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

这笔赠款将支持促进与双网络水凝胶的结构-性质关系相关的知识的研究，促进科学进步。生物摩擦系统的特殊润滑行为源于其两相组成，这是一个含有水基润滑剂的复杂的大分子网络。作为一个突出的例子，关节软骨平衡了润滑性和强度。到目前为止，迫切需要建立新的生物材料的摩擦学理解和模型，作为软骨的替代品。双网络水凝胶由两个类似软骨的相互穿透的聚合物网络组成，具有很强的韧性，因此是一种很有前途的生物材料。这项研究将促进对与DN水凝胶相关的机理的理解，特别是双网络如何提供摩擦控制。这项工作的意义超越了软物质摩擦学的基本原理，并扩展到生物医学应用和软机器人，在这些领域，迁移水凝胶界面上发生的过程是相关的。此外，该合作项目将有助于发展美国的劳动力队伍，扩大未被充分代表的群体参与研究，并对工程教育产生积极影响。本研究的总体目标是通过实验和建模，从根本上了解DN水凝胶的微观结构与其摩擦特性之间的关系。这里提出了两条主要的研究路线：一条是结合物理和化学交联的网络，另一条是结合两个化学交联的网络，这两条网络导致了本质上不同的微结构。这项研究的学术价值将包括：(1)通过(新颖的和改进的)实验工具箱和量化摩擦的新的力学模型，彻底了解DN水凝胶的摩擦、结构和力学性能随组成的函数关系；(2)在基本了解双网络、牺牲键、网络连接和电荷对摩擦耗散机制的影响方面取得进展；(3)发现水凝胶材料，能够通过精确控制其微观结构来实现低摩擦系数和提高耐磨性。为了研究润滑机制，将在水凝胶上进行摩擦、粘合和流变学测试，以探索多种消散机制。实验和模型结果之间的比较将使我们能够阐明潜在的机制。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.