Model of pore formation in a single cell in a flow-through channel with micro-electrodes

Normal and fibrotic liver parenchyma respond differently to irreversible electroporation

BACKGROUND

The safety and efficacy of irreversible electroporation (IRE) in treating hepatic, biliary, and pancreatic malignancies are active areas of clinical investigation. In addition, recent studies have shown that IRE may enable regenerative surgery and in vivo tissue engineering. To use IRE effectively in these clinical applications, it is important to understand how different tissue microenvironments impact the response to IRE. In this study, we characterize the electrical and histological properties of non-fibrotic and fibrotic liver parenchyma before and after IRE treatment.

METHODS

Electrical resistivity and histology of fibrotic liver from C57BL/6 mice fed a 0.1% 3,5-diethylcarbonyl-1,4-dihydrocollidine (DDC) diet were compared to those of non-fibrotic liver from matched control mice before and after IRE treatment.

RESULTS

At baseline, the electrical resistivity of fibrotic liver was lower than that of non-fibrotic liver. Post-IRE, resistivity of non-fibrotic liver declined and then recovered back to baseline with time, correlating with hepatocyte repopulation of the ablated parenchyma without deposition of fibrotic scar. In contrast, resistivity of fibrotic liver remained depressed after IRE treatment, correlating with persistent inflammation.

CONCLUSION

Non-fibrotic and fibrotic liver respond to IRE differently. The underlying tissue microenvironment is an important modifying factor to consider when designing IRE protocols for tissue ablation.

Non-electrolytic microelectroporation

Micro and nano technologies are of increasing importance in microfluidics devices used for electroporation (electroporation - the permeabilization of the cell membrane with brief high electric field pulses). Electrochemical reactions of electrolysis occur whenever an electric current flows between an electrode and an ionic solution. It can have substantial detrimental effects, both on the cells and solutions during the electroporation. As electrolysis is a surface phenomenon, between electrodes and solution, the extent of electrolysis is increased in micro and nano electroporation over macro-electroporation, because the surface area of the electrodes in micro and nano electroporation is much larger. A possible way to eliminate the electrolytic effect is to develop non-electrolytic microelectroporation by coating the microelectroporation devices with a dielectric insulating layer. In this study, we examine the effect of a dielectric insulating layer on the performance of a singularity microelectroporation device that we have recently designed. Using numerical analysis, we study the effects of various design parameters including, input sinusoidal voltage amplitude and frequency, geometrical configuration and material electrical properties on the electroporation performance of the non-electrolytic microelectroporation device. In the simulation, we used properties of four real dielectric materials and four solutions of interest for microelectroporation. We characterized the effect of various design parameters of relevance to singularity based microelectroporation, on non-electrolytic microelectroporation. Interestingly, we found that the system behaves in some aspects as a filter and in many circumstances saturation of performance is reached. After saturation is reached, changes in parameters will not affect the performance of the device.

Simultaneous electroporation and dielectrophoresis in non-electrolytic micro/nano-electroporation

It was recently shown that electrolysis may play a substantial detrimental role in microfluidic electroporation. To overcome this problem, we have developed a non-electrolytic micro/nano electroporation (NEME) electrode surface, in which the metal electrodes are coated with a dielectric. A COMSOL based numerical scheme was used to simultaneously calculate the excitation frequency and dielectric material properties dependent electric field delivered across the dielectric, fluid flow, electroporation field and Clausius-Mossotti factor for yeast and E. coli cells flowing in a channel flow across a NEME surface. A two-layer model for yeast and a three-layer model for E. coli was used. The numerical analysis shows that in NEME electroporation, the electric fields could induce electroporation and dielectrophoresis simultaneously. The simultaneous occurrence of electroporation and dielectrophoresis gives rise to several interesting phenomena. For example, we found that a certain frequency exists for which an intact yeast cell is drawn to the NEME electrode, and once electroporated, the yeast cell is pushed back in the bulk fluid. The results suggest that developing electroporation technologies that combine, simultaneously, electroporation and dielectrophoresis could lead to new applications. Obviously, this is an early stage numerical study and much more theoretical and experimental research is needed.

A simplified application (APP) for the parametric design of screw-plate fixation of bone fractures

Screw and plate fixation is commonly used to treat bone fractures. A prototype application (APP) for presurgical simulation was developed and validated by comparing it with current analytical approach and other models. In this APP, alternative plate designs and materials to limit the effects of stress shielding could be tested. In addition, the number and position of screws and the gap between bone and plate that achieved acceptable stability were predicted. The fixation stability providing a situation of interfragmentary strain between 2% and 10% is necessary for callus formation. However, improving the fixation stability leads to a stress shielding effect. The simultaneous alleviation of stress shielding and maintenance of stability are important in fracture healing. In this study, the feasibility of creating a specialized APP to evaluate different screw-plate configurations for diaphyseal femoral fractures was investigated. The ultimate goal is to extend this technique to computer-assisted preoperative planning for orthopedic surgery.

Theoretical Study of Molecular Transport Through a Permeabilized Cell Membrane in a Microchannel

A two-dimensional model is developed to study the molecular transport into an immersed cell in a microchannel and to investigate the effects of finite boundary (a cell is suspended in a microchannel), amplitude of electric pulse, and geometrical parameter (microchannel height and size of electrodes) on cell uptake. Embedded electrodes on the walls of the microchannel generate the required electric pulse to permeabilize the cell membrane, pass the ions through the membrane, and transport them into the cell. The shape of electric pulses is square with the time span of 6 ms; their intensities are in the range of 2.2, 2.4, 2.6, 3 V. Numerical simulations have been performed to comprehensively investigate the molecular uptake into the cell. The obtained results of the current study demonstrate that calcium ions enter the cell from the anodic side (the side near positive electrode); after a while, the cell faces depletion of the calcium ions on a positive electrode-facing side within the microchannel; the duration of depletion depends on the amplitude of electric pulse and geometry that lasts from microseconds to milliseconds. By keeping geometrical parameters and time span constant, increment of a pulse intensity enhances molecular uptake and rate of propagation inside the cell. If a ratio of electrode size to cell diameter is larger than 1, the transported amount of Ca ²⁺ into the cell, as well as the rate of propagation, will be significantly increased. By increasing the height of the microchannel, the rate of uptake is decreased. In an infinite domain, the peak concentration becomes constant after reaching the maximum value; this value depends on the intra-extracellular conductivity and diffusion coefficient of interior and exterior domains of the cell. In comparison, the maximum concentration is changed by geometrical parameters in the microchannel. After reaching the maximum value, the peak concentration reduces due to the depletion of Ca ²⁺ ions within the microchannel. Electrophoretic velocity has a significant effect on the cell uptake.

Micro-/nanoscale electroporation

Electroporation has been one of the most popular non-viral technologies for cell transfection. However, conventional bulk electroporation (BEP) shows significant limitations in efficiency, cell viability and transfection uniformity. Recent advances in microscale-electroporation (MEP) resulted in improved cell viability. Further miniaturization of the electroporation system (i.e., nanoscale) has brought up many unique advantages, including negligible cell damage and dosage control capabilities with single-cell resolution, which has enabled more translational applications. In this review, we give an insight into the fundamental and technical aspects of micro- and nanoscale/nanochannel electroporation (NEP) and go over several examples of MEP/NEP-based cutting-edge research, including gene editing, adoptive immunotherapy, and cellular reprogramming. The challenges and opportunities of advanced electroporation technologies are also discussed.

A review of basic to clinical studies of irreversible electroporation therapy

The use of irreversible electroporation (IRE) for cancer treatment has increased sharply over the past decade. As a nonthermal therapy, IRE offers several potential benefits over other focal therapies, which include 1) short treatment delivery time, 2) reduced collateral thermal injury, and 3) the ability to treat tumors adjacent to major blood vessels. These advantages have stimulated widespread interest in basic through clinical studies of IRE. For instance, many in vitro and in vivo studies now identify treatment planning protocols (IRE threshold, pulse parameters, etc.), electrode delivery (electrode design, placement, intraoperative imaging methods, etc.), injury evaluation (methods and timing), and treatment efficacy in different cancer models. Therefore, this study reviews the in vitro, translational, and clinical studies of IRE cancer therapy based on major experimental studies particularly within the past decade. Further, this study provides organized data and facts to assist further research, optimization, and clinical applications of IRE.

Basic features of a cell electroporation model: illustrative behavior for two very different pulses

Science increasingly involves complex modeling. Here we describe a model for cell electroporation in which membrane properties are dynamically modified by poration. Spatial scales range from cell membrane thickness (5 nm) to a typical mammalian cell radius (10 μm), and can be used with idealized and experimental pulse waveforms. The model consists of traditional passive components and additional active components representing nonequilibrium processes. Model responses include measurable quantities: transmembrane voltage, membrane electrical conductance, and solute transport rates and amounts for the representative "long" and "short" pulses. The long pulse--1.5 kV/cm, 100 μs--evolves two pore subpopulations with a valley at ~5 nm, which separates the subpopulations that have peaks at ~1.5 and ~12 nm radius. Such pulses are widely used in biological research, biotechnology, and medicine, including cancer therapy by drug delivery and nonthermal physical tumor ablation by causing necrosis. The short pulse--40 kV/cm, 10 ns--creates 80-fold more pores, all small (<3 nm; ~1 nm peak). These nanosecond pulses ablate tumors by apoptosis. We demonstrate the model's responses by illustrative electrical and poration behavior, and transport of calcein and propidium. We then identify extensions for expanding modeling capability. Structure-function results from MD can allow extrapolations that bring response specificity to cell membranes based on their lipid composition. After a pulse, changes in pore energy landscape can be included over seconds to minutes, by mechanisms such as cell swelling and pulse-induced chemical reactions that slowly alter pore behavior.