Parallel-Stranded Spiral Structure of Artificial Muscle Based on Polyethylene Fiber and Silver-Plated Nylon Wire

Electrothermal polymer artificial muscle has drawn great attention because of its unique structure for imitating the functions of natural muscles with the external thermal stimulus. Herein, we develop a thermal responsible twisted and coiled polymer fiber-based artificial muscle. In brief, the polyethylene fibers and silver-plated nylon wire are prepared; these types of fibers are twisted causing coil nucleation and ultimately nucleation of supercoils to obtain novel parallel-stranded spiral structure of artificial muscle (PE@SPN fiber artificial muscle). The excellent electrothermal property of silver-plated nylon wire contributed to the superior performance of the actuator compared to nickel wire and copper wire. The composite yarn actuator generates contractile strokes of up to 11% under 2.5 Mpa tension and outputs 140 J/kg energy density; the composite yarn actuator can work at ambient temperature about to 50 ℃ with high contractile stroke and long-term stability. In contrast to previous fiber actuators based on PA6 fishing line and sewing thread, which are normally operated at 100 ℃, the actuator based on PE@SPN fiber artificial muscle is operated at a temperature of about 50 ℃. Meanwhile, a bionic elbow joint is designed and driven by the actuator based on polyethylene fiber. We successfully demonstrate the flexion/extension of finger by using the actuation of PE@SPN fiber artificial muscle. The results of experiments show that the promise as a soft actuator towards prosthetics, wearable robot, and power-assisted device applications.