Real-time Impedance Monitoring Research Articles

Diffusion-based culture and real-time impedance monitoring of tumor spheroids in hydrogel microwells of a suspended membrane under microfluidic conditions

Tumor spheroids are widely studied for in vitro modeling of tumor growth and responses to anticancer drugs. However, current methods are mostly limited to static and perfusion-based cultures, which can be improved by more accurately mimicking pathological conditions. Here, we developed a diffusion-based dynamic culture system for tumor spheroids studies using a thin membrane of hydrogel microwells and a microfluidic device. This allows for effective exchange of nutrients and metabolites between the tumors and the culture medium flowing underneath, resulting in uniform tumor spheroids. To monitor the growth and drug response of the spheroids in real-time, we performed spectroscopic analyses of the system's impedance, demonstrating a close correlation between the tumor size and the resistance and capacitance of the system. Our results also indicate an enhanced drug effect on the tumor spheroids in the presence of a low AC electric field, suggesting a weakening mechanism of the spheroids induced by external perturbation.

Label-Free and Real-Time Electrical Impedance Monitoring of Macrophage Polarization of THP-1 Monocytes on Indium Tin Oxide Electrode

Label-Free and Real-Time Electrical Impedance Monitoring of Macrophage Polarization of THP-1 Monocytes on Indium Tin Oxide Electrode

Bio-Inspired Untethered Robot-Sensor Platform for Minimally Invasive Biomedical Sensing.

Conventional catheter- or probe-based in vivo biomedical sensing is uncomfortable, inconvenient, and sometimes infeasible for long-term monitoring. Existing implantable sensors often require an invasive procedure for sensor placement. Untethered soft robots with the capability to deliver the sensor to the desired monitoring point hold great promise for minimally invasive biomedical sensing. Inspired by the locomotion modes of snakes, we present here a soft kirigami robot for sensor deployment and real-time wireless sensing. The locomotion mechanism of the soft robot is achieved by kirigami patterns that offer asymmetric tribological properties that mimic the skin of the snake. The robot exhibits good deployability, excellent load capacity (up to 150 times its own weight), high-speed locomotion (0.25 body length per step), and wide environmental adaptability with multimodal movements (obstacle crossing, locomotion in wet and dry conditions, climbing, and inverted crawling). When integrated with passive sensors, the versatile soft robot can locomote inside the human body, deliver the passive sensor to the desired location, and hold the sensor in place for real-time monitoring in a minimally invasive manner. The proof-of-concept prototype demonstrates that the platform can perform real-time impedance monitoring for the diagnosis of gastroesophageal reflux disease.

A microfluidic tool for real-time impedance monitoring of in vitro renal tubular epithelial cell barrier

The cell barrier is built to delineate tissue compartments and regulate the substance exchange between different compartments. In this work, we developed a microfluidic tool for real-time impedance monitoring of in vitro renal tubular epithelial cell barrier (RTECB) to follow its formation dynamics and its drug responses. Madin-Darby canine kidney (MDCK) cells were cultured on an artificial basement membrane (ABM) and monitored inside a microfluidic device for up to 10 days. The recorded impedance spectra of the cell layer were analyzed based on an equivalent circuit, giving rise to a set of fitting parameters varying in time. This allowed us to assess the electrophysiological properties of the system and correlate them to the tightness of the epithelial barrier. A calcium switch assay was performed to illustrate the high sensibility of the barrier to biochemical stimuli. Finally, the formation characteristics of the barrier on ABM and conventional transwell membrane were compared, showing significant differences in terms of cell growth dynamics and cell layer stability.

On-chip real-time impedance monitoring of hiPSC-derived and artificial basement membrane-supported endothelium

Recent advances have shown the high sensibility of electrochemical impedance spectroscopy in real-time monitoring of cell barriers on a chip. Here, we applied this method to the investigation of human induced pluripotent stem cell (hiPSC) derived and artificial basement membrane (ABM) supported endothelial barrier. The ABM was obtained by self-assembling type IV collagen and laminin with a monolayer of crosslinked gelatin nanofibers. The hiPSCs were differentiated into brain microvascular endothelial cells (BMECs) and then plated on the ABM. After incubation for two days, the ABM-BMEC assembly was placed as a tissue insert into a microfluidic device for culture and real-time impedance monitoring over days. We found a significantly enhanced stability of the BMEC barrier in a serum-free and bromodeoxyuridine (BrdU) containing culture medium compared to the conventional culture due to the restricted cell proliferation. We also found that the BMEC barrier was sensitive to stimuli such as thrombin and that the change of the barrier impedance was mainly due to the change of the cell layer resistance. We can thus advocate this method to investigate the integrity of the cell barrier and the barrier-based assays.

Fast electrochemical impedance spectroscopy of lithium-ion batteries based on the large square wave excitation signal

Electrochemical impedance spectroscopy (EIS) is a technique for electrochemical characterization that is sensitive to the battery state and can uncover multidimensional electrochemical evolution information within the battery. Lithium-ion batteries usually need to be used in conjunction with power conversion circuits, while conventional EIS testing is conducted offline and is time-consuming, which cannot effectively monitor the battery characteristics during use. To match the characteristics of the square wave signal during power switching, a rapid EIS measurement method for lithium-ion batteries based on the large square wave excitation signal is proposed in this paper, and develops a testing device with a response time of microseconds. The proposed method and device are applied to estimate the state of health (SOH) of the battery. In conclusion, we proposed method enhances the capabilities of EIS testing technology and has a good application prospect in real-time online impedance monitoring.

Real-Time Temperature Rise Estimation during Irreversible Electroporation Treatment through State-Space Modeling

To evaluate the feasibility of real-time temperature monitoring during an electroporation-based therapy procedure, a data-driven state-space model was developed. Agar phantoms mimicking low conductivity (LC) and high conductivity (HC) tissues were tested under the influences of high (HV) and low (LV) applied voltages. Real-time changes in impedance, measured by Fourier Analysis SpecTroscopy (FAST) along with the known tissue conductivity and applied voltages, were used to train the model. A theoretical finite element model was used for external validation of the model, producing model fits of 95.8, 88.4, 90.7, and 93.7% at 4 mm and 93.2, 58.9, 90.0, and 90.1% at 10 mm for the HV-HC, LV-LC, HV-LC, and LV-HC groups, respectively. The proposed model suggests that real-time temperature monitoring may be achieved with good accuracy through the use of real-time impedance monitoring.

Real-Time Impedance Monitoring of Alkaline Phosphatase (ALP) Release by Microelectrode Arrays

Alkaline phosphatase (ALP) is a reporter enzyme widely used in point-of-care applications. Real-time monitoring of ALP accelerates understanding of emerging diseases and of cancer progression. This can be achieved through biosensor-based strategies. This paper outlines an approach that facilitates the real-time monitoring of ALP release from the differentiation of cultured human colon cancer cells (Ht-29). Electric cell-substrate impedance sensing was used to generate changes in Ht-29 cells during ALP release and the data were compared using amperometry. The findings indicate a correlation between cell response and shift in impedance magnitude and current. Relevant results had similar attitude during cell monitoring, which influenced cell morphology and cell viability. Our analysis is a clear advance on the current methods such as enzyme-linked immunosorbent assay. The developed method can contribute to the development of microfluidic testing that would facilitate work on small-scale techniques.

Stretchable electrical cell-substrate impedance sensor platform for monitoring cell monolayers under strain

Stretchable microelectrodes paired with an ultra-elastic substrate can be used for electrical sensing of mechanically stretched cells and cell monolayers. Here, we present the development of a cell-stretching platform with thin-film interdigitated microelectrodes. Up to 35 % cyclic stretch are feasible with a novel interlaced meander design connected to the microelectrodes and using Poly(dimethylsiloxane) (PDMS) with a Young’s modulus of 50 kPa as an ultra-elastic substrate. Reliable electrical contacting of the microelectrodes under stretch was achieved by perforation of the contact pads. The novel platform enables label-free, real-time electrical cell-substrate impedance (ECIS) monitoring of cell monolayers. Proof-of-concept experiments indicated that electrical impedance of Madin-Darby canine kidney (MDCK) cell monolayers increased sharply by uniaxial mechanical strain above 20 %. For comparison, human alveolar basal epithelial adenocarcinoma (A549) cell monolayers, which are known to lack mature cell junctions, showed a continuous decrease of electrical impedance over the whole applied strain range of 35 %. The data reveal that impedance changes upon stretching depend on epithelial cell types and existence of tight cellular junctions. The system provides the basis for reliable continuous long-term monitoring of electrical properties of cell monolayers under strain by electrical impedance spectroscopy, e.g., to monitor epithelial permeability changes in real time and under label-free conditions to screen the influence of pharmacological substances.

Real-time local impedance monitoring to assess tissue lesion during pulmonary vein isolation: a new tool for AF ablation

Abstract Background Contact force catheter ablation is the gold standard for treatment of atrial fibrillation (AF). Local tissue impedance (LI) evaluation has been recently studied to evaluate lesion formation during radiofrequency ablation. Purpose Aim of the study was to assess the outcomes of an irrigated catether with LI alghorithm compared to contact force (CF)-sensing catheters in the treatment of symptomatic AF. Methods A prospective, single-center, nonrandomized study was conducted, to compare outcomes between CF-AF ablation (Group 1) and LI-AF ablation (Group 2). For Group 1 ablation was performed using the Carto 3© System with the SmartTouch SF catheter and, as ablation target, an ablation index value of 500 anterior and 400 posterior. For Group 2, ablation was performed using the Rhythmia™ System with novel ablation catheter with a dedicated algorithm (DirectSense) used to measure LI at the distal electrode of this catheter. An absolute impedance drop greater than 20Ω was used at each targeted. According to the Close Protocol, ablation included a point by point pulmonary vein isolation (PVI) with an Inter-lesion space ≤5 mm in both Groups. Procedural endpoint was PVI, with confirmed bidirectional block. Results A total of 116 patients were enrolled, 59 patients in Group 1 (CF) and 57 in Group 2 (LI), 65 (63%) with a paroxismal AF and 36 (37%) with a persistent AF. Baseline patients features were not different between groups (P=ns). LI-Group showed a comparable procedural time (180±89 vs 180±56, P=0.59) but with a longer fluoroscopy time (20±12 vs 13±9 min, P=0.002). Wide antral isolation was more often observed in CF-Group (95% vs 80%, P=0.022), while LI-Group 2 required frequently additional right or left carina ablation (28% vs 14%, P=0.013). The mean LI was 106±14Ω prior to ablation and 92.5±11Ω after ablation (mean LI drop of 13.5±8Ω) during a median RF time of 26 [19–34] sec for each ablation spot. No steam pops or complications during the procedures were reported. The acute procedural success was 100%, with all PVs successfully isolated in all study patients. Regarding safety, only minor vascular complications were observed (5%), without differences between groups (p=0.97). During follow up, 9-month freedom from atrial fibrillation/atrial flutter/atrial tachycardia recurrence was 86% in Group 1 and 75% in Group 2 (P=0.2). Conclusions An LI-guided PV ablation strategy seems to be safe and effective, with acute and mid-term outcomes comparable to the current contact force strategy. LI monitoring could be a promising complementary parameter to evaluate not only wall contact but also lesion formation during power delivery. Procedural Outcomes Funding Acknowledgement Type of funding source: None

Single-cell individualized electroporation with real-time impedance monitoring using a microelectrode array chip

The ability to precisely deliver molecules into single cells while maintaining good cell viability is of great importance to applications in therapeutics, diagnostics, and drug delivery as it is an advancement toward the promise of personalized medicine. This paper reports a single-cell individualized electroporation method with real-time impedance monitoring to improve cell perforation efficiency and cell viability using a microelectrode array chip. The microchip contains a plurality of sextupole-electrode units patterned in an array, which are used to perform in situ electroporation and real-time impedance monitoring on single cells. The dynamic recovery processes of single cells under electroporation are tracked in real time via impedance measurement, which provide detailed transient cell states and facilitate understanding the whole recovery process at the level of single cells. We define single-cell impedance indicators to characterize cell perforation efficiency and cell viability, which are used to optimize electroporation. By applying the proposed electroporation method to different cell lines, including human cancer cell lines and normal human cell lines individually, optimum stimuli are determined for these cells, by which high transfection levels of enhanced green fluorescent protein (EGFP) plasmid into cells are achieved. The results validate the effectiveness of the proposed single-cell individualized electroporation/transfection method and demonstrate promising potential in applications of cell reprogramming, induced pluripotent stem cells, adoptive cell therapy, and intracellular drug delivery technology.

Real-Time Impedance Monitoring During Electroporation Processes in Vegetal Tissue Using a High-Performance Generator.

Classical application of electroporation is carried out by using fixed protocols that do not clearly assure the complete ablation of the desired tissue. Nowadays, new methods that pursue the control of the treatment by studying the change in impedance during the applied pulses as a function of the electric field are being developed. These types of control seek to carry out the treatment in the fastest way, decreasing undesired effects and treatment time while ensuring the proper tumour ablation. The objective of this research is to determine the state of the treatment by continuously monitoring the impedance by using a novel versatile high-voltage generator and sensor system. To study the impedance dynamics in real time, the use of pulses of reduced voltage, below the threshold of reversible electroporation, is tested to characterise the state-of-the-treatment without interfering with it. With this purpose, a generator that provides both low voltage for sense tissue changes and high voltage for irreversible electroporation (IRE) was developed. In conclusion, the characterisation of the effects of electroporation in vegetal tissue, combined with the real-time monitoring of the state-of-the-treatment, will enable the provision of safer and more effective treatments.

A multiparametric CAR T cell potency assay that employs real-time cellular impedance and live cell imaging

Background & Aim Chimeric antigen receptors (CARs) are engineered proteins that consist of an extracellular antigen binding domain that is linked, via a hinge region and transmembrane domain, to intracellular activation domains that drive T cell activation, proliferation, and target cell killing. A few decades of CAR engineering efforts have made it clear that merely linking these protein domains together is insufficient for generating an effective CAR; subtle differences in how the domains are linked to each other can greatly impact functionality. During CAR optimization biochemical assays can be used to assess critical quality attributes such as potency. Although these reductionistic approaches are useful, their results don't necessarily correlate with cancer killing efficacy within a more physiologically relevant context. To rigorously compare different CAR constructs and identify unwanted behavior such as tonic signaling, it is widely acknowledged that CAR function should be evaluated within the complex milieu of the immune synapse, using bona fide cancer cell killing as the readout. For this purpose, release assays (51Cr, LDH) have historically been the gold standard, but suffer from the fact that they require significant “hands on” time and only provide end point data. Requiring just target cancer cell seeding and a subsequent CAR T cell addition step, herein we use the Agilent xCELLigence RTCA eSight to quantitatively evaluate CAR T cell-mediated killing of cancer cells in real-time over multiple days and at physiologically relevant low E:T ratios. Methods, Results & Conclusion Providing a direct and objective assessment of target cancer cell number, cell size, and cell-substrate attachment strength, impedance biosensors embedded within the base of eSight microplates are shown to quantitatively track the continuum of target cell killing, spanning from early (reduced cell-substrate adhesion strength) to late (lysis) events. Concurrently, eSight is shown to capture live cell images in brightfield and three fluorescence channels, providing an orthogonal readout of the killing process – including real-time assessment of T cell activation and exhaustion markers such as CD69, CD107a, CTLA4, and LAG-3. By combining the strengths of real-time impedance monitoring (simplicity, analytical sensitivity, and objectivity) with that of live cell imaging (specificity of the readout), eSight is shown to increase the information richness of the CAR T cell killing assay without increasing the workload.

Real-time cellular impedance monitoring and imaging in a dual-flow bioreactor

The generation of physiologically relevant in vitro models of biological barriers can play a key role in understanding human diseases and in the development of more predictive methods for assessing toxicity and drug or nutrient absorption. Here, we present an advanced cell culture system able to mimic the dynamic environment of biological barriers, while monitoring cell behaviour through real-time impedance measurements and imaging. Caco-2 cells were cultured in the Trans Epithelial Electric Impedance (TEEI) bioreactor under both flow and static conditions. The cells in dynamic conditions developed higher impedance values at low frequencies and showed a typical RC behaviour, while the controls showed minimal capacitive behaviour. These results highlighted the differences between flow and static conditions and the ability of the TEEI measurements to provide a more precise indication of monolayer formation.

New Parylene Coating System with Real-Time and Non-Destructive Electrical Impedance Monitoring of Parylene Layer.

Parylene is one of the polymers widely used as an electrical insulating or waterproof layer in the fields of semiconductor, electronics, and biomedical engineering owing to its outstanding properties of chemically inertness, biocompatibility, water resistance, low conductivity, and flexibility. It is increasingly required for real-time and non-destructive characterization of the deposition of parylene layer for the quality control and assurance. In the present work, we suggested an impedance measurement based parylene coating system which can provide the electrical properties of the deposited parylene in real-time and non-destructively. For this, the impedance spectra of parylene C, N, or D were measured using the fabricated interdigitated and wave-shaped electrode (IWE) during the chemical vapor deposition (CVD) process. The results showed a feasibility to monitor the impedance change according to the parylene deposition, and that the resistance at the frequency of 2.15 kHz was decreased in dependency on the type of the deposited parylene.

Real-time cellular impedance monitoring and imaging of biological barriers in a dual-flow membrane bioreactor

The generation of physiologically relevant in-vitro models of biological barriers can play a key role in understanding human diseases and in the development of more predictive methods for assessing toxicity and drug or nutrient absorption. Here, we present an advanced cell culture system able to mimic the dynamic environment of biological barriers while monitoring cell behaviour through real-time impedance measurements and imaging. It consists of a fluidic device with an apical and a basal flow compartment separated by a semi-permeable membrane. The main features of the device are the integration of sensing through transepithelial electrical impedance (TEEI) measurements and transparent windows for optical monitoring within a dual flow system.Caco-2 cells were cultured in the TEEI bioreactor under both flow and static conditions. Although no differences in the expression of peripheral actin and occludin were visible, the cells in dynamic conditions developed higher impedance values at low frequencies, indicative of a higher paracellular electrical impedance with respect to the static cultures. TEEI measurements at high frequency also enabled monitoring monolayer formation, which can be correlated with the observation of an RC behaviour in the impedance spectra. In particular, the cells subject to flow showed accelerated barrier formation and increased vitality with respect to the static controls, again highlighting the importance of dynamic conditions for epithelial cells.

Real-time electrical impedance monitoring of carbon fiber-reinforced polymer laminates undergoing quasi-static indentation

Laminated composites are vulnerable to damage from out-of-plane loading, particularly impact loading, and the incurred damage is often only detected by evaluating the post-impact condition of the composites. Real-time monitoring techniques are desirable for early detection of damage. Utilizing changes in the electrical properties of composites to track incurred damage is promising, but the interpretation of such measurements is still challenging. Here, an electro-mechanical system is introduced to understand how well we could detect mechanical degradation in carbon-fiber-reinforced polymer (CFRP) plates undergoing a quasi-static indentation (QSI) test, which is representative of an impact load. The system measures the in situ, real-time changes in impedance and phase angle along the specified conductivity paths. Two different electrode configurations are proposed and tested. In all studied cases, the system effectively detected severe damage, characterized by an immediate reduction in strength, in CFRP. Using our proposed electrode configurations, we discovered that the early detection of barely visible damage strongly depends on two factors: (i) the location of the injection-measurement points with respect to the damage, and (ii) the orientation of the measurement paths with respect to the fibers orientation in the laminated CFRP surface.

Real-time impedance monitoring of oxygen reduction during surface modification of thinfilmcathodes.

Improvement of solid oxide fuel cells strongly relies on the development of cathode materials with high catalytic activity for the oxygen reduction reaction. Excellent activity was found for perovskite-type oxides such as La1-xSrxCoO3-δ (LSC), but performance degradation, probably caused by surface composition changes, hinders exploitation of the full potential of LSC. This study reveals that the potentially very high activity of the LSC surface can be traced back to few very active sites. Already tiny amounts of SrO, for example, 4% of a monolayer, deposited on an LSC surface, lead to severe deactivation. Co, on the other hand, causes (re-)activation, suggesting that active sites are strongly related to Co being present at the surface. These insights could be gained by a novel method to measure changes of the electrochemical performance of thin film electrodes in situ, while modifying their surface: impedance spectroscopy measurements during deposition of well-defined fractions of monolayers of Sr-, Co- and La-oxides by single laser pulses in a pulsed laser deposition chamber.

Periovulatory follicular fluid levels of estradiol trigger inflammatory and DNA damage responses in oviduct epithelial cells.

ObjectiveOvarian steroid hormones (mainly E2 and P4) regulate oviduct physiology. Serum-E2 acts on the oviduct epithelium from the basolateral cell compartment. Upon ovulation, the apical compartment of the oviduct epithelium is temporarily exposed to follicular fluid, which contains much higher levels of E2 than serum. The aim of this study was to evaluate the effects of human periovulatory follicular fluid levels of E2 on oviduct epithelial cells using two porcine in vitro models.MethodsA cell line derived from the porcine oviductal epithelium (CCLV-RIE270) was characterized (lineage markers, proliferation characteristics and transformation status). Primary porcine oviduct epithelial cells (POEC) were cultured in air-liquid interface and differentiation was assessed histologically. Both cultures were exposed to E2 (10 ng/ml and 200 ng/ml). Proliferation of CCLV-RIE270 and POEC was determined by real-time impedance monitoring and immunohistochemical detection of Ki67. Furthermore, marker gene expression for DNA damage response (DDR) and inflammation was quantified.ResultsCCLV-RIE270 was not transformed and exhibited properties of secretory oviduct epithelial cells. Periovulatory follicular fluid levels of E2 (200 ng/ml) upregulated the expression of inflammatory genes in CCLV-RIE270 but not in POEC (except for IL8). Expression of DDR genes was elevated in both models. A significant increase in cell proliferation could not be detected in response to E2.ConclusionsCCLV-RIE270 and POEC are complementary models to evaluate the consequences of oviduct exposure to follicular fluid components. Single administration of periovulatory follicular fluid E2 levels trigger inflammatory and DNA damage responses, but not proliferation in oviduct epithelial cells.

Dependence of Impedance Measurement Sensitivity of Cell Growth on Sensing Area of Circular Interdigitated Electrode.

A circular interdigitated electrode (IDE) array for label-free and real-time impedance monitoring of cell growth was fabricated and evaluated. Both the width and spacing of fingers were 50 μm, and the exposed sensing area of the circular IDE was 1.3~3.4 mm. The electrical characteristics of the fabricated circular IDE were modeled as an equivalent circuit, and the values of the circuit parameters extrapolated from the fitting to the measured spectra in different concentrations of NaCl or sensing areas of the circular IDE were analyzed. During cell growth, the resistance of cells extrapolated from the fitting was increased and the maximum rate of change in the real part of the impedance was observed at frequencies of 10 to 22 kHz. The normalized real part of the impedance measured at 10 kHz during cell growth was increased more with decreasing the electrode sensing area, albeit the number of cells to be investigated showed a corresponding increase.