Tied up in knots: the tiny knotted robot could find applications in agriculture and reforestation. (Courtesy: Bella Ciervo/Penn Engineering) Researchers at the University of Pennsylvania and the University of California, Los Angeles, have created a tiny, soft knot-like fibre that can jump metres into the air . The fibre is less than a millimetre thick, and a few millimetres long and contains a Kevlar core surrounded by a shell of liquid crystal elastomer (LCE). The Kevlar provides strength and stiffness while the LCE adds some flexibility and responsiveness. “People think of a knotted fibre as something passive,” says  Shu Yang from the University of Pennsylvania. “But if you design the elasticity and materials carefully, the knot itself becomes an active system.” When the fibre is knotted it behaves like a spring held in place by a latch, which can be undone via changing the temperature.…