Preparation of alginate coated chitosan microparticles for vaccine delivery

Absorption of antigens onto chitosan microparticles via electrostatic interaction is a common and relatively mild process suitable for mucosal vaccine. In order to increase the stability of antigens and prevent an immediate desorption of antigens from chitosan carriers in gastrointestinal tract, coating onto BSA loaded chitosan microparticles with sodium alginate was performed by layer-by-layer technology to meet the requirement of mucosal vaccine.

The prepared alginate coated BSA loaded chitosan microparticles had loading efficiency (LE) of 60% and loading capacity (LC) of 6% with mean diameter of about 1 mum. When the weight ratio of alginate/chitosan microparticles was greater than 2, the stable system could be obtained. The rapid charge inversion of BSA loaded chitosan microparticles (from +27 mv to -27.8 mv) was observed during the coating procedure which indicated the presence of alginate layer on the chitosan microparticles surfaces. According to the results obtained by scanning electron microscopy (SEM), the core-shell structure of BSA loaded chitosan microparticles was observed. Meanwhile, in vitro release study indicated that the initial burst release of BSA from alginate coated chitosan microparticles was lower than that observed from uncoated chitosan microparticles (40% in 8 h vs. about 84% in 0.5 h). SDS-polyacrylamide gel electrophoresis (SDS-PAGE) assay showed that alginate coating onto chitosan microparticles could effectively protect the BSA from degradation or hydrolysis in acidic condition for at least 2 h. The structural integrity of alginate modified chitosan microparticles incubated in PBS for 24 h was investigated by FTIR.

The prepared alginate coated chitosan microparticles, with mean diameter of about 1 mum, was suitable for oral mucosal vaccine. Moreover, alginate coating onto the surface of chitosan microparticles could modulate the release behavior of BSA from alginate coated chitosan microparticles and could effectively protect model protein (BSA) from degradation in acidic medium in vitro for at least 2 h. In all, the prepared alginate coated chitosan microparticles might be an effective vehicle for oral administration of antigens.