Jiahui Song

Simulation Studies of Ultrashort, High-Intensity Electric Pulse Induced Action Potential Block in Whole-Animal Nerves

A theoretical study of possible neuromuscular incapacitation based on the application of high-intensity, ultrashort electric pulses is presented. The analysis is applied to a rat, but the approach is general and can be extended to any whole-animal and applies for any arbitrary pulse waveform. It is hypothesized that repeatable and reversible action potential blocks in nerves can be attained based on the electroporation mechanism. Our numerical studies are based on the Hodgkin-Huxley distributed circuit representation of nerves, and incorporate a nodal analysis for the time-dependent and volumetric perturbing potentials and internal electric fields in whole animals. The predictions are compared to actual 600-ns experimental reports on rats and shown to be in very good agreement. Effective strength-duration plots for neuromuscular incapacitation are also generated.

Synergistic effects of local temperature enhancements on cellular responses in the context of high-intensity, ultrashort electric pulses.

Results of self-consistent analyses of cells show the possibility of temperature increases at membranes in response to a single nanosecond, high-voltage pulse, at least over small sections of the membrane. Molecular Dynamics simulations indicate that such a temperature increase could facilitate poration, which is one example of a bio-process at the plasma membrane. Our study thus suggests that the use of repetitive high-intensity voltage pulses could open up possibilities for a host of synergistic bio-responses involving both thermal and electrically driven phenomena.

Aspects of lipid membrane bio-responses to subnanosecond, ultrahigh voltage pulsing

Membrane electroporation is probably one of the best-known effects of applying external voltages to biological cells. Reports in the literature have focused on relatively long voltage pulse durations (100 ns-1 ms). Here we probe the very short (< 1 ns), but intense electric field (> 500 kV/cm) regime that is made possible by advances in pulsed power technology. Our analyses based on continuum Smoluchowski and molecular dynamics (MD) approaches, predict two new aspects. First, it is shown that pore formation rates would be dramatically lower than predicted by conventional theory due to their dependence on local pore area. Second, such high fields are predicted to affect membrane proteins and ion-channels, without causing electroporation in regions between the proteins. Hence, such high voltage, short duration pulsing should not be associated with electroporation alone, but rather be viewed as a novel vehicle that opens possibilities for a range of new electrically-driven bio-response phenomena.

Cellular apoptosis by nanosecond, high-intensity electric pulses: model evaluation of the pulsing threshold and extrinsic pathway.

A simple, bistable rate-equation based model is used to predict trends of cellular apoptosis following electric pulsing. The caspase-8 extrinsic pathway with inherent delays in its activation, cytochrome c release, and an internal feedback mechanism between caspase-3 and cleavage of Bid are incorporated. Results obtained were roughly in keeping with the experimental cell-survival data and include an electrical pulse-number threshold followed by a near-exponential fall-off. The extrinsic caspase-8 mechanism is predicted to be more sensitive than the mitochondrial intrinsic pathway for electric pulse induced cell apoptosis. Also, delays of about an hour are predicted for detectable molecular concentration increases following electrical pulsing. Finally, our results suggest that multi-needle electrode systems with adjustable field orientations would likely enhance apoptosis in the context of pulsed voltage-induced inactivation of tumor cells.

Model Analysis of Electric Fields Induced by High-Voltage Pulsing in Cylindrical Nerves

A cylindrical dielectric model is used to compute transmembrane potential changes and evaluate the axial electric field magnitudes produced within a nerve by a high-intensity relatively short electrical pulse. For concreteness, the pulse was taken to have a duration of about 700 ns and large current magnitudes in keeping with ongoing experimental studies within our group. Interest in this quantitative analysis arises from probing the possibility of triggering bioeffects at intracellular organelles in tissues (or even whole animals) through such electric stimulation. Almost all other studies have focused on simple spherical cells. This paper provides a theoretical framework for computing electric fields (especially the axial components) within such cylindrical geometries (e.g., nerve cells). It is shown that fields can become sufficiently high within microseconds and initiate electroporation, modulate electrochemical processes (e.g., calcium release), or trigger secondary biochemical effects depending on the electrical pulsing parameters.

Evaluation of Current Coil Positioning for an Enhanced Hybrid Active Space Radiation Bio-Shielding Concept

Developing successful and optimal solutions to mitigating the bio-hazards of severe space radiation is critical for the success of deep-space explorations. A recent report has explored the feasibility of using a hybrid configuration that utilized both electrostatic and magnetostatic fields. Here we extend the analyses in an effort to optimize the hybrid configuration. These include changes in the radius of the current-carrying ring, and the use of multiple rings for greater bio-protection. Our simulation results show GCR proton transmission to be reduced down to 15 percent at energies around 1 GeV for a magnetic ring with a 70 meter radius. Use of three orthogonal rings is predicted to reduce the 1GeV GCR proton transmission to ~12 percent, even with smaller (35 meter radius) rings.

Electro-thermal simulation studies for pulsed voltage induced energy absorption and potential failure in microstructured ZnO varistors

Summary form only given. Zinc oxide varistors are ceramic devices made by sintering ZnO powder together with small amounts of other additives such as Bi2O3, MnO2, Co3O4 etc... The presence of Bi-ions trapped at the grain-boundaries are thought to be responsible for a highly nonlinear behavior. The nonlinear current-voltage (I-V) characteristics and excellent energy absorption capabilities, make ZnO varistors very useful as electrical surge arresters. We present a coupled electro-thermal analyses to determine the voltage driven temperature increases and possible impact on material failure in a ZnO varistor. A two-dimensional, random Voronoi network model has been used. The inherently non-linear internal I-V characteristics have been included. A stochastic distribution of grains with varying sizes and barrier breakdown voltages has also been taken into account. The model is time-dependent and includes two-dimensional heat generation and flow. Issues relating to internal heating analyses, time-dependent localized melting, cracking due to thermal stresses, and dynamical evolution towards failure, are addressed. Our results show that application of high voltage pulses can lead to internal ZnO melting. Such phase change is known to permanently damage the non-linear GB chracter associated with the Bi2O3 present in such material. Comparisons between uniform and normally distributed barrier voltages were made. Physically, it was shown that differences would be associated would depend on grain size and the applied bias regime. It has also been shown that reduction in grain size would help lower the maximum internal stress. This is thus a desirable feature, and would also work to enhance the hold-off voltage for a given sample size.