If you’ve never been smacked by a porcupine, you might not understand just how hard it is to remove the quills once they’re lodged in your flesh. But as it turns out, these quills are inspiring better designs for medical devices.
The North American porcupine (Erethizon dorsatum) has about 30,000 defensive quills, which are actually stiff hair with a black, cone-shaped tip. Each come with a layer of microscopic, backward-pointing barbs. And up to 800 barbs line the 4-millimeter stretch nearest the tip.
A team led by MIT’s Jeffrey Karp used natural porcupine quills and replica-molded synthetic polyurethane quills to dissect the physical forces involved in the penetration/removal of the quills into/from tissues like pig skin and chicken muscle.
They found that the geometry of the quill lets it penetrate a preceived predator’s tissue easily and adhere in place; the topography and placement of the barbs allow all this to be done with minimal force from the porcupine itself.
To pierce your skin, a porcupine quill needs only about half the force of an 18-gauge hypodermic needle. The barbs concentrating force along the edges, like how the serrations on a knife make cutting meat easier, Karp explains.
Once the quill is pulled backwards, the barbs flare out, snagging tissue fibers. Barbs render a quill about four times harder to pull out once they're embedded.
“This is the only system with this dual functionality, where a single feature -- the barbs -- both reduces penetration force and increases pull-out force,” Karp says.
Some design ideas for biomedical devices:
- Hypodermic needles that penetrate easily (less painfully) and resist buckling.
- Wound dressings with tiny barbed needles that pierce the skin and then hold tight – replacing chemical adhesives and medical-grade superglue, which can be toxic or trigger allergies. Quill-inspired adhesives wouldn’t require the use of reactive chemistry.
- In fact, barbed quills can be embedded in tissue so firmly that they can bind internal tissues securely for patients undergoing gastric-bypass surgery or other types of intestinal surgery. Sutures and staples can leak and cause complications.
- Barbed staples could be shorter and have a smaller diameter than current staples used to hold surgical incisions shut. Extricating these would cause less overall damage.
- Hollow versions of quill-inspired needles could deliver drugs and chemicals through patches adhering to the skin.
The researchers are now working with biodegradable materials that can be broken down in the body after they're no longer needed.
The work was published in Proceedings of the National Academy of Sciences this week.
Image by J. Glover via Wikimedia