Influence of Mesh Size, Type of Crosslinking, Polymer Stiffness and Interfacial Rheology on the Frictional Characteristics of Hydrogels

这笔赠款将支持促进与水凝胶的结构-性质关系相关的知识的研究，促进科学进步和促进国民健康。水凝胶是一类软材料，由交联的聚合物网络组成，在水中显著膨胀，接近模拟许多自然生物组织，如粘性凝胶层。在呼吸道和胃肠道、口腔和眼睛中发生的生物润滑，依赖于这些粘液凝胶层提供的低摩擦系数。尽管进行了大量的研究工作，但对于这种低摩擦的起源仍然存在分歧，这阻碍了迄今为止能够实现高效生物溶解的生物材料的设计。因此，该项目将提供水凝胶特性与摩擦响应之间的关系所需的知识。因此，它将能够建立目标生物医学应用的水凝胶的设计原则，能够实现低摩擦系数和增强耐磨性，因此，这项研究的结果将造福于美国社会。这项研究涉及多个学科，包括材料化学和科学，以及摩擦学。多学科方法将有助于扩大未被充分代表的群体在研究中的参与，并对工程教育产生积极影响。为了填补概述的知识空白，将遵循两条主要研究路线：一条是比较具有广泛交联度的物理和化学交联水凝胶，另一条是研究聚合物链半柔性的影响。为了评估润滑机理，将使用胶体探针原子力显微镜和表面力仪器测量表征良好的水凝胶(具有广泛的组成范围)的摩擦力随载荷和滑动速度(跨越五个数量级)的函数来探索不同松弛时间的微观现象。实验工作将深入了解网目尺寸、交联剂类型、聚合物硬度以及界面老化对摩擦特性的影响。研究小组还将进行动态剪切力测量，以仔细研究摩擦力和水凝胶界面流变性之间的关系。这项研究所产生的知识将能够通过对水凝胶微观结构的精确控制来调节水凝胶的摩擦响应。该奖项反映了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 hydrogels, promoting both the progress of science and advancing national health. Hydrogels are a class of soft materials, composed of crosslinked polymeric networks that remarkably swell in water, which closely simulate many natural biological tissues, like mucous gel layers. Biological lubrication taking place in respiratory and gastrointestinal tracts, in the oral cavity and in the eyes, relies on the low friction coefficients provided by these mucous gel layers. Despite significant research effort, there is still disagreement about the origin of such low friction, which hinders the design of biomaterials capable of achieving efficient biolubrication to date. This project will thus deliver the needed knowledge of the relation between hydrogel's properties and frictional response. Thereby, it will enable to establish design principles of hydrogels for targeted biomedical applications capable of achieving low friction coefficients, and augmented wear resistance, and therefore, results from this research will benefit the U.S. society. This research involves several disciplines including materials chemistry and science, and tribology. The multi-disciplinary approach will help broaden participation of underrepresented groups in research and positively impact engineering education.In order to fill the outlined knowledge gap, two major lines of research will be followed: one comparing physically and chemically crosslinked hydrogels with a wide range of crosslinking degrees, and a second one that will study the influence of polymer chain semi-flexibility. To evaluate lubrication mechanisms, friction force measurements will be carried out on well-characterized hydrogels (with a wide range of compositions) by colloidal probe Atomic Force Microscopy and with a Surface Forces Apparatus as a function of load and sliding velocity (spanning over five orders of magnitude) to probe microscopic phenomena with different relaxation times. The experimental effort will provide insight into the effects of mesh size, type of crosslinking, polymer stiffness, as well as aging of the interface, on the frictional characteristics. The research team will also conduct dynamic shear-force measurements to scrutinize the relation between friction force and interfacial rheology of hydrogels. The knowledge generated by this research will afford to modulate the frictional response of hydrogels through the precise control of their microstructure.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.