仿生软硬复合取向结构表界面的构筑与自适应摩擦机制研究

A variety of natural surfaces are hard-soft composite that covered with micro- and nanostructures oriented at some angles to the supporting substrate, which cause mechanical anisotropy because of the anisotropic friction when rubbing with other surfaces. These mechanically anisotropic surfaces are crucial for generating propulsion for the biological locomotion or transporting items. Therefore, the biomimetic research on the surfaces with oriented structures has aroused increasing attentions in the fields of biomechanics, bioinspired materials, and material science and engineering, etc., which is believed to be valuable for bioinspired machines such as biomimetic robots, soft robots, and medical robots. Artificial construction of biomimetic interface with oriented structures has been focused on years yet still a challenging topic due to complexity of natural surfaces and short of techniques. The project, taking the Filefish skin and cat tongue as natural samples, with the unique advantages of 3D printing on the design and construction of complex three dimentional architecture and combinational design of materials, proposes to 3D printing the three dimentional biomimetic surface/interface with hard oriented spines embedded in soft substrate to investigate the anisotropic friction behaviors. The interrelationships between the orientation of spines, the physicochemical properties of the surface and the anisotropic friction performances will be investigated. It will discover the mechanism of the self-adaption behavior of oriented spines and substrate of the hard-soft interface system when rubbering with other surfaces and its influences on the surface anisotropic friction property. One of objectives of the project is to develop the biomimetic hard-soft interface materials and the surface friction tuning approach to realize the directional actuation and movement of the biomimetic hard-soft interface system driven by tuning its surface anisotropic friction. The achievements of the project on the design, manufacturing of the biomimetic hard-soft interface system, its self-adaption and frictional anisotropy with mechanical shearing, and the directional actuation and movement thereafter will found theoretical and technical foundations for the fields of biomimetic tribology, biomimetic mechanical motion control, and intelligent system.

自然界广泛存在的软硬复合取向结构表面及其各向异性摩擦行为对行走、移动和捕食等生物功能至关重要，因此，相应仿生表界面在机械剪切作用下的结构自适应性应变及各向异性摩擦行为机理和调控等关键科学技术问题研究对仿生摩擦、仿生机械等领域具有重要理论和实践意义。项目拟以马面鱼皮和猫舌倒刺表面为仿生对象，采用3D打印先进制造技术与传统模板复制等技术相结合的方式，构筑仿生软硬复合取向尖刺结构表界面，探索结构取向、材料力学强度等理化性能与表面摩擦各向异性行为之间的内在关系规律，揭示机械剪切作用下软硬复合界面的弯曲形变、取向角度变化等自适应行为机理及其对摩擦各向异性的影响机制，研究通过外场调控仿生软硬复合取向结构表界面摩擦学行为实现定向驱动和移动的技术，发展仿生软硬复合取向结构表界面材料及摩擦调控技术，为定向驱动/移动等功能界面和机构设计及其在智能仿生机器人、软机器人等领域应用提供理论指导和技术支持。

自然界经过亿万年的进化，生物表界面存在的软硬复合取向微结构及其各向异性摩擦行为对其行走、移动和传播等生物功能息息相关。因此，本项目以麦芒、马面鱼鱼皮以及其他生物表界面为仿生对象，利用3D打印先进制造技术与传统模板复制相结合的方法，结合发展的3D打印氰酸酯/异氰酸酯、聚酰亚胺、高强韧水凝胶与聚二甲基硅氧烷（PDMS）硅橡胶等新型软硬材料，制备了仿麦芒结构体、PDMS与丙烯酸酯相结合的硬结构-软基底表界面、PLA@Fe3O4 基底软硬可调控的仿生表界面以及动态形状记忆图案等多种用于研究各向异性摩擦的仿生表界面。相关摩擦学研究表明，相对于单一的硬结构-硬基底表界面，软硬复合表界面具有更低的摩擦力，但却有更显著的各向异性摩擦行为。同时，通过引入Fe3O4纳米光热颗粒、形状记忆聚合物（SMP）等智能材料，使得制备的仿生表界面在不同温度、远程光照等外部刺激条件下实现各向异性摩擦力的实时动态调控，如PLA@Fe3O4复合表界面在0.5 N载荷下通过控制近红外光（NIR）的开关可实现摩擦力从~0.53 N到~0.25 N的实时转变，而SMP@Fe3O4复合表界面则在80oC条件下摩擦各向异性行为几乎消失，但在近红外光照射下能够实现摩擦力从~0.63 N到~0.2 N的实时转变，表现出了优异的摩擦动态调控行为以及摩擦力的各向异性可控性。在此基础上，发展了在外部震动、橡胶管内的应力拉伸-松弛过程中的定向移动、以及近红外光控制下的实时制动与往返移动等智能摩擦驱动器件。如通过优化仿麦芒结构体的倒刺密度、尺寸、倾斜角等因素，在最大各向异性摩擦力作用下，一个质量仅0.01 g的3D打印仿麦芒模型体，可驱动质量高达120 g的货物在克服水平摩擦力的条件下产生定向移动。而SMP@Fe3O4复合表界面在震动条件下通过NIR光照~7 s可实现快速的往返移动，表现出了摩擦器件的智能性与可控性。本项目的实施，为软体机器人、仿生机器人在材料表界面设计、定向驱动、及其智能摩擦调控等应用领域的发展提供理论指导和技术支持。