Ion mediated cross-shield driven mucous swelling kinetics
We present an experimentally guided, bi-phasic, multi-species ionic gel model to compare and make quantitative predictions on the viscoelastic properties of healthy mucus versus Cystic-Fibrosis infected mucus. The mixture theory consists of the mucus (polymer phase) and water (solvent phase) as well as several different ions: H$^+$, Na$^+$, Cl$^-$ and Ca$^{2+}$. The model is calibrated with the experimental data of mucus diffusivities. Numerical studies reveal that the Donnan forces are the dominating mechanism driving the mucus swelling/deswelling transition. However, these transitions could be continuous or discontinuous, depending on the complex interplay between ionic bath concentrations, pH, polymer mass in the solvent and the average charge per monomer.