Biophysical properties of the dolphin skin reveal an eco-friendly defouling cycle

The rheological properties of the dolphin skin were analysed with particular emphasis on its fouling release performance. Employing stress-controlled rheometry deformability and stress resistance of skin material was measured. Results obtained showed that the skin material behaved like a yield stress fluids, whereby the yield point varied between 3 8 x 10^3 Pa. It was concluded from this result obtained that the structural stability and integrity of the skin was dependent on the hydrodynamic stress load. During swimming (2 - 80 Pa) and jumping of the dolphin, the skin is able to withstand various stresses (< 3 8 x 10^3 Pa). Cohesive failure occurs, if the stress exceeds the limit 3 8 x 10^3 Pa. Since attached marcofoulers, for example, barnacles transfer tension and shear stress from their base to the skin of the swimming dolphin in the same amount, the yield point characteristics ensures that cohesive failure of the skin is limited to the fouling situation. However, the mechanial failure of the covalently cross-linked skin material is irreversible and its renewal is mainly a consequence of the perpetually ongoing cell shedding process. With respect to the technical application this pseudo-reversible cycle was simulated by applying materials known as Bingham fluids. Application notes are presented how to design non-toxic defouling fluids with dolphin-like deformability and flow point characteristics