The ultimate goal of this project is to find an answer to the question: ‘how does gas plasma inactivate bacteria/cells or coagulate blood?' It is well known that gas plasma mainly consists of charged particles, neutral species, photons, and an electric field. No general agreement, however, has been reached in addressing the question due to the complex nature of the plasma. A reliable numerical model therefore would play an important role in exploring the mechanisms of the plasma-biomaterial interaction. From the viewpoint of numerical modeling, the plasma-biomaterial interaction is a multi-physics and multi-scale problem. The interaction involves various research fields such as medicine, biology, thermo-fluid dynamics, and plasma physics. In addition, the interaction occurs over a wide range of time and spatial scales. For instance, electron collision frequency is on the order of picoseconds, whereas the time scale of neutral gas flow is on the order of milliseconds. The plasma treatment takes from minutes to days to take effect, depending on the biomaterials being treated. Thus, the plasma-biomaterial interaction is quite a challenging problem. As of yet, no group has succeeded in developing such a numerical model.
Our numerical model using finite element method demonstrates that the plasma needle operates in two discharge mode: the corona-mode under low power condition and the glow-mode under high power condition. The mode transition observed in our simulation is consistent with experimental results. Also, the present study reveals that neutral gas flow plays a very important role in the experimentally observed killing pattern of bacteria by gas plasma at atmospheric pressure.