Spray-drying of solutions containing chitosan together with polyuronans and characterisation of the microspheres

Incubation of the rigid and transparent gel obtained upon pouring a chitosan hydrochloride solution into saturated ammonium hydrogen carbonate at 20 degreesC yielded chitosan carbamate, Chit-NHCO2-N4+, soluble at alkaline pH values, typically 9.6. Addition of water to the gel isolated by centrifugation promoted the dissolution of the gel. By spray-drying the alkaline solution thus obtained, microspheres of chitosan were obtained. When chitosan carbamate was mixed with alginic acid, polygalacturonic acid, carboxymethyl cellulose, carboxymethyl guaran, acacia gum, 6-oxychitin, xanthan, hyaluronic acid, pectin, k-carrageenan, and guaran, clear solutions were obtained from which chitosan-polyuronan microspheres were easily manufactured by spray-drying. Those made of chitosan-xanthan or chitosan-guaran were unexpectedly found to be soluble in water; similarly, the chitosan-pectin microspheres were almost soluble. The microspheres containing hyaluronic acid or k-carrageenan underwent swelling when contacted with water; the other ones were insoluble. The microspheres were characterized by FTIR, X-ray diffraction spectrometry and scanning electron microscopy. The structural alterations detected were mainly due to interactions between the amino groups and the carboxyl groups. (C) 2004 Elsevier Ltd. All rights reserved.