Meshless steady-state analysis of chemo-electro-mechanical coupling behavior of pH-sensitive hydrogel in buffered solution

The objective of the present study is to simulate the phenomenological behavior of the pH-sensitive hydrogels when the pH of their buffered aqueous environment is changed. A chemo-electro-mechanical formulation, referred to as the multi-effect-coupling pH-stimulus (MECpH) model, is also presented. This mathematical model, consisting of coupled nonlinear partial differential equations, takes account of the diffusion of ionic species, electric potential coupling and mechanical equilibrium deformation. On top of that, the correlation between diffusive hydrogen ion and charge groups fixed to the hydrogel polymeric chains is quantitatively incorporated into the MECpH model. As a novel meshless technique, the Hermite-Cloud method is employed to solve one-dimensional steady-state problems. For examination of the MECpH model, the computed results are compared numerically with experimental data available from literature, in which transitional volume changes in the HEMA hydrogel are studied when the environmental solution is in the range of pH 4.5-7.5. The comparisons validate the accuracy and robustness of the MECpH model. Additionally, several numerical studies are carried out to simulate the swelling hydrogel immersed in buffered solution. It is observed that the fixed-charge groups and the mechanical properties of the pH-stimulus-responsive hydrogel have significant influences on the volume variations of the hydrogels.