Mosquitoes are perhaps useful for something after all, besides feeding frogs.
Along with his colleagues at Osaka’s Kansai University, mechanical engineer Seiji Aoyagi has created an almost pain-free hypodermic needle that is based on a mosquito’s proboscis. Perhaps surprisingly, the needle’s patient-friendliness comes from the fact that its outer surface is jagged, not smooth.
While mosquito bites definitely do itch, the itching only occurs after the feeding is complete, due to bacteria in the anticoagulant injected by the insects. The initial “bite” itself can barely be felt. How is this possible?
A mosquito’s proboscis includes an internal tubular labrum (that does the bloodsucking), which is sheathed between two serrated maxillae – one on either side. The maxillae are what first penetrate the skin and then sink into it, after which the labrum slides down between them. Because the maxillae have a jagged outer surface, they present a minimum amount of surface area to nerves in the skin. A smooth steel hypodermic needle, by contrast, makes contact with a maximum number of nerves, and is therefore uncomfortable.
Professor Aoyagi’s needle, etched from silicon, mimics the labrum and maxillae. Two harpoon-like jagged-edged outer shanks first penetrate the skin, after which a smooth drug-delivering/blood-taking tube moves down between them, only touching the patient at its sharpened tip. Mosquitos vibrate their proboscis to help the maxillae ease down through the tissue, which Aoyagi has also copied – each of the three parts of his device are vibrated by tiny piezoelectric crystal motors at around 15 hertz.
The needle in its present form is tiny, at just one millimeter in length, 0.1 millimeters in diameter, and with walls a mere 1.6 micrometers thick. It is attached to a five-millimeter-wide tank, designed for storing fluids that the needle collects. To test the needle, Aoyagi’s Kansai team used it to puncture silicone rubber with a skin-like resistance, underneath which was a container of red dye. The needle successfully drew the dye into its tank.