Formulation, characterization and release studies of alginate microspheres encapsulated with tetanus toxoid

Alginate is a safe, non-immunogenic and inexpensive natural polymer with high mucoadhesive properties. Alginate microspheres can be used as a delivery system for antigens to mucosal surfaces. In the present study alginate microspheres were prepared by an emulsification technique. The effects of sonication time, concentration of alginate, emulsifier and calcium chloride, and also the volume of calcium solution, were evaluated on mean size, size range, surface roughness and porosity, sphericity and clumping of microspheres using an optical microscope and particle size analyzer. The most desirable conditions were 90 s sonication, 3% alginate solution, 2% surfactant and 60 ml of 0.33% CaCl2 in octanol. The resulting microspheres had a mean size of 1.34 +/- 0.3 microm and size range of 0.3 +/- 2.0 microm, with no surface roughness and porosity, low clumping and high sphericity. The encapsulation efficiency was about 47.7%. All batches showed nearly the same release profiles with a low burst release. The stability of the model antigen (tetanus toxoid (TT)) extracted from microspheres was confirmed by SDS-PAGE; and the antigenicity of TT was studied by ELISA and found to be 91 +/- 5% of the original TT. It can be concluded that, with regard to the size and morphological characteristics of the prepared microspheres and their ability in preserving the antigenicity of the encapsulated TT, they could be used as a delivery system for mucosal delivery of TT.