Optimization of preparative conditions for poly-DL-lactide-polyethylene glycol microspheres with entrapped Vibrio Cholera antigens

Poly-dl-lactide-polyethylene glycol (PELA) with different contents of polye thylene glycol(PEG) were synthesized and the PEG content was estimated acco rding to the integral height of hydrogen shown in H-1-NMR. PELA microsphere s containing V. cholera antigen, outer membrane protein (OMP) were prepared by a water-in-oil-in-water (W/O/W) based on solvent evaporation procedure. Antigen microspheres with smooth surface, suitable size for oral administr ation (0.5-5 mu m), high loading efficiency (about 60%) and low level of re sidual solvent (lower than 20ppm) were obtained. Microspheres prepared from PELA with PEG content of about 10% achieved the highest loading efficiency among PELA copolymers and poly-dl-lactide (PLA) homopolymer, which suggest ed that microspheres size, morphology and the precipitation rate of polymer showed considerable relations with OMP loading efficiency. The regulation of the solvent components of the oil phase contributes to a stable emulsion W/O, and it is concluded that the stable emulsion W/O plays a significant role in improving the protein loading efficiency of obtained microspheres. The addition of stabilizer, such as gelatin and polyvinyl alcohol, into the internal water phase before emulsification produced no significant differe nce in OMP entrapment and microspheres size. A higher OMP loading efficienc y was achieved by adding NaCl or adjusting the pH at the iso-electric point of OMP in the external water phase. It was indicated in vitro that PELA mi crospheres with smaller size showed larger extent of initial release and hi gher release rate, whereas microspheres with the diameter of 2.17 mu m show ed no apparent burst effect. (C) 1999 Elsevier Science B.V. All rights rese rved.