22P07622P076-P
Internal sterilization of a narrow tube using ECR plasma
ECRプラズマを用いた細管内部の滅菌
Daiki Anraku, Raiki Ichikawa, Akira Yonesu and Nobuya Hayashi
安楽大輝, 市川礼記, 米須 章, 林 信哉
University of the Ryukyus
1 Senbaru, Nishihara, Okinawa 903-0213, Japan
琉球大学 〒903-0213 沖縄県西原町千原１番地
Saga University
1 Honjyo, Saga, 840-8502, Japan
佐賀大学 〒840-8502 佐賀県佐賀市本庄町１番地
Internal sterilization of a narrow tube using the Electron Cyclotron Resonance (ECR) plasma has been
investigated. We succeeded in generating ECR plasma only inside a silicon narrow tube of 5mm in innerdiameter without a inner electrode. The existence of an effective UV and oxygen radical for sterilizationfrom the observation of the emission spectrum were able to be confirmed. From sterilization experiments,
it was found that our method can sterilize the spore of Geobacillus stearothermophilus of 7.9×104 CFU in
the narrow tube for 20 sec.

1. Introduction
Introduction
In plasma sterilization method, bacterias can be
killed by the effects of UV radiation andactive radicals that are generated in the plasma [1].
The plasma sterilization method is safer and more
short time process than a conventional sterilization
method. Therefore this method attracts attention asa new sterilization method of the medical device.
However, it is thought that the plasma sterilization
method is unsuitable for internal sterilization of anarrow tube such as a catheter, because the plasma
generation is generally very difficult in a smallspace.
In order to solve this problem, several methods tosterilize the inside of the tube by generating adielectric barrier discharge, using wire electrode isinstalled in the tube, has been studied [2, 3]. Wepropose a new method to sterilize the interior of thenarrow tubes using ECR (Electron CyclotronResonance) plasma that requires no electrode.
ECR plasma is preferentially produced around theresonant region where the magnetic field strength iscorresponding to an ECR frequency.
Thus, it is thought that we can produce the ECR
plasma in the narrow tube by means of locating theresonant region inside the tube. In this work,
internal sterilization of the narrow tube using ECR
plasma, have been investigated.
2. Experimental apparatus
Figure 1 shows a experimental apparatus. The
experiment was performed in the vacuum chamber
which
contains
arectangularmagnet(77×32×24mm). This magnet has a flux density of

3.7KG at it’s surface, so that the region of theresonant magnetic field for ECR (875G) exists near
the magnet surface. We set a silicon tube with an
inner diameter of 5mm and a length of 250mm at
the resonant region (see Figure 2). The microwave
with a frequency of 2.45GHz is introduced into thechamber through a tapered waveguide.
The tube temperature was measured by thermolabels that change color according to temperature.
Strip type of biological indicator (6×2mm) which
are coated with the bacteria Geobacillus
stearothermophilus with a population of 7.9×104
were used to assess the ability of sterilization. After
plasma irradiation, the irradiated B.I. samples werecultured in a culture tube with tryptic soy broth for
72 hour at 60°C. Then we evaluated the success ofthe sterilization by the presence of color change ofthe culture solution.
Microwave
Air
Chamber
SiliconetubeQuartz
pipe
Pump

TeflonMagnetFig.1. Schematic of Experimental apparatus.

A yoke of ironMicrowave

The temperature of the tube for exposure time 20
sec was 60-75°C. The heat resistance of the catheter
is about 90°C. Therefore thermal damage to thetube by ECR plasma sterilization is considered tobe low.

ECR plasma
resonance region

Siliconesamarium-cobalt
tube
magnetFig.2. Layout of the magnet and silicone tube

3. Result and Discussion
Figure 3 shows the photograph of the ECR
plasma generated in the narrow silicon tube with an
inner diameter of 5mm. As shown in the figure,
ECR plasma exits only inside the narrow tube. Theadvantage is that there is no pressure difference
between the outside and the inside of the narrowtube, and no electrode inside it.
In order to evaluate the presence of plasma
species responsible for antimicrobial effects, weinvestigated the optical emission spectra of the ECR
plasma. As shown in the typical emission spectrum
in Fig.4, excited oxygen atomic lines (777.2nm,844.6nm) and UV radiation were observed. It is
generally accepted that the principal agents
responsible for bacterias killing in the plasma are
active radicals and UV radiation.
For the sterilization test of the narrow tube by
ECR plasma, the biological indicator was located init. The ECR plasma was generated in the narrowtube under the following conditions; Air pressure of
1.0×10-1Pa, microwave power of 100W. The resultof the sterilization test was shown in table I. We
confirmed that the biological indicator located in
the narrow tube was sterilized for only 20 sec
plasma exposure time.

Silicone tube

Quartz Pipe

MagnetFig.3. Photograph of the ECR plasma generated in thesilicone narrow tube (Air pressure of 1.0×10-1Pa,
microwave power of 100W).

Fig.4. The typical emission spectrum of ECR plasma(Air pressure of 1.0×10-1Pa, microwave power of 100W).

Table I. The result of sterilization
exposure time [s]sterilization results

345101520××
○×
×○○○
○○×○○
×○○○
○○○○○

Temperature[°C]

50~55
60~70
60~70
60~75
○: sterilized ×: failed

4. Conclusion
We succeeded in generating ECR plasma inside
the silicon narrow tube of 5mm in diameter, andsterilizing
thesporeofGeobacillus
stearothermophilus of 7.9×104 CFU for 20 sec init. We consider this sterility was caused by the main
effect of oxygen radicals and UV radiation. The
temperature of the tube for exposure time of 20 sec
was 60-75°C. Therefore thermal damage to the tube
by ECR plasma sterilization is considered to be low.
References[1] M. Moisan, J. Barbeau, M. Crevier, J. Pelletier,N. Philip and
B. Saoudi: Pure and Applied
Chemistry 74 (2002) p.349-358[2] H. Eto, Y. Ono, A. Ogino and M. nagatsu: Plasma
Prossess. Polym. 5 (2008) 269[3] T. Sato, O. Furuya, K. Ikeda and T. Nakatani: Plasma
Prossess. Polym. 5 (2008) 606