Clean cut

Researchers at the University of Edinburgh have developed a new plasma-based process that is claimed to cleanse surgical instruments of the infectious agents responsible for Creutzfeldt-Jakob Disease (CJD).

While conventional sterilisation techniques can eliminate virtually all pathogens such as bacteria, viruses and fungi, the team at Edinburgh has devised a technique that removes prions. These are fundamentally different from other pathogens as they are proteins, making them resistant to high temperatures and far harder to remove.

CJD is the commonest form of prion disease in humans, comprising a range of disorders including sporadic CJD and variant CJD — the human form of BSE or ‘mad cow disease’.

The progressive neurological disorders are fatal and there is no known cure. In the case of variant CJD, the prion is found to be distributed widely throughout the body and not just confined to the central nervous system, raising fears that it may be transmitted by contaminated surgical instruments.

During the Edinburgh project the medical instrument decontamination and scanning team (MIDAS) — which researches new sterilisation technologies — adapted a technique well established in electronics and nanotech etching.

Prof Robert Baxter of the university’s school of chemistry said the surgical instruments are placed in a vacuum chamber. Here, radio waves are used to excite a reactive gas — in this case a helium oxygen mixture — converting it into a plasma that scours instruments, breaking down any traces of tissue and removing microscopic levels of bacteria far more efficiently.

‘It is essentially an etching process,’ said Baxter. ‘Excited atoms bombard biomolecules. Radicals form on the biomolecules and they spontaneously break down, producing CO2, nitrogen dioxide and water, which are innocuous compared to what you were dealing with.’

According to Baxter, the process overcomes the limitations of conventional techniques when it comes to removing prions.

‘A steam steriliser will clean virtually anything, but it doesn’t actually remove anything,’ he said.

‘There is no real microscopic cleaning. We reckon we can do about a thousand times better by using plasma cleaning.’

One of the key advantages of the technology is its ability to carry out sterilisation at a low pressure, which keeps down the temperature created during the process.

Baxter said surgical instruments can take heat up to approximately 150°C, but after that metal fatigue comes into the equation.

Development of the system has been backed by the Department of Health, and is currently at the prototype stage. MIDAS is looking to secure bridge funding to commercialise the technology.