Freeze substitution technique for identifying liposomes incorporated in emulsion and gel preparations

The freeze-substitution technique was utilized for identifying unilamellar and multilamellar liposomes incorporated in gel or emulsion preparations. Samples of each preparation were rapidly frozen in liquid propane and the ice formed in the process was substituted with acetone containing 2 per cent osmium tetroxide at -70 degrees C. Electron micrographs obtained by both freeze-fracture and freeze-substitution methods showed the presence of either small unilamellar or multilamellar vesicles in all the liposome preparations. Results clearly demonstrated that freeze-substitution is a simple and cost-effective technique in comparison to the traditional freeze-fracture method and can be successfully used to characterize liposomes incorporated in dermatological or cosmetic vehicles.