Characterization of polyacryl starch microparticles as carriers for proteins and drugs

Biodegradable microparticles of cross-linked starch (maltodextrin) have been designed as carriers of proteins and low molecular weight drugs in vivo. Methods are presented for the synthesis of acryloyl starch and its polymerization to microparticles. Macromolecules were immobilized in the microparticles in high yields, i.e., up to 40% of the dry weight consisted of the immobilized protein. The optimal conditions of immobilization were investigated by varying the concentration of starch (D), the concentration of acryloyl groups (T), and the amount of additional cross-linking agent (C). Exclusion of the cross-linking agent gave maximal immobilization of the macromolecules. Enzyme kinetics, release profiles, surface localization, and heat stability of the immobilized macromolecules are also presented. Microparticles based on starch with small amounts of acryloyl groups were completely degraded after incubation with amyloglucosidase. The degradation of microparticles in serum and in the target organelle, the lysosome, was investigated in vitro. The polyacrylic starch microspheres (mean diameter, 0.5 μm) constitute an attractive alternative to other drug and enzyme carriers.