Many strategies have been employed to change the mechanical properties of hydrogels in a controlled manner. Often, the crosslinking chemistry in a hydrogel network is targeted to affect this change and approaches typically proceed either through irreversible bond degradation or reversible events involving supramolecular or dynamic covalent bonding chemistry. Alternatively, photoisomerization of light-responsive molecules has also been employed, wherein the most frequently investigated substrates involve derivatives of azobenzene or spiropyran. The Barnes group at Washington University has developed a different approach that relies on radical molecular recognition of viologen-based redox-responsive polymers and crosslinkers that are integrated into gel polymer networks. The constituent viologens (V<sup>2+</sup>) can be reduced chemically, photochemically, or electrochemically to generate viologen radical cations (V<sup>●+</sup>) that stack intramolecularly, while decreasing by half the number of positive charges, resulting in collapsible polymers capable of actuating (i.e., shrinking and expanding reversibly) hydrogels consisting mostly of poly(hydroxyethyl acrylate). In my talk, I will discuss our investigations into gaining spatiotemporal control over changes in the mechanical properties of viologen-based hydrogel actuators using visible-light photoredox catalysis, while also describing new crosslinker designs and different light-absorbing catalysts that allow for faster contraction of hydrogels and enhanced photomechanical actuator performance.

Spatiotemporal control of hydrogel mechanical properties through visible-light activation of viologen-based macrocrosslinkers

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.