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Workshop overview

Invited Speakers

Plasmas which are operated in non-equilibrium mode at atmospheric pressure, often in contact with liquids, have generated increasing interest over the past decade as potential medical treatments to tackle challenging conditions such as cancer or antibiotic resistant infections. This is a very complex environment; research activity operates across a multitude of plasma systems, processes and biological targets and individual projects are often, by necessity, narrowly focussed. This impedes the building of a broader scientific framework that can handle the interaction between plasma science and technology, biology and medicine. Such a framework, if it could be achieved, would encourage collective progress in scientific understanding and technological innovation as well as encourage greater familiarity and uptake outside of the plasma community. To start this process, we need to ask what plasma science might be able to deliver to biology, that is not otherwise readily available, and what biology might like to receive. However, without in-depth knowledge of each discipline, these simple questions are actually major problems. The is a gap to be bridged. Practical projects necessarily focus on specifics i.e. the biological target and the plasma process. However in this workshop, we have the ambition to step back a little and look for more general principles, whether its in basic science or technical developments.

In the simplest terms, gas-plasma systems have the potential to supply “on tap” active agents at reasonably high dose levels. Such agents include reactive oxygen and nitrogen species  (RONS) such as H2O2, 1O2, O3, •NO, and •OH as well as electrons, ions, and photons. In principle, the numbers of each species are quantifiable and controllable with the possibility of individual species or precise mixture selection.Plasma induced high-electric fields within confined regions are also available. Plasma scientists routinely have to deal with the experimental and simulation challenges of multiscale phenomena, from metres and seconds down to nanometres and nanoseconds and, as physicists, detailed quantification of such phenomena is our primary goal. Plasma – biological studies have involved interactions with tissue, cells, cell membrane, proteins, amino acids, DNA etc. So we might start with the question: what important biological hypothesis might be tackled using plasmas to supply a quantified flux of specific individual radicals, e.g. •OH, or tailored mixtures of species to specific biological entities  e.g. cells or DNA. If so, this framework would provide the drive to develop plasma species selectability and experimental configurations that would allow real-time imaging and quantification of plasma – biological interactions.

Some tentative examples highlight the potential advantages to be gained.

Gamma radiolysis has been long-studied for application in radiotherapy. The production of ROS in liquid, e.g. •OH, and their effect on e.g. DNA or tumour cells has been studied and modelled. However energies are very high and tracking species to low and very low energies, where thresholds for dissociation or electron attachment occur, has proved immensely challenging. The direct impact of low energy electrons on DNA in liquid, as distinct from acting as sources of •OH, may also be very important for double strand breaks but this remains controversial due to the inability to generate such electrons in liquid. These questions also apply to the activity of chemo agents and nanoparticles. The potential of plasmas to supply ROS and electrons at low energy and under controlled observable conditions may provide a valuable complement to existing research as well as guide the future technical requirements for plasma-based cancer treatments.  

Investigations and trials to date of plasma – cancer cell interactions indicate, among other mechanisms, their immunogenic potential i.e. responses that reveal cancer to the immune system so that it can recognise, target and kill cancer cells. There are many fundamental questions yet to be resolved. However, there are also immediate technological issues related to plasma treatment which require both basic science and technical insights. One primary challenge facing plasma technology is how it should physically interact with the patient being treated. This raises questions as to how we measure and provably control such processes in that environment which in turn establishes the necessity for new process sensors, remote but active plasmas, plasma-activated liquids. Ultimately, the question will be: how can we insert a plasma inside the body through open surgery or via minimally-invasive procedures.   

Antibiotics, with different targets, are thought to share common mechanisms of  bactericidal activity through enhancing intracellular reactive oxygen species. Again the potential of plasmas to supply ROS selectively and in controlled mixtures, with sub-lethal to lethal doses may, along with in-situ monitoring and quantification, contribute to our understanding of antibiotic mechanisms and resistance, including the synergistic impact of plasma on antibiotic activity and the restoration of antibiotic sensitivity.