Shark scales are made of a hard material called dentin. Basically, the scales are tiny teeth. They all point backward, so a shark would feel smooth if you dared to stroke it from head to tail, but rough if you ran your hand the other way.
Studies have found that the scales act as armor for a shark and also create tiny vortices that reduce drag to make them faster. The scales also allow sharks to swim silently compared to other fish that generate considerable noise when they ply the water.
The design has proved useful to humans in many ways.
Norwegians applied real shark skin to the soles of their boots to prevent slippage on wet ship decks. In the 2000 Olympics, swimmers began wearing full-body suits modeled on shark skin....
Shark skin has been used by many cultures as sandpaper. It's kept shipmates safe in slippery-when-wet conditions. Swimsuits modeled on shark skin are said by Speedo to reduce drag by up to 4 percent.
Now, research by two separate groups could lead to synthetic shark skin that would make ships and submarines faster and less expensive to operate.
If the research pans out, submarines -- already stealthy and shark-like -- could become even more so.
http://www.livescience.com/technology/050715_shark_skin.html