A COMPARATIVE-STUDY ON THE ROLE PLAYED BY MUCUS GLYCOPROTEINS IN THE RHEOLOGICAL BEHAVIOR OF THE MUCOADHESIVE MUCOSAL INTERFACE

One proposed mechanism of mucoadhesion involves the interpenetration of the mucus/mucoadhesive molecules followed by the formation of non-covalent interactions. Mucus glycoproteins are believed to be the major structure forming component of mucus, giving rise to the cohesive and the viscoelastic nature of the mucus gel. The addition of a known mucoadhesive, the polyacrylic acid Carbopol 934P (paa), to purified mucus glycoprotein resulted in the formation of a strengthened gel network. This was indicated on visual examination, and also on rheological examination using mechanical spectroscopy. A large mean G' (the storage modulus, found between 10 and 0.1 HZ) was obtained for the glycoprotein/paa mix in comparison to when the glycoprotein and paa gels were tested separately at the same concentration. Similar results were obtained with crude and homogenised mucus samples. This gel strengthening phenomena was optimum at pH values around the pK(a) of paa. It was concluded that it is the glycoprotein component of mucus which interacts with paa to produce gel strengthening, and this may increase the cohesive nature of the weakest component of a mucoadhesive joint, thus allowing prolonged mucosal adhesion. A rheological investigation of a pH 6.2 glycoprotein/paa mix between 10 and 0.002 Hz indicated that this gel strengthening effect resulted from both chain entanglement and the formation of secondary chemical bonds.