Plasma-liquid interactions: a review and roadmap

Plasma-liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas

Argon plasma treatment and medium temperature.

<p>The average temperature in DMEM during plasma treatment up to 120 s is 25°C and remains constant up to a plasma treatment time of 180 s. Thus, negative thermal effects in the plasma-treated cell culture medium DMEM are excluded.</p

Cell membrane morphology of mHepR1 cells.

<p><i>a)</i> The surface structure of cells after 24 h in normal, untreated medium (left column) presents elongated microvilli with high densities, which extend over the entire cell surface. In contrast, the mHepR1 cells in 60 s plasma-treated medium (right column) show extremely shortened microvilli accompanied by a reduced density (bar = 4 µm, 5,000× magnification, SEM DSM 960 A, Carl Zeiss). <i>b)</i> The significantly shortened microvilli are impressively visible using a higher magnification (bar = 2 µm, 15,000× magnification, FE-SEM Zeiss Merlin VP compact, Carl Zeiss) (p<0.001, student's <i>t-</i>test, n = 410–500 microvilli). <i>c)</i> Scheme: microvilli at the cell surface in normal epithelial cells (left) and cells exposed to plasma-treated DMEM (right).</p

Oxygen content of 60 s plasma-treated DMEM.

<p>Note that in the plasma-treated complete DMEM the molecular oxygen concentration is decreased by half, which is equalised after only one day. (PreSens oxygen sensor, n = 3, student's <i>t</i>-test, *p<0.05, ** p<0.01, ***p<0.001).</p

Online-monitoring of respiration of living mHepR1 epithelial cells.

<p>Note that the respiration is immediately disturbed after addition of complete DMEM plasma-treated for 60 s (arrow) which was stored for 4 days at 37°C. (Bionas 1500 analysing system, n = 3, student's <i>t</i>-test * p<0.05 for all values from the time point of 3.5 hours).</p

Concentration of hydrogen peroxide in 60 s plasma-treated DMEM.

<p>Note the continuous decrease of hydrogen peroxide over various time periods. (n = 7, Mann-Whitney <i>U</i>-test, ***p<0.001).</p

Representative gel filtration chromatogram resulting from: (a) application of untreated complete medium, (b) complete argon-gas treated medium, (c) complete medium with 60 s or (d) 120 s of plasma treatment.

<p>The arrowheads mark the one peak which alters considerably after plasma treatment. (n = 6 independent experiments).</p

Oxygen content of cell culture medium immediately after plasma treatment for 60 and 120 s. (PreSens oxygen sensor, mean ± SD, n = 3; student's <i>t</i>-test).

<p>*p<0.05 <i>vs.</i> untreated,</p><p>***p<0.001 <i>vs.</i> untreated.</p><p>Oxygen content of cell culture medium immediately after plasma treatment for 60 and 120 s. (PreSens oxygen sensor, mean ± SD, n = 3; student's <i>t</i>-test).</p