Thermo-responsive drug release from self-assembled micelles of brush-like PLA/PEG analogues block copolymers

Thermo-responsive brush-like amphiphilic poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate]-b-poly(l-lactide)-b-poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate] [P(MEO2MA-co-OEGMA)-b-PLLA-b-P(MEO2MA-co-OEGMA)] triblock copolymers were synthesized by atom transfer radical polymerization of MEO2MA and OEGMA co-monomers using a α,ω-Bromopropionyl poly(l-lactide) (Br-PLLA-Br) macroinitiator. The resulting copolymers with MEO2MA/OEGMA molar ratio ranging from 79/21 to 42/58 were characterized by (1)H nuclear magnetic resonance and size exclusion chromatography. Thermo-responsive micelles were obtained by self-assembly of copolymers in aqueous medium. The micelles are spherical in shape with sizes varying from 20.7 to 102.5 nm. A hydrophobic anticancer drug, curcumin, was encapsulated in micelles by using membrane hydration method. The properties of drug loaded micelles were determined by dynamic light scattering, transmission electron microscopy and lower critical solution temperature (LCST) measurements. The micelles size decreases from 102.5 nm for blank micelles to 37.6 nm with 10.8% drug loading, suggesting that the drug plays an important role in the micellization procedure. The LCST decreases from 45.1°C for blank micelles to 40.6 and 38.3°C with 5.9 and 10.8% drug loading, respectively. In vitro drug release was performed in pH 7.4 PBS at different temperatures. Data show that the release rate was significantly enhanced above the LCST comparing with that below the LCST. The amount of released drug at 41°C was ca. 20% higher than that at 37°C. Burst-like release was depressed due to enhanced interaction between drug with hydrophobic PLA and PMA chains.