No one relishes getting injections, but a new type of hypodermic may soon take the sting out of shots.
Using micro-needles that can pierce the skin but are too small to stimulate sensitive nerve endings, various miniature devices may not only make injections painless but transform the way drugs are taken.
"Micro-needles could be used to deliver a broad range of therapeutics," says Mark Prausnitz, a chemical engineer at the Georgia Institute of Technology in Atlanta. "And with an essentially needle-free method of vaccinating people, we would be able to do mass vaccinations in developing countries."
Prausnitz's team and a handful of scientists elsewhere have created micro-needles in various sizes using inexpensive metal and plastic polymers that are sturdy enough to penetrate the skin yet can be mass produced for as little as 5 cents per device.
The micro-needle device developed by his team is about half the size of a thumbnail and contains up to 400 tiny needles. It's designed to be pressed onto the surface of the skin, not jabbed into the skin as traditional hypodermic needles are.
Micro-needles could be used in several ways. One method entails coating a collection of micro-needles, called an array, with drugs. The drugs would then be absorbed by the tiny blood vessels near the surface of the skin.
The devices also could be used with a hollow needle that would force fluids, such as insulin, through a micro-pump for continuous infusions.
Or a micro-needle patch, which is composed of a bed of hundreds of needles, could be used to punch microscopic holes in the skin.. Then even large-molecule drugs, such as insulin, genetically engineered medications or vaccines composed of viruses, could be delivered through a patch because the holes would make the skin more permeable.
This approach may vastly improve vaccination rates in places where efforts have been stymied by poor sanitary conditions and lack of medical personnel to administer injections. Because micro-needle patches containing freeze-dried vaccines needn't be combined with sterile water or stored in a cool place, they would be easy to distribute. They'd also be cost effective and could be administered by individuals with minimal training, says Prausnitz.
Micro-needles could potentially revolutionize drug development. Currently, most drugs are taken orally because it's more convenient, but this method has limitations. Medications must be potent enough to survive the gastrointestinal tract, but gentle enough that they don't damage the liver. As a result, many promising therapies don't make it out of the laboratory.
Injecting drugs through the skin enables them to enter the bloodstream directly, which expands the universe of compounds that can be used to fight disease.
"This makes it possible to look at drugs that we initially threw out because they were toxic," says Dorian Liepmann, a biomedical engineer at UC Berkeley who has devised a micro-needle patch. "And we could use less potent compounds to get the same effect."
Recent research is encouraging. A 2003 Georgia Institute of Technology test on cadaver skin and laboratory animals demonstrated that micro-needle arrays can deliver drugs and vaccines through the skin.
And earlier this year, researchers at Berkeley and at UC San Francisco Medical Center conducted human tests with micro-needles coated with a nicotine derivative. The micro-needle shot was painless and delivered the chemical faster than a traditional syringe: Within two minutes, the 11 volunteers experienced a reaction to the compound, compared with 16 minutes when the derivative was spread on their skin's surface, according to study coauthor Raja Sivamani of UC Berkeley.
It will be a few years before these tiny needles replace traditional hypodermics. "But it will happen," Liepmann says. "People hate getting shots, and they'll do anything to avoid them."