Preparation and in-vitro evaluation of sodium alginate microspheres containing diphtheria toxoid as new vaccine delivery

During last two decades, polysaccharides such as alginate (Alg) alone and in combination with other biopolymers are widely used in vaccine and drug delivery systems. The aim of the present work was to investigate the potential utility of microparticles made of alginate (Alg) as new vehicles for improving nasal vaccine delivery. For this purpose, diphtheria toxoid (DT) was chosen as a model antigen. DT was entrapped within microparticles made of Alg of different molecular weight cross-linked using 1M CaCl2 or 3.75 %w/w CaCl2 in n-octanol. DT-loaded microparticles were characterized for their size, loading efficiency and in vitro release of toxoid. The resulting microparticles had a size, which varied depending on formulation conditions and Alg Mw. The results of the in vitro release studies displayed a biphasic release of toxoid, the intensity of the first phase being less pronounced for microparticles cross linked with aqueous CaCl2 than octanolic CaCl2.