• microwave discharges;
  • processing;
  • sterilisation;
  • spores;
  • UV spectroscopy;
  • VUV irradiation


Thumbnail image of graphical abstract

Catheters, which comprise small diameter (≤4 mm), long (typically more than a meter), thermosensitive polymer tubings, are generally used only once. This is because conventional low temperature sterilisation techniques are considered inadequate for used catheters. The plasma sterilisation method proposed in the current paper should allow for the achievement of re-sterilisation of catheters according to accepted regulations. The plasma process described enables one to sterilise, in less than 10 min, the inner part of a long 4 mm i.d. Teflon tube contaminated initially with 106Bacillus atrophaeus spores. This result was obtained by achieving an argon discharge at reduced pressure (750 mTorr) within the hollow (dielectric) tube itself. The discharge was sustained using a microwave field-applicator called a stripline, fully enclosing the tube to be treated. This linear field-applicator yields a uniform plasma all along the tube, hence the uniform biocide action. The biocide agents are the vacuum ultra-violet (VUV) photons, which include oxygen and nitrogen atomic lines, the N2 Lyman-Birge-Hopfield (LBH) bands, the UV photons emitted by the NOβ and NOγ molecular systems resulting from the contamination, even though at a very low-level, of the argon gas (high purity argon is used) by air. Scanning electron microscopy (SEM) revealed no apparent damage to the external structure of the spores and to polystyrene microspheres exposed to plasma during the time required for reaching sterility.

To check for sterility in such narrow bore tubes without having to cut them into two pieces, a procedure was developed to introduce and afterwards collect the bacterial spores used as bio-indicators. This diagnostic procedure allowed, at the same time, the imaging of the microorganisms relatively efficiently with SEM, showing the eventual stacking of bacterial spores, a possible source of sterilisation failure.