Fig. 5. (a) Optimization of shark single denticle. The flow velocity of the optimized denticle in the wake area is more uniform. Also, the denticles act as vortex generators to energize the boundary layer to reduce the drag. Reproduced from ref. 89 with permission from IOP Publishing Ltd, copyright 2019. (b) Flexible shark skin and bristled shark denticles (magnified 40 times). Reproduced from ref. 36 with permission from Marine Technology Society Inc., copyright 2008. (c) The evolution of fluid in the fish-spindle form. Laminar flow to turbulent flow and then to boundary layer separation to form a wake area. Comparing the non-smooth surface on the axis with the smooth surface under the axis, it has been found that the denticles control the separation of the boundary layer to decrease the wake area, thereby reducing the pressure drag. Reproduced from ref. 11 with permission from the Royal Society, copyright 2014.