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A general, self-consistent scheme for analyzing cellular electroporation for bio-medical applications is developed to probe realistic biological shapes and different length scales ranging from nanometers to hundreds of micrometers. The COMSOL Multiphysics suite is used with suitable embellishments to incorporate the details of the electroporation (EP) process and the inherent internal physics. The results are obtained for the voltage pulse driven electroporation for a Jurkat cell with mitochondria (as an example organelle) where spatial dimensions on the order of a few nanometers become important, to hundreds of cells (with Bacillus as an example) where collective effects and mutual interactions can dominate. Thus, scalable computing to generalized geometries with the ability to include complex organelles is made available. The results obtained for mitochondrial EP in Jurkat cells compare well with available data. In addition, quantitative predictions of field attenuation and shielding in Bacillus clusters are made, which point to highly nonuniform field distributions and a strong need to engineer novel electrode designs. [ABSTRACT FROM AUTHOR]

Protocols surrounding electroporation have long been based on trapezoidal (or near rectangular) pulsing of biological cells. Here, we revisit cellular electroporation for biomedical applications, including tumor treatment, based on a self-consistent electro-thermal analysis with sinusoidal RF excitation. Predictions for the evolution of pores and their surface angular distribution, as well as potential heating and temperature increases, are given. Our results show an optimum frequency range from 5 to 7 MHz to achieve increased mass transport without detrimental heating in Jurkat cells. Through parametrized frequency sweeps, this work establishes potential optimized regimes that could guide experimental and clinical protocols. More significantly, a possible frequency for porating healthy B-cells is predicted to be ∼2.5 MHz, with almost no poration at 7 MHz. This opens up the exciting possibility for treating malignant tissue with a well-tuned frequency range for bioeffects while minimizing deleterious effects on healthy cells and tissues. [ABSTRACT FROM AUTHOR]

Multipactor mitigation is of relevance to microwave applications, and external magnetic fields, surface modifications, and materials engineering have previously been utilized for this purpose. In this contribution, geometric modifications made to rectangular waveguide surfaces in the form of nested grooves are investigated for the suppression of multipactor growth. A time-dependent kinetic scheme is used to simulate electron dynamics that folds in electron trapping at the nested groove structures, with inclusion of the electric field perturbations arising from the presence of various grooved geometries. The charge growth in the system is modeled based on an empirical approach that includes both energy and angular dependencies of secondary electron emission from all the different surfaces. A varying number of grooves, their widths, and their placement (either one sided or dual-sided) within the rectangular waveguide structure are included for a more complete analysis. The results demonstrate that nested grooves can lead to reductions in charge growth by over a factor of 280 when compared with a simple waveguide over the same time period. Furthermore, wider nested grooves are shown to have an advantage, with multiple aligned grooves across two parallel surfaces being especially useful at high external fields. Determining optimal combinations for an arbitrary field, operating frequency, and physical dimensions would require further work. [ABSTRACT FROM AUTHOR]

A distributed circuit approach is used to simulate the development of electric potentials across a cell membrane and the resulting poration dynamics for ∼700 ns duration voltage pulses. Besides electric field effects, temperature increases from a pulse train are included on an equal footing to probe heating effects. The results show (i) strong heating and power dissipation at the membrane in keeping with previous simpler models, (ii) an initial spike in the membrane temperature within 100 ns timescales, (iii) a monotonic increase in membrane temperature with successive pulses to about 8 K over twelve pulses within roughly 10 μs, and (iv) large temperature gradients in excess of 2 × 107 K/m at the polar membrane region indicative of a strong source for thermo-diffusive transport. Our results suggest that inherent heating during repeated pulse application may be used to tailor excitation sequences for maximal cellular transport, broaden the permeabilization beyond the polar regions for greater transmembrane conduction, and lower the electric field thresholds for greater efficiency in longer duration irreversible electroporation protocols. More generally, the present analysis represents an initial step toward a comprehensive analysis-based optimization for tumor treatment that could select waveforms for tissues, factor in heating effects (whether for synergistic action or to ascertain safe operating limits), and engineer temporal manipulation of wavetrains to synchronize with timescales of selective bio-processes of interest for desired transient responses. [ABSTRACT FROM AUTHOR]

Evaluation of the photoresponse in wurtzite GaN photoconductive switches is presented based on kinetic Monte Carlo simulations. The focus is on electron transport physics and assessment of high frequency operation. The roles of GaN band structure, Pauli exclusion, and treatment of internal fields based on the fast multipole method are all comprehensively included. The implementation was validated through comparisons of velocity-field characteristics for GaN with computational results in the literature. Photocurrent widths of less than ∼7 ps for the 1 μm device can be expected, which translates into a 100 GHz upper bound. Photocurrent pulse compression below the laser full width at half maxima at high applied fields are predicted based on the interplay of space-charge effects and the negative differential velocity characteristics of GaN. [ABSTRACT FROM AUTHOR]

Evaluations of the current output from emitter arrays have been carried out based on time-dependent kinetic simulations that include many-body Coulombic contributions from the electron swarm, geometric field enhancements with shielding based on a line charge model, and dynamic screening due to the evolution of the swarm in the position and velocity space. Numerical evaluations are applied to different multi-emitter array arrangements having a hexagonal lattice, with a focus on bimodal distributions. Our results show the expected role of field screening with reductions in emitter separation and positional dependence within the array based on connectivity. Different patterns were examined within a hexagonal lattice structure. For a bimodal distribution, output current optimization is shown for alternating arrangements with three or more successive emitters of the same length along primitive axes predicted to have an advantage. [ABSTRACT FROM AUTHOR]

Electroporation occurs when cells are exposed to an electric pulse of sufficient intensity E 0 and pulse duration τ. Many studies have attempted to develop universal scaling laws to predict membrane pore dynamics for pulsed electric fields (PEFs) of different durations; however, the differences in pore dynamics across these parameters makes this difficult both experimentally and numerically. This study uses the asymptotic Smoluchowski equation (ASME) to quantify the number of pores, average pore radius, and fractional pore area (FPA) during exposure to PEFs with durations from hundreds of picoseconds to a millisecond. We highlight pulse parameter regimes that favor increases in pore radius and number and show that the FPA is dominated by the number of pores formed on the cell membrane. Furthermore, the number of pores and the FPA depend almost entirely on E 0 for τ exceeding the charging time of the cell and both E 0 and τ for τ shorter than the charging time. Finally, the maps of pore number, average radius, and FPA demonstrate that a universal scaling law for pore dynamics across a wide range of pulse durations does not exist, although certain scaling behaviors may be valuable over narrow regimes. Practically, these maps provide a guideline for selecting PEF parameters to achieve desired membrane permeabilization.

Self-consistent evaluations of membrane electroporation along with local heating in single spherical cells arising from external AC radiofrequency electrical stimulation have been carried out. The present numerical study seeks to determine whether healthy and malignant cells exhibit separate electroporative responses with regards to operating frequency. It is shown that cells of Burkitt's lymphoma would respond to frequencies >4.5 MHz, while normal B-cells would have negligible porative effects in that higher frequency range. Similarly, a frequency separation between the response of healthy T-cells and malignant species is predicted with a threshold of about 4 MHz for cancer cells. The present simulation technique is general and so would be able to ascertain the beneficial frequency range for different cell types. The demonstration of higher frequencies to induce poration in malignant cells, while having minimal affecting healthy ones, suggests the possibility of selective electrical targeting for tumor treatments and protocols. It also opens the doorway for tabulating selectivity enhancement regimes as a guide for parameter selection towards more effective treatments while minimizing deleterious effects on healthy cells and tissues.