Bioadhesion of hydrated chitosans: An in vitro and in vivo study

The (bio)adhesivity of several chitosan chloride samples was screened in vitro and compared with hydroxypropyl methylcellulose (HPMC), Carbopol 934P and polycarbophil by a force of detachment method. This revealed differences between samples, but was judged to be insufficient to describe the bioadhesive behaviour of fully hydrated chitosan. Therefore, an ex vivo method was designed, where freshly excised cattle corneas were created with tritiated chitosan in solution. The contact time, pH, ionic strength and chitosan molecular weight were investigated by means of factorial design, and were shown to have significant effects on the adsorption. In addition, interactions were seen between the parameters. These effects were not seen when chitosan was incubated with polycarbonate membranes instead of corneas. It is concluded that fully hydrated chitosan has a specific bioadhesive activity towards biological surfaces. In the in vivo study, liposomes and chitosan-coated liposomes containing I-125-labelled bovine serum albumin (BSA) as a marker were applied to the eyes of anaesthetised rats and their retention at 10, 30 and 90 min compared. Both formulations showed significantly longer retention than a solution of the free I-125-BSA, but coating the liposomes with chitosan did not significantly improve their retention. It is concluded that the adhesive interaction between chitosan and a biological substrate is dependent on formulation factors as well as the chitosan quality. Copyright (C) 1997 Elsevier Science B.V.