Functionality of protective colloids affecting the formation, size uniformity and morphology of drug-free polylactic acid microspheres

Abstract

Drug-free polylactic acid (PLA) microsphcres were prepared by an emulsitication-solvent evaporation technique using different types of protective colloids. The influence of five types of hydrophilic prolymers (polysaccharides, proteins, synthetic cellulose derivatives, synthetic nonionic polymers and surfactants) on the formation, size uniformity and morphology of PLA microspheres was investigated. Four characteristic functions (surface activity, viscosity, electric charge and interfacial film formation) of the hydrophilic polymer aqueous solutions were used to evaluate the efficacy of these protective colloids used. The results indicate that these four functions were the key parameters to achieve the formation of PLA microspheres. The best protective colloid should have high surface activity, optimum viscosity, adequate electric charge, and form an interfacial film to give a higher recovery, better size uniformity and smoother topography of the PLA microsphcres.

Key Words:

• Protective colloid
• microsphere
• polylactic acid
• emulsion
• morphology
• size uniformity