Numerical simulation of pH-stimuli responsive hydrogel in buffer solutions

In this paper, the chemo-electro-mechanical behavior of the responsive hydrogel actuated by pH-stimuli is addressed. A chemo-electro-mechanical model, describing the hydrogel behavior with multi-field effects, is developed to simulate the swelling of the captivating biomaterials, and it is termed the multi-effect-coupling pH-stimulus (MECpH) model. This model delineates the effects of electric potential and mechanical deformations of the hydrogel as well as the transports of ionic fluxes within both the hydrogel and bath solution. The main contribution of this model laid on the incorporation of the relationship between the concentrations of the ionized fix-charge groups and the diffusive hydrogen ion, which follows a Langmuir isotherm theory, into the Poisson–Nernst–Planck system. In order to validate the MECpH model, one-dimensional steady-state simulations are conducted under varying pH conditions generated by buffer solution. The mathematical models are solved via a meshless Hermite–Cloud method and the numerical results are compared well with available experimental data. In conclusion, the presently developed MECpH model is able to predict the swelling behavior of the hydrogel precisely. This study provides a better understanding of the behavior of the pH-sensitive hydrogels.