# Mathematical Modelling of the Effects of Plasma Treatment on the Diffusivity of Biofilm
## 1 Introduction
implemented atmospheric pressure plasma jet for catheter contaminated with a suspension of _Staphylococcus aureus_ bacteria and reveals 5 and 6 log (complete inactivation) reduction for pure argon and with argon mixed with 0.25% air, respectively [22]. Another study by [PERSON] et al. demonstrates complete inactivation of _E. coli_ after 600 s of conventional atmospheric pressure microwave plasma source usage [23]. Similarly, [PERSON] et al. developed a non-thermal plasma discharge inside a sealed bag which showed a 6 log reduction of _P. aeruginosa_ and _S. aureus_ in 45 and 120 min, respectively, and 4 log reduction of _B. subtilis_ spores in 120 min [24]. One of the studies done with biofilm demonstrated nearly 100% of biofilm inactivation after 5 min of gas discharge plasma treatment [25]. Plasma has also been used effectively in dentistry. The dentin discs with _E. Faecalis_ biofilm treated with plasma for 5 min resulted in 92.4% killing of cells, which has a potential to replace existing treatment for root canal disinfection [26]. Thus, the various active plasma agents such as NO, atomic oxygen (O), ozone (O\({}_{3}\)), hydroxyl (OH), reactive oxygen (ROS) and nitrogen species (RNS), and high energy UV radiation are what makes these plasma an effective antimicrobial tool in several biomedical applications [20]. Electric field (EF) is another plasma agent that might be used for several biomedical applications and has been studied recently [12]. [PERSON] et al. experimentally measured the EF that reveals the propagation of plasma in region of an intense longitudinal EF component [11]. The authors further speculate that the plasma treatment could be a unique way to deliver intense transient EF and chemical reactive species. Another study by [PERSON] et al. showed the EF measurement within the plasma plume and mentions its importance for interactions to the plasma plume with surfaces in biomedical applications [10]. Similarly, several investigations have been made to identify the role of single plasma agents for the microorganism inactivation process [20]. The study carried by [PERSON] et al. states that both positive and negative plasma ions plays an important role in the interaction between biological organisms and plasma [20]. There are different mechanisms to inactivate microorganisms involving neutral, ionized and reactive species, and UV photons [24]. Initially, the fastest decrease in bacterial concentration is dominated by the UV radiations. These UV radiations damage the bacterial cell wall and penetrate the cell, which then inhibits the bacterial replication by damaging DNA. Similarly, charged particles and RONS (reactive oxygen and nitrogen species) initiate the bacterial membrane alteration by photodesorption or etching mechanisms [24]. The study by [PERSON] et al. [27] states that in atmospheric pressure plasma, the major decontaminating factors are radicals, ROS (e.g., OH, O, O\({}_{3}\)) charged particles (O\({}_{2}\)\({}^{-}\)), which causes oxidative damage to different cellular components [28]. UV radiation plays a role if photons in UV C germicide region or in vacuum UV are produced. Another study also states that the synergic action of reactive and/or charged particles plays a major role for cell wall damage, with UV radiation playing only a minor role [29]. The two principal theories used to explain the biofilm being more resistant to the antimicrobial treatment are based on transport limitations and its ability to protect the bacterial cells within the biofilm [30]. Transport-based explains biofilm resistance acting as a barrier to antibiotic diffusion. Bacterial protection is the result of the reduced susceptibility of bacteria in biofilm compared with the bacteria in planktonic phase [30]. Inactivation of the antimicrobial treatment by the matrix EPS and the inability of the antimicrobial molecules to diffuse through these EPS matrix are the primary reasons for biofilm resistant to the antimicrobial treatment [2].