors and actuators to monitor and control neural activity. For microendoscopic calcium imaging, injection of a virus followed by implantation of a lens probe is required to express a calcium sensor and enable optical access to the target brain region. This two-step process poses several challenges, chief among them being the risks associated with mistargeting and/or misalignment between virus expression zone, lens probe and target brain region. Here, an adeno-associated virus (AAV)-eluting polymer coating is engineered for gradient refractive index (GRIN) lenses enabling the expression of a genetically encoded calcium indicator (GCaMP) directly within the brain region of interest upon implantation of the lens. This approach requires only one surgical step and guarantees alignment between GCaMP expression and lens in the brain. Additionally, the slow virus release from these coatings increases the working time for surgical implantation, expanding the brain regions and species amenable to this approach. These enhanced capabilities should accelerate neuroscience research utilizing optical methods and advance the understanding of the neural circuit mechanisms underlying brain function and behavior in health and disease.

  View details for DOI 10.1002/mabi.202400359

  View details for PubMedID 39283817

• Water-Enhancing Gels Exhibiting Heat-Activated Formation of Silica Aerogels for Protection of Critical Infrastructure During Catastrophic Wildfire. Advanced materials (Deerfield Beach, Fla.) Dong, C., d'Aquino, A. I., Sen, S., Hall, I. A., Yu, A. C., Crane, G. B., Acosta, J. D., Appel, E. A. 2024: e2407375

  Abstract

  A promising strategy to address the pressing challenges with wildfire, particularly in the wildland-urban interface (WUI), involves developing new approaches for preventing and controlling wildfire within wildlands. Among sprayable fire-retardant materials, water-enhancing gels have emerged as exceptionally effective for protecting civil infrastructure. They possess favorable wetting and viscoelastic properties that reduce the likelihood of ignition, maintaining strong adherence to a wide array of surfaces after application. Although current water-enhancing hydrogels effectively maintain surface wetness by creating a barricade, they rapidly desiccate and lose efficacy under high heat and wind typical of wildfire conditions. To address this limitation, unique biomimetic hydrogel materials from sustainable cellulosic polymers crosslinked by colloidal silica particles are developed that exhibit ideal viscoelastic properties and facile manufacturing. Under heat activation, the hydrogel transitions into a highly porous and thermally insulative silica aerogel coating in situ, providing a robust protective layer against ignition of substrates, even when the hydrogel fire suppressant becomes completely desiccated. By confirming the mechanical properties, substrate adherence, and enhanced substrate protection against fire, these heat-activatable biomimetic hydrogels emerge as promising candidates for next-generation water-enhancing fire suppressants. These advancements have the potential to dramatically improve the ability to protect homes and critical infrastructure during wildfire.

  View details for DOI 10.1002/adma.202407375

  View details for PubMedID 39169738

• Saponin nanoparticle adjuvants incorporating Toll-like receptor agonists drive distinct immune signatures and potent vaccine responses. Science advances Ou, B. S., Baillet, J., Filsinger Interrante, M. V., Adamska, J. Z., Zhou, X., Saouaf, O. M., Yan, J., Klich, J. H., Jons, C. K., Meany, E. L., Valdez, A. S., Carter, L., Pulendran, B., King, N. P., Appel, E. A. 2024; 10 (32): eadn7187

  Abstract

  Over the past few decades, the development of potent and safe immune-activating adjuvant technologies has become the heart of intensive research in the constant fight against highly mutative and immune evasive viruses such as influenza, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and human immunodeficiency virus (HIV). Herein, we developed a highly modular saponin-based nanoparticle platform incorporating Toll-like receptor agonists (TLRas) including TLR1/2a, TLR4a, and TLR7/8a adjuvants and their mixtures. These various TLRa-saponin nanoparticle adjuvant constructs induce unique acute cytokine and immune-signaling profiles, leading to specific T helper responses that could be of interest depending on the target disease for prevention. In a murine vaccine study, the adjuvants greatly improved the potency, durability, breadth, and neutralization of both COVID-19 and HIV vaccine candidates, suggesting the potential broad application of these adjuvant constructs to a range of different antigens. Overall, this work demonstrates a modular TLRa-SNP adjuvant platform that could improve the design of vaccines and affect modern vaccine development.

  View details for DOI 10.1126/sciadv.adn7187

  View details for PubMedID 39110802

  View details for PubMedCentralID PMC11305391

• Biomimetic Non-ergodic Aging by Dynamic-to-covalent Transitions in Physical Hydrogels. ACS applied materials & interfaces Sen, S., Dong, C., D'Aquino, A. I., Yu, A. C., Appel, E. A. 2024

  Abstract

  Hydrogels are soft materials engineered to suit a multitude of applications that exploit their tunable mechanochemical properties. Dynamic hydrogels employing noncovalent, physically cross-linked networks dominated by either enthalpic or entropic interactions enable unique rheological and stimuli-responsive characteristics. In contrast to enthalpy-driven interactions that soften with increasing temperature, entropic interactions result in largely temperature-independent mechanical properties. By engineering interfacial polymer-particle interactions, we can induce a dynamic-to-covalent transition in entropic hydrogels that leads to biomimetic non-ergodic aging in the microstructure without altering the network mesh size. This transition is tuned by varying temperature and formulation conditions such as pH, which allows for multivalent tunability in properties. These hydrogels can thus be designed to exhibit either temperature-independent metastable dynamic cross-linking or time-dependent stiffening based on formulation and storage conditions, all while maintaining structural features critical for controlling mass transport, akin to many biological tissues. Such robust materials with versatile and adaptable properties can be utilized in applications such as wildfire suppression, surgical adhesives, and depot-forming injectable drug delivery systems.

  View details for DOI 10.1021/acsami.4c03303

  View details for PubMedID 38862125

• RGD-Modified Hydrogel Maintains Cell Growth in Mechanically-Induced Limbal Stem Cell Deficient Mouse Model Esmaeilkhanian, H., Swarup, A., Eckman, N., Dhowre, H., Ercal, O., Shadmani, A., Appel, E., Wu, A. Y. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2024

  View details for Web of Science ID 001312227700127

• Label-Free Composition Analysis of Supramolecular Polymer-Nanoparticle Hydrogels by Reversed-Phase Liquid Chromatography Coupled with a Charged Aerosol Detector. Analytical chemistry Tang, S., Pederson, Z., Meany, E. L., Yen, C., Swansiger, A. K., Prell, J. S., Chen, B., Grosskopf, A. K., Eckman, N., Jiang, G., Baillet, J., Pellett, J. D., Appel, E. A. 2024

  Abstract

  Supramolecular hydrogels formed through polymer-nanoparticle interactions are promising biocompatible materials for translational medicines. This class of hydrogels exhibits shear-thinning behavior and rapid recovery of mechanical properties, providing desirable attributes for formulating sprayable and injectable therapeutics. Characterization of hydrogel composition and loading of encapsulated drugs is critical to achieving the desired rheological behavior as well as tunable in vitro and in vivo payload release kinetics. However, quantitation of hydrogel composition is challenging due to material complexity, heterogeneity, high molecular weight, and the lack of chromophores. Here, we present a label-free approach to simultaneously determine hydrogel polymeric components and encapsulated payloads by coupling a reversed phase liquid chromatographic method with a charged aerosol detector (RPLC-CAD). The hydrogel studied consists of modified hydroxypropylmethylcellulose, self-assembled PEG-b-PLA nanoparticles, and a therapeutic compound, bimatoprost. The three components were resolved and quantitated using the RPLC-CAD method with a C4 stationary phase. The method demonstrated robust performance, applicability to alternative cargos (i.e., proteins) and was suitable for composition analysis as well as for evaluating in vitro release of cargos from the hydrogel. Moreover, this method can be used to monitor polymer degradation and material stability, which can be further elucidated by coupling the RPLC method with (1) a multi-angle light scattering detector (RPLC-MALS) or (2) high resolution mass spectrometry (RPLC-MS) and a Fourier-transform based deconvolution algorithm. We envision that this analytical strategy could be generalized to characterize critical quality attributes of other classes of supramolecular hydrogels, establish structure-property relationships, and provide rational design guidance in hydrogel drug product development.

  View details for DOI 10.1021/acs.analchem.3c05747

  View details for PubMedID 38567987

• Composite gels designed to stick to biological tissue NATURE Bailey, S. J., Appel, E. A. 2024; 625 (7995): 455-457

  View details for DOI 10.1038/d41586-023-03996-2

  View details for Web of Science ID 001143852900001

  View details for PubMedID 38212608

  View details for PubMedCentralID 7610850

• Nanoparticle-Conjugated Toll-Like Receptor 9 Agonists Improve the Potency, Durability, and Breadth of COVID-19 Vaccines. ACS nano Ou, B. S., Baillet, J., Picece, V. C., Gale, E. C., Powell, A. E., Saouaf, O. M., Yan, J., Nejatfard, A., Lopez Hernandez, H., Appel, E. A. 2024

  Abstract

  Development of effective vaccines for infectious diseases has been one of the most successful global health interventions in history. Though, while ideal subunit vaccines strongly rely on antigen and adjuvant(s) selection, the mode and time scale of exposure to the immune system has often been overlooked. Unfortunately, poor control over the delivery of many adjuvants, which play a key role in enhancing the quality and potency of immune responses, can limit their efficacy and cause off-target toxicities. There is a critical need for improved adjuvant delivery technologies to enhance their efficacy and boost vaccine performance. Nanoparticles have been shown to be ideal carriers for improving antigen delivery due to their shape and size, which mimic viral structures but have been generally less explored for adjuvant delivery. Here, we describe the design of self-assembled poly(ethylene glycol)-b-poly(lactic acid) nanoparticles decorated with CpG, a potent TLR9 agonist, to increase adjuvanticity in COVID-19 vaccines. By controlling the surface density of CpG, we show that intermediate valency is a key factor for TLR9 activation of immune cells. When delivered with the SARS-CoV-2 spike protein, CpG nanoparticle (CpG-NP) adjuvant greatly improves the magnitude and duration of antibody responses when compared to soluble CpG, and results in overall greater breadth of immunity against variants of concern. Moreover, encapsulation of CpG-NP into injectable polymeric-nanoparticle (PNP) hydrogels enhances the spatiotemporal control over codelivery of CpG-NP adjuvant and spike protein antigen such that a single immunization of hydrogel-based vaccines generates humoral responses comparable to those of a typical prime-boost regimen of soluble vaccines. These delivery technologies can potentially reduce the costs and burden of clinical vaccination, both of which are key elements in fighting a pandemic.

  View details for DOI 10.1021/acsnano.3c09700

  View details for PubMedID 38215338

• Use of a biomimetic hydrogel depot technology for sustained delivery of GLP-1 receptor agonists reduces burden of diabetes management. Cell reports. Medicine d'Aquino, A. I., Maikawa, C. L., Nguyen, L. T., Lu, K., Hall, I. A., Jons, C. K., Kasse, C. M., Yan, J., Prossnitz, A. N., Chang, E., Baker, S. W., Hovgaard, L., Steensgaard, D. B., Andersen, H. B., Simonsen, L., Appel, E. A. 2023; 4 (11): 101292

  Abstract

  Glucagon-like peptide-1 (GLP-1) is an incretin hormone and neurotransmitter secreted from intestinal L cells in response to nutrients to stimulate insulin and block glucagon secretion in a glucose-dependent manner. Long-acting GLP-1 receptor agonists (GLP-1 RAs) have become central to treating type 2 diabetes (T2D); however, these therapies are burdensome, as they must be taken daily or weekly. Technological innovations that enable less frequent administrations would reduce patient burden and increase patient compliance. Herein, we leverage an injectable hydrogel depot technology to develop a GLP-1 RA drug product capable of months-long GLP-1 RA delivery. Using a rat model of T2D, we confirm that one injection of hydrogel-based therapy sustains exposure of GLP-1 RA over 42 days, corresponding to a once-every-4-months therapy in humans. Hydrogel therapy maintains management of blood glucose and weight comparable to daily injections of a leading GLP-1 RA drug. This long-acting GLP-1 RA treatment is a promising therapy for more effective T2D management.

  View details for DOI 10.1016/j.xcrm.2023.101292

  View details for PubMedID 37992687

• A Regimen Compression Strategy for Commercial Vaccines Leveraging an Injectable Hydrogel Depot Technology for Sustained Vaccine Exposure ADVANCED THERAPEUTICS Yan, J., Ou, B. S., Saouaf, O. M., Meany, E. L., Eckman, N., Appel, E. A. 2023

  View details for DOI 10.1002/adtp.202300108

  View details for Web of Science ID 001004577500001

• Broad and Durable Humoral Responses Following Single Hydrogel Immunization of SARS-CoV-2 Subunit Vaccine. Advanced healthcare materials Ou, B. S., Saouaf, O. M., Yan, J., Bruun, T. U., Baillet, J., Zhou, X., King, N. P., Appel, E. A. 2023: e2301495

  Abstract

  Most vaccines require several immunizations to induce robust immunity, and indeed, most SARS-CoV-2 vaccines require an initial two-shot regimen followed by several boosters to maintain efficacy. Such a complex series of immunizations unfortunately increases the cost and complexity of populations-scale vaccination and reduces overall compliance and vaccination rate. In a rapidly evolving pandemic affected by the spread of immune-escaping variants, there is an urgent need to develop vaccines capable of providing robust and durable immunity. In this work, we developed a single immunization SARS-CoV-2 subunit vaccine that could rapidly generate potent, broad, and durable humoral immunity. We leveraged injectable polymer-nanoparticle (PNP) hydrogels as a depot technology for the sustained delivery of a nanoparticle COVID antigen displaying multiple copies of the SARS-CoV-2 receptor-binding-domain (RBD-NP), and potent adjuvants including CpG and 3M-052. Compared to a clinically relevant prime-boost regimen with soluble vaccines formulated with CpG/Alum or 3M-052/Alum adjuvants, PNP hydrogel vaccines more rapidly generated higher, broader, and more durable antibody responses. Additionally, these single-immunization hydrogel-based vaccines elicited potent and consistent neutralizing responses. Overall, we show that PNP hydrogels elicit improved anti-COVID immune responses with only a single administration, demonstrating their potential as critical technologies to enhance our overall pandemic readiness. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adhm.202301495

  View details for PubMedID 37278391

• Microfluidic encapsulation of photosynthetic cyanobacteria in hydrogel microparticles augments oxygen delivery to rescue ischemic myocardium. Journal of bioscience and bioengineering Stapleton, L. M., Farry, J. M., Zhu, Y., Lucian, H. J., Wang, H., Paulsen, M. J., Totherow, K. P., Roth, G. A., Brower, K. K., Fordyce, P. M., Appel, E. A., Woo, Y. J. 2023

  Abstract

  Cardiovascular disease, primarily caused by coronary artery disease, is the leading cause of death in the United States. While standard clinical interventions have improved patient outcomes, mortality rates associated with eventual heart failure still represent a clinical challenge. Macrorevascularization techniques inadequately address the microvascular perfusion deficits that persist beyond primary and secondary interventions. In this work, we investigate a photosynthetic oxygen delivery system that rescues the myocardium following acute ischemia. Using a simple microfluidic system, we encapsulated Synechococcus elongatus into alginate hydrogel microparticles (HMPs), which photosynthetically deliver oxygen to ischemic tissue in the absence of blood flow. We demonstrate that HMPs improve the viability of S. elongatus during the injection process and allow for simple oxygen diffusion. Adult male Wistar rats (n = 45) underwent sham surgery, acute ischemia reperfusion surgery, or a chronic ischemia reperfusion surgery, followed by injection of phosphate buffered saline (PBS), S. elongatus suspended in PBS, HMPs, or S. elongatus encapsulated in HMPs. Treatment with S. elongatus-HMPs mitigated cellular apoptosis and improved left ventricular function. Thus, delivery of S. elongatus encapsulated in HMPs improves clinical translation by utilizing a minimally invasive delivery platform that improves S. elongatus viability and enhances the therapeutic benefit of a novel photosynthetic system for the treatment of myocardial ischemia.

  View details for DOI 10.1016/j.jbiosc.2023.03.001

  View details for PubMedID 36966053

• Polyacrylamide-based hydrogel coatings improve biocompatibility of implanted pump devices. Journal of biomedical materials research. Part A Chan, D., Maikawa, C. L., d'Aquino, A. I., Raghavan, S. S., Troxell, M. L., Appel, E. A. 2023

  Abstract

  The introduction of transcutaneous and subcutaneous implants and devices into the human body instigates fouling and foreign body responses (FBRs) that limit their functional lifetimes. Polymer coatings are a promising solution to improve the biocompatibility of such implants, with potential to enhance in vivo device performance and prolong device lifetime. Here we sought to develop novel materials for use as coatings on subcutaneously implanted devices to reduce the FBR and local tissue inflammation in comparison to gold standard materials such as poly(ethylene glycol) and polyzwitterions. We prepared a library of polyacrylamide-based copolymer hydrogels, which were selected from materials previously shown to exhibit remarkable antifouling properties with blood and plasma, and implanted them into the subcutaneous space of mice to evaluate their biocompatibility over the course of 1month. The top performing polyacrylamide-based copolymer hydrogel material, comprising a 50:50 mixture of N-(2-hydroxyethyl)acrylamide (HEAm) and N-(3-methoxypropyl)acrylamide (MPAm), exhibited significantly better biocompatibility and lower tissue inflammation than gold standard materials. Moreover, when applied to polydimethylsiloxane disks or silicon catheters as a thin coating (45±1mum), this leading copolymer hydrogel coating significantly improved implant biocompatibility. Using a rat model of insulin-deficient diabetes, we showed that insulin pumps fitted with HEAm-co-MPAm hydrogel-coated insulin infusion catheters exhibited improved biocompatibility and extended functional lifetime over pumps fitted with industry standard catheters. These polyacrylamide-based copolymer hydrogel coatings have the potential to improve device function and lifetime, thereby reducing the burden of disease management for people regularly using implanted devices.

  View details for DOI 10.1002/jbm.a.37521

  View details for PubMedID 36861657

• Subcutaneous delivery of an antibody against SARS-CoV-2 from a supramolecular hydrogel depot. Biomaterials science Kasse, C. M., Yu, A. C., Powell, A. E., Roth, G. A., Liong, C. S., Jons, C. K., Buahin, A., Maikawa, C. L., Zhou, X., Youssef, S., Glanville, J. E., Appel, E. A. 2023

  Abstract

  Prolonged maintenance of therapeutically-relevant levels of broadly neutralizing antibodies (bnAbs) is necessary to enable passive immunization against infectious disease. Unfortunately, protection only lasts for as long as these bnAbs remain present at a sufficiently high concentration in the body. Poor pharmacokinetics and burdensome administration are two challenges that need to be addressed in order to make pre- and post-exposure prophylaxis with bnAbs feasible and effective. In this work, we develop a supramolecular hydrogel as an injectable, subcutaneous depot to encapsulate and deliver antibody drug cargo. This polymer-nanoparticle (PNP) hydrogel exhibits shear-thinning and self-healing properties that are required for an injectable drug delivery vehicle. In vitro drug release assays and diffusion measurements indicate that the PNP hydrogels prevent burst release and slow the release of encapsulated antibodies. Delivery of bnAbs against SARS-CoV-2 from PNP hydrogels is compared to standard routes of administration in a preclinical mouse model. We develop a multi-compartment model to understand the ability of these subcutaneous depot materials to modulate the pharmacokinetics of released antibodies; the model is extrapolated to explore the requirements needed for novel materials to successfully deliver relevant antibody therapeutics with different pharmacokinetic characteristics.

  View details for DOI 10.1039/d2bm00819j

  View details for PubMedID 36723072

• Stable High-Concentration Monoclonal Antibody Formulations Enabled by an Amphiphilic Copolymer Excipient. Advanced therapeutics Klich, J. H., Kasse, C. M., Mann, J. L., Huang, Y., d'Aquino, A. I., Grosskopf, A. K., Baillet, J., Fuller, G. G., Appel, E. A. 2023; 6 (1)

  Abstract

  Monoclonal antibodies are a staple in modern pharmacotherapy. Unfortunately, these biopharmaceuticals are limited by their tendency to aggregate in formulation, resulting in poor stability and often requiring low concentration drug formulations. Moreover, existing excipients designed to stabilize these formulations are often limited by their toxicity and tendency to form particles such as micelles. Here, we demonstrate the ability of a simple "drop-in", amphiphilic copolymer excipient to enhance the stability of high concentration formulations of clinically-relevant monoclonal antibodies without altering their pharmacokinetics or injectability. Through interfacial rheology and surface tension measurements, we demonstrate that the copolymer excipient competitively adsorbs to formulation interfaces. Further, through determination of monomeric composition and retained bioactivity through stressed aging, we show that this excipient confers a significant stability benefit to high concentration antibody formulations. Finally, we demonstrate that the excipient behaves as an inactive ingredient, having no significant impact on the pharmacokinetic profile of a clinically relevant antibody in mice. This amphiphilic copolymer excipient demonstrates promise as a simple formulation additive to create stable, high concentration antibody formulations, thereby enabling improved treatment options such as a route-of-administration switch from low concentration intravenous (IV) to high concentration subcutaneous (SC) delivery while reducing dependence on the cold chain.

  View details for DOI 10.1002/adtp.202200102

  View details for PubMedID 36684707

  View details for PubMedCentralID PMC9854243

• Injectable Polymer-Nanoparticle Hydrogel for the Sustained Intravitreal Delivery of Bimatoprost ADVANCED THERAPEUTICS Meany, E. L., Andaya, R., Tang, S., Kasse, C. M., Fuji, R. N., Grosskopf, A. K., D'Aquino, A. L., Bartoe, J. T., Ybarra, R., Shelton, A., Pederson, Z., Hu, C., Leung, D., Nagapudi, K., Ubhayakar, S., Wright, M., Yen, C., Appel, E. A. 2022

  View details for DOI 10.1002/adtp.202200207

  View details for Web of Science ID 000876774400001

• Stable High-Concentration Monoclonal Antibody Formulations Enabled by an Amphiphilic Copolymer Excipient ADVANCED THERAPEUTICS Klich, J. H., Kasse, C. M., Mann, J. L., Huang, Y., D'Aquino, A., Grosskopf, A. K., Baillet, J., Fuller, G. G., Appel, E. A. 2022

  View details for DOI 10.1002/adtp.202200102

  View details for Web of Science ID 000870541300001

• Angiogenic stem cell delivery platform to augment post-infarction neovasculature and reverse ventricular remodeling. Scientific reports Shin, H. S., Thakore, A., Tada, Y., Pedroza, A. J., Ikeda, G., Chen, I. Y., Chan, D., Jaatinen, K. J., Yajima, S., Pfrender, E. M., Kawamura, M., Yang, P. C., Wu, J. C., Appel, E. A., Fischbein, M. P., Woo, Y., Shudo, Y. 2022; 12 (1): 17605

  Abstract

  Many cell-based therapies are challenged by the poor localization of introduced cells and the use of biomaterial scaffolds with questionable biocompatibility or bio-functionality. Endothelial progenitor cells (EPCs), a popular cell type used in cell-based therapies due to their robust angiogenic potential, are limited in their therapeutic capacity to develop into mature vasculature. Here, we demonstrate a joint delivery of human-derived endothelial progenitor cells (EPC) and smooth muscle cells (SMC) as a scaffold-free, bi-level cell sheet platform to improve ventricular remodeling and function in an athymic rat model of myocardial infarction. The transplanted bi-level cell sheet on the ischemic heart provides a biomimetic microenvironment and improved cell-cell communication, enhancing cell engraftment and angiogenesis, thereby improving ventricular remodeling. Notably, the increased density of vessel-like structures and upregulation of biological adhesion and vasculature developmental genes, such as Cxcl12 and Notch3, particularly in the ischemic border zone myocardium, were observed following cell sheet transplantation. We provide compelling evidence that this SMC-EPC bi-level cell sheet construct can be a promising therapy to repair ischemic cardiomyopathy.

  View details for DOI 10.1038/s41598-022-21510-y

  View details for PubMedID 36266453

  View details for PubMedCentralID PMC9584918

• Extreme Extensibility in Physically Cross-Linked Nanocomposite Hydrogels Leveraging Dynamic Polymer-Nanoparticle Interactions. Macromolecules Grosskopf, A. K., Mann, J. L., Baillet, J., Lopez Hernandez, H., Autzen, A. A., Yu, A. C., Appel, E. A. 2022; 55 (17): 7498-7511

  Abstract

  Designing yield stress fluids to exhibit desired functional properties is an integral challenge in many applications such as 3D printing, drilling, food formulation, fiber spinning, adhesives, and injectable biomaterials. Extensibility in particular has been found to be a highly beneficial characteristic for materials in these applications; however, few highly extensible, high water content materials have been reported to date. Herein we engineer a class of high water content nanocomposite hydrogel materials leveraging multivalent, noncovalent, polymer-nanoparticle (PNP) interactions between modified cellulose polymers and biodegradable nanoparticles. We show that modulation of the chemical composition of the PNP hydrogels controls the dynamic cross-linking interactions within the polymer network and directly impacts yielding and viscoelastic responses. These materials can be engineered to stretch up to 2000% strain and occupy an unprecedented property regime for extensible yield stress fluids. Moreover, a dimensional analysis of the relationships between extensibility and the relaxation and recovery time scales of these nanocomposite hydrogels uncovers generalizable design criteria that will be critical for future development of extensible materials.

  View details for DOI 10.1021/acs.macromol.2c00649

  View details for PubMedID 36118599

  View details for PubMedCentralID PMC9476865

• Injectable Nanoparticle-Based Hydrogels Enable the Safe and Effective Deployment of Immunostimulatory CD40 Agonist Antibodies. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Correa, S., Meany, E. L., Gale, E. C., Klich, J. H., Saouaf, O. M., Mayer, A. T., Xiao, Z., Liong, C. S., Brown, R. A., Maikawa, C. L., Grosskopf, A. K., Mann, J. L., Idoyaga, J., Appel, E. A. 2022: e2103677

  Abstract

  When properly deployed, the immune system can eliminate deadly pathogens, eradicate metastatic cancers, and provide long-lasting protection from diverse diseases. Unfortunately, realizing these remarkable capabilities is inherently risky as disruption to immune homeostasis can elicit dangerous complications or autoimmune disorders. While current research is continuously expanding the arsenal of potent immunotherapeutics, there is a technological gap when it comes to controlling when, where, and how long these drugs act on the body. Here, this study explored the ability of a slow-releasing injectable hydrogel depot to reduce dose-limiting toxicities of immunostimulatory CD40agonist (CD40a) while maintaining its potent anticancer efficacy. A previously described polymer-nanoparticle (PNP) hydrogel system is leveraged that exhibits shear-thinning and yield-stress properties that are hypothesized to improve locoregional delivery of CD40a immunotherapy. Using positron emission tomography, it is demonstrated that prolonged hydrogel-based delivery redistributes CD40a exposure to the tumor and the tumor draining lymph node (TdLN), thereby reducing weight loss, hepatotoxicity, and cytokine storm associated with standard treatment. Moreover, CD40a-loaded hydrogels mediate improved local cytokine induction in the TdLN and improve treatment efficacy in the B16F10melanoma model. PNP hydrogels, therefore, represent a facile, drug-agnostic method to ameliorate immune-related adverse effects and explore locoregional delivery of immunostimulatory drugs.

  View details for DOI 10.1002/advs.202103677

  View details for PubMedID 35975424

• Formulation Excipients and Their Role in Insulin Stability and Association State in Formulation. Pharmaceutical research Maikawa, C. L., Nguyen, L. T., Mann, J. L., Appel, E. A. 2022

  Abstract

  While excipients are often overlooked as the "inactive" ingredients in pharmaceutical formulations, they often play a critical role in protein stability and absorption kinetics. Recent work has identified an ultrafast absorbing insulin formulation that is the result of excipient modifications. Specifically, the insulin monomer can be isolated by replacing zinc and the phenolic preservative metacresol with phenoxyethanol as an antimicrobial agent and an amphiphilic acrylamide copolymer excipient for stability. A greater understanding is needed of the interplay between excipients, insulin association state, and stability in order to optimize this formulation. Here, we formulated insulin with different preservatives and stabilizing excipient concentrations using both insulin lispro and regular human insulin and assessed the insulin association states using analytical ultracentrifugation as well as formulation stability. We determined that phenoxyethanol is required to eliminate hexamers and promote a high monomer content even in a zinc-free lispro formulation. There is also a concentration dependent relationship between the concentration of polyacrylamide-based copolymer excipient and insulin stability, where a concentration greater than 0.1g/mL copolymer is required for a mostly monomeric zinc-free lispro formulation to achieve stability exceeding that of Humalog in a stressed aging assay. Further, we determined that under the formulation conditions tested zinc-free regular human insulin remains primarily hexameric and is not at this time a promising candidate for rapid-acting formulations.

  View details for DOI 10.1007/s11095-022-03367-y

  View details for PubMedID 35978148

• Extreme Extensibility in Physically Cross-Linked Nanocomposite Hydrogels Leveraging Dynamic Polymer-Nanoparticle Interactions MACROMOLECULES Grosskopf, A. K., Mann, J. L., Baillet, J., Hernandez, H., Autzen, A. A., Yu, A. C., Appel, E. A. 2022

  View details for DOI 10.1021/acs.macromol.2c00649

  View details for Web of Science ID 000841632100001

• Yield-Stress and Creep Control Depot Formation and Persistence of Injectable Hydrogels Following Subcutaneous Administration ADVANCED FUNCTIONAL MATERIALS Jons, C. K., Grosskopf, A. K., Baillet, J., Yan, J., Klich, J. H., Saouaf, O. M., Appel, E. A. 2022

  View details for DOI 10.1002/adfm.202203402

  View details for Web of Science ID 000835848500001

• Sustained delivery approaches to improving adaptive immune responses. Advanced drug delivery reviews Ou, B. S., Saouaf, O. M., Baillet, J., Appel, E. A. 2022: 114401

  Abstract

  The immune system is one of the most important, complex biological networks regulating and protecting human health. Its precise modulation can prevent deadly infections and fight cancer. Accordingly, prophylactic vaccines and cancer immunotherapies are some of the most powerful technologies to protect against potential dangers through training of the immune system. Upon immunization, activation and maturation of B and T cells of the adaptive immune system are necessary for development of proper humoral and cellular protection. Yet, the exquisite organization of the immune system requires spatiotemporal control over the exposure of immunomodulatory signals. For example, while the human immune system has evolved to develop immunity to natural pathogenic infections that often last for weeks, current prophylactic vaccination technologies only expose the immune system to immunomodulatory signals for hours to days. It has become clear that leveraging sustained release technologies to prolong immunogen and adjuvant exposure can increase the potency, durability, and quality of adaptive immune responses. Over the past several years, tremendous breakthroughs have been made in the design of novel biomaterials such as nanoparticles, microparticles, hydrogels, and microneedles that can precisely control and the presentation of immunomodulatory signals to the immune system. In this review, we discuss relevant sustained release strategies and their corresponding benefits to cellular and humoral responses.

  View details for DOI 10.1016/j.addr.2022.114401

  View details for PubMedID 35750115

• Injectable liposome-based supramolecular hydrogels for the programmable release of multiple protein drugs MATTER Correa, S., Grosskopf, A. K., Klich, J. H., Hernandez, H., Appel, E. A. 2022; 5 (6)

  View details for DOI 10.1016/j.matt.2022.03.001

  View details for Web of Science ID 000810939100002

• Injectable Liposome-based Supramolecular Hydrogels for the Programmable Release of Multiple Protein Drugs. Matter Correa, S., Grosskopf, A. K., Klich, J. H., Hernandez, H. L., Appel, E. A. 2022; 5 (6): 1816-1838

  Abstract

  Directing biological functions is at the heart of next-generation biomedical initiatives in tissue and immuno-engineering. However, the ambitious goal of engineering complex biological networks requires the ability to precisely perturb specific signaling pathways at distinct times and places. Using lipid nanotechnology and the principles of supramolecular self-assembly, we developed an injectable liposomal nanocomposite hydrogel platform to precisely control the release of multiple protein drugs. By integrating modular lipid nanotechnology into a hydrogel, we introduced multiple mechanisms of release based on liposome surface chemistry. To validate the utility of this system for multi-protein delivery, we demonstrated synchronized, sustained, and localized release of IgG antibody and IL-12 cytokine in vivo, despite the significant size differences between these two proteins. Overall, liposomal hydrogels are a highly modular platform technology with the ability the mediate orthogonal modes of protein release and the potential to precisely coordinate biological cues both in vitro and in vivo.

  View details for DOI 10.1016/j.matt.2022.03.001

  View details for PubMedID 35800848

  View details for PubMedCentralID PMC9255852

• Combinatorial Polyacrylamide Hydrogels for Preventing Biofouling on Implantable Biosensors. Advanced materials (Deerfield Beach, Fla.) Chan, D., Chien, J., Axpe, E., Blankemeier, L., Baker, S. W., Swaminathan, S., Piunova, V. A., Zubarev, D. Y., Maikawa, C. L., Grosskopf, A. K., Mann, J. L., Soh, H. T., Appel, E. A. 2022: e2109764

  Abstract

  Biofouling on the surface of implanted medical devices and biosensors severely hinders device functionality and drastically shortens device lifetime. Poly(ethylene glycol) and zwitterionic polymers are currently considered "gold standard" device coatings to reduce biofouling. To discover novel anti-biofouling materials, we created a combinatorial library of polyacrylamide-based copolymer hydrogels and screened their ability to prevent fouling from serum and platelet-rich plasma in a high-throughput parallel assay. We found certain non-intuitive copolymer compositions exhibit superior anti-biofoulingproperties over current gold standard materials, and employed machine learning to identify key molecular features underpinning their performance. For validation, we coated the surfaces of electrochemical biosensors with our hydrogels and evaluated their anti-biofouling performance in vitro and in vivo in rodent models. Our copolymer hydrogels preserved device function and enabled continuous measurements of a small-molecule drug in vivo better than gold standard coatings. The novel methodology we describe enables the discovery of anti-biofouling materials that can extend the lifetime of real-time in vivo sensing devices. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202109764

  View details for PubMedID 35390209

• The living interface between synthetic biology and biomaterial design. Nature materials Liu, A. P., Appel, E. A., Ashby, P. D., Baker, B. M., Franco, E., Gu, L., Haynes, K., Joshi, N. S., Kloxin, A. M., Kouwer, P. H., Mittal, J., Morsut, L., Noireaux, V., Parekh, S., Schulman, R., Tang, S. K., Valentine, M. T., Vega, S. L., Weber, W., Stephanopoulos, N., Chaudhuri, O. 2022; 21 (4): 390-397

  Abstract

  Recent far-reaching advances in synthetic biology have yielded exciting tools for the creation of new materials. Conversely, advances in the fundamental understanding of soft-condensed matter, polymers and biomaterials offer new avenues to extend the reach of synthetic biology. The broad and exciting range of possible applications have substantial implications to address grand challenges in health, biotechnology and sustainability. Despite the potentially transformative impact that lies at the interface of synthetic biology and biomaterials, the two fields have, so far, progressed mostly separately. This Perspective provides a review of recent key advances in these two fields, and a roadmap for collaboration at the interface between the two communities. We highlight the near-term applications of this interface to the development of hierarchically structured biomaterials, from bioinspired building blocks to 'living' materials that sense and respond based on the reciprocal interactions between materials and embedded cells.

  View details for DOI 10.1038/s41563-022-01231-3

  View details for PubMedID 35361951

• PNP Hydrogel Prevents Formation of Symblephara in Mice After Ocular Alkali Injury. Translational vision science & technology Swarup, A., Grosskopf, A. K., Stapleton, L. M., Subramaniam, V. R., Li, B., Weissman, I. L., Appel, E. A., Wu, A. Y. 2022; 11 (2): 31

  Abstract

  Purpose: To create an alkali injury symblephara mouse model to study conjunctival fibrosis pathophysiology and test polymer nanoparticle (PNP) hydrogel as a preventative therapeutic.Methods: Mice were injured using NaOH-soaked filter paper to determine the optimal NaOH concentration to induce the formation of symblephara. Injured mice were observed for 7 days to detect the formation of symblephara. Forniceal shortening observed on hematoxylin and eosin (H&E)-stained tissue sections was used as a symblephara marker. Alpha-smooth muscle actin (alpha-SMA) expression, Masson's trichrome assay, and periodic acid-Schiff (PAS) staining were used to determine myofibroblast expression, collagen deposition, and goblet cell integrity. PNP hydrogel, with multivalent, noncovalent interactions between modified biopolymers and nanoparticles, was applied immediately after alkali injury to determine its ability to prevent the formation of symblephara.Results: Forniceal shortening was observed in H&E images with 1N NaOH for 2 minutes after 7 days without globe destruction. PNP hydrogel prevented forniceal shortening after alkali injury as observed by H&E histology. alpha-SMA expression and collagen deposition in eye tissue sections were increased in the fornix after injury with 1N NaOH compared with uninjured controls. PNP hydrogel treatment immediately after injury reduced alpha-SMA expression and collagen deposition in the forniceal region. Mucin-secreting goblet cells stained with PAS were significantly lower in alkali-injured and PNP hydrogel-treated conjunctivas than in uninjured control conjunctivas.Conclusions: We observed that 1N NaOH for 2 minutes induced maximal forniceal shortening and symblephara in mice. PNP hydrogel prevented forniceal shortening and conjunctival fibrosis after injury. This first murine model for symblephara will be useful to study fibrosis pathophysiology after conjunctival injury and to determine therapeutic targets for cicatrizing diseases.Translational Relevance: This mouse model of symblephara can be useful for studying conjunctival scarring disease pathophysiology and preventative therapeutics. We tested PNP hydrogel, which prevented the formation of symblephara after injury.

  View details for DOI 10.1167/tvst.11.2.31

  View details for PubMedID 35191963

• Real-time monitoring of drug pharmacokinetics within tumor tissue in live animals. Science advances Seo, J. W., Fu, K., Correa, S., Eisenstein, M., Appel, E. A., Soh, H. T. 2022; 8 (1): eabk2901

  Abstract

  [Figure: see text].

  View details for DOI 10.1126/sciadv.abk2901

  View details for PubMedID 34995112

• Multimerization of Ebola GPDeltamucin on protein nanoparticle vaccines has minimal effect on elicitation of neutralizing antibodies. Frontiers in immunology Powell, A. E., Xu, D., Roth, G. A., Zhang, K., Chiu, W., Appel, E. A., Kim, P. S. 2022; 13: 942897

  Abstract

  Ebola virus (EBOV), a member of the Filoviridae family of viruses and a causative agent of Ebola Virus Disease (EVD), is a highly pathogenic virus that has caused over twenty outbreaks in Central and West Africa since its formal discovery in 1976. The only FDA-licensed vaccine against Ebola virus, rVSV-ZEBOV-GP (Ervebo), is efficacious against infection following just one dose. However, since this vaccine contains a replicating virus, it requires ultra-low temperature storage which imparts considerable logistical challenges for distribution and access. Additional vaccine candidates could provide expanded protection to mitigate current and future outbreaks. Here, we designed and characterized two multimeric protein nanoparticle subunit vaccines displaying 8 or 20 copies of GPDeltamucin, a truncated form of the EBOV surface protein GP. Single-dose immunization of mice with GPDeltamucin nanoparticles revealed that neutralizing antibody levels were roughly equivalent to those observed in mice immunized with non-multimerized GPDeltamucin trimers. These results suggest that some protein subunit antigens do not elicit enhanced antibody responses when displayed on multivalent scaffolds and can inform next-generation design of stable Ebola virus vaccine candidates.

  View details for DOI 10.3389/fimmu.2022.942897

  View details for PubMedID 36091016

• Gelation and yielding behavior of polymer-nanoparticle hydrogels. Journal of polymer science (2020) Grosskopf, A. K., Saouaf, O. A., Lopez Hernandez, H., Appel, E. A. 2021; 59 (22): 2854-2866

  Abstract

  Polymer-nanoparticle hydrogels are a unique class of self-assembled, shear-thinning, yield-stress fluids that have demonstrated potential utility in many impactful applications. Here, we present a thorough analysis of the gelation and yielding behavior of these materials with respect to the polymer and nanoparticle component stoichiometry. Through comprehensive rheological and diffusion studies, we reveal insights into the structural dynamics of the polymer nanoparticle network that identify that stoichiometry plays a key role in gelation and yielding, ultimately enabling the development of hydrogel formulations with unique shear-thinning and yield-stress behaviors. Access to these materials opens new doors for interesting applications in a variety of fields including tissue engineering, drug delivery, and controlled solution viscosity.

  View details for DOI 10.1002/pol.20210652

  View details for PubMedID 35875706

  View details for PubMedCentralID PMC9298381

• Gelation and yielding behavior of polymer-nanoparticle hydrogels JOURNAL OF POLYMER SCIENCE Grosskopf, A. K., Saouaf, O. A., Lopez Hernandez, H., Appel, E. A. 2021

  View details for DOI 10.1002/pol.20210652

  View details for Web of Science ID 000709823700001

• Self-Assembled, Dilution-Responsive Hydrogels for Enhanced Thermal Stability of Insulin Biopharmaceuticals. ACS biomaterials science & engineering Meis, C. M., Salzman, E. E., Maikawa, C. L., Smith, A. A., Mann, J. L., Grosskopf, A. K., Appel, E. A. 2021; 7 (9): 4221-4229

  Abstract

  Biotherapeutics currently dominate the landscape of new drugs because of their exceptional potency and selectivity. Yet, the intricate molecular structures that give rise to these beneficial qualities also render them unstable in formulation. Hydrogels have shown potential as stabilizing excipients for biotherapeutic drugs, providing protection against harsh thermal conditions experienced during distribution and storage. In this work, we report the utilization of a cellulose-based supramolecular hydrogel formed from polymer-nanoparticle (PNP) interactions to encapsulate and stabilize insulin, an important biotherapeutic used widely to treat diabetes. Encapsulation of insulin in these hydrogels prevents insulin aggregation and maintains insulin bioactivity through stressed aging conditions of elevated temperature and continuous agitation for over 28 days. Further, insulin can be easily recovered by dilution of these hydrogels for administration at the point of care. This supramolecular hydrogel system shows promise as a stabilizing excipient to reduce the cold chain dependence of insulin and other biotherapeutics.

  View details for DOI 10.1021/acsbiomaterials.0c01306

  View details for PubMedID 34510910

• Ultra-Fast Insulin-Pramlintide Co-Formulation for Improved Glucose Management in Diabetic Rats. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Maikawa, C. L., Chen, P. C., Vuong, E. T., Nguyen, L. T., Mann, J. L., d'Aquino, A. I., Lal, R. A., Maahs, D. M., Buckingham, B. A., Appel, E. A. 2021: e2101575

  Abstract

  Dual-hormone replacement therapy with insulin and amylin in patients with type 1 diabetes has the potential to improve glucose management. Unfortunately, currently available formulations require burdensome separate injections at mealtimes and have disparate pharmacokinetics that do not mimic endogenous co-secretion. Here, amphiphilic acrylamide copolymers are used to create a stable co-formulation of monomeric insulin and amylin analogues (lispro and pramlintide) with synchronous pharmacokinetics and ultra-rapid action. The co-formulation is stable for over 16 h under stressed aging conditions, whereas commercial insulin lispro (Humalog) aggregates in 8 h. The faster pharmacokinetics of monomeric insulin in this co-formulation result in increased insulin-pramlintide overlap of 75 ± 6% compared to only 47 ± 7% for separate injections. The co-formulation results in similar delay in gastric emptying compared to pramlintide delivered separately. In a glucose challenge, in rats, the co-formulation reduces deviation from baseline glucose compared to insulin only, or separate insulin and pramlintide administrations. Further, comparison of interspecies pharmacokinetics of monomeric pramlintide suggests that pharmacokinetics observed for the co-formulation will be well preserved in future translation to humans. Together these results suggest that the co-formulation has the potential to improve mealtime glucose management and reduce patient burden in the treatment of diabetes.

  View details for DOI 10.1002/advs.202101575

  View details for PubMedID 34499434

• Consistent tumorigenesis with self-assembled hydrogels enables high-powered murine cancer studies. Communications biology Grosskopf, A. K., Correa, S., Baillet, J., Maikawa, C. L., Gale, E. C., Brown, R. A., Appel, E. A. 2021; 4 (1): 985

  Abstract

  Preclinical cancer research is heavily dependent on allograft and xenograft models, but current approaches to tumor inoculation yield inconsistent tumor formation and growth, ultimately wasting valuable resources (e.g., animals, time, and money) and limiting experimental progress. Here we demonstrate a method for tumor inoculation using self-assembled hydrogels to reliably generate tumors with low variance in growth. The observed reduction in model variance enables smaller animal cohorts, improved effect observation and higher powered studies.

  View details for DOI 10.1038/s42003-021-02500-8

  View details for PubMedID 34413455

• Affinity-Directed Dynamics of Host-Guest Motifs for Pharmacokinetic Modulation via Supramolecular PEGylation. Biomacromolecules Maikawa, C. L., d'Aquino, A. I., Vuong, E. T., Su, B., Zou, L., Chen, P. C., Nguyen, L. T., Autzen, A. A., Mann, J. L., Webber, M. J., Appel, E. A. 2021

  Abstract

  Proteins are an impactful class of therapeutics but can exhibit suboptimal therapeutic performance, arising from poor control over the timescale of clearance. Covalent PEGylation is one established strategy to extend circulation time but often at the cost of reduced activity and increased immunogenicity. Supramolecular PEGylation may afford similar benefits without necessitating that the protein be permanently modified with a polymer. Here, we show that insulin pharmacokinetics can be modulated by tuning the affinity-directed dynamics of a host-guest motif used to non-covalently endow insulin with a poly(ethylene glycol) (PEG) chain. When administered subcutaneously, supramolecular PEGylation with higher binding affinities extends the time of total insulin exposure systemically. Pharmacokinetic modeling reveals that the extension in the duration of exposure arises specifically from decreased absorption from the subcutaneous depot governed directly by the affinity and dynamics of host-guest exchange. The lifetime of the supramolecular interaction thus dictates the rate of absorption, with negligible impact attributed to association of the PEG upon rapid dilution of the supramolecular complex in circulation. This modular approach to supramolecular PEGylation offers a powerful tool to tune protein pharmacokinetics in response to the needs of different disease applications.

  View details for DOI 10.1021/acs.biomac.1c00648

  View details for PubMedID 34314146

• Engineering Insulin Cold Chain Resilience to Improve Global Access. Biomacromolecules Maikawa, C. L., Mann, J. L., Kannan, A., Meis, C. M., Grosskopf, A. K., Ou, B. S., Autzen, A. A., Fuller, G. G., Maahs, D. M., Appel, E. A. 2021

  Abstract

  There are 150 million people with diabetes worldwide who require insulin replacement therapy, and the prevalence of diabetes is rising the fastest in middle- and low-income countries. The current formulations require costly refrigerated transport and storage to prevent loss of insulin integrity. This study shows the development of simple "drop-in" amphiphilic copolymer excipients to maintain formulation integrity, bioactivity, pharmacokinetics, and pharmacodynamics for over 6 months when subjected to severe stressed aging conditions that cause current commercial formulation to fail in under 2 weeks. Further, when these copolymers are added to Humulin R (Eli Lilly) in original commercial packaging, they prevent insulin aggregation for up to 4 days at 50 °C compared to less than 1 day for Humulin R alone. These copolymers demonstrate promise as simple formulation additives to increase the cold chain resilience of commercial insulin formulations, thereby expanding global access to these critical drugs for treatment of diabetes.

  View details for DOI 10.1021/acs.biomac.1c00474

  View details for PubMedID 34213889

• More than a fertilizer: wastewater-derived struvite as a high value, sustainable fire retardant GREEN CHEMISTRY Kim, A. H., Yu, A. C., El Abbadi, S. H., Lu, K., Chan, D., Appel, E. A., Criddle, C. S. 2021

  View details for DOI 10.1039/d1gc00826a

  View details for Web of Science ID 000657677100001

• Modulation of injectable hydrogel properties for slow co-delivery of influenza subunit vaccine components enhance the potency of humoral immunity. Journal of biomedical materials research. Part A Saouaf, O. M., Roth, G. A., Ou, B. S., Smith, A. A., Yu, A. C., Gale, E. C., Grosskopf, A. K., Picece, V. C., Appel, E. A. 2021

  Abstract

  Vaccines are critical for combating infectious diseases across the globe. Influenza, for example, kills roughly 500,000 people annually worldwide, despite annual vaccination campaigns. Efficacious vaccines must elicit a robust and durable antibody response, and poor efficacy often arises from inappropriate temporal control over antigen and adjuvant presentation to the immune system. In this work, we sought to exploit the immune system's natural response to extended pathogen exposure during infection by designing an easily administered slow-delivery influenza vaccine platform. We utilized an injectable and self-healing polymer-nanoparticle (PNP) hydrogel platform to prolong the co-delivery of vaccine components to the immune system. We demonstrated that these hydrogels exhibit unique dynamic physical characteristics whereby physicochemically distinct influenza hemagglutinin antigen and a toll-like receptor 7/8 agonist adjuvant could be co-delivered over prolonged timeframes that were tunable through simple alteration of the gel formulation. We show a relationship between hydrogel physical properties and the resulting immune response to immunization. When administered in mice, hydrogel-based vaccines demonstrated enhancements in the magnitude and duration of humoral immune responses compared to alum, a widely used clinical adjuvant system. We found stiffer hydrogel formulations exhibited slower release and resulted in the greatest improvements to the antibody response while also enabling significant adjuvant dose sparing. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

  View details for DOI 10.1002/jbm.a.37203

  View details for PubMedID 33955657

• Translational Applications of Hydrogels. Chemical reviews Correa, S., Grosskopf, A. K., Lopez Hernandez, H., Chan, D., Yu, A. C., Stapleton, L. M., Appel, E. A. 2021

  Abstract

  Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

  View details for DOI 10.1021/acs.chemrev.0c01177

  View details for PubMedID 33938724

• Full closed loop open-source algorithm performance comparison in pigs with diabetes. Clinical and translational medicine Lal, R. A., Maikawa, C. L., Lewis, D., Baker, S. W., Smith, A. A., Roth, G. A., Gale, E. C., Stapleton, L. M., Mann, J. L., Yu, A. C., Correa, S., Grosskopf, A. K., Liong, C. S., Meis, C. M., Chan, D., Garner, J. P., Maahs, D. M., Buckingham, B. A., Appel, E. A. 2021; 11 (4): e387

  Abstract

  Understanding how automated insulin delivery (AID) algorithm features impact glucose control under full closed loop delivery represents a critical step toward reducing patient burden by eliminating the need for carbohydrate entries at mealtimes. Here, we use a pig model of diabetes to compare AndroidAPS and Loop open-source AID systems without meal announcements. Overall time-in-range (70-180mg/dl) for AndroidAPS was 58% ± 5%, while time-in-range for Loop was 35% ± 5%. The effect of the algorithms on time-in-range differed between meals and overnight. During the overnight monitoring period, pigs had an average time-in-range of 90% ± 7% when on AndroidAPS compared to 22% ± 8% on Loop. Time-in-hypoglycemia also differed significantly during the lunch meal, whereby pigs running AndroidAPS spent an average of 1.4% (+0.4/-0.8)% in hypoglycemia compared to 10% (+3/-6)% for those using Loop. As algorithm design for closed loop systems continues to develop, the strategies employed in the OpenAPS algorithm (known as oref1) as implemented in AndroidAPS for unannounced meals may result in a better overall control for full closed loop systems.

  View details for DOI 10.1002/ctm2.387

  View details for PubMedID 33931977

• Controlling properties of thermogels by tuning critical solution behaviour of ternary copolymers dagger POLYMER CHEMISTRY Smith, A. A., Maikawa, C. L., Lopez Hernandez, H., Appel, E. A. 2021

  View details for DOI 10.1039/d0py01696a

  View details for Web of Science ID 000633040700001

• Enhanced Humoral Immune Response by High Density TLR Agonist Presentation on Hyperbranched Polymers ADVANCED THERAPEUTICS Liong, C. S., Smith, A. A., Mann, J. L., Roth, G. A., Gale, E. C., Maikawa, C. L., Ou, B. S., Appel, E. A. 2021

  View details for DOI 10.1002/adtp.202000081

  View details for Web of Science ID 000620203300001

• Injectable Supramolecular Polymer-Nanoparticle Hydrogels for Cell and Drug Delivery Applications. Journal of visualized experiments : JoVE Meis, C. M., Grosskopf, A. K., Correa, S., Appel, E. A. 2021

  Abstract

  These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels foruse as biomaterials. PNP hydrogels are composed of two components: hydrophobically modified cellulose as the network polymer and self-assembled core-shell nanoparticles that act as non-covalent cross linkers through dynamic, multivalent interactions. These methods describe both the formation of these self-assembled nanoparticles through nanoprecipitation as well as the formulation and mixing of the two components to form hydrogels with tunable mechanical properties. The use of dynamic light scattering (DLS) and rheology to characterize the quality of the synthesized materials is also detailed. Finally, the utility of these hydrogels for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery is demonstrated through in vitro experiments to characterizedrug release, thermal stability, and cell settling and viability. Due to its biocompatibility, injectability, and mild gel formation conditions, this hydrogel system is a readily tunable platform suitable for a range of biomedical applications.

  View details for DOI 10.3791/62234

  View details for PubMedID 33616104

• Seasonal Impact of Phosphate-Based Fire Retardants on Soil Chemistry Following the Prophylactic Treatment of Vegetation. Environmental science & technology Yu, A. C., Reinhart, M., Hunter, R., Lu, K., Maikawa, C. L., Rajakaruna, N., Acosta, J. D., Stubler, C., Appel, C., Appel, E. A. 2021

  Abstract

  A preventative treatment of fire retardants at high-risk locales can potentially stop a majority of wildfires. For example, over 80% of wildfire ignitions in California occur at high-risk locales such as adjacent to roadsides and utility infrastructure. Recently a new class of ammonium polyphosphate retardants was developed with enhanced adherence and retention on vegetation to enable prophylactic treatments of these high-risk locals to provide season-long prevention of ignitions. Here, we compare three different ammonium (poly)phosphate-based wildland retardant formulations and evaluate their resistance to weathering and analyze their seasonal impact on soil chemistry following application onto grass. Soil samples from all three treatments demonstrated no changes in soil pH and total soil carbon and nitrogen amounts. Total soil phosphorus amounts increased by 2-3* following early precipitation, always remaining within typical topsoil amounts, and returned to the same level as control soil before spring. Available indices of ammonium, nitrate, and phosphate levels for all groups were elevated compared to the untreated control samples, again remaining within typical topsoil ranges across all time points and rainfall amounts evaluated. Microbial activity was decreased, potentially because the addition of available nutrients from retardant application reduced the need for organic decomposition. These results demonstrate that the application of ammonium (poly)phosphate-based retardants does not alter soil chemistry beyond typical topsoil compositions and are thus suitable for use in prophylactic wildfire prevention strategies.

  View details for DOI 10.1021/acs.est.0c05472

  View details for PubMedID 33529000

• Dynamic Hydrogels for Prevention of Post-Operative Peritoneal Adhesions ADVANCED THERAPEUTICS Stapleton, L. M., Lucian, H. J., Grosskopf, A. K., Smith, A. A., Totherow, K. P., Woo, Y., Appel, E. A. 2021

  View details for DOI 10.1002/adtp.202000242

  View details for Web of Science ID 000606949300001

• Prolonged Codelivery of Hemagglutinin and a TLR7/8 Agonist in a Supramolecular Polymer-Nanoparticle Hydrogel Enhances Potency and Breadth of Influenza Vaccination. ACS biomaterials science & engineering Roth, G. A., Saouaf, O. M., Smith, A. A., Gale, E. C., Hernandez, M. A., Idoyaga, J., Appel, E. A. 2021

  Abstract

  The sustained release of vaccine cargo has been shown to improve humoral immune responses to challenging pathogens such as influenza. Extended codelivery of antigen and adjuvant prolongs germinal center reactions, thus improving antibody affinity maturation and the ability to neutralize the target pathogen. Here, we develop an injectable, physically cross-linked polymer-nanoparticle (PNP) hydrogel system to prolong the local codelivery of hemagglutinin and a toll-like receptor 7/8 agonist (TLR7/8a) adjuvant. By tethering the TLR7/8a to a NP motif within the hydrogels (TLR7/8a-NP), the dynamic mesh of the PNP hydrogels enables codiffusion of the adjuvant and protein antigen (hemagglutinin), therefore enabling sustained codelivery of these two physicochemically distinct molecules. We show that subcutaneous delivery of PNP hydrogels carrying hemagglutinin and TLR7/8a-NP in mice improves the magnitude and duration of antibody titers in response to a single injection vaccination compared to clinically used adjuvants. Furthermore, the PNP gel-based slow delivery of influenza vaccines led to increased breadth of antibody responses against future influenza variants, including a future pandemic variant, compared to clinical adjuvants. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

  View details for DOI 10.1021/acsbiomaterials.0c01496

  View details for PubMedID 33404236

• Engineering biopharmaceutical formulations to improve diabetes management. Science translational medicine Maikawa, C. L., d'Aquino, A. I., Lal, R. A., Buckingham, B. A., Appel, E. A. 2021; 13 (578)

  Abstract

  Insulin was first isolated almost a century ago, yet commercial formulations of insulin and its analogs for hormone replacement therapy still fall short of appropriately mimicking endogenous glycemic control. Moreover, the controlled delivery of complementary hormones (such as amylin or glucagon) is complicated by instability of the pharmacologic agents and complexity of maintaining multiple infusions. In this review, we highlight the advantages and limitations of recent advances in drug formulation that improve protein stability and pharmacokinetics, prolong drug delivery, or enable alternative dosage forms for the management of diabetes. With controlled delivery, these formulations could improve closed-loop glycemic control.

  View details for DOI 10.1126/scitranslmed.abd6726

  View details for PubMedID 33504649

• Isthmin-1 is an adipokine that promotes glucose uptake and improves glucose tolerance and hepatic steatosis. Cell metabolism Jiang, Z., Zhao, M., Voilquin, L., Jung, Y., Aikio, M. A., Sahai, T., Dou, F. Y., Roche, A. M., Carcamo-Orive, I., Knowles, J. W., Wabitsch, M., Appel, E. A., Maikawa, C. L., Camporez, J. P., Shulman, G. I., Tsai, L., Rosen, E. D., Gardner, C. D., Spiegelman, B. M., Svensson, K. J. 2021

  Abstract

  With the increasing prevalence of type 2 diabetes and fatty liver disease, there is still an unmet need to better treat hyperglycemia and hyperlipidemia. Here, we identify isthmin-1 (Ism1) as an adipokine and one that has a dual role in increasing adipose glucose uptake while suppressing hepatic lipid synthesis. Ism1 ablation results in impaired glucose tolerance, reduced adipose glucose uptake, and reduced insulin sensitivity, demonstrating an endogenous function for Ism1 in glucose regulation. Mechanistically, Ism1 activates a PI3K-AKT signaling pathway independently of the insulin and insulin-like growth factor receptors. Notably, while the glucoregulatory function is shared with insulin, Ism1 counteracts lipid accumulation in the liver by switching hepatocytes from a lipogenic to a protein synthesis state. Furthermore, therapeutic dosing of recombinant Ism1 improves diabetes in diet-induced obese mice and ameliorates hepatic steatosis in a diet-induced fatty liver mouse model. These findings uncover an unexpected, bioactive protein hormone that might have simultaneous therapeutic potential for diabetes and fatty liver disease.

  View details for DOI 10.1016/j.cmet.2021.07.010

  View details for PubMedID 34348115

• miR-106a-363 cluster in extracellular vesicles promotes endogenous myocardial repair via Notch3 pathway in ischemic heart injury. Basic research in cardiology Jung, J. H., Ikeda, G. n., Tada, Y. n., von Bornstädt, D. n., Santoso, M. R., Wahlquist, C. n., Rhee, S. n., Jeon, Y. J., Yu, A. C., O'brien, C. G., Red-Horse, K. n., Appel, E. A., Mercola, M. n., Woo, J. n., Yang, P. C. 2021; 116 (1): 19

  Abstract

  Endogenous capability of the post-mitotic human heart holds great promise to restore the injured myocardium. Recent evidence indicates that the extracellular vesicles (EVs) regulate cardiac homeostasis and regeneration. Here, we investigated the molecular mechanism of EVs for self-repair. We isolated EVs from human iPSC-derived cardiomyocytes (iCMs), which were exposed to hypoxic (hEVs) and normoxic conditions (nEVs), and examined their roles in in vitro and in vivo models of cardiac injury. hEV treatment significantly improved the viability of hypoxic iCMs in vitro and cardiac function of severely injured murine myocardium in vivo. Microarray analysis of the EVs revealed significantly enriched expression of the miR-106a-363 cluster (miR cluster) in hEVs vs. nEVs. This miR cluster preserved survival and contractility of hypoxia-injured iCMs and maintained murine left-ventricular (LV) chamber size, improved LV ejection fraction, and reduced myocardial fibrosis of the injured myocardium. RNA-Seq analysis identified Jag1-Notch3-Hes1 as a target intracellular pathway of the miR cluster. Moreover, the study found that the cell cycle activator and cytokinesis genes were significantly up-regulated in the iCMs treated with miR cluster and Notch3 siRNA. Together, these results suggested that the miR cluster in the EVs stimulated cardiomyocyte cell cycle re-entry by repressing Notch3 to induce cell proliferation and augment myocardial self-repair. The miR cluster may represent an effective therapeutic approach for ischemic cardiomyopathy.

  View details for DOI 10.1007/s00395-021-00858-8

  View details for PubMedID 33742276

• A fluorescence sandwich immunoassay for the real-time continuous detection of glucose and insulin in live animals. Nature biomedical engineering Poudineh, M., Maikawa, C. L., Ma, E. Y., Pan, J., Mamerow, D., Hang, Y., Baker, S. W., Beirami, A., Yoshikawa, A., Eisenstein, M., Kim, S., Vuckovic, J., Appel, E. A., Soh, H. T. 2020

  Abstract

  Biosensors that continuously measure circulating biomolecules in real time could provide insights into the health status of patients and their response to therapeutics. But biosensors for the continuous real-time monitoring of analytes in vivo have only reached nanomolar sensitivity and can measure only a handful of molecules, such as glucose and blood oxygen. Here we show that multiple analytes can be continuously and simultaneously measured with picomolar sensitivity and sub-second resolution via the integration of aptamers and antibodies into a bead-based fluorescence sandwich immunoassay implemented in a custom microfluidic chip. After an incubation time of 30s, bead fluorescence is measured using a high-speed camera under spatially multiplexed two-colour laser illumination. We used the assay for continuous quantification of glucose and insulin concentrations in the blood of live diabetic rats to resolve inter-animal differences in the pharmacokinetic response to insulin as well as discriminate pharmacokinetic profiles from different insulin formulations. The assay can be readily modified to continuously and simultaneously measure other blood analytes in vivo.

  View details for DOI 10.1038/s41551-020-00661-1

  View details for PubMedID 33349659

• Lipid Nanodiscs via Ordered Copolymers CHEM Smith, A. A., Autzen, H. E., Faust, B., Mann, J. L., Muir, B. W., Howard, S., Postma, A., Spakowitz, A. J., Cheng, Y., Appel, E. A. 2020; 6 (10): 2782–95

  View details for DOI 10.1016/j.chempr.2020.08.004

  View details for Web of Science ID 000580615300022

• The COVID-19 lockdowns: a window into the Earth System NATURE REVIEWS EARTH & ENVIRONMENT Diffenbaugh, N. S., Field, C. B., Appel, E. A., Azevedo, I. L., Baldocchi, D. D., Burke, M., Burney, J. A., Ciais, P., Davis, S. J., Fiore, A. M., Fletcher, S. M., Hertel, T. W., Horton, D. E., Hsiang, S. M., Jackson, R. B., Jin, X., Levi, M., Lobell, D. B., McKinley, G. A., Moore, F. C., Montgomery, A., Nadeau, K. C., Pataki, D. E., Randerson, J. T., Reichstein, M., Schnell, J. L., Seneviratne, S., Singh, D., Steiner, A. L., Wong-Parodi, G. 2020; 1 (9): 470-481

  View details for DOI 10.1038/s43017-020-0079-1

  View details for Web of Science ID 000649448400008

• Highly Branched Polydimethylacrylamide Copolymers as Functional Biomaterials. Biomacromolecules Mann, J. L., Grosskopf, A. K., Smith, A. A., Appel, E. A. 2020

  Abstract

  Controlled radical polymerization of vinyl monomers with multivinyl cross-linkers leads to the synthesis of highly branched polymers with controlled spatial density of functional chain ends. The resulting polymers synthesized in this manner have large dispersities resulting from a mixture of unreacted primary chains, low molecular weight branched species, and high molecular weight highly branched species. Through the use of fractional precipitation, we present a synthetic route to high molecular weight highly branched polymers that are absent of low molecular weight species and that contain reactivity toward amines for controlled postpolymerization modification. The controlled spatial density of functional moieties on these high molecular weight macromolecular constructs enable new functional biomaterials with the potential for application in regenerative medicine, immunoengineering, imaging, and controlled drug delivery.

  View details for DOI 10.1021/acs.biomac.0c00539

  View details for PubMedID 32786733

• Site-selective modification of proteins using cucurbit[7]uril as supramolecular protection for N-terminal aromatic amino acids. Organic & biomolecular chemistry Smith, A. A., Maikawa, C. L., Roth, G. A., Appel, E. A. 2020

  Abstract

  Cucurbit[7,8]urils are known to form inclusion complexes with aromatic amino acids, hosting the hydrohobic side chains within the cavity and adjacent cations within the portal of the macrocyclic host. Here we show that cucurbit[7]uril binding with N-terminal phenylalanine significantly reduces the nucleophilicity of the amine, likely due to an increase in stability of the ammonium ion, rendering it unreactive at neutral pH. Using insulin as a model protein, we show that this supramolecular protection strategy can drive selectivity of N-terminal amine conjugation away from the preferred B chain N-terminal phenylalanine towards the A chain N-terminal glycine. Cucurbit[7]uril can therefore be used as a supramolecular protecting group for site-selective protein modification.

  View details for DOI 10.1039/d0ob01004a

  View details for PubMedID 32459261

• Reply to Santin et al.: Viscoelastic retardant fluids enable treatments to prevent wildfire on landscapes subject to routine ignitions. Proceedings of the National Academy of Sciences of the United States of America Appel, E. A., Criddle, C. S., Acosta, J. D., Yu, A. C. 2020

  View details for DOI 10.1073/pnas.1922877117

  View details for PubMedID 32079729

• A human mission to Mars: Predicting the bone mineral density loss of astronauts. PloS one Axpe, E., Chan, D., Abegaz, M. F., Schreurs, A., Alwood, J. S., Globus, R. K., Appel, E. A. 2020; 15 (1): e0226434

  Abstract

  A round-trip human mission to Mars is anticipated to last roughly three years. Spaceflight conditions are known to cause loss of bone mineral density (BMD) in astronauts, increasing bone fracture risk. There is an urgent need to understand BMD progression as a function of spaceflight time to minimize associated health implications and ensure mission success. Here we introduce a nonlinear mathematical model of BMD loss for candidate human missions to Mars: (i) Opposition class trajectory (400-600 days), and (ii) Conjunction class trajectory (1000-1200 days). Using femoral neck BMD data (N = 69) from astronauts after 132-day and 228-day spaceflight and the World Health Organization's fracture risk recommendation, we predicted post-mission risk and associated osteopathology. Our model predicts 62% opposition class astronauts and 100% conjunction class astronauts will develop osteopenia, with 33% being at risk for osteoporosis. This model can help in implementing countermeasure strategies and inform space agencies' choice of crew candidates.

  View details for DOI 10.1371/journal.pone.0226434

  View details for PubMedID 31967993

• Nanoparticles Presenting Potent TLR7/8 Agonists Enhance Anti-PD-L1 Immunotherapy in Cancer Treatment. Biomacromolecules Smith, A. A., Gale, E. C., Roth, G. A., Maikawa, C. L., Correa, S. n., Yu, A. C., Appel, E. A. 2020

  Abstract

  Cancer immunotherapy can be augmented with toll-like receptor agonist (TLRa) adjuvants, which interact with immune cells to elicit potent immune activation. Despite their potential, use of many TLRa compounds has been limited clinically due to their extreme potency and lack of pharmacokinetic control, causing systemic toxicity from unregulated systemic cytokine release. Herein, we overcome these shortcomings by generating poly(ethylene glycol)-poly(lactic acid) (PEG-PLA) nanoparticles (NPs) presenting potent TLR7/8a moieties on their surface. The NP platform allows precise control of TLR7/8a valency and resulting surface presentation through self-assembly using nanoprecipitation. We hypothesize that the pharmacokinetic profile of the NPs minimizes systemic toxicity, localizing TLR7/8a presentation to the tumor bed and tumor-draining lymph nodes. In conjunction with antiprogrammed death-ligand 1 (anti-PD-L1) checkpoint blockade, peritumoral injection of TLR7/8a NPs slows tumor growth, extends survival, and decreases systemic toxicity in comparison to the free TLR7/8a in a murine colon adenocarcinoma model. These NPs constitute a modular platform for controlling pharmacokinetics of immunostimulatory molecules, resulting in increased potency and decreased toxicity.

  View details for DOI 10.1021/acs.biomac.0c00812

  View details for PubMedID 32816460

• Stable Monomeric Insulin Formulations Enabled by Supramolecular PEGylation of Insulin Analogues. Advanced therapeutics Maikawa, C. L., Smith, A. A., Zou, L., Meis, C. M., Mann, J. L., Webber, M. J., Appel, E. A. 2020; 3 (1)

  Abstract

  Current "fast-acting" insulin analogues contain amino acid modifications meant to inhibit dimer formation and shift the equilibrium of association states toward the monomeric state. However, the insulin monomer is highly unstable and current formulation techniques require insulin to primarily exist as hexamers to prevent aggregation into inactive and immunogenic amyloids. Insulin formulation excipients have thus been traditionally selected to promote insulin association into the hexameric form to enhance formulation stability. This study exploits a novel excipient for the supramolecular PEGylation of insulin analogues, including aspart and lispro, to enhance the stability and maximize the prevalence of insulin monomers in formulation. Using multiple techniques, it is demonstrated that judicious choice of formulation excipients (tonicity agents and parenteral preservatives) enables insulin analogue formulations with 70-80% monomer and supramolecular PEGylation imbued stability under stressed aging for over 100 h without altering the insulin association state. Comparatively, commercial "fast-acting" formulations contain less than 1% monomer and remain stable for only 10 h under the same stressed aging conditions. This simple and effective formulation approach shows promise for next-generation ultrafast insulin formulations with a short duration of action that can reduce the risk of post-prandial hypoglycemia in the treatment of diabetes.

  View details for DOI 10.1002/adtp.201900094

  View details for PubMedID 32190729

  View details for PubMedCentralID PMC7079736

• MRBLES 2.0: High-throughput generation of chemically functionalized spectrally and magnetically encoded hydrogel beads using a simple single-layer microfluidic device. Microsystems & nanoengineering Feng, Y., White, A. K., Hein, J. B., Appel, E. A., Fordyce, P. M. 2020; 6: 109

  Abstract

  The widespread adoption of bead-based multiplexed bioassays requires the ability to easily synthesize encoded microspheres and conjugate analytes of interest to their surface. Here, we present a simple method (MRBLEs 2.0) for the efficient high-throughput generation of microspheres with ratiometric barcode lanthanide encoding (MRBLEs) that bear functional groups for downstream surface bioconjugation. Bead production in MRBLEs 2.0 relies on the manual mixing of lanthanide/polymer mixtures (each of which comprises a unique spectral code) followed by droplet generation using single-layer, parallel flow-focusing devices and the off-chip batch polymerization of droplets into beads. To streamline downstream analyte coupling, MRBLEs 2.0 crosslinks copolymers bearing functional groups on the bead surface during bead generation. Using the MRBLEs 2.0 pipeline, we generate monodisperse MRBLEs containing 48 distinct well-resolved spectral codes with high throughput (>150,000/min and can be boosted to 450,000/min). We further demonstrate the efficient conjugation of oligonucleotides and entire proteins to carboxyl MRBLEs and of biotin to amino MRBLEs. Finally, we show that MRBLEs can also be magnetized via the simultaneous incorporation of magnetic nanoparticles with only a minor decrease in the potential code space. With the advantages of dramatically simplified device fabrication, elimination of the need for custom-made equipment, and the ability to produce spectrally and magnetically encoded beads with direct surface functionalization with high throughput, MRBLEs 2.0 can be directly applied by many labs towards a wide variety of downstream assays, from basic biology to diagnostics and other translational research.

  View details for DOI 10.1038/s41378-020-00220-3

  View details for PubMedID 33299601

• Towards brain-tissue-like biomaterials. Nature communications Axpe, E. n., Orive, G. n., Franze, K. n., Appel, E. A. 2020; 11 (1): 3423

  View details for DOI 10.1038/s41467-020-17245-x

  View details for PubMedID 32647269

• Engineered biomaterials for heart disease. Current opinion in biotechnology Stapleton, L. n., Zhu, Y. n., Woo, Y. J., Appel, E. n. 2020; 66: 246–54

  Abstract

  Ischemic heart disease is the most common type of heart disease, responsible for roughly 10 million deaths worldwide annually. While standard clinical interventions have resulted in improved patient outcomes, access to small diameter vessels required for cardiovascular interventions, and long-term patient mortality rates associated with eventual heart failure, remain critical challenges. In this current opinion piece we discuss novel methodologies for the advancement of vascular grafts, cardiac patches, and injectable drug delivery depot technologies as they relate to treatment of ischemic heart disease, including bilayered conduits, acellular bioactive extracellular matrix (ECM) scaffolds, and protease-responsive hydrogel delivery platforms. We address the motivation for innovation and current limitations in the field of engineered biomaterials for myocardial ischemia therapeutics and interventions.

  View details for DOI 10.1016/j.copbio.2020.08.008

  View details for PubMedID 33011453

• Multi-phase catheter-injectable hydrogel enables dual-stage protein-engineered cytokine release to mitigate adverse left ventricular remodeling following myocardial infarction in a small animal model and a large animal model. Cytokine Steele, A. N., Paulsen, M. J., Wang, H. n., Stapleton, L. M., Lucian, H. J., Eskandari, A. n., Hironaka, C. E., Farry, J. M., Baker, S. W., Thakore, A. D., Jaatinen, K. J., Tada, Y. n., Hollander, M. J., Williams, K. M., Seymour, A. J., Totherow, K. P., Yu, A. C., Cochran, J. R., Appel, E. A., Woo, Y. J. 2020; 127: 154974

  Abstract

  Although ischemic heart disease is the leading cause of death worldwide, mainstay treatments ultimately fail because they do not adequately address disease pathophysiology. Restoring the microvascular perfusion deficit remains a significant unmet need and may be addressed via delivery of pro-angiogenic cytokines. The therapeutic effect of cytokines can be enhanced by encapsulation within hydrogels, but current hydrogels do not offer sufficient clinical translatability due to unfavorable viscoelastic mechanical behavior which directly impacts the ability for minimally-invasive catheter delivery. In this report, we examine the therapeutic implications of dual-stage cytokine release from a novel, highly shear-thinning biocompatible catheter-deliverable hydrogel. We chose to encapsulate two protein-engineered cytokines, namely dimeric fragment of hepatocyte growth factor (HGFdf) and engineered stromal cell-derived factor 1α (ESA), which target distinct disease pathways. The controlled release of HGFdf and ESA from separate phases of the hyaluronic acid-based hydrogel allows extended and pronounced beneficial effects due to the precise timing of release. We evaluated the therapeutic efficacy of this treatment strategy in a small animal model of myocardial ischemia and observed a significant benefit in biological and functional parameters. Given the encouraging results from the small animal experiment, we translated this treatment to a large animal preclinical model and observed a reduction in scar size, indicating this strategy could serve as a potential adjunct therapy for the millions of people suffering from ischemic heart disease.

  View details for DOI 10.1016/j.cyto.2019.154974

  View details for PubMedID 31978642

• Injectable supramolecular polymer-nanoparticle hydrogels enhance human mesenchymal stem cell delivery. Bioengineering & translational medicine Grosskopf, A. K., Roth, G. A., Smith, A. A., Gale, E. C., Hernandez, H. L., Appel, E. A. 2020; 5 (1): e10147

  Abstract

  Stem cell therapies have emerged as promising treatments for injuries and diseases in regenerative medicine. Yet, delivering stem cells therapeutically can be complicated by invasive administration techniques, heterogeneity in the injection media, and/or poor cell retention at the injection site. Despite these issues, traditional administration protocols using bolus injections in a saline solution or surgical implants of cell-laden hydrogels have highlighted the promise of cell administration as a treatment strategy. To address these limitations, we have designed an injectable polymer-nanoparticle (PNP) hydrogel platform exploiting multivalent, noncovalent interactions between modified biopolymers and biodegradable nanoparticles for encapsulation and delivery of human mesenchymal stem cells (hMSCs). hMSC-based therapies have shown promise due to their broad differentiation capacities and production of therapeutic paracrine signaling molecules. In this work, the fundamental hydrogel mechanical properties that enhance hMSC delivery processes are elucidated using basic in vitro models. Further, in vivo studies in immunocompetent mice reveal that PNP hydrogels enhance hMSC retention at the injection site and retain administered hMSCs locally for upwards of 2 weeks. Through both in vitro and in vivo experiments, we demonstrate a novel scalable, synthetic, and biodegradable hydrogel system that overcomes current limitations and enables effective cell delivery.

  View details for DOI 10.1002/btm2.10147

  View details for PubMedID 31989036

  View details for PubMedCentralID PMC6971438

• Structural considerations for physical hydrogels based on polymer-nanoparticle interactions MOLECULAR SYSTEMS DESIGN & ENGINEERING Yu, A. C., Smith, A. A., Appel, E. A. 2020; 5 (1): 401–7

  View details for DOI 10.1039/c9me00120d

  View details for Web of Science ID 000508398900034

• Universal Scaling Behavior during Network Formation in Controlled Radical Polymerizations. Macromolecules Mann, J. L., Rossi, R. L., Smith, A. A., Appel, E. A. 2019; 52 (24): 9456–65

  Abstract

  Despite the ubiquity of branched and network polymers in biological, electronic, and rheological applications, it remains difficult to predict the network structure arising from polymerization of vinyl and multivinyl monomers. While controlled radical polymerization (CRP) techniques afford modularity and control in the synthesis of (hyper)branched polymers, a unifying understanding of network formation providing grounded predictive power is still lacking. A current limitation is the inability to predict the number and weight average molecular weights that arise during the synthesis of (hyper)branched polymers using CRP. This study addresses this literature gap through first building intuition via a growth boundary analysis on how certain environmental cues (concentration, monomer choice, and cross-linker choice) affect the cross-link efficiency during network formation through experimental gel point measurements. We then demonstrate, through experimental gel point normalization, universal scaling behavior of molecular weights in the synthesis of branched polymers corroborated by previous literature experiments. Moreover, the normalization employed in this analysis reveals trends in the macroscopic mechanical properties of networks synthesized using CRP techniques. Gel point normalization employed in this analysis both enables a polymer chemist to target specific number and weight average molecular weights of (hyper)branched polymers using CRP and demonstrates the utility of CRP for gel synthesis.

  View details for DOI 10.1021/acs.macromol.9b02109

  View details for PubMedID 31894160

• Stable Monomeric Insulin Formulations Enabled by Supramolecular PEGylation of Insulin Analogues ADVANCED THERAPEUTICS Maikawa, C. L., Smith, A. A., Zou, L., Meis, C. M., Mann, J. L., Webber, M. J., Appel, E. A. 2019

  View details for DOI 10.1002/adtp.201900094

  View details for Web of Science ID 000503161700001

• A Nanoparticle Platform for Improved Potency, Stability, and Adjuvanticity of Poly(I:C) ADVANCED THERAPEUTICS Gale, E. C., Roth, G. A., Smith, A. A., Alcantara-Hernandez, M., Idoyaga, J., Appel, E. A. 2019

  View details for DOI 10.1002/adtp.201900174

  View details for Web of Science ID 000502045100001

• Injectable supramolecular polymer-nanoparticle hydrogels enhance human mesenchymal stem cell delivery BIOENGINEERING & TRANSLATIONAL MEDICINE Grosskopf, A. K., Roth, G. A., Smith, A. A., Gale, E. C., Hernandez, H., Appel, E. A. 2019

  View details for DOI 10.1002/btm2.10147

  View details for Web of Science ID 000491537900001

• Block copolymer composition drives function of self-assembled nanoparticles for delivery of small-molecule cargo JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Maikawa, C. L., Sevit, A., Lin, B., Wallstrom, R. J., Mann, J. L., Yu, A. C., Waymouth, R. M., Appel, E. A. 2019; 57 (12): 1322–32

  View details for DOI 10.1002/pola.29393

  View details for Web of Science ID 000469938700008

• A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering ADVANCED HEALTHCARE MATERIALS Steele, A. N., Stapleton, L. M., Farry, J. M., Lucian, H. J., Paulsen, M. J., Eskandari, A., Hironaka, C. E., Thakore, A. D., Wang, H., Yu, A. C., Chan, D., Appel, E. A., Woo, Y. 2019; 8 (5)

  View details for DOI 10.1002/adhm.201801147

  View details for Web of Science ID 000461575200003

• A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering. Advanced healthcare materials Steele, A. N., Stapleton, L. M., Farry, J. M., Lucian, H. J., Paulsen, M. J., Eskandari, A., Hironaka, C. E., Thakore, A. D., Wang, H., Yu, A. C., Chan, D., Appel, E. A., Woo, Y. J. 2019: e1801147

  Abstract

  Hydrogels have emerged as a diverse class of biomaterials offering a broad range of biomedical applications. Specifically, injectable hydrogels are advantageous for minimally invasive delivery of various therapeutics and have great potential to treat a number of diseases. However, most current injectable hydrogels are limited by difficult and time-consuming fabrication techniques and are unable to be delivered through long, narrow catheters, preventing extensive clinical translation. Here, the development of an easily-scaled, catheter-injectable hydrogel utilizing a polymer-nanoparticle crosslinking mechanism is reported, which exhibits notable shear-thinning and self-healing behavior. Gelation of the hydrogel occurs immediately upon mixing the biochemically modified hyaluronic acid polymer with biodegradable nanoparticles and can be easily injected through a high-gauge syringe due to the dynamic nature of the strong, yet reversible crosslinks. Furthermore, the ability to deliver this novel hydrogel through a long, narrow, physiologically-relevant catheter affixed with a 28-G needle is highlighted, with hydrogel mechanics unchanged after delivery. Due to the composition of the gel, it is demonstrated that therapeutics can be differentially released with distinct elution profiles, allowing precise control over drug delivery. Finally, the cell-signaling and biocompatibility properties of this innovative hydrogel are demonstrated, revealing its wide range of therapeutic applications.

  View details for PubMedID 30714355

• Injectable Polymer-Nanoparticle Hydrogels for Local Immune Cell Recruitment. Biomacromolecules Fenton, O. S., Tibbitt, M. W., Appel, E. A., Jhunjhunwala, S. n., Webber, M. J., Langer, R. n. 2019

  Abstract

  The ability to engineer immune function has transformed modern medicine, highlighted by the success of vaccinations and recent efforts in cancer immunotherapy. Further directions in programming the immune system focus on the design of immunomodulatory biomaterials that can recruit, engage with, and program immune cells locally in vivo. Here, we synthesized shear-thinning and self-healing polymer-nanoparticle (PNP) hydrogels as a tunable and injectable biomaterial platform for local dendritic cell (DC) recruitment. PNP gels were formed from two populations of poly(ethylene glycol)-block-polylactide (PEG-b-PLA) NPs with the same diameter but different PEG brush length (2 or 5 kDa). PEG-b-PLA NPs with the longer PEG brush exhibited improved gel formation following self-assembly and faster recovery after shear-thinning. In all cases, model protein therapeutics were released via Fickian diffusion in vitro, and minor differences in the release rate between the gel formulations were observed. PNP hydrogels were loaded with the DC cytokine CCL21 and injected subcutaneously in a murine model. CCL21-loaded PNP hydrogels recruited DCs preferentially to the site of injection in vivo relative to non-CCL21-loaded hydrogels. Thus, PNP hydrogels comprise a simple and tunable platform biomaterial for in vivo immunomodulation following minimally invasive subcutaneous injection.

  View details for DOI 10.1021/acs.biomac.9b01129

  View details for PubMedID 31682423

• Non-Newtonian Polymer-Nanoparticle Hydrogels Enhance Cell Viability during Injection MACROMOLECULAR BIOSCIENCE Hernandez, H., Grosskopf, A. K., Stapleton, L. M., Agmon, G., Appel, E. A. 2019; 19 (1)

  View details for DOI 10.1002/mabi.201800275

  View details for Web of Science ID 000458817700008

• Non-Newtonian Polymer-Nanoparticle Hydrogels Enhance Cell Viability during Injection. Macromolecular bioscience Lopez Hernandez, H., Grosskopf, A. K., Stapleton, L. M., Agmon, G., Appel, E. A. 2018: e1800275

  Abstract

  Drug delivery and cell transplantation require minimally invasive deployment strategies such as injection through clinically relevant high-gauge needles. Supramolecular hydrogels comprising dodecyl-modified hydroxypropylmethylcellulose and poly(ethylene glycol)-block-poly(lactic acid) have been previously demonstrated for the delivery of drugs and proteins. Here, it is demonstrated that the rheological properties of these hydrogels allow for facile injectability, an increase of cell viability after injection when compared to cell viabilities of cells injected in phosphate-buffered saline, and homogeneous cell suspensions that do not settle. These hydrogels are injected at 1mL min-1 with pressures less than 400kPa, despite the solid-like properties of the gel when at rest. The cell viabilities immediately after injection are greater than 86% for adult human dermal fibroblasts, human umbilical vein cells, smooth muscle cells, and human mesenchymal stem cells. Cells are shown to remain suspended and proliferate in the hydrogel at the same rate as observed in cell media. The work expands on the versatility of these hydrogels and lays a foundation for the codelivery of drugs, proteins, and cells.

  View details for PubMedID 30369048

• Self-assembled biomaterials using host-guest interactions SELF-ASSEMBLING BIOMATERIALS: MOLECULAR DESIGN, CHARACTERIZATION AND APPLICATION IN BIOLOGY AND MEDICINE Yu, A. C., Stapleton, L. M., Mann, J. L., Appel, E. A., Azevedo, H. S., DaSilva, R. M. 2018: 205–31

  View details for DOI 10.1016/B978-0-08-102015-9.00010-1

  View details for Web of Science ID 000462711900010

• Engineering the Mechanical Properties of Polymer Networks with Precise Doping of Primary Defects. ACS applied materials & interfaces Chan, D., Ding, Y., Dauskardt, R. H., Appel, E. A. 2017

  Abstract

  Polymer networks are extensively utilized across numerous applications ranging from commodity superabsorbent polymers and coatings to high-performance microelectronics and biomaterials. For many applications, desirable properties are known; however, achieving them has been challenging. Additionally, the accurate prediction of elastic modulus has been a long-standing difficulty owing to the presence of loops. By tuning the prepolymer formulation through precise doping of monomers, specific primary network defects can be programmed into an elastomeric scaffold, without alteration of their resulting chemistry. The addition of these monomers that respond mechanically as primary defects is used both to understand their impact on the resulting mechanical properties of the materials and as a method to engineer the mechanical properties. Indeed, these materials exhibit identical bulk and surface chemistry, yet vastly different mechanical properties. Further, we have adapted the real elastic network theory (RENT) to the case of primary defects in the absence of loops, thus providing new insights into the mechanism for material strength and failure in polymer networks arising from primary network defects, and to accurately predict the elastic modulus of the polymer system. The versatility of the approach we describe and the fundamental knowledge gained from this study can lead to new advancements in the development of novel materials with precisely defined and predictable chemical, physical, and mechanical properties.

  View details for PubMedID 29135222

• Supramolecular polymeric biomaterials. Biomaterials science Mann, J. L., Yu, A. C., Agmon, G., Appel, E. A. 2017

  Abstract

  Polymeric chains crosslinked through supramolecular interactions-directional and reversible non-covalent interactions-compose an emerging class of modular and tunable biomaterials. The choice of chemical moiety utilized in the crosslink affords different thermodynamic and kinetic parameters of association, which in turn illustrate the connectivity and dynamics of the system. These parameters, coupled with the choice of polymeric architecture, can then be engineered to control environmental responsiveness, viscoelasticity, and cargo diffusion profiles, yielding advanced biomaterials which demonstrate rapid shear-thinning, self-healing, and extended release. In this review we examine the relationship between supramolecular crosslink chemistry and biomedically relevant macroscopic properties. We then describe how these properties are currently leveraged in the development of materials for drug delivery, immunology, regenerative medicine, and 3D-bioprinting (253 references).

  View details for PubMedID 29164196

• Mechanistic understanding of in vivo protein corona formation on polymeric nanoparticles and impact on pharmacokinetics. Nature communications Bertrand, N., Grenier, P., Mahmoudi, M., Lima, E. M., Appel, E. A., Dormont, F., Lim, J. M., Karnik, R., Langer, R., Farokhzad, O. C. 2017; 8 (1): 777

  Abstract

  In vitro incubation of nanomaterials with plasma offer insights on biological interactions, but cannot fully explain the in vivo fate of nanomaterials. Here, we use a library of polymer nanoparticles to show how physicochemical characteristics influence blood circulation and early distribution. For particles with different diameters, surface hydrophilicity appears to mediate early clearance. Densities above a critical value of approximately 20 poly(ethylene glycol) chains (MW 5 kDa) per 100 nm2 prolong circulation times, irrespective of size. In knockout mice, clearance mechanisms are identified for nanoparticles with low and high steric protection. Studies in animals deficient in the C3 protein showed that complement activation could not explain differences in the clearance of nanoparticles. In nanoparticles with low poly(ethylene glycol) coverage, adsorption of apolipoproteins can prolong circulation times. In parallel, the low-density-lipoprotein receptor plays a predominant role in the clearance of nanoparticles, irrespective of poly(ethylene glycol) density. These results further our understanding of nanopharmacology.Understanding the interaction between nanoparticles and biomolecules is crucial for improving current drug-delivery systems. Here, the authors shed light on the essential role of the surface and other physicochemical properties of a library of nanoparticles on their in vivo pharmacokinetics.

  View details for DOI 10.1038/s41467-017-00600-w

  View details for PubMedID 28974673

  View details for PubMedCentralID PMC5626760

• Decoupled Associative and Dissociative Processes in Strong yet Highly Dynamic Host-Guest Complexes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Appel, E. A., Biedermann, F., Hoogland, D., del Barrio, J., Driscoll, M. D., Hay, S., Wales, D. J., Scherman, O. A. 2017; 139 (37): 12985–93

  Abstract

  Kinetics and thermodynamics in supramolecular systems are intimately linked, yet both are independently important for application in sensing assays and stimuli-responsive switching/self-healing of materials. Host-guest interactions are of particular interest in many water-based materials, sensing, and drug delivery applications. Herein we investigate the binding dynamics of a variety of electron-rich aromatic moieties forming hetero-ternary complexes with the macrocycle cucurbit[8]uril (CB[8]) and an auxiliary guest, dimethyl viologen, with high selectivity and equilibrium binding constants (Keq up to 1014 M-2). Using stopped-flow spectrofluorimetry, association rate constants were observed to approach the diffusion limit and were found to be insensitive to the structure of the guest. Conversely, the dissociation rate constants of the ternary complexes varied dramatically with the guest structure and were correlated with the thermodynamic binding selectivity. Hence differing molecular features were found to contribute to the associative and dissociative processes, mimicking naturally occurring reactions and giving rise to a decoupling of these kinetic parameters. Moreover, we demonstrate the ability to exploit these phenomena and selectively perturb the associative process with external stimuli (e.g., viscosity and pressure). Significantly, these complexes exhibit increased binding equilibria with increasing pressure, with important implications for the application of the CB[8] ternary complex for the formation of hydrogels, as these gels exhibit unprecedented pressure-insensitive rheological properties. A high degree of flexibility therefore exists in the design of host-guest systems with tunable kinetic and thermodynamic parameters for tailor-made applications across a broad range of fields.

  View details for PubMedID 28661667

• Mixed Reversible Covalent Crosslink Kinetics Enable Precise, Hierarchical Mechanical Tuning of Hydrogel Networks ADVANCED MATERIALS Yesilyurt, V., Ayoob, A. M., Appel, E. A., Borenstein, J. T., Langer, R., Anderson, D. G. 2017; 29 (19)

  Abstract

  Hydrogels play a central role in a number of medical applications and new research aims to engineer their mechanical properties to improve their capacity to mimic the functional dynamics of native tissues. This study shows hierarchical mechanical tuning of hydrogel networks by utilizing mixtures of kinetically distinct reversible covalent crosslinks. A methodology is described to precisely tune stress relaxation in PEG networks formed from mixtures of two different phenylboronic acid derivatives with unique diol complexation rates, 4-carboxyphenylboronic acid, and o-aminomethylphenylboronic acid. Gel relaxation time and the mechanical response to dynamic shear are exquisitely controlled by the relative concentrations of the phenylboronic acid derivatives. The differences observed in the crossover frequencies corresponding to pKa differences in the phenylboronic acid derivatives directly connect the molecular kinetics of the reversible crosslinks to the macroscopic dynamic mechanical behavior. Mechanical tuning by mixing reversible covalent crosslinking kinetics is found to be independent of other attributes of network architecture, such as molecular weight between crosslinks.

  View details for DOI 10.1002/adma.201605947

  View details for Web of Science ID 000401170600014

  View details for PubMedID 28295624

• Single-Chain Polymeric Nanocarriers: A Platform for Determining Structure-Function Correlations in the Delivery of Molecular Cargo BIOMACROMOLECULES Chan, D., Yu, A. C., Appel, E. A. 2017; 18 (4): 1434-1439

  Abstract

  There has been growing interest in producing stable, biocompatible nanocarriers for the controlled delivery of therapeutics. With micelles, it remains a challenge to predict a priori the size, aggregation number, and functionality of the self-assembled aggregates. Utilizing controlled radical polymerization techniques, we have prepared tunable high molecular weight amphiphilic comb copolymers that self-assemble into unimolecular "micelle-like" nanocarriers of predictable size and functionality. Excellent control over self-assembly behavior and structure allows for systematic determination of the role of important polymeric material properties (i.e., glass transition) on the release of model therapeutics while simultaneously controlling for size, dispersity, structural, and functionality effects. Moreover, these single-chain polymeric nanocarriers represent a class of drug delivery systems allowing for interrogation of the limitations of standard methods for characterization of micellar aggregates.

  View details for DOI 10.1021/acs.biomac.7b00249

  View details for Web of Science ID 000399061100040

  View details for PubMedID 28263572

• Engineering the Mechanical Properties of Polymer Networks with Precise Doping of Primary Defects ACS Applied Materials and Interfaces Chan, D., Ding, Y., Dauskardt, R., Appel, E. A. 2017; 9: 42217-42224
• Synthesis and Biological Evaluation of Ionizable Lipid Materials for the In Vivo Delivery of Messenger RNA to B Lymphocytes Advanced Materials Fenton, O. S., et al 2017; 29: e1606944
• Distinguishing the Respective Mechanical Contributions of Polymer and Supramolecular Dynamics in Transiently Crosslinked Polymeric Networks Polymer Chemistry Tan, C. S., Agmon, G., Hoogland, D., Janecek, E., Toprakcioglu, C., Appel, E. A., Scherman, O. A. 2017; 8: 5336-5343
• Decoupled Associative and Dissociative Processes in Strong yet Highly Dynamic Host-Guest Complexes Journal of the American Chemical Society Appel, E. A., Biedermann, F., Driscoll, M. D., Hay, S., Wales, D. J., Scherman, O. A. 2017; 139: 12985-12993
• Supramolecular Polymeric Biomaterials Biomaterials Science Mann, J. L., Yu, A. C., Agmon, G., Appel, E. A. 2017; 6: 10-37
• Mechanistic understanding of in vivo protein corona formation on polymeric nanoparticles and impact on pharmacokinetics Nature Communication Bertrand, N., et al 2017; 8: e777
• Supramolecular PEGylation of biopharmaceuticals PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Webber, M. J., Appel, E. A., Vinciguerra, B., Cortinas, A. B., Thapa, L. S., Jhunjhunwala, S., Isaacs, L., Langer, R., Anderson, D. G. 2016; 113 (50): 14189-14194

  Abstract

  The covalent modification of therapeutic biomolecules has been broadly explored, leading to a number of clinically approved modified protein drugs. These modifications are typically intended to address challenges arising in biopharmaceutical practice by promoting improved stability and shelf life of therapeutic proteins in formulation, or modifying pharmacokinetics in the body. Toward these objectives, covalent modification with poly(ethylene glycol) (PEG) has been a common direction. Here, a platform approach to biopharmaceutical modification is described that relies on noncovalent, supramolecular host-guest interactions to endow proteins with prosthetic functionality. Specifically, a series of cucurbit[7]uril (CB[7])-PEG conjugates are shown to substantially increase the stability of three distinct protein drugs in formulation. Leveraging the known and high-affinity interaction between CB[7] and an N-terminal aromatic residue on one specific protein drug, insulin, further results in altering of its pharmacological properties in vivo by extending activity in a manner dependent on molecular weight of the attached PEG chain. Supramolecular modification of therapeutic proteins affords a noncovalent route to modify its properties, improving protein stability and activity as a formulation excipient. Furthermore, this offers a modular approach to append functionality to biopharmaceuticals by noncovalent modification with other molecules or polymers, for applications in formulation or therapy.

  View details for DOI 10.1073/pnas.1616639113

  View details for Web of Science ID 000389696700033

  View details for PubMedID 27911829

• Scalable manufacturing of biomimetic moldable hydrogels for industrial applications PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yu, A. C., Chen, H., Chan, D., Agmon, G., Stapleton, L. M., Sevit, A. M., Tibbitt, M. W., Acosta, J. D., Zhang, T., Franzia, P. W., Langer, R., Appel, E. A. 2016; 113 (50): 14255-14260

  Abstract

  Hydrogels are a class of soft material that is exploited in many, often completely disparate, industrial applications, on account of their unique and tunable properties. Advances in soft material design are yielding next-generation moldable hydrogels that address engineering criteria in several industrial settings such as complex viscosity modifiers, hydraulic or injection fluids, and sprayable carriers. Industrial implementation of these viscoelastic materials requires extreme volumes of material, upwards of several hundred million gallons per year. Here, we demonstrate a paradigm for the scalable fabrication of self-assembled moldable hydrogels using rationally engineered, biomimetic polymer-nanoparticle interactions. Cellulose derivatives are linked together by selective adsorption to silica nanoparticles via dynamic and multivalent interactions. We show that the self-assembly process for gel formation is easily scaled in a linear fashion from 0.5 mL to over 15 L without alteration of the mechanical properties of the resultant materials. The facile and scalable preparation of these materials leveraging self-assembly of inexpensive, renewable, and environmentally benign starting materials, coupled with the tunability of their properties, make them amenable to a range of industrial applications. In particular, we demonstrate their utility as injectable materials for pipeline maintenance and product recovery in industrial food manufacturing as well as their use as sprayable carriers for robust application of fire retardants in preventing wildland fires.

  View details for DOI 10.1073/pnas.1618156113

  View details for Web of Science ID 000389696700044

  View details for PubMedID 27911849

  View details for PubMedCentralID PMC5167152

• Injectable and Glucose-Responsive Hydrogels Based on Boronic Acid-Glucose Complexation LANGMUIR Dong, Y., Wang, W., Veiseh, O., Appel, E. A., Xue, K., Webber, M. J., Tang, B. C., Yang, X., Weir, G. C., Langer, R., Anderson, D. G. 2016; 32 (34): 8743-8747

  Abstract

  Injectable hydrogels have been widely used for a number of biomedical applications. Here, we report a new strategy to form an injectable and glucose-responsive hydrogel using the boronic acid-glucose complexation. The ratio of boronic acid and glucose functional groups is critical for hydrogel formation. In our system, polymers with 10-60% boronic acid, with the balance being glucose-modified, are favorable to form hydrogels. These hydrogels are shear-thinning and self-healing, recovering from shear-induced flow to a gel state within seconds. More importantly, these polymers displayed glucose-responsive release of an encapsulated model drug. The hydrogel reported here is an injectable and glucose-responsive hydrogel constructed from the complexation of boronic acid and glucose within a single component polymeric material.

  View details for DOI 10.1021/acs.langmuir.5b04755

  View details for Web of Science ID 000382513900022

  View details for PubMedID 27455412

  View details for PubMedCentralID PMC5242094

• Bioinspired Alkenyl Amino Alcohol Ionizable Lipid Materials for Highly Potent In Vivo mRNA Delivery ADVANCED MATERIALS Fenton, O. S., Kauffman, K. J., McClellan, R. L., Appel, E. A., Dorkin, J. R., Tibbitt, M. W., Heartlein, M. W., DeRosa, F., Langer, R., Anderson, D. G. 2016; 28 (15): 2939-2943

  Abstract

  Thousands of human diseases could be treated by selectively controlling the expression of specific proteins in vivo. A new series of alkenyl amino alcohol (AAA) ionizable lipid nanoparticles (LNPs) capable of delivering human mRNA with unprecedented levels of in vivo efficacy is demonstrated. This study highlights the importance of utilizing synthesis tools in tandem with biological inspiration to understand and improve nucleic acid delivery in vivo.

  View details for DOI 10.1002/adma.201505822

  View details for Web of Science ID 000374336700011

  View details for PubMedID 26889757

  View details for PubMedCentralID PMC5245883

• Supramolecular biomaterials NATURE MATERIALS Webber, M. J., Appel, E. A., Meijer, E. W., Langer, R. 2016; 15 (1): 13-26

  View details for DOI 10.1038/NMAT4474

  View details for Web of Science ID 000366690600014

• Injectable Self-Healing Glucose Responsive Hydrogels with pH-Regulated Mechanical Properties Advanced Materials Yesilyurt, V., Webber, M. J., Appel, E. A., Godwin, C., Langer, R., Anderson, D. G. 2016; 28: 86-91
• Water soluble, biodegradable amphiphilic polymeric nanoparticles and the molecular environment of hydrophobic encapsulates: Consistency between simulation and experiment POLYMER Miller, R. D., Yusoff, R. M., Swope, W. C., Rice, J. E., Carr, A. C., Parker, A. J., Sly, J., Appel, E. A., Nguyen, T., Piunova, V. 2015; 79: 255-261

  View details for DOI 10.1016/j.polymer.2015.10.008

  View details for Web of Science ID 000365042500028

• Formation of Cucurbit[8]uril-Based Supramolecular Hydrogel Beads Using Droplet-Based Microfluidics BIOMACROMOLECULES Xu, X., Appel, E. A., Liu, X., Parker, R. M., Scherman, O. A., Abell, C. 2015; 16 (9): 2743-2749

  Abstract

  Herein we describe the use of microdroplets as templates for the fabrication of uniform-sized supramolecular hydrogel beads, assembled by supramolecular cross-linking of functional biopolymers with the macrocyclic host molecule, cucurbit[8]uril (CB[8]). The microdroplets were formed containing diluted hydrogel precursors in solution, including the functional polymers and CB[8], in a microfluidic device. Subsequent evaporation of water from collected microdroplets concentrated the contents, driving the formation of the CB[8]-mediated host-guest ternary complex interactions and leading to the assembly of condensed three-dimensional polymeric scaffolds. Rehydration of the dried particles gave monodisperse hydrogel beads. Their equilibrium size was shown to be dependent on both the quantity of material loaded and the dimensions of the microfluidic flow focus. Fluorescein-labeled dextran was used to evaluate the efficacy of the hydrogel beads as a vector for controlled cargo release. Both passive, sustained release (hours) and triggered, fast release (minutes) of the FITC-dextran was observed, with the rate of sustained release dependent on the formulation. The kinetics of release was fitted to the Ritger-Peppas controlled release equation and shown to follow an anomalous (non-Fickian) transport mechanism.

  View details for DOI 10.1021/acs.biomac.5b01048

  View details for Web of Science ID 000361341700020

  View details for PubMedID 26256409

• Exploiting Electrostatic Interactions in Polymer-Nanoparticle Hydrogels ACS MACRO LETTERS Appel, E. A., Tibbitt, M. W., Greer, J. M., Fenton, O. S., Kreuels, K., Anderson, D. G., Langer, R. 2015; 4 (8): 848-852

  View details for DOI 10.1021/acsmacrolett.5b00416

  View details for Web of Science ID 000359891200009

• A Facile Method for the Stain-Free Visualization of Hierarchical Structures with Electron Microscopy JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Williams, P. E., Appel, E. A., Jones, S. T., del Barrio, J., Lan, Y., Scherman, O. A. 2015; 53 (7): 842-845

  View details for DOI 10.1002/pola.27517

  View details for Web of Science ID 000350278400002

• Non-Cell-Adhesive Substrates for Printing of Arrayed Biomaterials ADVANCED HEALTHCARE MATERIALS Appel, E. A., Larson, B. L., Luly, K. M., Kim, J. D., Langer, R. 2015; 4 (4): 501-505

  Abstract

  Cellular microarrays have become extremely useful in expediting the investigation of large libraries of (bio)materials for both in vitro and in vivo biomedical applications. An exceedingly simple strategy is developed for the fabrication of non-cell-adhesive substrates supporting the immobilization of diverse (bio)material features, including both monomeric and polymeric adhesion molecules (e.g., RGD and polylysine), hydrogels, and polymers.

  View details for DOI 10.1002/adhm.201400594

  View details for Web of Science ID 000351225700002

  View details for PubMedID 25430948

  View details for PubMedCentralID PMC4447497

• Self-Assembled Hydrogels Utilising Polymer-Nanoparticle Interactions Nature Communications Appel, E. A., Tibbitt, M. W., Webber, M. J., Mattix, B. A., Veiseh, O., Langer, R. 2015; 6: e6295
• The control of cargo release from physically crosslinked hydrogels by crosslink dynamics BIOMATERIALS Appel, E. A., Forster, R. A., Rowland, M. J., Scherman, O. A. 2014; 35 (37): 9897-9903

  Abstract

  Controlled release of drugs and other cargo from hydrogels has been an important target for the development of next generation therapies. Despite the increasingly strong focus in this area of research, very little of the published literature has sought to develop a fundamental understanding of the role of molecular parameters in determining the mechanism and rate of cargo release. Herein, a series of physically crosslinked hydrogels have been prepared utilizing host-guest binding interactions of cucurbit[8]uril that are identical in strength (plateau modulus), concentration and structure, yet exhibit varying network dynamics on account of the use of different guests for supramolecular crosslinking. The diffusion of molecular cargo through the hydrogel matrix and the release characteristics from these hydrogels were investigated. It was determined that the release processes of the hydrogels could be directly correlated with the dynamics of the physical interactions responsible for crosslinking and corresponding time-dependent mesh size. These observations highlight that network dynamics play an indispensable role in determining the release mechanism of therapeutic cargo from a hydrogel, identifying that fine-tuning of the release characteristics can be gained through rational design of the molecular processes responsible for crosslinking in the carrier hydrogels.

  View details for DOI 10.1016/j.biomaterials.2014.08.001

  View details for Web of Science ID 000343639700015

  View details for PubMedID 25239043

• GLUING GELS A nanoparticle solution NATURE MATERIALS Appel, E. A., Scherman, O. A. 2014; 13 (3): 231-232

  View details for DOI 10.1038/nmat3893

  View details for Web of Science ID 000331945200014

  View details for PubMedID 24553651

• Activation Energies Control Macroscopic Properties of Supramolecular Crosslinked Materials Angewandte Chemie International Edition Appel, E. A., Forster, R. A., Koutsioumpas, A., , Scherman, O. A. 2014; 53: 10038-10043
• Rapidly Healable, Temporally Stable and Stiff Hydrogels: Combining Conflicting Properties Using Highly Dynamic and Selective Three-Component Recognition with Reinforcing Cellulose Nanorods Advanced Functional Materials Jason, M., Appel, E. A., Seitsonen, J., Kontturi, E., Scherman, O. A., Ikkala, O. 2014; 24: 2706-2713
• Dynamically crosslinked materials via recognition of amino acids by cucurbit[8]uril JOURNAL OF MATERIALS CHEMISTRY B Rowland, M. J., Appel, E. A., Coulston, R. J., Scherman, O. A. 2013; 1 (23): 2904-2910

  View details for DOI 10.1039/c3tb20180e

  View details for Web of Science ID 000319273100002

• Triggered insulin release studies of triply responsive supramolecular micelles POLYMER CHEMISTRY Loh, X. J., Tsai, M., del Barrio, J., Appel, E. A., Lee, T., Scherman, O. A. 2012; 3 (11): 3180-3188

  View details for DOI 10.1039/c2py20380d

  View details for Web of Science ID 000310421200021

• Ultra-High Water-Content Hydrogels from Renewable Resources Exhibiting Multi-Stimuli Responsiveness J. Am. Chem. Soc. Appel, E. A., Loh, X., Jones, S. T., Biedermann, F., Dreiss, C. A., Scherman, O. A. 2012; 134: 11767-11773
• Triply Triggered Doxorubicin Release From Supramolecular Nanocontainers BIOMACROMOLECULES Loh, X. J., del Barrio, J., Toh, P. P., Lee, T., Jiao, D., Rauwald, U., Appel, E. A., Scherman, O. A. 2012; 13 (1): 84-91

  Abstract

  The synthesis of a supramolecular double hydrophilic block copolymer (DHBC) held together by cucurbit[8]uril (CB[8]) ternary complexation and its subsequent self-assembly into micelles is described. This system is responsive to multiple external triggers including temperature, pH and the addition of a competitive guest. The supramolecular block copolymer assembly consists of poly(N-isopropylacrylamide) (PNIPAAm) as a thermoresponsive block and poly(dimethylaminoethylmethacrylate) (PDMAEMA) as a pH-responsive block. Moreover, encapsulation and controlled drug release was demonstrated with this system using the chemotherapeutic drug doxorubicin (DOX). This triple stimuli-responsive DHBC micelle system represents an evolution over conventional double stimuli-responsive covalent diblock copolymer systems and displayed a significant reduction in the viability of HeLa cells upon triggered release of DOX from the supramolecular micellar nanocontainers.

  View details for DOI 10.1021/bm201588m

  View details for Web of Science ID 000298897300009

  View details for PubMedID 22148638

• Toward biodegradable nanogel star polymers via organocatalytic ROP CHEMICAL COMMUNICATIONS Appel, E. A., Lee, V. Y., Nguyen, T. T., McNeil, M., Nederberg, F., Hedrick, J. L., Swope, W. C., Rice, J. E., Miller, R. D., Sly, J. 2012; 48 (49): 6163-6165

  Abstract

  Organocatalytic ring opening polymerization (OROP) is used to effect the rapid, scalable, room temperature formation of size-controlled, highly uniform, polyvalent, nanogel star polymer nanoparticles of biodegradable composition.

  View details for DOI 10.1039/c2cc31406a

  View details for Web of Science ID 000304363500028

  View details for PubMedID 22590707

• High Molecular Weight Polyacrylamides by ATRP: Enabling Advancements in Water-based Applications J. Poly. Sci. Part A: Polym. Chem. Appel, E. A., del Barrio, J., Loh, X., Dyson, J., Scherman, O. A. 2012; 50: 181-186
• Metastable single-chain polymer nanoparticles prepared by dynamic cross-linking with nor-seco-cucurbit[10]uril CHEMICAL SCIENCE Appel, E. A., del Barrio, J., Dyson, J., Isaacs, L., Scherman, O. A. 2012; 3 (7): 2278-2281

  View details for DOI 10.1039/c2sc20285a

  View details for Web of Science ID 000304919200014

• Enhanced Stability and Activity of Temozolomide in Primary GBM Cells with Cucurbit[n]uril Chemical Communications Appel, E. A., Rowland, M. J., Loh, X., Heywood, R. M., Watts, C., Scherman, O. A. 2012: 9843-9845
• Supramolecular polymeric hydrogels CHEMICAL SOCIETY REVIEWS Appel, E. A., del Barrio, J., Loh, X. J., Scherman, O. A. 2012; 41 (18): 6195-6214

  Abstract

  The supramolecular crosslinking of polymer chains in water by specific, directional and dynamic non-covalent interactions has led to the development of novel supramolecular polymeric hydrogels. These aqueous polymeric networks constitute an interesting class of soft materials exhibiting attractive properties such as stimuli-responsiveness and self-healing arising from their dynamic behaviour and that are crucial for a wide variety of emerging applications. We present here a critical review summarising the formation of dynamic polymeric networks through specific non-covalent interactions, with a particular emphasis on those systems based on host-guest complex formation, as well as the characterisation of their physical characteristics. Aqueous supramolecular chemistry has unlocked a versatile toolbox for the design and fine-tuning of the material properties of these hydrogels (264 references).

  View details for DOI 10.1039/c2cs35264h

  View details for Web of Science ID 000307779600021

  View details for PubMedID 22890548

• Formation of Single-Chain Polymer Nanoparticles in Water through Host-Guest Interactions ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Appel, E. A., Dyson, J., del Barrio, J., Walsh, Z., Scherman, O. A. 2012; 51 (17): 4185-4189

  View details for DOI 10.1002/anie.201108659

  View details for Web of Science ID 000303001000037

  View details for PubMedID 22422662

• Sustained Release of Proteins from a High-Water-Content Supramolecular Polymer Hydrogel Biomaterials Appel, E. A., Loh, X., Jones, S. T., Dreiss, C. A., Scherman, O. A. 2012; 33: 4646-4652
• Postpolymerization Modification of Hydroxyl-Functionalized Polymers with Isocyanates MACROMOLECULES Biedermann, F., Appel, E. A., del Barrio, J., Gruendling, T., Barner-Kowollik, C., Scherman, O. A. 2011; 44 (12): 4828-4835

  View details for DOI 10.1021/ma2008018

  View details for Web of Science ID 000291895700037

• Supramolecular gold nanoparticle-polymer composites formed in water with cucurbit[8]uril CHEMICAL COMMUNICATIONS Coulston, R. J., Jones, S. T., Lee, T., Appel, E. A., Scherman, O. A. 2011; 47 (1): 164-166

  Abstract

  A gold nanoparticle-polymer composite material has been prepared in water using cucurbit[8]uril as a supramolecular "handcuff" to hold together viologen-functionalised gold nanoparticles and a naphthol-functionalised acrylamide copolymer.

  View details for DOI 10.1039/c0cc03250f

  View details for Web of Science ID 000285068300008

  View details for PubMedID 20842297

• Supramolecular Cross-Linked Networks via Host-Guest Complexation with Cucurbit[8]uril JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Appel, E. A., Biedermann, F., Rauwald, U., Jones, S. T., Zayed, J. M., Scherman, O. A. 2010; 132 (40): 14251-14260

  Abstract

  The ability to finely tune the solution viscosity of an aqueous system is critical in many applications ranging from large-scale fluid-based industrial processes to free-standing hydrogels important in regenerative medicine, controlled drug delivery, and 'green' self-healing materials. Herein we demonstrate the use of the macrocyclic host molecule cucurbit[8]uril (CB[8]) to facilitate reversible cross-linking of multivalent copolymers with high binding constants (K(a) > 10(11)-10(12) M(-2)) leading to a supramolecular hydrogel. Multivalent copolymers were prepared by free radical polymerization techniques and contained either pendant methyl viologen (a good first guest for CB[8]) or naphthoxy derivatives (good second guests for CB[8]). A colorless solution of the two multivalent copolymers bearing first and second guests, respectively, can be transformed into a highly viscous, colored supramolecular hydrogel with the cross-link density being easily controlled through CB[8] addition. Moreover, the cross-links (1:1:1 supramolecular ternary complexes of CB[8]/viologen/naphthoxy) are dynamic and stimuli-responsive, and the material properties can be modulated by temperature or other external stimuli. Rheological characterization of the bulk material properties of these dynamically cross-linked networks provided insight into the kinetics of CB[8] ternary complexation responsible for elastically active cross-linking with a second guest dissociation rate constant (k(d)) of 1200 s(-1) for the ternary complex. These materials exhibited intermediate mechanical properties at 5 wt % in water (plateau modulus = 350-600 Pa and zero-shear viscosity = 5-55 Pa·s), which is complementary to existing supramolecular hydrogels. Additionally, these supramolecular hydrogels exhibited thermal reversibility and subsequent facile modulation of microstructure upon further addition of CB[8] and thermal treatment. The fundamental knowledge gained from the study of these dynamic materials will facilitate progress in the field of smart, self-healing materials, self-assembled hydrogels, and controlled solution viscosity.

  View details for DOI 10.1021/ja106362w

  View details for Web of Science ID 000282660100064

  View details for PubMedID 20845973

• Hierarchical Supermolecular Structures for Sustained Drug Release SMALL Tan, J. P., Kim, S. H., Nederberg, F., Appel, E. A., Waymouth, R. M., Zhang, Y., Hedrick, J. L., Yang, Y. Y. 2009; 5 (13): 1504-1507

  View details for DOI 10.1002/smll.200801756

  View details for Web of Science ID 000267903200003

  View details for PubMedID 19326354

• Simple Approach to Stabilized Micelles Employing Miktoarm Terpolymers and Stereocomplexes with Application in Paclitaxel Delivery BIOMACROMOLECULES Nederberg, F., Appel, E., Tan, J. P., Kim, S. H., Fukushima, K., Sly, J., Miller, R. D., Waymouth, R. M., Yang, Y. Y., Hedrick, J. L. 2009; 10 (6): 1460-1468

  Abstract

  A simple and versatile approach to miktoarm co- and terpolymers from carbonate functional oligomers is described. The key building block employed is a carboxylic acid functional cyclic carbonate, derived from 2,2-bis(methylol)propionic acid, that was readily coupled to a hydroxyl functional monomethylether poly(ethylene glycol) oligomer. Ring-opening of the cyclic carbonate using functional amines generates a carbamate linkage bearing a functional group capable of initiating either controlled radical or ring-opening polymerization, together with a primary hydroxyl group for ring-opening polymerization. Two tandem polymerization steps were possible which add the second two arms, thus generating the targeted ABC miktoarm terpolymer. The resulting amphiphilic miktoarm terpolymers containing poly(D- and L-lactide) formed polylactide stereocomplexes in the bulk. In aqueous solution, the stereocomplex mixture of Y-shaped miktoarm copolymers, poly(ethylene glycol)-poly(D-lactide)-poly(D-lactide) and poly(ethylene glycol)-poly(L-lactide)-poly(L-lactide), or the stereoblock miktoarm poly(ethylene glycol)-poly(D-lactide)-poly(L-lactide) form stabilized micelles with a significantly lower critical micelle concentration than those derived from conventional stereo regular linear or Y-shaped amphiphiles. This simple and versatile approach provides a useful synthetic route to complex macromolecular architectures that can assemble into stable micelles. These micelles provide high capacity for loading of the anticancer drug paclitaxel and possess narrow size distribution as well as unique structure, leading to sustained and near zero-ordered release of drug without significant initial burst.

  View details for DOI 10.1021/bm900056g

  View details for Web of Science ID 000266860700018

  View details for PubMedID 19385659