The formation of carbon monoxide, oxygen and ozone in a barrier corona discharge (BCD) operating in pure carbon dioxide (CO₂) and binary mixtures of CO₂ and argon is studied. The asymmetric electrode configuration of the BCDs allows plasma operation at pressures exceeding 1 atm, up to 6 bar, at moderate high-voltage amplitudes below 15 kV. Charge–voltage plots and an equivalent circuit model are employed to characterize the electrical parameters at different pressures and gas compositions. Depending on these conditions and the voltage amplitude, full or partial coverage of the electrodes with plasma is obtained. The existence of an optimum pressure for power dissipation for each given operation voltage amplitude and gas composition can be confirmed and explained by the equivalent circuit model. Increasing the CO₂ concentration in the working gas increases the mean reduced electric field strength E/N while pressure reduces it in the BCD. The CO₂ conversion shows a maximum efficiency of about 4% at 1.5 bar for the gas mixture Ar/CO₂ = 1:1 and a voltage amplitude of about 10 kV. The calculation of thermodynamic equilibrium parameters reveals that a relatively small increase in pressure can affect both, the equilibrium parameters and the reaction rates. As a result, the specific required energy for the reaction ( $$\Delta \mathrm{H}/\mathrm{SEI}$$Δ H / SEI ) shows an optimum, but only 8% of the electrical input energy is spent for CO₂ dissociation at these optimum conditions.

Despite global research and continuous improvement in therapy, cancer remains a challenging disease globally, substantiating the need for new treatment avenues. Medical gas plasma technology has emerged as a promising approach in oncology in the last years. Several investigations have provided evidence of an antitumor action in vitro and in vivo, including our recent work on plasma-mediated reduction of breast cancer in mice. However, studies of gas plasma exposure on patient-derived tumors with their distinct microenvironment (TME) are scarce. To this end, we here investigated patient-derived breast cancer tissue after gas plasma-treated ex vivo. The tissues were disjoint to pieces smaller than 100 µm, embedded in collagen, and incubated for several days. The viability of the breast cancer tissue clusters and their outgrowth into their gel microenvironment declined with plasma treatment. This was associated with caspase 3-dependent apoptotic cell death, paralleled by an increased expression of the anti-metastatic adhesion molecule epithelial (E)-cadherin. Multiplex chemokine/cytokine analysis revealed a marked decline in the release of the interleukins 6 and 8 (IL-6, IL-8) and monocyte-chemoattractant-protein 1 (MCP) known to promote a cancer-promoting milieu in the TME. In summary, we provide here, for the first time, evidence of a beneficial activity of gas plasma exposure on human patient-derived breast cancer tissue.

Breast cancer (BC) and oral squamous cell carcinoma (OSCC) are among the most common types of cancer, but current clinical outcomes remain unsatisfactory. Available therapies have limitations in terms of efficacy and may also cause severe side effects. Cold physical plasma is a promising approach for selectively eliminating cancer cells while avoiding genotoxic effects on non-malignant cells. In this study, we investigated the potential of cold physical plasma as a therapeutic intervention for BC and OSCC through in vitro and ex vivo studies on toxicity. For the in vitro study, T-47 BC cells and SCC-4 and SCC-9 OSCC cell lines were used, and we found cold plasma to be toxic in a treatment time-dependent manner. Moreover, we investigated the safety of physical plasma therapy and found no genotoxic potential in plasma-treated human keratinocytes in vitro. Finally, for the first time, 20 BC and OSCC patient-derived tumor tissues were punch biopsied and ex vivo-exposed to cold physical plasmas to study responses in the tumor microenvironment TME). Cold physical plasma caused significant apoptosis in patient-derived BC and OSCC tumor tissues, and decreased the number of CD163⁺ cells (e.g., tumor-associated macrophages, TAM) in BC tissue plasma-treated ex vivo. Collectively, our findings motivate the investigation of cold physical plasma as a potential adjuvant treatment in oncology.