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The transportation of reactive oxygen species (ROS) to lesion site through human tissue is crucial for plasma medicine. For this reason, the spatial‐temporal distributions of ROS in model tissues irradiated by a He + O2 plasma jet were investigated in this paper. It was found that the ROS formed a ring‐shaped surface pattern on the model tissue, of which the diameter increased with the gas flow rate but remained unchanged with the plasma treatment time. The surface pattern changed significantly with the inclination angle of plasma irradiation, suggesting that the ROS dosage is difficult to precisely control for clinical applications. Moreover, the penetration depth of O3 increased linearly with the plasma treatment time or the water content of the model tissue.

Reactive oxygen and reactive nitrogen species (RONS) are believed to play a key role in biomedical applications, which means that RONS must reach the target tissue to produce a therapeutic effect. Existing methods (electron spin spectrometry and microplate reading) to determine the RONS concentration are not suitable for experimental real-time measurements because they require adding an indicating reagent to the plasma-treated medium, which may alter the chemical composition of the medium. In this paper, we propose a method to measure the long-lived RONS concentration in plasma-activated water (PAW) by using UV absorption spectroscopy. Based on an analysis and fit of the absorption spectra of standard solutions (H2O2, NaNO2, and NaNO3), we propose a detailed fitting procedure that allows us to calculate the concentrations of simplex H2O2, NO2−, and NO3−. The results show that the pH and the cross reactivity between RONS in PAW correlate strongly with the absorption spectra. To confirm the accuracy of the calculations, we also use a microplate reader and add chemical reagents to measure the concentrations of H2O2, NO2−, and NO3−. The results show that the concentrations calculated by the proposed fitting method are relatively accurate and that the error range is acceptable. Additionally, the time-dependent diffusion of RONS in PAW is measured and analyzed at different depths in the PAW. This fitting approach constitutes a nonintrusive approach to measure RONS at different depths in PAW.

Cold atmospheric plasmas are reportedly capable of enhancing the percutaneous absorption of drugs, which is a development direction of plasma medicine. This motivated us to study how the enhancement effect was realized. In this letter, gelatin gel films were used as surrogates of human tissues, NaNO2 was used as a representative of small-molecule drugs, and cross-field and linear-field plasma jets were used for the purpose of enhancing the penetration of NaNO2 through the gelatin gel films. The permeability of gelatin gel films was quantified by measuring the NO2− concentration in water which was covered by those films. It was found that the gas flow and electric field of cold plasmas played a crucial role in the permeability enhancement of the model tissues, but the effect of gas flow was mainly confined in the surface layer, while the effect of the electric field was holistic. Those effects might be attributed to the localized squeezing of particles by gas flow and the weakening of the ion-dipole interaction by the AC electric field. The enhancement effect decreases with the increasing mass fraction of gelatin because the macromolecules of gelatin could significantly hinder the penetration of small molecules in the model tissues.

Recently, some researches were reported to investigate the transportation of ROS/RNS in living tissues [11][12][13]. For example, real animal tissues such as mouse models or pig muscle tissues were used by Duan et al and Collet et al to study the penetration of plasma-generated ROS/RNS in living tissues [11,14,15]. Bekeschus et al mentioned that setup of suitable tissue-like models that allow to investigate plasmamedical effects is necessary for plasma biology [16], therefore, besides the real animal tissues, model tissues are more frequently used because of the ease of operation and stability. Gelatin gel or agarose gel was used by Szili et al and our group to mimic real tissues to study the penetration of plasma-generated ROS/RNS, and it was shown that plasma can transport several ROS/RNS into the model tissues and the penetration depth increases almost linearly with the plasma treatment