Preparation of internally-crosslinked alginate microspheres: Optimization of process parameters and study of pH-responsive behaviors.

In this study, the effects of various parameters of the water-in-oil emulsification/internal gelation method on the properties of calcium-alginate microparticles were evaluated and optimized. Results showed that the spherical-shaped microparticles with the highest circularity and high production yield can be produced by alginate solution with a concentration of 2 wt.%, calcium carbonate/alginate ratio of 10/1 (w/w), water/oil volume ratio of 1/20, emulsifier concentration of 5 % (v/v), and emulsification speed of 1000 rpm. Two model drugs including simvastatin lactone and simvastatin β-hydroxyacid were loaded into the microspheres with promising encapsulation efficiencies of 73 % and 69 %, respectively. The microspheres showed a pH-responsive swelling behavior with a percentage of 10.60 %, 352.65 %, 690.03 %, and 1211.46 % at the pH values of 2.0, 4.5, 7.4, and 8.5, respectively. The microspheres showed an increasing trend of release rate in direct proportion to pH. These findings would be useful for therapeutic applications which need pH-responsive drug carriers.