Participant Support Costs. CAREER: Photocontrolled Dynamic Covalent Crosslinkers for Light‐Responsive Polymer Networks

The objective of this proposal is to develop photoswitches that independently modulate the stiffness and stress relaxation of viscoelastic polymer networks. Polymers that respond to external stimuli with changes in their physical properties can serve as sensors, actuators, controlled delivery systems, tissue mimics, and healable materials. Light is one of the most appealing stimuli because it offers tunable energy and intensity, and spatiotemporal control. A key limitation of the dominant strategies for reversible photocontrol of polymer networks is that they rely on the chromophore itself as the dynamic crosslink, which provides only binary changes in crosslink density or conformation. We propose that photoswitchable control of dynamic covalent crosslinks will translate into reversible, reproducible, and dramatic changes in network mechanical properties. To support this hypothesis, we have designed new photoswitches that reversibly control the stiffening and softening of boronate ester-linked hydrogels. We will pursue our research objectives by exploring three distinct mechanisms for photoswitching dynamic covalent crosslinkers: crosslink stability, crosslink exchange rate, and crosslink topology. We hypothesize that each mechanism will access a different range of dynamic materials. Our research and education plans are highly integrated through the themes of polymer education and gel-based assistive technologies. We will partner with local institutions serving visually impaired K-12 students to adapt hands-on outreach activities with polymers. We will also host education specialists who work with blind or low-vision students to provide STEM research experiences for these highly sought-after teachers. Their research projects will focus on the adaptation of our light-responsive gels to tactile displays for the visually impaired. We will also work with Northwestern’s accessibility center to identify accessible course materials and assistive technologies for chemistry courses.