Non thermal plasma propagation in micro sized structures including bifurcations and connections

Abstract

International audienceThis work reports on the development and characterization of a non thermal plasma source, labelled plasma gun, based on the generation and propagation of atmospheric pressure plasma in small diameter and large length flexible capillary. Among various potential applications in biomedical applications, our main target consists in the plasma gun matching for cancer therapeutic approach. Two unique features, dealing with the remote long distance plasma generation and the operation of the plasma gun at very moderate rare gas flow rate down to a few sccm, in comparison with the great variety of recently developed plasma jets, appear particularly attractive to first achieve plasma delivery in the tumor vicinity and second assess the toxicity and antitumor action of non thermal plasma. Both lung and colorectal cancers have been selected considering their rather poor prognosis using conventional therapies, while being especially challenging for in vivo studies using mice as animal models for these human pathologies.Besides the determination of the physical processes at the origin of plasma propagation at very high velocities, up to a few 108 cm.s-1, recent experiments have been performed to study the plasma expansion through micro sized in diameter silicon capillaries which can be used for mice tracheal intubation or colon endoscopy. The plasma delivery can either be planed as a direct exposure of the tumor surface or for less accessible targets through the plasma propagation in the organ cavities leading to the cancerous location. The first technique requires implementing non destructive diagnostic to monitor the capillary outlet position while the second protocol imposes preliminary characterization of the possibility for plasma splitting, expansion, shrinking, and connection as may be encountered in real organ topography. To this end, the plasma splitting and mixing have been studied in multi branched glass assemblies and in circular rings, using fast ICCD imaging. Both plasma splitting in glass assembly presenting up to ten successive bifurcations, and mixing of two “colliding” plasmas have been observed and characterized. These encouraging properties of atmospheric pressure ionization wave sustained plasma, lead us to perform preliminary endoscopic experiment on mice both for lung and colon targets. The propagation of plasma through small diameter flexible capillaries flushed at very gas flow in the lung and colon of anesthetized mice was recently successfully achieved. This first step opens up the possibility to plan in vivo plasma tolerance studies and antitumor evaluation