Wang Lixin, Tao Dashuai, Dong Shiyun, Li Shanshan, Tian Yu
School of Mechanical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, People's Republic of China.
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, People's Republic of China.
R Soc Open Sci. 2018 Sep 5;5(9):180766. doi: 10.1098/rsos.180766. eCollection 2018 Sep.
slippery zone presents surface anisotropy depending on its specialized structures. Herein, via macro-micro-nano scaled experiments, we analysed the contributions of lunate cells and wax crystals to this anisotropy. Macroscopic climbing of insects showed large displacements (triple body length within 3 s) and high velocities (6.16-20.47 mm s) in the inverted-fixed (towards digestive zone) slippery zone, but failed to climb forward in the normal-fixed (towards peristome) one. Friction force of insect claws sliding across inverted-fixed lunate cells was about 2.4 times of that sliding across the normal-fixed ones, whereas showed unobvious differences (1.06-1.11 times) between the inverted- and normal-fixed wax crystals. Innovative results from atomic force microscope scanning and microstructure examination demonstrated the upper layer of wax crystals causes the cantilever tip to generate rather small differences in friction data (1.92-2.72%), and the beneath layer provides slightly higher differences (4.96-7.91%). The study confirms the anisotropic configuration of lunate cells produces most of the anisotropy, whereas both surface topography and structural features of the wax crystals generate a slight contribution. These results are helpful for understanding the surface anisotropy of slippery zone, and guide the design of bioinspired surface with anisotropic properties.
光滑区域因其特殊结构呈现出表面各向异性。在此，通过宏观 - 微观 - 纳米尺度的实验，我们分析了新月形细胞和蜡晶体对这种各向异性的贡献。昆虫在倒置固定（朝向消化区）的光滑区域进行宏观攀爬时，表现出较大的位移（3秒内达到三倍体长）和较高的速度（6.16 - 20.47毫米/秒），但在正常固定（朝向口缘）的光滑区域无法向前攀爬。昆虫爪子在倒置固定的新月形细胞上滑动的摩擦力约为在正常固定的新月形细胞上滑动摩擦力的2.4倍，而在倒置和正常固定的蜡晶体上滑动时摩擦力差异不明显（1.06 - 1.11倍）。原子力显微镜扫描和微观结构检查的创新结果表明，蜡晶体的上层使悬臂尖端产生的摩擦数据差异较小（1.92 - 2.72%），而下层产生的差异略高（4.96 - 7.91%）。该研究证实新月形细胞的各向异性构型产生了大部分的各向异性，而蜡晶体的表面形貌和结构特征也有轻微贡献。这些结果有助于理解光滑区域的表面各向异性，并指导具有各向异性特性的仿生表面的设计。
