Exposure of biological cells to electric pulses is a useful tool for manipulating the permeability of the cell membrane. It is believed that even a brief exposure to the electric field causes structural changes in lipid membrane through the formation of hydrophilic pores. This temporarily makes the membrane more permeable to molecules that normally lack the mechanism to overcome the membrane’s hydrophobic barrier. The chemical and physical processes that occur at the molecular level during electroporation are relatively well studied. However, some processes are still less known and will be investigated in this doctoral dissertation.
Electroporation can be described as an application of high voltage electric pulses passing direct electric current through electrodes in contact with the tissue. Application of electric pulses unavoidable causes electrochemical reactions at the electrode-electrolyte interface, specifically, metal release from the electrodes. Metal release can have adverse effects on the electroporation process, equipment and biological tissue leading to lipid oxidation. The processes described can be studied with in silico numerical models or in vitro cell membrane models such as liposomes and planar lipid bilayers.
In silico numerical models are based on a set of differential equations and can be used to describe a physical problem, for example the occurrence of electrochemical reactions at the electrode-electrolyte interface during electroporation. By solving these equations, concentration profiles of dissolved substances in dependence of applied pulse amplitude and pulse polarity are obtained. Developed and validated numerical model is therefore a very useful tool, to study the effects of different electroporation protocols on the extent of electrochemical reactions, in a fast and reliable way.
In vitro models such as liposomes and planar lipid bilayers can be used to study various processes at the molecular level. The artificial lipid bilayer is a simple model of the cell membrane with less complexity compared to the biological cell membrane. We can form liposomes with structure that is very similar to the cell, but the composition of the membrane is greatly simplified. Electroporation processes can also be studied with planar lipid bilayers. The composition of the planar lipid bilayer can be arbitrarily changed to mimic the composition of a real cell membrane. Thus, in a simple membrane model, we can study how the cell membrane is affected by metal ions that are physiologically present in the biological environment or released from electrodes during the application of high-voltage electric pulses. What is more, using planar lipid bilayers, we can also study the influence of lipid oxidation on electrical properties of cell membranes.
In this doctoral dissertation, we were able to develop in silico numerical model describing the dissolution of metal ions from aluminium and iron electrodes during the application of high-voltage electric pulses. The numerical model was validated using experimental results from the study of electrolyte contamination by Kotnik et al. Furthermore, in vitro membrane models were used to study the effect of metal ions on membrane structure. Using planar lipid bilayers and liposomes, changes in the phospholipid membrane, namely increased membrane thickness, were observed due to the addition of metal ions, such as calcium, aluminium, and iron. Finally, lipid oxidation was studied using planar lipid bilayers. An increase in electric conductivity and capacitance was observed, leading us to believe that lipid oxidation indeed plays a role in prolonged membrane permeability after electroporation.
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