An integrated microfluidic system for studying cell-microenvironmental interactions versatilely and dynamically

Emerging In Vitro and In Vivo Models: Hope for the Better Understanding of Cancer Progression and Treatment

Various cancer models have been developed to aid the understanding of the underlying mechanisms of tumor development and evaluate the effectiveness of various anticancer drugs in preclinical studies. These models accurately reproduce the critical stages of tumor initiation and development to mimic the tumor microenvironment better. Using these models for target validation, tumor response evaluation, resistance modeling, and toxicity comprehension can significantly enhance the drug development process. Herein, various in vivo or animal models are presented, typically consisting of several mice and in vitro models ranging in complexity from transwell models to spheroids and CRISPR-Cas9 technologies. While in vitro models have been used for decades and dominate the early stages of drug development, they are still limited primary to simplistic tests based on testing on a single cell type cultivated in Petri dishes. Recent advancements in developing new cancer therapies necessitate the generation of complicated animal models that accurately mimic the tumor's complexity and microenvironment. Mice make effective tumor models as they are affordable, have a short reproductive cycle, exhibit rapid tumor growth, and are simple to manipulate genetically. Human cancer mouse models are crucial to understanding the neoplastic process and basic and clinical research improvements. The following review summarizes different in vitro and in vivo metastasis models, their advantages and disadvantages, and their ability to serve as a model for cancer research.

A dental implant-on-a-chip for 3D modeling of host-material-pathogen interactions and therapeutic testing platforms

The precise spatiotemporal control and manipulation of fluid dynamics on a small scale granted by lab-on-a-chip devices provide a new biomedical research realm as a substitute for in vivo studies of host-pathogen interactions. While there has been a rise in the use of various medical devices/implants for human use, the applicability of microfluidic models that integrate such functional biomaterials is currently limited. Here, we introduced a novel dental implant-on-a-chip model to better understand host-material-pathogen interactions in the context of peri-implant diseases. The implant-on-a-chip integrates gingival cells with relevant biomaterials - keratinocytes with dental resin and fibroblasts with titanium while maintaining a spatially separated co-culture. To enable this co-culture, the implant-on-a-chip's core structure necessitates closely spaced, tall microtrenches. Thus, an SU-8 master mold with a high aspect-ratio pillar array was created by employing a unique backside UV exposure with a selective optical filter. With this model, we successfully replicated the morphology of keratinocytes and fibroblasts in the vicinity of dental implant biomaterials. Furthermore, we demonstrated how photobiomodulation therapy might be used to protect the epithelial layer from recurrent bacterial challenges (∼3.5-fold reduction in cellular damage vs. control). Overall, our dental implant-on-a-chip approach proposes a new microfluidic model for multiplexed host-material-pathogen investigations and the evaluation of novel treatment strategies for infectious diseases.

In Vitro 3D Cultures to Model the Tumor Microenvironment

Simple Summary

Tumor stroma is known to significantly influence cancer initiation and progression. In the last decade, 3D cell cultures have shown potential in modeling the tumor microenvironment. This review summarizes the main features of current 3D models, shedding light on their importance in the study of cancer biology and treatment.

Abstract

It is now well established that the tumor microenvironment plays a key role in determining cancer growth, metastasis and drug resistance. Thus, it is fundamental to understand how cancer cells interact and communicate with their stroma and how this crosstalk regulates disease initiation and progression. In this setting, 3D cell cultures have gained a lot of interest in the last two decades, due to their ability to better recapitulate the complexity of tumor microenvironment and therefore to bridge the gap between 2D monolayers and animal models. Herein, we present an overview of the 3D systems commonly used for studying tumor–stroma interactions, with a focus on recent advances in cancer modeling and drug discovery and testing.

A review on microfluidics manipulation of the extracellular chemical microenvironment and its emerging application to cell analysis

Spatiotemporal manipulation of extracellular chemical environments with simultaneous monitoring of cellular responses plays an essential role in exploring fundamental biological processes and expands our understanding of underlying mechanisms. Despite the rapid progress and promising successes in manipulation strategies, many challenges remain due to the small size of cells and the rapid diffusion of chemical molecules. Fortunately, emerging microfluidic technology has become a powerful approach for precisely controlling the extracellular chemical microenvironment, which benefits from its integration capacity, automation, and high-throughput capability, as well as its high resolution down to submicron. Here, we summarize recent advances in microfluidics manipulation of the extracellular chemical microenvironment, including the following aspects: i) Spatial manipulation of chemical microenvironments realized by convection flow-, diffusion-, and droplet-based microfluidics, and surface chemical modification; ii) Temporal manipulation of chemical microenvironments enabled by flow switching/shifting, moving/flowing cells across laminar flows, integrated microvalves/pumps, and droplet manipulation; iii) Spatiotemporal manipulation of chemical microenvironments implemented by a coupling strategy and open-space microfluidics; and iv) High-throughput manipulation of chemical microenvironments. Finally, we briefly present typical applications of the above-mentioned technical advances in cell-based analyses including cell migration, cell signaling, cell differentiation, multicellular analysis, and drug screening. We further discuss the future improvement of microfluidics manipulation of extracellular chemical microenvironments to fulfill the needs of biological and biomedical research and applications.

Inertial-Force-Assisted, High-Throughput, Droplet-Free, Single-Cell Sampling Coupled with ICP-MS for Real-Time Cell Analysis

Single-cell analysis facilitates perception into the most essential processes in life's mysteries. While it is highly challenging to quantify them at the single-cell level, where precise single-cell sampling is the prerequisite. Herein, a real-time single-cell quantitative platform was established for high-throughput droplet-free single-cell sampling into time-resolved (TRA) ICP-MS and real-time quantification of intracellular target elements. The concentrated cells (2 × 10⁶ cells mL^-1) were spontaneously and orderly aligned in a spiral microchannel with 104 periodic dimensional confined micropillars. The quantification is conducted simultaneously by internal standard inducing from another branch channel in the chip. The flow-rate-independent feature of single-cell focusing into an aligned stream within a wide range of fluidic velocities (100-800 μL min^-1) facilitates high-throughput, oil-free, single-cell introduction into TRA-ICP-MS. The system was used for real-time exploration of intracellular antagonism of Cu²⁺ against Cd²⁺. an obvious antagonistic effect was observed for the MCF-7 cell by culturing for 3, 6, 9, and 12 h with 100 μg L^-1 Cd²⁺ and 100 μg L^-1 Cu²⁺, and a rivalry rate of 12.8% was achieved at 12 h. At identical experimental conditions, however, limited antagonistic effect was encountered for a bEnd3 cell within the same incubation time period, with a rivalry rate of 4.81%. On the contrary, an antagonistic effect was not observed for the HepG2 cell by culturing for 6 h, while an obvious antagonistic effect was found by further culturing to 12 h, with a rivalry rate of 10.43%. For all three cell lines, significant heterogeneity was observed among individual cells.

A Micro-Optic Stalk (μOS) System to Model the Collective Migration of Retinal Neuroblasts

Contemporary regenerative therapies have introduced stem-like cells to replace damaged neurons in the visual system by recapitulating critical processes of eye development. The collective migration of neural stem cells is fundamental to retinogenesis and has been exceptionally well-studied using the fruit fly model of Drosophila Melanogaster. However, the migratory behavior of its retinal neuroblasts (RNBs) has been surprisingly understudied, despite being critical to retinal development in this invertebrate model. The current project developed a new microfluidic system to examine the collective migration of RNBs extracted from the developing visual system of Drosophila as a model for the collective motile processes of replacement neural stem cells. The system scales with the microstructure of the Drosophila optic stalk, which is a pre-cursor to the optic nerve, to produce signaling fields spatially comparable to in vivo RNB stimuli. Experiments used the micro-optic stalk system, or μOS, to demonstrate the preferred sizing and directional migration of collective, motile RNB groups in response to changes in exogenous concentrations of fibroblast growth factor (FGF), which is a key factor in development. Our data highlight the importance of cell-to-cell contacts in enabling cell cohesion during collective RNB migration and point to the unexplored synergy of invertebrate cell study and microfluidic platforms to advance regenerative strategies.

Pneumatically Actuated Microfluidic Platform for Reconstituting 3D Vascular Tissue Compression

In vivo, blood vessels constitutively experience mechanical stresses exerted by adjacent tissues and other structural elements. Vascular collapse, a structural failure of vascular tissues, may stem from any number of possible compressive forces ranging from injury to tumor growth and can promote inflammation. In particular, endothelial cells are continuously exposed to varying mechanical stimuli, internally and externally, resulting in blood vessel deformation and injury. This study proposed a method to model biomechanical-stimuli-induced blood vessel compression in vitro within a polydimethylsiloxane (PDMS) microfluidic 3D microvascular tissue culture platform with an integrated pneumatically actuated compression mechanism. 3D microvascular tissues were cultured within the device. Histological reactions to compressive forces were quantified and shown to be the following: live/dead assays indicated the presence of a microvascular dead zone within high-stress regions and reactive oxygen species (ROS) quantification exhibited a stress-dependent increase. Fluorescein isothiocyanate (FITC)-dextran flow assays showed that compressed vessels developed structural failures and increased leakiness; finite element analysis (FEA) corroborated the experimental data, indicating that the suggested model of vascular tissue deformation and stress distribution was conceptually sound. As such, this study provides a powerful and accessible in vitro method of modeling microphysiological reactions of microvascular tissues to compressive stress, paving the way for further studies into vascular failure as a result of external stress.

3DμF - Interactive Design Environment for Continuous Flow Microfluidic Devices

The design of microfluidic Lab on a Chip (LoC) systems is an onerous task requiring specialized skills in fluid dynamics, mechanical design drafting, and manufacturing. Engineers face significant challenges during the labor-intensive process of designing microfluidic devices, with very few specialized tools that help automate the process. Typical design iterations require the engineer to research the architecture, manually draft the device layout, optimize for manufacturing processes, and manually calculate and program the valve sequences that operate the microfluidic device. The problem compounds when engineers not only have to test the functionality of the chip but are also expected to optimize them for the robust execution of biological assays. In this paper, we present an interactive tool for designing continuous flow microfluidic devices. 3DμF is the first completely open source interactive microfluidic system designer that readily supports state of the art design automation algorithms. Through various case studies, we show 3DμF can be used to reproduce designs from literature, provide metrics for evaluating microfluidic design complexity and showcase how 3DμF is a platform for integrating a wide assortment of engineering techniques used in the design of microfluidic devices as a part of the standard design workflow.

Analysis of tumoral spheres growing in a multichamber microfluidic device

Lab on a Chip (LOC) farming systems have emerged as a powerful tool for single cell studies combined with a non-adherent cell culture substrate and single cell capture chips for the study of single cell derived tumor spheres. Cancer is characterized by its cellular heterogeneity where only a small population of cancer stem cells (CSCs) are responsible for tumor metastases and recurrences. Thus, the in vitro strategy to the formation of a single cell-derived sphere is an attractive alternative to identify CSCs. In this study, we test the effectiveness of microdevices for analysis of heterogeneity within CSC populations and its interaction with different components of the extracellular matrix. CSC could be identify using specific markers related to its pluripotency and self-renewal characteristics such as the transcription factor Oct-4 or the surface protein CD44. The results confirm the usefulness of LOC as an effective method for quantification of CSC, through the formation of spheres under conditions of low adhesion or growing on components of the extracellular matrix. The device used is also a good alternative for evaluating the individual growth of each sphere and further identification of these CSC markers by immunofluorescence. In conclusion, LOC devices have not only the already known advantages, but they are also a promising tool since they use small amounts of reagents and are under specific culture parameters. LOC devices could be considered as a novel technology to be used as a complement or replacement of traditional studies on culture plates.

In Vitro Microfluidic Models for Neurodegenerative Disorders

Microfluidic devices enable novel means of emulating neurodegenerative disease pathophysiology in vitro. These organ-on-a-chip systems can potentially reduce animal testing and substitute (or augment) simple 2D culture systems. Reconstituting critical features of neurodegenerative diseases in a biomimetic system using microfluidics can thereby accelerate drug discovery and improve our understanding of the mechanisms of several currently incurable diseases. This review describes latest advances in modeling neurodegenerative diseases in the central nervous system and the peripheral nervous system. First, this study summarizes fundamental advantages of microfluidic devices in the creation of compartmentalized cell culture microenvironments for the co-culture of neurons, glial cells, endothelial cells, and skeletal muscle cells and in their recapitulation of spatiotemporal chemical gradients and mechanical microenvironments. Then, this reviews neurodegenerative-disease-on-a-chip models focusing on Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Finally, this study discusses about current drawbacks of these models and strategies that may overcome them. These organ-on-chip technologies can be useful to be the first line of testing line in drug development and toxicology studies, which can contribute significantly to minimize the phase of animal testing steps.

Microfluidic Module for Real-Time Generation of Complex Multimolecule Temporal Concentration Profiles

We designed a microfluidic module that generates complex and dynamic concentration profiles of multiple molecules over a large concentration range using pulse-width modulation (PWM). Our PWM module can combine up to six different inputs and select among three downstream mixing channels, as required by the application. The module can produce concentrations with a dynamic range of three decades. We created complex, temporal concentration profiles of two molecules, with each concentration independently controllable, and show that the PWM module can execute rapid concentration changes as well as long-time scale pharmacokinetic profiles. Concentration profiles were generated for molecules with molecular weights ranging from 560 Da to 150 kDa. Our PWM module produces robust and precise concentration profiles under a variety of operating conditions, making it ideal for integration with existing microfluidic devices for advanced cell and pharmacokinetic studies.

Spiral microchannel with ordered micro-obstacles for continuous and highly-efficient particle separation

Controllable manipulation of fluid flow is crucial for efficient particle separation, which is associated with plenty of biomedical and industrial applications. Microfluidic technologies have achieved promising progress in particle positioning depending on inertial force with or without the help of the Dean effect. Herein, we describe an inertial microfluidic system containing a spiral microchannel for various highly efficient particle separations. We demonstrated that Dean-like secondary flow can be regulated by geometric confinement in the microchannel. On the introduction of a library of micro-obstacles into the spiral microchannels, the resulting linear acceleration of secondary flow can be applied to remarkably enhance particle focusing in time and space. Further, multiple separating and sorting manipulations of particles including polymeric particles, circulating tumor cells, and blood cells, can be successfully accomplished in the dimension-confined spiral channels in a sheathless, high-throughput (typically 3 ml min^-1), long-term (at least 4 h), and highly-efficient (up to 99.8% focusing) manner. The methodological achievement pointing to ease-of-use, effective, and high-throughput particle manipulations is useful for both laboratory and commercial developments of microfluidic systems in life and material sciences.

High-Throughput 3D Tumor Culture in a Recyclable Microfluidic Platform

Three-dimensional (3D) tumor culture miniaturized platforms are of importance to biomimetic model construction and pathophysiological studies. Controllable and high-throughput production of 3D tumors is desirable to make cell-based manipulation dynamic and efficient at micro-scale. Moreover, the 3D culture platform being reusable is convenient to research scholars. In this chapter, we describe a dynamically controlled 3D tumor manipulation and culture method using pneumatic microstructure-based microfluidics, which has potential applications in the fields of tissue engineering, tumor biology, and clinical medicine in a high-throughput way.

In Vitro Tumor Models: Advantages, Disadvantages, Variables, and Selecting the Right Platform

In vitro tumor models have provided important tools for cancer research and serve as low-cost screening platforms for drug therapies; however, cancer recurrence remains largely unchecked due to metastasis, which is the cause of the majority of cancer-related deaths. The need for an improved understanding of the progression and treatment of cancer has pushed for increased accuracy and physiological relevance of in vitro tumor models. As a result, in vitro tumor models have concurrently increased in complexity and their output parameters further diversified, since these models have progressed beyond simple proliferation, invasion, and cytotoxicity screens and have begun recapitulating critical steps in the metastatic cascade, such as intravasation, extravasation, angiogenesis, matrix remodeling, and tumor cell dormancy. Advances in tumor cell biology, 3D cell culture, tissue engineering, biomaterials, microfabrication, and microfluidics have enabled rapid development of new in vitro tumor models that often incorporate multiple cell types, extracellular matrix materials, and spatial and temporal introduction of soluble factors. Other innovations include the incorporation of perfusable microvessels to simulate the tumor vasculature and model intravasation and extravasation. The drive toward precision medicine has increased interest in adapting in vitro tumor models for patient-specific therapies, clinical management, and assessment of metastatic potential. Here, we review the wide range of current in vitro tumor models and summarize their advantages, disadvantages, and suitability in modeling specific aspects of the metastatic cascade and drug treatment.

Stoichiometric control of live cell mixing to enable fluidically-encoded co-culture models in perfused microbioreactor arrays

A cell mixer microbioreactor array platform that permits the rapid establishment of perfused cell co-culture models in a high-throughput, programmable fashion.

Two-dimensional arrays of cell-laden polymer hydrogel modules

Microscale technologies offer the capability to generate in vitro artificial cellular microenvironments that recapitulate the spatial, biochemical, and biophysical characteristics of the native extracellular matrices and enable systematic, quantitative, and high-throughput studies of cell fate in their respective environments. We developed a microfluidic platform for the generation of two-dimensional arrays of micrometer-size cell-laden hydrogel modules (HMs) for cell encapsulation and culture. Fibroblast cells (NIH 3T3) and non-adherent T cells (EL4) encapsulated in HMs showed high viability and proliferation. The platform was used for real-time studies of the effect of spatial constraints and structural and mechanical properties of HMs on cell growth, both on the level of individual cells. Due to the large number of cell-laden HMs and stochastic cell distribution, cell studies were conducted in a time- and labor efficient manner. The platform has a broad range of applications in the exploration of the role of chemical and biophysical cues on individual cells, studies of in vitro cell migration, and the examination of cell-extracellular matrix and cell-cell interactions.

On-chip monitoring of skeletal myoblast transplantation for the treatment of hypoxia-induced myocardial injury

A comprehensive elucidation of the unexpected adverse events that occur in skeletal myoblast transplantation is fundamental for the optimization of myocardial therapeutic effects. However, a well-defined method to study the interactions between skeletal myoblasts and cardiomyocytes during the healing process is out of reach. Here, we describe a microfluidic method for monitoring the interactions between skeletal myoblasts and hypoxia-injured cardiomyocytes in a spatiotemporally-controlled manner, mimicking the in vivo cell transplantation process. A myocardial hypoxia environment was created using an oxygen consumption blocking reagent, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. Meanwhile, the interactions between the skeletal L6 myoblasts and hypoxia-injured myocardium H9c2 cells were investigated, and the effects of a L6 conditional medium on H9c2 cells were comparatively analyzed by quantitatively measuring the morphological and pathophysiological dynamics of H9c2 cells. The results showed that skeletal myoblasts could repair hypoxia-injured H9c2 cells mainly through direct cell-to-cell interactions. This simple on-chip assay for investigating myocardial repair processes may provide avenues for the in vitro screening of drug-induced cardiotoxicity.

A lab-on-a-chip for hypoxic patch clamp measurements combined with optical tweezers and spectroscopy- first investigations of single biological cells

The response and the reaction of the brain system to hypoxia is a vital research subject that requires special instrumentation. With this research subject in focus, a new multifunctional lab-on-a-chip (LOC) system with control over the oxygen content for studies on biological cells was developed. The chip was designed to incorporate the patch clamp technique, optical tweezers and absorption spectroscopy. The performance of the LOC was tested by a series of experiments. The oxygen content within the channels of the LOC was monitored by an oxygen sensor and verified by simultaneously studying the oxygenation state of chicken red blood cells (RBCs) with absorption spectra. The chicken RBCs were manipulated optically and steered in three dimensions towards a patch-clamp micropipette in a closed microfluidic channel. The oxygen level within the channels could be changed from a normoxic value of 18% O ₂ to an anoxic value of 0.0-0.5% O ₂. A time series of 3 experiments were performed, showing that the spectral transfer from the oxygenated to the deoxygenated state occurred after about 227 ± 1 s and a fully developed deoxygenated spectrum was observed after 298 ± 1 s, a mean value of 3 experiments. The tightness of the chamber to oxygen diffusion was verified by stopping the flow into the channel system while continuously recording absorption spectra showing an unchanged deoxygenated state during 5400 ± 2 s. A transfer of the oxygenated absorption spectra was achieved after 426 ± 1 s when exposing the cell to normoxic buffer. This showed the long time viability of the investigated cells. Successful patching and sealing were established on a trapped RBC and the whole-cell access (Ra) and membrane (Rm) resistances were measured to be 5.033 ± 0.412 M Ω and 889.7 ± 1.74 M Ω respectively.

A microfluidic live cell assay to study anthrax toxin induced cell lethality assisted by conditioned medium

It is technically challenging to investigate the function of secreted protein in real time by supply of conditioned medium that contains secreted protein of interest. The internalization of anthrax toxin is facilitated by a secreted protein Dickkopf-1 (DKK1) and its receptor, and eventually leads to cell lethality. To monitor the dynamic interplay between these components in live cells, we use an integrated microfluidic device to perform the cell viability assays with real-time controlled culture microenvironment in parallel. Conditioned medium, which contains the secreted proteins from specific cell lines, can be continuously pumped towards the cells that exposed to toxin. The exogenous DKK1 secreted from distant cells is able to rescue the sensitivity to toxin for those DKK1-knocked-down cells. This high-throughput assay allows us to precisely quantify the dynamic interaction between key components that cause cell death, and provide independent evidence of the function of DKK1 in the complex process of anthrax toxin internalization.

Controllable organization and high throughput production of recoverable 3D tumors using pneumatic microfluidics

Three-dimensional tumor culture methods offer a high degree of biological and clinical relevance to in vitro models as well as cancer therapy. However, a straightforward, dynamic, and high-throughput method for micro-manipulation of 3D tumors is not yet well established. In this study, we present a novel and simple strategy for producing biomimetic 3D tumors in a controllable, high throughput manner based on an integrated microfluidic system with well-established pneumatic microstructures. Serial manipulations, including one-step cell localization, array-like self-assembly, and real-time analysis of 3D tumors, are accomplished smoothly in the microfluidic device. The recovery of tumor products from the chip is performed by dynamic off-switch of the pneumatic microstructures. In addition, this microfluidic platform is demonstrated to be capable of producing multiple types of 3D tumors and performing the evaluation of tumor targeting by nanomedicine. The pneumatic microfluidic-based 3D tumor production shows potential for research on tumor biology, tissue engineering, and drug delivery.

Design of a 2D no-flow chamber to monitor hematopoietic stem cells

Hematopoietic stem cells (HSCs) are the most commonly used cell type in cell-based therapy. However, the investigation of their behavior in vitro has been limited by the difficulty of monitoring these non-adherent cells under classical culture conditions. Indeed, fluid flow moves cells away from the video-recording position and prevents single cell tracking over long periods of time. Here we describe a large array of 2D no-flow chambers allowing the monitoring of single HSCs for several days. The chamber design has been optimized to facilitate manufacturing and routine use. The chip contains a single inlet and 800 chambers. The chamber medium can be renewed by diffusion within a few minutes. This allowed us to stain live human HSCs with fluorescent primary antibodies in order to reveal their stage in the hematopoiesis differentiation pathway. Thus we were able to correlate human HSCs' growth rate, polarization and migration to their differentiation stage.

High throughput and multiplex localization of proteins and cells for in situ micropatterning using pneumatic microfluidics

We present a micropatterning method for protein/cell localization by using pneumatically controllable microstructures in an integrated microfluidic device.

Integration of microfluidics into the synthetic biology design flow

One goal of synthetic biology is to design and build genetic circuits in living cells for a range of applications. Major challenges in these efforts include increasing the scalability and robustness of engineered biological systems and streamlining and automating the synthetic biology workflow of specification-design-assembly-verification. We present here a summary of the advances in microfluidic technology, particularly microfluidic large scale integration, that can be used to address the challenges facing each step of the synthetic biology workflow. Microfluidic technologies allow precise control over the flow of biological content within microscale devices, and thus may provide more reliable and scalable construction of synthetic biological systems. The integration of microfluidics and synthetic biology has the capability to produce rapid prototyping platforms for characterization of genetic devices, testing of biotherapeutics, and development of biosensors.

Miniaturized pre-clinical cancer models as research and diagnostic tools

Cancer is one of the most common causes of death worldwide. Consequently, important resources are directed towards bettering treatments and outcomes. Cancer is difficult to treat due to its heterogeneity, plasticity and frequent drug resistance. New treatment strategies should strive for personalized approaches. These should target neoplastic and/or activated microenvironmental heterogeneity and plasticity without triggering resistance and spare host cells. In this review, the putative use of increasingly physiologically relevant microfabricated cell-culturing systems intended for drug development is discussed. There are two main reasons for the use of miniaturized systems. First, scaling down model size allows for high control of microenvironmental cues enabling more predictive outcomes. Second, miniaturization reduces reagent consumption, thus facilitating combinatorial approaches with little effort and enables the application of scarce materials, such as patient-derived samples. This review aims to give an overview of the state-of-the-art of such systems while predicting their application in cancer drug development.

Tubeless biochip for chemical stimulation of cells in closed-bioreactors: anti-cancer activity of the catechin–dextran conjugate

Here we introduce a tubeless microbioreactor for chemically stimulation of cells in microchambers, based on automatic cell valving, hydrostatic-pressure pumping and on-chip liquid reservoirs.

Microfluidic chip-based technologies: emerging platforms for cancer diagnosis

The development of early and personalized diagnostic protocols is considered the most promising avenue to decrease mortality from cancer and improve outcome. The emerging microfluidic-based analyzing platforms hold high promises to fulfill high-throughput and high-precision screening with reduced equipment cost and low analysis time, as compared to traditional bulky counterparts in bench-top laboratories. This article overviewed the potential applications of microfluidic technologies for detection and monitoring of cancer through nucleic acid and protein biomarker analysis. The implications of the technologies in cancer cytology that can provide functional personalized diagnosis were highlighted. Finally, the future niches for using microfluidic-based systems in tumor screening were briefly discussed.

Recent developments in microfluidic large scale integration

In 2002, Thorsen et al. integrated thousands of micromechanical valves on a single microfluidic chip and demonstrated that the control of the fluidic networks can be simplified through multiplexors [1]. This enabled realization of highly parallel and automated fluidic processes with substantial sample economy advantage. Moreover, the fabrication of these devices by multilayer soft lithography was easy and reliable hence contributed to the power of the technology; microfluidic large scale integration (mLSI). Since then, mLSI has found use in wide variety of applications in biology and chemistry. In the meantime, efforts to improve the technology have been ongoing. These efforts mostly focus on; novel materials, components, micromechanical valve actuation methods, and chip architectures for mLSI. In this review, these technological advances are discussed and, recent examples of the mLSI applications are summarized.

Probing cell-cell communication with microfluidic devices

Intercellular communication is a mechanism that regulates critical events during embryogenesis and coordinates signalling within differentiated tissues, such as the nervous and cardiovascular systems. To perform specialized activities, these tissues utilize the rapid exchange of signals among networks that, while are composed of different cell types, are nevertheless functionally coupled. Errors in cellular communication can lead to varied deleterious effects such as degenerative and autoimmune diseases. However, the intercellular communication network is extremely complex in multicellular organisms making isolation of the functional unit and study of basic mechanisms technically challenging. New experimental methods to examine mechanisms of intercellular communication among cultured cells could provide insight into physiological and pathological processes alike. Recent developments in microfluidic technology allow miniaturized and integrated devices to perform intercellular communication experiments on-chip. Microfluidics have many advantages, including the ability to replicate in vitro the chemical, mechanical, and physical cellular microenvironment of tissues with precise spatial and temporal control combined with dynamic characterization, high throughput, scalability and reproducibility. In this Focus article, we highlight some of the recent work and advances in the application of microfluidics to the study of mammalian intercellular communication with particular emphasis on cell contact and soluble factor mediated communication. In addition, we provide some insights into likely direction of the future developments in this field.

Construction of oxygen and chemical concentration gradients in a single microfluidic device for studying tumor cell-drug interactions in a dynamic hypoxia microenvironment

Recent microfluidic advancements in oxygen gradients have greatly promoted controllable oxygen-sensitive cellular investigations at microscale resolution. However, multi-gradient integration in a single microfluidic device for tissue-mimicking cell investigation is not yet well established. In this study, we describe a method that can generate oxygen and chemical concentration gradients in a single microfluidic device via the formation of an oxygen gradient in a chamber and a chemical concentration gradient between adjacent chambers. The oxygen gradient dynamics were systematically investigated, and were quantitatively controlled using simple exchange between the aerial oxygen and the oxygen-free conditions in the gas-permeable polydimethylsiloxane channel. Meanwhile, the chemical gradient dynamics was generated using a special channel-branched device. For potential medical applications of the established oxygen and chemical concentration gradients, a tumor cell therapy assessment was performed using two antitumor drugs (tirapazamine and bleomycin) and two tumor cell lines (human lung adenocarcinoma A549 cells and human cervical carcinoma HeLa cells). The results of the proof-of-concept experiment indicate the dose-dependent antitumor effect of the drugs and hypoxia-induced cytotoxicity of tirapazamine. We demonstrate that the integration of oxygen and chemical concentration gradients in a single device can be applied to investigating oxygen- and chemical-sensitive cell events, which can also be valuable in the development of multi-gradient generating procedures and specific drug screening.

Microfluidics for manipulating cells

Microfluidics, a toolbox comprising methods for precise manipulation of fluids at small length scales (micrometers to millimeters), has become useful for manipulating cells. Its uses range from dynamic management of cellular interactions to high-throughput screening of cells, and to precise analysis of chemical contents in single cells. Microfluidics demonstrates a completely new perspective and an excellent practical way to manipulate cells for solving various needs in biology and medicine. This review introduces and comments on recent achievements and challenges of using microfluidics to manipulate and analyze cells. It is believed that microfluidics will assume an even greater role in the mechanistic understanding of cell biology and, eventually, in clinical applications.

Biomimetic tumor microenvironment on a microfluidic platform

Tumor microenvironment is a highly complex system consisting of non-cancerous cells, soluble factors, signaling molecules, extracellular matrix, and mechanical cues, which provides tumor cells with integrated biochemical and biophysical cues. It has been recognized as a significant regulator in cancer initiation, progression, metastasis, and drug resistance, which is becoming a crucial component of cancer biology. Modeling microenvironmental conditions of such complexity in vitro are particularly difficult and technically challenging. Significant advances in microfluidic technologies have offered an unprecedented opportunity to closely mimic the physiological microenvironment that is normally encountered by cancer cells in vivo. This review highlights the recent advances of microfluidic platform in recapitulating many aspects of tumor microenvironment from biochemical and biophysical regulations. The major events relevant in tumorigenesis, angiogenesis, and spread of cancer cells dependent on specific combinations of cell types and soluble factors present in microenvironmental niche are summarized. The questions and challenges that lie ahead if this field is expected to transform the future cancer research are addressed as well.

Microfluidic devices for cell cultivation and proliferation

Microfluidic technology provides precise, controlled-environment, cost-effective, compact, integrated, and high-throughput microsystems that are promising substitutes for conventional biological laboratory methods. In recent years, microfluidic cell culture devices have been used for applications such as tissue engineering, diagnostics, drug screening, immunology, cancer studies, stem cell proliferation and differentiation, and neurite guidance. Microfluidic technology allows dynamic cell culture in microperfusion systems to deliver continuous nutrient supplies for long term cell culture. It offers many opportunities to mimic the cell-cell and cell-extracellular matrix interactions of tissues by creating gradient concentrations of biochemical signals such as growth factors, chemokines, and hormones. Other applications of cell cultivation in microfluidic systems include high resolution cell patterning on a modified substrate with adhesive patterns and the reconstruction of complicated tissue architectures. In this review, recent advances in microfluidic platforms for cell culturing and proliferation, for both simple monolayer (2D) cell seeding processes and 3D configurations as accurate models of in vivo conditions, are examined.

Investigation of hypoxia-induced myocardial injury dynamics in a tissue interface mimicking microfluidic device

Myocardial infarction is a major cause of morbidity and mortality worldwide. However, the methodological development of a spatiotemporally controllable investigation of the damage events in myocardial infarction remains challengeable. In the present study, we describe a micropillar array-aided tissue interface mimicking microfluidic device for the dynamic study of hypoxia-induced myocardial injury in a microenvironment-controllable manner. The mass distribution in the device was visually characterized, calculated, and systematically evaluated using the micropillar-assisted biomimetic interface, physiologically relevant flows, and multitype transportation. The fluidic microenvironment in the specifically functional chamber for cell positioning and analysis was successfully constructed with high fluidic relevance to the myocardial tissue. We also performed a microenvironment-controlled microfluidic cultivation of myocardial cells with high viability and regular structure integration. Using the well-established culture device with a tissue-mimicking microenvironment, a further on-chip investigation of hypoxia-induced myocardial injury was carried out and the varying apoptotic responses of myocardial cells were temporally monitored and measured. The results show that the hypoxia directionally resulted in observable cell shrinkage, disintegration of the cytoskeleton, loss of mitochondrial membrane potential, and obvious activation of caspase-3, which indicates its significant apoptosis effect on myocardial cells. We believe this microfluidic device can be suitable for temporal investigations of cell activities and responses in myocardial infarction. It is also potentially valuable to the microcontrol development of tissue-simulated studies of multiple clinical organ/tissue disease dynamics.

Dynamic trapping and high-throughput patterning of cells using pneumatic microstructures in an integrated microfluidic device

Microfluidic trapping methods create significant opportunities to establish highly controlled cell positioning and arrangement for the microscale study of numerous cellular physiological and pathological activities. However, a simple, straightforward, dynamic, and high-throughput method for cell trapping is not yet well established. In the present paper, we report a direct active trapping method using an integrated microfluidic device with pneumatic microstructures (PμSs) for both operationally and quantitatively dynamic localization of cells, as well as for high-throughput cell patterning. We designed and fabricated U-shape PμS arrays to replace the conventional fixed microstructures for reversible trapping. Multidimensional dynamics and spatial consistency of the PμSs were optically characterized and quantitatively demonstrated. Furthermore, we performed a systematic trapping investigation of the PμSs actuated at a pressure range of 0 psi to 20 psi using three types of popularly applied mammalian cells, namely, human lung adenocarcinoma A549 cells, human hepatocellular liver carcinoma HepG2 cells, and human breast adenocarcinoma MCF-7 cells. The cells were quantitatively trapped and controlled by the U-shape PμSs in a programmatic and parallel manner, and could be opportunely released. The trapped cells with high viability were hydrodynamically protected by the real-time actuation of specifically designed umbrella-like PμSs. We demonstrate that PμSs can be applied as an active microfluidic component for large-scale cell patterning and manipulation, which could be useful in many cell-based tissue organization, immunosensor, and high-throughput imaging and screening.

Precisely targeted delivery of cells and biomolecules within microchannels using aqueous two-phase systems

Laminar and pulsatile flow of aqueous solutions in microfluidic channels can be useful for controlled delivery of cells and molecules. Dispersion effects resulting from diffusion and convective disturbances, however, result in reagent delivery profiles becoming blurred over the length of the channels. This issue is addressed partially by using oil-in-water phase systems. However, there are limitations in terms of the biocompatibility of these systems for adherent cell culture. Here we present a fully biocompatible aqueous two-phase flow system that can be used to pattern cells within simple microfluidic channel designs, as well as to deliver biochemical treatments to cells according to discrete boundaries. We demonstrate that aqueous two-phase systems are capable of precisely delivering cells as laminar patterns, or as islands by way of forced droplet formation. We also demonstrate that these systems can be used to precisely control chemical delivery to preformed monolayers of cells growing within channels. Treatments containing trypsin were localized more reliably using aqueous two-phase delivery than using conventional delivery in aqueous medium.

Cell signaling analysis by mass spectrometry under coculture conditions on an integrated microfluidic device

A microfluidic device was integrated in a controlled coculture system, in which the secreted proteins were qualitatively and semiquantitatively determined by a directly coupled mass spectrometer. PC12 cells and GH3 cells were cocultured under various conditions as a model of the regulation of the organism by the nervous system. A micro-solid phase extraction (SPE) column was integrated in order to remove salts from the cells secretion prior to mass spectrometry detection. A three layer polydimethylsiloxane (PDMS) microfluidic device was fabricated to integrate valves for avoiding contamination between the cells coculture zone and the pretreatment zone. Electrospray ionization (ESI)-quadrupole (Q)-time of flight (TOF)-mass spectrometry was employed to realize highly sensitive qualitative analysis and to implement semiquantitative analysis. Furthermore, cell migrations under various coculture conditions were observed and discussed. The inhibition on growth hormone secretion from GH3 cells by dopamine released from PC12 cells was investigated and demonstrated. Thus, the developed platform provides a useful tool on cell to cell signaling studies for disease monitoring and drug delivery control.

Biomimetic approaches to control soluble concentration gradients in biomaterials

Soluble concentration gradients play a critical role in controlling tissue formation during embryonic development. The importance of soluble signaling in biology has motivated engineers to design systems that allow precise and quantitative manipulation of gradient formation in vitro. Engineering techniques have increasingly moved to the third dimension in order to provide more physiologically relevant models to study the biological role of gradient formation and to guide strategies for controlling new tissue formation for therapeutic applications. This review provides an overview of efforts to design biomimetic strategies for soluble gradient formation, with a focus on microfluidic techniques and biomaterials approaches for moving gradient generation to the third dimension.