Ooh, strong and stretchy. I like that!
A new material inspired by mussels is flexing its muscles. It can stretch without snapping and repair its own molecular bonds, so it could be useful in robot joints that lift heavy objects, or for packaging to protect delicate cargo from accidental falls.
If you're fond of exploring the sea, you might've noticed these snail-like creatures that hang onto solid surfaces like rocks. Mussels (and some other molluscs) are able to do this thanks to an adhesive protein and tough, plasticky fibres. The latter even enables them to repair themselves when some molecular bonds get broken like when they're hit by a strong wave.
Megan Valentine at the University of California, Santa Barbara, and her colleagues were fascinated by this--so fascinated that they've created a plastic that mimics such. The strength and flexibility of their material lies on molecular bonds between iron and an organic compound called catechol. So, when the material gets hit, such bonds disperse the energy that comes with it. However, the bonds break along the process to make the overall structure intact.
“It’s like a bike helmet: if you’re in a bike accident, the foam inside the helmet crushes and dissipates some of the energy. All that energy that would have gone into a skull fracture, instead goes into the helmet,” says Valentine. “In our case, instead of foam we have this sacrificial bonding that protects the underlying polymer system.”
With these "sacrificial bonds", the material can stretch up to 50 per cent! But it's not entirely goodbye for these iron-catechol bonds for they just easily reform when the stress ends. They make the plastic 770 times stretchier and 58 times stronger while being reusable.
“Typically, there’s a trade-off: you can make a material harder to break but less stretchy, or easier to break and easier to stretch,” says Niels Holten-Andersen at the Massachusetts Institute of Technology. “But by adding these mussel-inspired bonds, they’ve made it so that you don’t have to make that choice.”
This can possibly be used for our packaging and protect fragile objects from shock or even be used as a material for a body armour that repairs itself, Holten-Andersen says. With more research, this can even go a long way and be used for the joints of robotic arms or even help repair the tendons in our joints.
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