The team says the brush layer protects cells from the sticky mucus and acts as a "second barrier" in case viruses or bacteria penetrate the mucus.

BBC: 'Brush' offers clues to fighting lung disease

With a standard Pap, a little brush scrapes off cells from the cervix, which are stored in a vial to examine for signs of cervical cancer.

NPR: Retooling Pap Test To Spot More Kinds Of Cancer

But in conditions such as cystic fibrosis or chronic obstructive pulmonary disease (COPD), the "brush" fails to work properly, they suggest, becoming squashed and trapping mucus, which then becomes stuck to cells.

BBC: 'Brush' offers clues to fighting lung disease