This bite won’t hurt a bit

A team works to emulate a mosquito bite and design gentler needles

Researchers have dissected the physics of mosquito bites, hoping to learn some of the bugs’ stealthy tricks and to gain inspiration for designing needles that hurt less.

This scanning electron microscope image shows a mosquito’s needle-like organ inside a sheath that enables it to puncture skin without buckling. This structure could inspire the design of pain-free microneedles. . Ramasubramanian/Bioinspiration & Biomimetics

Reporting in the December Bioinspiration & Biomimetics, a team at North CarolinaStateUniversity in Raleigh proposes an explanation for the mosquito’s ability to pierce the skin.

“How does a mosquito bite, and it’s able to penetrate painlessly?” asks lead author and mechanical engineer Melur Ramasubramanian. “Maybe we can learn something from that.”

The issue, Ramasubramanian says, is how a mosquito’s fascicle, the needle in its proboscis, can be pushed into the skin without buckling — despite being just 20 micrometers across and not particularly stiff.

Normally, the fascicle is wrapped in a sheath called the labium. Ramasubramanian and his colleagues have made a theoretical model to show that the labium increases the stiffness of the fascicle by a factor of five, preventing it from buckling. As a mosquito inserts the fascicle into the skin, the labium pulls back, so that only the fascicle penetrates the surface.

The labium was previously known to contain ducts that lubricate the fascicle and deliver anticoagulants into the skin, but the team’s model shows the sheath has a more structural function as well. “The labium is thought of as something that holds everything together and keeps it lubricated. But it has an important role in helping the mosquito bite,” Ramasubramanian says.

To corroborate their idea, the team used high-speed camera videos of the feeding behavior of Aedes aegypti, a mosquito that carries yellow fever and dengue fever.

“I am quite happy with the observation that the mosquito can’t get an initial wound in the skin without extra support from the labium,” says Julian Vincent, a biologist at the University of Bath in England. But Vincent also says that the researchers haven’t proved conclusively that the mechanism alone can enable the bug to push the needle in — in other words, that mosquitoes aren’t employing some other trick as well. To validate its model, the team should have “chopped off” a mosquito’s proboscis and directly measured the fascicle’s resistance to buckling, with and without a sheath, Vincent says.

Ramasubramanian now wants to imitate nature’s design and experiment with polymer microneedles that would penetrate the skin and hardly be felt. These needles could be used to inject small amounts of drugs or to monitor blood glucose levels in diabetics. Other labs have experimented with silicon microneedles, which are stiffer and buckle less, but are also more brittle and tend to break, Ramasubramanian says. Polymer needles with retractable sheaths might overcome those limitations.

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