Modeling the mechanics, kinetics, and network evolution of photopolymerized hydrogels

Photopolymerized hydrogels are critical to soft devices, mechanobiology, regenerative medicine, and next generation drug delivery. However, the optimization of processing protocols for all of these applications of photopolymerized hydrogels has been at least semi-empirical due to the lack of a comprehensive predictive framework. Herein, we developed the first comprehensive predictive framework for how the chemical kinetics, optical properties, and mechanical properties of a photopolymerized hydrogel emerge from a precursor solution as the solution is illuminated, and of how these processing parameters relate to the final mechanics of the hydrogel. We validated the model experimentally using an eosin Y-initiated di-acrylate system. The model revealed that processing kinetics were dominated by photobleaching and crosslinking, and that network mechanics were dominated by chain growth and loop formation. We demonstrated the utility of the model by using it to design and then synthesize hydrogels with specified gradients in mechanical properties. The modeling framework is general and enables design of a broad range of hydrogels.