Effects of cold plasma on the dielectric properties and microcirculation of rat skin: A randomized preclinical study

Abstract

Background. Plasma medicine is a rapidly evolving field that has increasingly attracted the attention of researchers in biomedicine and physics over the past two decades. Despite the growing interest, many aspects of plasma interaction remain unexplored. In particular, the biophysical mechanisms of interaction, molecular processes in living tissues exposed to plasma, and limiting factors that influence the response of biological systems require clarification. The key limiting factors include the technical characteristics of the plasma flow (such as the type of ionization, generation medium, and applied voltage), as well as the influence of modulating agents (the use of airflow or inert gases and the chemical purity of the gas-air mixture). Analyzing the role of these factors requires the development of high-precision diagnostic techniques. Objective. To evaluate the influence of non-ionized argon and argon cold plasma on dielectric parameters and microcirculation in a selected biological object (rat skin). Methods. This preclinical experimental study was conducted on 40 mature male outbred Wistar rats from a genetically controlled, closed colony. The animals were randomized into four groups based on the type of intervention: the first group served as an untreated control; the second group received a course of treatments with a non-ionized argon flow with a one-minute exposure time; the third group was treated with argon cold plasma using a regimen identical to that used in the second group; the fourth group was treated with argon cold plasma with an exposure time of two minutes. Interventions were performed on a depilated area of back skin measuring 1×1 cm. The course consisted of ten procedures performed once daily. Cold plasma generation was carried out using a device based on the principle of high-frequency gas flow ionization. The dielectric parameters of the skin were studied via microwave sounding at the site of cold plasma exposure upon completion of all described interventions. Microcirculation was evaluated through laser Doppler flowmetry using an LAKK-M device (Lazma, Moscow). Calculations were performed using Microsoft Office 2013 software (Microsoft Corporation, USA) and Statistica, version 10 (StatSoft, USA). The level of statistical significance was set at p ≤ 0.05. Results. Treating rat skin with gas flows of varying ionization levels induces a specific functional-metabolic and morphostructural response, whose nature depends on the characteristics of the gas flow. Non-ionized argon significantly reduces both dielectric parameters and microcirculation intensity. The effect of argon cold plasma depends on the agent exposure time: the one-minute regimen proved optimal for dielectric and microcirculatory parameters, maintaining permittivity at control levels, moderately decreasing tissue conductivity, and prompting adaptive remodeling of the microcirculatory network by engaging intravascular mechanisms. The two-minute exposure leads to a significant rise in permittivity without increasing conductivity. Conclusion. The conducted experiments show that exposure to argon-containing gas flows induces a local multicomponent functional-metabolic response in integumentary tissues, whose nature is directly determined by the composition and properties of the applied exogenous agent. Microcirculatory changes induced by cold plasma include physiological vasodilation with a proportional decrease in the linear microvascular blood flow velocity and an increase in the blood filling at the exposure site. This effect depends on the duration of skin treatment with cold plasma and can be recommended for practical application.