Porcupines are slow-moving creatures that lack the speed to run away from predators. Instead, defense comes in the form of some 30,000 quills that cover the back of each animal. And it doesn't take much pressure for the quills to leave a porcupine's body and enter the tissue of its attacker.
Scientists have long known that North American porcupine quills have barbs on their ends that make post-attack removal difficult and painful. To better understand how the quills pack their punch, Karp and colleagues inserted gently removed quills into a variety of targets, including chicken muscles, pig skin and synthetic human skin.
Using a mechanical tester, the researchers found that it took much less force than expected for the quills to penetrate tissues and more force than expected to pull them out, the team reports today in the Proceedings of the National Academy of Sciences.
The barbs, which cover just the last four millimeters (0.2 inches) of each quill's tip, proved to be essential. When the researchers painstakingly removed barbs from quills, tests showed that it took more force for penetration to occur and less force for ejection.
Removing just some of the barbs showed that the hooks at the very last millimeter of the tip were most important for stickiness. But all of the barbs seem to work cooperatively.
As a last step, the researchers used plastic to mold model quills, which behaved just like the porcupine-made versions. That opens the way to developing medical applications. By isolating the ease with which quills penetrate skin and muscle, for example, scientists could develop porcupine-inspired needles that cause less pain.
The team also used their synthetic quills to create a barbed patch, which stuck well to tissues. Compared with a barbless-patch, it required 30 times more force to remove.
Like Velcro (which was inspired by cockleburs), penicillin (which came from yeast) and super-sticky tapes that are being developed using insights gained from gecko feet, the new study offers yet another example of technological advancements derived from the natural world, said Anthony Atala, director of the Wake Forest Institute for Regenerative Medicine in Winston-Salem, North Carolina.
With so many species adapted to so many conditions, he said, there is still a lot left for us to learn.
"A lot of major accomplishments in the field of medicine have been made by replicating what nature does," Atala said.
"This is the first time porcupine quills have actually been looked at to see how they work," he added. "For anyone who has been in the doctor's office and been constantly prodded and poked, this could have major applications."