A Continuum Model of Mucosa with Glycan‐Ion Pairing

Advances in the study of glycosoaminoglycan biohydrogels, label‐free electrokinetic analysis of soft‐diffuse layers in contact with saline solutions, and elucidation of ion‐specific behavior in many biochemical systems offer the opportunity to marry these principal features in a new mathematical model of the mucosal glycocalyx. The model is based on the electroquasistatic subset of Maxwell's equations in the form of the steady‐state continuum Poisson–Boltzmann equation for electrostatics with explicit incorporation of pairwise binding of ions to fixed charged‐groups in the hydrogel. The pairwise association is modeled using reversible bimolecular reactions via stoichiometric dissociation constants that represent the rule of matching water affinities—the observation that similar hydration structures of the pair results in less dissociation. Applications of the model to specific gels and salts, including a heparin star polyethylene glycol (starPEG) biohydrogel and the airway surface liquid layer in cystic fibrosis, are presented to postulate some quantitative consequences of glycocalyx ion partitioning. A model of biohydrogels that includes ion‐specific behavior is presented. The mucosal surface is rich in anionic glycans of glycosoaminoglycans and mucins that pair with cations and biopolymers to establish ion gradients and electrical Donnan potentials. The model is applied to a heparin star polyethylene glycol (starPEG) gel and the effects of pairing of different cations to carboxylates and sulfates are explored.