Evaluation of mucoadhesion for two polyelectrolyte gels in simulated physiological conditions using a rheological method.

A rheological method to measure mucoadhesion was evaluated for two ion-sensitive polymers, Carbopol 934 and Gelrite((R)) (deacetylated gellan gum), in a simulated physiological environment using two commercially available mucins. The method simulates the interpenetration layer in the mucoadhesion process. The elastic modulus for a polymer/mucin mixture is compared with the elastic modulus for the polymer alone, and an increase in the elastic modulus for the mixture compared to the polymer is interpreted as a positive interaction caused by mucoadhesion. In this study the influence of polymer concentration, type of mucin and experimental rheological factors, such as gap width, were examined. The choice of polymer concentration was crucial, especially with the porcine gastric mucin. We found that one is more likely to obtain positive interactions with weak gels. It was also shown that the choice of mucin has a large influence on the results obtained. Carbopol 934 interacted more strongly with the bovine submaxillary gland mucin than with the porcine gastric mucin, whereas the gel structure of Gelrite((R)) was destroyed when mixed with the bovine mucin. Furthermore, it was concluded that with hydrogels consisting of gel particles (such as Carbopol 934), rheological measurements can give highly varying results, depending on, for example, the concentration and ion-sensitivity of the polymer, the quantity of ions present, as well as the gap width of the measuring system.