https://www.smithsonianmag.com/innovation/shark-skin-inspired-materials-have-a-long-way-to-go-before-they-work-like-the-real-thing-180980973/

Few people have gotten close enough to a shark to pet it. If you could run your hand from a shark’s head to its tail—not that you should—it would feel smooth, almost like suede. Reverse direction and it’s rough like sandpaper. Viewed under a microscope, shark skin is composed of ribbed, dragonesque scales layered over each other like shingles on a roof. These structures, called dermal denticles, are more like teeth than skin