An investigation of some factors influencing the in vitro assessment of mucoadhesion

Abstract

The ultimate aim of this research is to develop in vitro systems that allow the prediction of in vivo performance of a mucoadhesive drug delivery system. In this novel approach a modified Dia-Stron rheometer was used that was capable of measuring the maximum force required, as well as the total work necessary, to detach a mucoadhesive containing disc from a model mucosal surface. Some of the factors that may affect the in vitro assessment of mucoadhesion were investigated, namely the method of measuring the adhesive strength, the nature of the mucosal surface, and the means of applying stress to the adhesive joint. A mucus gel, rat small intestine and, as a control, the non-adhesive surface of poly(vinyl chloride) tape were used as model mucosal surfaces. Test discs of various mucosa-adhesive materials were left in contact with the model mucosal surface for 2 min in a pH 6.0 isotonic phosphate buffer at 37°C, prior to testing. The model mucosal surface was then pulled away from the test disc at a rate of 2 mm min −1 until adhesive failure occurred. The attempt to apply and measure shear forces met with limited success. The results obtained on application of tensile stresses indicated that both the maximum detachment force and the total work of adhesion provided very similar measures of the relative adhesive strength for each test material. The discs were found to adhere to the control poly(vinyl chloride) tape stronger than rat's small intestine, with the weakest adhesion being obtained with the mucus gel. It was concluded that these mucoadhesive materials on hydrating are capable of adhering to a variety of different surfaces and a specific mucus/mucoadhesion interaction is not an important factor.