Modelling of pulsed electric field treatment on microorganisms : transient electric field and forces acting on cell membrane, local thermal effects

Abstract

Irreversible or reversible pores could be generated in the cell membrane of microorganisms by pulsed electric field (PEF) treatment, which is generally called electroporation. Such process could be used for inactivation of microorganisms or bio-medical extraction. Both reversible and irreversible pores can be generated in bio-membranes this changes the permeabilization of the cell membrane, with the former allowing for transfection (DNA, RNA, etc.) and the latter for cell inactivation and bio fuel extraction. However, the PEF treatment is generally considered as ‘nonthermal’ due to the lesser significance of the thermal effect among the treatment samples. Although PEF is reported to be a non-thermal method, local heating effects which were not reported before does occur among biological cells during PEF treatment, different level of thermal excitation will be investigated in this study. Besides, the exact mechanism between the pulsed electric field and microorganisms were not fully understood. This study aimed to investigate the interaction between pulsed electric field and microorganisms, with thermal effects (local heating effects) also taken into account. Three different novel analytical models were developed in this study: a linear model, a QuickField model and a COMSOL model. ‘Hot spots’ (due to local heating effects) were observed in the models and the characteristics of local heating effects were also investigated. The contribution of induced electric field strength in cell membrane and local heating effects were evaluated for electroporation process during PEF treatment. The results suggest that the significant induced electric field strength in cell membrane made the main contribution to electroporation. However, local heating effects could be significant when the treatment samples were highly conductive. The thermal force and electromagnetic force on the cell membrane were also investigated. Finally, the situation of penetrated membrane (pore was included in the cell membrane) was also modelled and it was found that the local heating effects in the penetrated membrane were significant and could enhance the expansion of pores. The cell nucleus was also included in the novel QuickField and COMSOL models, which were used to investigate the interactions between microorganism and external electric field, both electric field strength in membranes (cell membrane and nuclear membrane) and thermal effects were investigated. It was observed that, with nano-second PEF treatment, the induced electric field strength in the cell nucleus was strong enough to cause electroporation. Thermal effects could also be generated in cytoplasm. The experimental works were performed using a self-built HV Blumlein generator. Different test cells were used to investigate the inactivation process of PEF treatment with different number of impulses. An alternative plasma treatment was also implemented to compare the inactivation effects between PEF treatment and Plasma treatment with the same Blumlein generator. It was found that the plasma treatment in metallic dish test cell could achieve stronger inactivation compared with PEF treatment with the same number of impulses.Irreversible or reversible pores could be generated in the cell membrane of microorganisms by pulsed electric field (PEF) treatment, which is generally called electroporation. Such process could be used for inactivation of microorganisms or bio-medical extraction. Both reversible and irreversible pores can be generated in bio-membranes this changes the permeabilization of the cell membrane, with the former allowing for transfection (DNA, RNA, etc.) and the latter for cell inactivation and bio fuel extraction. However, the PEF treatment is generally considered as ‘nonthermal’ due to the lesser significance of the thermal effect among the treatment samples. Although PEF is reported to be a non-thermal method, local heating effects which were not reported before does occur among biological cells during PEF treatment, different level of thermal excitation will be investigated in this study. Besides, the exact mechanism between the pulsed electric field and microorganisms were not fully understood. This study aimed to investigate the interaction between pulsed electric field and microorganisms, with thermal effects (local heating effects) also taken into account. Three different novel analytical models were developed in this study: a linear model, a QuickField model and a COMSOL model. ‘Hot spots’ (due to local heating effects) were observed in the models and the characteristics of local heating effects were also investigated. The contribution of induced electric field strength in cell membrane and local heating effects were evaluated for electroporation process during PEF treatment. The results suggest that the significant induced electric field strength in cell membrane made the main contribution to electroporation. However, local heating effects could be significant when the treatment samples were highly conductive. The thermal force and electromagnetic force on the cell membrane were also investigated. Finally, the situation of penetrated membrane (pore was included in the cell membrane) was also modelled and it was found that the local heating effects in the penetrated membrane were significant and could enhance the expansion of pores. The cell nucleus was also included in the novel QuickField and COMSOL models, which were used to investigate the interactions between microorganism and external electric field, both electric field strength in membranes (cell membrane and nuclear membrane) and thermal effects were investigated. It was observed that, with nano-second PEF treatment, the induced electric field strength in the cell nucleus was strong enough to cause electroporation. Thermal effects could also be generated in cytoplasm. The experimental works were performed using a self-built HV Blumlein generator. Different test cells were used to investigate the inactivation process of PEF treatment with different number of impulses. An alternative plasma treatment was also implemented to compare the inactivation effects between PEF treatment and Plasma treatment with the same Blumlein generator. It was found that the plasma treatment in metallic dish test cell could achieve stronger inactivation compared with PEF treatment with the same number of impulses