Self-assembled micellar nanoparticles of a novel amphiphilic cholesteryl-poly(L-lactic acid)-b-poly(poly(ethylene glycol)methacrylate) block-brush copolymer

摘要

The biodegradable cholesteryl-(L-lactic acid)_n (CPLA) was synthesized via ring opening polymerization of L-lactide in the presence of cholesterol as an initiator and the catalytic amount of Sn(Oct)_2. The resulting monohydroxyl-terminated CPLA was subsequently converted to a bromine-ended macroinitiator (CPLA-Br) by esterification with 2-bromoisobutyryl bromide. Amphiphilic block-brush copolymers with different lengths of hydrophilic block (CPLA-b-P(PEGMA)_4 and CPLA-b-P(PEGMA)_12) were synthesized in a subsequent atom transfer radical polymerization of the poly(ethylene glycol)monomethyl ether methacrylate (PEGMA). The prepared polymers were characterized by FTIR, 1~H NMR and GPC. The self-assembly of the copolymers into the micellar aggregates in aqueous media was followed with dynamic light scattering, transmission electron microscopy and fluorescence analysis. The CMC values of the CPLA-b-P(PEGMA)_4 and CPLA-b-P(PEGMA)_12 samples were estimated approximately 56 × 10~(-4) and 72 × 10~(-4) g/L in an aqueous solution by fluorescence probe technique, respectively. The hydropho-bic/hydrophilic chain ratio of the amphiphilic copolymers could have demonstrated a correlation with micelle formation ability and inter-micellar aggregation in an aqueous solution. Using the naproxen as a hydrophobic model drug, the drug-loading efficiency and drug release properties of the CPLA-PEG nanoparticles were investigated. In vitro release study of the naproxen-loaded micelles with about 54-60 % loading efficiency and 11-12 % loading capacity was performed using dialysis method in phosphate-buffered solution at 37 ℃. Accordingly, these polymeric micelles may be provided as an effective drug carrier for drug controlled release by modulating the copolymer composition and molecular weight of blocks.