In vivo skin optical clearing by glycerol solutions: mechanism.

The penetration of light in biological tissues can be enhanced by using optical-clearing techniques. However, researches on the mechanism are limited to in vitro experiments. In this study, rat dorsal skin was used to discuss the mechanism for in vivo optical clearing. Glycerol solutions with different concentrations were applied by dermal injection; then the skin reflectance spectrum, SHG imaging and microstructural changes were monitored. The results showed that with the skin becoming transparent, the corresponding reflectance decreased, and the thickness of dermis and diameter of collagen fibril decreased, but no collagen fiber was dissolved or fractured. Hence, it can be concluded that the thickness decrease of dermis and corresponding more regular packing of tissue fibers plays an important role in the mechanism for glycerol-induced optical clearing of skin in vivo.