Hierarchically organized micellization of thermoresponsive rod-coil copolymers based on poly[oligo(ethylene glycol) methacrylate] and poly(ε-caprolactone)

Novel Amphiphilic, Biodegradable, Biocompatible, Thermo-Responsive ABA Triblock Copolymers Based on PCL and PEG Analogues via a Combination of ROP and RAFT: Synthesis, Characterization, and Sustained Drug Release from Self-Assembled Micelles

Well-defined novel, linear, biodegradable, amphiphilic thermo-responsive ABA-type triblock copolymers, poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate]-b-poly(ε-caprolactone)-b-poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate] [P(MEO₂MA-co-OEGMA)-b-PCL-b-P(MEO₂MA-co-OEGMA)] (tBPs), were synthesized via a combination of ring-opening polymerization (ROP) of ε-caprolactone (εCL) and reversible addition-fragmentation chain transfer polymerization (RAFT) of MEO₂MA and OEGMA comonomers. The chemical structures and compositions of these copolymers were characterized using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H NMR). The molecular weights of the copolymers were obtained using gel permeation chromatography (GPC) measurements. Thermo-responsive micelles were obtained by self-assembly of copolymers in aqueous medium. The temperature sensitivity and micelllization behavior of amphiphilic triblock copolymers solutions were studied by transmittance, fluorescence probe, surface tension, dynamic light scattering (DLS) and transmission electron microscopy (TEM). A hydrophobic drug, anethole, was encapsulated in micelles by using the dialysis method. The average particle sizes of drug-loaded micelles were determined by dynamic light scattering measurement. In vitro, the sustained release of the anethole was performed in pH 7.4 phosphate-buffered saline (PBS) at different temperatures. Results showed that the triblock copolymer's micelles were quite effective in the encapsulation and controlled release of anethole. The vial inversion test demonstrated that the triblock copolymers could trigger the sol-gel transition which also depended on the temperature, and its sol-gel transition temperature gradually decreased with increasing concentration. The hydrogel system could also be used as a carrier of hydrophobic drugs in medicine.

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.