Shape-Memory Actuation in Aligned Zirconia Nanofibers for Artificial Muscle Applications at Elevated Temperatures

Artificial muscle is one of the key technologies to accelerate the development of robotics, automation, and artificial-intelligence-embedded systems. This work aims to develop shape-memory ceramic (SMC) nanofiber-based coiled yarns for artificial muscle applications at elevated temperatures. Highly aligned SMC nanofiber (zirconia-based) yarns and springs have been successfully fabricated by electrospinning. The microstructure and tensile properties of the SMC nanofibers and the shape-memory actuation performance of the SMC yarns/springs have been characterized. A significant shape-memory effect with a recoverable strain of up to ∼5% and short recovery time (0.16 s) has been demonstrated in the SMC yarns at actuation temperatures of 328–388 °C. The SMC springs can lift up to 87 times their own weight when heated by a Bunsen burner, and the stroke is ∼3.9 mm. The SMC yarns/springs exhibit an output stress of 14.5–22.6 MPa, a work density of ∼15–20 kJ//m³, and a tensile strength of ∼100–200 MPa, which are much higher than those of human muscles and some other polymer-based artificial muscles. Benefiting from the advantages of large output stress, high tensile strength, high actuation temperatures, and fast response, the SMC nanofiber-based yarns/springs have a great potential to be used as artificial muscles at elevated temperatures.