Meshless simulation of equilibrium swelling/deswelling of PH-sensitive hydrogels

Hydrogels have been widely used in microelectromechanical systems (MEMS) and Bio-MEMS devices. In this article, the equilibrium swelling/deswelling of the pH-stimulus cylindrical hydrogel in the microchannel is studied and simulated by the meshless method. The multi-field coupling model, called multi-effect-coupling pH-stimulus (MECpH) model, is presented and used to describe the chemical field, electric field, and the mechanical field involved in the problem. The partial differential equations (PDEs) describing these three fields are either nonlinear or coupled together. This multi-field coupling and high nonlinear characteristics produce difficulties for the conventional numerical methods (e.g., the finite element method or the finite difference method), so an alternative-meshless method is developed to discretize the PDEs, and the efficient iteration technique is adopted to solve the nonlinear problem. The computational results for the swelling/deswelling diameter of the hydrogel under the different pH values are firstly compared with experimental results, and they have a good agreement. The influences of other parameters on the mechanical properties of the hydrogel are also investigated in detail. It is shown that the multi-field coupling model and the developed meshless method are efficient, stable, and accurate for simulation of the properties of the stimuli-sensitive hydrogel. (c) 2005 Wiley Periodicals, Inc.