A RHEOLOGICAL EXAMINATION OF THE MUCOADHESIVE MUCUS INTERACTION - THEEFFECT OF MUCOADHESIVE TYPE AND CONCENTRATION/

The ability of mucoadhesive polymers to produce a large increase in th e resistance to deformation when incorporated into a mucus gel, relati ve to when the mucus gel and test materials are evaluated separately a t the same concentration, has been reported in several previous studie s. It has been proposed that this phenomenon, termed rheological syner gism, can be used as a measure of the strength of the mucoadhesive int eraction. In this investigation rheological synergism was investigated for a large range of putative mucoadhesive gels by dynamic oscillator y theology. Changes in the storage modulus (G'), loss modulus (G ''), and loss tangent (tan delta) were found and the 'relative' rheological synergism calculated. Rheological synergism was evident for a range o f materials with known mucoadhesive properties giving behaviour betwee n that of strongly cross-linked polymers gels and a physically entangl ed system, This effect was most marked with materials known to be of h igh mucoadhesive strength even when fully hydrated. Hence, polymers li ke sodium carboxymethylcellulose and high molecular weight poly(ethyle ne oxide) showed limited rheological synergism. When the effect of muc oadhesive concentration was investigated, 'relative' rheological syner gism occurred within a limited concentration range only, the values of which varied between materials. It was concluded that macromolecules possessing numerous hydrogen bond-forming groups and an open expanded network in the test environment gave pronounced rheological synergism, and the relevance of this to mucoadhesion studies will be investigate d in further work. This study also confirmed the advantages of dynamic oscillatory rheology over simple viscosity measurement in the study o f these systems. (C) 1998 Elsevier Science B.V.