UCLA

The field of cell and tissue engineering is far from being systematic. Historically, the field follows a guess-and-test methodology; new materials are produced and tested in search of the “right” combination of material properties, chemical/growth factor concentrations, reactor conditions, etc. While developmental biologists have extensively studied signaling factors, gene expression and other components governing early tissue development, researchers still do not have a full picture of how these signaling cascades are initiated or how spatial and temporal tissue inhomogeneities initially form. To address this issue, new materials must be developed that can mimic the intricacies of native tissue in order to correctly study their behavior. Hydrogels incorporating controlled photodegradation are a novel class of polymeric biomaterials that our group at UCLA has developed. The outstanding benefit of these materials is that their physical and chemical properties can be altered on-demand, in real-time without the presence of toxic compounds, allowing cells to be present during modification. In addition, the degradation, and thus the mechanical properties, is a strict function of the exposure of light (exposure time, wavelength, and intensity) such that the precise spatial and temporal control of the degree of degradation far surpasses that of hydrolytic and enzymatic degradation mechanisms. In this dissertation, I develop new photodegradable materials, find solutions to better characterize their behavior, and expand the techniques necessary for their successful use in cell biology. First, by developing a series of mass-action and kinetic mathematical models, I examine the physical properties of photodegradable gels formed by end-linking gelation. I pay special attention to how diffusion of photoabsorbing byproducts affect degradation. These models are further enhanced by examining the specific microstructure and micro-heterogeniety of the gels formed. Second, I expand the photodegradable materials library. In order to better mimic three-dimensional cellular environments, I successfully synthesize photodegradable protein-based gels and showcase their applicability towards three-dimensional cell culture. I specifically fabricate photodegradable gelatin gels, however, the techniques I develop here more generally aid in the conjugation of hydrophobic moieties to protein materials. Next, I synthesize and fabricate photodegradable polyacrylamide gels. I utilize the flexibility of the polyacrylamide gel system by exploring cell response to both changes in cell binding domain and dynamic softening of the underlying matrix. Finally, I develop the application of maskless photolithography for photodegradable hydrogels. Using this technique, I rapidly pattern grayscale stiffness patterns into photodegradable hydrogels in a highly controlled fashion with sub-micron resolutions. Cell response to complex patterns of grayscale stiffness are tested. Through the developments made in this dissertation, I expand our ability to test cell behavior in spatially and temporally heterogeneous environments.