The internal properties of the bioadhesive bond
The movement and concentration of water inside hydrophilic matrices and the bioadhesive bonds formed by them have been proposed as important factors in the bioadhesion of hydrophilic matrices (Smart et al, 1991, and Mortazavi and Smart, 1993). This thesis has developed a non-invasive magnetic resonance imaging (MRI) technique to spatially resolve the self-diffusion coefficient (SDC) and concentration profiles of water inside the bioadhesive bonds formed by dry and hydrated hydrophilic matrices. The bioadhesive interaction between mucin and adhesive may affect the network structure and diffusion retarding properties of either polymer. The mobility of solutes may be used as an indicator of such changes. This thesis has developed a fluorescence recovery after photobleaching (FRAP) technique to measure the mobility of fluorescently tagged dextrans in the mucin and adhesive polymer networks. These methods were combined with basic studies of liquid uptake kinetics and bond strength through detachment force testing to study the bioadhesive bonds formed between alginate matrices and pig gastric mucus. These studies provided evidence to suggest that the bioadhesion of dry and hydrated alginate matrices involved several underlying mechanisms. In the case of bioadhesive bonds formed by dry alginate matrices, the SDC profiles indicated that the hydration of alginate and the formation of a viscous gel layer may cause the localised dehydration of mucus directly adjacent to the alginate matrix. Furthermore, the work of adhesion (Wa) of bioadhesive bonds formed between pig gastric mucus and dry alginate matrices suggested that polymer interpenetration and secondary chemical bonding might also be involved. In the case of bonds formed by hydrated alginate matrices, similar studies indicated that the bioadhesion of hydrated alginate matrices might involve polymer interpenetration and secondary chemical bonding as well as mucus dehydration, although the latter phenomenon appeared to be dependent on the molecular weight of alginate.