video: The movie shows the injector firing into open air without a skin or gel target. The jet, which is approximately the diameter of a human hair, seems dispersed but a target would be placed within the jet breakup distance of a few millimeters, so splash-free injection is achieved. view more
Credit: Video courtesy Jack You/Seoul National University.
WASHINGTON, Sept. 13—From annual flu shots to childhood immunizations, needle injections are among the least popular staples of medical care. Though various techniques have been developed in hopes of taking the "ouch" out of injections, hypodermic needles are still the first choice for ease-of-use, precision, and control.
A new laser-based system, however, 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, or Er:YAG, laser to propel a tiny, precise stream of medicine with just the right amount of force. This type of laser is 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 today in the Optical Society's (OSA) journal Optics Letters.
The laser is combined with a small adaptor that contains the drug to be delivered, in liquid form, plus a chamber containing water that acts as a "driving" fluid. A flexible membrane separates these 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 a mere 150 millionths of a meter (micrometers) in diameter, just a little 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. Tests on guinea pig skin show that 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 says. "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," he says.
In previous studies, the 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 the new work, Yoh and colleagues use a laser with a wavelength of 2,940 nanometers, which is readily absorbed by water. This allows the formation of a larger and more stable vapor bubble "which then induces higher pressure on the membrane," he explains. "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 strength and the drug dosage, Yoh says. "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 now 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 says. "Further work would be necessary to adopt it for scenarios like mass vaccine injections for children."
Paper: "Er:YAG laser pulse for small-dose splashback-free microjet transdermal drug delivery," Optics Letters, Vol. 37, Issue 18, pp. 3894-3896 (2012). http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-37-18-3894
EDITOR'S NOTE: High-resolution images and a video clip are available to members of the media upon request. Contact Angela Stark, astark@osa.org.
About Optics Letters
Published by the Optical Society (OSA), Optics Letters offers rapid dissemination of new results in all areas of optics with short, original, peer-reviewed communications. Optics Letters covers the latest research in optical science, including optical measurements, optical components and devices, atmospheric optics, biomedical optics, Fourier optics, integrated optics, optical processing, optoelectronics, lasers, nonlinear optics, optical storage and holography, optical coherence, polarization, quantum electronics, ultrafast optical phenomena, photonic crystals, and fiber optics. This journal, edited by Alan E. Willner of the University of Southern California and published twice each month, is where readers look for the latest discoveries in optics. Visit www.OpticsInfoBase.org/OL.
About OSA
Uniting more than 180,000 professionals from 175 countries, the Optical Society (OSA) brings together the global optics community through its programs and initiatives. Since 1916 OSA has worked to advance the common interests of the field, providing educational resources to the scientists, engineers and business leaders who work in the field by promoting the science of light and the advanced technologies made possible by optics and photonics. OSA publications, events, technical groups and programs foster optics knowledge and scientific collaboration among all those with an interest in optics and photonics. For more information, visit www.osa.org.
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Optics Letters