Researchers at Glyndŵr University in Wrexham, North Wales, have developed a highly effective, portable, low-cost sterilisation technology
Researchers at Glyndŵr University in Wrexham, North Wales, have developed a highly effective, portable, low-cost sterilisation technology
Sterilisation of medical instruments is essential before their use on patients. Traditionally, this has been undertaken by high-temperature steam-based methods in high-pressure autoclaves (much like a pressure cooker). However, the evolutionary rise of MRSA (methicillin-resistant Staphylococcus aureus) pathogens has spurred on the development and uptake of more aggressive methods of sterilisation using chemical agents such as ethylene oxide gas, active chlorine chemistries and even combined vacuum plasma/hydrogen peroxide environments.
However, these newer approaches to sterilisation suffer from the drawbacks of the use of toxic chemicals (ethylene oxide is a potential carcinogen), damage to plastic parts (active chlorine can damage rubber parts) or very high costs (reliable systems can cost around £70,000).
A team of researchers in the Advanced Materials Unit at Glyndŵr University, led by Dr Andy Wright, has developed a simple, low-cost implementation of vacuum plasma technology that provides solutions for many of these problems using the clean sterilising power of oxygen-based plasma discharges. Interestingly, the technology was developed out of basic research into nano-structured thin films.
Etching away bacteria
Plasmas are often referred to as the fourth state of matter. They occur when gases become ionised when they are stripped of electrons from their constituent atoms by either extreme heat (as in our sun) or, more practically, by the application of a sufficiently strong electric field, most easily achieved at low gas pressures.
Dr Wright and his team discovered that the electric field inside a common domestic microwave oven run at low power can generate a plasma discharge inside a small vacuum vessel. This discharge is in ordinary air at a pressure of a few milliTorr and generates a strong concentration of atomic oxygen atoms. Atomic oxygen is a very aggressive species towards organic and bacterial/viral agents. Organic matter is simply etched away to water vapour and carbon dioxide, leaving no residue. Indeed, it is possible to strip heavy soot deposits from a surface in minutes using air plasmas. The etching action can be speeded up greatly by using oxygen-enriched argon gas instead of air. The overall sterilising action comes from a combination of physical etching, ultraviolet light emission and heat generation.
“Using standard thermally stable bacterial spore (Bacillus stearothermophilus) test strips, we have been able to demonstrate complete inactivation within 5 minutes’ exposure to the air plasma. An oxygen-enriched argon plasma would be able to sterilise in even less time with reduced heating effect.” - Tony Hawkins, Glyndŵr Innovations
Portable sterilisation
The Glyndŵr team modified a conventional microwave oven system (pictured) to create an innovative steriliser. The oven chosen is the simplest type commercially available and the retail price is around £30. The modifications include a small cylindrical glass vessel to be pumped out to low air pressure. [do you mean it pumps out air, to lower the pressure inside?] The total cost of the modified system, including a vacuum pump, is less than £2000 – making it very cost-effective compared with other sterilisation technologies.
The technology now exists for hospitals, surgeries and dentists to move away from steam-based sterilisation methods and take up a plasma-based approach that has been shown to be 100% effective against the most difficult pathogens. The cost of implementing this type of steriliser is far less than that for the larger systems currently available, so it is well suited for use in small doctor, dentist or veterinary surgeries, where items such as small