Paper/PMMA Hybrid 3D Cell Culture Microfluidic Platform for the Study of Cellular Crosstalk

Microfluidic Technologies in Advancing Cancer Research

This review explores the significant role of microfluidic technologies in advancing cancer research, focusing on the below key areas: droplet-based microfluidics, organ-on-chip systems, paper-based microfluidics, electrokinetic chips, and microfluidic chips for the study of immune response. Droplet-based microfluidics allows precise manipulation of cells and three-dimensional microtissues, enabling high-throughput experiments that reveal insights into cancer cell migration, invasion, and drug resistance. Organ-on-chip systems replicate human organs to assess drug efficacy and toxicity, particularly in the liver, heart, kidney, gut, lung, and brain. Paper-based microfluidics offers an alternative approach to accomplish rapid diagnostics and cell- and tissue-based bioassays. Electrokinetic microfluidic chips offer precise control over cell positioning and behavior, facilitating drug screening and cellular studies. Immune response studies leverage real-time observation of interactions between immune and cancer cells, supporting the development of immunotherapies. These microfluidic advances are paving the way for personalized cancer treatments while addressing challenges of scalability, cost, and clinical integration.

Microfluidics chips fabrication techniques comparison

This study investigates various microfluidic chip fabrication techniques, highlighting their applicability and limitations in the context of urgent diagnostic needs showcased by the COVID-19 pandemic. Through a detailed examination of methods such as computer numerical control milling of a polymethyl methacrylate, soft lithography for polydimethylsiloxane-based devices, xurography for glass-glass chips, and micromachining-based silicon-glass chips, we analyze each technique's strengths and trade-offs. Hence, we discuss the fabrication complexity and chip thermal properties, such as heating and cooling rates, which are essential features of chip utilization for a polymerase chain reaction. Our comparative analysis reveals critical insights into material challenges, design flexibility, and cost-efficiency, aiming to guide the development of robust and reliable microfluidic devices for healthcare and research. This work underscores the importance of selecting appropriate fabrication methods to optimize device functionality, durability, and production efficiency.

Development of a Folding Paper System To Enable the Analysis of Gene Profile of Short- and Long-Distance Cancer Cell Migration

In cancer metastasis, where mortality rates remain high despite advancements in medical treatments, understanding the molecular pathways and cellular dynamics underlying tumor spread is critical for devising more effective therapeutic strategies. Here, a folding paper system was proposed and developed to mimic native tumor microenvironment. This system, composed of 7 stacked layers of paper enclosed in a holder, allows for the culture of cancer cells under conditions mimicking those found in solid tumors, including limited oxygen and nutrients. Because of the migratory capabilities of cancer cells, the cells in the center layer could migrated to outer layers of the paper stack, enabling the differentiation of cells based on their migratory potential. Subsequent gene expression analysis, conducted through RT-PCR and RNA sequencing, revealed significant correlations between cancer cell migration distance and the expression of genes associated with hypoxia, metabolism, ATP production, and cellular process. Moreover, our study identified cells with aggressive phenotypic traits from the outer layers of the paper stack, highlighting the potential of this system for enabling the study of aggressive cancer cell characteristics. Validation of the folding paper system against clinical carcinoma tissue demonstrated its ability to faithfully mimic the native tumor microenvironment. Overall, our findings underscore the utility of the folding paper system as a valuable tool for investigating and identifying critical molecular pathways involved in cancer metastasis.

Bionanotechnology and bioMEMS (BNM): state-of-the-art applications, opportunities, and challenges

The development of micro- and nanotechnology for biomedical applications has defined the cutting edge of medical technology for over three decades, as advancements in fabrication technology developed originally in the semiconductor industry have been applied to solving ever-more complex problems in medicine and biology. These technologies are ideally suited to interfacing with life sciences, since they are on the scale lengths as cells (microns) and biomacromolecules (nanometers). In this paper, we review the state of the art in bionanotechnology and bioMEMS (collectively BNM), including developments and challenges in the areas of BNM, such as microfluidic organ-on-chip devices, oral drug delivery, emerging technologies for managing infectious diseases, 3D printed microfluidic devices, AC electrokinetics, flexible MEMS devices, implantable microdevices, paper-based microfluidic platforms for cellular analysis, and wearable sensors for point-of-care testing.

Analysis of Cellular Crosstalk and Molecular Signal between Periosteum-Derived Precursor Cells and Peripheral Cells During Bone Healing Process Using a Paper-Based Osteogenesis-On-A-Chip Platform

Periosteum-derived progenitor cells (PDPCs) are highly promising cell sources that are indispensable in the bone healing process. Adipose-derived stem cells (ADSCs) are physiologically close to periosteum tissue and release multiple growth factors to promote the bone healing process. Co-culturing PDPCs and ADSCs can construct periosteum-bone tissue microenvironments for the study of cellular crosstalk and molecular signal in the bone healing process. In the current work, a paper-based osteogenesis-on-a-chip platform was successfully developed to provide an in vitro three-dimensional coculture model. The platform was a paper substrate sandwiched between PDPC-hydrogel and ADSC-hydrogel suspensions. Cell secretion could be transferred through the paper substrate from one side to another side. Growth factors including BMP2, TGF-β, POSTN, Wnt proteins, PDGFA, and VEGFA were directly analyzed by a paper-based immunoassay. Cellular crosstalk was studied by protein expression on the paper substrate. Moreover, osteogenesis of PDPCs was investigated by examining the mRNA expressions of PDPCs after culture. Neutralizing and competitive assays were conducted to understand the correlation between growth factors secreted from ADSCs and the osteogenesis of PDPCs. In vitro periosteum-bone tissue microenvironment was established by the paper-based osteogenesis-on-a-chip platform. The proposed approach provides a promising assay of cellular crosstalk and molecular signal in 3D coculture microenvironment that may potentially lead to the development of effective bone regeneration therapy.

Bone/cartilage organoid on-chip: Construction strategy and application

The necessity of disease models for bone/cartilage related disorders is well-recognized, but the barrier between ex-vivo cell culture, animal models and the real human body has been pending for decades. The organoid-on-a-chip technique showed opportunity to revolutionize basic research and drug screening for diseases like osteoporosis and arthritis. The bone/cartilage organoid on-chip (BCoC) system is a novel platform of multi-tissue which faithfully emulate the essential elements, biologic functions and pathophysiological response under real circumstances. In this review, we propose the concept of BCoC platform, summarize the basic modules and current efforts to orchestrate them on a single microfluidic system. Current disease models, unsolved problems and future challenging are also discussed, the aim should be a deeper understanding of diseases, and ultimate realization of generic ex-vivo tools for further therapeutic strategies of pathological conditions.

Tetrahedral DNA framework assisted rotational paper-based analytical device for differential detection of SARS-CoV-2 and influenza A H1N1 virus

Coronavirus disease 2019 (COVID-19) and influenza A are two respiratory infectious diseases with similar clinical manifestations. Because of the complex global epidemic situation of COVID-19, the distinction and diagnosis of COVID-19 and influenza A infected persons is crucial for epidemic prevention and control. In this study, tetrahedral DNA framework (TDF) was combined with a rotational paper-based analytical device, and the color change generated by the reaction between horseradish peroxidase (HRP) and 3,3'5,5'-tetramethylbenzidine (TMB)-H₂O₂ was used for grayscale signal analysis by ImageJ software. The quantitative detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A H1N1 virus were realized simultaneously. Under the optimal conditions, the paper-based analytical device showed a good linear relationship between the two viruses in the range of 10^-14-10^-8g/mL, and the two viruses were not affected by cross reaction. This sensor provides a convenient and reliable method for clinical rapid differentiation and diagnosis of COVID-19 and influenza A.

Cytotoxicity evaluation of sodium lauryl sulfate in a paper-based 3D cell culture system

Because three-dimensional (3D) cell culture is more similar to in vivo cell microenvironments than two-dimensional (2D) cell culture, various 3D cell culture systems have been developed. Recently, paper has been used as a promising material for 3D cell culture and tissue models due to its flexibility, ease of manufacture, low cost, and widespread accessibility. In this study, we fabricated a paper-based 3D cell culture platform consisting of a hydrophilic region for cell attachment and a hydrophobic region printed with wax. Using this paper platform for 3D culture of L929 cells, we evaluated the cytotoxicity of a model substance, sodium lauryl sulfate (SLS), using water-soluble tetrazolium salt, Live/Dead, and luminescence assays. Then we compared those cytotoxicity results with results from a conventional 3D cell culture kit and 2D cell culture. We found that 3D cultured cells on paper responded more sensitively to SLS than 2D cultured cells, and the cytotoxicity of SLS to cells grown on the paper-based 3D cell culture platform was similar to that of cells grown using a commercially available 3D cell culture kit. Therefore, we expect that our paper-based 3D cell culture platform can be applied as a simple and facile tool for cell viability evaluation.

A Review of Optical Imaging Technologies for Microfluidics

Microfluidics can precisely control and manipulate micro-scale fluids, and are also known as lab-on-a-chip or micro total analysis systems. Microfluidics have huge application potential in biology, chemistry, and medicine, among other fields. Coupled with a suitable detection system, the detection and analysis of small-volume and low-concentration samples can be completed. This paper reviews an optical imaging system combined with microfluidics, including bright-field microscopy, chemiluminescence imaging, spectrum-based microscopy imaging, and fluorescence-based microscopy imaging. At the end of the article, we summarize the advantages and disadvantages of each imaging technology.

In Situ Detection of Hydrogen Sulfide in 3D-Cultured, Live Prostate Cancer Cells Using a Paper-Integrated Analytical Device

In this study, a paper-integrated analytical device that combined a paper-based colorimetric assay with a paper-based cell culture platform was developed for the in situ detection of hydrogen sulfide (H2S) in three-dimensional (3D)-cultured, live prostate cancer cells. Two kinds of paper substrates were fabricated using a simple wax-printing methodology to form the cell culture and detection zones, respectively. LNCaP cells were seeded directly on the paper substrate and grown in the paper-integrated analytical device. The cell viability and H2S production of LNCaP cells were assessed using a simple water-soluble tetrazolium salt colorimetric assay and H2S-sensing paper, respectively. The H2S-sensing paper showed good sensitivity (sensitivity: 6.12 blue channel intensity/μM H2S, R2 = 0.994) and a limit of quantification of 1.08 μM. As a result, we successfully measured changes in endogenous H2S production in 3D-cultured, live LNCaP cells within the paper-integrated analytical device while varying the duration of incubation and substrate concentration (L-cysteine). This paper-integrated analytical device can provide a simple and effective method to investigate H2S signaling pathways and drug screening in a 3D culture model.

Analysis of the Internal Hypoxic Environment in Solid Tumor Tissue Using a Folding Paper System

Hypoxia is a nonphysiological oxygen tension which is common in most malignant tumors. Hypoxia stimulates complicated cell signaling networks in cancer cells, e.g., the HIF, PI3K, MAPK, and NFκB pathways. Then, cells release a number of cytokines such as VEGFA to promote the growth of peripheral blood vessels and lead to metastasis. In the current work, understanding of the internal hypoxic environment in solid tumor tissue was attempted by developing a folding paper system. A paper-based solid tumor was constructed by folding a filter paper cultured with cancer cells. The cellular response in each layer could be analyzed by disassembling the folded paper after the culture course. The result showed that an internal hypoxic environment was successfully reproduced in the paper-based solid tumor. The cells in the inner layer expressed high levels of HIF1-α and VEGFA. Hence, proliferation and migration of endothelial cells were shown to be induced by the cells located in the internal hypoxic environment. Moreover, the paper-based solid tumor was transplanted into nude mice for the study of hypoxic response and angiogenesis. The crosstalk between internal and external parts of solid tumor tissue could be analyzed by sectioning each layer of the paper-based solid tumor. This approach provides a favorable analytical method for the discovery of the interaction between cancer cells, hypoxia, and peripheral angiogenesis.

Recent innovations in cost-effective polymer and paper hybrid microfluidic devices

Hybrid microfluidic systems that are composed of multiple different types of substrates have been recognized as a versatile and superior platform, which can draw benefits from different substrates while avoiding their limitations. This review article introduces the recent innovations of different types of low-cost hybrid microfluidic devices, particularly focusing on cost-effective polymer- and paper-based hybrid microfluidic devices. In this article, the fabrication of these hybrid microfluidic devices is briefly described and summarized. We then highlight various hybrid microfluidic systems, including polydimethylsiloxane (PDMS)-based, thermoplastic-based, paper/polymer hybrid systems, as well as other emerging hybrid systems (such as thread-based). The special benefits of using these hybrid systems have been summarized accordingly. A broad range of biological and biomedical applications using these hybrid microfluidic devices are discussed in detail, including nucleic acid analysis, protein analysis, cellular analysis, 3D cell culture, organ-on-a-chip, and tissue engineering. The perspective trends of hybrid microfluidic systems involving the improvement of fabrication techniques and broader applications are also discussed at the end of the review.

Microfluidic technologies for immunotherapy studies on solid tumours

Immunotherapy is a powerful and targeted cancer treatment that exploits the body's immune system to attack and eliminate cancerous cells. This form of therapy presents the possibility of long-term control and prevention of recurrence due to the memory capabilities of the immune system. Various immunotherapies are successful in treating haematological malignancies and have dramatically improved outcomes in melanoma. However, tackling other solid tumours is more challenging, mostly because of the immunosuppressive tumour microenvironment (TME). Current in vitro models based on traditional 2D cell monolayers and animal models, such as patient-derived xenografts, have limitations in their ability to mimic the complexity of the human TME. As a result, they have inadequate translational value and can be poorly predictive of clinical outcome. Thus, there is a need for robust in vitro preclinical tools that more faithfully recapitulate human solid tumours to test novel immunotherapies. Microfluidics and lab-on-a-chip technologies offer opportunities, especially when performing mechanistic studies, to understand the role of the TME in immunotherapy, and to expand the experimental throughput when using patient-derived tissue through its miniaturization capabilities. This review first introduces the basic concepts of immunotherapy, presents the current preclinical approaches used in immuno-oncology for solid tumours and then discusses the underlying challenges. We provide a rationale for using microfluidic-based approaches, highlighting the most recent microfluidic technologies and methodologies that have been used for studying cancer-immune cell interactions and testing the efficacy of immunotherapies in solid tumours. Ultimately, we discuss achievements and limitations of the technology, commenting on potential directions for incorporating microfluidic technologies in future immunotherapy studies.

Hemp-Based Microfluidics

Hemp is a sustainable, recyclable, and high-yield annual crop that can be used to produce textiles, plastics, composites, concrete, fibers, biofuels, bionutrients, and paper. The integration of microfluidic paper-based analytical devices (µPADs) with hemp paper can improve the environmental friendliness and high-throughputness of µPADs. However, there is a lack of sufficient scientific studies exploring the functionality, pros, and cons of hemp as a substrate for µPADs. Herein, we used a desktop pen plotter and commercial markers to pattern hydrophobic barriers on hemp paper, in a single step, in order to characterize the ability of markers to form water-resistant patterns on hemp. In addition, since a higher resolution results in densely packed, cost-effective devices with a minimized need for costly reagents, we examined the smallest and thinnest water-resistant patterns plottable on hemp-based papers. Furthermore, the wicking speed and distance of fluids with different viscosities on Whatman No. 1 and hemp papers were compared. Additionally, the wettability of hemp and Whatman grade 1 paper was compared by measuring their contact angles. Besides, the effects of various channel sizes, as well as the number of branches, on the wicking distance of the channeled hemp paper was studied. The governing equations for the wicking distance on channels with laser-cut and hydrophobic side boundaries are presented and were evaluated with our experimental data, elucidating the applicability of the modified Washburn equation for modeling the wicking distance of fluids on hemp paper-based microfluidic devices. Finally, we validated hemp paper as a substrate for the detection and analysis of the potassium concentration in artificial urine.

Biocompliant Composite Au/pHEMA Plasmonic Scaffolds for 3D Cell Culture and Noninvasive Sensing of Cellular Metabolites

The field of 3D printing is an area of active research, with a substantial focus given to the design and construction of customized tools for applications in technology. There exists a particular need in these developing areas of opportunity for new multi-functional soft materials that are biologically compatible for the growth and directed culturing of cells. Herein, a composite material consisting of gold nanoparticles with useful plasmonic properties embedded within a highly hydrophilic poly-2-hydroxyethylmethacrylate matrix is described and characterized. This composite material serves dual functions as both host framework scaffold for cell lines such as pre-osteoblasts as well as a plasmonic biosensor for in situ measurements of living cells. The plasmonic properties of this system are characterized as a function of the material properties and related to compositional features of the material through a proposed light-directed mechanism. This chemistry provides a tunable, 3D printable plasmonic composite material of encapsulated gold nanoparticles in a biologically-compliant, acrylate-based hydrogel matrix. Surface-enhanced Raman scattering studies of 3D-microcultures supported by the scaffolds are carried out and the strong influence of perm-selective molecular diffusion in its analytical responses is established. Most notably, specific, largely hydrophilic, cellular metabolites are detected within the supported live cultures.

Microfibrous Extracellular Matrix Changes the Liver Hepatocyte Energy Metabolism via Integrins

Cell line-based liver models are critical tools for liver-related studies. However, the conventional monolayer culture of hepatocytes, the most widely used in vitro model, does not have the extracellular matrix (ECM), which contributes to the three-dimensional (3D) arrangement of the hepatocytes in the liver. As a result, the metabolic properties of the hepatocytes in the monolayer tissue culture may not accurately reflect those of the hepatocytes in the liver. Here, we developed a modular platform for 3D hepatocyte cultures on fibrous ECMs produced by electrospinning, a technique that can turn a polymer solution to the micro/nanofibers and has been widely used to produce scaffolds for 3D cell cultures. Metabolomics quantitation by liquid chromatography-mass spectrometry (LC-MS) indicated that Huh7 hepatocytes grown in microfibers electrospun from silk fibroin exhibited reduced glycolysis and tricarboxylic acid (TCA) cycle, as compared to the cells cultured as a monolayer. Further mechanistic studies suggested that integrins were correlated to the ECM's effects. This is the first time to report how an ECM scaffold could affect the fundamental metabolism of the hepatocytes via integrins.

Traversing behavior of tumor cells in three-dimensional platforms with different topography

Three-dimensional polydimethylsiloxane platforms were developed to mimic the extracellular matrix with blood vessels by having scaffolds with micropatterns, porous membrane and trenches. Precisely controlled physical dimensions, layouts, and topography as well as different surface chemical treatments were applied to study their influences on nasopharyngeal carcinoma cell (10-15 μm in diameter) migration in mimicked platforms over 15-hour of time-lapse imaging. By placing the pores at different distance from the edges of the trenches, pores with different trench sidewall exposures and effective sizes were generated. Pores right next to the trench sidewalls showed the highest cell traversing probability, most likely related to the larger surface contact area with cells along the sidewalls. Straight grating oriented perpendicular to trenches below the top layer increased cell traversing probability. Pore shape as well as pore size influenced the cell traversing probability and cells could not traverse through pores that were 6 μm or less in diameter, which is much smaller than the cell size. Trench depth of 15 μm could induce more cells to traverse through the porous membrane, while shallower trenches impeded cell traversing and longer time was needed for cells to traverse because 3 and 6 μm deep trenches were much smaller than cell size which required large cell deformation. Hydrophobic surface coating on the top layer and fibronectin in pores and trenches increased the cell traversing probability and reduced the pore size that cells could traverse from 8 to 6 μm, which indicated that cells could have larger deformation with certain surface coatings.

Application of Microfluidic Chip Technology in Food Safety Sensing

Food safety analysis is an important procedure to control food contamination and supervision. It is urgently needed to construct effective methods for on-site, fast, accurate and popular food safety sensing. Among them, microfluidic chip technology exhibits distinguish advantages in detection, including less sample consumption, fast detection, simple operation, multi-functional integration, small size, multiplex detection and portability. In this review, we introduce the classification, material, processing and application of the microfluidic chip in food safety sensing, in order to provide a good guide for food safety monitoring.

A Disposable Passive Microfluidic Device for Cell Culturing

In this work, a disposable passive microfluidic device for cell culturing that does not require any additional/external pressure sources is introduced. By regulating the height of fluidic columns and the aperture and closure of the source wells, the device can provide different media and/or drug flows, thereby allowing different flow patterns with respect to time. The device is made of two Polymethylmethacrylate (PMMA) layers fabricated by micro-milling and solvent assisted bonding and allows us to ensure a flow rate of 18.6 μl/ℎ - 7%/day, due to a decrease of the fluid height while the liquid is driven from the reservoirs into the channels. Simulations and experiments were conducted to characterize flows and diffusion in the culture chamber. Melanoma tumor cells were used to test the device and carry out cell culturing experiments for 48 hours. Moreover, HeLa, Jurkat, A549 and HEK293T cell lines were cultivated successfully inside the microfluidic device for 72 hours.

Hybrid Three Dimensionally Printed Paper-Based Microfluidic Platform for Investigating a Cell's Apoptosis and Intracellular Cross-Talk

In this paper, we first proposed a novel hybrid three-dimensional (3D) printed and paper-based microfluidic platform and applied it for investigating the cell's apoptosis and intracellular cross-talk. The fabrication of a 3D-printed microfluidic chip is much easier than polydimethylsiloxane (PDMS) chip and can be applied in many common labs without soft lithogrophy fabrication equipment. Moreover, 3D printing can be perfectly combined with paper-based chips that can provide 3D scaffold for cell culture and analysis. In addition, these paper chips are disposable after use, greatly reducing the experimental cost. We integrated "Christmas Tree" structure with the top layer of the 3D-printed microfluidic chip to generate a continuous concentration gradient, and the bottom layer contained paper-based chips as cell culture area. The two-layer structure allows the concentration gradient forming layer to be separated from the cell culture layer, which can simplify the planting of cells in the microfluidic chip and make sure the cells stay in the culture chambers and don't clog the microfluidic channels. Applying this hybrid platform, we examined the effect of H₂S on cancer cells. Continuous exposure to a low concentration of H₂S inhibited cancer cell SMMC-7721 proliferation by inducing cell apoptosis. We also found that two gaseous molecules H₂S and NO have cross-talk in cancer cells; they formed bioactive intermediate polysulfides in cancer cells. It is expected that this novel hybrid 3D-printed and paper-based microfluidic platform will have widespread application prospects in cell investigation.

Review of 3D Cell Culture with Analysis in Microfluidic Systems

A review with 105 references that analyzes the emerging research area of 3D cell culture in microfluidic platforms with integrated detection schemes. Over the last several decades a central focus of cell culture has been the development of better in vivo mimics. This has led to the evolution from planar cell culture to cell culture on 3D scaffolds, and the incorporation of cell scaffolds into microfluidic devices. Specifically, this review explores the incorporation of suspension culture, hydrogels scaffolds, paper-based scaffolds, and fiber-based scaffolds into microfluidic platforms. In order to decrease analysis time, simplify sample preparation, monitor key signaling pathways involved in cell-to-cell communication or cell growth, and combat the limitations of sample volume/ dilution seen in traditional assays, researchers have also started to focus on integrating detection schemes into the cell culture devices. This review will highlight the work that has been performed towards combining these techniques and will discuss potential future directions. It is clear that microfluidic-based 3D cell culture coupled with quantitative analysis can greatly improve our ability to mimic and understand in vivo systems.

Biofunctionalized cellulose paper matrix for cell delivery applications

The present study delineates the preparation, characterization, and application of (3-Aminopropyl)triethoxysilane (APTES)/Caprine liver-derived extracellular matrix (CLECM) coated paper matrix for cell delivery. Here, we exploited positively charged surface of the paper matrix (as imparted by APTES derivatization) to improve the biological responses of the cells. Our results demonstrated that the functionalized paper matrixes favored the adhesion, growth, and proliferation of multiple cell types including normal, transformed, cancerous, and stem cells as compared to the pristine paper matrix. Upon implantation into the mice model, the developed paper matrix supported infiltration of the host cells and vasculature without showing any evidence of significant systemic toxicity. Moreover, the cells cultured on the paper matrix, when delivered to the CAM and mouse models, showed an enhanced vascular network around the substrate, thereby confirming its potential to deliver the cells in vivo. Together, the study confirms that the reported paper-based platform is easy to fabricate, cheap, portable and could efficiently be applied to cell delivery applications for either tissue repair or the development of humanized animal model.

Paper/polymer composited microfluidic platform for screening cell viability and protein expression under a chemical gradient environment

Culturing cells in three-dimensional (3D) environment can obtain a better clinical prediction for evaluating chemotherapy protocols and become a standard culture practice in cancer research. However, it involves tedious and time consuming operation. In the current work, a paper/polymer composited microfluidic platform was developed for screening cell viability and protein expression under chemical gradient environment. Cells were cultured in a paper sheet and expressed cell properties in 3D environment. The paper sheet was encapsulated in the microfluidic platform generating chemical gradient. After the culture course, investigations of cell viability and protein expression were respectively achieved by directly adding reagent and conducting on-paper immunoassay. Activation of respective signaling pathway could be identified and responded to different stimulations including nutrient gradient, IL-6 cytokine gradient, and anti-cancer drug gradient. On-paper analysis of protein expression could be completed within 1.5 h. The present technique integrates tedious operations on a single paper substrate. It provides a first-tier screening tool for cellular response under chemical gradient.

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.

Paper Microfluidics for Cell Analysis

Paper microfluidics has attracted much attention since its first introduction around one decade ago due to the merits such as low cost, ease of fabrication and operation, portability, and facile integration with other devices. The dominant application for paper microfluidics still lies in point-of-care testing (POCT), which holds great promise to provide diagnostic tools to meet the ASSURED criteria. With micro/nanostructures inside, paper substrates provide a natural 3D scaffold to mimic native cellular microenvironments and create excellent biointerfaces for cell analysis applications, such as long-term 3D cell culture, cell capture/phenotyping, and cell-related biochemical analysis (small molecules, protein DNA, etc.). This review summarizes cell-related applications based on various engineered paper microdevices and provides some perspectives for paper microfluidics-based cell analysis.

Microfluidic implementation of functional cytometric microbeads for improved multiplexed cytokine quantification

Functional microbeads have been widely applied in molecular identification and other biochemical applications in the past decade, owing to the compatibility with flow cytometry and the commercially available microbeads for a wide range of molecular identification. Nevertheless, there is still a technical hurdle caused by the significant sample volume required (∼50 μl), limited molecular detection limit (∼20 pg/ml), complicated liquid/microbead handling procedures, and the long reaction time (>2 h). In this work, we optimize the operation of an automated microbead-based microfluidic device for the reagent mixing and the dynamic cytokine detection. In particular, we adopt fluorescence microscopy for quantification of multiple microbeads in each microchamber instead of flow cytometry for a lower detection limit. The operation parameters are then configured for improved measurement performance. As demonstrated, we consider the cytokine secretion of human macrophage-differentiating lymphocytes stimulated by lipopolysaccharides. We examine requirements on the mixing duration, minimal sample volume, and the image analysis scheme for the smaller biosample volume (<5 μl), the lower cytokine detection limit (∼5 pg/ml), and shorter process time (∼30 min). Importantly, this microfluidic strategy can be further extended in the molecular profiling using other functional microbeads for a broad range of biomedical applications.

Towards a high throughput impedimetric screening of chemosensitivity of cancer cells suspended in hydrogel and cultured in a paper substrate

In order to achieve high predictive value of cell chemosensitivity test for clinical efficacy, cancer cells were suggested to be encapsulated and cultured in hydrogel to mimic the natural microenvironment of tumors. However, handling 3D cells/hydrogel culture construct is tedious and cellular response is difficult to be quantitatively analyzed. In the current study, a novel platform for conducting 3D cell culture and analyzing cell viability has been developed towards a high throughput drug screening. Cells encapsulated in the hydrogel were cultured in the microwells of a paper substrate. The substrate was then immersed in the culture medium containing drug for 2 days. At 24 and 48h during the culture course, the paper substrate was placed on the measurement electrodes for conducting the impedance measurement in order to quantify the cell viability in the hydrogel. Cell viability of two human hepatoma cell lines (Huh7 and Hep-G2) was quantitatively investigated under the treatment of two drugs (doxorubicin and etoposide). The results represented by IC₅₀ values revealed that Huh7 cells had a higher drug resistance than Hep-G2 cells and doxorubicin had a higher efficacy than etoposide for treating hepatocellular carcinoma. The current work has demonstrated a high throughput, convenient, and quantitative platform for the investigation of chemosensitivity of cells cultured in the 3D environment.