Three-dimensional Micromechanics of Adhesion and Friction between Micro-pillar Arrays and Soft Gel Substrates

该奖项研究具有微米大小的柱子的合成表面如何附着在柔软和潮湿的基板上并在其上滑动的机械原理。微柱阵列已经被引入到机器人设备的车轮踏面上，以提高它们在软组织上的机动性，但其潜在的机制尚不清楚。现有的大多数微结构表面接触力学的理论模型都假定衬底是刚性的，因此不能直接适用于软衬底的情况，因为软衬底在粘接和摩擦接触过程中会发生显著变形。这项研究成果将为下一代非侵入性医疗诊断和手术技术改进活体机器人设备的设计。更广泛地说，软材料接触力学的新知识还可以实现食品、医疗移植和植入物的机器人处理，从而使食品和医疗保健行业受益。将开发教育和推广计划，吸引高中到研究生院的学生，让他们接触到力学的基本概念和令人兴奋的前沿。活动包括课程开发、本科生研究计划和外展课程。柔软的衬底与微柱阵列接触时会发生大变形，微柱阵列本质上是三维的，本质上是非线性的。衬底的大变形预计将导致微柱的法向载荷和剪切载荷之间以及相邻柱之间的强烈耦合。了解这种耦合将有助于寻找最佳的柱子布置，以实现所需的粘着和摩擦性能。PIS将开发一种新的实验设备，以实现在接触、粘合和摩擦情况下原位绘制软水凝胶基质中的三维变形场。软凝胶基质用作模拟生物组织或其他软湿材料的模型材料。原位变形映射能力将与粘着和摩擦测试以及有限元建模相结合。有限元模型将通过实验验证的柱面界面模型，将单个柱子水平上的局部细观力学与整体粘着和摩擦联系起来。研究结果将为微柱阵列与软基之间的接触机理提供新的理论见解，并使高保真模拟能够驱动微柱结构的设计，以优化软基上的粘着和摩擦。

This award investigates the mechanics of how synthetic surfaces with micrometer-sized pillars adhere to and slide on soft and wet substrates. Micro-pillar arrays have been introduced on the wheel treads of robotic devices to improve their mobility on soft tissues, but the underlying mechanism is yet to be understood. Most existing theoretical models on the contact mechanics of micro-structured surfaces assume stiff substrates, and thus are not directly transferable to the case of soft substrates which can deform significantly during adhesive and frictional contact. Results of this research will improve the design of in vivo robotic devices for the next generation technology of non-invasive medical diagnosis and surgery. More broadly, new knowledge in soft material contact mechanics can also enable robotic handling of food, medical transplants and implants, thus benefiting the food and healthcare industries. Education and outreach programs will be developed to engage high school though graduate school students, exposing them to the fundamental concepts and exciting forefront of mechanics. Activities include course development, undergraduate student research program, and outreach lessons.A soft substrate can undergo large deformation upon contact with a micro-pillar array, which is three-dimensional in nature and inherently nonlinear. The large substrate deformation is expected to lead to a strong coupling between the normal and shear loadings of the micro-pillars, as well as between neighboring pillars. Understanding this coupling will facilitate the search for optimal pillar arrangement to achieve desired adhesion and friction properties. The PIs will develop a new experimental apparatus to achieve in situ mapping of the three-dimensional deformation fields in soft hydrogel substrates under contact, adhesion and friction. The soft gel substrate serves as a model material to simulate biological tissue or other soft and wet materials. The in situ deformation mapping capability will be combined with adhesion and friction tests and finite element modeling. The finite element model will connect the local micromechanics at the level of individual pillars to the global adhesion and friction, through an experimentally validated pillar-surface interface model. Results will offer new theoretical insights on the contact mechanics between micro pillar arrays and soft substrates, and enable high-fidelity simulations to drive the design of micro-pillar structures for optimized adhesion and friction on soft substrates.