COMPARATIVE RHEOLOGICAL INVESTIGATION OF CRUDE GASTRIC MUCIN AND NATURAL GASTRIC MUCUS

Mucus is a viscoelastic gel covering the entire alimentary tract. It r epresents a pre-epithelial diffusion barrier influencing the drug abso rption process. In this way the rheological properties of mucus play a n important role. The purpose of our investigation was to evaluate and compare the rheological properties of rehydrated dried crude porcine gastric mucin (Sigma mucin) and isolated natural porcine gastric mucus . Two different rheological approaches were used: constant shear and o scillatory shear conditions. The results obtained under steady shear c onditions show that the reduction of apparent viscosity is caused by t ime, shear rate and temperature. With increasing Sigma mucin concentra tion the rheological behaviour changes from time-independent systems f itting in with the Casson model to time-dependent systems fitting in w ith the Herschel-Bulkley rheological model. Measurements performed und er oscillatory shear conditions clearly show how the mechanical respon se of different concentrated systems has changed from dispersions with prevailing plastic to prevailing elastic properties. Mechanical defor mation and frequency response of natural gastric porcine mucus have sh own a strong gel structure with elastic properties. Comparing both sys tems it can be concluded that after rehydration of dried crude gastric porcine mucin, a model mucus system with rheological properties equiv alent to natural mucus cannot be obtained. (C) 1997 Elsevier Science L imited.