The temporal dynamics of electroporation of cells subjected to ultrashort voltage pulses are studied based on a coupled scheme involving the Laplace, Nernst-Plank, and Smoluchowski equations. A pore radius dependent energy barrier for ionic transport, accounts for cellular variations. It is shown that a finite time delay exists in pore formation, and leads to a transient overshoot of the transmembrane potential V(mem) beyond 1.0 V. Pore resealing is shown to consist of an initial fast process, a 10(-4) s delay, followed by a much slower closing at a time constant of about 10(-1) s. This establishes a time-window during which the pores are mostly open, and hence, the system is most vulnerable to destruction by a second electric pulse. The existence of such a time window for effective killing by a second pulse is amply supported by our experimental data for E. coli cells. The time constant for the longer process also matches experiments. The study suggests that controlled manipulation of the pore "open times" can be achieved through multiple, ultrashort pulses.

A self-consistent model analysis of electroporation in biological cells has been carried out based on an improved energy model. The simple energy model used in the literature is somewhat incorrect and unphysical for a variety of reasons. Our model for the pore formation energy E(r) includes a dependence on pore population and density. It also allows for variable surface tension, incorporates the effects of finite conductivity on the electrostatic correction term, and is dynamic in nature. Self-consistent calculations, based on a coupled scheme involving the Smoluchowski equation and the improved energy model, are presented. It is shown that E(r) becomes self-adjusting with variations in its magnitude and profile, in response to pore population, and inhibits uncontrolled pore growth and expansion. This theory can be augmented to include pore-pore interactions to move beyond the independent pore picture.

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An electromechanical analysis based on thin-shell theory is presented to analyze cell shape changes in response to external electric fields. This approach can be extended to include osmotic-pressure changes. Our calculations demonstrate that at large fields, the spherical cell geometry can be significantly modified, and even ellipsoidal forms would be inappropriate to account for the deformation. Values of the surface forces obtained from our calculations are in very good agreement with the 1--10 mN/m range for membrane rupture reported in the literature. The results, in keeping with reports in the literature, demonstrate that the final shape depends on membrane thickness. This has direct implications for tissues in which significant molecular restructuring can occur. It is also shown that, at least for the smaller electric fields, both the cellular surface area and volume change roughly in a quadratic manner with the electric field. Finally, it is shown that the bending moments are generally quite small and can be neglected for a simpler analysis.

We have measured room-temperature band-to-band recombination decay kinetics in superior quality GaAs heterostructures, and have observed the longest lifetime (2.5 μs) observed for any GaAs/AlxGa1−xAs structure to date. Additionally, using a novel time-resolved optical photoluminescence imagining technique, analogous to the Haynes–Shockley experiment, we have also measured room-temperature minority-carrier transport in this series of ‘‘surface-free’’ GaAs/Al0.3Ga0.7As double heterostructures, measurements only possible in high-quality samples with long lifetimes and intense photoluminescence. We find the transport to be diffusive with diffusion lengths of ≳100 μm. Further, we find, for thick structures, minority-carrier transport is hole-dominated ambipolar diffusion, as expected for high-purity n-type material. However, for thinner structures, we find that the minority-carrier transport is time dependent, changing from ambipolar diffusion at early times, as in thick structures, to electron-dominated diffusion at later times. We show that these structures become effectively p-type modulation doped due to the relative ‘‘impurity’’ and thickness of the AlxGa1−xAs compared to the GaAs. As a result, the minority-carrier species changes from holes to electrons for decreasing GaAs layer thicknesses. Cumulatively, we show the band-to-band recombination decay kinetics and carrier transport results to be in excellent qualitative and quantitative agreement. Moreover, our results are in excellent agreement with electrical transport measurements of electron and hole mobilities. Finally, with our measured room-temperature lifetimes and minority-carrier transport measurements versus GaAs layer thickness, we accurately calculate the interface recombination velocity for these structures, with the result S∼40 cm/s, among the lowest ever reported for any GaAs/AlxGa1−xAs structure.