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Cotton Swab Drug Testing

Finding new ways to deliver drugs through the skin has always been a challenge. Researchers from the Harvard-Massachusetts Institute of Technology (MIT) Division of Health Sciences and Technology are developing a new technique that can painlessly blast medication through the skin, eliminating the need for hypodermic needles for drug delivery and blood analysis.

As explained by MIT's researchers, the technique, called "microscission," uses a stream of gas to bombard small areas of the skin with tiny (25 [micro]m) crystals of inert aluminum oxide. James Weaver, PhD, biophysicist from the Harvard-MIT Division of Health Sciences and Technology, says, "The process removes the stratum corneum (outermost layer of skin) over a tiny area allowing for access to the viable epidermis."

The sharp particles remove the rough surface-layer of the skin and create tiny holes, or microconduits, that lead into the lower layers of skin and serve as receptacles for drugs. The particles "scize" (cut) tissue, which is removed by the gas flow. The resulting microconduits formed are invisible to the naked eye, measuring less than 1/4 mm in diameter and between 1/20 and 1/5 mm in depth. The entire process takes less than 20 s.

The researchers have demonstrated "proof-of-principle" that microscissioning can be used for drug delivery and is much less painful than a needle prick. The technology development team included medical doctors and dermatologists, as well as physicists and biophysicists.

Researchers tested the technique by seeing whether they could administer lidocaine from a cotton swab to human volunteers through four microconduits. The volunteers said they felt only a gentle stream of air against the skin. The patch of skin was tested by sharp-point probing, and proved to be anesthetized within minutes. By contrast, topical application without the microconduit took over an hour.

During this study, Weaver's research team observed that the onset of anesthesia takes longer in microconduits deep enough to yield blood than in shallower, non-blood producing microconduits. "Possibly the blood outflow impedes inflow of the externally-applied lidocaine, or the clotting blood partially obstructs the microconduit," he says. Deep blood-yielding microconduits could be useful, however, as a painless way for people with diabetes to check their blood sugar levels.

Microscissioning may have multiple applications. For example, blood glucose measurements were taken with two commercial monitoring systems, and 180 [micro]m-deep microconduits yielded volumes of several [micro]L, with a faint pricking sensation as blood entered tissue. Other testing has shown microconduits reduce through-skin electrical impedance between two ECG electrodes from 4000 to 500 [ohm]. In all applications tested to date, microscissioning has been shown to be painless, rapid, and free of scarring.

Although further studies are needed, researchers say microscission is a minimally-invasive drug delivery approach to those with "needle-phobia," and could be set to revolutionize extraction of interstitial fluid and blood samples. The research team hopes to move the technology into initial clinical trials by the end of 2004.

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