Effect of hydrophilically modified ibuprofen on thermoresponsive gelation of pluronic copolymer

Abstract

This paper concerns the effect of hydrophilically modified ibuprofen (IBU-PEO9, IP400), which is an amphiphilic anti-inflammatory drug, on the thermoresponsive gelation of Pluronic F127 (poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide), PEO97-PPO68-PEO97). Rheology, small angle X-ray scattering (SAXS), 1H nuclear magnetic resonance (1H NMR), two-dimensional nuclear Overhauser effect spectroscopy (2D-NOESY), and spin-lattice relaxation time (T1) are applied to investigate the interaction mechanism on both macroscopic scale and molecular level. The results show that the addition of IP400 strongly affects the gelation and the microstructure of gel. The addition of IP400 at low concentration facilitates the temperature-induced gelation of F127, while the body centered cubic structure of the gel is persevered. The results confirm that the hydrophobic interactions between PPO chains of F127 and the hydrophobic tails of IP400 are dominant in the enhancement of the micellization and subsequently the gelation of F127. At higher IP400 concentration, the promotion of the temperature-induced gelation by IP400 diminishes, and the gel with more primitive structure and weaker strength is formed. This is because the insertion of IP400 into F127 micelles results in the enhanced separation and mobility of PEO chains of F127, substantially the entanglement and interpenetration of the PEO chains are disturbed within the cubic structure. This information sheds some light on the prediction of the controlled release patterns of the modified drug in the mixed system.