Yanpeng Lv

Bipolar Microsecond Pulses and Insulated Needle Electrodes for Reducing Muscle Contractions During Irreversible Electroporation

Objective: To minimize the effect of muscle contractions during irreversible electroporation (IRE), this paper attempts to research the ablation effect and muscle contractions by applying high-frequency IRE (H-FIRE) ablation to liver tissue in vivo. Methods: An insulated needle electrode was produced by painting an insulating coating on the outer surface of the needle electrode tip. A series of experiments were conducted using insulated needle electrodes and traditional needle electrodes to apply H-FIRE pulses and traditional monopolar IRE pulses to rabbit liver tissues. The finite element model of the rabbit liver tissue was established to determine the lethal thresholds of H-FIRE in liver tissues. Muscle contractions were measured by an accelerometer. Results: With increased constitutive pulse width and pulse voltage, the ablation area and muscle contraction strength are also increased, which can be used to optimize the ablation parameters of H-FIRE. Under the same pulse parameters, the ablation areas are similar for the two types of electrodes, and the ablation region has a clear boundary. H-FIRE and insulated needle electrodes can mitigate the extent of muscle contractions. The lethal thresholds of H-FIRE in rabbit liver tissues were determined. Conclusion: This paper describes the relationships between the ablation area, muscle contractions, and pulse parameters; the designed insulated needle electrodes can be used in IRE for reducing muscle contraction. Significance: The study provides guidance for treatment planning and reducing muscle contractions in the clinical application of H-FIRE.

Irreversible electroporation ablation area enhanced by synergistic high- and low-voltage pulses

Irreversible electroporation (IRE) produced by a pulsed electric field can ablate tissue. In this study, we achieved an enhancement in ablation area by using a combination of short high-voltage pulses (HVPs) to create a large electroporated area and long low-voltage pulses (LVPs) to ablate the electroporated area. The experiments were conducted in potato tuber slices. Slices were ablated with an array of four pairs of parallel steel electrodes using one of the following four electric pulse protocols: HVP, LVP, synergistic HVP+LVP (SHLVP) or LVP+HVP. Our results showed that the SHLVPs more effectively necrotized tissue than either the HVPs or LVPs, even when the SHLVP dose was the same as or lower than the HVP or LVP doses. The HVP and LVP order mattered and only HVPs+LVPs (SHLVPs) treatments increased the size of the ablation zone because the HVPs created a large electroporated area that was more susceptible to the subsequent LVPs. Real-time temperature change monitoring confirmed that the tissue was non-thermally ablated by the electric pulses. Theoretical calculations of the synergistic effects of the SHLVPs on tissue ablation were performed. Our proposed SHLVP protocol provides options for tissue ablation and may be applied to optimize the current clinical IRE protocols.

Characterization of Conductivity Changes During High-Frequency Irreversible Electroporation for Treatment Planning

For irreversible-electroporation (IRE)-based therapies, the underlying electric field distribution in the target tissue is influenced by the electroporation-induced conductivity changes and is important for predicting the treatment zone. Objective: In this study, we characterized the liver tissue conductivity changes during high-frequency irreversible electroporation (H-FIRE) treatments of widths 5 and 10 μs and proposed a method for predicting the ablation zones. Methods: To achieve this, we created a finite-element model of the tissue treated with H-FIRE and IRE pulses based on experiments conducted in an in-vivo rabbit liver study. We performed a parametric sweep on a Heaviside function that captured the tissue conductivity versus electric field behavior to yield a model current close to the experimental current during the first burst/pulse. A temperature module was added to account for the current increase in subsequent bursts/pulses. The evolution of the electric field at the end of the treatment was overlaid on the experimental ablation zones determined from hematoxylin and eosin staining to find the field thresholds of ablation. Results: Dynamic conductivity curves that provided a statistically significant relation between the model and experimental results were determined for H-FIRE. In addition, the field thresholds of ablation were obtained for the tested H-FIRE parameters. Conclusion: The proposed numerical model can simulate the electroporation process during H-FIRE. Significance: The treatment planning method developed in this study can be translated to H-FIRE treatments of different widths and for different tissue types.

Synergistic combinations of short high-voltage pulses and long low-voltage pulses enhance irreversible electroporation efficacy

Irreversible electroporation (IRE) uses ~100 μs pulsed electric fields to disrupt cell membranes for solid tumor ablation. Although IRE has achieved exciting preliminary clinical results, implementing IRE could be challenging because of volumetric limitations at the ablation region. Combining short high-voltage (SHV: 1600V, 2 μs, 1 Hz, 20 pulses) pulses with long low-voltage (LLV: 240–480 V, 100 μs, 1 Hz, 60–80 pulses) pulses induces a synergistic effect that enhances IRE efficacy. Here, cell cytotoxicity and tissue ablation were investigated. The results show that combining SHV pulses with LLV pulses induced SKOV3 cell death more effectively, and compared to either SHV pulses or LLV pulses applied alone, the combination significantly enhanced the ablation region. Particularly, prolonging the lag time (100 s) between SHV and LLV pulses further reduced cell viability and enhanced the ablation area. However, the sequence of SHV and LLV pulses was important, and the LLV + SHV combination was not as effective as the SHV + LLV combination. We offer a hypothesis to explain the synergistic effect behind enhanced cell cytotoxicity and enlarged ablation area. This work shows that combining SHV pulses with LLV pulses could be used as a focal therapy and merits investigation in larger pre-clinical models and microscopic mechanisms.

Dielectric variations of potato induced by irreversible electroporation under different pulses based on the cole-cole model

To investigate dielectric property variations induced by electric pulses, equivalent doses of conventional irreversible electroporation (IRE) and high-frequency IRE were used to treat potato slices. The dielectric property of the potatoes were measured before and after treatment in the frequency band of 0.1 Hz-10 MHz, and then the Cole-Cole model was used to fit the experimental data in the frequency band of 1 kHz-10 MHz to explain the β dispersion mechanism. The Cole-Cole model parameters showed that under an equivalent dose, the conventional IRE pulses were more efficient than the high-frequency IRE pulses for electroporation. After treatment with conventional IRE pulses, the DC conductivity greatly increased at time 0 after the pulses and showed little recovery over time. The electroporation effect of the high-frequency IRE pulses improved with increasing pulse duration. This study presents a potential new method for evaluating the effects of IRE during and immediately after the treatment process.

Differences in the Effects of Duty Cycle and Interval on Cell Response Induced by High-Frequency Pulses Under Different Pulse Durations

High-frequency pulses constitute a new method for tumor treatment and have been proposed to solve the problems of muscle contraction and tumor recurrence caused by the nonuniform distribution of the electric field. However, the killing mechanism of high-frequency pulses remains unclear. Different pulse parameters have varying influences on the killing effect on cells. We studied the influence of the pulse duty cycle and the interval between pulses on the cellular response, including the transmembrane potential (TMP), pore radii, and the pore density, using finite-element simulation. Results showed that, given a pulse duration of 5 μs, the pulse duty cycle has an insignificant effect on the cellular response, and the cellular responses under monopolar pulses and bipolar pulses are similar. Given a bipolar pulse duration of 300 ns, the TMP and the pulse radii become larger if the interval between pulses is longer under bipolar pulses. Given a pulse duration of 300 ns, the TMP and pore radii under the monopolar pulse are larger than those under the bipolar pulse. Normal human epidermal cells (Hacat) and tumor cells (Gll19) are used to verify the simulation results, which show that the duty has an insignificant effect on cell killing. The simulation with the duration of 300 ns is verified using an experiment reported in the literature.

Cell electrofusion based on nanosecond/microsecond pulsed electric fields

Traditionally, microsecond pulsed electric field was widely used in cell electrofusion technology. However, it was difficult to fuse the cells with different sizes. Because the effect of electroporation based on microsecond pulses was greatly influenced by cell sizes. It had been reported that the differences between cell sizes can be ignored when cells were exposed to nanosecond pulses. However, pores induced by those short nanosecond pulses tended to be very small (0.9 nm) and the pores were more easy to recover. In this work, a finite element method was used to simulate the distribution, radius and density of the pores. The innovative idea of “cell electrofusion based on nanosecond/microsecond pulses” was proposed in order to combine the advantages of nanosecond pulses and microsecond pulses. The model consisted of two contact cells with different sizes. Three kinds of pulsed electric fields were made up of two 100-ns, 10-kV/cm pulses; two 10-μs, 1-kV/cm pulses; and a sequence of a 100-ns, 10-kV/cm pulse, followed by a 10-μs, 1-kV/cm pulse. Some obvious advantageous can be found when nanosecond/microsecond pulses were considered. The pore radius was large enough (70nm) and density was high (5×1013m-2) in the cell junction area. Moreover, pores in the non-contact area of the cell membrane were small (1–10 nm) and sparse (109-1012m-2). Areas where the transmembrane voltage was higher than 1V were only concentrated in the cell junction. The transmembrane voltage of other areas were at most 0.6V when we tested the rest of the cell membrane. Cell fusion efficiency can be improved remarkably because electroporation was concentrated in the cell contact area.

Analysis of Dynamic Processes in Single-Cell Electroporation and Their Effects on Parameter Selection Based on the Finite-Element Model

Pulsed electric fields have recently been the focus of considerable attention because of their potential application in biomedicine. However, their practical clinical applications are limited by poor understanding of the interaction mechanism between pulsed electric fields and cells, particularly in the process of electroporation and its effect on parameter selection. This paper established a multishelled dielectric model based on finite elements to simulate and analyze the processes involved in electroporation. In particular, the processes include the dynamic development of the pore radius and electroporation region: the distribution of recoverable, nonrecoverable, and nonelectroporation areas on the cell; and the influence of pulse parameters on varying degrees of electroporation. Results showed that membrane conductivity, pore density, transmembrane potential, and distribution of pore radii are functions of time and position on the cell. The electroporation areas were divided into recoverable, nonrecoverable, and no-electroporation pores. For

Comparative Study of the Biological Responses to Conventional Pulse and High-Frequency Monopolar Pulse Bursts

10~\mu \text{s}

Targeted cell membrane damage by bipolar high repeated frequency pulses

, 1.5-kV/cm pulse was observed in the regions exposed to sufficiently high transmembrane voltage (1 V), electroporation occurred, membrane conductivity and pore density (up to