ON THE MECHANISMS OF IN-VITRO AND IN-VIVO PHONOPHORESIS

The physical explanations found in the literature for the mechanism(s) of phonophoresis (sonophoresis), are critically reviewed. It is shown that temperature and stirring can cause flux enhancements, and the orders of magnitude of the corresponding flux increases are consistent with the values observed experimentally. But these two factors are not sufficient to explain the phenomenon. It is found that the radiation pressure hypothesis should be discarded, and that a satisfying microscopic physical interpretation of the supposed decrease in the donor solution-membrane interfacial potential energy barrier, caused by ultrasound, is missing. It is likely that microstreaming is a mechanism responsible for the in vitro phonophoresis through membranes. Possible mechanisms are discussed for the in vivo phonophoresis through skin.