Small-angle neutron scattering studies of microenvironmental and structural changes of Pluronic micelles upon encapsulation of paclitaxel

Pluronic micelles represent a novel type of nanocarriers that enhance the therapeutic efficacy of paclitaxel (PTX) by increasing its solubility and circulation time. However, encapsulation or incorporation of a drug influences the micellar structure and subsequently alters the pharmacokinetic behavior of the drug delivery system. In this study, we investigated the structural properties of micelles after micellar solubilization of PTX. Proton nuclear magnetic resonance ( 1 H NMR) and Fourier transform infrared spectroscopy (FTIR) studies showed that PTX was incorporated into the poly (propylene oxide) (PPO) blocks of the micelle cores. Small-angle neutron scattering (SANS) was used to probe changes in the core-shell structure of Pluronic P123 micelles as a function of increasing PTX and Pluronic concentration. Model-independent analyses and cryogenictransmission electron microscopy (cryo-TEM) confirmed that both pure and PTXincorporated micelles were spherical. However, an increase in PTX concentration led to a slight increase in the micellar dimension and was associated with the appearance of the larger Pluronic-drug aggregates as confirmed by evaluation of cryo-TEM images. At higher Pluronic concentration and a constant PTX concentration, the dimensions of micelles increased, most likely due to the altered hydrophobic environment promoting the interaction of PPO and poly (ethylene oxide) (PEO) blocks. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.