Localised mapping of water movement and hydration inside a developing bioadhesive bond

Few studies have investigated the internal processes involved in bioadhesive bond formation, particularly where mucus and hydrated polymer contribute jointly to bond structure. This paper reports the first study to spatially map the internal environment within a developing bioadhesive bond, utilising nuclear magnetic resonance (NMR) microscopy to measure localised water self-diffusion coefficients (SDC) and confocal laser scanning microscopy (CLSM) to estimate mucin concentration. In a model bioadhesive bond formed between an alginate matrix and mucin gel, characteristic profiles were observed in which fluorescence measurements showed a region of increasing mucin concentration in the mucus layer region adjacent to the matrix, corresponding closely with a zone of restricted water SDC in the diffusion profiles. These regions extended 144 microm (a normal human gastric layer thickness [Clin. Sci. 95 (1998) 97]) into the mucin layer after just 30 s, increasing to 800 microm after 30 min. The formation of a hydrated polymer layer at the matrix surface, confirmed visually, was also reflected in corresponding gradient changes. The results suggest a progressive dehydration of the mucus gel during bond formation, and the study demonstrates how together, these microscopies can provide non-invasive, quantitative, spatial and time-resolved evidence of internal hydration behaviour during bioadhesive bond formation.