YOU never notice mosquito bites until it鈥檚 too late鈥攂ecause the bite itself is painless. So why not try to mimic the mosquito鈥檚 unique 鈥渟tinger鈥� to make a needle that you won鈥檛 feel when it鈥檚 taking blood or injecting drugs? That鈥檚 precisely what a team of Japanese microengineers has done.
Contrary to popular belief, a mosquito can stab you with its proboscis without you feeling a thing. It then injects anticoagulant saliva to stop your blood clotting while it feeds, and it鈥檚 this gunk that carries the bacteria which cause irritation and pain.
Seiji Aoyagi at Kansai University in Osaka and his colleagues concluded that the initial bite is painless because the mosquito鈥檚 proboscis is highly serrated. Unlike the smooth surface of a syringe needle, which leaves a lot of metal in contact with skin tissue, the jagged edge of the proboscis leaves only small points in contact. This greatly reduces stimulation of the nerves, says Aoyagi, causing far less pain.
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To mimic this effect, Aoyagi and his engineering team created a needle just 1 millimetre long and 0.1 millimetres in diameter. They did this by etching slices of silicon dioxide into a jagged shape and then bonding them together. The needle鈥檚 walls were just 1.6 micrometres thick.
Then they fitted the needle with a 5-millimetre-wide tank, which in future could store blood or fluids collected by the needle. An optical fibre inserted in the tank would allow doctors to analyse samples.
To test the needle鈥檚 strength, the researchers pushed the needle into a piece of silicone rubber鈥攚hich has puncture resistance similar to skin鈥攚rapped around a vessel containing a red dye. The tank filled with the dye, indicating that the needle is up to the challenge of puncturing skin.
The inventors hope the microneedle will be the forerunner of small wireless devices for collecting blood that could be permanently attached to the body. Such devices could monitor blood-sugar levels in diabetic people or collect blood samples from patients for diagnosis in a lab.
Aoyagi plans to conduct human trials eventually, but there are still some hurdles to overcome. 鈥淚t is still a big problem that our needle is brittle,鈥� he says. 鈥淚f a piece broke off in a hypodermic injection a blood clot could form.鈥� And if such a clot entered the bloodstream and travelled to the brain or heart it could be lethal. Aoyagi hopes further research will resolve the issue and lead to safer designs.