Preparation and Characterization of Polymeric Micelles from Poly(D, L-lactide) and Methoxypolyethylene Glycol Block Copolymers as Potential Drug Carriers

Amphiphilic diblock copolymers composed of methoxy polyethylene glycol (MePEG) and poly(D,L-lactide) (PDLLA) were prepared for the preparation of polymeric micelles. The use of MePEG-PDLLA as drug carriers has been reported in the open literature, but there are only few data on the application of a series of MePEG-PDLLA copolymers with different lengths in the medical field. The shape of the polymeric micelles is also important in drug delivery. Studies on in vitro drug release profiles require a good sink condition. The critical micelle concentration of a series of MePEG-PDLLA has a significant role in drug release. To estimate their feasibility as a drug carrier, polymeric micelles made of MePEG-PDLLA block copolymer were prepared by the oil in water (O/W) emulsion method. From dynamic light scattering (DLS) measurements, the size of the micelle formed was less than 200 nm. The critical micelle concentration of polymeric micelles with various compositions was determined using pyrene as a fluorescence probe. The critical micelle concentration decreased with increasing number of hydrophobic segments. MePEG-PDLLA micelles have a considerably low critical micelle concentration (0.4-0.5 µg/mL), which is apparently an advantage in utilizing these micelles as drug carriers. The morphology of the polymeric micelles was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The micelles were found to be nearly spherical. The yield of the polymeric micelles obtained from the O/W method is as high as 85%.