Originally Published MDDI January 2006
R&D Digest: The monthly review of new technologies and medical device innovations.
By Heather Thompson
A handheld device that generates a thin plume of charged gas can kill bacteria, heal wounds, and treat plaque. Eventually it may also be used to remove tumors.
Created by biophysicist Mounir Laroussi, PhD, at Old Dominion University in Norfolk, VA, the 12-cm-long plasma pencil is portable, safe on skin, and remains stable for up to 8 hours.
The device works by harnessing what is known as cold plasma. Plasmas are generated anywhere atoms are stripped of electrons. The neutral particles and charged ions and electrons form a mixture that has been likened to soup. In dense atmospheres, like Earth, plasmas are extremely hot and hard to control. However, since the mid-1990s, researchers have concentrated on designing cold plasmas.
Laroussi is considered an expert in this field and has built several large machines to produce usable plasma. This new device, however, marks the first time cold plasma has been available in a relatively inexpensive and reliable handheld instrument.
“People get very confused when you talk about cold plasma, because everything is relative,” he says. “What I mean is, there are so-called cold-plasma machines that produce plasma at 70º–100ºC. That is too hot for biomedical use. We are producing a true room-temperature plasma that can be used outside a vacuum on human skin.”
For the design, Laroussi says, there were two major issues to address: flow and power source. The team had to create a plume that would be long enough to use effectively. They also had to design an electrical source that would both create plasma and keep it at room temperature. Cold plasma is generated by an electrical source that targets lighten electrons and forces them into high speeds, but leaves heavier ions alone. When electricity is pulsed 1000 times per second rather than left on as a steady stream, the temperature remains stable. Pulsing the energy source helped the team solve both problems.
“In cold plasma, as in life, timing is everything,” quips Laroussi. “The timed pulses keep the temperature down and energize the plume so that it reaches to about two inches past the end of the pencil.”
A clear benefit of the device is that, although it can break open bacteria cell walls, the plasma does not damage human skin. “Cold plasma affects prokaryotic cells, like bacteria, differently than eukaryotic cells found in mammals,” Laroussi explains.
The plume produces only a slight tingle on skin, but it contains highly reactive oxygen atoms that attack bacteria. “Right now it is more effective on some types of bacteria than others, and we are fine-tuning it to be more efficient,” Laroussi adds.
The researchers have used the pencil very successfully on Escherichia coli, making it plausible for removing dental plaque. Laroussi is also working to make the pencil usable for disinfecting wounds.
Although it is far in the future, he says, the pencil may also be used to trigger programmed cell death in cancerous tissues. “We are still trying to find out what level of power we need to induce apoptosis, but not necrosis,” he says. There is also the possibility for the plasma device to remove or etch unwanted cells. Again, cautions Laroussi, that type of refinement will take many more years.
Laroussi says that the device needs a few more tests before it is ready for commercialization, and that the university will be eager to partner with industry to create a marketable device, most likely within the next few years. And Laroussi will continue his cold plasma research. “I will keep refining the device and collaborating with microbiologists.”
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