Microneedle patch provides painless test for tuberculosis

US scientists have developed a disposable patch that tests for tuberculosis as a simpler, more reliable and painless alternative to the traditional injection.

The patch, created at the University of Washington, contains microneedles that penetrate the skin on the arm to administer a reactant that causes a bump to form if the infection is present.

The current method for injecting the reactant, known as PPD tuberculin, is with a hypodermic needle that must be inserted at a precise angle and depth.

‘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 the university’s Marco Rolandi, senior author of a paper on the research.

‘This test is painless and easier to administer than the traditional skin test with a hypodermic needle.’

Tuberculosis causes more deaths than any other single infectious disease except HIV/AIDS and one third of the world’s population carry the TB bacteria.

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 tested the patch on guinea pigs and found that the skin reaction associated with having a tuberculosis infection caused by the patch test was the same as when using the standard hypodermic needle test.

Rolandi said a microneedle patch test had potential as a simpler, more reliable option than the traditional tuberculosis test, and would be particularly useful for children who are needle-shy, or in developing countries where medical care is limited.

‘It’s like putting on a bandage,’ he said. ‘As long as the patch is applied on the skin, the test is always delivered to the same depth underneath the skin.’

Microneedles penetrate the skin at a set depth and angle whereas hypodermic needles can be more easily used incorrectly.

Microneedle patches are increasingly being used as an alternative to traditional needles to administer medical tests, vaccines and drug treatments for a variety of diseases.

The needles can be made from silicon, metals and synthetic polymers but scientists have more recently been using natural, biodegradable materials such as silk and chitin, a material found in hard outer shells of some insects and crustaceans.

The University of Washington team developed microneedles made from chitin that are each 750 micrometers long and coated with PPD. The researchers found that these microneedles were strong enough to penetrate the skin and deliver the tuberculosis test.

The researchers will continue developing the microneedle tuberculosis test and plan to test it next on humans. They also hope to develop different diagnostic tests using microneedles, including allergy tests.