A comparison of different in vitro methods for measuring mucoadhesive performance

Abstract

The purpose of this study was to assess and compare several in vitro methods for measuring mucoadhesive performance, using a controlled-stress rheometer and a penetrometer (texture analyser). Three poly(acrylic acid) (PAA) polymers, differing in their cross-linking status, were selected, namely Carbopol 974P, Carbopol 971P and Noveon AA-1 (polycarbophil). The polymers were used in two neutralisation states (acidic and neutralised with triethanolamine) and two physical states (hydrogel and compact). The in vitro methods tested were categorised as ‘bulk’ and ‘tensile’. Bulk techniques concerned the structure analysis of polymer gels and polymer/mucin mixtures by oscillatory rheology and penetrometry. Rheological synergy, dependent on the frequency of oscillation, was detected in the case of neutralised PAA/mucin mixtures, as opposed to unneutralised mixtures, where only a decrease in elasticity were found. A linear relationship was found between the phase angle δ and the area under the penetration/withdrawal curve when samples of similar structure were examined. The tensile methods involved the assessment of maximum detachment force and work of adhesion between polymer gels (or compacts) and a layer of 30% mucin gel. In the case of compacts, the hydration time was varied from 1 to 20 min and was found to affect the mucoadhesive performance. The tensile methods detected differences in mucoadhesive properties among the three structurally similar polymers, giving the same rank order as was found for the rheological properties.