Peer into any fishbowl, and you'll see that pet goldfish and guppies have nimble fins. With a few flicks of these appendages, aquarium swimmers can turn in circles, dive deep down or even bob to the surface.
Researcher from the University of Colorado Boulder have uncovered (Science Robotics) the engineering secrets behind what makes fish fins so strong yet flexible. The insights could one day lead to new designs for robotic surgical tools or even airplane wings that change their shape with the push of a button. The fins are remarkable as they achieve feats of dexterity even though they don't contain a single muscle.
The fins are made of many stiff 'rays’ and each of the rays can be manipulated individually just like the fingers, but there are 20 or 30 of them in each fin.
They report that the key to fish fins may lie in their unique design. Each ray in a fin is made up of multiple segments of a hard material that stack on top of much softer collagen, making them the perfect balance between bouncy and stiff.
Each of the rays in a fin in Goldfish has a layered structure, a bit like a bakery éclair: The spikes include two layers of stiff and mineralized materials called hemitrichs that surround an inner layer of spongy collagen. But those layers of hemitrichs aren't solid. The engineer and his team decided to use computer simulations to examine the mechanical properties of fins. They discovered that those segments can make all the difference.
