The Effect of Tube Diameter on the Surface Distributions of ROS in Model Tissue Treated with a He + O₂ Plasma Jet

The influence of quartz tube size on the surface distributions of reactive oxygen species (ROS) in model tissue treated with a He + O₂ plasma jet was investigated. Gelatin gel was used to construct the model tissue, and a KI-starch color agent was mixed with the model tissue to visualize the distribution of ROS. With increasing quartz tube diameter, the uniformity of the ROS distribution on the model tissue decreased, and the change in the surface distribution area of the ROS on the model tissue over the irradiation distance was quite different for different quartz tube diameters. The surface distribution of ROS on the model tissue was affected mainly by the working gas flow; thus, the diffusion range of the working gas flow on the model tissue surface determined the surface distribution area of ROS on the model tissue. The working gas flow was accelerated, and the diffusion range of the working gas flow on the model tissue surface expanded when the plasma was ignited, resulting from the modification of the working gas flow by the electrohydrodynamic (EHD) effect. The EHD effect on the expansion of the diffusion range of working gas flow on the model tissue was different for different quartz tube diameters, and the effect was determined mainly by the discharge current density of the plasma jet and the plasma propagation length.