<title>Dynamics of optical clearing of human skin in vivo</title>

Optical clearing of skin using flashlamp-induced enhancement of epidermal permeability

“…Such biocompatible OCAs can be glucose, mannitol, propylene glycol, glycerol, polyethylene glycol, polypropylene glycol, X-ray contrasting agents (Verografin, Trazograph, and Hypaque), demethylsulfoxide (DMSO), and their combinations. Experimental studies on optical clearing of normal and pathological skin and its components (epidermis and dermis), and the control of skin reflectance and transmittance spectra using water, glycerol, glycerol-water solutions, glucosewater solutions, sunscreen creams, cosmetic lotions, gels, and pharmaceutical products have been carried out [6,[8][9][10][11][12][13][14][15][16][17][18]. The control of skin optical properties was related to the matching of refractive indices of scatterers (keratinocyte components in epidermis, collagen, and elastic fibers in dermis) and ground matter induced by OCA permeation and/or tissue dehydration due to the osmotic properties of OCA [8][9][10][11][12][13][14][15][16][17][18].…”

“…Stripping of the stratum corneum (SC) represents the simplest approach to physical enhancement of the percutaneous absorption of a topically applicated compound [9,19,26]. Ultrasound technique (phonophoresis or sonophoresis) provides the enhanced skin absorption of lowmolecular-weight compounds as well as proteins such as insulin [19].…”

“…In vivo application of ultrasound of 20 kHz to skin of hairless rats for 1 hour resulted in a 100-fold increase in transepidermal water loss and sufficient delivery of insulin through the skin. Iontophoresis refers to the enhancement of agent percutaneous absorption by the application of moderate (0.5 V/cm) voltages across the skin [9,19]. At higher voltages (5-200 V/cm) and short pulse exposure electroporation of biological membranes may occur, that also enhances agent permeation into a tissue.…”

Investigating the optical clearing effects of 50% glycerol in ex vivo human skin by harmonic generation microscopy

“…However, in different tissues such as sclera 3 , liver [4][5][6] , muscle 7 , tendon 5,7 , skin 5,[8][9][10][11][12][13][14][15][16][17][18][19][20][21] , the OC effect varies. Among these studies, skin optical clearing with glycerol attracts high attention 5,[8][9][10][11][12][13][14][15]17,18,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] . Glycerol is a low toxic substance and widely used for the food i...…”

“…However, the skin is a high scattering tissue that comprises multiple layers with a variation of refractive index. Although OC of human skin have been studied by many different optical imaging techniques such as near-infrared (NIR) spectrophotometer 9 – 12 , 23 , 29 , 36 , confocal microscopy 13 , 14 , multi-photon microscopy 8 , 15 , 35 , SHG microscopy 8 , and optical coherence tomography (OCT) 5 , 12 , 17 , 18 , 26 , 29 , 30 , 34 , 36 , 37 in the past few decades, the effects and mechanisms of optical clearing in human skin with glycerol topically applied are not fully understood and are with inconsistent results, especially for the case of glycerol at low concentration. Observation of the OC effect inside the topmost epidermis layer is thus important to understand its mechanisms for topical applications.…”