Many marine organisms have been an inspiration for the design of bioinspired robots and other structures. Shark skin is one such organism due to its role in reducing drag and enhancing thrust. Researchers believe these properties are due to the textured surface composed of ridges on the surface of individual tooth-like scales, called denticles. Understanding the desing of shark skin can assist in developing bioinspired materials to the hulls of both surface and underwater vehicles to reduce the energetic cost of moving through water.
Attempts to replicate the hydrodynamic performance of shark skin have involved manufacturing both engineered riblets and fabrics for competition swimsiuts, that are often proposed as having a comparable surface texture to shark skin, with textured surfaces. However, there are no studies that compare the surface ornamentation of shark denticles to bioinspired materials.
In a new study in Frontiers in Marine Science postdoctoral researcher Molly K. Gabler-Smith and Professor George Lauder used three-dimensional surface profilometry to analyze the cross-sectional profile of the surface of shark denticles at two locations on 17 species. They then compared these data to values obtained from engineered structures (e.g., riblets) and competition swimsuits. Of the variables measured, crown aspect ratio, ridge height, ridge spacing, ridge aspect ratio, and ridge bumpiness differed among the three materials.
Overall, engineered riblet surfaces were very different from 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.
There are few data published on hydrodynamic flow patterns over shark skin. Gabler-Smith and Lauder future experiments include measuirng flow over shark skin with different surface textures, especially under dynamic conditions. This is a key stip in understanding the effect of shark skin-inspired designs.
Image: "Shark" by Enrico Strocchi, Lisbon Oceanarium on Flickr