The skin of sea cucumbers was the inspiration for a new material that can change dramatically from rigid to floppy when soaked in water.
The material could be useful for brain implants that cause less inflammation, researchers say. A version switched by electric pulses that is currently in development could find many more uses 鈥� such as clothing that morphs into armour.
Sea cucumbers鈥� skin is usually supple, allowing them to slide through narrow spaces between rocks and corals. But when touched a defensive reaction makes their skin go rigid in seconds, thanks to enzymes that binds protein fibres together. A second set of enzymes can break those bonds to make the skin soft again.
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Sea cucumber skin can become more than 10 times stiffer in this way, but the new material can go further 鈥� softening by more than 2500 times. Simply soaking the transparent material in warm water for 15 minutes is all it takes to complete the transformation. After drying out it is identical to its original rigid state.
The new material behaves differently to more common materials that go floppy in water like foam or cardboard. It changes its properties more dramatically and does not take on large amounts of water when soaked.
Cellulose 鈥榳hiskers鈥�
Developed by and of Case Western Reserve University, Cleveland, Ohio, US, the material is a polymer made from two different compounds and shot through with microscopic cellulose fibres. 鈥淚t鈥檚 directly inspired by the sea cucumber,鈥� Rowan says.
鈥淲e have the elastic polymer, so that鈥檚 the mimic for the sea cucumber skin, and then we put in the cellulose whiskers,鈥� Rowan says. 鈥淵ou can get these from paper pulp, but we got ours from another little sea creature called a .鈥�
When dry, the cellulose fibres keep the material rigid by forming a scaffold held together by hydrogen bonds. But water molecules are better at forming such bonds, so when wet, the fibres lose their grip on one another and bond to the water molecules instead.
The material could be useful for electrodes implanted into the brain, such as for patients with Parkinson鈥檚 disease or for brain control interfaces, the researchers say.
Electric switch
The rigid material could easily be inserted into brain tissue, before softening into its floppy state. That would reduce the problems with inflammation solid electrodes can cause.
Rowan says they鈥檙e now working on versions of the material that switch stiffness in response to a pulse of electricity.
鈥淚 think it is one of the most exciting recent opportunities in the design of new materials,鈥� says of the University of California in Santa Barbara, US. 鈥淚t will open the door to applications in a number of different fields.鈥�
鈥淥ne can imagine protective clothing for example, which is flexible and comfortable to wear, but becomes rigid and protective when necessary,鈥� Hawker adds. 鈥淭his is essentially what sea cucumbers use this process for.鈥� of Massachusetts Institute of Technology, US, adds, 鈥減erhaps it could also be used as a stimuli responsive system for drug delivery鈥�.
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