IntroductionCold Atmospheric Plasma Jet (CAPJ), with ion temperature close to room temperature, has tremendous potential in biomedical engineering, and can potentially offer a therapeutic option that allows cancer cell elimination without damaging healthy tissue. We developed a hand-held flexible device for the delivery of CAPJ to the treatment site, with a modified high-frequency pulse generator operating at a RMS voltage of <1.2 kV and gas flow in the range 0.3–3 l/min. The aims of our study were to characterize the CAPJ emitted from the device, and to evaluate its efficacy in elimination of cancer cells in-vitro and in-vivo.Methods and ResultsThe power delivered by CAPJ was measured on a floating or grounded copper target. The power did not drastically change over distances of 0–14 mm, and was not dependent on the targets resistance. Temperature of CAPJ-treated target was 23°-36° C, and was dependent on the voltage applied. Spectroscopy indicated that excited OH- radicals were abundant both on dry and wet targets, placed at different distances from the plasma gun. An in-vitro cell proliferation assay demonstrated that CAPJ treatment of 60 seconds resulted in significant reduction in proliferation of all cancer cell lines tested, and that CAPJ activated medium was toxic to cancer cells. In-vivo, we treated cutaneous melanoma tumors in nude mice. Tumor volume was significantly decreased in CAPJ-treated tumors relatively to controls, and high dose per fraction was more effective than low dose per fraction treatment. Importantly, pathologic examination revealed that normal skin was not harmed by CAPJ treatment.ConclusionThis preliminary study demonstrates the efficacy of flexible CAPJ delivery system against melanoma progression both in-vitro and in-vivo. It is envisioned that adaptation of CAPJ technology for different kinds of neoplasms use may provide a new modality for the treatment of solid tumors.

An inductively coupled discharge was obtained at low gas pressure. Unlike an ordinary inductively coupled discharge with an inductorlike rf antenna, we used a magnetic core with a primary winding (“ferroinductor”). In this way, we increased the electric field and eliminated the magnetic field of the winding. Gas breakdown was obtained at a pressure as low as 10−4Torr, the discharge plasma ionization rate reached almost 100%, and the maximum plasma density was about 1013cm−3. The high inductance of the ferroinductor allowed us to work even with single pulses. The efficiency of such a discharge as a plasma source could reach 90%, which makes this kind of discharge attractive for many applications.

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We present a theory of plasma sheath resonance in the neighborhood of the ion plasma frequency. Properly implementing the boundary conditions on the moving sheath edge leads to the possibility of reactive current compensation in the plasma sheath. We derive conditions which certain plasma parameters must satisfy in order for this resonance to exist and to be stable. The theory explains experimental results which have appeared to disagree with each other as well as with certain theoretical assertions.