An Analytical Solution and FEM Simulation for the Behavior of Sensitive FG Micro-valve in Response to pH Stimuli

In this paper, an analytical solution and a numerical simulation of the pH-sensitive hydrogel micro-valves exposed to pH variation are proposed. Case studies consist of micro-valve with homogeneous single-layer and FG hydrogel as the active part. The results of both methods are in good agreement indicating the validity of both methods. In addition, The numerical and analytical solutions were compared between two ranges of cross-linking densities of hydrogels. In order to reach a convergent solution for the finite element model of the micro-valve, the hydrogel layer is considered to have a number of different layers, and an appropriate number of layers are considered. In the next step, parameters affecting the micro-valve behavior are studied, which are the dimensionless thickness ratio, the number of acidic groups in the network, and the salt molarity of the external solution. The findings show that as the thickness ratio, number of acidic groups, and salt concentration in the external solution result increases, the hydrogel part of the micro-valve experiences a higher degree of swelling and deformation, which should be considered when designing these devices.