Wetting behavior of bile salt-lipid dispersions and dissolution media patterned after intestinal fluids

The wetting properties of bile salt-lipid solutions and dispersions patterned after the contents of the upper intestine in the fed and fasted states were evaluated using poly(methyl methacrylate) (PMMA) as a model substrate. The surface tension of the solutions and their contact angles on PMMA were measured. Media compositions for the intestinal fed and fasted states were estimated on the basis of physiologic data. The effect of various individual lipids and media composition was also evaluated relative to the adhesional, immersional, and spreading stages of wetting. In micellar systems, both the type and concentration of lipid present in the bile salt solution had an influence on wetting. The wetting of media patterned after gastrointestinal contents showed marked differences with respect to the fed or fasted state compositions. For the fed state compositions, alteration of the solution pH from 7.5 to 5.0 resulted in a significant change in wetting. The surface tension of the medium representative of the fasted state was 15 mN/m higher than that of the fed state. The wetting properties of the physiologically representative media formulated in this study were markedly different compared with other media proposed in the literature. Analysis of the wetting behavior of individual lipids as a function of concentration in bile salt solutions showed that they adsorb in a manner that progressively reduces the expected wetting of the surface. The results have implications for the design and formulation of both biorelevant and surfactant-based dissolution media.