When the metal core of the fiber breaks, the material doesn’t fail – the polymer sheath absorbs the strain between the breaks in the metal and transfers the stress back to the metal core. Source: Michael Dickey, North Carolina State University

A new material that combines the elasticity of rubber with the strength of a metal could prove of value in soft robotics and textile development applications. The fiber replicates the mechanics of collagen and other strong biological materials, and is capable of stretching up to seven times its length without breaking.

North Carolina State University materials engineers encased a gallium metal core in an elastic sheath composed of poly(styrene-ethylene butylene-styrene). The fiber features the strength of the metal core when under stress, and if the core breaks, the polymer sheath absorbs the strain and transfers the stress back to the metal component. The new material is tougher than either the metal or polymer alone as it can absorb and dissipate energy and deform without breaking.

The fiber was demonstrated to be 2.5 times tougher than titin, the giant protein responsible for the passive elasticity of human muscle, and to hold more than 15,000 times its weight for 100 times longer than a hollow polymer fiber. Fabrication features relatively simple and low-cost chemistry without the need for polymer synthesis or complex structural architectures such as interpenetrating polymer networks.

The research is published in Science Advances.