Theoretical analysis of a parallel-plate electroosmotic hydrogel actuation and sensing platform

This paper addresses the dynamic electrical response of a charged or uncharged hydrogel that is sandwiched between a bottom fixed plate and a top floating, parallel plate. We demonstrate how this configuration might be adopted as a novel chemical- or bio-sensing platform. It might also be used for nano-positioning, or for studying the rheology and physiochemical characteristics of hydrogels. Here, the gel is modelled as a continuum composite comprising a porous, charged, elastic skeleton saturated by an aqueous electrolyte. Electrostatics satisfy the Debye–Hückel approximation, with zero-slip boundary conditions between the skeleton, solvent, and walls. For large channel gaps, the steady electric-field-induced displacement of the top plate is proportional to the difference between the top- and bottom-wall ζ-potentials. Under oscillatory electrical stimulation, resonant peaks, with amplitudes from picometers to micrometers, reflect hydrogel elasticity and charge density. Such displacements are within the detection range of modern interferometric displacement sensors.