Study of the diffusion of plasma-generated reactive species in hydrogel-based tissue models

Understanding the diffusion process of reactive species produced by cold atmospheric plasma in human tissues and knowing their diffusion coefficients represents a key aspect for the optimization and expansion of plasma-based biomedical applications. In this final master project, an experimental system was developed and optimized to determine the diffusion coefficients of nitrites and hydrogen peroxide, which represent the main long-lived reactive species produced by plasma, within hydrogels used as surrogates of living tissues. The system consists of placing the hydrogel between two compartments: one containing a known concentration of reactive species and the other only solvent at the beginning of the experiment. By monitoring over time the variation of the concentration of the diffusing species in the compartment initially containing only solvent, it was possible to determine the corresponding diffusion velocity. In parallel, a literature review on the diffusion process through thin membranes allowed the selection of a suitable model that describes the experimental system and that can be used to obtain the diffusion coefficients. Experimentally, two hydrogels characterized by different chemical structures were employed: gelatin, a protein-based polymer, and agarose, a polysaccharide. Furthermore, the dependence of the diffusion coefficients on the hydrogel thickness and on the concentration of the initial standard solution was investigated. The results show that no significant differences were observed between the diffusion coefficients of nitrites and hydrogen peroxide within the same hydrogel, both for gelatin and agarose. However, a comparison between the two materials revealed significantly lower diffusion coefficients in gelatin than in agarose for both species. Overall, these results provide useful data for modeling the penetration and diffusion of reactive species in living tissues and support the targeted development of plasma-based biomedical therapies.