Temoporfin-loaded liposomal gels: Viscoelastic properties and in vitro skin penetration

Temoporfin (mTHPC) is a potent second-generation photosensitizer. The primary object of this study was to develop a topical mTHPC-loaded liposomal hydrogel able to deliver mTHPC into the stratum corneum (SC) and deeper skin layers. This study was conducted (1) to determine the effect of carbomer concentration, used as a gelling agent, and the effect of phosphatidylcholine (PC) content of lecithin, used for the liposome preparation, on viscoelastic properties and viscosity of liposomal gels and (2) to determine the relationship between rheological properties of gels and the skin penetration of mTHPC. Liposomal hydrogels revealed plastic flow behaviour. The increase of carbomer concentration induced a domination of elastic over viscous behaviour of gels. There was an inverse relationship between the elasticity of gels and mTHPC-penetration. Viscosity also increased with the increment of carbomer concentration, reducing the mTHPC-penetration. Liposomal gels containing lecithin of smaller PC-content (i.e. smaller purity) exhibited a more elastic solid behaviour than gels containing lecithin with high PC-content, and showed smaller mTHPC-penetration. The gel containing 0.75%, w/w, carbomer and lecithin with high PC-content was considered to be the optimal formulation, since it delivered high amounts of mTHPC to the SC and deeper skin layers, and it possessed desirable rheological properties.