Every year, millions of people get a tuberculosis (TB) skin test to determine if they have the bacterial infection, which usually attacks the lungs. But the standard diagnostic test is difficult to give, because a hypodermic needle must be inserted at a precise angle and depth in the arm to successfully check for tuberculosis. But now, a team of engineers at the University of Washington (UW), Settle, say that they have created a patch filled with tiny, biodegradable needles that can penetrate the skin perfectly and precisely deliver a tuberculosis test.

With the standard test, if a hypodermic needle is inserted at the wrong angle, the solution to check for tuberculosis is injected either too deep or shallow into the skin, and the test fails. Microneedles act as a painless alternative to hypodermic needles to deliver drugs to the body. The microneedle patch can be placed on an arm or leg, which then creates small holes in the skin's outermost layer, allowing the drugs coated on each needle to diffuse into the body.

"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," said senior author Marco Rolandi, a UW assistant professor of materials science and engineering. "This test is painless and easier to administer than the traditional skin test with a hypodermic needle."

The UW team developed microneedles made from chitin, found in the shells of some insects and crustaceans, that are each 750 micrometers long, or about one-fortieth of an inch. Each needle tip is coated with purified protein derivative, the material used for testing for tuberculosis. The researchers found that these microneedles were strong enough to penetrate the skin and deliver the tuberculosis test.

Rolandi's lab and collaborators at the Infectious Disease Research Institute in Seattle believe this is the first time microneedles made from biomaterials have been used as a diagnostic tool for tuberculosis. They say their test will be easier to use, less painful and has potential as a simpler, more reliable option for children who are needle-shy, or in developing countries where medical care is limited.