Photopolymeric thiol-ene biomaterials: Controlling network structure to tune degradation behavior and material properties

Biomaterials play a critical role in a variety of biomedical arenas. As such, efforts to develop novel biomaterials focus on the ability to control and manipulate biomaterial properties including mechanics, biocompatibility, and degradation in a predictable, systematic manner. Here, we have developed and characterized thiol-ene and thiol-acrylate photopolymerizations as a novel class of biomaterials that facilitate a broad, controllable range of material properties.; Biomaterial structure influences both the degradation behavior and mechanical properties. In this research the unique polymer structures and properties of thiol-ene and thiol-acrylate photopolymer networks were explored. Thiol-acrylate network formation was shown to occur rapidly, even in the absence of added photoinitiator, which allowed samples with thicknesses in excess of 10 cm to be fabricated. Thiol and acrylate polymerization kinetics were analyzed using FTIR, from which theoretical distributions of thiol-polyacrylate backbone chains were calculated. This structural information was used to predict the temporal thiol-acrylate degradation and mass loss. Calculated and experimentally determined mass loss profiles and polyacrylate chain length data (obtained by GPC analysis of degraded network components) both confirmed that increasing thiol monomer functionality or decreasing the thiol functional group ratio decreased mass loss rates.; Next, the influence of structure on degradation behavior was investigated in thiol-ene step growth networks. In these materials, the solvent concentration, monomer molecular weight, monomer functionality, and concentration of degradable sites within the network were systematically varied, and the resulting mass loss profiles, swelling ratios, and compressive moduli measured. While these parameters impacted degradation behavior in unique ways, changes in the network structure that decreased crosslink density (e.g., increasing monomer molecular weight or decreasing average monomer functionality) generally increased the mass loss rate and decreased the modulus.; Finally, the ability to modify thiol-ene networks chemically post-polymerization was examined. A technique was first developed to detect changes in pendant reactive group concentration during chemical modification. Photocoupling was then used to create patterned regions of chemical modification in thiol-ene networks.; The studies presented herein identify the unique ability afforded by degradable thiol-ene photopolymers for chemical and mechanical control of biomaterial network structure and properties.