Simulation of Hydrogel Responsiveness to Blood Glucose

This paper presents the results of our fully coupled, two-dimensional (2D) simulation of the swelling behavior of glucose-sensitive hydrogels at a constant glucose level with change in the surrounding pH. The model consists of a system of glucose-sensitive hydrogel and ionic fluid as a solvent. The hydrogel consists of two enzymes: glucose-oxidase and catalase, which are immobilized on the polymeric network. The surrounding solvent has certain level of glucose. The diffusion of glucose from a solvent and its reaction within the hydrogel are simulated using the Nernst-Planck equation. The local electrical charge is calculated by the Poisson’s equation, and deformation of the hydrogel is determined by the mechanical field equation. These equations are fully coupled and simulations are performed for varying pH and glucose concentrations. The glucose concentration was taken at 7.7mM (140mg/mL) and the pH is varied from 6.8 to 7.4. As glucose reacts with oxygen, gluconic acid is produced in the presence of glucose-oxidase. The formation of gluconic acid within the gel results in protonation and thereby causes the hydrogel expansion. The glucose level in the surrounding solution limits diffusion in the hydrogel. As the surrounding solution pH increases the available fixed charged for ionization increases, which results in an increase in maximum equilibrium swelling and gluconic acid as a product of the reaction. The gluconic acid production was found to be proportional to the change in pH. The gluconic acid decreases the internal pH of the hydrogel, which ultimately reduced the deformation of the gel.