ABSTRACT
In order to understand the mode of adhesion of polymers to mucus or soft tissues and to help the formulator in designing suitable bioadhesive dosage forms, the essential features of the structure of mucus, the mechanism of mucoadhesion, and the various techniques reported in the literature to screen the polymers for bioadhesion are reviewed briefly. The potential of bioadhesive microparticles to increase the bioavailability of nasally or orally administered drugs is obvious from the literature.
Several factors which may influence the bioadhesion of polymer-coated microparticles were studied in detail and the results are presented. Increase in the nominal viscosity of the polymer in the coat increased the adhesion of the particles to the intestine but not to the stomach. This shows that polymer chain length is important for bioadhesion. Strong adhesion of hydroxypropylmethyl-cellulose (HPMC)- coated particles to the intestine, when the amount of mucus was minimal, indicates that HPMC has a strong affinity for epithelial cells. Increase in the thickness of the HPMC coat increased the adhesion, but this did not occur with polycarbophil (PC). Synergistic increase in the viscosity due to the presence of both HPMC and sodium carboxymethylcellulose (Na CMC) in the coat did not increase the adhesion. PC and Na CMC-coated particles adhered less well to the duodenum than to the jejunum. All the particles adhered less well to the distal end of small intestine than to the jejunum. The contact time and moisture content are important for the celluloses, but not for PC. Viscosity and the structure of the mucus are important for the mucoadhesion. The results revealed that polymers of high molecular weight and/or polymers having ionizable groups can adhere strongly to the mucus of the gastro-intestinal tract.
