Preparation of temperature-sensitive microemulsion-based gels formed from a triblock copolymer

Temperature-sensitive microemulsion-based gels (MBGs) of Pluronic F127 (PEO99-PPO67-PEO99) were formed in microemulsion systems composed of isopropyl myristate (IPM)/Span20/TWeen20/H2O, with or without a model drug (chloramphenicol), and the phase behaviors of the systems were investigated. The viscoelastic properties and gelation temperatures of the systems were characterized by theological measurements. Effects of the concentration of F127 and the model drug (chloramphenicol) on the viscoelastic properties and gelation temperatures were also studied. It was observed that the viscosities of the gels increased and the gelation temperatures decreased with increasing F127 concentration. Chloramphenicol had little effect on the viscosities and gelation temperatures of the MBG. Moreover, chloramphenicol was sustainably released from the MBG system. Freeze-fracture transmission electron microscopy (FF-TEM) demonstrated that the amphiphilic triblock copolymer (F127) self-assembled in the selected microemulsion system and formed network structures. The microstructures of the microemulsion droplets were maintained in the MBG after the addition of F127. The results of fluorescence spectroscopy also supported this conclusion. Based on these results, a plausible schematic model was proposed to explain the mechanism of MBG formation. (c) 2007 Elsevier B.V. All rights reserved.