A team at the Wyss Institute is honing a tough, rubbery hydrogel initially developed at Harvard’s School of Engineering and Applied Sciences. The gel is 90 percent water, yet it stretches without breaking to more than 20 times its original length and recoils like rubber, the researchers first reported in Nature in 2012. In fact, a tough hydrogel as thin as a nickel can rebound a stainless steel ball bearing dropped from more then seven feet. The gel combines two different types of polymers – a seaweed extract called alginate that is used to thicken food, and polyacrylamide, the main material in soft contact lenses. Each of these polymers alone form a soft, weak gel, but when combined they become entangled, creating a molecular network – and therefore a gel -- that is far stronger and more resilient. What’s more, this tough new gel is safe when implanted into the body, the researchers reported in 2013 in Biomaterials. Potential applications: • Replace cartilage for knee surgery • Stand in for injured spinal disks • Replace injured tendons and ligaments • Repair wounds • Deliver drugs to tissues

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