Mosquitoes inspire' pain-free' injections

Mosquitoes' bites are painless

Scientists looking for a method of giving pain-free injections think the mosquito may hold the clue.

Mosquito bites are painless, so Japanese microengineers decided to try to replicate the mosquito's proboscis in a needle that patients would not feel as doctors took blood or injected drugs.

They hope the so-called "microneedle" will be the forerunner of small wireless devices for collecting blood that could be permanently attached to the body.

Blood-sugar levels in diabetics could be monitored in this way, or blood samples collected, the researchers suggest.

Anything that takes away people's pain and their fear of needles is exciting

Peter Simpson, Royal College of Anaesthetists

The mosquito bites by stabbing the skin painlessly, then injecting anticoagulant saliva to stop your blood clotting while it feeds, which is what carries the bacteria which cause irritation and pain.

Researchers at Kansai University in Osaka suggest the mosquito's bite is painless because it's proboscis is highly serrated.

Syringe needles are smooth, and leave a lot of metal in contact with skin tissue. But the mosquito's proboscis leaves only small points in contact, reducing the stimulation of nerves.

Silicone tests

The team created a tiny needle one millimetre long and 0.1 millimetres in diameter by cutting slices of silicon dioxide into a jagged shape and then bonding them together. The needle's walls were just 1.6 micrometres thick.

A 5mm-wide tank, which could store blood or fluids collected by the needle was added.

Doctors could analyse the samples via an optical fibre inserted into the tank.

The team tested the needle on silicone rubber, which mimics the reaction of skin. The rubber was wrapped around a vessel containing red dye.

The tank attached to the needle filled with the dye, showing the 'skin' had been successfully punctured.

Seji Aoyag, who led the research, said there were some problems to overcome before the needle could be tested on humans.

'Exciting'

He said: "It is still a big problem that our needle is brittle. If a piece broke off in a hypodermic injection a blood clot could form."

If such a clot entered the bloodstream and travelled to the brain or heart it could be fatal.

Peter Simpson, vice-president of the Royal College of Anaesthetists, told BBC News Online: "Anything that takes away people's pain and their fear of needles is exciting."

He said the needles were too small to be used in anaesthetics, but added that if they were made more robust, they could be useful in other areas of medicine.

The research is published in New Scientist magazine.