Ultrashort electric pulse induced changes in cellular dielectric properties

Optimal Irreversible Electroporation Combined with Nano-Enabled Immunomodulatory to Boost Systemic Antitumor Immunity

In this work, we proposed nµPEF, a novel pulse configuration combining nanosecond and microsecond pulses (nµPEF), to enhance tumor ablation in irreversible electroporation (IRE) for oncological therapy. nµPEF demonstrated improved efficacy in inducing immunogenic cell death, positioning it as a potential candidate for next-generation ablative therapy. However, the immune response elicited by nµPEF alone was insufficient to effectively suppress distant tumors. To address this limitation, we developed PPR@CM-PD1, a genetically engineered nanovesicle. PPR@CM-PD1 employed a polyethylene glycol-polylactic acid-glycolic acid (PEG-PLGA) nanoparticle encapsulating the immune adjuvant imiquimod and coated with a genetically engineered cell membrane expressing programmed cell death protein 1 (PD1). This design allowed PPR@CM-PD1 to target both the innate immune system through toll-like receptor 7 (TLR7) agonism and the adaptive immune system through programmed cell death protein 1/programmed cell death-ligand 1 (PD1/PDL1) checkpoint blockade. In turn, nµPEF facilitated intratumoral infiltration of PPR@CM-PD1 by modulating the tumor stroma. The combination of nµPEF and PPR@CM-PD1 generated a potent and systemic antitumor immune response, resulting in remarkable suppression of both nµPEF-treated and untreated distant tumors (abscopal effects). This interdisciplinary approach presents a promising perspective for oncotherapy and holds great potential for future clinical applications.

Determining tissue conductivity in tissue ablation by nanosecond pulsed electric fields

Nanosecond pulsed electric field (nsPEF) causes the permeabilization of the cell membrane and has been used to non-thermally treat cancerous tissues. As increased permeabilization in membranes were reported to be accompanied by impedance changes, the ablation effect of nsPEF on tissues can be monitored via the changes in tissue conductivity. In this study, effects of nsPEF on biological tissues were evaluated by determining the conductivities of potato and 4 T1-luc breast tumor tissues ex vivo from a murine model subjected to multiple 100-ns, 1-10 kV pulses. Using a four-needle electrode system with a calibrated electrode constant of 1.1 ± 0.1 cm, the conductivities of tissues was determined from both the network-analyzer measurement, before and after treatment, and voltage-current measurement in real-time. The conductivity of the potato tissue was measured for a frequency range of 0.1-3 MHz, and it increased with increasing pulse number and voltage amplitude. The conductivity of the tumor tissue was also observed to increase with pulse number and pulse voltage over a similar frequency range. In addition, the linear correlation between the ablation area in a treated potato tissue and the conductivity change in the tissue suggests that conductivity analysis of biological tissue under treatment could be a fast and sensitive approach to evaluate the effectiveness of a nsPEF treatment.

Correlation between electrical characteristics and biomarkers in breast cancer cells

Both electrical properties and biomarkers of biological tissues can be used to distinguish between normal and diseased tissues, and the correlations between them are critical for clinical applications of conductivity (σ) and permittivity (ε); however, these correlations remain unknown. This study aimed to investigate potential correlations between electrical characteristics and biomarkers of breast cancer cells (BCC). Changes in σ and ε of different components in suspensions of normal cells and BCC were analyzed in the range of 200 kHz-5 MHz. Pearson's correlation coefficient heatmap was used to investigate the correlation between σ and ε of the cell suspensions at different stages and biomarkers of cell growth and microenvironment. σ and ε of the cell suspensions closely resembled those of tissues. Further, the correlations between Na⁺/H⁺ exchanger 1 and ε and σ of cell suspensions were extremely significant among all biomarkers (p_ε < 0.001; p_σ < 0.001). There were significant positive correlations between cell proliferation biomarkers and ε and σ of cell suspensions (p_ε/σ < 0.05). The microenvironment may be crucial in the testing of cellular electrical properties. ε and σ are potential parameters to characterize the development of breast cancer.

Electrical stimulation of whole blood for growth factor release and potential clinical implications

Clinicians have increasingly applied platelet-rich plasma (PRP) for wound healing treatments. Topical treatments commonly require biochemical agents such as bovine thrombin to activate PRP ex vivo for clotting and growth factor release to facilitate healing upon application to the wound of interest. Recent studies have explored electrical stimulation as an alternative to bovine thrombin for PRP activation due to the former's cost, workflow complexity and potentially significant side effects; however, both approaches require separating the PRP from whole blood (WB) prior to activation. Eliminating the separation (typically centrifugation) step would reduce the cost and duration of the clinical procedure, which may be critical in trauma and surgical applications. We hypothesize that electric pulses (EPs) can release growth factors from WB, as they do from PRP, without requiring centrifugation of WB into PRP. A pilot study for two donors demonstrates the potential for EP stimulated growth factor release from WB. This motivates future experiments assessing EP parameter optimization for WB activation and in vivo studies to determine the clinical benefits for topical treatments and, especially, for injections in orthopedic applications that already utilize non-treated/non-activated WB.

Ten-Second Electrophysiology: Evaluation of the 3DEP Platform for high-speed, high-accuracy cell analysis

Electrical correlates of the physiological state of a cell, such as membrane conductance and capacitance, as well as cytoplasm conductivity, contain vital information about cellular function, ion transport across the membrane, and propagation of electrical signals. They are, however, difficult to measure; gold-standard techniques are typically unable to measure more than a few cells per day, making widespread adoption difficult and limiting statistical reproducibility. We have developed a dielectrophoretic platform using a disposable 3D electrode geometry that accurately (r² > 0.99) measures mean electrical properties of populations of ~20,000 cells, by taking parallel ensemble measurements of cells at 20 frequencies up to 45 MHz, in (typically) ten seconds. This allows acquisition of ultra-high-resolution (100-point) DEP spectra in under two minutes. Data acquired from a wide range of cells – from platelets to large cardiac cells - benchmark well with patch-clamp-data. These advantages are collectively demonstrated in a longitudinal (same-animal) study of rapidly-changing phenomena such as ultradian (2–3 hour) rhythmicity in whole blood samples of the common vole (Microtus arvalis), taken from 10 µl tail-nick blood samples and avoiding sacrifice of the animal that is typically required in these studies.

Characterization of Single-Nucleus Electrical Properties by Microfluidic Constriction Channel

As key bioelectrical markers, equivalent capacitance (C_ne, i.e., capacitance per unit area) and resistance (R_ne, i.e., resistivity multiply thickness) of nuclear envelopes have emerged as promising electrical indicators, which cannot be effectively measured by conventional approaches. In this study, single nuclei were isolated from whole cells and trapped at the entrances of microfluidic constriction channels, and then corresponding impedance profiles were sampled and translated into single-nucleus C_ne and R_ne based on a home-developed equivalent electrical model. C_ne and R_ne of A549 nuclei were first quantified as 3.43 ± 1.81 μF/cm² and 2.03 ± 1.40 Ω·cm² (N_n = 35), which were shown not to be affected by variations of key parameters in nuclear isolation and measurement. The developed approach in this study was also used to measure a second type of nuclei, producing C_ne and R_ne of 3.75 ± 3.17 μF/cm² and 1.01 ± 0.70 Ω·cm² for SW620 (N_n = 17). This study may provide a new perspective in single-cell electrical characterization, enabling cell type classification and cell status evaluation based on bioelectrical markers of nuclei.

Tunable activation of therapeutic platelet-rich plasma by pulse electric field: Differential effects on clot formation, growth factor release, and platelet morphology

BACKGROUND

Activation of platelet-rich plasma (PRP) by pulse electric field (PEF) releases growth factors which promote wound healing (e.g., PDGF, VEGF for granulation, EGF for epithelialization).

AIMS

To determine after PEF activation of therapeutic PRP: 1) platelet gel strength; 2) profile of released growth factors; 3) alpha- and T-granule release; 4) platelet morphology.

METHODS

Concentrated normal donor PRP was activated by 5 μsec (long) monopolar pulse, ~4000 V/cm (PEF A) or 150 nsec (short) bipolar pulse, ~3000 V/cm (PEF B) in the presence of 2.5 mM (low) or 20 mM (high) added CaCl2. Clot formation was evaluated by thromboelastography (TEG). Surface exposure of alpha granule (P-selectin) and T-granule (TLR9 and protein disulfide isomerase [PDI]) markers were assessed by flow cytometry. Factors in supernatants of activated PRP were measured by ELISA. Platelet morphology was evaluated by transmission electron microscopy (TEM).

RESULTS

Time to initial clot formation was shorter with thrombin (<1 min) than with PEF A and B (4.4-8.7 min) but clot strength (elastic modulus, derived from TEG maximum amplitude) was greater with PEF B than with either thrombin or PEF A (p<0.05). Supernatants of PRP activated with PEF A had higher EGF levels than supernatants from all other conditions. In contrast, levels of PF4, PDGF, and VEGF in supernatants were not significantly different after PEF A, PEF B, and thrombin activation. T-granule markers (TLR9 and PDI) were higher after thrombin than after PEF A or B with low or high CaCl2. By TEM, platelets in PEF-treated samples retained a subset of granules suggesting regulated granule release.

CONCLUSION

Pulse length and polarity can be modulated to produce therapeutic platelet gels as strong or stronger than those produced by thrombin, and this is tunable to produce growth factor profiles enhanced in specific factors important for different stages of wound healing.

Ablation outcome of irreversible electroporation on potato monitored by impedance spectrum under multi-electrode system

BACKGROUND

Irreversible electroporation (IRE) therapy relies on pulsed electric fields to non-thermally ablate cancerous tissue. Methods for evaluating IRE ablation in situ are critical to assessing treatment outcome. Analyzing changes in tissue impedance caused by electroporation has been proposed as a method for quantifying IRE ablation. In this paper, we assess the hypothesis that irreversible electroporation ablation outcome can be monitored using the impedance change measured by the electrode pairs not in use, getting more information about the ablation size in different directions.

METHODS

Using a square four-electrode configuration, the two diagonal electrodes were used to electroporate potato tissue. Next, the impedance changes, before and after treatment, were measured from different electrode pairs and the impedance information was extracted by fitting the data to an equivalent circuit model. Finally, we correlated the change of impedance from various electrode pairs to the ablation geometry through the use of fitted functions; then these functions were used to predict the ablation size and compared to the numerical simulation results.

RESULTS

The change in impedance from the electrodes used to apply pulses is larger and has higher deviation than the other electrode pairs. The ablation size and the change in resistance in the circuit model correlate with various linear functions. The coefficients of determination for the three functions are 0.8121, 0.8188 and 0.8691, respectively, showing satisfactory agreement. The functions can well predict the ablation size under different pulse numbers, and in some directions it did even better than the numerical simulation method, which used different electric field thresholds for different pulse numbers.

CONCLUSIONS

The relative change in tissue impedance measured from the non-energized electrodes can be used to assess ablation size during treatment with IRE according to linear functions.

Red blood cell membrane damage by light-induced thermal gradient under optical trap

Rapid membrane damage of optically trapped red blood cells (RBCs) was observed at trapping powers ≥280 mW. An excellent agreement between the estimated laser-induced thermal gradient across trapped cell's membrane and that typically required for membrane electropermeabilization suggests a mechanism involving temperature gradient-induced electropermeabilization of membrane. Also the rapid collapse of the trapped cell due to membrane rupture was seen to cause shock waves in the surroundings permeabilizing nearby untrapped cells. When the experiments were carried out with RBCs collected from type II diabetic patients, a noticeable change in the damage rate compared to normal RBCs was seen suggesting a novel optical diagnosis method for the disease.

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.

Adrenal Chromaffin Cells Exposed to 5-ns Pulses Require Higher Electric Fields to Porate Intracellular Membranes than the Plasma Membrane: An Experimental and Modeling Study

Nanosecond-duration electric pulses (NEPs) can permeabilize the endoplasmic reticulum (ER), causing release of Ca²⁺ into the cytoplasm. This study used experimentation coupled with numerical modeling to understand the lack of Ca²⁺ mobilization from Ca²⁺-storing organelles in catecholamine-secreting adrenal chromaffin cells exposed to 5-ns pulses. Fluorescence imaging determined a threshold electric (E) field of 8 MV/m for mobilizing intracellular Ca²⁺ whereas whole-cell recordings of membrane conductance determined a threshold E-field of 3 MV/m for causing plasma membrane permeabilization. In contrast, a 2D numerical model of a chromaffin cell, which was constructed with internal structures representing a nucleus, mitochondrion, ER, and secretory granule, predicted that exposing the cell to the same 5-ns pulse electroporated the plasma and ER membranes at the same E-field amplitude, 3-4 MV/m. Agreement of the numerical simulations with the experimental results was obtained only when the ER interior conductivity was 30-fold lower than that of the cytoplasm and the ER membrane permittivity was twice that of the plasma membrane. A more realistic intracellular geometry for chromaffin cells in which structures representing multiple secretory granules and an ER showed slight differences in the thresholds necessary to porate the membranes of the secretory granules. We conclude that more sophisticated cell models together with knowledge of accurate dielectric properties are needed to understand the effects of NEPs on intracellular membranes in chromaffin cells, information that will be important for elucidating how NEPs porate organelle membranes in other cell types having a similarly complex cytoplasmic ultrastructure.

Design, characterization and experimental validation of a compact, flexible pulsed power architecture for ex vivo platelet activation

Electric pulses can induce various changes in cell dynamics and properties depending upon pulse parameters; however, pulsed power generators for in vitro and ex vivo applications may have little to no flexibility in changing the pulse duration, rise- and fall-times, or pulse shape. We outline a compact pulsed power architecture that operates from hundreds of nanoseconds (with the potential for modification to tens of nanoseconds) to tens of microseconds by modifying a Marx topology via controlling switch sequences and voltages into each capacitor stage. We demonstrate that this device can deliver pulses to both low conductivity buffers, like standard pulsed power supplies used for electroporation, and higher conductivity solutions, such as blood and platelet rich plasma. We further test the effectiveness of this pulse generator for biomedical applications by successfully activating platelets ex vivo with 400 ns and 600 ns electric pulses. This novel bioelectrics platform may provide researchers with unprecedented flexibility to explore a wide range of pulse parameters that may induce phenomena ranging from intracellular to plasma membrane manipulation.

Dielectrophoresis study of temporal change in internal conductivity of single CHO cells after electroporation by pulsed electric fields

Applying sufficiently strong pulsed electric fields to a cell can permeabilize the membrane and subsequently affect its dielectric properties. In this study, we employ a microfluidic dielectrophoresis cytometry technique to simultaneously electroporate and measure the time-dependent dielectric response of single Chinese hamster ovary cells. Using experimental measurements along with numerical simulations, we present quantitative results for the changes in the cytoplasm conductivity of single cells within seconds after exposure to 100 μs duration pulsed electric fields with various intensities. It is shown that, for electroporation in a medium with conductivity lower than that of the cell's cytoplasm, the internal conductivity of the cell decreases after the electroporation on a time scale of seconds and stronger pulses cause a larger and more rapid decrease. We also observe that, after the electroporation, the cell's internal conductivity is constrained to a threshold. This implies that the cell prevents some of the ions in its cytoplasm from diffusing through the created pores to the external medium. The temporal change in the dielectric response of each individual cell is continuously monitored over minutes after exposure to pulsed electric fields. A time constant associated with the cell's internal conductivity change is observed, which ranges from seconds to tens of seconds depending on the applied pulse intensity. This experimental observation supports the results of numerical models reported in the literature.

Modification of Pulsed Electric Field Conditions Results in Distinct Activation Profiles of Platelet-Rich Plasma

Background

Activated autologous platelet-rich plasma (PRP) used in therapeutic wound healing applications is poorly characterized and standardized. Using pulsed electric fields (PEF) to activate platelets may reduce variability and eliminate complications associated with the use of bovine thrombin. We previously reported that exposing PRP to sub-microsecond duration, high electric field (SMHEF) pulses generates a greater number of platelet-derived microparticles, increased expression of prothrombotic platelet surfaces, and differential release of growth factors compared to thrombin. Moreover, the platelet releasate produced by SMHEF pulses induced greater cell proliferation than plasma.

Aims

To determine whether sub-microsecond duration, low electric field (SMLEF) bipolar pulses results in differential activation of PRP compared to SMHEF, with respect to profiles of activation markers, growth factor release, and cell proliferation capacity.

Methods

PRP activation by SMLEF bipolar pulses was compared to SMHEF pulses and bovine thrombin. PRP was prepared using the Harvest SmartPreP2 System from acid citrate dextrose anticoagulated healthy donor blood. PEF activation by either SMHEF or SMLEF pulses was performed using a standard electroporation cuvette preloaded with CaCl₂ and a prototype instrument designed to take into account the electrical properties of PRP. Flow cytometry was used to assess platelet surface P-selectin expression, and annexin V binding. Platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), endothelial growth factor (EGF) and platelet factor 4 (PF4), and were measured by ELISA. The ability of supernatants to stimulate proliferation of human epithelial cells in culture was also evaluated. Controls included vehicle-treated, unactivated PRP and PRP with 10 mM CaCl₂ activated with 1 U/mL bovine thrombin.

Results

PRP activated with SMLEF bipolar pulses or thrombin had similar light scatter profiles, consistent with the presence of platelet-derived microparticles, platelets, and platelet aggregates whereas SMHEF pulses primarily resulted in platelet-derived microparticles. Microparticles and platelets in PRP activated with SMLEF bipolar pulses had significantly lower annexin V-positivity than those following SMHEF activation. In contrast, the % P-selectin positivity and surface P-selectin expression (MFI) for platelets and microparticles in SMLEF bipolar pulse activated PRP was significantly higher than that in SMHEF-activated PRP, but not significantly different from that produced by thrombin activation. Higher levels of EGF were observed following either SMLEF bipolar pulses or SMHEF pulses of PRP than after bovine thrombin activation while VEGF, PDGF, and PF4 levels were similar with all three activating conditions. Cell proliferation was significantly increased by releasates of both SMLEF bipolar pulse and SMHEF pulse activated PRP compared to plasma alone.

Conclusions

PEF activation of PRP at bipolar low vs. monopolar high field strength results in differential platelet-derived microparticle production and activation of platelet surface procoagulant markers while inducing similar release of growth factors and similar capacity to induce cell proliferation. Stimulation of PRP with SMLEF bipolar pulses is gentler than SMHEF pulses, resulting in less platelet microparticle generation but with overall activation levels similar to that obtained with thrombin. These results suggest that PEF provides the means to alter, in a controlled fashion, PRP properties thereby enabling evaluation of their effects on wound healing and clinical outcomes.

Dielectric model for Chinese hamster ovary cells obtained by dielectrophoresis cytometry

We present a dielectric model and its parameters for Chinese hamster ovary (CHO) cells based on a double-shell structure which includes the cell membrane, cytoplasm, nuclear envelope, and nucleoplasm. Employing a dielectrophoresis (DEP) based technique and a microfluidic system, the DEP response of many single CHO cells is measured and the spectrum of the Clausius-Mossotti factor is obtained. The dielectric parameters of the model are then extracted by curve-fitting to the measured spectral data. Using this approach over the 0.6-10 MHz frequency range, we report the values for CHO cells' membrane permittivity, membrane thickness, cytoplasm conductivity, nuclear envelope permittivity, and nucleoplasm conductivity. The size of the cell and its nuclei are obtained using optical techniques.

The safety and efficacy of irreversible electroporation for the ablation of prostate cancer: a multicentre prospective human in vivo pilot study protocol

INTRODUCTION

Current surgical and ablative treatment options for prostate cancer have a relatively high incidence of side effects, which may diminish the quality of life. The side effects are a consequence of procedure-related damage of the blood vessels, bowel, urethra or neurovascular bundle. Ablation with irreversible electroporation (IRE) has shown to be effective in destroying tumour cells and harbours the advantage of sparing surrounding tissue and vital structures. The aim of the study is to evaluate the safety and efficacy and to acquire data on patient experience of minimally invasive, transperineally image-guided IRE for the focal ablation of prostate cancer.

METHODS AND ANALYSIS

In this multicentre pilot study, 16 patients with prostate cancer who are scheduled for a radical prostatectomy will undergo an IRE procedure, approximately 30 days prior to the radical prostatectomy. Data as adverse events, side effects, functional outcomes, pain and quality of life will be collected and patients will be controlled at 1 and 2 weeks post-IRE, 1 day preprostatectomy and postprostatectomy. Prior to the IRE procedure and the radical prostatectomy, all patients will undergo a multiparametric MRI and contrast-enhanced ultrasound of the prostate. The efficacy of ablation will be determined by whole mount histopathological examination, which will be correlated with the imaging of the ablation zone.

ETHICS AND DISSEMINATION

The protocol is approved by the ethics committee at the coordinating centre (Academic Medical Center (AMC) Amsterdam) and by the local Institutional Review Board at the participating centres. Data will be presented at international conferences and published in peer-reviewed journals.

CONCLUSIONS

This pilot study will determine the safety and efficacy of IRE in the prostate. It will show the radiological and histopathological effects of IRE ablations and it will provide data to construct an accurate treatment planning tool for IRE in prostate tissue.

TRIAL REGISTRATION NUMBER

Clinicaltrials.gov database: NCT01790451.

Cell electrofusion using nanosecond electric pulses

Electrofusion is an efficient method for fusing cells using short-duration high-voltage electric pulses. However, electrofusion yields are very low when fusion partner cells differ considerably in their size, since the extent of electroporation (consequently membrane fusogenic state) with conventionally used microsecond pulses depends proportionally on the cell radius. We here propose a new and innovative approach to fuse cells with shorter, nanosecond (ns) pulses. Using numerical calculations we demonstrate that ns pulses can induce selective electroporation of the contact areas between cells (i.e. the target areas), regardless of the cell size. We then confirm experimentally on B16-F1 and CHO cell lines that electrofusion of cells with either equal or different size by using ns pulses is indeed feasible. Based on our results we expect that ns pulses can improve fusion yields in electrofusion of cells with different size, such as myeloma cells and B lymphocytes in hybridoma technology.

Molecular dynamic simulation of transmembrane pore growth

A molecular dynamic approach was applied for simulation of dynamics of pore formation and growth in a phospholipid bilayer in the presence of an external electric field. Processing the simulation results permitted recovery of the kinetic coefficients used in the Einstein-Smoluchowski equation describing the dynamics of pore evolution. Two different models of the bilayer membrane were considered: membrane consisting of POPC and POPE lipids. The simulations permitted us to find nonempirical values of the pore energy parameters, which are compared with empirical values. It was found that the parameters are sensitive to membrane type.

Electroporation of intracellular liposomes using nanosecond electric pulses--a theoretical study

Nanosecond (ns) electric pulses of sufficient amplitude can provoke electroporation of intracellular organelles. This paper investigates whether such pulses could provide a method for controlled intracellular release of a content of small internalized artificial lipid vesicles (liposomes). To estimate the pulse parameters needed to selectively electroporate liposomes while keeping the plasma and nuclear membranes intact, we constructed a numerical model of a biological cell containing a nucleus and liposomes of different sizes (with radii from 50 to 500 nm), which were placed in various sites in the cytoplasm. Our results show that under physiological conditions selective electroporation is only possible for the largest liposomes and when using very short pulses (few ns). By increasing the liposome interior conductivity and/or decreasing the cytoplasmic conductivity, selective electroporation of even smaller liposomes could be achieved. The location of the liposomes inside the cell does not play a significant role, meaning that liposomes of similar size could all be electroporated simultaneously. Our results indicate the possibility of using ns pulse treatment for liposomal drug release.

Cytoplasmic electric fields and electroosmosis: possible solution for the paradoxes of the intracellular transport of biomolecules

The objective of the paper is to show that electroosmotic flow might play an important role in the intracellular transport of biomolecules. The paper presents two mathematical models describing the role of electroosmosis in the transport of the negatively charged messenger proteins to the negatively charged nucleus and in the recovery of the fluorescence after photobleaching. The parameters of the models were derived from the extensive review of the literature data. Computer simulations were performed within the COMSOL 4.2a software environment. The first model demonstrated that the presence of electroosmosis might intensify the flux of messenger proteins to the nucleus and allow the efficient transport of the negatively charged phosphorylated messenger proteins against the electrostatic repulsion of the negatively charged nucleus. The second model revealed that the presence of the electroosmotic flow made the time of fluorescence recovery dependent on the position of the bleaching spot relative to cellular membrane. The magnitude of the electroosmotic flow effect was shown to be quite substantial, i.e. increasing the flux of the messengers onto the nucleus up to 4-fold relative to pure diffusion and resulting in the up to 3-fold change in the values of fluorescence recovery time, and therefore the apparent diffusion coefficient determined from the fluorescence recovery after photobleaching experiments. Based on the results of the modeling and on the universal nature of the electroosmotic flow, the potential wider implications of electroosmotic flow in the intracellular and extracellular biological processes are discussed. Both models are available for download at ModelDB.

Microfluidic impedance spectroscopy as a tool for quantitative biology and biotechnology

A microfluidic device that is able to perform dielectric spectroscopy is developed. The device consists of a measurement chamber that is 250 μm thick and 750 μm in radius. Around 1000 cells fit inside the chamber assuming average quantities for cell radius and volume fraction. This number is about 1000 folds lower than the capacity of conventional fixtures. A T-cell leukemia cell line Jurkat is tested using the microfluidic device. Measurements of deionized water and salt solutions are utilized to determine parasitic effects and geometric capacitance of the device. Physical models, including Maxwell-Wagner mixture and double shell models, are used to derive quantities for sub-cellular units. Clausius-Mossotti factor of Jurkat cells is extracted from the impedance spectrum. Effects of cellular heterogeneity are discussed and parameterized. Jurkat cells are also tested with a time domain reflectometry system for verification of the microfluidic device. Results indicate good agreement of values obtained with both techniques. The device can be used as a unique cell diagnostic tool to yield information on sub-cellular units.

Novel passive element circuits for microdosimetry of nanosecond pulsed electric fields

Microdosimetric models for biological cells have assumed increasing significance in the development of nanosecond pulsed electric field technology for medical applications. In this paper, novel passive element circuits, able to take into account the dielectric dispersion of the cell, are provided. The circuital analyses are performed on a set of input pulses classified in accordance with the current literature. Accurate data in terms of transmembrane potential are obtained in both time and frequency domains for different cell models. In addition, a sensitivity study of the transfer function for the cell geometrical and dielectric parameters has been carried out. This analysis offers a new, simple, and efficient tool to characterize the nsPEFs' action at the cellular level.

Irreversible electroporation: a new challenge in "out of operating theater" anesthesia

BACKGROUND

Bioelectrics, an interesting new area of medicine, combines pulsed high-voltage engineering with cell biology and has many potential applications. Pulsed electric current can be used to produce irreversible electroporation (IRE) of cell membranes with resulting cell death. This process has been shown to ablate tumors in animal studies.

METHODS

A clinical trial of IRE as a tumor ablation therapy was performed at our institution. A pulsating direct current of 20 to 50 A and 500 to 3000 V was delivered into metastatic or primary tumors in the liver, kidney, or lung via needle electrodes inserted under computed tomography (CT) or ultrasound guidance. Patients required a relaxant general anesthetic. We describe some challenges presented to anesthesiologists. Guidelines for anesthesia were produced and modified as issues became apparent. The patients' charts were audited throughout.

RESULTS

We noted a number of issues. The electrical discharge produced generalized upper body muscular contractions requiring neuromuscular blockade. Two patients developed positional neuropraxia because of the extended arm position requested for CT scanning. After experimentation, we have developed a modified arm position. Some patients developed self-limiting ventricular tachycardias that are now minimized by using an electrocardiogram synchronizer. Three patients developed pneumothoraces as a result of the needle electrode insertion.

CONCLUSIONS

Relaxant general anesthesia is required for IRE of the liver, lung, and kidney. An electrocardiogram synchronizer should be used to minimize the risk of arrhythmias. Attention to the position of the arms is required to maximize CT scan quality but minimize brachial plexus strain. Simple postoperative analgesia is all that is required in most patients.

Effect of pulsed electromagnetic field on the proliferation and differentiation potential of human bone marrow mesenchymal stem cells

Pulsed electromagnetic fields (PEMFs) have been used clinically to slow down osteoporosis and accelerate the healing of bone fractures for many years. The aim of this study is to investigate the effect of PEMFs on the proliferation and differentiation potential of human bone marrow mesenchymal stem cells (BMMSC). PEMF stimulus was administered to BMMSCs for 8 h per day during culture period. The PEMF applied consisted of 4.5 ms bursts repeating at 15 Hz, and each burst contained 20 pulses. Results showed that about 59% and 40% more viable BMMSC cells were obtained in the PEMF-exposed cultures at 24 h after plating for the seeding density of 1000 and 3000 cells/cm2, respectively. Although, based on the kinetic analysis, the growth rates of BMMSC during the exponential growth phase were not significantly affected, 20-60% higher cell densities were achieved during the exponentially expanding stage. Many newly divided cells appeared from 12 to 16 h after the PEMF treatment as revealed by the cell cycle analysis. These results suggest that PEMF exposure could enhance the BMMSC cell proliferation during the exponential phase and it possibly resulted from the shortening of the lag phase. In addition, according to the cytochemical and immunofluorescence analysis performed, the PEMF-exposed BMMSC showed multi-lineage differentiation potential similar to the control group.