MicroJet injector for painless injections

Mar 21 2005

Parents know all too well the pain experienced by their children - and themselves - when the time comes for immunizations at the doctor's office.

But a new MicroJet injector being developed by bioengineering students at the University of California, Berkeley, may help ease some of that dread by taking the needle - and the pain - out of the equation. The MicroJet uses an electronic actuator that could one day propel vaccinations, insulin or other drugs through the skin of the patient - without the device even touching the skin - with far less pain than a hypodermic needle.

The MicroJet improves upon current jet injectors now on the market, which also forgo the conventional needle but have less control over the volume and speed of drug delivered. The UC Berkeley bioengineers were able to achieve liquid jet speeds as high as 140 meters per second, or about 315 miles per hour, with the MicroJet.

The researchers will demonstrate their prototype during the March 17-19 annual meeting of the National Collegiate Inventors and Innovators Alliance (NCIIA) in San Diego.

"The World Health Organization advocates developing needleless drug delivery technologies because of the problems of contamination and disposal that go along with hypodermic needles," said Laleh Jalilian, one of the three UC Berkeley bioengineering undergraduates on the project. "There are other jet injectors on the market, but they are plagued by variability in the percentage of liquid delivered, which means that it is difficult to know exactly how much of the drug actually gets into the patient. The MicroJet we are developing uses a tunable electronic circuit to offer a finer level of control than the air- and spring-powered models available now."

The researchers modified a traditional syringe by taking out the needle and adding a tiny piezoelectric actuator that propels the liquid out of the tube. The actuator expands or contracts in response to an applied voltage. Because the MicroJet's source of power is electrical rather than mechanical, its range of control is continuous, allowing a far higher level of customization than the jet injectors used today.

"Other jet injection systems have only three or four factory settings, but human skin is tremendously variable, with some skin being thicker and tougher than others," said Dan Fletcher, UC Berkeley assistant professor of bioengineering and faculty advisor to the undergraduates. "Not only are there differences from person to person, there are significant differences within a single individual."

The researchers pointed out that the palm of the hand, for example, is tougher than the back of the hand, and that the skin of an adult is likely to be tougher than that of a child. They said there is a need for an injector that can be tailored to these variations.

The students were able to control the jet velocity of the MicroJet from 33 meters per second up to 140 meters per second. The amount of liquid they were able to eject ranged from 45 nanoliters to 140 nanoliters. They tested the MicroJet on agarose gel to mimic human skin and found that they could vary the penetration depth of the liquid from 1 to 8 millimeters.

While they have not yet started tests on humans, the researchers said the range of the injector is well beyond what would be needed to deliver drugs through human skin.

"Another great feature of the MicroJet is that the diameter of the nozzle is only 70 microns, which is nearly three times smaller than the thinnest conventional hypodermic needles," said Marcio von Muhlen, another of the UC Berkeley undergraduate researchers. "Since the area of the jet stream decreases with the square of the diameter, that's at least a nine-fold reduction in the area of skin affected. With smaller nozzle diameters and without the need to jam a needle some substantial distance under your skin, you won't trigger as many nerve receptors in the surrounding tissue, which means a relatively pain-free experience."

While current jet injectors also promise a less painful injection, in reality, reports of pain can vary depending upon the patient and the location of the shot. The researchers acknowledge the real life reports, but noted that the level of pain experienced can be a function of the settings on the injector.

"The beauty of the MicroJet is that it has a wide range of settings that can be customized to the patient's comfort and needs," said Jalilian.

Fletcher said the inspiration for the project came from the ubiquitous inkjet printer. "The printer's ink cartridges essentially deliver a very controlled, repetitive shot of liquid onto the paper," he said. "The liquid in an inkjet cartridge is propelled at relatively low speeds, but the idea is the same."

So does this signal the end of scary needles and crying babies in doctors' offices?

"We don't think the MicroJet will ever replace needles entirely, but we see this as providing an innovative option for physicians and patients," said von Muhlen.

The researchers noted that the precision of the MicroJet could one day make it a good candidate for microsurgery as well as for delivering arthritis drugs into the joints of hands and knees, areas that are too shallow for hypodermic needles. They even joke that the MicroJet injector could be used to make getting tattoos much more bearable.

The MicroJet project began two years ago as part of the Berkeley Summer Bioengineering Research Program, sponsored by the Guidant Foundation. Through the program, UC Berkeley undergraduate students compete for the chance to participate in funded research projects with department faculty.

Jalilian, von Muhlen and Menzies Chen joined the MicroJet project as part of that program. Once the program ended, the students on the MicroJet project applied for and won a $20,000 grant from the NCIIA to continue their research. (Chen graduated in December 2004, but is still working on the project).

They have also been supported by UC Berkeley's College of Engineering's Undergraduate Research Opportunities program, which funds student research in a variety of campus engineering labs.

"It's not common for such innovative research projects to be entirely run by undergraduates," said Fletcher. "Not only have they done excellent work on the research, they have applied for and received grants to fund the project. This illustrates the importance of having university programs that provide students with initiative the opportunity to go beyond the typical undergraduate curricula."

The project is also part of the California Institute for Quantitative Biomedical Research (QB3), which integrates the fields of engineering, physics, mathematics, biology and medical sciences at three UC campuses to catalyze human health research.

Future tests are planned on animal models and cadaver skins to fine-tune the device.