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

这项教师早期职业发展（Career）资助将支持研究一种新型的水凝胶粘附机制，这种机制可以通过外部刺激打开和关闭。水凝胶是一种柔软的水合物质，类似于人体组织。这种相似性使得它们在制造能够更好地与人体互动的软体机器时非常有用。软机器的应用包括医疗植入物、可穿戴设备和仿生机器人。与由螺母和螺栓等刚性部件组装的传统机器不同，软机器是通过可变形的粘合剂组装的。虽然现有的一些研究已经实现了能够可靠地承受较大变形的水凝胶粘附，但很难可逆地切换粘附的开启和关闭，从而使软机器可以通过部件交换进行维修或重新配置，这是传统机器的常见做法。这个项目将研究新的粘附机制，使软机器的可逆组装。该项目的成功将彻底改变软机器的设计，这反过来将影响许多相关应用的发展。此外，该项目还将制作培训材料，帮助研究生将前沿研究成果转化为易于理解的短视频。这些视频在免费的在线平台上分享时，可以将最新的研究成果带给比传统学术期刊和研讨会更广泛、更多样化的受众。该项目旨在通过水凝胶界面上的刺激响应渗透毛细管和静电相互作用来实现可切换的粘附。虽然基于这些机制的刺激响应粘附已被报道用于一些物质刺激系统，但控制这些机制的机制尚未得到充分研究。本项目将通过(1)表征受控热力学状态下的粘附，从而建立渗透毛细管和静电粘附的热力学本构关系；(2)表征受控体积耗散下的粘附，并进行有限元模拟，研究界面相互作用与体积耗散之间的耦合关系。(3)利用已建立的水凝胶场理论建立随时间变化的黏附模型，并通过实验对模型进行验证。该项目的结果将大大加深对水凝胶界面上渗透毛细管和静电相互作用的理解，并将为设计具有可定制刺激响应开关行为的可逆粘附铺平道路。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.