Painless Drug Injections

Researchers at Hewlett Packard Labs (HP Labs) have engineered a drug patch that painlessly delivers medications through the skin via tiny micro-needles. The technology is modeled after HP’s inkjet-printer technology.

A single patch outfitted with hundreds of micro-needles could potentially deliver multiple drugs at preprogrammed intervals, without the pain and hassle of conventional needles. The company has announced a licensing deal with Crospon, a medical-device developer based in Galway, Ireland, that will manufacture and market the “smart” patch.

“There are a few patches out there for drugs like nicotine and fentanyl, very small and potent molecules that go across the skin on their own,” says Samir Mitragotri, a researcher at the University of California, Santa Barbara (UCSB), who specializes in new drug-delivery devices. “They don’t need any help. For these molecules, you can buy a patch and it can last up to a week. The problem comes when you try to deliver drugs that are large in size, or water-soluble. And those are the kinds of molecules for which we need to break the skin barrier.”

A single micro-needle measures a couple hundred micrometers, a length that could penetrate the outer layer of skin, delivering a drug directly to the underlying capillary bed without triggering nerve endings located deeper in the skin.

Over the past few years, researchers have explored several methods of using such micro-needles for drug delivery; strategies ranged from coating the micro-needles with drugs to pumping tiny amounts through micro-needles in controlled doses. Scientists at HP Labs realized that this latter approach resembled the inner workings of an inkjet printer–hundreds of tiny nozzles, spraying small amounts of ink at specific times and in preprogrammed patterns.

Janice Nickel, principal scientist at HP Labs, worked to reengineer the inkjet technology as a drug-delivery system, using HP’s thermal inkjet printer, or bubble jet, as a model. The bubble jet gets its name from its ink-pumping mechanism: each ink reservoir contains a tiny resistor that heats the area, creating a bubble that displaces the ink, pushing a small amount through the nozzle and onto the paper. Nickel and her colleagues designed the drug-dispensing patch in a similar manner, using heat to pump a fluid through tiny, 150-micrometer-long needles.

The prototype patch, which is about one inch square, contains 400 cylindrical reservoirs, each less than one cubic millimeter. Each reservoir is connected to a micro-needle, and the whole array is fueled by a low-power battery and controlled by an embedded microchip that’s programmed to heat up any given reservoir to deliver a specific drug. The design challenge, according to Nickel, was in localizing the thermal energy to a specific reservoir. “You have 400 reservoirs close together, and you want to activate one reservoir without activating any reservoirs around it, so you don’t get any cross talk.”

Crospon, the company that licensed the technology, has expressed interest in using the patch to painlessly deliver insulin. It’s also exploring the possibility of delivering multiple drugs through a single patch, over a long period of time. The array is also scalable, and it can be designed to contain tens or even hundreds of reservoirs, depending on its intended therapeutic use.

Nickel adds that down the line, the patch may be customized to the patient. For example, tiny sensors embedded in a patch could detect when medication is needed and treat an asthma attack in the middle of the night. Or a patch could automatically deliver insulin when it detects that glucose levels are low.

“I even had ideas in terms of military applications,” says Nickel. “You could put sensors on the device to detect chemical or biological weapons, and develop the appropriate antidote for the pathogen dependent on what was detected by the sensors. So there are a myriad of applications for this technology.”

Mitragotri of UCSB says that, with such advances in transdermal drug-delivery systems, the hypodermic needle may one day be no more than a painful memory. “A decade down the road, I envision more drugs to be delivered through patches,” he says. “For the patient, it means that instead of hypodermic needles, they could slap on a patch that could be delivered over a long period of time, in a painless way, and they can control delivery.”