An octopus tentacle bends, grabs, and stretches — all without a single bone. The secret is that inside it, sections that contract alternate with sections that remain passive. Scientists have long tried to replicate this trick in artificial materials, but until now they couldn't precisely dictate how a material would change shape.
Now researchers have proposed 3D-printing elastic threads from two materials at once. One of them, a liquid crystal elastomer, shrinks along a specific direction when heated, like a released rubber band. The second material stays unchanged. The arrangement of these materials inside the thread defines its 'memory': when heated, the thread bends and twists exactly as intended. Scientists can control bending in two planes and twisting independently at each cross-section of the thread.
From such threads, they assembled lattices whose cells consist of wavy bent threads. When heated, some lattices contract, others expand, and still others bulge out of plane. A computer model accurately predicts the lattice's behavior if the properties of each thread are known.
This is a step toward materials that change shape without motors and wires, like pea tendrils that wrap around a support, or an elephant's trunk that reaches for a leaf.
Liquid crystal elastomers can contract several times when heated, like a muscle, but they don't require electricity, just heat is enough.
In the movie 'Terminator 2', liquid metal changes shape on command — printed threads make a first step toward such materials, only they are controlled by heat, not a chip.