Porcupines Inspire Less-Painful Needles

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Porcupine quills could inspire a new class of less-painful medical needles that slide effortlessly through flesh, scientists say.

In a new study, researchers examined porcupine quills to characterize the forces they need to enter and exit the skin. The researchers used as their model the North American porcupine, which has about 30,000 barbed quills to defend against predators. Each quill is several centimeters long, with tips covered in microscopic, backward-facing barbs.

These barbs allow the quills to slide easily into flesh, but make them difficult to pull out. The barbs act to localize the penetration forces, allowing the quills to tear through tissue fibers much more easily, just as a serrated knife cuts through tomato skin far more cleanly than a straight-edged knife.

When it comes to the force required for the pullout, the barbs act like anchors that keep the quill from exiting.

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To determine the full importance of the barbs, the researchers carefully removed them from some quills and compared these smoother quills to regular, barbed quills. Tests found that barbed quills require 60 to 70 percent less force to penetrate muscle tissue and were four times harder to remove.

Using what they've learned, the researchers have already created a synthetic porcupine quill that they will test in a variety of medical applications. They think the synthetic quills could be tweaked so they can penetrate tissue easily, without being as difficult to remove as real porcupine quills.

"If you can still create the stress concentrations, but without having a barb that catches tissue on removal, potentially you could create something with just easy insertion, without the adhesion," study coauthor James Ankrum of MIT said in a statement.

The synthetic quills could function not only as less-painful needles for injection, but as alternatives to staples used in surgery.

Porcupine quills "can strongly grip tissue with minimal depth of penetration, less than half a centimeter is enough and they don't need to bend like staples to achieve secure fixation," Ankrum said.

The grippy barbs on porcupine quills could also lead to stronger adhesives that can bind internal tissues more securely, the team says.

There is a great need for such adhesives, especially in patients who have undergone gastric-bypass surgery or other types of gastric or intestinal surgery, according to the researchers. These surgical incisions are now sealed with sutures or staples, which can leak and cause complications.

The research is detailed in this week's issue of the journal the Proceedings of the National Academy of Sciences.

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