Pulling out a porcupine quill is painful and slow, as many a dog
discovers to its dismay after tangling with the big rodent. But
those tenacious quills are inspiring efforts to develop better
medical devices, including less painful needles. It turns out
that no one had really picked apart why it's so hard to remove a
porcupine quill. Barbs, sure. But the barbs not only stick like
mad. They also make it much easier for the quill to pierce skin
and flesh. "We found the barbs have this dual functionality,"
says Jeffrey Karp, a bioengineer and a chairman of the Center
for Regenerative Therapeutics at Brigham and Women's Hospital in
Boston. "That was a surprise." It doesn't seem to make sense
that a barbed quill would go in more easily than a smooth one.
But Karp and his colleagues discovered that the barbs work just
like the bumps on a serrated knife. The knife's wavy blade
concentrates force at the tips of the teeth, requiring less
power overall to cut soft foods like tomatoes or bread. Knife
makers have known t