Irreversible Electroporation of the Liver Increases the Transplant Engraftment of Hepatocytes.

INTRODUCTION: Irreversible electroporation (IRE) is a tissue ablation technology that kills cells with short electrical pulses that do not induce thermal damage, thereby preserving the extracellular matrix. Preclinical research suggests that IRE may be developed as a tool for regenerative surgery by clearing existing host cells within a solid organ and creating a supportive niche for new cell engraftment. We hypothesized that hepatocytes transplanted by injection into the portal circulation would preferentially engraft within liver parenchyma pretreated with IRE. METHODS: Transgene-positive ß-galactosidase-expressing hepatocytes were isolated from B6.129S7-Gt(ROSA)26Sor/J (ROSA26) mice and transplanted by intrasplenic injection into wild-type littermates that received liver IRE pretreatment or control sham treatment. Engraftment of donor hepatocytes in recipient livers was determined by X-gal staining. RESULTS: Significantly higher numbers of X-gal+ donor hepatocytes engrafted in the livers of IRE-treated mice as compared to sham-treated mice. X-gal+ hepatocytes persisted in IRE-treated recipients for at least 11 d post-transplant and formed clusters. Immunostaining demonstrated the presence of HNF4A/Ki67/ß-galactosidase triple-positive cells within IRE-ablation zones, indicating that transplanted hepatocytes preferentially engrafted in IRE-treated liver parenchyma and proliferated. CONCLUSIONS: IRE pretreatment of the liver increased engraftment of transplanted hepatocytes within the IRE-ablation zone. IRE treatment of the host liver may be developed clinically as a strategy to increase engraftment efficiency of primary hepatocytes and/or hepatocytes derived from stem cells in cell transplant therapies.

Direct comparison of isobaric and isochoric vitrification of two aqueous solutions with photon counting X-ray computed tomography.

Vitrification is a promising approach for ice-free cryopreservation of biological material, but progress is hindered by the limited set of experimental tools for studying processes in the interior of the vitrified matter. Isochoric cryopreservation chambers are often metallic, and their opacity prevents direct visual observation. In this study, we introduce photon counting X-ray computed tomography (CT) to compare the effects of rigid isochoric and unconfined isobaric conditions on vitrification and ice formation during cooling of two aqueous solutions: 50 wt% DMSO and a coral vitrification solution, CVS1. Previous studies have only compared vitrification in isochoric systems with isobaric systems that have an exposed air-liquid interface. We use a movable piston to replicate the surface and thermal boundary conditions of the isochoric system yet maintain isobaric conditions. When controlling for the boundary conditions we find that similar ice and vapor volume fractions form during cooling in isochoric and isobaric conditions. Interestingly, we observe distinct ice and vapor cavity morphology in the isochoric systems, possibly due to vapor outgassing or cavitation as rapid cooling causes the pressure to drop in the confined systems. These observations highlight the array of thermal-fluid processes that occur during vitrification in confined aqueous systems and motivate the further application of imaging techniques such as photon counting X-ray CT in fundamental studies of vitrification.

Experimental observation of cavity-free ice-free isochoric vitrification via combined pressure measurements and photon counting x-ray computed tomography.

Isochoric (constant-volume or volumetrically confined) vitrification has shown potential as an alternative cryopreservation-by-vitrification technique, but the complex processes at play within the chamber are yet poorly characterized, and recent investigations have prompted significant debate around whether a truly isochoric vitrification process (in which the liquid remains completely confined by solid boundaries) is indeed feasible. Based on a recent thermomechanical simulation of a high-concentration Me2SO solution, Solanki and Rabin (Cryobiology, 2023, 111, 9-15.) argue that isochoric vitrification is not feasible, because differential thermal contraction of the solution and container will necessarily drive generation of a cavity, corrupting the rigid confinement of the liquid. Here, we provide direct experimental evidence to the contrary, demonstrating cavity-free isochoric vitrification of a ∼3.5 M vitrification solution by combined isochoric pressure measurement (IPM) and photon-counting x-ray computed tomography (PC-CT). We hypothesize that the absence of a cavity is due to the minimal thermal contraction of the solution, which we support with additional volumetric analysis of the PC-CT reconstructions. In total, this study provides experimental evidence both demonstrating the feasibility of isochoric vitrification and highlighting the potential of designing vitrification solutions that exhibit minimal thermal contraction.

Ice modulatory effect of the polysaccharide FucoPol in directional freezing.

Directional freezing harnesses crystal growth development to create aligned solid structures or etchable patterns, useful for directed ice growth in cryobiology and cryoprinting for tissue engineering. We have delved into the ice-modulating properties of FucoPol, a fucose-rich, bio-based polysaccharide. Previous research on FucoPol revealed its non-colligative hysteresis in kinetic freezing point, reduced crystal dimensions and cryoprotective effect. Here, FucoPol reshaped developing sharp, anisotropic obloid ice dendrites into linearly-aligned, thin, isotropic spicules or tubules (cooling rate-dependent morphology). The effect was enhanced by increased concentration and decreased cooling rate, but major reshaping was observed with 5 µM and below. These structures boasted remarkable enhancements: uniform alignment (3-fold), tip symmetry (5.9-fold) and reduced thickness (5.3-fold). The ice-modulating capability of FucoPol resembles the Gibbs-Thomson effect of antifreeze proteins, in particular the ice reshaping profiles of type I antifreeze proteins and rattlesnake venom lectins, evidenced by a 52.6 ± 2.2° contact angle (θ) and spicular structure generation. The high viscosity of FucoPol solutions, notably higher than that of sucrose, plays a crucial role. This viscosity dynamically intensifies during directional freezing, leading to a diffusion-limited impediment that influences dendritic formation. Essentially, the ice-modulating prowess of FucoPol not only reinforces its established cryoprotective qualities but also hints at its potential utility in applications that harness advantageous ice growth for intentional structuring. For instance, its potential in cryobioprinting is noteworthy, offering an economical, biodegradable resource, of easy removal, sidestepping the need for toxic reagents. Moreover, FucoPol fine-tunes resulting ice structures, enabling the ice-etching of biologically relevant patterns within biocompatible matrices for advanced tissue engineering endeavors.

An extreme value statistics model of heterogeneous ice nucleation for quantifying the stability of supercooled aqueous systems.

The propensity of water to remain in a metastable liquid state at temperatures below its equilibrium melting point holds significant potential for cryopreserving biological material such as tissues and organs. The benefits conferred are a direct result of progressively reducing metabolic expenditure due to colder temperatures while simultaneously avoiding the irreversible damage caused by the crystallization of ice. Unfortunately, the freezing of water in bulk systems of clinical relevance is dominated by random heterogeneous nucleation initiated by uncharacterized trace impurities, and the marked unpredictability of this behavior has prevented the implementation of supercooling outside of controlled laboratory settings and in volumes larger than a few milliliters. Here, we develop a statistical model that jointly captures both the inherent stochastic nature of nucleation using conventional Poisson statistics as well as the random variability of heterogeneous nucleation catalysis through bivariate extreme value statistics. Individually, these two classes of models cannot account for both the time-dependent nature of nucleation and the sample-to-sample variability associated with heterogeneous catalysis, and traditional extreme value models have only considered variations of the characteristic nucleation temperature. We conduct a series of constant cooling rate and isothermal nucleation experiments with physiological saline solutions and leverage the statistical model to evaluate the natural variability of kinetic and thermodynamic nucleation parameters. By quantifying freezing probability as a function of temperature, supercooled duration, and system volume while accounting for nucleation site variability, this study also provides a basis for the rational design of stable supercooled biopreservation protocols.

Isochoric supercooling cryomicroscopy.

We introduce an isochoric (constant-volume) supercooling cryomicroscope (ISCM), enabling the ice-free study of biological systems and biochemical reactions at subzero temperatures at atmospheric pressure absent ice. This technology draws from thermodynamic findings on the behavior of water in isochoric systems at subfreezing temperatures. A description of the design of the ISCM and a demonstration of the stability of the supercooled solution in the ISCM is followed by an illustration of the possible use of the ISCM in the preservation of biological matter research. A comparison was made between the survival of HeLa cells in the University of Wisconsin (UW) solution in the ISCM at +4 °C under conventional atmospheric conditions and at -5 °C under isochoric supercooled conditions. Continuous real-time monitoring at cryopreservation temperature via fluorescence microscopy showed that after three days of isochoric supercooling storage, the percentage of compromised cells remained similar to fresh controls, while storage at +4 °C yielded approximately three times the mortality rate of cells preserved at -5 °C.

Methods to stabilize aqueous supercooling identified by use of an isochoric nucleation detection (INDe) device.

Stable aqueous supercooling has shown significant potential as a technique for human tissue preservation, food cold storage, conservation biology, and beyond, but its stochastic nature has made its translation outside the laboratory difficult. In this work, we present an isochoric nucleation detection (INDe) platform for automated, high-throughput characterization of aqueous supercooling at >1 mL volumes, which enables statistically-powerful determination of the temperatures and time periods for which supercooling in a given aqueous system will remain stable. We employ the INDe to investigate the effects of thermodynamic, surface, and chemical parameters on aqueous supercooling, and demonstrate that various simple system modifications can significantly enhance supercooling stability, including isochoric (constant-volume) confinement, hydrophobic container walls, and the addition of even mild concentrations of solute. Finally, in order to enable informed design of stable supercooled biopreservation protocols, we apply a statistical model to estimate stable supercooling durations as a function of temperature and solution chemistry, producing proof-of-concept supercooling stability maps for four common cryoprotective solutes.

Relating Metabolism Suppression and Nucleation Probability During Supercooled Biopreservation.

Aqueous supercooling provides a method by which to preserve biological matter at subfreezing temperatures without the deleterious effects of ice formation. The extended longevity of the preserved biologic is a direct result of a reduction in the rate of metabolism with decreasing temperature. However, because the nucleation of ice from a supercooled solution is a stochastic process, supercooled preservation carries the risk of random ice nucleation. Theoretical supercooled biopreservation research to date has largely treated these biological and thermophysical phenomena separately. Here, we apply a statistical model of stochastic ice nucleation to demonstrate how the possible reduction in metabolic rate is inherently related to supercooling stability (i.e., the likelihood of ice nucleation). We develop a quantitative approach by which to weigh supercooling stability versus potential metabolic reduction, and further show how the stability-metabolism relationship varies with system size for two assumed modes of nucleation. Ultimately, this study presents a generalizable framework for the informed design of supercooled biopreservation protocols that considers both phase transformation kinetics and biochemical or biophysical kinetics.

Glucose and glycerol temperature-pressure correlations for the design of cryopreservation protocols in an isochoric system at subfreezing temperature.

There is growing interest in the use of isochoric (constant volume) freezing for cryopreservation of biological matter. The goal of this study is to generate fundamental experimental data on the pressure temperature relation during the freezing of an isochoric system of aqueous solutions of two compounds, glucose and glycerol. Glucose and glycerol are commonly used as cryoprotectants in conventional isobaric (constant pressure) cryopreservation protocols. Earlier studies have shown that the increase in pressure during isochoric freezing is detrimental to biological matter and limits the range of temperatures in which isochoric freezing can be used for preservation to temperatures corresponding to pressures below 40 MPa. In physiological saline solution this pressure corresponds to a temperature of - 4 °C. Our new experimental data shows that the addition of 2 M glycerol to the saline solution lowers the temperature at which the isochoric freezing pressure is 40 MPa to -11 °C, 3 M glycerol to - 16.5 °C, and 4 M glycerol to - 24.5 °C, thereby substantially expending the range of temperatures in which cryopreservation by isochoric freezing can be practiced.

Mass transfer into biological matter using isochoric freezing.

This paper is a theoretical study of a protocol for transport of high concentrations of cryoprotectants into biological matter, using isochoric freezing. Unlike isobaric freezing, where the entire system freezes at temperatures lower than the freezing temperature, in isochoric freezing a substantial portion of the system remains unfrozen at temperatures below freezing. In isochoric freezing cryopreservation, the system is designed in such a way that the biological matter remains unfrozen and surrounded by an unfrozen solution. The protocol in this study involves the freezing of an isochoric systems along the "liquidus line" at which water and ice are in thermodynamic equilibrium. Rejection of solutes by ice increases the concentration of the solutes in the unfrozen solution surrounding the unfrozen biological matter, leading, thereby, to transport of increasingly higher concentrations of cryoprotectants into the biological matter, as the temperature of the system is lowered and the toxicity of the cryoprotectants is reduced.

High-Voltage Electrical Pulses in Oncology: Irreversible Electroporation, Electrochemotherapy, Gene Electrotransfer, Electrofusion, and Electroimmunotherapy.

This review summarizes the use of high-voltage electrical pulses (HVEPs) in clinical oncology to treat solid tumors with irreversible electroporation (IRE) and electrochemotherapy (ECT). HVEPs increase the membrane permeability of cells, a phenomenon known as electroporation. Unlike alternative ablative therapies, electroporation does not affect the structural integrity of surrounding tissue, thereby enabling tumors in the vicinity of vital structures to be treated. IRE uses HVEPs to cause cell death by inducing membrane disruption, and it is primarily used as a radical ablative therapy in the treatment of soft-tissue tumors in the liver, kidney, prostate, and pancreas. ECT uses HVEPs to transiently increase membrane permeability, enhancing cellular cytotoxic drug uptake in tumors. IRE and ECT show immunogenic effects that could be augmented when combined with immunomodulatory drugs, a combination therapy the authors term electroimmunotherapy. Additional electroporation-based technologies that may reach clinical importance, such as gene electrotransfer, electrofusion, and electroimmunotherapy, are concisely reviewed. HVEPs represent a substantial advancement in cancer research, and continued improvement and implementation of these presented technologies will require close collaboration between engineers, interventional radiologists, medical oncologists, and immuno-oncologists.

A Theoretical Analysis of the Effects of Tumor-Treating Electric Fields on Single Cells.

Tumor-treating fields (TTFields) are low-intensity and intermediate-frequency alternating electric fields that have been found to inhibit tumor cell growth. While effective, the mechanism by which TTFields affect cell growth is not yet clearly understood. Although numerous mathematical studies on the effects of electromagnetic fields on single cells exist, the effect of TTFields on single cells have been analyzed less frequently. The goal of this study is to explore through a mathematical analysis the effects of TTFields on single cells, with particular emphasis on the thermal effect. We examine herein two single-cell models, a simplified spheroidal model and a simulation of a U-87 MG glioblastoma cell model obtained from microscopic images. A finite element method is used to analyze the electric field distribution, electromagnetic loss, and thermal field distribution. The results further prove that the electric field in the cytoplasm is too weak and its thermal damage can be excluded as a mechanism for cell death in TTFields. Bioelectromagnetics. 2020;41:438-446. © 2020 Bioelectromagnetics Society.

Multifrequency Analysis of Single Inductive Coil Measurements Across a Gel Phantom Simulation of Internal Bleeding in the Brain.

The present study is part of an ongoing effort to develop a simple diagnostic technology for detecting internal bleeding in the brain, which can be used in lieu or in support of medical imaging and thereby reduce the cost of diagnostics in general, and in particular, would make diagnostics accessible to economically disadvantaged populations. The study deals with a single coil inductive device to be used for detecting cerebral hemorrhage. It presents a first-order experimental study that examines the predictions of our recently published theoretical study. The experimental model employs a homogeneous cylindrical phantom in which internal head bleeding was simulated by way of a fluid inclusion. We measured the changes in amplitude and phase across the coil with a network vector analyzer as a function of frequency (100-1,000 MHz), volume of blood simulating fluid, and the site of the fluid injection. We have developed a new mathematical model to statistically analyze the complex data produced in this experiment. We determined that the resolution for the fluid volume increase following fluid injection is strongly dependent on frequency as well as the location of liquid accumulation. The experimental data obtained in this study supports the predictions of our previous theoretical study, and the statistical analysis shows that the simple single coil device is sensitive enough to detect changes due to fluid volume alteration of two milliliters. Bioelectromagnetics. 2020;41:21-33 © 2019 Bioelectromagnetics Society.

A theoretical study on real time monitoring of single cell mitosis with micro electrical impedance tomography.

Real time monitoring of cell division, mitosis, at the single cell level, has value for many biomedical applications; such as developing optimal cancer treatments that target the cell division process. The goal of this theoretical study is to explore the feasibility of using Micro Electrical Impedance Tomography (MEIT) for real time monitoring of mitosis in a single cell, through imaging. MEIT employs a micro (single cell) scale electrode cage with electrodes placed around the cell. The electrodes deliver subsensory current and the consequential voltages on the electrodes are measured. An inverse image reconstruction algorithm uses the electric data from the electrodes to generate a map of electrical conductivity distribution in the chamber, which is the image. EIT is a well-known medical imaging technology that is simple to use but lacks good resolution. Therefore, it is not a-priori obvious that EIT has sufficient resolution to monitor single cell mitosis. To accomplish the goal of this study we have developed a mathematical model of MEIT of single cell mitosis, in which an in silico experiment provided the data for the MEIT image reconstruction. This theoretical study shows that MEIT can detect the outlines of the dividing cell during the various stages of mitosis (metaphase, anaphase and telophase) and, therefore, has potential as a technology for real time monitoring of single cell mitosis.

Isochoric conditions enable high subfreezing temperature pancreatic islet preservation without osmotic cryoprotective agents.

While biological systems are typically studied under isobaric (constant pressure) conditions, recent reports on the bio-thermodynamics of isochoric (constant volume) systems point to their potential for subfreezing-temperature preservation of biological matter. This preliminary study, in which we report that pancreatic islets can survive multi-day preservation at high subfreezing temperatures in an isochoric chamber without osmotic cryoprotective agents (CPA), highlights the potential of isochoric cryopreservation in an application of clinical value.

Thermodynamic Theory and Experimental Validation of a Multiphase Isochoric Freezing Process.

Freezing of the aqueous solutions that comprise biological materials, such as isotonic physiological saline, results in the formation of ice crystals and the generation of a hypertonic solution, both of which prove deleterious to biological matter. The field of modern cryopreservation, or preservation of biological matter at subfreezing temperatures, emerged from the 1948 discovery that certain chemical additives such as glycerol, known as cryoprotectants, can protect cells from freeze-related damage by depressing the freezing point of water in solution. This gave rise to a slew of important medical applications, from the preservation of sperm and blood cells to the recent preservation of an entire liver, and current cryopreservation protocols thus rely heavily on the use of additive cryoprotectants. However, high concentrations of cryoprotectants themselves prove toxic to cells, and thus there is an ongoing effort to minimize cryoprotectant usage while maintaining protection from ice-related damage. Herein, we conceive from first principles a new, purely thermodynamic method to eliminate ice formation and hypertonicity during the freezing of a physiological solution: multiphase isochoric freezing. We develop a comprehensive thermodynamic model to predict the equilibrium behaviors of multiphase isochoric systems of arbitrary composition and validate these concepts experimentally in a simple device with no moving parts, providing a baseline from which to design tailored cryopreservation protocols using the multiphase isochoric technique.

The Effect of Textiles Impregnated With Particles With High Emissivity in the Far Infrared, on the Temperature of the Cold Hand.

In engineering and medicine, there is a growing interest in using textiles made of composites with enhanced thermal properties. One such type of textile is fabric impregnated with ceramics and mineral particles. This material has high emissivity in the infrared range and may have therapeutic benefits for treatments of diseases, like Raynaud's syndrome. While there is significant clinical and commercial interest, there is an evident lack of fundamental studies on the heat transfer aspects of these fabrics. The goal of this technical brief is to present results from a fundamental study examining the thermal effects of fabric with ceramics and minerals (produced by Nanobionic, Inc., Athens, Greece) on the temperatures of the hands. With a confidence level of 90%, the results show that the textile with ceramics and minerals has an enhanced thermal effect on warming a cold hand in comparison to a placebo fabric without ceramics or minerals. Much more research is needed to increase the level of confidence and develop a fundamental understanding of the mechanism.

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.

Molecular and histological study on the effects of non-thermal irreversible electroporation on the liver.

Non-thermal irreversible electroporation (NTIRE) is a biophysical phenomenon in which certain electric fields delivered across the cell membrane in tissue, cause cell death, without affecting the extracellular matrix. "Minimally invasive regenerative surgery" is a new medical modality for treatment of end-stage organ or tissue failure in which exogenous cells are implanted in a decellularized niche in tissue, formed by the delivery of NTIRE electric fields across a targeted volume of tissue. We anticipate that the success of the procedure will depend on the time of implantation relative to the application of NTIRE. This study was performed to elucidate the histological and molecular events that occur within 24 h after NTIRE, in the context of optimal criteria for the time of implantation. To this end, we examined the histology of NTIRE treated rat liver with H&E, Masson trichrome and TUNEL staining. Western blot was used to examine pro and cleaved caspase-3 (marker for apoptosis), pro and cleaved caspase-1 and gasdermin D (markers for pyroptosis), and RIP3 and MLKL (markers for necroptosis). The key findings are that, complete hepatocytes disintegration within an intact extracellular matrix is seen at 6 h and, new hepatocytes are seen in the treated region at 24 h, after NTIRE. There is no evidence of apoptotic cell death from NTIRE, contrary to commonly made claims in the NTIRE literature. However, molecular pathways of pyroptosis and necroptosis, programed necrosis associated with inflammation, are activated at 6 h after NTIRE and are not evident at 24 h after NTIRE. These are fundamental new findings of basic value to the field of NTIRE in all its applications. Taken together the results suggest the hypothesis that an optimal time for implantation is about 24 h after NTIRE. Future studies in which exogenous cells are implanted at different times after NTIRE are required to examine this hypothesis.

Preservation of rat hearts in subfreezing temperature isochoric conditions to - 8 °C and 78 MPa.

Isochoric (constant volume) preservation at subfreezing temperatures is being investigated as a novel method for preserving cells and organs. This study is a first initial effort to evaluate the efficacy of this method for heart preservation, and to provide a preliminary outline of appropriate preservation parameters. To establish a baseline for further studies, rat hearts were preserved in a University of Wisconsin (UW) intracellular solution for one hour under isochoric conditions at: 0 °C (atmospheric pressure - 0.1 MPa), - 4 °C (41 MPa), - 6 °C (60 MPa) and - 8 °C (78 MPa). The viability of the heart was evaluated using Langendorff perfusion and histological examination. The physiological performance of hearts preserved at - 4 °C (41 MPa) was comparable to that of a heart preserved on ice at atmospheric pressure, with no statistically significant difference in histological injury score. However, hearts preserved at -4 °C displayed substantially reduced interstitial edema compared to hearts preserved by conventional hypothermic preservation in UW on ice at atmospheric pressure, suggesting significant protection from increased vascular permeability following preservation. Hearts preserved at - 6 °C (60 MPa) suffered injury from cellular swelling and extensive edema, and at - 8 °C (78 MPa) hearts experienced significant morphological disruption. To the best of our knowledge, this is the first publication showing that a mammalian organ can survive low subfreezing temperatures without the use of a cryoprotective additive. Lowering the preservation temperature reduces metabolism and improves preservation quality, and these results suggest that improvements in preservation are possible at subzero temperatures with low to moderate pressures observed at -4 °C. Notably, tissue damage was observed at lower temperatures (-6 °C or below) accompanying further elevation of pressure associated with isochoric preservation that may prove detrimental. Therefore, subfreezing temperature isochoric preservation protocols should optimize, a combination of temperature and pressure that will minimize the negative effects of elevated pressure while retaining the beneficial effect of lower temperatures and reduced metabolism.