INTERACTIONS BETWEEN LIPOSOMES AND HUMAN STRATUM-CORNEUM IN-VITRO - FREEZE-FRACTURE ELECTRON-MICROSCOPIC VISUALIZATION AND SMALL-ANGLE X-RAY-SCATTERING STUDIES

The interactions between three liposomal formulations and human stratu m corneum were visualized using freeze fracture electron microscopy. A new replica cleaning method was introduced. Human stratum corneum was submerged for 48 h in liposome suspensions prepared from commercially available phospholipid mixtures. The size, lamellarity and lipid moie ties of the liposomes were similar. The main difference between the th ree phospholipid formulations was the hydrophilicity of the headgroups . The composition dependence of the interactions between these vesicle s and human stratum corneum was investigated. In essence, two types of interaction were observed: adsorption of the liposomes on to the oute r surface of the stratum corneum, and ultrastructural changes in deepe r layers of the stratum corneum caused by mixing of the liposomal cons tituents and the stratum corneum lipids. The electron-microscopic obse rvations were verified with small-angle X-ray scattering. It was found that liposomes composed of phospholipids containing relatively small hydrophilic headgroups showed a marked interaction with the skin lipid s of human stratum corneum in vitro. The complexity of the phospholipi d mixtures, however, made it very difficult to determine the exact eff ect each of these headgroups has on the interactions between these ves icles and human stratum corneum.