Using sandpaper for noninvasive transepidermal optical skin clearing agent delivery

We present a gentle mechanical method for the noninvasive transepidermal delivery of topically applied optical skin clearing agents. Optical skin clearing reduces light scattering in highly turbid skin with the aid of hyperosmotic chemicals such as glycerol, polyethylene glycol, and solutions of dextrose. Transepidermal delivery of such agents is believed to be most patient compliant and most likely to be used in a clinical environment. Optical skin clearing has the potential to expand the current limited use of laser light in medicine for diagnostic and therapeutic applications. Light scattering limits the penetration depth of collimated light into skin. In order to increase the diffusion of topically applied optical skin clearing agents into skin, we present a gentle mechanical delivery method involving glycerol and dextrose as optical skin clearing agents and fine 220-grit sandpaper to rub the clearing agent into the tissue. Gentle rubbing causes abrasion of the superficial skin layer including the stratum corneum, which otherwise prevents these optical skin clearing agents from freely diffusing into skin. Results indicate very fast optical skin clearing rates. In vivo hamster skin turned transparent within 2 min. The 1e light penetration depth increased by 36+/-3.75% for dextrose and 43+/-8.24% for glycerol. Optical skin clearing was reversed using phosphate buffered saline solution. Skin viability was observed 70 h post-treatment and showed scabbing and erythema on a few percent of the total optically cleared skin surface.