Fish fins are educating us the key to versatile robots and new shape-changing supplies

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By Francois Barthelat

Flying fish use their fins each to swim and glide by the air. Smithsonian Establishment/Flickr

The large thought

Segmented hinges within the lengthy, skinny bones of fish fins are essential to the unimaginable mechanical properties of fins, and this design might encourage improved underwater propulsion techniques, new robotic supplies and even new plane designs.

A pink and pale colored fish tail with thin lines radiating out from the base.
The skinny traces within the tail of this crimson snapper are rays that permit the fish to manage the form and stiffness of its fins.
Francois Barthelat, CC BY-ND

Fish fins usually are not easy membranes that fish flap proper and left for propulsion. They most likely signify one in every of essentially the most elegant methods to work together with water. Fins are versatile sufficient to morph into all kinds of shapes, but they’re stiff sufficient to push water with out collapsing.

The key is within the construction: Most fish have rays – lengthy, bony spikes that stiffen the skinny membranes of collagen that make up their fins. Every of those rays is made from two stiff rows of small bone segments surrounding a softer inside layer. Biologists have lengthy identified that fish can change the form of their fins utilizing muscular tissues and tendons that push or pull on the bottom of every ray, however little or no analysis has been completed wanting particularly on the mechanical advantages of the segmented construction.

A pufferfish makes use of its small however environment friendly fins to swim towards, and maneuver in, a robust present.

To check the mechanical properties of segmented rays, my colleagues and I used theoretical fashions and 3D-printed fins to check segmented rays with rays made from a non-segmented versatile materials.

We confirmed that the quite a few small, bony segments act as hinge factors, making it straightforward to flex the 2 bony rows within the ray aspect to aspect. This flexibility permits the muscular tissues and tendons on the base of rays to morph a fin utilizing minimal quantities of pressure. In the meantime, the hinge design makes it laborious to deform the ray alongside its size. This prevents fins from collapsing when they’re subjected to the stress of water throughout swimming. In our 3D-printed rays, the segmented designs have been 4 occasions simpler to morph than steady designs whereas sustaining the identical stiffness.

Photos of a straight ray and a bent ray showing how pulling on one half and pushing on the other half of a ray will make it bend.
The segmented nature of fish fin rays permits them to be simply morphed by pulling on the backside of the ray.
Francois Barthelat, CC BY-ND

Why it issues

Morphing supplies – supplies whose form may be modified – are available two varieties. Some are very versatile – like hydrogels – however these supplies collapse simply once you topic them to exterior forces. Morphing supplies will also be very stiff – like some aerospace composites – but it surely takes loads of pressure to make small modifications of their form.

Image showing how 3D printed continuous and segmented fin rays bend.
It requires way more pressure to manage the form of a steady 3D-printed ray (prime two photos) than to morph a segmented ray (backside two photos).
Francois Barthelat, CC BY-ND

The segmented construction design of fish fins overcomes this purposeful trade-off by being extremely versatile in addition to sturdy. Supplies primarily based on this design may very well be utilized in underwater propulsion and enhance the agility and velocity of fish-inspired submarines. They is also extremely precious in comfortable robotics and permit instruments to vary into all kinds of shapes whereas nonetheless having the ability to grasp objects with loads of pressure. Segmented ray designs might even profit the aerospace discipline. Morphing wings that would seriously change their geometry, but carry giant aerodynamic forces, might revolutionize the way in which plane take off, maneuver and land.

What nonetheless isn’t identified

Whereas this analysis goes a great distance in explaining how fish fins work, the mechanics at play when fish fins are bent removed from their regular positions are nonetheless a little bit of a thriller. Collagen tends to get stiffer the extra deformed it will get, and my colleagues and I believe that this stiffening response – along with how collagen fibers are oriented inside fish fins – improves the mechanical efficiency of the fins when they’re extremely deformed.

What’s subsequent

I’m fascinated by the biomechanics of pure fish fins, however my final purpose is to develop new supplies and units which are impressed by their mechanical properties. My colleagues and I are at present growing proof-of-concept supplies that we hope will persuade a broader vary of engineers in academia and the personal sector that fish fin-inspired designs can present improved efficiency for a wide range of purposes.

The Conversation

Francois Barthelat doesn’t work for, seek the advice of, personal shares in or obtain funding from any firm or group that may profit from this text, and has disclosed no related affiliations past their educational appointment.

This text appeared in The Dialog.

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The Dialog
is an impartial supply of reports and views, sourced from the educational and analysis group and delivered direct to the general public.

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