In vitro evaluation of the mucoadhesive properties of chitosan microspheres

Abstract

The mucoadhesive properties of chitosan and chitosan microspheres were evaluated by studying the interaction between mucin and chitosan in aqueous solution by turbidimetric measurements and the measurement of mucin adsorbed on the microspheres. A strong interaction between chitosan microspheres and mucin was detected. Adsorption studies were carried out for the adsorption of mucin to chitosan microspheres with different crosslinking levels. The adsorption of type III mucin (1% sialic acid content), to chitosan microspheres followed Freundlich or Langmuir adsorption isotherms. When the contents of sialic acid was increased (i.e. type I-S mucin, 12% sialic acid content), the adsorption type followed more closely an electrostatic attraction type of isotherm. The heat of the adsorption was found to be 13–23 kJ/mol. A salt-bridge effect has been proposed for the interaction of the positively charged mucoadhesive chitosan microspheres with the negatively charged mucus glycoprotein. The extent of mucus adsorption was proportional to the absolute values of the positive zeta potential of chitosan microspheres and negative `zeta potential' of mucus glycoprotein. Factors leading to a reduction or a reversal of these absolute values (e.g. different crosslinking levels of chitosan microspheres, different types of mucin, different pH, or ionic strength of the medium used) led to a reduction in the amount adsorbed. The extent of this reduction depended upon the decreasing extent of the repective zeta potentials. Biological studies showed that chitosan microspheres were retained by a biological tissue; rat small intestine.