Deposition temperature effect on release rate of indomethacin microcrystals from microcapsules of layer-by-layer assembled chitosan and alginate multilayer films.

Indomethacin (IDM) microcrystals sized 5 approximately 10 microm were directly encapsulated with nature polysaccharides chitosan (CHI) and sodium alginate (ALG) through layer-by-layer (LbL) self-assembly. Due to partial dissolution of IDM in the deposition solution, the retention of the IDM microcrystals gradually decreased with increasing deposition times and became 47.7% as 10 layers of polysaccharides formed. The release rate of the IDM from the microcapsules was monitored with UV absorbance. The half release time t(1/2) of IDM in the microcapsule increased with the layer number and the initial burst phenomenon was relieved after encapsulation. It was found that added NaCl did not affect the release rate even up to 0.5 M of its concentration, while increasing the release temperature remarkably speeded up the release process. The prolonged release of the encapsulated IDM was still observed when the aqueous release solution containing 20 vol.% ethanol. It was very significant that increasing deposition temperature from 20 to 60 degrees C reduced the release rate efficiently, owing to the increase in multilayer thickness and formation of a more perfect multilayer film. This finding provides a new and simple method to control the permeability of the LbL assembled multilayer films. Because of the biodegradability of CHI and ALG and various methods to tune the release rate, the LbL self-assembly on drug microcrystals promises high potential for encapsulation used in controlled release.