Engineers at University of Washington and colleagues from the Infectious Disease Research Institute in Seattle found a patch made with material from crustacean shells can deliver a tuberculosis skin test as successfully as current needle-based methods. The findings from the lab of Washington materials scientist Marco Rolandi appear online in the journal Advanced Healthcare Materials (paid subscription required).
Tests for tuberculosis are recommended as a precaution for some occupations, such as teachers and health care workers, or travelers to areas of the world where the disease is still prevalent. Current methods call for injecting a tiny amount of test fluid, a purified protein derivative of the tuberculosis bacteria, in the forearm under the skin surface with a hypodermic needle.
If administered successfully and a tuberculosis infection is present, the test will produce in two or three days a small, hardened swelling at the site of the injection. Current test methods, however, require the needle to be inserted to a specified depth and at a specific angle. If not done properly, the test may return a false negative or require being repeated.
Rolandi and colleages developed an alternative test method they feel is easier to administer and less prone to error. Their process uses a skin patch of microneedles — 750 microns in length (1 micron equals 1 millionth of a meter) — made with chitin, the material in the outer shells of crustaceans like lobster and crab. The chitin microneedles in the patch are coated with the purified protein derivative used in conventional tuberculosis tests.
To test the patch, the researchers immunized guinea pigs with the bacille Calmette-Guerin or BCG vaccine for tuberculosis used overseas and among high-risk populations. Individuals receiving the BCG vaccine often return positive results from tuberculosis tests. The results showed the patch delivers the test fluid to the appropriate skin depth and returns the same reaction as a test done properly with a hypodermic needle.
Rolandi says the microneedle patch can offer a simpler and more reliable option to test for tuberculosis, particularly with children who may be frightened by convetnional needles or where trained health care workers may be in short supply. The researchers plan to next test the patch with humans, and are investigating developing similar microneedle tests for other conditions, such as allergies.
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