CAREER: Robust, Reversible, and Stimuli-responsive Thermodynamic Adhesion in Hydrogels

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This Faculty Early Career Development (CAREER) grant will support research that investigates a new type of hydrogel adhesion mechanism that can be switched on and off using external stimuli. Hydrogels are soft and hydrated materials similar to our body tissues. This similarity makes them useful for creating soft machines that better interact with human bodies. Applications of soft machines include medical implants, wearable devices, and biomimetic robots. Unlike conventional machines that are assembled by rigid parts like nuts and bolts, soft machines are assembled through deformable adhesion. Although some existing studies have realized hydrogel adhesion that can reliably survive larger deformation, it is difficult to reversibly switch the adhesion on and off so that the soft machine can be repaired or reconfigured by part exchange, which is a common practice in conventional machines. This project will investigate novel adhesion mechanisms that enable the reversible assembly of soft machines. The success of the project will revolutionize the design of soft machines, which in turn will impact the development of many relevant applications. Moreover, the project will create training materials to help graduate students turn cutting-edge research findings into short, easy-to-understand videos. These videos, when shared on free online platforms, can bring the latest research to a much wider and diverse audience than is possible through traditional academic journals and seminars.The project aims to realize switchable adhesions through stimuli-responsive osmocapillary and electrostatic interactions on hydrogel interfaces. While stimuli-responsive adhesion based on these mechanisms has been reported for some material-stimulus systems, the mechanics governing these mechanisms is understudied. This project will explore the underlying mechanics by (1) characterizing the adhesion under controlled thermodynamic states, thus establishing the thermodynamic constitutive relations of osmocapillary and electrostatic adhesion, (2) characterizing the adhesion with controlled bulk dissipation and performing finite element simulations to study the coupling between interfacial interactions and bulk dissipation, and (3) modeling time-dependent adhesion using established hydrogel field theories and validating the model with experiments. The outcome of the project will significantly deepen the understanding of osmocapillary and electrostatic interactions on hydrogel interfaces and will pave the way for designing reversible adhesion with customizable stimuli-responsive switching behaviors.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.