Biomimetic shark skin: design, fabrication and hydrodynamic function

Abstract

Although the functional properties of shark skin have been of considerable interest to both biologists and engineers because of the complex hydrodynamic effects of surface roughness, no study to date has successfully fabricated a flexible biomimetic shark skin that allows detailed study of hydrodynamic function. We present the first study of the design, fabrication and hydrodynamic testing of a synthetic, flexible, shark skin membrane. A three-dimensional (3D) model of shark skin denticles was constructed using micro-CT imaging of the skin of the shortfin mako (Isurus oxyrinchus). Using 3D printing, thousands of rigid synthetic shark denticles were placed on flexible membranes in a controlled, linear-arrayed pattern. This flexible 3D printed shark skin model was then tested in water using a robotic flapping device that allowed us to either hold the models in a stationary position or move them dynamically at their self-propelled swimming speed. Compared with a smooth control model without denticles, the 3D printed shark skin showed increased swimming speed with reduced energy consumption under certain motion programs. For example, at a heave frequency of 1.5 Hz and an amplitude of ±1 cm, swimming speed increased by 6.6% and the energy cost-of-transport was reduced by 5.9%. In addition, a leadingedge vortex with greater vorticity than the smooth control was generated by the 3D printed shark skin, which may explain the increased swimming speeds. The ability to fabricate synthetic biomimetic shark skin opens up a wide array of possible manipulations of surface roughness parameters, and the ability to examine the hydrodynamic consequences of diverse skin denticle shapes present in different shark species.

Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model

“…The "self-propelled" condition (sensu [17,19,31,33,[37][38][39]) describes a state of steady swimming, where thrust and drag forces balance, and so the fish experiences zero net forces or torques. For a swimming body, this steady-state condition is met at a characteristic swimming speed for each motion program type (i.e., combination of heave amplitude, flapping frequency, and pitch program), called the self-propelled speed (SPS).…”

Investigation of Fish Caudal Fin Locomotion Using a Bio-Inspired Robotic Model

“…By isolating critical factors we can focus on the effect of a single element without the need for processing of complex data that incorporate too many irrelevant factors. Many studies have already successfully applied robotic models to the investigation of the mechanisms behind fish swimming [35][36][37][38].…”

Textiles: Fabrics of life

“…Swimwear companies such as Speedo have claimed to make shark-skin-like fabrics, but George Lauder, an ichthyologist at Harvard University, has demonstrated that the Speedo suits that were banned after the 2008 Olympics do not contain the microscopic shark scales, called denticles, that reduce drag 5 . Using a threedimensional (3D) printer, Lauder last year constructed true artificial skin of the shortfin mako shark (Isurus oxyrinchus) and showed that it not only limits drag but also increases thrust 6 .…”