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The blood–brain barrier (BBB) represents the tightest endothelial barrier within the cardiovascular system characterized by very low ionic permeability. Our aim was to describe the setups, electrodes, and instruments to measure electrical resistance across brain microvessels and culture models of the BBB, as well as critically assess the influence of often neglected physical and technical parameters such as temperature, viscosity, current density generated by different electrode types, surface size, circumference, and porosity of the culture insert membrane. We demonstrate that these physical and technical parameters greatly influence the measurement of transendothelial electrical resistance/resistivity (TEER) across BBB culture models resulting in severalfold differences in TEER values of the same biological model, especially in the low-TEER range. We show that elevated culture medium viscosity significantly increases, while higher membrane porosity decreases TEER values. TEER data measured by chopstick electrodes can be threefold higher than values measured by chamber electrodes due to different electrode size and geometry, resulting in current distribution inhomogeneity. An additional shunt resistance at the circumference of culture inserts results in lower TEER values. A detailed description of setups and technical parameters is crucial for the correct interpretation and comparison of TEER values of BBB models.

Background The lack of predictive models that mimic the blood–brain barrier (BBB) hinders the development of effective drugs for neurodegenerative diseases. Animal models behave differently from humans, are expensive and have ethical constraints. Organ-on-a-chip (OoC) platforms offer several advantages to resembling physiological and pathological conditions in a versatile, reproducible, and animal-free manner. In addition, OoC give us the possibility to incorporate sensors to determine cell culture features such as trans-endothelial electrical resistance (TEER). Here, we developed a BBB-on-a-chip (BBB-oC) platform with a TEER measurement system in close distance to the barrier used for the first time for the evaluation of the permeability performance of targeted gold nanorods for theranostics of Alzheimer’s disease. GNR-PEG-Ang2/D1 is a therapeutic nanosystem previously developed by us consisting of gold nanorods (GNR) functionalized with polyethylene glycol (PEG), angiopep-2 peptide (Ang2) to overcome the BBB and the D1 peptide as beta amyloid fibrillation inhibitor, finally obtaining GNR-PEG-Ang2/D1 which showed to be useful for disaggregation of the amyloid in in vitro and in vivo models. In this work, we evaluated its cytotoxicity, permeability, and some indications of its impact on the brain endothelium by employing an animal-free device based on neurovascular human cells. Results In this work, we fabricated a BBB-oC with human astrocytes, pericytes and endothelial cells and a TEER measuring system (TEER-BBB-oC) integrated at a micrometric distance of the endothelial barrier. The characterization displayed a neurovascular network and the expression of tight junctions in the endothelium. We produced GNR-PEG-Ang2/D1 and determined its non-cytotoxic range (0.05–0.4 nM) for plated cells included in the BBB-oC and confirmed its harmless effect at the highest concentration (0.4 nM) in the microfluidic device. The permeability assays revealed that GNR-PEG-Ang2/D1 cross the BBB and this entry is facilitated by Ang2 peptide. Parallel to the permeability analysis of GNR-PEG-Ang2/D1, an interesting behavior of the TJs expression was observed after its administration probably related to the ligands on the nanoparticle surface. Conclusions BBB-oC with a novel TEER integrated setup which allow a correct read-out and cell imaging monitoring was proven as a functional and throughput platform to evaluate the brain permeability performance of nanotherapeutics in a physiological environment with human cells, putting forward a viable alternative to animal experimentation.

Fire resistance tests rely on the use of standardized furnaces to apply specific thermal boundary conditions to assess the performance of construction materials and systems in fire conditions. However, these tests are very expensive and encounter challenges related to repeatability and uncertainties in establishing thermal boundary conditions. Moreover, their incapacitance to tailor experiments hinders advancements in understanding structural behaviour during fire exposure. In this work, a novel type of radiant panel, that operates on electricity, is introduced: the High-Intensity Fast-Response Electric radiant Panel (HIFREP). This innovation offers enhanced sustainability performance while ensuring more precise control over thermal boundary conditions. By eliminating the need for gas combustion, the panel can be used in a traditional structural testing lab to investigate non-combustible materials (e.g. concrete), without requiring extraction hoods and other provisions. The presented electric radiant panel system represents a significant step forward from fire resistance furnace testing.

Using a laser-heated diamond-anvil cell to measure the electrical resistivity of iron under the high temperature and pressure conditions of the Earth’s core yields a value that means Earth’s core has high thermal conductivity, suggesting that its inner core is less than 0.7 billion years old, much younger than thought. Earth's inner core, ancient or modern The thermal conductivity of iron and its alloys at high pressure and temperature is a critical factor in the evolution and dynamics of Earth-like planets. Recently, increasing uncertainty in these values has produced dramatically variable predictions for Earth's history that challenge traditional geophysical theories. Two groups reporting in this issue of Nature use laser-heated diamond-anvil cells to study the properties of iron at the extreme temperatures and pressures relevant to Earth's core, but using different methodologies, and they arrive at contrasting results. Kenji Ohta and co-authors measured the electrical resistivity of iron at up to 4,500 kelvin and obtained an estimate that is even lower than the low values predicted from recent ab initio studies. They conclude that this suggests a high thermal conductivity for Earth's core, which would imply rapid core cooling by conduction and a relatively young inner core. Zuzana Konôpková and co-authors measured heat pulses propagating through solid iron after heating with a laser pulse at pressures and temperatures relevant to the cores of planets ranging in size from Mercury to Earth. Their measurements place the thermal conductivity of Earth's core near the low end of previous estimates, implying that thermal convection in Earth's core could have driven the geodynamo for billions of years, and allowing for an ancient inner core. In a linked News & Views, David Dobson discusses the interpretation of these two tours de force of experimental geophysics. Earth continuously generates a dipole magnetic field in its convecting liquid outer core by a self-sustained dynamo action. Metallic iron is a dominant component of the outer core, so its electrical and thermal conductivity controls the dynamics and thermal evolution of Earth’s core 1 . However, in spite of extensive research, the transport properties of iron under core conditions are still controversial 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Since free electrons are a primary carrier of both electric current and heat, the electron scattering mechanism in iron under high pressure and temperature holds the key to understanding the transport properties of planetary cores. Here we measure the electrical resistivity (the reciprocal of electrical conductivity) of iron at the high temperatures (up to 4,500 kelvin) and pressures (megabars) of Earth’s core in a laser-heated diamond-anvil cell. The value measured for the resistivity of iron is even lower than the value extrapolated from high-pressure, low-temperature data using the Bloch–Grüneisen law, which considers only the electron–phonon scattering. This shows that the iron resistivity is strongly suppressed by the resistivity saturation effect at high temperatures. The low electrical resistivity of iron indicates the high thermal conductivity of Earth’s core, suggesting rapid core cooling and a young inner core less than 0.7 billion years old 10 . Therefore, an abrupt increase in palaeomagnetic field intensity around 1.3 billion years ago 11 may not be related to the birth of the inner core.

An on-line multi-frequency electrical resistance tomography (mfERT) device with a melt-resistive sensor and noise reduction hardware has been proposed for crystalline phase imaging in high-temperature molten oxide. The melt-resistive sensor consists of eight electrodes made of platinum-rhodium (Pt-20mass%Rh) alloy covered by non-conductive aluminum oxide (Al2O3) to prevent an electrical short. The noise reduction hardware has been designed by two approaches: (1) total harmonic distortion (THD) for the robust multiplexer, and (2) a current injection frequency pair: low fL and high fH, for thermal noise compensation. THD is determined by a percentage evaluation of k-th harmonic distortions of ZnO at f=0.1~10,000 Hz. The fL and fH are determined by the thermal noise behavior estimation at different temperatures. At  f <100 Hz, the THD percentage is relatively high and fluctuates; otherwise, THD dramatically declines, nearly reaching zero. At the determined fL≥ 10,000 Hz and fH≈ 1,000,000 Hz, thermal noise is significantly compensated. The on-line mfERT was tested in the experiments of a non-conductive Al2O3 rod dipped into conductive molten zinc-borate (60ZnO-40B2O3) at 1000~1200 °C. As a result, the on-line mfERT is able to reconstruct the Al2O3 rod inclusion images in the high-temperature fields with low error, ςfL, T = 5.99%, at 1000 °C, and an average error ⟨ςfL⟩ = 9.2%.

The temperature (T) dependence of the electrical resistivity offers clues about the behavior of electrical carriers. One of the more puzzling observations is the T-linear resistivity found in systems known or suspected to exhibit quantum criticality, such as cuprate and organic superconductors, and heavy fermion materials; the origin of this behavior remains elusive. Bruin et al. (p. 804 ) find that the ruthenate Sr 3 Ru 2 O 7 also exhibits T-linear resistivity in the vicinity of its quantum critical point, and that its scattering rate per kelvin is approximately given by the inverse of a characteristic time made up of the Planck and Boltzmann constants. A comprehensive analysis of other systems with T-linear resistivity, including ordinary metals at high temperatures, indicates that their scattering rates are similarly close to the characteristic rate. That the rates are similar across a wide range of materials with diverse microscopic scattering mechanisms may indicate universal behavior. Transport measurements show little variation across metals with resistivity that scales linearly with temperature. Many exotic compounds, such as cuprate superconductors and heavy fermion materials, exhibit a linear in temperature ( T ) resistivity, the origin of which is not well understood. We found that the resistivity of the quantum critical metal Sr 3 Ru 2 O 7 is also T- linear at the critical magnetic field of 7.9 T. Using the precise existing data for the Fermi surface topography and quasiparticle velocities of Sr 3 Ru 2 O 7 , we show that in the region of the T- linear resistivity, the scattering rate per kelvin is well approximated by the ratio of the Boltzmann constant to the Planck constant divided by 2π. Extending the analysis to a number of other materials reveals similar results in the T- linear region, in spite of large differences in the microscopic origins of the scattering.

In this work, a theoretical model for the metal powder consolidation technique known as Electrical Resistance Sintering (ERS) is proposed and validated. This technique consists of the consolidation of a mass of metal powder by the simultaneous action of pressure and the passage of a high intensity electric current. This electric current heats the powder mass by the Joule effect, while softening it so that the imposed pressure causes its densification. The proposed model meets the set objective of seeking the greatest possible simplicity, without ignoring the key aspects of the technique. In line with this simplicity, the proposed model has a one-dimensional character and is solved numerically by means of Finite Difference through a simulator implemented in the Microsoft Excel™ spreadsheet environment, programming in VBA, with computation times not exceeding 5 min. The adopted strategy takes into account the strong electrical–mechanical-thermal coupling present in the process. The sensors incorporated in the ERS equipment allow the recording of the data necessary to construct the evolution curves of the global porosity and the thermal energy released. The theoretical predictions provided by the simulator have been compared with experimental curves obtained from the electrical consolidation experiments with commercially pure iron powder. Discrepancies between experimental and theoretical values for final global porosity are around 5% (although approaching 20% in the vicinity of critical conditions) and those for final specific thermal energy do not exceed 7%. The reasonable agreement between the experimental and theoretical curves gives confidence that the model, despite its simplifications, reproduces the main characteristics of the process.

The present research aims to investigate the two-phase air/water flow in a vertical pipe using an electrical resistance sensor and a high-speed camera. An electrical resistance sensor is designed and embedded in the inner wall of the tube. A flow pattern map is drawn at the height of 270 cm from the testbed inlet for 320 different phase velocities using a high-speed camera. By measuring the output voltage of the electrical resistance sensor and using the Maxwell relation, the volume fraction in bubbly and slug flow regimes are calculated for different phase velocities. The volume fraction values detected from the output signal of the electrical resistance sensor are compared with the results obtained from the high-speed camera images. The width of the output signal from the electrical resistance sensor indicates the length of the Taylor bubble. The output signal width is compared to the obtained Taylor bubble length from high-speed camera images, for several different velocities of the phases. It is noticed that at a constant velocity of the phases, the output signal width from the sensor is linearly related to the length of the Taylor bubble. The variations of the output signal width are plotted in terms of the ratio of the Taylor bubble length to the summation of air and water superficial velocities. By linear fitting of the available data, a novel equation is presented to calculate the Taylor bubble length in terms of the signal output from the electrical resistance sensor and the total superficial velocity of the phases.

Background The intestinal epithelial barrier, which works as the first line of defense between the luminal environment and the host, once destroyed, it will cause serious inflammation or other intestinal diseases. Tight junctions (TJs) play a vital role to maintain the integrity of the epithelial barrier. Lipopolysaccharide (LPS), one of the most important inflammatory factors will downregulate specific TJ proteins including Occludin and Claudin-1 and impair integrity of the epithelial barrier. Betaine has excellent anti-inflammatory activity but whether betaine has any effect on TJ proteins, particularly on LPS-induced dysfunction of epithelial barriers remains unknown. The purpose of this study is to explore the pharmacological effect of betaine on improving intestinal barrier function represented by TJ proteins. Intestinal porcine epithelial cells (IPEC-J2) were used as an in vitro model. Results The results demonstrated that betaine enhanced the expression of TJ proteins while LPS (1 μg/mL) downregulates the expression of these proteins. Furthermore, betaine attenuates LPS-induced decreases of TJ proteins both shown by Western blot (WB) and Reverse transcription-polymerase chain reaction (RT-PCR). The immunofluorescent images consistently revealed that LPS induced the disruption of TJ protein Claudin-1 and reduced its expression while betaine could reverse these alterations. Similar protective role of betaine on intestinal barrier function was observed by transepithelial electrical resistance (TEER) approach. Conclusion In conclusion, our research demonstrated that betaine attenuated LPS-induced downregulation of Occludin and Claudin-1 and restored the intestinal barrier function.

Trans-endothelial electrical resistance (TEER) is one of the most widely used indicators to quantify the barrier integrity of endothelial layers. Over the last decade, the integration of TEER sensors into organ-on-a-chip (OOC) platforms has gained increasing interest for its efficient and effective measurement of TEER in OOCs. To date, microfabricated electrodes or direct insertion of wires has been used to integrate TEER sensors into OOCs, with each method having advantages and disadvantages. In this study, we developed a TEER-SPE chip consisting of carbon-based screen-printed electrodes (SPEs) embedded in a poly(methyl methacrylate) (PMMA)-based multi-layered microfluidic device with a porous poly(ethylene terephthalate) membrane in-between. As proof of concept, we demonstrated the successful cultures of hCMEC/D3 cells and the formation of confluent monolayers in the TEER-SPE chip and obtained TEER measurements for 4 days. Additionally, the TEER-SPE chip could detect changes in the barrier integrity due to shear stress or an inflammatory cytokine (i.e., tumor necrosis factor-α). The novel approach enables a low-cost and facile fabrication of carbon-based SPEs on PMMA substrates and the subsequent assembly of PMMA layers for rapid prototyping. Being cost-effective and cleanroom-free, our method lowers the existing logistical and technical barriers presenting itself as another step forward to the broader adoption of OOCs with TEER measurement capability.