In vivo experimental study on the enhancement of optical clearing effect by laser irradiation in conjunction with a chemical penetration enhancer

The penetration of optical clearing agents (OCAs) is restricted by the natural barrier function of the stratum corneum (SC) of the skin, which can be breached by physical and chemical methods to enhance the transcutaneous delivery of OCAs. To breach the barrier function of SC, we carried out the in vivo experimental study to enhance the optical clearing effect of PEG-400 by laser irradiation in conjunction with a chemical penetration enhancer thiazone. We compared the reflectance spectra of skin without laser irradiation or thiazone. Mono-treatment of thiazone could not significantly enhance the optical clearing efficacy of the skin. After 60 min, the reflectance spectrum decreased by only approximately 10%. With the combined treatment, the reflectance spectrum decreased by approximately 30% after 10 min. Subsequently, the effect of laser dose on the enhancement of optical clearing efficacy was studied. The optimal irradiation dose was determined. The reflectance of skins irradiated by a laser dose at 0.7 J/cm² decreased by approximately 10% and were 20% lower than those at 0.5 and 0.9 J/cm². The laser at 0.5 J/cmc could not damage the SC completely, whereas the laser at 0.9 J/cm² influenced the epidermis and dermis; thus, the reflectance of skin samples irradiated by 0.9 J/cm² did not decrease.