Supersonic microjets may be key to needle-free injections

Technology Review : Although needles have long been used for medical injections, they can be painful, need to be carefully cleaned if reused, and have other downsides as well. Previous attempts to create needle-free injection methods have not been able to overcome the tendency of liquids to splash on the skin, and liquid jets are often painful or can damage the skin. A new technique developed by a team led by Yoshiyuki Tagawa of the University of Twente in the Netherlands may have solved all those problems. Tagawa’s method uses a laser pulse to heat a portion of liquid in a specially designed capillary tube. The heated liquid vaporizes, sending a shockwave through the rest of the liquid and forcing it out of the capillary at speeds around 850 m/s. When the liquid hits the skin, the tip of the stream is a width of only a few tens of micrometers. The combination of speed and a small cross section allows the liquid to easily penetrate the skin with almost no splashing. Tagawa’s team tested the technique on gelatin covered with synthetic skin and used colored water. Although the method is promising, there is concern that the laser pulse and heat could damage some drug molecules.