The Preliminary Study on Antifouling Mechanism of Shark Skin

Abstract

Biofouling, which is the result of marine organisms settling, attaching, and growing on submerged marine surfaces, is a usually-seeing phenomenon for the ocean-going ships and submarines. And, it can decrease the range, speed, and maneuverability of these vessels and increase the fuel consumption. Contrarily, the sharks remain largely free of bioadhesion despite spending their entire lives submerged. The sharks have placoid scales, which consist of rectangular base embedded in the skin with tiny spines that poke up from the surface. It is found that this special structure can make great deal of function for antifouling. In our report, parallel works for antifouling mechanisms were motivated by Triakidae shark feeding, observations on shark skin, and the experiments of benthic diatoms adhesion and Mytilus edulis byssus attachment. And, the optical configurations were acquired by using 3D video microscope and environment scanning electron microscope (ESEM). The results showed that, the benthic diatoms adhesion on the naked skin of living sharks was obviously fewer than the dead ones, and could not be found on the surface of placoid scales. As the time progressed, the rate of Mytilus edulis byssus attachment reduced gradually. It was thought that, the water turbulent boundary on the surface was changed greatly and innumerable minimal vortex was generated when the water flow on the shark skin. The strong exchange of momentum in a turbulent boundary layer would produce high-speed lumps approaching the surface, which could develop strong shear stress. Benthic diatoms and mussel could not attached firmly or be cleared easily when the shear stress became stronger than the adhesion power of these organisms. After finding the real working mechanism of antifouling for sharks, it could be used to direct the progresses of synthesizing biomimetic coatings or materials with antifouling performance in the future.