Efficiency Comparison on Varies Optical Clearing Agents for In Vivo Human Skin Imaging

Optical clearing is a method to overcome the limitation of optical imaging depth especially for clinical in vivo microscopies of dermatology. According to previous studies, glycerol could effectively increase the signal intensity deep inside dermis. Other optical clearing agents (OCAs), like propylene glycol (PG) and polyethylene glycol (PEG) 400, were reported to cause better optical clearing effects. However the experiment conditions of different OCAs varied, including the penetration enhancers, application time, selection of samples and areas, and microscopy technologies. These inconsistent conditions lead to inconclusive results. Moreover, it is difficult to study this effect on human skin in vivo due to the different conditions of skin pH value, temperature, moisture, and microbiology. In this study, we aim to compare the efficacy among varies OCAs that improve the image quality deep inside the dermis for in vivo human skin imaging. Harmonic generation microscopy was used for in vivo imaging which could provide high resolution and distinguish epidermis from dermis. Several OCAs (25% PG, 40% PG, 25% PEG 400, 50% PG, 50% PEG 400, 50% glycerol, water) with or without ultrasound treatment were included. Among these treatments, 25% PG with 5 minutes of ultrasound treatment for total 60 minutes of application times was found to be with the best efficacy, judged by the in vivo maximum second harmonic generation signals from collagen fibers in dermis. This finding will not only be helpful for the optical clearing research but would also benefit the in vivo human skin imaging techniques in the future.