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 °C yielded chitosan carbamate, Chit-NHCO2−NH4+, 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.