Modeling the Impact of pH- and Oxygen-Coupled Stimuli on Osmotic Pressure and Electrical Potential Responses of Hemoglobin-Loaded Polyampholyte Hydrogel.

Abstract

A unique character of (bio) responsive materials is their capability to convert specific environmental biochemical cues into an electromechanical response. Thereby, this paper describes the impact of pH- and oxygen-coupled stimuli on osmotic pressure and electrical potential responses of hemoglobin-loaded polyampholyte hydrogel. Herein, a multiphysics model is developed for elucidating the multiphysical interaction between immobile functional components bounded onto polymeric network chains of the hydrogel and hydrogen ion-oxygen-enriched environmental solution. Two constitutive relationships are incorporated into the model to capture: (1) ionization of fixed charge group as a function of its ionization strength coupled with hydrogen ion concentration and (2) bioactivity of hemoglobin as a function of both its ionization and saturation states. The multiphysics model is verified by comparing with experimental observations in open-literature, capturing the oxygen-induced hemoglobin saturation and the pH-actuated deformation of polyampholyte hydrogel. The numerical finding demonstrates that the pH-activated osmotic pressure response of the present hemoglobin-loaded polymeric system is independent of ambient oxygen O2, whereas its electrical potential response is insensitive of ambient oxygen O2 level at pH neutral conditions. Furthermore, the pH-induced swelling deformation of initially balanced polyampholyte hydrogel changes from a "V-" to a "bowl"-shaped like pattern with increase in fixed acidic and basic group ionization strength, whereas the initially unbalanced polyampholyte hydrogel achieves a collapse state at environmental pH coinciding with acid-base dissociation constant of dominant immobile charge group, if the initial dominant immobile charge group density is twice that of its counter one.