Molly Shoichet searches her desk for a sandwich-sized zip-up bag. Stowed in the bag is a syringe containing roughly 2 millilitres of a rich-turquoise fluid. She pops the cap off the needle and pushes the plunger gently until a small bead of the material emerges. She tilts the syringe upside down, but the tiny bulb stays put. Almost instantly, the liquid had transformed into a gel - one that Shoichet hopes will be able to deliver drugs directly to the brain. The material in the syringe is a three-dimensional network of polymers called a hydrogel. It is a viscous fluid when flowing down a narrow-gauged needle, but becomes a gel once it has been injected into the body. "It's important that it gels quickly, so that it doesn't disperse too widely," says Shoichet, a polymer chemist and biomedical engineer at the University of Toronto in Canada.
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