Fully-Coupled Transient Fluid–Solid Interaction Simulation of the pH-Sensitive Hydrogel-Based Microvalve

The pH-sensitive hydrogels are attractive candidates to act like a microvalve in microfluidic devices. In this study, we build a theory for the transient simulation of a pH-sensitive hydrogel-based microvalve. Three fields are involved in the theory, namely the electrochemical, mechanical and fluid fields. We utilize the Nernst–Planck equation to describe the ionic flux into the hydrogel through diffusion, electrical migration and convection. We model the hydrogel as a compressible isotropic hyperelastic material with the Gent model. Then we implement the theory in a nonlinear finite element framework to simulate the time-dependent fluid–solid interaction (FSI) behavior of the pH-sensitive microvalve. Our focus is on exploring the physics and phenomena involving in the simulation rather than simulating a complex geometry or presenting a new design. We manifest the significance of the FSI by comparing the transient FSI and non-FSI simulation of the microvalve. The most highlighted novelty of our study is accounting for time-dependent effects. The results demonstrate that the microvalve perfectly closes the channel much before it reaches its stationary state and the closing state, which is of high interest in the microvalve study is different from the stationary state.