Biocompatible low-voltage electrothermal actuators with biological operational temperature range

Muscle loss can severely affect movement and physiological functions, driving interest in artificial muscle development. Although various soft actuators exist, ensuring biocompatibility-especially in terms of heat transfer and non-cytotoxicity-remains a key challenge. To address these issues, here we develop Bio35, a low-voltage (3.6 V) electrothermal actuator that operates at mild hyperthermic temperatures (38.9 °C). Bio35 is synthesized using a one-pot, solvent-free process with Epikote 828, poly(propyleneglycol) bis (2-amino-propyl-ether) (PPG), and 1,4-diamino-diphenyl-sulfone (DDS). It demonstrates high chemical stability, maintaining actuation performance after more than 100 cycles over 200 min. Initial biological tests confirm that these materials are biocompatible and non-cytotoxic. As proof of concept, we demonstrate two systems: a simple gripper capable of holding objects up to 225 mg and a sphincter-like valve, showcasing its potential for use in treating conditions like urinary incontinence, where precise, muscle-like actuation is critical for function.