Soft Magnetic Artificial Muscles with High Work Density and Actuation Strain via Dual Cross-Linking Design

Abstract

Soft artificial muscles offer transformative potential in robotics, wearable electronics, and biomedical devices due to their light weight, mechanical compliance, and multidirectional actuation. However, their broader utility is hindered by an intrinsic trade-off between stretchability and energy output, often resulting in limited work densities. Here, a high-performance magnetic composite actuator is presented that addresses this limitation through an optimized dual cross-linked polymer network comprising covalent bonds and dynamic physical interactions. The actuator incorporates a stiffness-tunable polymer matrix embedded with surface-functionalized magnetic microparticles, enabling reversible, on-demand stiffness modulation and reprogrammable actuation. This composite architecture achieves exceptional deformability (elongation at break of 1274%) and programmable stiffness switching from 213 kPa to 292 MPa (switching ratio of 1.37 x 103), with shape fixation exceeding 99%. Together, these properties yield a work density of 1150 kJ m-3 and an actuation strain of 86.4%, representing one of the highest values reported for soft artificial muscles. It also supports loads exceeding 4000 times its own weight, demonstrating a powerful and reconfigurable platform for next-generation soft actuation.