Urease catalytic behaviors induced by both urea and salt concentrations in ion-exchange hydrogels as dialysis membranes

This paper provides an insight into the urease catalytic responsive behaviors in ion-exchange hydrogels, subjected to variation of environmental concentrations of urea and sodium chloride with different urease enzymatic properties, including catalytic and Michaelis constants. Herein, a multiphysics model is formulated to quantify the catalytic activity of the immobilized urease, accounting for the multiphysics interaction between the environmental solution and the functional components of the urease-loaded charged hydrogel, including the immobilized urease, fixed charge group, the polymeric network chains. The effects of both the urease inactivation and denaturation are also incorporated into the model to capture the pH- coupled with temperature-induced urease catalytic behaviors. It is found that the urease catalytic activity patterns differ in anionic and cationic urease-loaded hydrogels, when subjected to the increase in environmental concentration of sodium chloride at a relatively higher environmental concentration of urea. It is also observed that the urease catalytic activity remains almost unchanged, when the environmental pH increases above the acid-base dissociation constant pK of the present charged hydrogel. Consequently, these findings would facilitate the development of a high-performance hydrogel-based dialysis membrane for highly efficient removal of the toxic urea and separation of the ionic metabolites in an wearable artificial kidney system.