The mechanism of plasma-assisted penetration of NO₂^- in model tissues

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.