A multifunctional hollow TPU fiber filled with liquid metal exhibiting fast electrothermal deformation and recovery.

Conductive fibers have received considerable interest due to their potential applications in the flexible electronics field. Fabricating a conductive fiber that can realize fast deformation with stretchability for multifunctional applications is still highly appealing. Here, we present a deformable conductive fiber (DCF) fabricated by injecting liquid metal (LM) into a hollow thermoplastic polyurethane (TPU) fiber; the DCF can be shaped into a 2D or 3D shape by an electrothermal method at the thermoplastic transition point of TPU. Combined with the solid-liquid phase transition characteristics of the LM at its melting point, the DCF exhibits a variable shape memory feature at two transition points. We have demonstrated that the double-torsional DCF and the helical DCF can act as a capacitive sensor and an inductive sensor, respectively, and they have both been used for human motion monitoring. In addition, the helical DCF can also act as a stretchable electrode with excellent electrical properties (resistance change <2%) under a maximal mechanical strain of 3300%. Overall, the DCF presents great potential for applications in human motion monitoring, soft robotics and smart electronic textiles.