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A painless "microneedle" that mimics the way a female mosquito sucks blood has been built by engineers in India and Japan. The needle could be used to draw blood, inject drugs, and as a glucose-level monitor for diabetics.

A female mosquito sucks blood by flexing and relaxing certain muscles in its proboscis. This creates suction (or negative pressure) that draws blood into its mouthparts.

The new biocompatible microneedle, designed by Suman Chakraborty of the Indian Institute of Technology in Kharagpur and Kazuyoshi Tsuchiya of Tokai University in Kanagawa is based on the same principle.

In this case, the sucking action is provided by a microelectromechanical pump, which works using a piezoelectric actuator attached to the needle.

Contrary to popular belief, a mosquito bite does not hurt. It is the anticoagulant saliva that the creature injects to stop your blood clotting that causes inflammation and pain.
Snap safe

The new needle has an inner diameter of around 25 microns and an external diameter of 60 microns, which is about the same size as a mosquito's mouthpart. Its size and the fact that it works by suction, makes it painless. To compare, a conventional syringe needle has an outer diameter of around 900 microns.

In contrast to previous microneedles, which were made of silicon dioxide, the new device is robust because it is made of stronger titanium and related alloys, which dramatically reduces the risk of it snapping during injections.

The needle is also strong enough to penetrate as far as 3 millimetres into skin and reach capillary blood vessels.

Its size compared to earlier models also means that surface tension effects are exploited further, and the same capillary flow that draws water up into trees helps draw blood into the microneedle.

The researchers have calculated that their needle can extract 5 microlitres of blood per second. This volume is sufficient for measuring blood-sugar levels in diabetics using a glucose sensor that can be attached to the needle in a "wristwatch" design.
Production challenges

The design uses a shape-memory alloy to drive the needle into skin and a micro-pump for delivering drugs. The latter could be used to inject insulin (or other drugs) into the patient when required.

"The working principle of this device follows on from our discovery that in a well-designed microneedle, surface tension forces may overcome resistance from friction and draw up blood with unprecedented efficiency," Chakraborty told New Scientist.

Chakraborty and Tsuchiya hope to commercialise their needle, but there are still some challenges to overcome, including cost, scaling up the fabrication method, and making it more user-friendly.

"This new blood extraction is interesting, but I question its ability to be fabricated and initialised en masse," said Geoffrey Thomas of the University of Calgary, Canada, who is working on a similar blood glucose sampling and analysis project.

Journal reference: Journal of Applied Physics (DOI: 10.1063/1.2936856)