Doctor of Philosophy, Stanford University, BIOE-PHD (2017)
Master of Science, Harvard University, Engineering Sciences (BioE) (2012)
Bachelor of Arts, Harvard University, Engineering Sciences (BioE) (2012)
Tyrosine-Selective Functionalization for Bio-Orthogonal Cross-Linking of Engineered Protein Hydrogels.
Engineered protein hydrogels have shown promise as artificial extracellular matrix materials for the 3D culture of stem cells due to the ability to decouple hydrogel biochemistry and mechanics. The modular design of these proteins allows for incorporation of various bioactive sequences to regulate cellular behavior. However, the chemistry used to cross-link the proteins into hydrogels can limit what bioactive sequences can be incorporated, in order to prevent nonspecific cross-linking within the bioactive region. Bio-orthogonal cross-linking chemistries may allow for the incorporation of any arbitrary bioactive sequence, but site-selective and scalable incorporation of bio-orthogonal reactive groups such as azides that do not rely on commonly used amine-reactive chemistry is often challenging. In response, we have optimized the reaction of an azide-bearing 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) with engineered elastin-like proteins (ELPs) to selectively azide-functionalize tyrosine residues within the proteins. The PTAD-azide functionalized ELPs cross-link with bicyclononyne (BCN) functionalized ELPs via the strain-promoted azide-alkyne cycloaddition (SPAAC) reaction to form hydrogels. Human mesenchymal stem cells and murine neural progenitor cells encapsulated within these hydrogels remain highly viable and maintain their phenotypes in culture. Tyrosine-specific modification may expand the number of bioactive sequences that can be designed into protein-engineered materials by permitting incorporation of lysine-containing sequences without concern for nonspecific cross-linking.
View details for DOI 10.1021/acs.bioconjchem.6b00720
View details for PubMedID 28151642
YAP-dependent mechanotransduction is required for proliferation and migration on native-like substrate topography
2017; 115: 155-166
Native vascular extracellular matrices (vECM) consist of elastic fibers that impart varied topographical properties, yet most in vitro models designed to study the effects of topography on cell behavior are not representative of native architecture. Here, we engineer an electrospun elastin-like protein (ELP) system with independently tunable, vECM-mimetic topography and demonstrate that increasing topographical variation causes loss of endothelial cell-cell junction organization. This loss of VE-cadherin signaling and increased cytoskeletal contractility on more topographically varied ELP substrates in turn promote YAP activation and nuclear translocation, resulting in significantly increased endothelial cell migration and proliferation. Our findings identify YAP as a required signaling factor through which fibrous substrate topography influences cell behavior and highlights topography as a key design parameter for engineered biomaterials.
View details for DOI 10.1016/j.biomaterials.2016.11.019
View details for Web of Science ID 000390642100014
View details for PubMedID 27889666
- Bio-Orthogonally Crosslinked, Engineered Protein Hydrogels with Tunable Mechanics and Biochemistry for Cell Encapsulation ADVANCED FUNCTIONAL MATERIALS 2016; 26 (21): 3612-3620
- Matrix elasticity of void-forming hydrogels controls transplanted-stem-cell-mediated bone formation NATURE MATERIALS 2015; 14 (12): 1269-1277
Matrix interactions modulate neurotrophin-mediated neurite outgrowth and pathfinding
NEURAL REGENERATION RESEARCH
2015; 10 (4): 514-517
Both matrix biochemistry and neurotrophic factors are known to modulate neurite outgrowth and pathfinding; however, the interplay between these two factors is less studied. While previous work has shown that the biochemical identity of the matrix can alter the outgrowth of neurites in response to neurotrophins, the importance of the concentration of cell-adhesive ligands is unknown. Using engineered elastin-like protein matrices, we recently demonstrated a synergistic effect between matrix-bound cell-adhesive ligand density and soluble nerve growth factor treatment on neurite outgrowth from dorsal root ganglia. This synergism was mediated by Schwann cell-neurite contact through L1CAM. Cell-adhesive ligand density was also shown to alter the pathfinding behavior of dorsal root ganglion neurites in response to a gradient of nerve growth factor. While more cell-adhesive matrices promoted neurite outgrowth, less cell-adhesive matrices promoted more faithful neurite pathfinding. These studies emphasize the importance of considering both matrix biochemistry and neurotrophic factors when designing biomaterials for peripheral nerve regeneration.
View details for DOI 10.4103/1673-5374.155426
View details for Web of Science ID 000354156200002
View details for PubMedID 26170800
View details for PubMedCentralID PMC4424732
Matrix RGD ligand density and L1CAM-mediated Schwann cell interactions synergistically enhance neurite outgrowth.
2015; 11: 48-57
The innate biological response to peripheral nerve injury involves a complex interplay of multiple molecular cues to guide neurites across the injury gap. Many current strategies to stimulate regeneration take inspiration from this biological response. However, little is known about the balance of cell-matrix and Schwann cell-neurite dynamics required for regeneration of neural architectures. We present an engineered extracellular matrix (eECM) microenvironment with tailored cell-matrix and cell-cell interactions to study their individual and combined effects on neurite outgrowth. This eECM regulates cell-matrix interactions by presenting integrin-binding RGD (Arg-Gly-Asp) ligands at specified densities. Simultaneously, the addition or exclusion of nerve growth factor (NGF) is used to modulate L1CAM-mediated Schwann cell-neurite interactions. Individually, increasing the RGD ligand density from 0.16 to 3.2mM resulted in increasing neurite lengths. In matrices presenting higher RGD ligand densities, neurite outgrowth was synergistically enhanced in the presence of soluble NGF. Analysis of Schwann cell migration and co-localization with neurites revealed that NGF enhanced cooperative outgrowth between the two cell types. Interestingly, neurites in NGF-supplemented conditions were unable to extend on the surrounding eECM without the assistance of Schwann cells. Blocking studies revealed that L1CAM is primarily responsible for these Schwann cell-neurite interactions. Without NGF supplementation, neurite outgrowth was unaffected by L1CAM blocking or the depletion of Schwann cells. These results underscore the synergistic interplay between cell-matrix and cell-cell interactions in enhancing neurite outgrowth for peripheral nerve regeneration.
View details for DOI 10.1016/j.actbio.2014.10.008
View details for PubMedID 25308870
View details for PubMedCentralID PMC4528982
- Co-Release of Cells and Polymeric Nanoparticles from Sacrificial Microfibers Enhances Nonviral Gene Delivery Inside 3D Hydrogels TISSUE ENGINEERING PART C-METHODS 2014; 20 (10): 798-805
Co-release of cells and polymeric nanoparticles from sacrificial microfibers enhances nonviral gene delivery inside 3D hydrogels.
Tissue engineering. Part C, Methods
2014; 20 (10): 798-805
Hydrogels can promote desirable cellular phenotype by mimicking tissue-like stiffness or serving as a gene delivery depot. However, nonviral gene delivery inside three-dimensional (3D) hydrogels remains a great challenge, and increasing hydrogel stiffness generally results in further decrease in gene delivery efficiency. Here we report a method to enhance nonviral gene delivery efficiency inside 3D hydrogels across a broad range of stiffness using sacrificial microfibers for co-releasing cells and polymeric nanoparticles (NPs). We fabricated hydrolytically degradable alginate as sacrificial microfibers, and optimized the degradation profile of alginate by varying the degree of oxidization. Scanning electron microscopy confirmed degradation of alginate microfibers inside hydrogels, leaving behind microchannel-like structures within 3D hydrogels. Sacrificial microfibers also serve as a delivery vehicle for co-releasing encapsulated cells and NPs, allowing cell attachment and spreading within the microchannel surface upon microfiber degradation. To examine the effects of sacrificial microfibers on nonviral gene delivery inside 3D hydrogels, alginate microfibers containing human embryonic kidney 293 cells and polymeric NPs were encapsulated within 3D hydrogel scaffolds with varying stiffness (9, 58, and 197 kPa). Compared with cells encapsulated in bulk hydrogels, we observed up to 15-fold increase in gene delivery efficiency using sacrificial microfibers, and gene delivery efficiency increased as hydrogel stiffness increased. The platform reported herein provides a strategy for enhancing nonviral gene delivery inside 3D hydrogels across a broad range of stiffness, and may aid tissue regeneration by engaging both mechanotransduction and nonviral gene delivery.
View details for DOI 10.1089/ten.TEC.2013.0669
View details for PubMedID 24483329
Presentation of BMP-2 Mimicking Peptides in 3D Hydrogels Directs Cell Fate Commitment in Osteoblasts and Mesenchymal Stem Cells
2014; 15 (2): 445-455
Many strategies for controlling the fate of transplanted stem cells rely on the concurrent delivery of soluble growth factors that have the potential to produce undesirable secondary effects in surrounding tissue. Such off target effects could be eliminated by locally presenting growth factor peptide mimics from biomaterial scaffolds to control stem cell fate. Peptide mimics of bone morphogenetic protein 2 (BMP-2) were synthesized by solid phase Fmoc-peptide synthesis and covalently bound to alginate hydrogels via either carbodiimide or sulfhydryl-based coupling strategies. Successful peptide conjugation was confirmed by (1)H NMR spectroscopy and quantified by fluorescently labeling the peptides. Peptides derived from the knuckle epitope of BMP-2, presented from both 2D surfaces and 3D alginate hydrogels, were shown to increase alkaline phosphatase activity in clonally derived murine osteoblasts. Furthermore, when presented in 3D hydrogels, these peptides were shown to initiate Smad signaling, upregulate osteopontin production, and increase mineral deposition with clonally derived murine mesenchymal stem cells. These data suggest that these peptide-conjugated hydrogels may be effective alternatives to local BMP-2 release in directly and spatially eliciting osteogenesis from transplanted or host osteoprogenitors in the future.
View details for DOI 10.1021/bm401726u
View details for Web of Science ID 000331342200001
View details for PubMedID 24400664
View details for PubMedCentralID PMC3930060
- Synthesis and bonding of trans-dichlorobis(1,3-diaminopropane)ruthenium(III) chloride to a self assembled monolayer and its effect on conducting polymer sheet conductivity INORGANICA CHIMICA ACTA 2012; 383: 320-326
- Vapor phase polymerization of poly (3,4-ethylenedioxythiophene) on flexible substrates for enhanced transparent electrodes SYNTHETIC METALS 2011; 161 (13-14): 1159-1165