Microcavity array (MCA)-based biosensor chip for functional drug screening of 3D tissue models

Patient-derived melanoma models

Melanoma is a very aggressive, rapidly metastasizing tumor that has been studied intensively in the past regarding the underlying genetic and molecular mechanisms. More recently developed treatment modalities have improved response rates and overall survival of patients. However, the majority of patients suffer from secondary treatment resistance, which requires in depth analyses of the underlying mechanisms. Here, melanoma models based on patients-derived material may play an important role. Consequently, a plethora of different experimental techniques have been developed in the past years. Among these are 3D and 4D culture techniques, organotypic skin reconstructs, melanoma-on-chip models and patient-derived xenografts, Every technique has its own strengths but also weaknesses regarding throughput, reproducibility, and reflection of the human situation. Here, we provide a comprehensive overview of currently used techniques and discuss their use in different experimental settings.

Microcavity well-plate for automated parallel bioelectronic analysis of 3D cell cultures

Three-dimensional (3D) in vitro cell culture models serve as valuable tools for accurately replicating cellular microenvironments found in vivo. While cell culture technologies are rapidly advancing, the availability of non-invasive, real-time, and label-free analysis methods for 3D cultures remains limited. To meet the demand for higher-throughput drug screening, there is a demanding need for analytical methods that can operate in parallel. Microelectrode systems in combination with microcavity arrays (MCAs), offer the capability of spatially resolved electrochemical impedance analysis and field potential monitoring of 3D cultures. However, the fabrication and handling of small-scale MCAs have been labour-intensive, limiting their broader application. To overcome this challenge, we have established a process for creating MCAs in a standard 96-well plate format using high-precision selective laser etching. In addition, to automate and ensure the accurate placement of 3D cultures on the MCA, we have designed and characterized a plug-in tool using SLA-3D-printing. To characterize our new 96-well plate MCA-based platform, we conducted parallel analyses of human melanoma 3D cultures and monitored the effect of cisplatin in real-time by impedance spectroscopy. In the following we demonstrate the capabilities of the MCA approach by analysing contraction rates of human pluripotent stem cell-derived cardiomyocyte aggregates in response to cardioactive compounds. In summary, our MCA system significantly expands the possibilities for label-free analysis of 3D cell and tissue cultures, offering an order of magnitude higher parallelization capacity than previous devices. This advancement greatly enhances its applicability in real-world settings, such as drug development or clinical diagnostics.

A review of electrochemical impedance as a tool for examining cell biology and subcellular mechanisms: merits, limits, and future prospects

Herein the development of cellular impedance biosensors, electrochemical impedance spectroscopy, and the general principles and terms associated with the cell-electrode interface is reviewed. This family of techniques provides quantitative and sensitive information into cell responses to stimuli in real-time with high temporal resolution. The applications of cell-based impedance biosensors as a readout in cell biology is illustrated with a diverse range of examples. The current state of the field, its limitations, the possible available solutions, and the potential benefits of developing biosensors are discussed.

Organic Bioelectronics for In Vitro Systems

Bioelectronics have made strides in improving clinical diagnostics and precision medicine. The potential of bioelectronics for bidirectional interfacing with biology through continuous, label-free monitoring on one side and precise control of biological activity on the other has extended their application scope to in vitro systems. The advent of microfluidics and the considerable advances in reliability and complexity of in vitro models promise to eventually significantly reduce or replace animal studies, currently the gold standard in drug discovery and toxicology testing. Bioelectronics are anticipated to play a major role in this transition offering a much needed technology to push forward the drug discovery paradigm. Organic electronic materials, notably conjugated polymers, having demonstrated technological maturity in fields such as solar cells and light emitting diodes given their outstanding characteristics and versatility in processing, are the obvious route forward for bioelectronics due to their biomimetic nature, among other merits. This review highlights the advances in conjugated polymers for interfacing with biological tissue in vitro, aiming ultimately to develop next generation in vitro systems. We showcase in vitro interfacing across multiple length scales, involving biological models of varying complexity, from cell components to complex 3D cell cultures. The state of the art, the possibilities, and the challenges of conjugated polymers toward clinical translation of in vitro systems are also discussed throughout.

Diversity Models and Applications of 3D Breast Tumor-on-a-Chip

Breast disease is one of the critical diseases that plague females, as is known, breast cancer has high mortality, despite significant pathophysiological progress during the past few years. Novel diagnostic and therapeutic approaches are needed to break the stalemate. An organ-on-chip approach is considered due to its ability to repeat the real conditions found in the body on microfluidic chips, offsetting the shortcomings of traditional 2D culture and animal tests. In recent years, the organ-on-chip approach has shown diversity, recreating the structure and functional units of the real organs/tissues. The applications were also developed rapidly from the laboratory to the industrialized market. This review focuses on breast tumor-on-a-chip approaches concerning the diversity models and applications. The models are summarized and categorized by typical biological reconstitution, considering the design and fabrication of the various breast models. The breast tumor-on-a-chip approach is a typical representative of organ chips, which are one of the precedents in the market. The applications are roughly divided into two categories: fundamental mechanism research and biological medicine. Finally, we discuss the prospect and deficiencies of the emerging technology. It has excellent prospects in all of the application fields, however there exist some deficiencies for promotion, such as the stability of the structure and function, and uniformity for quantity production.

From cells-on-a-chip to organs-on-a-chip: scaffolding materials for 3D cell culture in microfluidics

It is an emerging research area to integrate scaffolding materials in microfluidic devices for 3D cell culture (organs-on-a-chip). The technology of organs-on-a-chip holds the potential to obviate the gaps between pre-clinical and clinical studies. As accumulating evidence shows the importance of extracellular matrix in in vitro cell culture, significant efforts have been made to integrate 3D ECM/scaffolding materials in microfluidics. There are two families of materials that are commonly used for this purpose: hydrogels and electrospun fibers. In this review, we briefly discuss the properties of the materials, and focus on the various technologies to obtain the materials (e.g. extraction of collagen from animal tissues) and to include the materials in microfluidic devices. Challenges and potential solutions of the current materials and technologies were also thoroughly discussed. At the end, we provide a perspective on future efforts to make these technologies more translational to broadly benefit pharmaceutical and pathophysiological research.

Advances in Multidimensional Cardiac Biosensing Technologies: From Electrophysiology to Mechanical Motion and Contractile Force

Cardiovascular disease is currently a leading killer to human, while drug-induced cardiotoxicity remains the main cause of the withdrawal and attrition of drugs. Taking clinical correlation and throughput into account, cardiomyocyte is perfect as in vitro cardiac model for heart disease modeling, drug discovery, and cardiotoxicity assessment by accurately measuring the physiological multiparameters of cardiomyocytes. Remarkably, cardiomyocytes present both electrophysiological and biomechanical characteristics due to the unique excitation-contraction coupling, which plays a significant role in studying the cardiomyocytes. This review mainly focuses on the recent advances of biosensing technologies for the 2D and 3D cardiac models with three special properties: electrophysiology, mechanical motion, and contractile force. These high-performance multidimensional cardiac models are popular and effective to rebuild and mimic the heart in vitro. To help understand the high-quality and accurate physiologies, related detection techniques are highly demanded, from microtechnology to nanotechnology, from extracellular to intracellular recording, from multiple cells to single cell, and from planar to 3D models. Furthermore, the characteristics, advantages, limitations, and applications of these cardiac biosensing technologies, as well as the future development prospects should contribute to the systematization and expansion of knowledge.

Advancing Biosensors with Machine Learning

Chemometrics play a critical role in biosensors-based detection, analysis, and diagnosis. Nowadays, as a branch of artificial intelligence (AI), machine learning (ML) have achieved impressive advances. However, novel advanced ML methods, especially deep learning, which is famous for image analysis, facial recognition, and speech recognition, has remained relatively elusive to the biosensor community. Herein, how ML can be beneficial to biosensors is systematically discussed. The advantages and drawbacks of most popular ML algorithms are summarized on the basis of sensing data analysis. Specially, deep learning methods such as convolutional neural network (CNN) and recurrent neural network (RNN) are emphasized. Diverse ML-assisted electrochemical biosensors, wearable electronics, SERS and other spectra-based biosensors, fluorescence biosensors and colorimetric biosensors are comprehensively discussed. Furthermore, biosensor networks and multibiosensor data fusion are introduced. This review will nicely bridge ML with biosensors, and greatly expand chemometrics for detection, analysis, and diagnosis.

Parallelized Wireless Sensing System for Continuous Monitoring of Microtissue Spheroids

Currently, the use of electrical readout methods for the investigation of microtissue spheroids in combination with lab automation tools is hindered by the cable connections that are required to interrogate the on-chip-integrated electrodes. To overcome this limitation, we developed a wireless sensor scheme, which can detect the size variation of microtissues during long-term culturing and drug exposure assays. The sensor system includes an interrogation board, which is composed of an inductor-capacitor (LC) readout circuit, and the tissue culture platform with integrated split-ring sensors. The magnetic coupling between the LC circuit and the sensors enables the interrogation of the on-chip sensors without any wire connection to the culture platform. By optimizing the sensor dimensions and the LC resonance frequencies, we were able to avoid cross talk between neighboring sensors. We integrated 12 tissue compartments on a standard microscopy slide with a sensor-to-sensor pitch of 9 mm, which is in accordance with standard 96-well plate dimensions. As a proof-of-concept experiment for the developed system, we monitored continuously and during more than four days the growth inhibition of colon cancer microtissue spheroids that had been exposed to different concentrations of doxorubicin, a chemotherapeutic compound. The stability of the measurements during long-term culturing and the compatibility of the sensor scheme with standard lab equipment offer great potential for automated electrical microtissue spheroid characterization.

Multisensor Systems and Arrays for Medical Applications Employing Naturally-Occurring Compounds and Materials

The significant improvement of quality of life achieved over the last decades has stimulated the development of new approaches in medicine to take into account the personal needs of each patient. Precision medicine, providing healthcare customization, opens new horizons in the diagnosis, treatment and prevention of numerous diseases. As a consequence, there is a growing demand for novel analytical devices and methods capable of addressing the challenges of precision medicine. For example, various types of sensors or their arrays are highly suitable for simultaneous monitoring of multiple analytes in complex biological media in order to obtain more information about the health status of a patient or to follow the treatment process. Besides, the development of sustainable sensors based on natural chemicals allows reducing their environmental impact. This review is concerned with the application of such analytical platforms in various areas of medicine: analysis of body fluids, wearable sensors, drug manufacturing and screening. The importance and role of naturally-occurring compounds in the development of electrochemical multisensor systems and arrays are discussed.

Impedance Spectroscopy as a Tool for Monitoring Performance in 3D Models of Epithelial Tissues

In contrast to traditional 2D cell cultures, both 3D models and organ-on-a-chip devices allow the study of the physiological responses of human cells. These models reconstruct human tissues in conditions closely resembling the body. Translation of these techniques into practice is hindered by associated labor costs, a need which may be remedied by automation. Impedance spectroscopy (IS) is a promising, automation-compatible label-free technology allowing to carry out a wide range of measurements both in real-time and as endpoints. IS has been applied to both the barrier cultures and the 3D constructs. Here we provide an overview of the impedance-based analysis in different setups and discuss its utility for organ-on-a-chip devices. Most attractive features of impedance-based assays are their compatibility with high-throughput format and supports for the measurements in real time with high temporal resolution, which allow tracing of the kinetics. As of now, IS-based techniques are not free of limitations, including imperfect understanding of the parameters that have their effects on the impedance, especially in 3D cell models, and relatively high cost of the consumables. Moreover, as the theory of IS stems from electromagnetic theory and is quite complex, work on popularization and explanation of the method for experimental biologists is required. It is expected that overcoming these limitations will lead to eventual establishing IS based systems as a standard for automated management of cell-based experiments in both academic and industry environments.

Electrochemical live monitoring of tumor cell migration out of micro-tumors on an innovative multiwell high-dense microelectrode array

Understanding of cell migration and spreading out of tumor tissue is of great interest concerning the mechanism and causes of tumor malignancy and metastases. Although there are methods available for studying cell migration on monolayer cell cultures like transwell assays, novel techniques for monitoring cell spreading out of 3D organoids or tumor tissue samples are highly required. In this context, we developed an innovative high-dense microelectrode array for impedimetric monitoring of cell migration from 3D tumor cultures. For a proof of concept, a strongly migrating breast cancer cell line (MDA-MB-231) and two malignant melanoma cell lines (T30.6.9, T12.8.10ZII) were used for generating viable micro-tumor models. The migration propensity was determined by impedimetric monitoring over 144 hours, correlated by microscopy and validated by transwell assays. The impedimetric analysis of covered electrodes and the relative impedance maximum values revealed extended information regarding the contribution of proliferative effects. More strikingly, using reference populations of mitomycin C treated spheroids where proliferation was suppressed, distinction of proliferation and migration was possible. Therefore, our high-dense microelectrode array based impedimetric migration monitoring has the capability for an automated quantitative analysis system that can be easily scaled up as well as integrated in lab on chip devices.

Sensor-Instrumented Scaffold Integrated with Microporous Spongelike Ultrabuoy for Long-Term 3D Mapping of Cellular Behaviors and Functions

Real-time monitoring of cellular behaviors and functions with sensor-instrumented scaffolds can provide a profound impact on fundamental studies of the underlying biophysics and disease modeling. Although quantitative measurement of predictive data for in vivo tests and physiologically relevant information in these contexts is important, the long-term reliable monitoring of cellular functions in three-dimensional (3D) environments is limited by the required set under wet cell culture conditions that are unfavorable to electronic instrument settings. Here, we introduce an ultrabuoyant 3D instrumented scaffold that can remain afloat on the surface of culture medium and thereby provides favorable environments for the entire electronic components in the air while the cells reside and grow underneath. This setting enables high-fidelity recording of electrical cell-substrate impedance and electrophysiological signals for a long period of time (weeks). Comprehensive in vitro studies reveal the utility of this platform as an effective tool for drug screening and tissue development.

Micro/nanoelectrochemical probe and chip devices for evaluation of three-dimensional cultured cells

Herein, we present an overview of recent research progress in the development of micro/nanoelectrochemical probe and chip devices for the evaluation of three-dimensional (3D) cultured cells. First, we discuss probe devices: a general outline, evaluation of O₂ consumption, enzyme-modified electrodes, evaluation of endogenous enzyme activity, and the collection of cell components from cell aggregates are discussed. The next section is focused on integrated chip devices: a general outline, electrode array devices, smart electrode array devices, droplet detection of 3D cultured cells, cell manipulation using dielectrophoresis (DEP), and electrodeposited hydrogels used for fabrication of 3D cultured cells on chip devices are discussed. Finally, we provide a summary and discussion of future directions of research in this field.

Comprehensive human stem cell differentiation in a 2D and 3D mode to cardiomyocytes for long-term cultivation and multiparametric monitoring on a multimodal microelectrode array setup

Human pluripotent stem cell derived cardiomyocytes are a promising cell source for research and clinical applications like investigation of cardiomyopathies and therefore, identification and testing of novel therapeutics as well as for cell based therapy approaches. However, actually it´s a challenge to generate matured adult cardiomyocyte-like phenotype in a reasonable time. Moreover, there is a lack of applicable non-invasive label-free monitoring techniques providing quantitative parameters for analysing the culture stability and maturation status. In this context, we established an efficient protocol based on a combined differentiation of hiPSC in 2D cultures followed by a forced reaggregation step that leads to highly enriched (>90% cardiomyocytes) cardiomyocyte clusters. Interestingly, 3D cultures revealed an accelerated maturation as well as phenotype switch from atrial to ventricular cardiomyocytes. More strikingly using combined impedimetric and electrophysiological monitoring the high functionality and long-term stability of 3D cardiomyocyte cultures, especially in comparison to 2D cultures could be demonstrated. Additionally, chronotropic as well as QT-prolongation causing reference compounds were used for validating the cardio specific and sensitive reaction over the monitored time range of more than 100 days. Thus, the approach of multiparametric bioelectronic monitoring offers capabilities for the long-term quantitative analysis of hiPS derived cardiomyocyte culture functionality and long-term stability. Moreover, the same multiparametric bioelectronic platform can be used in combination with validated long-term stable cardiomyocyte cultures for the quantitative detection of compound induced effects. This could pave the way for more predictive in vitro chronic/repeated dose cardiotoxicity testing assays.

One Hour In Vivo-like Phenotypic Screening System for Anti-cancer Drugs Using a High Precision Surface Plasmon Resonance Device

In anti-cancer drug (candidate) screening, there is the need for evaluation at physiological concentrations similar to in vivo. This is often performed by three-dimensionally (3D) cultured cells; however, it requires a long culture period of 2 - 4 weeks with tedious experimental procedures. Here, we report on a high precision surface plasmon resonance (HP-SPR)-3D system. We developed the system with average fluctuation of 50 ndeg s^-1 using two-dimensionally cultured cells attached onto a sensor chip by applying collagen on the top to change their activity into in vivo-like conditions without cell division. It allowed in vivo-like phenotypic screening for anti-cancer drugs within 1 h of drug addition. The data were collected as the stable linear signal change parts for at least 5 min after 25 min following drug addition. The results provided compatibility to clinically related chemosensitivity test for anti-cancer (P <0.001) using two cell lines of pancreatic cancer and three anti-cancer drugs to represent differences in individual gene expression and drug mode of action.

Smart Cell Culture Systems: Integration of Sensors and Actuators into Microphysiological Systems

Technological advances in microfabrication techniques in combination with organotypic cell and tissue models have enabled the realization of microphysiological systems capable of recapitulating aspects of human physiology in vitro with great fidelity. Concurrently, a number of analysis techniques has been developed to probe and characterize these model systems. However, many assays are still performed off-line, which severely compromises the possibility of obtaining real-time information from the samples under examination, and which also limits the use of these platforms in high-throughput analysis. In this review, we focus on sensing and actuation schemes that have already been established or offer great potential to provide in situ detection or manipulation of relevant cell or tissue samples in microphysiological platforms. We will first describe methods that can be integrated in a straightforward way and that offer potential multiplexing and/or parallelization of sensing and actuation functions. These methods include electrical impedance spectroscopy, electrochemical biosensors, and the use of surface acoustic waves for manipulation and analysis of cells, tissue, and multicellular organisms. In the second part, we will describe two sensor approaches based on surface-plasmon resonance and mechanical resonators that have recently provided new characterization features for biological samples, although technological limitations for use in high-throughput applications still exist.

Label-Free and Regenerative Electrochemical Microfluidic Biosensors for Continual Monitoring of Cell Secretomes

Development of an efficient sensing platform capable of continual monitoring of biomarkers is needed to assess the functionality of the in vitro organoids and to evaluate their biological responses toward pharmaceutical compounds or chemical species over extended periods of time. Here, a novel label-free microfluidic electrochemical (EC) biosensor with a unique built-in on-chip regeneration capability for continual measurement of cell-secreted soluble biomarkers from an organoid culture in a fully automated manner without attenuating the sensor sensitivity is reported. The microfluidic EC biosensors are integrated with a human liver-on-a-chip platform for continual monitoring of the metabolic activity of the organoids by measuring the levels of secreted biomarkers for up to 7 d, where the metabolic activity of the organoids is altered by a systemically applied drug. The variations in the biomarker levels are successfully measured by the microfluidic regenerative EC biosensors and agree well with cellular viability and enzyme-linked immunosorbent assay analyses, validating the accuracy of the unique sensing platform. It is believed that this versatile and robust microfluidic EC biosensor that is capable of automated and continual detection of soluble biomarkers will find widespread use for long-term monitoring of human organoids during drug toxicity studies or efficacy assessments of in vitro platforms.

Automated, Multiplexed Electrical Impedance Spectroscopy Platform for Continuous Monitoring of Microtissue Spheroids

Microtissue spheroids in microfluidic devices are increasingly used to establish novel in vitro organ models of the human body. As the spheroids are comparably sizable, it is difficult to monitor larger numbers of them by optical means. Therefore, electrical impedance spectroscopy (EIS) emerges as a viable alternative to probing spheroid properties. Current spheroid EIS systems are, however, not suitable for investigating multiple spheroids in parallel over extended time in an automated fashion. Here we address this issue by presenting an automated, multiplexed EIS (AMEIS) platform for impedance analysis in a microfluidic setting. The system was used to continuously monitor the effect of the anticancer drug fluorouracil (5-FU) on HCT116 cancer spheroids. Simultaneous EIS monitoring of up to 15 spheroids was performed in parallel over 4 days at a temporal resolution of 2 min without any need for pumps. The measurements were continuous in nature, and the setup was kept in a standard incubator under controlled conditions during the measurements. A baseline normalization method to improve robustness and to reduce the influence of slow changes in the medium conductivity on the spheroid EIS readings has been developed and validated by experiments and means of a finite-element model. The same method and platform was then used for online monitoring of cardiac spheroids. The beating frequency of each cardiac spheroid could be read out in a completely automated fashion. The developed system constitutes a promising method for simultaneously evaluating drug impact and/or toxic effects on multiple microtissue spheroids.

Electrical Impedance Spectroscopy for Microtissue Spheroid Analysis in Hanging-Drop Networks

Electrical impedance spectroscopy (EIS) as a label free and noninvasive analysis method receives growing attention for monitoring three-dimensional tissue constructs. In this Article, we present the integration of an EIS readout function into the hanging-drop network platform, which has been designed for culturing microtissue spheroids in perfused multitissue configurations. Two pairs of microelectrodes have been implemented directly in the support of the hanging drops by using a small glass inlay inserted in the microfluidic structure. The pair of bigger electrodes is sensitive to the drop size and allows for drop size control over time. The pair of smaller electrodes is capable of monitoring, on the one hand, the size of microtissue spheroids to follow, for example, the growth of cancer microtissues, and, on the other hand, the beating of cardiac microtissues in situ. The presented results demonstrate the feasibility of an EIS readout within the framework of multifunctional hanging-drop networks.

Autonomous beating rate adaptation in human stem cell-derived cardiomyocytes

The therapeutic success of human stem cell-derived cardiomyocytes critically depends on their ability to respond to and integrate with the surrounding electromechanical environment. Currently, the immaturity of human cardiomyocytes derived from stem cells limits their utility for regenerative medicine and biological research. We hypothesize that biomimetic electrical signals regulate the intrinsic beating properties of cardiomyocytes. Here we show that electrical conditioning of human stem cell-derived cardiomyocytes in three-dimensional culture promotes cardiomyocyte maturation, alters their automaticity and enhances connexin expression. Cardiomyocytes adapt their autonomous beating rate to the frequency at which they were stimulated, an effect mediated by the emergence of a rapidly depolarizing cell population, and the expression of hERG. This rate-adaptive behaviour is long lasting and transferable to the surrounding cardiomyocytes. Thus, electrical conditioning may be used to promote cardiomyocyte maturation and establish their automaticity, with implications for cell-based reduction of arrhythmia during heart regeneration.

Three-dimensional cell culture systems and their applications in drug discovery and cell-based biosensors

Three-dimensional (3D) cell culture systems have gained increasing interest in drug discovery and tissue engineering due to their evident advantages in providing more physiologically relevant information and more predictive data for in vivo tests. In this review, we discuss the characteristics of 3D cell culture systems in comparison to the two-dimensional (2D) monolayer culture, focusing on cell growth conditions, cell proliferation, population, and gene and protein expression profiles. The innovations and development in 3D culture systems for drug discovery over the past 5 years are also reviewed in the article, emphasizing the cellular response to different classes of anticancer drugs, focusing particularly on similarities and differences between 3D and 2D models across the field. The progression and advancement in the application of 3D cell cultures in cell-based biosensors is another focal point of this review.

Quantitative analysis of spherical microbubble cavity array formation in thermally cured polydimethylsiloxane for use in cell sorting applications

Microbubbles are spherical cavities formed in thermally cured polydimethylsiloxane (PDMS) using the gas expansion molding technique. Microbubble cavity arrays are generated by casting PDMS over a silicon wafer mold containing arrays of deep etched pits. To be useful in various high throughput cell culture and sorting applications it is imperative that uniform micron-sized cavities can be formed over large areas (in(2)). This paper provides an in-depth quantitative analysis of the fabrication parameters that effect the microbubble cavity formation efficiency and size. These include (1) the hydrophobic coating of the mold, (2) the mold pit dimensions, (3) the spatial arrangement of the pit openings, (4) the curing temperature of PDMS pre-polymer, (5) PDMS thickness, and (6) the presence and composition of residual gas in the PDMS pre-polymer mixture. Results suggest that the principles of heterogeneous nucleation and gas diffusion govern microbubble cavity formation, and that surface tension prevents detachment of the vapor bubble that forms in the PDMS over the pit. Paramerters are defined that enable the fabrication of large format arrays with uniform cavity size over 6 in(2) with a coefficient-of-variation <10 %. The architecture of the microbubble cavity is uniquely advantageous for cell culture. Large format arrays provide a highly versatile system that can be adapted for use in various high-throughput cell sorting applications. Herein, we demonstrate the use of microbubble cavity arrays to dissect the cellular heterogeneity that exists in a tumorigenic cutaneous squamous cell carcinoma cell line at the single cell level.

Direct chemosensitivity monitoring ex vivo on undissociated melanoma tumor tissue by impedance spectroscopy

Stage III/IV melanoma remains incurable in most cases due to chemotherapeutic resistance. Thus, predicting and monitoring chemotherapeutic responses in this setting offer great interest. To overcome limitations of existing assays in evaluating the chemosensitivity of dissociated tumor cells, we developed a label-free monitoring system to directly analyze the chemosensitivity of undissociated tumor tissue. Using a preparation of tumor micro-fragments (TMF) established from melanoma biopsies, we characterized the tissue organization and biomarker expression by immunocytochemistry. Robust generation of TMF was established successfully and demonstrated on a broad range of primary melanoma tumors and tumor metastases. Organization and biomarker expression within the TMF were highly comparable with tumor tissue, in contrast to dissociated, cultivated tumor cells. Using isolated TMF, sensitivity to six clinically relevant chemotherapeutic drugs (dacarbazine, doxorubicin, paclitaxel, cisplatin, gemcitabine, and treosulfan) was determined by impedance spectroscopy in combination with a unique microcavity array technology we developed. In parallel, comparative analyses were performed on monolayer tumor cell cultures. Lastly, we determined the efficacy of chemotherapeutic agents on TMF by impedance spectroscopy to obtain individual chemosensitivity patterns. Our results demonstrated nonpredictable differences in the reaction of tumor cells to chemotherapy in TMF by comparison with dissociated, cultivated tumor cells. Our direct impedimetric analysis of melanoma biopsies offers a direct ex vivo system to more reliably predict patient-specific chemosensitivity patterns and to monitor antitumor efficacy.

A novel 96-well multielectrode array based impedimetric monitoring platform for comparative drug efficacy analysis on 2D and 3D brain tumor cultures

Aggressive cancer entities like neuroblastoma and glioblastoma multiforme are still difficult to treat and have discouraging prognosis in malignant stage. Since each tumor has its own characteristics concerning the sensitivity towards different chemotherapeutics and moreover, can obtain resistance, the development of novel chemotherapeutics with a broad activity spectrum, high efficacy and minimum side effects is a continuous process. Sophisticated in vitro assays for comprehensive prediction of in vivo drug efficacy and side effects represent an actual bottleneck in the drug development process. In this context, we developed a novel in vitro 2D and 3D multiwell-multielectrode device for drug efficacy monitoring based on direct real-time impedance spectroscopy measurement in combination with our unique 96-well multielectrode arrays and microcavity arrays. For demonstration, we used three neuro- and glioblastoma cell lines that were cultured as monolayer and multicellular tumor spheroids for recapitulating in vivo conditions. Using our novel 96-well multielectrode array based system it was possible to detect time and concentration dependent responses concerning treatment with doxorubicin, etoposide and vincristine. While all tested chemotherapeutics revealed high potency for apoptosis induction in neuroblastoma cells, etoposide was ineffective for glioblastoma cell lines. Determination of IC50 values allowed us to compare drug efficacy in 2D and 3D culture models and moreover, revealed chemotherapeutic and tumor cell line specific activity patterns. These pharmacokinetic patterns are of great interest in the context of preclinical drug development. Thus, impedance spectroscopy based monitoring systems could be used for the fast in vitro based in vivo prediction of novel anti-tumor drugs.

Quantitative impedimetric NPY-receptor activation monitoring and signal pathway profiling in living cells

Label-free and non-invasive monitoring of receptor activation and identification of the involved signal pathways in living cells is an ongoing analytic challenge and a great opportunity for biosensoric systems. In this context, we developed an impedance spectroscopy-based system for the activation monitoring of NPY-receptors in living cells. Using an optimized interdigital electrode array for sensitive detection of cellular alterations, we were able for the first time to quantitatively detect the NPY-receptor activation directly without a secondary or enhancer reaction like cAMP-stimulation by forskolin. More strikingly, we could show that the impedimetric based NPY-receptor activation monitoring is not restricted to the Y1-receptor but also possible for the Y2- and Y5-receptor. Furthermore, we could monitor the NPY-receptor activation in different cell lines that natively express NPY-receptors and proof the specificity of the observed impedimetric effect by agonist/antagonist studies in recombinant NPY-receptor expressing cell lines. To clarify the nature of the observed impedimetric effect we performed an equivalent circuit analysis as well as analyzed the role of cell morphology and receptor internalization. Finally, an antagonist based extensive molecular signal pathway analysis revealed small alterations of the actin cytoskeleton as well as the inhibition of at least L-type calcium channels as major reasons for the observed NPY-induced impedance increase. Taken together, our novel impedance spectroscopy based NPY-receptor activation monitoring system offers the opportunity to identify signal pathways as well as for novel versatile agonist/antagonist screening systems for identification of novel therapeutics in the field of obesity and cancer.

Towards an Automated MEMS-based Characterization of Benign and Cancerous Breast Tissue using Bioimpedance Measurements

Micro-Electro-Mechanical-Systems (MEMS) are desirable for use within medical diagnostics because of their capacity to manipulate and analyze biological materials at the microscale. Biosensors can be incorporated into portable lab-on-a-chip devices to quickly and reliably perform diagnostics procedure on laboratory and clinical samples. In this paper, electrical impedance-based measurements were used to distinguish between benign and cancerous breast tissues using microchips in a real-time and label-free manner. Two different microchips having inter-digited electrodes (10 µm width with 10 µm spacing and 10 µm width with 30 µm spacing) were used for measuring the impedance of breast tissues. The system employs Agilent E4980A precision impedance analyzer. The impedance magnitude and phase were collected over a frequency range of 100 Hz to 2 MHz. The benign group and cancer group showed clearly distinguishable impedance properties. At 200 kHz, the difference in impedance of benign and cancerous breast tissue was significantly higher (3110 Ω) in the case of microchips having 10 µm spacing compared to microchip having 30 µm spacing (568 Ω).

A novel 3D label-free monitoring system of hES-derived cardiomyocyte clusters: a step forward to in vitro cardiotoxicity testing

Unexpected adverse effects on the cardiovascular system remain a major challenge in the development of novel active pharmaceutical ingredients (API). To overcome the current limitations of animal-based in vitro and in vivo test systems, stem cell derived human cardiomyocyte clusters (hCMC) offer the opportunity for highly predictable pre-clinical testing. The three-dimensional structure of hCMC appears more representative of tissue milieu than traditional monolayer cell culture. However, there is a lack of long-term, real time monitoring systems for tissue-like cardiac material. To address this issue, we have developed a microcavity array (MCA)-based label-free monitoring system that eliminates the need for critical hCMC adhesion and outgrowth steps. In contrast, feasible field potential derived action potential recording is possible immediately after positioning within the microcavity. Moreover, this approach allows extended observation of adverse effects on hCMC. For the first time, we describe herein the monitoring of hCMC over 35 days while preserving the hCMC structure and electrophysiological characteristics. Furthermore, we demonstrated the sensitive detection and quantification of adverse API effects using E4031, doxorubicin, and noradrenaline directly on unaltered 3D cultures. The MCA system provides multi-parameter analysis capabilities incorporating field potential recording, impedance spectroscopy, and optical read-outs on individual clusters giving a comprehensive insight into induced cellular alterations within a complex cardiac culture over days or even weeks.

Impedance spectroscopy--an outstanding method for label-free and real-time discrimination between brain and tumor tissue in vivo

Until today, brain tumors especially glioblastoma are difficult to treat and therefore, results in a poor survival rate of 0-14% over five years. To overcome this problem, the development of novel therapeutics as well as optimization of neurosurgical procedures to remove the tumor tissue are subject of intensive research. The main problem of the tumor excision, as the primary clinical intervention is the diffuse infiltration of the tumor cells in unaltered brain tissue that complicates the complete removal of residual tumor cells. In this context, we are developing novel approaches for the label-free discrimination between tumor tissue and unaltered brain tissue in real-time during the surgical process. Using our impedance spectroscopy-based measurement system in combination with flexible microelectrode arrays we could successfully demonstrate the discrimination between a C6-glioma and unaltered brain tissue in an in vivo rat model. The analysis of the impedance spectra revealed specific impedance spectrum shape characteristics of physiologic neuronal tissue in the frequency range of 10-500 kHz that were significantly different from the tumor tissue. Moreover, we used an adapted equivalent circuit model to get a deeper understanding for the nature of the observed effects. The impedimetric label-free and real-time discrimination of tumor from unaltered brain tissue offers the possibility for the implementation in surgical instruments to support surgeons to decide, which tissue areas should be removed and which should be remained.

Induced tauopathy in a novel 3D-culture model mediates neurodegenerative processes: a real-time study on biochips

Tauopathies including Alzheimer's disease represent one of the major health problems of aging population worldwide. Therefore, a better understanding of tau-dependent pathologies and consequently, tau-related intervention strategies is highly demanded. In recent years, several tau-focused therapies have been proposed with the aim to stop disease progression. However, to develop efficient active pharmaceutical ingredients for the broad treatment of Alzheimer's disease patients, further improvements are necessary for understanding the detailed neurodegenerative processes as well as the mechanism and side effects of potential active pharmaceutical ingredients (API) in the neuronal system. In this context, there is a lack of suitable complex in vitro cell culture models recapitulating major aspects of taupathological degenerative processes in sufficient time and reproducible manner.Herewith, we describe a novel 3D SH-SY5Y cell-based, tauopathy model that shows advanced characteristics of matured neurons in comparison to monolayer cultures without the need of artificial differentiation promoting agents. Moreover, the recombinant expression of a novel highly pathologic fourfold mutated human tau variant lead to a fast and emphasized degeneration of neuritic processes. The neurodegenerative effects could be analyzed in real time and with high sensitivity using our unique microcavity array-based impedance spectroscopy measurement system. We were able to quantify a time- and concentration-dependent relative impedance decrease when Alzheimer's disease-like tau pathology was induced in the neuronal 3D cell culture model. In combination with the collected optical information, the degenerative processes within each 3D-culture could be monitored and analyzed. More strikingly, tau-specific regenerative effects caused by tau-focused active pharmaceutical ingredients could be quantitatively monitored by impedance spectroscopy.Bringing together our novel complex 3D cell culture taupathology model and our microcavity array-based impedimetric measurement system, we provide a powerful tool for the label-free investigation of tau-related pathology processes as well as the high content analysis of potential active pharmaceutical ingredient candidates.

An integrated enzyme-linked immunosorbent assay system with an organic light-emitting diode and a charge-coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.

Electromagnetic exposure of scaffold-free three-dimensional cell culture systems

In recent years, a number of in vitro studies have reported on the possible athermal effects of electromagnetic exposure on biological tissue. Typically, this kind of study is performed on monolayers of primary cells or cell lines. However, two-dimensional cell layer systems lack physiological relevance since cells in vivo are organized in a three-dimensional (3D) architecture. In monolayer studies, cell-cell and cell-ECM interactions obviously differ from live tissue and scale-ups of experimental results to in vivo systems should be considered carefully. To overcome this problem, we used a scaffold-free 3D cell culture system, suitable for the exploration of electrophysiological effects due to electromagnetic fields (EMF) at 900 MHz. Dissociated cardiac myocytes were reaggregated into cellular spheres by constant rotation, and non-invasive extracellular recordings of these so-called spheroids were performed with microelectrode arrays (MEA). In this study, 3D cell culture systems were exposed to pulsed EMFs in a stripline setup. We found that inhomogeneities in the EMF due to electrodes and conducting lines of the MEA chip had only a minor influence on the field distribution in the spheroid if the exposure parameters were chosen carefully.

Microfluidic cell culture systems for drug research

In pharmaceutical research, an adequate cell-based assay scheme to efficiently screen and to validate potential drug candidates in the initial stage of drug discovery is crucial. In order to better predict the clinical response to drug compounds, a cell culture model that is faithful to in vivo behavior is required. With the recent advances in microfluidic technology, the utilization of a microfluidic-based cell culture has several advantages, making it a promising alternative to the conventional cell culture methods. This review starts with a comprehensive discussion on the general process for drug discovery and development, the role of cell culture in drug research, and the characteristics of the cell culture formats commonly used in current microfluidic-based, cell-culture practices. Due to the significant differences in several physical phenomena between microscale and macroscale devices, microfluidic technology provides unique functionality, which is not previously possible by using traditional techniques. In a subsequent section, the niches for using microfluidic-based cell culture systems for drug research are discussed. Moreover, some critical issues such as cell immobilization, medium pumping or gradient generation in microfluidic-based, cell-culture systems are also reviewed. Finally, some practical applications of microfluidic-based, cell-culture systems in drug research particularly those pertaining to drug toxicity testing and those with a high-throughput capability are highlighted.

Real-time electrical impedance detection of cellular activities of oral cancer cells

In this study, the electric cell-substrate impedance sensing (ECIS) system was used to study the cellular activities of oral squamous cell carcinoma (OSCC) cells in a real-time and label-free manner. Various cellular activities, including cell adhesion, spreading, proliferation, and drug-induced apoptosis and inhibition of apoptosis, were monitored. A linear relationship was found between the impedance-based cell index and the cell number in the range of 3500 to 35,000 cells/well. Anti-cancer drug-cisplatin-induced OSCC cell apoptosis at the minimal concentration of 5 microM after 20 h of treatment and followed a linear dose-dependent manner in the concentration range from 10 microM to 25 microM. The inhibition of cisplatin-induced apoptosis by the carcinogen, nicotine, at concentrations from 0.1 microM to 10 microM was monitored. The most significant inhibitory effect of nicotine on cisplatin-induced apoptosis was observed at concentrations of 0.5-1 microM. The results obtained with impedance method correlated well with microscopic imaging analysis of cellular morphology and cell viability analysis. This study demonstrated that the impedance-based method can provide real-time information about the cellular activity of viable cells and detect drug-induced cellular activities much earlier than commonly used cell-based image analysis. This impedance-based method has the potential to provide a useful analytical approach for cancer research.