Penetration of hypodermic needles at precisely the right angle and arm depth required for a standard diagnostic test to determine a patient’s TB status may soon be a thing of the past!

A TB skin test typically involves injecting a small amount of substance called PPD tuberculin into the layer beneath the skin of the forearm with a steady hand. If infection is present, a hard swollen red bump appears in two to three days after the injection. The size of the bump reflects the severity of the infection.

Now, University of Washington engineers have developed a revolutionary new method of tuberculosis skin testing. They have created a patch comprising of biodegradable needles that has the potential to pierce the skin and deliver an accurate tuberculosis test.

Senior author Marco Rolandi, a UW assistant professor of materials science and engineering explained, “With a microneedle test there’s little room for user error, because the depth of delivery is determined by the microneedle length rather than the needle-insertion angle. This test is painless and easier to administer than the traditional skin test with a hypodermic needle.”

Biodegradable option
The microneedles that line the patch are made from silicon, metals, synthetic polymers and chitin, a biodegradable component derived from the outer shells of crabs, lobsters, shrimp, and cicadas.

The material shows promise and strength to break the skin and deliver the PPD tuberculin used in TB tests. Each needle of equal size (750 micrometers long/one-fourth of an inch) is glazed with purified protein derivative, which is used to test tuberculosis.

“It’s a great application of this technology and I hope it will become a commercial product,” said paper co-author Darrick Carter, a biochemist and a vice president at the Infectious Disease Research Institute, in a news release.

Test on guinea pigs
Rolandi and his team along with researchers at the Infectious Disease Research Institute in Seattle tested the efficacy of the patch on guinea pig subjects. It was noted that skin reactions from the patch in TB-positive animals matched those that occurred via hypodermic needle tests.

The patch could prove to be a simple, accurate alternative for patients who break into a cold sweat at the thought of needles. Scientists hope to start testing the TB patch on humans in the near future.

“It’s like putting on a bandage,” Rolandi noted. And “as long as the patch is applied on the skin, the test is always delivered to the same depth underneath the skin.”

The findings were published in the journal Advanced Healthcare Materials.

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