Collagen type I is the main structural protein of the body and it plays vital roles in various functions including wound healing, cell signaling, and force transmission. At appropriate pH, temperature, and ionic conditions, the collagen protein monomers can assemble into fibrils that interweave and trap water into a hydrogel in vitro. This property has been used to make hydrogels for wound healing applications, cell culture research, and drug delivery. Current techniques for manufacturing collagen I hydrogels allow fine control over macrostructural features on the order of 100 \u00b5m, but have limited control over microstructural features, such as fibril diameter and mesh size, that influence mechanical properties of these gels.
\r\n\r\nWe employed the use of a phenylglyoxylate cyclohexylammonium (PGA-CHA) photobase generator (PBG) that dissolves in acidic collagen solutions and releases a base upon interaction with light, raising the pH and triggering the collagen assembly. After exploring the parameter space, we elucidate the design parameters, including light absorptivity, PBG quantum yield, buffering effects, and heat generation, needed assemble collagen at physiologically relevant pH values (pH 6, 7, 8) using a single formula irradiated with 365 nm light for different durations. Areas of the solution masked from light did not form a gel and remained a solution.
\r\n\r\nCollagen gels assembled using the PBG showed increasing storage modulus, decreasing fibril thickness, and decreasing characteristic mesh size with increasing assembly pH. This behavior aligns well with the Morse model of un-crosslinked semi-flexible polymers and agrees with previous literature on the behavior of collagen hydrogels made with the current state-of-the-art techniques.
\r\n\r\nHuman foreskin fibroblasts grown on collagen gels assembled at different pH conditions using the PBG exhibited a variety of behaviors in morphology and migration. These behaviors provided insight into the length scale of mechanical properties that cells probe, as well as ways in which subtle changes in the mechanical properties influence cell speed and persistence. In this way, we introduce a new platform for microstructural control over collagen hydrogels using a PBG, which may be useful in influencing cells through their mechanical environment.
", "doi": "10.7907/d3th-cf97", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18734", "collection": "thesis", "collection_id": "18734", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012026-074934324", "primary_object_url": { "basename": "Final.pdf", "content": "final", "filesize": 4988091, "license": "other", "mime_type": "application/pdf", "url": "/18734/1/Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Ion Transport and Rheological Behavior in Polymeric Systems", "author": [ { "family_name": "Tsamopoulos", "given_name": "Alexandros", "orcid": "0009-0003-5924-5512", "clpid": "Tsamopoulos-Alexandros" } ], "thesis_advisor": [ { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "thesis_committee": [ { "family_name": "Brady", "given_name": "John F.", "orcid": "0000-0001-5817-9128", "clpid": "Brady-J-F" }, { "family_name": "Datta", "given_name": "Sujit", "orcid": "0000-0003-2400-1561", "clpid": "Datta-Sujit-S" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Ion-containing polymers are an important class of soft materials, owing to their applications in electrochemical energy storage, fuel cells, and membrane separations, as well as their rich ion transport and mechanical behavior. Their properties are governed by the interplay of polymer connectivity, ion correlations, segmental dynamics, and viscoelastic response across multiple length and time scales. This thesis examines these couplings using molecular simulations of polymer electrolytes, polymerized ionic liquids, and model polymeric fluids. We first investigate ion transport in salt-doped polymer electrolytes and show how temperature and salt concentration jointly control ionic conductivity through their effect on polymer mobility. We then examine polymerized ionic liquids, focusing on how ion correlations and chain length influence polymer relaxation, Onsager transport coefficients, and ion conductivity. Next, we return to the polymer electrolyte system to study the role of salt in controlling their linear and nonlinear rheological response. Finally, we develop a hydrodynamic framework for the diffusion of anisotropic probes in complex fluids, demonstrating that probe motion is governed by the length-scale-dependent viscous response of the surrounding medium. Overall, the range of systems considered here reflects the broader challenge of understanding ion-containing and polymeric materials.", "doi": "10.7907/3x2q-xx89", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" } ]