The interaction of electric fields with vesicles and cells
Creators: name: Sadik, Mohamed M.
Publisher: name: No Publisher Supplied
Year: 2013

description: The application of electric pulses to cells or vesicles induces complex responses. When electric field shocks are applied, a lipid membrane may become porated, which is a phenomenon known as electroporation. The lipid membrane may also deform under electromechanical and electrohydrodynamic forces, applied via electric fields,which is a phenomenon known as electrodeformation. Electroporation is widely employed in both biological research and clinical applications including areas such as drug and gene delivery, protein insertion, cancer therapy, and other processes where access to the cytoplasm is desired. Electrodeformation, on the other hand, can be harnessed as a means to probe the membrane's properties, and to detect pathological changes in cells. Despite its broad applicability, electroporation still suffers from low delivery efficiency and cell viability, in part due to a lack of a fundamental understanding of the mechanisms involved in this technique. Meanwhile, the electrodeformation phenomenon only received attention in the past decade, and therefore, a significant body of data only became available in the recent years. This is mainly due to the development of high-performance optical imaging systems which gave the opportunity to capture the dynamics associated with electrodeformation. In this work, we have designed and implemented experiments to study the electrodeformation of giant unilamellar vesicles, and to investigate the complex transport mechanisms involved in electroporation-mediated molecular delivery. In addition, we quantified the molecular uptake and cellular viability in electroporation experiments. First, we characterized the prolate deformations of giant unilamellar vesicles under strong DC electric fields. The vesicles exhibited prolate elongations along the direction of the electric field. In some cases, the aspect ratio of a deformed vesicle exceeded 10, representing a novel strong-deformation regime never before explored. Second, we studied the spatial and temporal transport of molecules via fluorescence microscopy, at the single cell level. The experimental results demonstrated that electrophoresis, not diffusion, is the dominant mode of of delivery during the pulse. Furthermore, we found that an electrokinetic mechanism known as field-amplified sample stacking (FASS) mediated an inverse correlation between delivery and the extracellular electrical conductivity. Following our accomplishment in the second task, we investigated a two-stage pulsing electroporation protocol that delivers separate pulses to porate the membrane and to electrokinetically-mediate species transport across the cell membrane. We found that while both delivery and viability are linearly dependent with respect to the duration of the second pulses, they both show a strong dependence on field strength. Moreover, a critical regime for maximized delivery and viability is achieved. This dissertation contributes to the electroporation and electrodeformation fields by generating explanations to several experimental observations based on physical mechanisms which were not previously available. In addition, the experimental tools for quantifying delivery and viability may help develop and improve the efficacy of electroporation protocols.