State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.
Department of Engineering for Innovation, Universitá del Salento, 73100 Monteroni-Lecce, Italy.
Small. 2019 Jan;15(1):e1802931. doi: 10.1002/smll.201802931. Epub 2018 Nov 16.
Anisotropic friction plays a key role in natural systems, particularly for realizing the purpose of locomotion and strong attachment for the survival of organisms. Of particular interest, here, is the observation that friction anisotropy is promoted numerous times by nature, for example, by wild wheat awn for its targeted and successful seed anchorage and dispersal. Such feature is, however, not fully exploited in man-made systems, such as microbots, due to technical limitations and lack of full understanding of the mechanisms. To unravel the complex dynamics occurring in the sliding interaction between anisotropic microstructured surfaces, the friction induced by asymmetric plant microstructures is first systematically investigated. Inspired by this, anisotropic polymer microactuators with three-dimensional (3D) printed microrelieves are then prepared. By varying geometric parameters, the capability of microactuators to generate strong friction anisotropy and controllable motion in remotely stretched cylindrical tubes is investigated. Advanced theoretical models are proposed to understand and predict the dynamic behavior of these synthetic systems and to shed light on the parameters and mechanisms governing their behavior. Finally, a microbot prototype is developed and cargo transportation functions are successfully realized. This research provides both in-depth understanding of anisotropic friction in nature and new avenues for developing intelligent actuators and microbots.
各向异性摩擦在自然系统中起着关键作用，特别是对于实现生物的运动和强附着的目的。特别有趣的是，自然界中存在着无数次的摩擦各向异性增强现象，例如，野生小麦芒为了实现有针对性和成功的种子锚固和传播。然而，由于技术限制和对机制的不完全理解，这种特性在人造系统中，如微机器人，并没有得到充分利用。为了揭示各向异性微结构表面滑动相互作用中发生的复杂动力学，首先系统地研究了不对称植物微结构引起的摩擦。受此启发，然后制备了具有三维（3D）打印微凸起的各向异性聚合物微致动器。通过改变几何参数，研究了微致动器在远程拉伸圆柱管中产生强摩擦各向异性和可控运动的能力。提出了先进的理论模型，以理解和预测这些合成系统的动态行为，并阐明控制其行为的参数和机制。最后，开发了一个微机器人原型，并成功实现了货物运输功能。这项研究不仅深入了解了自然界中的各向异性摩擦，而且为开发智能致动器和微机器人提供了新途径。
