One of the least favored staples of medical care, but one of the most common, needle injections have been used to deliver medicine to children and adults. Still, various techniques have been implemented in hopes of providing more pain-free alternatives. A laser-based system, however, one that blasts microscopic streams of drugs into the skin could soon make receiving a shot as painless as routine as a hit with a short blast of air.
Using and erbium-doped yttrium aluminum garnet, or Er:YAG, laser to shoot a highly concentrated stream of medicine with just the right level of force. This type of laser has been commonly used by dermatologists "particularly for facial esthetic treatments," says Jack Yoh, professor of mechanical and aerospace engineering at Seoul National University in South Korea, who developed the device along with his graduate students. Yoh and his team describe the injector in a paper published in the Optical Society's (OSA) journal Optics Letters.
The laser is combined with a tiny adaptor that houses the drug to be delivered, in liquid form, plus a chamber full of water that acts a a "driver" fluid. A flexible membrane separates the two liquids. Each blast from the laser, which lasts about 250 millionths of a second, generates a vapor bubble inside the driving fluid. The pressure of the bubble puts elastic strain on the membrane and causes the drug to be forcefully ejected from a tiny nozzle in a skinny jet just a micrometer (150 millionths of a meter) in diameter. For reference, the beam is slightly larger than the width of a human hair.
"The impacting jet pressure is higher than the skin tensile strength and thus causes the jet to smoothly penetrate into the targeted depth underneath the skin, without any splashback of the drug," Yoh says. Thus far, tests have been performed on guinea pig skin, and show no damage to the tissue. Because of the width and quickness of the jet, it shouldn't cause any pain. "However, our aim is the epidermal layer," which is located closer to the skin surface, at a depth of only about 500 micrometers. This region of the skin has no nerve endings, so the method "will be completely pain-free," says Yoh.
Previous researchers used a laser wavelength that wasn't well absorbed by the driving liquid, causing the formation of tiny shockwaves that dissipated energy and impeded the formation of the vapor bubble. In the new study, Yoh and his colleagues use a laser with a wavelength of 2,940 nanometers which is readily absorbed into the water. This creates a larger and more stable vapor bubble "which then induces higher pressure on the membrane," Yoh explains. "This is ideal for creating the jet and significantly improves skin penetration."
Though similar injectors have been developed, they are mechanically driven and utilize piston-like mechanisms to force drugs into the skin. This gives less control over the jet strength and the drug dosage. "The laser-driven microjet injector can precisely control dose and the depth of drug penetration underneath the skin. Control via laser power is the major advancement over other devices, I believe."
Yoh is working with a company to manufacture low-cost replaceable injectors for clinician use. "In the immediate future, this technology could be most easily adopted to situations where small doses of drugs are injected at multiple sites," he says. "Further work would be necessary to adopt it for scenarios like mass vaccine injections for children."
For more information, visit the link here: http://www.eurekalert.org/pub_releases/2012-09/osoa-lp091312.php