(598c) Transient Stimulation of Hydrogel Environments for Non-Equilibrium Mechanical Control

Synthetic hydrogels offer an intriguing platform for biomaterial applications due to their wide chemical library and top-down design. One of the most important considerations for these systems is the crosslinking chemistry. Recent research has highlighted the utility of dynamic crosslinking, such as guest-host interactions, ionic bonding, and reversible covalent chemistries. Our lab specializes in the incorporation of reversible covalent chemistries into hydrogel networks in order to control the viscoelastic properties for a variety of applications. In this research, we show that transient stimulation of a reversibly crosslinked hydrogel can control the resulting hydrogel mechanics in a reversible way, whether that be through nanoparticle controlled temperature spikes or chemical-fuel induced sequestering. The starting hydrogel in this system relies on an inert poly(ethylene-glycol) (PEG) star polymer functionalized with either conjugate acceptors or thiols. These crosslink through a reversible thia-conjugate addition mechanism. Our work demonstrates how temperature can effectively control the crosslinking reaction, and the incorporation of photothermal nanoparticles allows near-IR light to be the temperature change trigger. Additionally, the conjugate acceptors naturally hydrolyze in the native aqueous hydrogel environment. Through a combination of hydrolytically labile orthogonal chemistries, the concentration of conjugate acceptor can be controlled in a transient fashion. This setup allows a mechanical change in the hydrogel in the presence of a reactive fueling molecule that spontaneously reverts to the original state when that reactive fuel is consumed. Our research demonstrates how transient non-equilibrium systems can be an effective way to stimulate hydrogel mechanical changes that naturally revert back to the originally state.