Biodegradable thermo-sensitive nanoparticles from poly(l-lactic acid)/poly(ethylene glycol) alternating multi-block copolymer for potential anti-cancer drug carrier

In order to produce biodegradable thermo-sensitive nanoparticles, alternating multi-block copolymers (MBC) were synthesized by coupling dicarboxylated poly(ethylene glycol) (PEG; Mw 2000) with poly(l-lactic acid) (PLLA)/PEG/PLLA triblock copolymers. Three different multi-block copolymers were synthesized by varying PLLA molecular weight (800 (MBC1), 1600 (MBC2), and 2800 (MBC3)). The MBC formed self-assembled nanoparticles with a unimodal size distribution during a dialysis process. The nanoparticles (NP) had a spherical shape with a size range of 90–330 nm in diameter and critical aggregation concentrations in a range of 5.6–12.6 μg/mL, depending on PLLA length in MBC. The thermo-sensitivity of MBC NP was monitored by the changes in particle size and interior structure as a function of temperature. The particle size slightly decreased as increasing temperature from 37 to 42 °C. The interior structure of the NP responded to temperature by altering microviscosity. The microviscosity, measured by the anisotropy (r value) of a fluorescence probe, of MBC1 NP significantly changed with increasing temperature (r = 0.187 at 25 °C and 0.216 at 42 °C), while MBC2 and MBC3 showed negligible changes in the microviscosity. This indicates that the temperature-dependent interior structure of the NP relied on the portion of PLLA in MBC. The thermo-sensitivity affected to the drug release behavior and cell cytotoxicity. At 42 °C, doxorubicin (DOX) loaded MBC1 NP showed enhanced cytotoxicity (∼20 times) against Lewis Lung Carcinoma (LLC) cells when compared to that at 37 °C.