Understanding the Potential of Plasma Activated Liquids for Biomedical Applications

Atmospheric cold plasma has evolved as a new technology for applications used in biomedicine, agriculture and food industry. Recently, treatment of liquids using various atmospheric pressure plasmas has attracted much attention owing to multiple practical applications such as water purification, surface cleaning and decontamination with impact in dentistry, wound healing and sterilisation, or cancer therapy. The over-arching aim of this study is to build a better understanding of the parameters which govern the liquid chemistry generated in a liquid exposed to cold plasma and how these translate into biological effects on pro- and eu-karyotic organisms. The objective was to investigate the effects of plasma activated liquids (PAL) generated by different custom-made plasma systems in Technological University Dublin. Non-buffered and buffered liquids treated by a high voltage dielectric barrier discharge system were used to investigate the role of the liquid composition on resultant reactive species and their bactericidal and cytotoxic effects against prokaryotic and eukaryotic cells, respectively. The impact of process and storage parameters such as temperature and storage time on chemical composition and bactericidal efficacy of plasma activated water and saline was also investigated, including the influence of supra and sub-ambient temperatures and long-term storage of up to 18 months. Bactericidal efficacy showed stability to mild heating and remained at lowest temperatures over prolonged storage, whereas changes in the physicochemical properties of solutions were observed after different storage times and temperatures. A reactive species selective spark and glow discharge set-up was used to elucidate the role of ROS and RNS in bacterial inactivation and cytotoxic effects of plasma iv activated water and saline. The effects of treatment time, mode of discharge and contact time of PAL on antimicrobial efficacy and cytotoxic effects in various cancerous and healthy cell lines were investigated to provide a primary understanding of how ROS and RNS affect different biological targets. Finally, a co-culture model consisting of bacteria and keratinocytes was developed to mimic the environment of an infected wound and provide a more complex challenge for microbial inactivation. Results showed that plasma activated saline can reduce the bacterial load under these conditions but caused cytotoxic effects with earlier onset than the bactericidal efficacy. A mechanistic approach for the mammalian cell death showed that PAL with acidic pH can cause increase of intracellular ROS and mitochondria depolarisation, reduction of glutathione, cytokine alteration and finally lysis of mammalian cells. Overall, these data demonstrate that plasma activated liquids show an efficient decontamination approach against bacteria and have anticancer effects, with the chemical composition playing a crucial role in the inactivation processes, highlighting the potential to make plasma solutions attractive for applications in biomedicine but also indicating limiting factors which require further elucidation