Investigating the Decay Mechanism in Sodium Alginate-Based Artificial Muscles: Modeling and Analysis of Mechanical-Actuation Coupling

Bionic artificial muscles often face a major challenge: their performance tends to degrade over prolonged or cyclic operation. In this study, we zero in on sodium alginate (SA) based artificial muscles, aiming to systematically uncover the mechanisms behind this degradation by developing a comprehensive model that couples mechanical and actuation dynamics. We also take a close look at how nickel doping can help modulate and even enhance the material's performance. Through both single-stage and bidirectional voltage excitation experiments, we observe clear degradation patterns. A dynamic model is established, which incorporates the influence of electrochemical polarization and viscoelastic behavior with experimental data accurately fitted using the Levenberg-Marquardt algorithm. The results show that nickel doping significantly boosts the output force and material robustness by facilitating efficient charge transfer. That said, under high-voltage bidirectional excitation, the same doping may compromise the structural stability. From both theoretical and experimental perspectives, this study offers a systematic analysis of the coupled mechanics-actuation degradation mechanism in bionic artificial muscles, contributing a modeling foundation and design guidance for developing high-performance, long-life flexible actuators suited for robotics and biomedical applications.