Effect of pH and salt on the rheology of 10mg/mL MUC5AC gels. The linear viscoelastic response measured macroscopically (symbols) as well as the predicted moduli from the MSD data (lines) are presented. Filled symbols and solid lines represent the elastic property G′(ω), while the hollow symbols and dashed lines represent the viscous property G″(ω). The aggregate MSD of all particle trajectories was used to calculate the viscoelastic moduli for all gels except the pH2 sample, for which only the MSD of a specific subset of ‘exponential’ particles (see text for details) was used. In (a) the pH is varied with no added salt, and data is presented at pH2, pH4, and pH7. In (b), the pH is maintained at pH7 and data is presented for salt concentrations of 0 mM, 50 mM, 200 mM and 400 mM.