Polymeric micelles are nanoscopic core/shell structures formed by amphiphilic block copolymers. Both the inherent and modifiable properties of polymeric micelles make them particularly well suited for drug delivery purposes. An emphasis of this review has been placed on both the description and characterization techniques of the physical properties of polymeric micelles. Relevant properties discussed include micellar association, morphology, size and stability. These properties and characterization techniques are included to provide context for the known advantages and applications of polymeric micelles for drug delivery. The advantages and applications discussed include solubilization of poorly soluble molecules, sustained release and size advantages, and protection of encapsulated substances from degradation and metabolism. The three most widely studied block copolymer classes are characterized by their hydrophobic blocks, and are poly(propylene oxide), poly(L-amino acid)s and poly(ester)s. These three classes of block copolymers are reviewed with multiple examples of current research in which formulation techniques with polymeric micelles have been applied to some of the most challenging molecules in the pharmaceutical industry. The polymeric micelles used for drug delivery in these examples have shown the abilities to attenuate toxicities, enhance delivery to desired biological sites and improve the therapeutic efficacy of active pharmaceutical ingredients.
Adriamycin, a hydrophobic anticancer drug, was conjugated with poly(ethylene oxide)-poly(aspartic acid) block copolymers composed of various lengths of each block copolymer segment ranging from 1000 to 12,000 in molecular weight and from 10 to 80 units, respectively. Conjugation was achieved without precipitation by adjusting the ratio of adriamycin to aspartic acid residues of the block copolymer and the quantity of DMF used for the reaction. Thus obtained conjugates showed high water solubility irrespective of a large amount of the conjugated adriamycin. Furthermore, these conjugates were found to form micellar structures with a hydrophobic inner core and a hydrophilic outer shell. This micellar architecture may be utilized for effective drug targeting.
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