A SURFACE-ENERGY ANALYSIS OF MUCOADHESION .2. PREDICTION OF MUCOADHESIVE PERFORMANCE BY SPREADING COEFFICIENTS

Mucoadhesion refers to the adhesion of polymeric materials to mucosal tissues. Some mucoadhesive polymers show appreciable binding to mucus even when hydrated and in the presence of an interstitial aqueous medi um. The mucoadhesive performance (i.e. binding strength) is expected t o depend on the interfacial energy thermodynamics in a three phase (so lid-liquid-solid) system. According to known theories, such a system c an be described in terms of spreading coefficients which are given by the free surface energy of each phase. Dispersion (alpha) and polar (b eta) surface energy parameters were available from previously reported contact angle measurements of captive air/octane bubbles on polymeric hydrogels and pig intestinal mucosa immersed in aqueous test media. I t was found that individual spreading coefficients, as calculated from these surface energy parameters by the geometric mean equation, can b e combined to one single parameter, called combined spreading coeffici ent S(c). The latter is defined by the geometric mean of the polymer s preading coefficient and the Griffith fracture energy. This criterion provided a good correlation between predicted and measured mucoadhesiv e performance under various experimental circumstances. In its present form, this approach is based only on dispersion and polar surface ene rgy components, without taking into account other forces due to ionic interactions, hydrogen bonding or acid-base interactions and eventual polymer chain interpenetration. Nevertheless, correct predictions were obtained. It is therefore concluded that the formation of a mucoadhes ive bond is primarily governed by the aforementioned surface energy ef fects and spreading processes. The surface energy concept provides use ful information for the search for better mucoadhesive materials and t he identification of favored target sites in the human body for mucoad hesive drug delivery systems.