Researchers Develop Laser Injection Technology

Needles are unpleasant. They often can be painful, they can provoke fear in people, it can be difficult to use them on children, and some people—diabetics particularly—have a hard time giving themselves injections due to discomfort. But as technology advances, small improvements constantly are made to needle design, width and comfort levels. For instance, Becton Dickinson and Company just announced a line of ultra-fine pen needles designed to improve injection comfort.

A new development, however, may offer the hope of replacing needles altogether for some applications. A group of researchers from Seoul National University in Seoul, South Korea, have developed a laser-based system intended to replace needle injections. The system that blasts microscopic jets of drugs into the skin could soon make getting a shot as painless as being hit with a puff of air.

The system uses an erbium-doped yttrium aluminum garnet (Er:YAG) laser to propel a tiny, precise stream of medicine with just the right amount of force, say the researchers. This type of laser commonly is used by dermatologists, “particularly for facial aesthetic treatments,” said Jack Yoh, professor of mechanical and aerospace engineering at the university, who developed the device with graduate students. Yoh and his team describe the injector in a paper published in the Optical Society’s journal Optics Letters.

The laser system consists of a small adapter that contains the drug to be delivered in liquid form, and a chamber containing water that acts as a “driving” fluid. A flexible membrane separates the two liquids. Each laser pulse, which lasts just 250 millionths of a second, generates a vapor bubble inside the driving fluid. The pressure of that bubble puts elastic strain on the membrane, causing the drug to be forcefully ejected from a miniature nozzle in a narrow jet that is 150 millionths of a meter (micrometers) in diameter, 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,” explained Yoh. Tests on guinea pig skin show the drug-laden jet can penetrate up to several millimeters beneath the skin surface, with no damage to the tissue. Because of the narrowness and quickness of the jet, it should cause little or no pain, Yoh said. The real aim, however, is the epidermal layer, located closer to the skin surface at a depth of about 500 micrometers. Since this layer of skin has no nerve endings, the method should be completely painless, researchers theorize.

In previous studies, researchers used a laser wavelength that was not well absorbed by the water of the driving liquid, causing the formation of tiny shock waves that dissipated energy and hampered the formation of the vapor bubble. In this new study, Yoh and colleagues use a laser with a wavelength of 2,940 nanometers, which readily is absorbed by water. This allows the formation of a larger and more stable vapor bubble “which then induces higher pressure on the membrane,” Yoh noted. “This is ideal for creating the jet and significantly improves skin penetration.”

Although other research groups have developed similar injectors, they are mechanically driven, using piston-like devices to force drugs into the skin, which gives less control over the jet’s strength and the drug dosage, Yoh said. “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,” he added.

Yoh now is working with a company to produce low-cost replaceable injectors for clinical 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 said. “Further work would be necessary to adopt it for scenarios like mass vaccine injections for children.”

The paper detailing this technology is titled “Er:YAG laser pulse for small-dose splashback-free microjet transdermal drug delivery.”