Tumors on chips: oncology meets microfluidics

Progress and application of lung-on-a-chip for lung cancer

Lung cancer is a malignant tumour with the highest incidence and mortality worldwide. Clinically effective therapy strategies are underutilized owing to the lack of efficient models for evaluating drug response. One of the main reasons for failure of anticancer drug therapy is development of drug resistance. Anticancer drugs face severe challenges such as poor biodistribution, restricted solubility, inadequate absorption, and drug accumulation. In recent years, "organ-on-a-chip" platforms, which can directly regulate the microenvironment of biomechanics, biochemistry and pathophysiology, have been developed rapidly and have shown great potential in clinical drug research. Lung-on-a-chip (LOC) is a new 3D model of bionic lungs with physiological functions created by micromachining technology on microfluidic chips. This approach may be able to partially replace animal and 2D cell culture models. To overcome drug resistance, LOC realizes personalized prediction of drug response by simulating the lung-related microenvironment in vitro, significantly enhancing therapeutic effectiveness, bioavailability, and pharmacokinetics while minimizing side effects. In this review, we present an overview of recent advances in the preparation of LOC and contrast it with earlier in vitro models. Finally, we describe recent advances in LOC. The combination of this technology with nanomedicine will provide an accurate and reliable treatment for preclinical evaluation.

Brachytherapy on-a-chip: a clinically-relevant approach for radiotherapy testing in 3d biology

We describe the first microfluidic device for in vitro testing of brachytherapy (BT), with applications in translational cancer research. Our PDMS-made BT-on-chip system allows highly precise manual insertion of clinical BT seeds, reliable dose calculation using standard clinically-used TG-43 formalism and easy culture of naturally hypoxic spheroids in less than 3 days, thereby increasing the translational potential of the device. As the BT-on-chip platform is designed to be versatile, we showcase three different gold-standard post-irradiation bioassays and recapitulate, for the first time on-chip, key clinical observations such as dose rate effect and hypoxia-induced radioresistance. Our results suggest that BT-on-chip can be used to safely and efficiently integrate BT and radiotherapy to translational research and drug development pipelines, without expensive equipment or complex workflows.

Human Intestinal Organoids and Microphysiological Systems for Modeling Radiotoxicity and Assessing Radioprotective Agents

Radiotherapy is a commonly employed treatment for colorectal cancer, yet its radiotoxicity-related impact on healthy tissues raises significant health concerns. This highlights the need to use radioprotective agents to mitigate these side effects. This review presents the current landscape of human translational radiobiology, outlining the limitations of existing models and proposing engineering solutions. We delve into radiotherapy principles, encompassing mechanisms of radiation-induced cell death and its influence on normal and cancerous colorectal cells. Furthermore, we explore the engineering aspects of microphysiological systems to represent radiotherapy-induced gastrointestinal toxicity and how to include the gut microbiota to study its role in treatment failure and success. This review ultimately highlights the main challenges and future pathways in translational research for pelvic radiotherapy-induced toxicity. This is achieved by developing a humanized in vitro model that mimics radiotherapy treatment conditions. An in vitro model should provide in-depth analyses of host-gut microbiota interactions and a deeper understanding of the underlying biological mechanisms of radioprotective food supplements. Additionally, it would be of great value if these models could produce high-throughput data using patient-derived samples to address the lack of human representability to complete clinical trials and improve patients' quality of life.

Numerical simulation of fluid flow mixing in flow-focusing microfluidic devices

A numerical simulation through computational fluid dynamics is presented on the fluid flow mixing in a flow-focusing microfluidic device with three inlet channels confluence angles of 45, 67.5, and 90°. The effect of various parameters such as aspect ratio (0.5, 1, and 1.5), mixing channel length (1–4 mm), and Reynolds number (1–20) on the mixing efficiency, and the pressure drop are evaluated. The results demonstrate that the increase in mixing efficiency results from an increase in the Reynolds number and aspect ratio for all the angles. In addition, an increase in the pressure drop due to an increase in the Reynolds number and a decrease in the aspect ratio is observed. A longer length of the mixing channel indicates a higher mixing efficiency. The mixing efficiency is more suitable at an angle of 45° among the applied angles in terms of the operational and geometric parameters due to an increase in the contact surface of the flows at the inlet channels junction since the mixing index range is between 0.54 and 1 by varying the mentioned parameters.

Digital Microfluidics with an On-Chip Drug Dispenser for Single or Combinational Drug Screening

Rapid and accurate cancer drug screening is of great importance in precision medicine. However, the limited amount of tumor biopsy samples has hindered the application of traditional drug screening methods with microwell plates for individual patients. A microfluidic system provides an ideal platform for handling trace amounts of samples. This emerging platform has a good role in nucleic acid-related and cell related assays. Nevertheless, convenient drug dispensing remains a challenge for clinical on-chip cancer drug screening. Similar sized droplets are merged to add drugs for a desired screened concentration which significantly complicated the on-chip drug dispensing protocols. Here, we introduce a novel digital microfluidic system with a specially structured electrode (a drug dispenser) to dispense drugs by droplet electro-ejection under a high-voltage actuation signal, which can be conveniently adjusted by external electric controls. With this system, the screened drug concentrations span up to four orders of magnitude with small sample consumption. Various amounts of drugs can be delivered to the cell sample with desired amount in a flexible electric control. Moreover, single drug or combinatorial multidrug on-chip screening can be readily achieved. The drug response of normal MCF-10A breast cells and MDA-MB-231 breast tumor cells to two chemotherapeutic substances, cisplatin (Cis) and epirubicin (EP), was tested individually and in combination for proof-of-principle verification. The comparable on-chip and off-chip results confirmed the feasibility of our innovative DMF system for cancer drug screening.

Organs-on-Chips Platforms Are Everywhere: A Zoom on Biomedical Investigation

Over the decades, conventional in vitro culture systems and animal models have been used to study physiology, nutrient or drug metabolisms including mechanical and physiopathological aspects. However, there is an urgent need for Integrated Testing Strategies (ITS) and more sophisticated platforms and devices to approach the real complexity of human physiology and provide reliable extrapolations for clinical investigations and personalized medicine. Organ-on-a-chip (OOC), also known as a microphysiological system, is a state-of-the-art microfluidic cell culture technology that sums up cells or tissue-to-tissue interfaces, fluid flows, mechanical cues, and organ-level physiology, and it has been developed to fill the gap between in vitro experimental models and human pathophysiology. The wide range of OOC platforms involves the miniaturization of cell culture systems and enables a variety of novel experimental techniques. These range from modeling the independent effects of biophysical forces on cells to screening novel drugs in multi-organ microphysiological systems, all within microscale devices. As in living biosystems, the development of vascular structure is the salient feature common to almost all organ-on-a-chip platforms. Herein, we provide a snapshot of this fast-evolving sophisticated technology. We will review cutting-edge developments and advances in the OOC realm, discussing current applications in the biomedical field with a detailed description of how this technology has enabled the reconstruction of complex multi-scale and multifunctional matrices and platforms (at the cellular and tissular levels) leading to an acute understanding of the physiopathological features of human ailments and infections in vitro.

Droplet transportation by adjusting the temporal phase shift of surface acoustic waves in the exciter-exciter mode

Droplet actuation using Surface Acoustic Wave (SAW) technology has been widely employed in 'lab-on-a-chip' applications, such as for on-chip Polymerase Chain Reactions. The current strategy uses the exciter-absorber mode (exciting a single InterDigital Transducer, IDT) to form a pure Travelling Surface Acoustic Wave (TSAW) and to actuate the droplet, where the velocity and direction of the droplet can be adjusted by controlling the on-off and amplitude of the excitation signals applied to a pair of IDTs. Herein, in a way that is different from using the exciter-absorber mode, we propose a method of actuating droplets by using the exciter-exciter mode (exciting a pair of IDTs simultaneously), where the velocity and directional adjustment of the droplet can be realized by changing only one excitation parameter for the signals (the temporal phase shift, θ), and the droplet velocity can also be significantly improved. Specifically, we report for the first time the equation of the vibration of the mixed waves (TSAW and Standing Surface Acoustic Wave (SSAW)) formed on the substrate surface using the exciter-exciter mode. This is analyzed theoretically, where it is shown in this work that the amplitude and direction of the TSAW component of the mixed waves can be adjusted by changing θ. Following that, the velocity and directional adjustment of the droplet has been realized by changing θ and the improvement of the droplet velocity has been verified on a one-dimensional SAW device, using this exciter-exciter mode. Moreover a series of experiments on droplet transportation, along different trajectories in an x-y plane, has been carried out using a two-dimensional SAW device and this has demonstrated the effectiveness of the θ changing-based approach. Here this exciter-exciter mode provides an alternative method for the transportation of droplets in 'lab-on-a-chip' applications.

Radiotherapy on-chip: microfluidics for translational radiation oncology

The clinical importance of radiotherapy in the treatment of cancer patients justifies the development and use of research tools at the fundamental, pre-clinical, and ultimately clinical levels, to investigate their toxicities and synergies with systemic agents on relevant biological samples. Although microfluidics has prompted a paradigm shift in drug discovery in the past two decades, it appears to have yet to translate to radiotherapy research. However, the materials, dimensions, design versatility and multiplexing capabilities of microfluidic devices make them well-suited to a variety of studies involving radiation physics, radiobiology and radiotherapy. This review will present the state-of-the-art applications of microfluidics in these fields and specifically highlight the perspectives offered by radiotherapy on-a-chip in the field of translational radiobiology and precision medicine. This body of knowledge can serve both the microfluidics and radiotherapy communities by identifying potential collaboration avenues to improve patient care.

Production of doxorubicin-loaded PCL nanoparticles through a flow-focusing microfluidic device: encapsulation efficacy and drug release

The present study shows a facile route for producing doxorubicin (DOX)-loaded polycaprolactone (PCL) nanoparticles using a microfluidic device with a flow-focusing platform in a single step. Indeed, the evaluation of the performance of the flow-focusing microfluidic device for the preparation of DOX-loaded PCL (DOX/PCL) nanoparticles with a uniform size distribution and high encapsulation efficiency (EE) by applying the liquid non-solvent precipitation process is very important. Accordingly, the physicochemical characteristics of the DOX/PCL nanoparticles such as their mean size, polydispersity index (PDI), and EE were investigated by studying different parameters such as the flow rate ratio (FRR) and DOX concentration. Also, the release study was carried out at two pH of 5.5 and 7.4. The mean size of DOX/PCL nanoparticles achieved was in the range of 120-320 nm with a PDI ≤ 0.29 and EE between 48% and 87%. Moreover, the release profile of DOX/PCL nanoparticles was sustained for 10 days (≤66%) at pH 7.4. This means that the production process can result in a high EE and low release of the DOX drug.

Angiogenic Sprouting Dynamics Mediated by Endothelial-Fibroblast Interactions in Microfluidic Systems

Angiogenesis, the development of new blood vessels from existing vasculature, is a key process in normal development and pathophysiology. In vitro models are necessary for investigating mechanisms of angiogenesis and developing antiangiogenic therapies. Microfluidic cell culture models of angiogenesis are favored for their ability to recapitulate 3D tissue structures and control spatiotemporal aspects of the microenvironments. To capture the angiogenesis process, microfluidic models often include endothelial cells and a fibroblast component. However, the influence of fibroblast organization on resulting angiogenic behavior remains unclear. Here a comparative study of angiogenic sprouting on a microfluidic chip induced by fibroblasts in 2D monolayer, 3D dispersed, and 3D spheroid culture formats, is conducted. Vessel morphology and sprout distribution for each configuration are measured, and these observations are correlated with measurements of secreted factors and numerical simulations of diffusion gradients. The results demonstrate that angiogenic sprouting varies in response to fibroblast organization with correlating variations in secretory profile and secreted factor gradients across the microfluidic device. This study is anticipated to shed light on how sprouting dynamics are mediated by fibroblast configuration such that the microfluidic cell culture design process includes the selection of a fibroblast component where the effects are known and leveraged.

Recent progress in cytometric technologies and their applications in ecotoxicology and environmental risk assessment

Environmental toxicology focuses on identifying and predicting impact of potentially toxic anthropogenic chemicals on biosphere at various levels of biological organization. Presently there is a significant drive to gain deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity. Most notable is increased focus on elucidation of cellular-response networks, interactomes, and greater implementation of cell-based biotests using high-throughput procedures, while at the same time decreasing the reliance on standard animal models used in ecotoxicity testing. This is aimed at discovery and interpretation of molecular pathways of ecotoxicity at large scale. In this regard, the applications of cytometry are perhaps one of the most fundamental prospective analytical tools for the next generation and high-throughput ecotoxicology research. The diversity of this modern technology spans flow, laser-scanning, imaging, and more recently, Raman as well as mass cytometry. The cornerstone advantages of cytometry include the possibility of multi-parameter measurements, gating and rapid analysis. Cytometry overcomes, thus, limitations of traditional bulk techniques such as spectrophotometry or gel-based techniques that average the results from pooled cell populations or small model organisms. Novel technologies such as cell imaging in flow, laser scanning cytometry, as well as mass cytometry provide innovative and tremendously powerful capabilities to analyze cells, tissues as well as to perform in situ analysis of small model organisms. In this review, we outline cytometry as a tremendously diverse field that is still vastly underutilized and often largely unknown in environmental sciences. The main motivation of this work is to highlight the potential and wide-reaching applications of cytometry in ecotoxicology, guide environmental scientists in the technological aspects as well as popularize its broader adoption in environmental risk assessment.

Light-Addressable Actuator-Sensor Platform for Monitoring and Manipulation of pH Gradients in Microfluidics: A Case Study with the Enzyme Penicillinase

The feasibility of light-addressed detection and manipulation of pH gradients inside an electrochemical microfluidic cell was studied. Local pH changes, induced by a light-addressable electrode (LAE), were detected using a light-addressable potentiometric sensor (LAPS) with different measurement modes representing an actuator-sensor system. Biosensor functionality was examined depending on locally induced pH gradients with the help of the model enzyme penicillinase, which had been immobilized in the microfluidic channel. The surface morphology of the LAE and enzyme-functionalized LAPS was studied by scanning electron microscopy. Furthermore, the penicillin sensitivity of the LAPS inside the microfluidic channel was determined with regard to the analyte’s pH influence on the enzymatic reaction rate. In a final experiment, the LAE-controlled pH inhibition of the enzyme activity was monitored by the LAPS.

Colorectal Adenocarcinoma Cell Culture in a Microfluidically Controlled Environment with a Static Molecular Gradient of Polyphenol

To study the simultaneous effect of the molecular gradient of polyphenols (curcumin, trans-resveratrol, and wogonin) and biological factors released from tumor cells on apoptosis of adjacent cells, a novel microfluidic system was designed and manufactured. The small height/volume of microfluidic culture chambers and static conditions allowed for establishing the local microenvironment and maintaining undisturbed concentration profiles of naturally secreted from cells biochemical factors. In all trials, we observe that these conditions significantly affect cell viability by stimulating cell apoptosis at lower concentrations of polyphenols than in traditional multiwell cultures. The observed difference varied between 20.4-87.8% for curcumin, 11.0-37.5% for resveratrol, and 21.7-62.2% for wogonin. At low concentrations of polyphenols, the proapoptotic substances released from adjacent cells, like protein degradation products, significantly influence cell viability. The mean increase in cell mortality was 38.3% for microfluidic cultures. Our research has also confirmed that the gradient microsystem is useful in routine laboratory tests in the same way as a multiwell plate and may be treated as its replacement in the future. We elaborated the new repetitive procedures for cell culture and tests in static gradient conditions, which may become a gold standard of new drug investigations in the future.

Microfluidic Reconstitution of Tumor Microenvironment for Nanomedical Applications

Nanoparticles have an extensive range of diagnostic and therapeutic applications in cancer treatment. However, their current clinical translation is slow, mainly due to the failure to develop preclinical evaluation techniques that can draw similar conclusions to clinical outcomes by adequately mimicking nanoparticle behavior in complicated tumor microenvironments (TMEs). Microfluidic methods offer significant advantages over conventional in vitro methods to resolve these challenges by recapitulating physiological cues of the TME such as the extracellular matrix, shear stress, interstitial flow, soluble factors, oxygen, and nutrient gradients. The methods are capable of de-coupling microenvironmental features, spatiotemporal controlling of experimental sequences, and high throughput readouts in situ. This progress report highlights the recent achievements of microfluidic models to reconstitute the physiological microenvironment, especially for nanomedical tools for cancer treatment.

Prostate cancer and microfluids

Microfluidic systems aim to detect sample matter quickly with high sensitivity and resolution, on a small scale. With its increased use in medicine, the field is showing significant promise in prostate cancer diagnosis and management due, in part, to its ability to offer point-of-care testing. This review highlights some of the research that has been undertaken in respect of prostate cancer and microfluidics. Firstly, this review considers the diagnosis of prostate cancer through use of microfluidic systems and analyses the detection of prostate specific antigen, proteins, and circulating tumor cells to highlight the scope of current advancements. Secondly, this review analyses progressions in the understanding of prostate cancer physiology and considers techniques used to aid treatment of prostate cancer, such as the creation of a micro-environment. Finally, this review highlights potential future roles of microfluidics in assisting prostate cancer, such as in exosomal analysis. In conclusion, this review shows the vast scope and application of microfluidic systems and how these systems will ensure advancements to future prostate cancer management.

Microsystems for biofilm characterization and sensing - A review

Biofilms are the primary cause of clinical bacterial infections and are impervious to typical amounts of antibiotics, necessitating very high doses for elimination. Therefore, it is imperative to have suitable methods for characterization to develop novel methods of treatment that can complement or replace existing approaches using significantly lower doses of antibiotics. This review presents some of the current developments in microsystems for characterization and sensing of bacterial biofilms. Initially, we review current standards for studying biofilms that are based on invasive and destructive end-point biofilm characterization. Additionally, biofilm formation and growth is extremely sensitive to various growth and environmental parameters that cause large variability in biofilms between repeated experiments, making it very difficult to compare experimental repeats and characterize the temporal characteristics of these organisms. To address these challenges, recent developments in the field have moved toward systems and miniature devices that can aid in the non-invasive characterization of bacterial biofilms. Our review focuses on several types of microsystems for biofilm evaluation including optical, electrochemical, and mechanical systems. This review will show how these devices can lead to better understanding of the physiology and function of these communities of bacteria, which can eventually lead to the development of novel treatments that do not rely on high-dosage antibiotics.

CombiANT: Antibiotic interaction testing made easy

Antibiotic combination therapies are important for the efficient treatment of many types of infections, including those caused by antibiotic-resistant pathogens. Combination treatment strategies are typically used under the assumption that synergies are conserved across species and strains, even though recent results show that the combined treatment effect is determined by specific drug–strain interactions that can vary extensively and unpredictably, both between and within bacterial species. To address this problem, we present a new method in which antibiotic synergy is rapidly quantified on a case-by-case basis, allowing for improved combination therapy. The novel CombiANT methodology consists of a 3D-printed agar plate insert that produces defined diffusion landscapes of 3 antibiotics, permitting synergy quantification between all 3 antibiotic pairs with a single test. Automated image analysis yields fractional inhibitory concentration indices (FICis) with high accuracy and precision. A technical validation with 3 major pathogens, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, showed equivalent performance to checkerboard methodology, with the advantage of strongly reduced assay complexity and costs for CombiANT. A synergy screening of 10 antibiotic combinations for 12 E. coli urinary tract infection (UTI) clinical isolates illustrates the need for refined combination treatment strategies. For example, combinations of trimethoprim (TMP) + nitrofurantoin (NIT) and TMP + mecillinam (MEC) showed synergy, but only for certain individual isolates, whereas MEC + NIT combinations showed antagonistic interactions across all tested strains. These data suggest that the CombiANT methodology could allow personalized clinical synergy testing and large-scale screening. We anticipate that CombiANT will greatly facilitate clinical and basic research of antibiotic synergy.

Existing methods for identifying efficient combinations of antibiotics are time-consuming and costly, restricting their use in clinics and research. This study describes the novel CombiANT methodology, which uses defined diffusion landscapes of three antibiotics to permit rapid and low-cost synergy quantification between all antibiotic pairs.

The Use of Microfluidic Platforms to Probe the Mechanism of Cancer Cell Extravasation

Powerful experimental tools have contributed a wealth of novel insight into cancer etiology from the organ to the subcellular levels. However, these advances in understanding have outpaced improvements in clinical outcomes. One possible reason for this shortcoming is the reliance on animal models that do not fully replicate human physiology. An alternative in vitro approach that has recently emerged features engineered microfluidic platforms to investigate cancer progression. These devices allow precise control over cellular components, extracellular constituents, and physical forces, while facilitating detailed microscopic analysis of the metastatic process. This review focuses on the recent use of microfluidic platforms to investigate the mechanism of cancer cell extravasation.

Dielectric Characterization and Separation Optimization of Infiltrating Ductal Adenocarcinoma via Insulator-Dielectrophoresis

The dielectrophoretic separation of infiltrating ductal adenocarcinoma cells (ADCs) from isolated peripheral blood mononuclear cells (PBMCs) in a ~1.4 mm long Y-shaped microfluidic channel with semi-circular insulating constrictions is numerically investigated. In this work, ADCs (breast cancer cells) and PBMCs' electrophysiological properties were iteratively extracted through the fitting of a single-shell model with the frequency-conductivity data obtained from AC microwell experiments. In the numerical computation, the gradient of the electric field required to generate the necessary dielectrophoretic force within the constriction zone was provided through the application of electric potential across the whole fluidic channel. By adjusting the difference in potentials between the global inlet and outlet of the fluidic device, the minimum (effective) potential difference with the optimum particle transmission probability for ADCs was found. The radius of the semi-circular constrictions at which the effective potential difference was swept to obtain the optimum constriction size was also obtained. Independent particle discretization analysis was also conducted to underscore the accuracy of the numerical solution. The numerical results, which were obtained by the integration of fluid flow, electric current, and particle tracing module in COMSOL v5.3, reveal that PBMCs can be maximally separated from ADCs using a DC power source of 50 V. The article also discusses recirculation or wake formation behavior at high DC voltages (>100 V) even when sorting of cells are achieved. This result is the first step towards the production of a supplementary or confirmatory test device to detect early breast cancer non-invasively.

Application of microfluidic technology in cancer research and therapy

Cancer is a heterogeneous disease that requires a multimodal approach to diagnose, manage and treat. A better understanding of the disease biology can lead to identification of novel diagnostic/prognostic biomarkers and the discovery of the novel therapeutics with the goal of improving patient outcomes. Employing advanced technologies can facilitate this, enabling better diagnostic and treatment for cancer patients. In this regard, microfluidic technology has emerged as a promising tool in the studies of cancer, including single cancer cell analysis, modeling angiogenesis and metastasis, drug screening and liquid biopsy. Microfluidic technologies have opened new ways to study tumors in the preclinical and clinical settings. In this chapter, we highlight novel application of this technology in area of fundamental, translational and clinical cancer research.

High-throughput analysis of cell-cell crosstalk in ad hoc designed microfluidic chips for oncoimmunology applications

Understanding the interactions between immune and cancer cells occurring within the tumor microenvironment is a prerequisite for successful and personalized anti-cancer therapies. Microfluidic devices, coupled to advanced microscopy systems and automated analytical tools, can represent an innovative approach for high-throughput investigations on immune cell-cancer interactions. In order to study such interactions and to evaluate how therapeutic agents can affect this crosstalk, we employed two ad hoc fabricated microfluidic platforms reproducing advanced 2D or 3D tumor immune microenvironments. In the first type of chip, we confronted the capacity of tumor cells embedded in Matrigel containing one drug or Matrigel containing a combination of two drugs to attract differentially immune cells, by fluorescence microscopy analyses. In the second chip, we investigated the migratory/interaction response of naïve immune cells to danger signals emanated from tumor cells treated with an immunogenic drug, by time-lapse microscopy and automated tracking analysis. We demonstrate that microfluidic platforms and their associated high-throughput computed analyses can represent versatile and smart systems to: (i) monitor and quantify the recruitment and interactions of the immune cells with cancer in a controlled environment, (ii) evaluate the immunogenic effects of anti-cancer therapeutic agents and (iii) evaluate the immunogenic efficacy of combinatorial regimens with respect to single agents.

Cancer-on-a-chip for Drug Screening

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The oncology pharmaceutical research spent a shocking amount of money on target validation and drug optimization in preclinical models because many oncology drugs fail during clinical trial phase III. One of the most important reasons for oncology drug failures in clinical trials may due to the poor predictive tool of existing preclinical models. Therefore, in cancer research and personalized medicine field, it is critical to improve the effectiveness of preclinical predictions of the drug response of patients to therapies and to reduce costly failures in clinical trials. Three dimensional (3D) tumor models combine micro-manufacturing technologies mimic critical physiologic parameters present in vivo, including complex multicellular architecture with multicellular arrangement and extracellular matrix deposition, packed 3D structures with cell–cell interactions, such as tight junctions, barriers to mass transport of drugs, nutrients and other factors, which are similar to in vivo tumor tissues. These systems provide a solution to mimic the physiological environment for improving predictive accuracy in oncology drug discovery.

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his review gives an overview of the innovations, development and limitations of different types of tumor-like construction techniques such as self-assemble spheroid formation, spheroids formation by micro-manufacturing technologies, micro-dissected tumor tissues and tumor organoid. Combination of 3D tumor-like construction and microfluidic techniques to achieve tumor on a chip for in vitro tumor environment modeling and drug screening were all included. Eventually, developmental directions and technical challenges in the research field are also discussed. We believe tumor on chip models have provided better sufficient clinical predictive power and will bridge the gap between proof-of-concept studies and a wider implementation within the oncology drug development for pathophysiological applications.

Multi-Organs-on-Chips: Towards Long-Term Biomedical Investigations

With advantageous features such as minimizing the cost, time, and sample size requirements, organ-on-a-chip (OOC) systems have garnered enormous interest from researchers for their ability for real-time monitoring of physical parameters by mimicking the in vivo microenvironment and the precise responses of xenobiotics, i.e., drug efficacy and toxicity over conventional two-dimensional (2D) and three-dimensional (3D) cell cultures, as well as animal models. Recent advancements of OOC systems have evidenced the fabrication of 'multi-organ-on-chip' (MOC) models, which connect separated organ chambers together to resemble an ideal pharmacokinetic and pharmacodynamic (PK-PD) model for monitoring the complex interactions between multiple organs and the resultant dynamic responses of multiple organs to pharmaceutical compounds. Numerous varieties of MOC systems have been proposed, mainly focusing on the construction of these multi-organ models, while there are only few studies on how to realize continual, automated, and stable testing, which still remains a significant challenge in the development process of MOCs. Herein, this review emphasizes the recent advancements in realizing long-term testing of MOCs to promote their capability for real-time monitoring of multi-organ interactions and chronic cellular reactions more accurately and steadily over the available chip models. Efforts in this field are still ongoing for better performance in the assessment of preclinical attributes for a new chemical entity. Further, we give a brief overview on the various biomedical applications of long-term testing in MOCs, including several proposed applications and their potential utilization in the future. Finally, we summarize with perspectives.

Dynamic in vitro models for tumor tissue engineering

Cancer research uses in vitro studies for controllable analysis of tumor behavior and preclinical testing of therapeutics. Shortcomings of basic cell culture systems in recreating in vivo interactions have driven the development of more efficient and biomimetic in vitro environments for cancer research. Assimilation of certain developments in tissue engineering will accelerate and improve the design of these environments. With the continual improvement of the tumor engineering field, the next step is towards macroscopic systems such as scaffold-supported, flow-perfused macroscale tumor bioreactors. Surface modifications of synthetic scaffolds allow for targeted cell adhesion and improved ECM development. Flow perfusion has emerged as means to expose cancerous tissues to critical biomechanical forces for tumor progression while simultaneously improving nutrient and waste transport. Macroscale perfusable systems allow for non-destructive real-time monitoring using biosensors capable of improving understanding of in vitro tumor development at reduced cost and waste. The combination of macroscale perfusable systems, surface-modified synthetic scaffolds, and non-destructive real-time monitoring will provide advanced platforms for in vitro modeling of tumor development, with broad applications in basic tumor research and preclinical drug development.

Organ-on-Chip Devices Toward Applications in Drug Development and Screening

As a necessary pathway to man-made organs, organ-on-chips (OOC), which simulate the activities, mechanics, and physiological responses of real organs, have attracted plenty of attention over the past decade. As the maturity of three-dimensional (3D) cell-culture models and microfluidics advances, the study of OOCs has made significant progress. This review article provides a comprehensive overview and classification of OOC microfluidics. Specifically, the review focuses on OOC systems capable of being used in preclinical drug screening and development. Additionally, the review highlights the strengths and weaknesses of each OOC system toward the goal of improved drug development and screening. The various OOC systems investigated throughout the review include, blood vessel, lung, liver, and tumor systems and the potential benefits, which each provides to the growing challenge of high-throughput drug screening. Published OOC systems have been reviewed over the past decade (2007–2018) with focus given mainly to more recent advances and improvements within each organ system. Each OOC system has been reviewed on how closely and realistically it is able to mimic its physiological counterpart, the degree of information provided by the system toward the ultimate goal of drug development and screening, how easily each system would be able to transition to large scale high-throughput drug screening, and what further improvements to each system would help to improve the functionality, realistic nature of the platform, and throughput capacity. Finally, a summary is provided of where the broad field of OOCs appears to be headed in the near future along with suggestions on where future efforts should be focused for optimized performance of OOC systems in general.

Study of oxygen tension variation within live tumor spheroids using microfluidic devices and multi-photon laser scanning microscopy

Three-dimensional cell spheroid culture using microfluidic devices provides a convenient in vitro model for studying tumour spheroid structures and internal microenvironments. Recent studies suggest that oxygen deprived zones inside solid tumors are responsible for stimulating local cytokines and endothelial vasculature proliferation during angiogenesis. In this work, we develop an integrated approach combining microfluidic devices and multi-photon laser scanning microscopy (MPLSM) to study variations in oxygen tension within live spheroids of human osteosarcoma cells. Uniform shaped, size-controlled spheroids are grown and then harvested using a polydimethylsiloxane (PDMS) based microfluidic device. Fluorescence live imaging of the harvested spheroids is performed using MPLSM and a commercially available oxygen sensitive dye, Image-iT Red, to observe the oxygen tension variation within the spheroids and those co-cultured with monolayers of human umbilical vein endothelial cells (HUVECs). Oxygen tension variations are observed within the spheroids with diameters ranging from 90 ± 10 μm to 140 ± 10 μm. The fluorescence images show that the low-oxygenated cores diminish when spheroids are co-cultured with HUVEC monolayers for 6 hours to 8 hours. In the experiments, spheroids subjected to HUVEC conditioned medium treatment and with a cell adherent substrate are also measured and analyzed to study their significance on oxygen tension within the spheroids. The results show that the oxygenation within the spheroids is improved when the spheroids are cultured under those conditions. Our work presents an efficient method to study oxygen tension variation within live tumor spheroids under the influence of endothelial cells and conditioned medium. The method can be exploited for further investigation of tumor oxygen microenvironments during angiogenesis.

Clogging-free continuous operation with whole blood in a radial pillar device (RAPID)

Pillar-based passive microfluidic devices combine the advantages of simple designs, small device footprint, and high selectivity for size-based separation of blood cells. Most of these device designs have been validated with dilute blood samples. Handling whole blood in pillar-based devices is extremely challenging due to clogging. The high proportion of cells (particularly red blood cells) in blood, the varying sizes and stiffness of the different blood cells, and the tendency of the cells to aggregate lead to clogging of the pillars within a short period. We recently reported a ra dial pi llar d evice (RAPID) design for continuous and high throughput separation of multi-sized rigid polystyrene particles in a single experiment. In the current manuscript, we have given detailed guidelines to modify the design of RAPID for any application with deformable objects (e.g. cells). We have adapted RAPID to work with whole blood without any pre-processing steps. We were successful in operating the device with whole blood for almost 6 h, which is difficult to achieve with most pillar-based devices. The availability of multiple parallel paths for the cells and the provision for a self-generating cross flow in the device design were the main reasons behind the minimal clogging in our device. We also observed that a vibrator motor attached to the inlet tubing occasionally disturbed the cell clumps. As an illustration of the improved device design, we demonstrated up to ∼ 60-fold enrichment of platelets.

Tumor-on-a-chip platforms for assessing nanoparticle-based cancer therapy

Cancer has become the most prevalent cause of deaths, placing a huge economic and healthcare burden worldwide. Nanoparticles (NPs), as a key component of nanomedicine, provide alternative options for promoting the efficacy of cancer therapy. Current conventional cancer models have limitations in predicting the effects of various cancer treatments. To overcome these limitations, biomimetic and novel 'tumor-on-a-chip' platforms have emerged with other innovative biomedical engineering methods that enable the evaluation of NP-based cancer therapy. In this review, we first describe cancer models for evaluation of NP-based cancer therapy techniques, and then present the latest advances in 'tumor-on-a-chip' platforms that can potentially facilitate clinical translation of NP-based cancer therapies.

Preclinical models for precision oncology

Precision medicine approaches have revolutionized oncology. Personalized treatments require not only identification of the driving molecular alterations, but also development of targeted therapies and diagnostic tests to identify the appropriate patient populations for clinical trials and subsequent therapeutic implementation. Preclinical in vitro and in vivo models are widely used to predict efficacy of newly developed treatments. Here we discuss whether, and to what extent, preclinical models including cell lines, organoids and tumorgrafts recapitulate key features of human tumors. The potential of preclinical models to anticipate treatment efficacy and clinical benefit is also presented, using examples in different tumor types.

A Microfluidic System for the Investigation of Tumor Cell Extravasation

Metastatic dissemination of cancer cells is a very complex process. It includes the intravasation of cells into the metastatic pathways, their passive distribution within the blood or lymph flow, and their extravasation into the surrounding tissue. Crucial steps during extravasation are the adhesion of the tumor cells to the endothelium and their transendothelial migration. However, the molecular mechanisms that are underlying this process are still not fully understood. Novel three dimensional (3D) models for research on the metastatic cascade include the use of microfluidic devices. Different from two dimensional (2D) models, these devices take cell⁻cell, structural, and mechanical interactions into account. Here we introduce a new microfluidic device in order to study tumor extravasation. The device consists of three different parts, containing two microfluidic channels and a porous membrane sandwiched in between them. A smaller channel together with the membrane represents the vessel equivalent and is seeded separately with primary endothelial cells (EC) that are isolated from the lung artery. The second channel acts as reservoir to collect the migrated tumor cells. In contrast to many other systems, this device does not need an additional coating to allow EC growth, as the primary EC that is used produces their own basement membrane. VE-Cadherin, an endothelial adherence junction protein, was expressed in regular localization, which indicates a tight barrier function and cell⁻cell connections of the endothelium. The EC in the device showed in vivo-like behavior under flow conditions. The GFP-transfected tumor cells that were introduced were of epithelial or mesenchymal origin and could be observed by live cell imaging, which indicates tightly adherent tumor cells to the endothelial lining under different flow conditions. These results suggest that the new device can be used for research on molecular requirements, conditions, and mechanism of extravasation and its inhibition.

Ecotoxicology Goes on a Chip: Embracing Miniaturized Bioanalysis in Aquatic Risk Assessment

Biological and environmental sciences are, more than ever, becoming highly dependent on technological and multidisciplinary approaches that warrant advanced analytical capabilities. Microfluidic lab-on-a-chip technologies are perhaps one the most groundbreaking offshoots of bioengineering, enabling design of an entirely new generation of bioanalytical instrumentation. They represent a unique approach to combine microscale engineering and physics with specific biological questions, providing technological advances that allow for fundamentally new capabilities in the spatiotemporal analysis of molecules, cells, tissues, and even small metazoan organisms. While these miniaturized analytical technologies experience an explosive growth worldwide, with a substantial promise of a direct impact on biosciences, it seems that lab-on-a-chip systems have so far escaped the attention of aquatic ecotoxicologists. In this Critical Review, potential applications of the currently existing and emerging chip-based technologies for aquatic ecotoxicology and water quality monitoring are highlighted. We also offer suggestions on how aquatic ecotoxicology can benefit from adoption of microfluidic lab-on-a-chip devices for accelerated bioanalysis.

Controlling Differentiation of Stem Cells for Developing Personalized Organ-on-Chip Platforms

Organ-on-chip (OOC) platforms have attracted attentions of pharmaceutical companies as powerful tools for screening of existing drugs and development of new drug candidates. OOCs have primarily used human cell lines or primary cells to develop biomimetic tissue models. However, the ability of human stem cells in unlimited self-renewal and differentiation into multiple lineages has made them attractive for OOCs. The microfluidic technology has enabled precise control of stem cell differentiation using soluble factors, biophysical cues, and electromagnetic signals. This study discusses different tissue- and organ-on-chip platforms (i.e., skin, brain, blood-brain barrier, bone marrow, heart, liver, lung, tumor, and vascular), with an emphasis on the critical role of stem cells in the synthesis of complex tissues. This study further recaps the design, fabrication, high-throughput performance, and improved functionality of stem-cell-based OOCs, technical challenges, obstacles against implementing their potential applications, and future perspectives related to different experimental platforms.

Functional and Biomimetic Materials for Engineering of the Three-Dimensional Cell Microenvironment

The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell-microenvironment interactions continue to overturn much early progress in the field. Key challenges continue to be dissecting the roles of chemistry, structure, mechanics, and electrophysiology in the cell microenvironment, and understanding and harnessing the roles of periodicity and drift in these factors. This review encapsulates where recent advances appear to leave the ever-shifting state of the art, and it highlights areas in which substantial potential and uncertainty remain.

Rapid Staining of Circulating Tumor Cells in Three-Dimensional Microwell Dialysis (3D-μDialysis) Chip

The conventional techniques to detect circulating tumour cells (CTCs) are lengthy and the use of centrifugal forces in this technique may cause cell mortality. As the number of CTCs in patients is quite low, the present study aims towards a gentler diagnostic procedure so as not to lose too many CTCs during the sample preparation process. Hence, a Three-Dimensional Microwell dialysis (3D-μDialysis) chip was designed in this study to perform gentle fluorescence-removal process by using dialysis-type flow processes without centrifuging. This leads to a minimum manual handling of CTCs obtained in our study without any contamination. In addition, a rapid staining process which necessitates only about half the time of conventional techniques (35 minutes instead of 90 minutes) is being illustrated by the employment of dialysis process (by dynamically removing water and waste at once) instead of only static diffusion (by statically removing only waste by diffusion). Staining efficiency of our technique is improved over conventional staining because of the flow rate in 3D-μDialysis staining. Moreover, the staining process has been validated with clinical whole blood samples from three TNM stage IV colon cancer patients. The current technique may be termed as “miniature rapid staining and dialysing system”.

In silico characterization of cell-cell interactions using a cellular automata model of cell culture

BACKGROUND

Cell proliferation is a key characteristic of eukaryotic cells. During cell proliferation, cells interact with each other. In this study, we developed a cellular automata model to estimate cell-cell interactions using experimentally obtained images of cultured cells.

RESULTS

We used four types of cells; HeLa cells, human osteosarcoma (HOS) cells, rat mesenchymal stem cells (MSCs), and rat smooth muscle A7r5 cells. These cells were cultured and stained daily. The obtained cell images were binarized and clipped into squares containing about 10⁴ cells. These cells showed characteristic cell proliferation patterns. The growth curves of these cells were generated from the cell proliferation images and we determined the doubling time of these cells from the growth curves. We developed a simple cellular automata system with an easily accessible graphical user interface. This system has five variable parameters, namely, initial cell number, doubling time, motility, cell-cell adhesion, and cell-cell contact inhibition (of proliferation). Within these parameters, we obtained initial cell numbers and doubling times experimentally. We set the motility at a constant value because the effect of the parameter for our simulation was restricted. Therefore, we simulated cell proliferation behavior with cell-cell adhesion and cell-cell contact inhibition as variables. By comparing growth curves and proliferation cell images, we succeeded in determining the cell-cell interaction properties of each cell. Simulated HeLa and HOS cells exhibited low cell-cell adhesion and weak cell-cell contact inhibition. Simulated MSCs exhibited high cell-cell adhesion and positive cell-cell contact inhibition. Simulated A7r5 cells exhibited low cell-cell adhesion and strong cell-cell contact inhibition. These simulated results correlated with the experimental growth curves and proliferation images.

CONCLUSIONS

Our simulation approach is an easy method for evaluating the cell-cell interaction properties of cells.

Microfluidics in flow cytometry and related techniques

Technological advances in laboratory automation are now well understood and applied as they considerably improved the speed and robustness of haematological laboratory data, in the companion fields of blood analyzers and flow cytometry. Still rather confidential is the field of microfluidics, mostly confined so far to academic settings and research laboratories. The literature in the field of microfluidics is growing and applications in hematology range from cell counting to flow cytometry, cell sorting, or ex vivo testing. A literature search allows to identify many innovative solutions developed to master the specific physics of fluid movements in microchips. Miniaturization also dwells on findings that have emerged from different areas such as electronics and nanoengineering. This review proposes an overview of the major principles guiding developments in microfluidics and describes a necessarily limited and nonexhaustive series of specific applications. Readers are strongly encouraged to consult the documents referred to in the references section to learn more about this world knocking at our door and possibly liable to revolutionize our profession of hematology biologists in a not so far future.

Cancer-on-a-chip systems at the frontier of nanomedicine

Nanomedicine provides a unique opportunity for promoting drug efficacy through enhanced delivery mechanisms. However, its translation into the clinics has been relatively slow compared with the large amount of research occurring in laboratory settings. Given the limitations of conventional cell culture models and preclinical animal models, we discuss the potential utility of recently developed cancer-on-a-chip platforms, which maximally replicate the pathophysiology of the human tumor microenvironments, as alternatives for effective evaluation of nanomedicine. We begin with a brief discussion of nanomedicine, then chart the history of organ-on-a-chip platform development and their recent evolution as tools for modeling different cancers for assessing nanomedicine efficacy, concluding with future perspectives for the field.

A microfluidic platform for drug screening in a 3D cancer microenvironment

Development of resistance to chemotherapy treatments is a major challenge in the battle against cancer. Although a vast repertoire of chemotherapeutics is currently available for treating cancer, a technique for rapidly identifying the right drug based on the chemo-resistivity of the cancer cells is not available and it currently takes weeks to months to evaluate the response of cancer patients to a drug. A sensitive, low-cost diagnostic assay capable of rapidly evaluating the effect of a series of drugs on cancer cells can significantly change the paradigm in cancer treatment management. Integration of microfluidics and electrical sensing modality in a 3D tumour microenvironment may provide a powerful platform to tackle this issue. Here, we report a 3D microfluidic platform that could be potentially used for a real-time deterministic analysis of the success rate of a chemotherapeutic drug in less than 12h. The platform (66mm×50mm; L×W) is integrated with the microsensors (interdigitated gold electrodes with width and spacing 10µm) that can measure the change in the electrical response of cancer cells seeded in a 3D extra cellular matrix when a chemotherapeutic drug is flown next to the matrix. B16-F10 mouse melanoma, 4T1 mouse breast cancer, and DU 145 human prostate cancer cells were used as clinical models. The change in impedance magnitude on flowing chemotherapeutics drugs measured at 12h for drug-susceptible and drug tolerant breast cancer cells compared to control were 50,552±144 Ω and 28,786±233 Ω, respectively, while that of drug-susceptible melanoma cells were 40,197±222 Ω and 4069±79 Ω, respectively. In case of prostate cancer the impedance change between susceptible and resistant cells were 8971±1515 Ω and 3281±429 Ω, respectively, which demonstrated that the microfluidic platform was capable of delineating drug susceptible cells, drug tolerant, and drug resistant cells in less than 12h.

Microfluidics for research and applications in oncology

Cancer is currently one of the top non-communicable human diseases, and continual research and developmental efforts are being made to better understand and manage this disease. More recently, with the improved understanding in cancer biology as well as the advancements made in microtechnology and rapid prototyping, microfluidics is increasingly being explored and even validated for use in the detection, diagnosis and treatment of cancer. With inherent advantages such as small sample volume, high sensitivity and fast processing time, microfluidics is well-positioned to serve as a promising platform for applications in oncology. In this review, we look at the recent advances in the use of microfluidics, from basic research such as understanding cancer cell phenotypes as well as metastatic behaviors to applications such as the detection, diagnosis, prognosis and drug screening. We then conclude with a future outlook on this promising technology.

Clarifying intact 3D tissues on a microfluidic chip for high-throughput structural analysis

On-chip imaging of intact three-dimensional tissues within microfluidic devices is fundamentally hindered by intratissue optical scattering, which impedes their use as tissue models for high-throughput screening assays. Here, we engineered a microfluidic system that preserves and converts tissues into optically transparent structures in less than 1 d, which is 20× faster than current passive clearing approaches. Accelerated clearing was achieved because the microfluidic system enhanced the exchange of interstitial fluids by 567-fold, which increased the rate of removal of optically scattering lipid molecules from the cross-linked tissue. Our enhanced clearing process allowed us to fluorescently image and map the segregation and compartmentalization of different cells during the formation of tumor spheroids, and to track the degradation of vasculature over time within extracted murine pancreatic islets in static culture, which may have implications on the efficacy of beta-cell transplantation treatments for type 1 diabetes. We further developed an image analysis algorithm that automates the analysis of the vasculature connectivity, volume, and cellular spatial distribution of the intact tissue. Our technique allows whole tissue analysis in microfluidic systems, and has implications in the development of organ-on-a-chip systems, high-throughput drug screening devices, and in regenerative medicine.