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Hydrogels are categorized as soft materials that undergo large deformation when they are subjected to even minor external forces. In this work, the performance of a variety of micro-valves, based on pH-sensitive hydrogel jackets coated on rigid pillars, is studied considering the gel deformation under fluid flow, employing fluid–structure interaction simulations. In this regard, an analytical solution to plane-strain inhomogeneous swelling of a cylindrical jacket is proposed. This is used as a tool to validate the finite element model. Then, a micro-valve consisting of one hydrogel jacket is studied in various inlet pressure and pH values performing fluid–structure interaction simulations. Thereafter, a variety of jacket patterns are investigated in order to identify the effects of the pattern on the micro-valve performance for various fluid stream pressures and pH values. The leakage pressure of the valves is also computed for each of the patterns. Fluid–structure interaction simulation is found to be essential to accurate design of the hydrogel-based microfluidic devices.

Recently bilayer smart hydrogel beams are widely used in various applications such as sensors, actuators, self-folding structures and switches. Developing a strong tool for designing these bilayer smart hydrogel beams is necessary. In this article, we developed an analytical method to solve the swelling induced bending of bilayer beams made of a pH-sensitive layer attached to an inert elastomer layer. A total deformation gradient tensor, without assuming any intermediary virtual state, is defined to map the initial configuration to the deformed state. An exponential function with four constants is employed to describe the deformation of the pH-sensitive gel layer. The proposed method leads to a system of equations with six unknowns that can be simply solved via numerical techniques. As a case study, this method is implemented to solve the swelling induced bending of several bilayer beams with various parameters. The outcomes of the analytical solution are in excellent agreement with the finite element method results, thus confirming the strength of the presented method.

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