Surface modified polymeric nanoparticles for immunisation against equine strangles

The successful development of particulate vaccines depends on the understanding of their physicochemical and biological characteristics. Therefore, the main purpose of this study was to develop and characterise stable surface modified poly(lactic acid) (PLA) nanoparticles, using polyvinyl alcohol (PVA), alginate (ALG) and glycolchitosan (GCS) containing a Streptococcus equi enzymatic extract adsorbed onto the surface. The characterisation of the preparations and a physicochemical study of the adsorption process were performed. The adsorption of S. equi proteins is a rapid process reaching, within 1 h, maximum adsorption efficiency values of 75.2 ± 1.9% (w/w) for PLA–PVA, 84.9 ± 0.2% (w/w) for PLA–GCS and 78.1 ± 0.4% (w/w) for PLA–ALG nanoparticles. No protein degradation was detected throughout the formulation procedures. As expected from a complex mixture of proteins, adsorption data suggest a Freundlich-type of equilibrium with regression coefficients (r²) of 0.9958, 0.9839 and 0.9940 for PLA–PVA, PLA–GCS and PLA–ALG, respectively. Desorption studies revealed a burst release within the first 6 h, for all formulations, followed by a sustained release profile. Nanoparticle surface modification with GCS improved the sustained release profile, as 20% of protein remained attached to the particle surface after 30 days. The results show that adsorption is an alternative method for the production of S. equi antigen carriers for vaccination purposes.