Scanning electron microscopic evaluation of the skin surface after ultrasound exposure

Abstract

Background: Transdermal drug-delivery systems have become widely accepted clinically for the administration of several systemic drugs. Recently, research on ultrasound irradiation to facilitate the penetration of drugs through the skin have been reported. The present study investigated the morphological changes induced in skin after ultrasound irradiation to hairless mouse skin and human skin. Methods: Hairless mice and human skin were immersed in an ultrasound irradiation water tank. Ultrasound was delivered for a duration of 5 min. Ultrasound frequency of 48 kHz was generated at an intensity of 0.5 W/cm2. The surface of the skin was observed with scanning electron microscopy for comparison with skin samples unexposed to ultrasound energy. Results: For hairless mouse exposed to ultrasound, the cells of the stratum corneum of the skin surface were almost completely removed. The polygonal cells of the stratum spinosum and basal cells were exposed. In addition, large craterlike pores with a diameter of 100 μm were formed sporadically in some of the skin samples. In contrast, the surface of human skin exposed to ultrasound showed only slight removal of keratinocytes around the hair follicles. Conclusion: The removal of the stratum corneum and other alterations in hairless mouse and human skin by ultrasound may explain the enhancement of transdermal drug penetration. The effect on human skin was relatively miner compared with that on hairless mouse skin.