Design of Force-Sensitive Hydrogels for Adhesives and Strain Sensors

水凝胶在固体和柔软表面（如人体皮肤、生物组织和金属基底）上的粘附在许多实际应用中是重要的，例如坚固的人造组织、智能机器人、电子皮肤和运动/损伤传感器。这些广泛的应用领域表明它们对发展美国经济的关键部门的重要性，包括医疗保健和国防系统。然而，产生具有适当粘附水平的水凝胶，以及在去除表面后重新粘附的需要，一直是非常具有挑战性的。这项研究将专注于创造一个新的基于物理的坚韧水凝胶和水凝胶粘合剂家族，这些水凝胶和粘合剂在散装和固体基材上具有卓越的机械、自修复和刺激响应特性。在水凝胶中使用两种聚合物网络，这些网络相互交织，具有不同的特性，对材料的性能至关重要，这是该方法的一个新特点。一种网络可以提供机械韧性，而另一种网络可以在表面形成可改造的粘合键，从而结合典型的不相容性能。一旦开发成功，这两种聚合物网络也可以用于制造医学应用中用于人体运动检测的应变传感器。从该项目中获得的新知识、新技术和新材料将在其他软材料的工程和设计以及推进新型智能材料的制造和性能方面发挥重要作用。该项目将为所有水平的学生，特别是来自弱势群体的学生提供研究机会，学习聚合物物理/化学、芯片实验室设计和人体工程学方面的动手技能，从而促进下一代STEM教育。大多数水凝胶胶粘剂对各种表面的粘附力较弱，附着能很低，多次开断剥离试验后容易失去粘接能力，缺乏自恢复和自修复功能来恢复其粘接性能和力学性能。目前的材料设计策略无法在同一水凝胶中同时呈现体积和界面韧性，因为水凝胶的体积和界面韧性来源于不同的来源。为了克服这些科学障碍，本研究通过理解、耦合和设计不同网络之间的相互作用以及相关的能量机制，努力设计一种新的物理连接双网络水凝胶家族，以实现多种力激活功能，包括高体/界面韧性、多重刺激自愈性能以及在体和固体基板上的可逆粘附。并将水凝胶黏合剂制成多功能应变传感器，用于人体运动检测。这种新型物理连接水凝胶的功能和性能将通过以可编程的方式调整其网络组件和结构来控制。本研究将为新型智能材料的合理设计提供基础知识和实用原理，更好地理解材料的组件-结构-性能-性能相互关系，提高材料的多功能，加工和制造。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。

The adhesion of hydrogels on solid and soft surfaces, such as human skin, biological tissues, and metal substrates, is important in many practical applications, such as robust artificial tissues, smart robots, electronic skins, and motion/damage sensors. These broad application areas indicate their importance to developing key sectors of the US economy including health care and defense systems. The generation of hydrogels with the appropriate level of adhesion, and the need to re-adhere to a surface once removed, however, has been very challenging. This research will focus on creation of a new family of physically-based tough hydrogels and hydrogel adhesives with integrated superior mechanical, self-healing, and stimuli-responsive properties in bulk and on solid substrates. The use of two polymer networks in the hydrogel, with the networks intertwined and possessing differing properties key to the performance of the material, is a novel feature of the approach. One network could provide mechanical toughness while the other network could lead to reformable adhesive bonds to a surface leading to the incorporation of typically incompatible properties. Once developed, the two polymer networks can also be used in the fabrication of strain sensors for human motion detection in medical applications. New knowledge, techniques, and materials derived from this project will be important in the engineering and design of other soft materials and in advancing the manufacture and performance of new smart materials. The project will provide research opportunities to all-level students, particularly from underrepresented groups, learning hands-on skills from polymer physics/chemistry, lab-on-chip design, and ergonomic engineering, thus promoting the next-generation of STEM education. Most of hydrogel adhesives adhere weakly to diverse surfaces with very low adhesion energy, easily lose adhesive capacity after multiple on-and-off peeling tests, and lack self-recovery and self-healing functions to recover their adhesive and mechanical properties. The current materials design strategy prevents both bulk and interfacial toughness to be presented in the same hydrogel, because the bulk and interfacial toughness of hydrogels stem from different origins. To overcome these scientific barriers, this research strives to design a new family of physically-linked double network hydrogels by understanding, coupling, and engineering the interactions between different networks and the associated energy mechanisms to achieve multiple force-activated functionalities, including high bulk/interfacial toughness, multiple-stimuli self-healing property, and reversible adhesion both in bulk and on solid substrates, as well as to fabricate the hydrogel adhesives into strain sensors with integrated multi-functions for human motion detection. The function and performance of this new class of physically-linked hydrogels will be controlled by tuning their network components and structures in a programmable way. This research will advance fundamental knowledge and practical principles for rational design of new smart materials, better understanding of component-structure-property-performance interrelationship of the materials, and improvement of materials multi-functionality, processing, and fabrication.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.