The prospect of less painful medicine shots without needles came a step closer this month, as US researchers revealed how they have developed a device that delivers a controlled, tiny, high-pressure jet into the skin without using a hyperdermic needle.
While there are already several jet-devices on the market, they tend to be of an "all or nothing" design that delivers the same amount of drug to the same depth each time.
However the new jet-injection device that researchers at MIT have engineered can be programmed to deliver medicine into the skin in a range of doses to variable depths in a controlled manner.
A statement released earlier this week gives details of the new technology, with comments from study leader Ian Hunter, the George N. Hatsopoulos Professor of Mechanical Engineering at MIT, and some members of his team. Earlier this year, the journal Medical Engineering & Physics also published a paper where they describe the progress of their development.
Hunter and colleagues see a number of advantages to the technology.
One advantage is a reduction in needle-stick injuries. For instance, according to the US Centers for Disease Control and Prevention (CDC), there are around 385,000 cases a year in the US of health workers in hospitals accidentally pricking themselves with needles.
Another advantage of a needle-less device is it may help improve compliance, for instance among diabetes patients who are reluctant to use hyperdermic needles to inject themselves with insulin.
Team member Catherine Hogan is a research scientist in MIT's Department of Mechanical Engineering. She said:
"If you are afraid of needles and have to frequently self-inject, compliance can be an issue."
"We think this kind of technology ... gets around some of the phobias that people may have about needles," she added.
Scientists have been working for some time to find alternatives to the hypodermic needle. For instance, nicotine patches are one example of how to release drugs through the skin. But there is a limit to the size of the molecule you can use in a patch: it has to be small enough to pass through the pores of the skin, which rules out larger protein-based drugs, for instance, which are increasing in use.
A jet injector device delivers a high-velocity jet that penetrates the skin. But while these are commercially available, many have spring-loaded designs, they are all limited by the fact they deliver the same amount of drug each time to the same depth of skin.
But thanks partly to a "custom high-stroke linear Lorentz-force motor that is feed-back controlled during the time-course of an injection", the MIT jet injector can deliver a range of doses to variable depth in a highly controlled manner.
The feed-back control aspect of it allows the device to react in "real time" and adjust itself accordingly to meet the programmed instruction.
The Lorentz-force motor is essentially a small, powerful magnet surrounded by a wire coil attached to a piston located inside a drug ampoule.
When an electric current passes through the coil it produces a magnetic field that forces the piston forward, ejecting the drug at very high pressure and speed (nearly as fast as the speed of sound) through the nozzle of the ampoule, which is about the same thickness as the proboscis of a mosquito.
The researchers have shown how using this device, they can monitor and modulate continuously the speed of the drug jet, and "regulate precisely the volume of drug delivered during the injection process", as they write in their paper.
They also report being able to control injection depth up to 16 mm, and "repeatably and precisely inject volumes of up to 250 μL into transparent gels and post-mortem animal tissue".
By controlling the amount of current, the researchers control the speed and pressure. They have generated pressure profiles that modulate the current.
There is a high-pressure phase that ejects drug at a speed sufficient to "breach" the skin and reach the desired depth, and there is a lower-pressure phase that delivers drug in a slower stream that can easily be absorbed by the surrounding tissue.
From tests, the team established that different skin types may require different pressures to deliver the right volume to the right depth in the skin, as Hogan explained:
"If I'm breaching a baby's skin to deliver vaccine, I won't need as much pressure as I would need to breach my skin."
"We can tailor the pressure profile to be able to do that, and that's the beauty of this device," she added.
The team is also developing a version of the device that delivers drugs normally dispensed in powdered form: by programming the device to vibrate, the powder becomes "fluidized" and can penetrate the skin like a liquid.
This version would be very useful in situations where there is risk of a "cold chain" problem. This problem is not uncommon in developing countries, where whole batches of drugs and vaccines have to be destroyed if they can't continuously be kept refrigerated in liquid form.
Written by Catharine Paddock PhD
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