A time-lapse image showing a microjet fired from the laser-based injection system. Traveling through the air, the liquid in this experiment reaches a velocity of 30 meters per second (nearly 100 feet per second). Credit: Optics Letters. |
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.
To test the effectiveness of the drug delivery system, a special gel is used to mimic the behavior of human skin. Here the jet first creates a hole on the surface of the gel, then, at a lower jet pressure, the drug is delivered into the skin. This gel simulation also reveals that there is no “splashback” from the injection, which is an important patient safety factor. Credit: Optics Letters. |
“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 nm, 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.”
Er:YAG laser pulse for small-dose splashback-free microjet transdermal drug delivery
Source: Optical Society of America
