Germ-free in space

On a ride-along with a plasma researcher

by Julia Weiler  

February 1, 2015


Junior professor Katharina Stapelmann is searching for new ways of efficiently ridding medical equipment and components for aerospace applications of germs – by means of plasmas. With her work, the electrical engineer is thus continuing a long family tradition.

Junior professor Dr Katharina Stapelmann has built a plasma steriliser prototype at RUB.Katharina Stapelmann’s steriliser is suitable not only for medical instruments and aerospace components. It can also remove germs from drill templates for tooth implants – and is thus of interest for dental technicians who haven’t as yet had any sterilisation devices for treating sensitive metal and plastic parts at their disposal. Plasma – the state of matter with the highest energy level – is familiar to many in nature in the form of fire. Using cold plasmas, many items can be efficiently sterilised. Three screws are treated with a hydrogen plasma in the RUB steriliser. The steriliser at the RUB lab deploys a hydrogen plasma that is characterised by its pink glow. The researcher designed the sterilisation chamber as a convenient drawer with a surface in DIN-A4 format.

“When I was ten, I wanted to become a physicist,” tells us Katharina Stapelmann (fig. 1), and remembers how little understanding her friends showed when she talked about her plans. Astrophysics, that was her dream. Today, she is on the Ruhr-Universität Bochum payroll, as newly appointed junior professor. Her task: researching the correlation between plasmas and biological systems. That doesn’t sound like astrophysics and it isn’t; except it is a bit. In her capacity as electrical engineer, Katharina Stapelmann works at an intersection to biology. She researches ways of sterilising surfaces by means of plasmas. In the first place, the technology is applied to medical equipment, but her method is also of interest for the aerospace industry. Planetary protection is the keyword in this context.

Fig. 1© RUBIN, photo: Gorczany

The researcher designed the sterilisation chamber as a convenient drawer with a surface in DIN-A4 format.

“If a space probe is sent to Mars to take samples, we don’t want it to introduce any Earth bacteria to an alien planet,” says Dr-Ing. Stapelmann. Conversely, potential extra-terrestrial life forms should not be able to get to Earth unchecked. Accordingly, everything that is sent into space and that comes back from space is carefully sterilised. Various methods are applied, including autoclaves that operate with heat, chemical treatment and UV radiation. Still, not all germs are killed in this multi-stage process, which has given birth to extremely resistant bacteria strains over time – we cannot rule out that those strains could survive the journey to another planet on board a spacecraft. The key for fighting pathogens may well be plasmas.

With the support of the in-house workshop, Katharina Stapelmann built her own plasma steriliser (fig. 2) in the RUB lab, based on the work done by her predecessor. Many of the required components could not be simply bought off the peg. The researcher personally planned every screw and every hole in her experiment set-up (see "Building a steriliser"); she asked for advice at the workshop and assembled the parts manufactured there in the lab. “For a long time, the workshop was my best friend,” she remembers. In order to be able to observe her experiments precisely, she had two plasma chambers built from transparent Plexiglas – milled from a solid block and polished by hand. “Afterwards, the workshop told me never to approach them again with anything like that,” laughs Stapelmann. “But I would also bring them cake and Mett sandwiches.”

Fig. 2© RUBIN, photo: Gorczany

The steriliser at the RUB lab deploys a hydrogen plasma that is characterised by its pink glow.

Originally, the electrical engineer designed the device for medical applications (see below “Plasmas in hospitals”). But she soon realised that the aerospace industry could also benefit from her work. The first results look promising as far as planetary protection is concerned. In collaboration with the German Aerospace Center (DLR), Katharina Stapelmann tested the method for metal screws which were riddled with the particularly stubborn pathogen Bacillus pumilis SAFR032 (fig. 3). This bacteria strain is resistant to standard sterilisation methods. The plasma treatment, however, destroyed all germs within only five minutes – at a temperature of a mere 60 degrees centigrade. Theoretically, plasma sterilisation may achieve similar positive results at room temperature, as the researcher from Bochum estimates. The method would therefore be suited for heat-sensitive components.

Fig. 3© RUBIN, images: Stapelmann

For her sterilisation experiments, Katharina Stapelmann used screws that were coated by some 25 layers of a particularly persistent bacterium. By magnifying it by the factor 1000 under the scanning electron microscope (right), the single spherical bacteria cells are rendered visible. A magnification by the factor 25 (left) shows the screw thread.

Together with DLR, Katharina Stapelmann has now submitted a research funding application to the “European Space Agency”. Her idea: a plasma steriliser for the “International Space Station” (ISS). Space stations suffer from biofilms depositing inside them over time. Those biofilms are well organised bacteria colonies that set up stabilising structures outside the cells and are therefore particularly difficult to remove. They can be harmful to health and cause material damage. “Not many know that the MIR space station was abandoned due to such biofilms,” explains Katharina Stapelmann. This is not to happen again with the ISS. If the junior professor’s application is approved, she plans to demonstrate that her method is effective when it comes to bacteria that had grown in zero gravity. For this purpose, she would send a plasma to the space station that is capable of sterilising simple glass object slides. Her vision, however, is a plasma which can be used for treating large surfaces. “The system is versatile and can be adapted to individual requirements,” explains Dr Stapelmann. “If biofilms keep occurring in a certain location, it is feasible that something could be designed that stays in that location permanently and triggers a plasma automatically in certain intervals.” This is how one could kill off germs in space in good time.

“I was incredibly happy that I was able to enter the astro field through the backdoor, so to speak,” she says enthusiastically. But why the detour, rather than studying physics directly? “I asked myself in secondary school what I was planning to do with a degree in physics,” says Stapelmann. “I wasn’t sure if I would ever get a job as astrophysicist; it’s quite difficult to find one in the industrial segment. I assumed that I would have to get a PhD in physics, but I had no way of knowing if this was something I’d want to do and if my grades would be good enough.” Accordingly, Katharina Stapelmann asked herself what her strengths were. She soon found the answer: electrical engineering. That did not come as a great surprise: “My father had also studied electrical engineering in Bochum, my grandfather had been to an engineering school and later got a diploma, my great-grandfather had been an electrician.” The researcher has thus continued a family tradition, and she’s been more than happy with it. Should her plasma made it all the way up to ISS, it would be a dream come true.


Plasmas in hospitals

When Katharina Stapelmann designed her plasma steriliser, she was doing it with clinical applications in mind. She designed the sterilisation chamber as a convenient drawer with a surface in DIN-A4 format to hold standard tablets for medical instruments. The drawer could even be used as a sterile container. “You can, for example, put a set that’s going to be used in an appendectomy into the device, sterilise it and store the closed container in the cupboard right until surgery,” explains the junior professor from Bochum.

Compared with traditional methods, plasma sterilisation offers numerous benefits. It is more energy-saving, quicker and does not rely on harmful radiation or carcinogenic chemicals. Surgical instruments, for example, could be sterilised at 60 degrees centigrade within five minutes. Unlike autoclaves, plasma can moreover be also used for treating synthetic components. Autoclaves deploy damp heat which melts plastic and blunts metallic instruments. In the long run, this results in much wear and tear and, consequently, in high costs. Plasma treatment would lower material consumption significantly, and it could be performed at room temperature. Metallic objects that are very unevenly shaped are the only ones posing a challenge for plasma treatment.

Katharina Stapelmann has already designed a plasma steriliser prototype that could be utilised in hospitals. First, she worked out the parameters for an optimal sterilisation result using a complicated experimental set-up. Then, she implemented the thus gained insights into the prototype, which can now be operated much more easily via a touchscreen. What she now needs is an industrial partner who will make the product market-ready by validating and certifying the process and manufacturing the devices.

Plasma: the state of matter with the highest energy level

The ancient Greeks considered earth, water, air and fire the elements of all being. Today, we refer to solid, liquid, gas and plasma as states of matter. Plasma is the state with the highest energy and occurs in nature as, for example, lightning or fire. Its technical applications are researched at Ruhr-Universität at the Research Department “Plasmas with Complex Interactions”, which includes scientists from five faculties, including the Faculty of Electrical Engineering and Information Technology.

Contact faculty

Dr-Ing. Katharina Stapelmann
Institute for Electrical Engineering and Plasma Technology
Faculty of Electrical Engineering and Information Technology
Ruhr-Universität Bochum
44780 Bochum, Germany
phone: +49/234/32-29445

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