CAREER: Gas-regulated Mechanochemical Activation for Bio-inspired Responses in Polymer Networks

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NON-TECHNICAL SUMMARY:In nature, biological systems can constructively respond to mechanical force, such as the healing of skin after a cut. Taking this as inspiration, this project aims to develop force-responsive synthetic polymeric materials that can remodel after force is applied. The goal is to externally regulate the extent of force-triggered activation and remodeling using carbon dioxide as an external stimulus. To do this, the material will include two components. One component is designed to respond to carbon dioxide by swelling and the other includes force-sensitive groups called mechanophores, which will remodel the material in response to the extent of swelling. Using this approach, the project describes systematic studies examining the structure-property relationships that underlie mechanophore activation and their time scales in polymer networks. This project will help advance research towards developing materials offering enhanced safety, longer lifespan, and reduced environmental impact. The project will also include educational and outreach activities including mentored research opportunities for undergraduates from diverse backgrounds attending a primarily undergraduate institution (PUI), the development of a hands-on module based on this project for a technical elective in polymers, and the implementation of a career module to expose students to career paths in the field. Further, this project supports hosting two visiting graduate students who have interest in a career at a PUI for the summer to begin building the skills needed to develop an undergraduate-driven research program.TECHNICAL SUMMARY:The ability of biological systems to respond constructively to mechanical force inspires the design of mechano-responsive polymer networks that similarly elicit constructive responses. However, strategies to develop synthetic materials capable of force-triggered remodeling remain limited. This effort will take a stepwise approach towards regulating mechanochemical activation using an external stimulus in double network (DN) hydrogels. Using a DN structure, external control will be afforded by a carbon dioxide (CO2)-responsive primary network, which regulates the extent of mechanochemical scission in the secondary network via swelling. CO2-regulated, force-triggered activation of the mechanophore will be coupled to a subsequent crosslinking polymerization to strengthen and remodel the material in response to deformation. This system will be used to determine the structure-property relationships that govern mechanophore activation and kinetics, which may enable new strategies to study mechanochemistry in basic and applied research.Educational and outreach components of the project include: 1) enhancing undergraduate education and training; 2) enriching graduate professional development; and 3) building research infrastructure and enhancing educator development. The first area includes providing mentored research opportunities for undergraduates of diverse backgrounds attending a PUI, development of a hands-on module and career module targeted towards undergraduates enrolled in a technical elective focused on polymers, and hosting a workshop to aid undergraduates in submitting competitive applications to a fellowship program. The second area includes hosting two visiting graduate students who have interest in pursuing a career at a PUI for the summer to gain first-hand experience of conducting research at a PUI and to begin building the skills needed to develop an undergraduate-driven research program. The third area focuses on developing and disseminating materials to prospective and new faculty at PUIs to help them perform and fund their research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.