Photolabile hydrogels for dynamic tuning of physical and chemical properties to probe cell-cell and cell-material interactions

Hydrogels are used in the biomaterials community for two- and three-dimensional cell culture and as cell and drug delivery vehicles for tissue regeneration. Sophisticated control of the gel structure in both space and time is needed in these applications to answer questions about the dynamic relationship between biomaterial properties and biological function. For example, physical and chemical cues within the cell microenvironment regulate temporal cell processes, such as differentiation and extracellular matrix production, and consequently, strategies for controlling presentation of those cues at the appropriate time and place within the gel are needed. This thesis research aimed to develop photolabile hydrogels, whose physical or chemical properties could be tuned with light exposure, for application as a photoresponsive cell culture platform, allowing the examination of how cell-cell and cell-material interactions influence cell function. First, photodegradable monomers containing a nitrobenzyl ether photolabile group were synthesized: a photodegradable diacrylate PEG-based crosslinking macromer and a photoreleasable monoacrylate biomolecule tether macromer. Hydrogels were synthesized with each of these macromers by redox-initiated free radical chain polymerization to create a hydrogel whose structure could be tuned by degradation or whose chemistry could be tuned by biomolecule release with irradiation. Second, degradation of these hydrogels in response to UV and visible light was characterized in both space and time for the rational design of dynamic cell culture platforms. Last, these hydrogels were used for two- and three-dimensional cell culture, where individual chemical and structural cues were modulated and their influence on cell function examined. Specifically, the influence of RGD temporal regulation on human mesenchymal stem cell (hMSC) chondrogenic differentiation was demonstrated. The influence of a gel crosslinking density gradient on hMSC morphology was studied, as well as the role of substrate elasticity in valvular interstitial cell myofibroblastic differentiation. Finally, cell migration and cell-cell connectivity were regulated by patterned erosion of gel features. Collectively, this research developed photodegradable hydrogels and demonstrated their use for dynamic cell culture, establishing a platform for elucidating the influence of microenvironmental cues on cell function and subsequently exploiting them for tissue regeneration.