US scientists study low-temperature plasmas as a sterilisation technique
They say results might depend on what the plasma is made of
Researchers at two American universities have teamed up to study how low-temperature plasmas can deactivate potentially dangerous biomolecules left behind by conventional sterilisation methods.
Using low-temperature plasmas is a promising technique for sterilisation and deactivation of surgical instruments and medical devices, but the researchers from the University of California at Berkeley and the University of Maryland at College Park say its effectiveness is not yet fully understood.
‘Bacteria are known to create virulence factors – biomolecules expressed and secreted by pathogens – even if they have been killed,’ says David Graves, a professor working on the research at UC Berkeley's Department of Chemical and Biomolecular Engineering. These molecules are not always inactivated by conventional sterilisation methods, such as heating surgical equipment in an autoclave, and can cause severe medical problems.
Graves says the prions that are thought to cause mad cow disease are a well-known example of harmful biomolecules.
‘These molecules may not be inactivated by conventional autoclaves or other methods of disinfection or sterilisation,’ he says. ‘In some cases, expensive endoscopes used in the brain must be discarded after a single use because the only way reliably to decontaminate them would destroy them.’
Another harmful biomolecule, lipopolysaccharide (LPS), is found in the membranes of E. coli bacteria. In humans, LPS can initiate an immune response that includes fever, hypotension and respiratory dysfunction, and might even lead to multiple organ failure and death.
Graves' research team, with a group led by Gottlieb Oehrlein at the University of Maryland, has focused its attention on Lipid A, the major immune-stimulating region of LPS. The researchers exposed Lipid A to the effects of low-temperature plasmas using a vacuum-beam system.
‘Low-temperature plasma generates vacuum ultraviolet photons, ions/electrons, and radicals that are known to be able to deactivate these molecules even at low temperature,’ says Graves.
‘However, the mechanisms by which they do this [are] poorly understood, so we can't be sure when they work and when they don't. Our measurements and calculations are designed to reveal this information.’
The scientists' results suggest that plasma-generated vacuum ultraviolet light can reduce the toxicity of Lipid A.
‘We have been surprised by the high sensitivity of endotoxins to UV or vacuum UV irradiation,’ says Oehrlein. ‘The results mean that the ability of plasma to sterilise equipment might strongly depend on what the plasma is made of, since plasma optical emissions vary based on plasma compositions.’
As a next step, the team will focus their efforts on understanding the influence of plasma-generated radicals on the deactivation of biomolecules.