An anonymous reader writes with news of research from MIT, where engineers have found a better way to use ultrasound waves to boost the permeability of skin for the delivery of drugs. "Ultrasound — sound waves with frequencies greater than the upper limit of human hearing — can increase skin permeability by lightly wearing away the top layer of the skin, an effect that is transient and pain-free. ... When ultrasound waves travel through a fluid, they create tiny bubbles that move chaotically. Once the bubbles reach a certain size, they become unstable and implode. Surrounding fluid rushes into the empty space, generating high-speed 'microjets' of fluid that create microscopic abrasions on the skin. In this case, the fluid could be water or a liquid containing the drug to be delivered. In recent years, researchers working to enhance transdermal drug delivery have focused on low-frequency ultrasound, because the high-frequency waves don’t have enough energy to make the bubbles pop. However, those systems usually produce abrasions in scattered, random spots across the treated area. In the new study (abstract), the MIT team found that combining high and low frequencies offers better results. The high-frequency ultrasound waves generate additional bubbles, which are popped by the low-frequency waves."