Poly(d,l-lactic acid) nanoparticle preparation and colloidal characterization

Nano size-ranged poly(d,l-lactic acid) (PLA) particles were obtained from 2 and 10 w% PLA solution in water-saturated ethyl acetate by the emulsification-diffusion method. An increase in the PLA solution concentration resulted in an increase of the particle mean size from ca 260 nm to 530 nm with a broadening of the distribution. After fractionation by centrifugation, the particle mean size was 980 nm. The Pluronic F68 used in the formulations at concentration ranging from 0.5 to 5% w/v, was shown to adsorb at the interface at 0.5 mg/m² for both particle sizes. The molecular occupied area of 24 nm²/molecule suggested an expanded conformation of the surfactant at the interface, though an incomplete coverage could not be excluded. Coagulation kinetics measurements revealed a critical coagulation concentration (CCC) of 1.5 M sodium chloride, indicating a steric stabilization of the colloids by the adsorbed triblock copolymer. Nonetheless, variations in zeta potential with increasing salt concentration were observed, suggesting that the surface carboxylate groups were still accessible for further modifications.