Mechanistic Analysis of Temperature-Dependent Curcumin Release from Poly(lactic-co-glycolic acid)/Poly(lactic acid) Polymer Nanoparticles

In this study, we investigated the mechanism of curcumin (CUR) release from poly­(lactic-co-glycolic acid) (PLGA) and poly­(lactic acid) (PLA) nanoparticles (NPs) by evaluating the temperature-dependent CUR release. NPs were prepared by the nanoprecipitation method using various PLGA/PLA polymers with different lactic:glycolic ratios (L:G ratios) and molecular weights. Increasing the polymer molecular weight resulted in a decrease in the particle size of NPs. The wet glass transition temperature (T_g) of PLGA/PLA NPs was lower than the intrinsic polymer T_g, which can be derived from the water absorption and nanosizing of the polymer. The reduction in T_g was more significant for the PLGA/PLA NPs with lower polymer L:G ratios and lower polymer molecular weight. The greater decrease of T_g in the lower polymer L:G ratios was possibly caused by the higher water absorption due to the more hydrophilic nature of the glycolic acid segment than that of the lactic acid segment. The efficient water absorption in PLGA/PLA NPs with lower molecular weight could cause a significant reduction of T_g as it has lower hydrophobicity. CUR release tests from the PLGA/PLA NPs exhibited enhanced CUR release with increasing temperatures, irrespective of polymer species. By fitting the CUR release profiles into mathematical models, the CUR release process was well described by an initial burst release followed by a diffusion-controlled release. The wet T_g and particle size of the PLGA/PLA NPs affected the amount and temperature dependence of the initial burst release of CUR. Above the wet T_g of NPs, the initial burst release of CUR increased sharply. Smaller particle sizes of PLGA/PLA NPs led to a higher fraction of initial CUR burst release, which was more pronounced above the wet T_g of NPs. The wet T_g and particle sizes of the PLGA/PLA NPs also influenced the diffusion-controlled CUR release. The diffusion rate of CUR in the NPs increased as the wet T_g values of the NPs decreased. The diffusion path length of CUR was affected by the particle size, with larger particle size resulting in a prolonged diffusion-controlled release of CUR. This study highlighted that for the formulation development of PLGA/PLA NPs, suitable PLGA/PLA polymers should be selected considering the physicochemical properties of PLGA/PLA NPs and their correlation with the release behavior of encapsulated drugs at the application temperature.