Cyclical Electrical Stimulation of Hydrogel Microactuators Employing Parylene-N Coated Electrodes

This work presents the cyclical actuation of electric field sensitive microscale hydrogels employing dielectric coated coplanar electrodes. Microscale hydrogels are photopolymerized in-situ, and AC frequency-based actuation combined with pulse width modulation enabled controlled manipulation of hydrogel deformation. Stable actuation cycles are achieved with applied electric potentials from 20 V_pk-pk to 40 _Vpk-pk, with a maximum true strain of 29% and a minimum rise time of 4.7 s. The peak and trough osmotic pressure for each system´ s cycle is also analytically determined, with a peak pressure at 40 V_pk-pk of 201.1±38.3 kPa. A plateau in the peak-to-trough true strain is observed above 30 V_pk-pk. For comparative purposes a system without dielectric coated electrodes and employing external syringe pumps is also examined, and stable cyclical actuation was achieved for applied electric potentials of 5 V_pk-pk and 10 V_pk-pk. For this system the maximum stable rise time, true strain, and osmotic pressure are 8.1 s, 57%, and 429.2±81.9 kPa, respectively. The difference between the two systems highlights how optimization of the dielectric layer´s thickness and uniformity can further enhance actuation performance. The electronically responsive hydrogel-based cyclical actuator developed within this work could be further employed for microfluidic regulation in portable low-power systems.