Modeling the effect of environmental solution pH on the mechanical characteristics of glucose-sensitive hydrogels.

Many environmental conditions can influence the mechanical characteristics of the glucose-sensitive hydrogels. In this paper, a multi-effect-coupling glucose-stimulus (MECglu) model is developed to study the influence of environmental solution pH on the swelling behavior of soft smart hydrogels responding to change in surrounding blood glucose concentration. In order to characterize the chemo-electro-mechanical behaviors of the hydrogels, the model is composed of the Nernst-Planck type of diffusion-reaction partial differential equations for mobile species with consideration of the enzyme reaction catalyzed by the glucose oxidase and the catalase, the Poisson equation for electric potential, and the nonlinear equilibrium equation for mechanical large deformation of the glucose-sensitive hydrogel. In the MECglu model, the formulation of the fixed charge groups bound onto the corsslinked polymeric network is associated with the change of the ambient solution pH. Using these nonlinear coupled partial differential equations, we demonstrate that the computational mechanical deformation by the MECglu model consists well with the experimental observations published in the range of practical physiological glucose concentration from 0 to 16.5 mM (300 mg/ml). The simulations are also carried out for analysis of the influences of physiological pH on the distributive profiles of reacting and diffusive species concentrations and the electric potential as well as the mechanical deformation of the glucose-sensitive hydrogels. The simulations by the model can efficiently support the design and optimization of the insulin delivery system based on the glucose-sensitive hydrogels with the immobilized glucose oxidase and catalase.