Table_2_Ridges and riblets: Shark skin surfaces versus biomimetic models.docx

Shark skin has been an inspiration for biomimetic materials and structures due to its role in reducing drag and enhancing thrust, properties believed to be due to the textured surface composed of ridges on the surface of individual tooth-like scales (denticles). Attempts to replicate the hydrodynamic performance of shark skin have involved manufacturing both engineered riblets and fabrics with textured surfaces. However, there are no studies that compare the surface ornamentation of shark denticles to bioinspired materials. Using three-dimensional surface profilometry we analyzed the cross-sectional profile of the surface of shark denticles at two locations on 17 species and compared these data to values obtained from engineered structures (e.g., riblets) and competition swimsuits that are often proposed as having a comparable surface texture to shark skin. Of the variables measured, crown aspect ratio (p = 0.007), ridge height, ridge spacing, ridge aspect ratio, and ridge bumpiness (all p < 0.001) differed among the three materials. Overall, engineered riblet surfaces were very different than biological shark skin. Some of the competition swimsuit materials were more shark-like, with the fabric texture having similar height variation, but with irregular ridge spacing. Cross-sectional profile, which includes pathlength and aspect ratio in addition to ridge spacing and height, is an important feature of the skin’s surface, affecting water flow over the individual denticles, and future research will address these parameters. Quantitative 3D analysis of the surface of real shark denticle ridges enables the design of more biomimetic engineered shark skin surfaces.

鲨鱼皮肤凭借其减阻增推的特性，长期以来都是仿生材料与结构的重要灵感来源，这类性能被认为源自其表面由齿状鳞片（denticles）构成的纹理结构。此前为复刻鲨鱼皮肤的流体力学性能，学界已开展了多项制造工程化肋条（riblets）与带纹理表面织物的研究。然而，目前尚无研究将鲨鱼齿状鳞片的表面纹饰与仿生材料进行系统性对比。本研究采用三维表面轮廓测量技术，分析了17个鲨鱼物种的两处不同位置的齿状鳞片表面横截面轮廓，并将所得数据与工程结构（如肋条）以及常被宣称具备与鲨鱼皮肤相近表面纹理的竞技游泳衣材料进行对比。在所测量的各项变量中，冠部长宽比（p = 0.007）、脊高、脊间距、脊部长宽比以及脊部起伏度（所有p < 0.001）在三类材料间均存在显著差异。整体而言，工程化肋条表面与天然鲨鱼皮肤的差异显著。部分竞技游泳衣材料的纹理更接近鲨鱼皮肤，其织物纹理具备相似的高度变化，但脊间距并不规则。横截面轮廓（除脊间距与高度外，还涵盖路径长度与长宽比）是皮肤表面的重要特征，会影响水流在单个齿状鳞片表面的流动状态，未来的研究将针对这些参数展开深入探索。对真实鲨鱼齿状鳞片脊部表面开展定量三维分析，可为设计更具仿生效果的工程化鲨鱼皮肤表面提供支撑。