Development of a rheometric technique to measure the mucoadhesive capacity of a dry powder formulation

In the present study, the use of an in vitro technique applying oscillatory shear rheology to determine the interaction between a dry polymer powder and mucin is investigated. The polymers examined are Carbopol 974P, Noveon AA1 and a polymer mixture containing Carbopol 974P and Drum Dried Waxy Maize Starch. The degree of interaction is assessed by analysing the variation of the elastic and viscous modulus as a function of oscillation stress. Both moduli are used to calculate a mucoadhesive index at a selected single stress/frequency combination. The contribution of physical entanglements and secondary bond formation to the interaction can be derived from the mathematical analysis of the relation between the moduli and the oscillation frequency. When considering the stress sweep data, the interaction between mucin and the various polymers investigated seems very similar. This similarity is also observed when calculating the mucoadhesive indexes. On the contrary, the mathematical analysis of the frequency sweep data clearly indicates that the secondary bond formation between the polymer powder particles and mucin can be obtained only in the case of Carbopol 974 P.