Mechanical Properties and Degradation of Chain and Step Polymerized Photodegradable Hydrogels

The relationship between polymeric hydrogel microstructure and macroscopic properties is of specific interest to the materials science and polymer science communities for the rational design of materials for targeted applications. Specifically, research has focused on elucidating the role of network formation and connectivity on mechanical integrity and degradation behavior. Here, we compared the mechanical properties of chain and step polymerized, photodegradable hydrogels. Increased ductility, tensile toughness, shear strain to yield were observed in step polymerized hydrogels, as compared to the chain polymerized gels, indicating that increased homogeneity and network cooperativity in the gel backbone improves mechanical integrity. Furthermore, the ability to degrade the hydrogels in a controlled fashion with light was exploited to explore how hydrogel microstructure influences photodegradation and erosion. Here, the decreased network connectivity at the junction points in the step polymerized gels resulted in more rapid erosion. Finally, a relationship between the reverse gelation threshold and erosion rate was developed for the general class of photodegradable hydrogels. In all, these studies further elucidate the relationship between hydrogel formation and microarchitecture with macroscale behavior to facilitate the future design of polymer networks, degradable hydrogels, as well as photoresponsive materials as cell culture templates, drug delivery vehicles, responsive coatings, and anisotropic materials.