Amphiphilogels for drug delivery: Formulation and characterization

Purpose. This study examines the microstructure, gelation temperatures, and flow properties of novel amphiphilogels consisting solely of non-ionic surfactants. Methods. Gels were prepared by mixing the solid gelator (sorbitan monostearate or sorbitan monopalmitate) and the liquid phase (liquid sorbitan esters or polysorbates) and heating them at 60degreesC to form a clear isotropic sol phase, and cooling the sol phase to form an opaque semisolid at room temperature. Gel microstructure was examined by light and electron microscopy and by small angle neutron scattering ( SANS); gelation temperatures were measured by hot-stage microscopy, a melting point apparatus, and high sensitivity differential scanning calorimetry (HSDSC). Flow rheograms were performed to establish the zero-rate viscosity of the gels and their performance under shear. Results. Gel microstructures consisted mainly of clusters of tubules of gelator molecules that had aggregated upon cooling of the sol phase, forming a 3D network throughout the continuous phase. The gels demonstrated thermoreversibility. Gelation temperature and viscosity increased with increasing gelator concentration, indicating a more robust gel network. At temperatures near the skin surface temperature, the gels softened considerably; this would allow topical application. Conclusions. This study has demonstrated the formation/preparation of stable, thermoreversible, thixtropic surfactant gels (amphiphilogels) with suitable physical properties for topical use.