Stratum corneum lipid remodeling as a proposed mechanism for liposomal penetration enhancement

The stratum corneum (SC) is the principal barrier to topical and transdermal delivery, yet how lipid-based formulations interact with the SC lipid matrix remains incompletely resolved. Here, we compared conventional lecithin/cholesterol liposomes, hexosomes, ultradeformable liposomes, and a surfactant-only micelle control in ex vivo human skin after 4 h Franz-cell exposure. Depth-resolved Laurdan generalized polarization (GP) imaging of cryosections was used to quantify formulation-induced changes in SC lipid organization, while DiD fluorescence and deuterated-lipid stimulated Raman scattering (SRS) provided orthogonal readouts of formulation-derived material within the tissue. Across formulations, GP decreased relative to matched controls, with the largest effects in the outer SC. Hexosomes produced larger outer-SC GP reductions than conventional liposomes (ΔGP ≈ 0.25-0.33 vs 0.14-0.18). In a separate donor-matched series, ultradeformable vesicles induced stronger SC remodeling than conventional liposomes, whereas Tween 20 micelles produced smaller effects. DiD and SRS signals were predominantly localized to the SC and decreased with depth, with SRS indicating a more surface-weighted distribution for rigid liposomes than for ultradeformable vesicles. Together, these findings identify formulation-dependent SC lipid remodeling, involving lipid redistribution and reduced local packing order, as a plausible mechanism by which lipid-based formulations may contribute to penetration enhancement reported in previous studies.