Elasto-thixotropic properties of bronchial mucus and polymer analogs

Abstract

The non-newtonian viscous and elasto-thixotropic properties of native and lyophilized pathological bronchial mucus and of polymer solutions (3% and 6% PIB in decalin) used as mucus analogs were analyzed using a cone-plate Carri-Med rheometer and a Couette viscoelastometer that we have specifically developed for measuring the rheological properties of bronchial mucus in clinical practice. The master curves obtained for apparent viscosity under steady conditions as a function of shear rates ( $\dot{\mathit{\gamma }}$ : 2.6×10¹ to 6.9×10 sec⁻¹) were fairly similar, whatever the apparatus used. Under transient conditions, at low shear rate ( $\dot{\mathit{\gamma }}$ < 1.4 sec⁻¹), PIB and mucus exhibited a typical viscoelastic behavior: the shear stress increased slightly up to a steady-state value. At higher $\dot{\mathit{\gamma }}$ , a transitory overshoot of σ characteristic of the elastothixotropic systems appeared. Such a behavior can be interpreted as resulting from structural changes such as formation and rupture of the three-dimensional network present in bronchial mucus as in polymer solutions.