Painless Drug Injections

HP Labs has used its inkjet technology to make a micro-needle drug patch.

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.

Ouchless: A close-up of the prototype skin patch designed by researchers at HP Labs reveals the intricate components involved in this drug-delivery system. Micro-needles (the sparkling dots on the top of the black square platform) dispense medicine from tiny reservoirs. A microprocessor (gold square) is programmed to control dosage timing, size, and history. Credit: Brett Bausk, HP

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.

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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."