The field of medicine often requires materials that need to be sterile at the same time as having low thermal stability. The Institute of Plasma Research at the University of Stuttgart has developed a dry-heat plasma sterilisation method that is a faster, more effective and less dangerous alternative to previously used methods.
For quite some time plasma has been used for a broad range of everyday devices including plasma screens and energy saving light bulbs as well as in the treatment of materials and the modification of surfaces. It is envisaged that fusion research will solve human energy problems in an environmentally friendly way. The EU has high hopes of fusion research and this is reflected in the fact that funding for the ITER nuclear fusion research reactor was doubled in July 2010. The reactor is due to become operative in 2019.
The researchers from Stuttgart have turned their attention to another area of everyday life: hygiene in the fields of medicine and pharmacy. The Institute of Plasma Research at the University of Stuttgart, which consists of the Departments of Fusion-Oriented Plasma Physics, Plasmadynamics and Diagnostics and Plasma Technology and is led by Prof. Dr. Stroth, deals with the entire range of plasmas. In the field of fusion research, the Institute offers know-how for the creation of fusion plasmas using microwaves. In addition, the researchers carry out experiments and computer simulations related to the energy- and particle transport in fusion plasmas.
What is plasma?
Plasma is often called the fourth state of matter. It consists partially or completely of free charge carriers such as ions and electrons. Neutral atoms and molecules can also be present in plasma. Plasmas usually have a characteristic glow, which is caused by the excitation of gas particles.
The Stuttgart researchers mainly use low-pressure microwave plasmas for their investigations. 2.45 GHz microwaves act on the gas and accelerate the relatively light and extremely mobile free electrons. Due to the inertness of the neutral particles and the relatively heavy ions, the high-frequency electromagnetic fields have hardly any effect on the neutral particles. In this way the free electrons move around on a largely inactive background. Energy is transferred when the so-called “hot electrons” collide with the bound electrons in the gas-particle envelope. The researchers are extremely skilled in using this energy in many ways.The Department of Plasma Technology is mainly focused on the activation and cleaning of surfaces, the formation of barrier layers, encapsulation and sterilisation.
"For example, we can alter the surface characteristics of substrates," explained plasma physicist Dr. Andreas Schulz. "We are very careful not to damage the surfaces." Through the action of the electron-cyclotron resonance (ECR) phenomenon, charged particles are forced by magnetic fields into circular paths, thereby creating local, very intensive, but nevertheless non-thermal plasma. The high density of the plasma is associated with a huge degree of chemical reactivity and therefore enables high coating rates. This enables plastic bottles to be coated with a very gas-tight, razor-thin quartz layer within a few seconds. The industrial application of plasma is made possible by the Duo Plasmaline, developed and patented by the Institute of Plasma Research. The Duo Plasmaline enables the linear and homogeneous production of plasma several metres long.
The physicists also concentrate on combating microorganisms. In order to test the sterilising effect of plasma, the Stuttgart researchers have investigated several gases and their effect on a broad range of microorganisms. Effective deactivation of Bacillus atrophaeus, bacteria that are generally very resistant and able to protect themselves against heat, was achieved with plasma in air. Analyses carried out by the Fraunhofer Institute for Process Engineering and Packaging (IVV) in Freising, Germany, showed that a one-second exposure to plasma led to a reduction of the colony-forming bacteria of five orders of magnitude. The high proportion of UV and the radicals produced by the plasma work hand in hand in this process. "We have an extremely broad UV spectrum, and the pathogens have never been exposed to a spectrum of this kind in their natural environment," said Dr. Andreas Schulz.
Plasma is not only used to deactivate the pathogens, but also to remove organic residues. The Stuttgart researchers have found that a 20-minute treatment in oxygen plasma leads to the complete removal of organic Bacillus atrophaeus residues. "The low energy of the ions and the neutral particles practically prevents any damage occurring to the surface of the substrate," said Joachim Schneider. This makes plasma sterilisation a quick and uncomplicated sterilisation and cleaning method.