Enhanced Hill's Muscle Model for Tissue‐Engineered Skeletal Muscle and its Application to Reverse‐Action Tweezers Actuation

Many bioactuator studies focus on muscle tissue construction, with limited attention to control engineering aspects. This study develops an enhanced Hill's muscle model (EHMM) for tissue‐ engineered skeletal muscle (TESM) to account for mechanical property changes between the static and contracted states. First, the conventional Hill's muscle model (CHMM), a widely used model for native muscle, is applied to TESM. However, parameters determined from the elongation test fail to reproduce the rapid rise and fall of tension observed in isometric contraction tests. To address this, next, a seven‐element EHMM is introduced, incorporating an active viscoelastic branch in parallel with the static branch to represent actin–myosin interactions. In the former branch, both contractile and viscoelastic elements scale with muscle activity, fatigue decay, and length dependence, modeling viscoelastic changes during contraction. Since the viscous element in the active branch has a negligible effect, it is removed to yield a six‐element EHMM. For the reverse‐action tweezer structure driven by TESM, the displacement predicted by the CHMM is greatly overestimated, whereas the six‐element EHMM results closely match the experimental data. The developed model thus provides a physiological description of TESM contraction and a basis for future research on feedback control and advanced biohybrid actuator development.