Influence of Double Network, Internetwork Connectivity and Sacrificial Bonds on the Frictional Characteristics of Double Network Hydrogels: Experiments and Modeling

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This grant will support research that will advance the knowledge related to a structure-property relation for double network hydrogels, promoting the progress of science. The exceptional lubrication behavior of biological tribosystems stems from its biphasic composition, a complex macromolecular network with a water-based lubricant. As a prominent example, articular cartilage balances lubricity with strength. To date, there is an urgent need to generate tribological understanding and models for novel biomaterials that can serve as replacement for cartilage. Double network (DN) hydrogels consist of two interpenetrating polymer network that resemble cartilage, are strong and tough, and have thus emerged as promising biomaterials. This research will advance the understanding of the mechanics associated with DN hydrogels, and specifically how double networks afford control of friction. The implications of this work go beyond fundamentals of soft matter tribology and extend to biomedical applications and soft robotics, where the processes occurring at the migrating hydrogel interface are relevant. Furthermore, the collaborative project will help develop the workforce in the U.S., broaden the participation of underrepresented groups in research, and positively impact engineering education.The overall objective of this research is to provide a fundamental understanding of the relation between microstructure of DN hydrogels and their frictional characteristics via experiments and modeling. Two major lines of research are proposed here: one combining physically and chemically crosslinked networks and a second one combining two chemically crosslinked networks, which lead to intrinsically different microstructures. The intellectual merit of this research will include: (1) thorough data of friction, structural, and mechanical properties of DN hydrogels as a function of composition via (novel and improved) experimental toolsets and a new mechanics model to quantify friction; (2) advances in the fundamental understanding of the effect of double network, sacrificial bonds, internetwork connections and charge on frictional dissipation mechanisms; and (3) discovery of hydrogel materials, capable of achieving low friction coefficients and augmented wear resistance through the precise control of their microstructure. To examine lubrication mechanisms, friction, adhesion and rheological measurements will be carried out on hydrogels to probe multiple dissipation mechanisms. The comparison between experimental and modeling results will enable us to elucidate the underlying mechanisms.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.