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The phenomenon of back-relaxation in ionic polymer metal composites (IPMCs) has attracted the interest of\ud the scientific community for two decades, but its physical origins largely remain elusive. Here, we propose an\ud explanation of this phenomenon based on Maxwell stress. From first principles, we demonstrate that IPMC\ud actuation is controlled by the nonlinear interplay between osmotic and electrostatic phenomena. While\ud osmotic pressure tends to produce a rapid bending toward the anode, Maxwell stress generates a slow\ud relaxation toward the cathode. The relative weight of these phenomena is determined by the applied voltage.\ud At voltage levels comparable to the thermal voltage, IPMC actuation is dominated by osmotic effects. As the\ud applied voltage is increased, Maxwell stress overcomes the osmotic pressure, leading to back-relaxation

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The role of endogenous bioelectricity in morphogenesis has recently been explored through the finite volume-based code BioElectric Tissue Simulation Engine . We extend this platform to electrostatic and osmotic forces due to bioelectrical ion fluxes, causing cell cluster deformation. We further account for mechanosensitive ion channels, which, gated by membrane tension, modulate ion fluxes and, ultimately, bioelectrical forces. We illustrate the potentialities of this combined model of actuation and sensing with reference to cancer progression, osmoregulation, symmetry breaking and long-range signalling. This suggests control strategies for the manipulation of cell networks in vivo .