Chitosan/gelatin microspheres prepared by modified emulsification and ionotropic gelation

Chitosan microspheres were prepared by an emulsion-phase separation techniq ue without the use of chemical cross-linking agents; alternatively, ionotro pic gelation was employed in a w/o emulsion. The possibility of three kinds of anions (tripolyphosphate, citrate and sulphate) to interact with chitos an was investigated by turbidimetric titration. The results indicate that t here are electrostatic interactions between the above anions and chitosan i n a certain region of solution pH (1.0-7.5 for sulphate/chitosan, 4.5-7.5 f or citrate/chitosan and 1.9-7.5 for tripolyphosphate/chitosan), that is rel ated to the natural characteristics of the anions. Out of the pH region whe re anions interact with chitosan, no microspheres were formed. However, eve n in the pH region where anions can interact with chitosan, only irregular microparticles were obtained in the case of the conventional emulsification and ionotropic gelation method, while spherical microspheres with diameter s in the range of tens of microns were obtained when a modified process was employed. The key point of the modified process is the introduction of gel atin and allowing the ionic cross-linking process of chitosan/gelatin w/o e mulsions to take place under coagulation conditions at a low temperature. T he surface of sodium sulphate cross-linked chitosan/gelatin and sodium citr ate cross-linked chitosan/gelatin microspheres was very smooth, but large g aps were observed on the surface of tripolyphosphate/chitosan microspheres. The increase of stirring speed led to a decrease in diameter and a narrowi ng in size distribution.