A bioinspired microdevice unifying energy storage and actuation through hydration control

Biological systems seamlessly integrate energy storage and actuation within compact architectures, whereas synthetic approaches largely implement these functions as separate components. Conjugated polymers can couple both, yet their operation relies on ion insertion accompanied by hydration water within the polymer backbone, creating an intrinsic trade-off between performance and stability. Here we show that anion hydration governs this trade-off. In-operando Raman spectroscopy and time-resolved mass measurements reveal that reducing anion hydration suppresses water ingress, mitigates backbone degradation and converts the polymer response from a two-step swelling process into a single, rapid volumetric relaxation. Leveraging this principle, we realize a sub-millimetre monolithic device that integrates energy storage and actuation within a 0.56 mm² footprint. A centrally configured dual-cell microbattery delivers 161 mAh cm^-2 and reduces the energy consumption of surrounding actuators by fourfold. Hydration control, as the governing design parameter for multifunctional devices, holds translational promise for integrated energy-motion architectures at the microscale.