Rapid time-lapse 3D oxygen tension measurements within hydrogels using widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) and image segmentation.

Understanding the influence of oxygen tension on cellular functions and behaviors is crucial for investigating various physiological and pathological conditions. In vitro cell culture models, particularly those based on hydrogel extracellular matrices, have been developed to study cellular responses in specific oxygen microenvironments. However, accurately characterizing oxygen tension variations with great spatiotemporal resolutions, especially in three dimensions, remains challenging. This paper presents an approach for rapid time-lapse 3D oxygen tension measurements in hydrogels using a widely available inverted fluorescence microscope. Oxygen-sensitive fluorescent microbeads and widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) are utilized for oxygen tension estimation. To incorporate the third dimension, a motorized sample stage is implanted that enables automated image acquisition in the vertical direction. A machine learning algorithm based on K-means clustering is employed for microbead position identification. Using an upside-down microfluidic device, 3D oxygen gradients are generated within a hydrogel sample, and z-stack images are acquired using the FD-FLIM system. Analyses of the acquired images, involving microbead position identification, lifetime calculation, and oxygen tension conversion, are then performed offline. The results demonstrate the functionality of the developed approach for rapid time-lapse 3D oxygen tension measurements in hydrogels. Furthermore, the 3D oxygen tension adjacent to a tumor spheroid within a hydrogel during media exchange is characterized. The results further confirm that the 3D spatiotemporal oxygen tension profiles can be successfully measured quantitatively using the established setup and analysis process and that the approach may have great potential for investigating cellular activities within oxygen microenvironments.

Malignancy progression and treatment efficacy estimation of osteosarcoma patients based on in vitro cell culture model and analysis.

BACKGROUND: Osteosarcoma (OS) usually happens in patients under 20 years old and is notorious for its low survivorship and limb loss. Personalized medicine is a viable approach to increase the efficiency of chemotherapy which is the main prognostic factor for survivorship after surgical treatment. METHODS: In this five-year prospective observational study, we collected primary cells of osteosarcoma from 15 patients, and examined the correlation between clinical characters of patients and cell properties characterized using various in vitro assays. The properties including genes expression, pro-angiogenic capability and anti-cancer drug response are characterized respectively by using RT-PCR, tube formation assay, osteogenesis assay and drug testing on 3D tumor spheroid model. RESULT: The results suggest that OS patients with higher MMP9 expression levels have higher probability to develop skip metastasis (p = 0.041). The 3D tumor spheroid test based on the median lethal dose from 2D culture provides some prognostic value. Patients do not response well to methotrexate (MTX) show higher percentage of high pathology grade (p = 0.009) and lung metastasis (p = 0.044). Also, patients respond well to ifosfamide (IFO) have higher probability to achieve high tumor necrosis rate (p = 0.007). CONCLUSION: The association between cell properties and clinical characters of patients provided by our data can act as potential prognostic factors to help physicians to develop effective personalized chemotherapy for osteosarcoma treatments.

Study 3D Endothelial Cell Network Formation under Various Oxygen Microenvironment and Hydrogel Composition Combinations Using Upside-Down Microfluidic Devices.

Formation of 3D networks is a crucial process for endothelial cells during development of primary blood vessels under both normal and pathological conditions. In order to investigate effects of oxygen microenvironment and matrix composition on the 3D network formation, an upside-down microfluidic cell culture device capable of generating oxygen gradients is developed in this paper. In cell experiments, network formation of human umbilical vein endothelial cells (HUVECs) within fibrinogen-based hydrogels with different concentrations of hyaluronic acid (HA) is systematically studied. In addition, five different oxygen microenvironments (uniform normoxia, 5%, and 1% O2 ; oxygen gradients under normoxia and 5% O2 ) are also applied for the cell culture. The generated oxygen gradients are characterized based on fluorescence lifetime measurements. The experimental results show increased 3D cell network length when the cells are cultured under the oxygen gradients within the hydrogels with the HA addition suggesting their roles in promoting network formation. Furthermore, the formed networks tend to align along the direction of the oxygen gradients indicating the presence of gradient-driven cellular response. The results demonstrate that the developed upside-down microfluidic device can provide an advanced platform to investigate 3D cell culture under the controlled oxygen microenvironments for various biomedical studies in vitro.

MCT-1/miR-34a/IL-6/IL-6R signaling axis promotes EMT progression, cancer stemness and M2 macrophage polarization in triple-negative breast cancer.

BACKGROUND: Triple-negative breast cancer (TNBC) is a poor prognostic breast cancer with the highest mutations and limited therapeutic choices. Cytokine networking between cancer cells and the tumor microenvironment (TME) maintains the self-renewing subpopulation of breast cancer stem cells (BCSCs) that mediate tumor heterogeneity, resistance and recurrence. Immunotherapy of those factors combined with targeted therapy or chemoagents may advantage TNBC treatment. RESULTS: We found that the oncogene Multiple Copies in T-cell Malignancy 1 (MCT-1/MCTS1) expression is a new poor-prognosis marker in patients with aggressive breast cancers. Overexpressing MCT-1 perturbed the oncogenic breast epithelial acini morphogenesis and stimulated epithelial-mesenchymal transition and matrix metalloproteinase activation in invasive TNBC cells, which were repressed after MCT-1 gene silencing. As mammary tumor progression was promoted by oncogenic MCT-1 activation, tumor-promoting M2 macrophages were enriched in TME, whereas M2 macrophages were decreased and tumor-suppressive M1 macrophages were increased as the tumor was repressed via MCT-1 knockdown. MCT-1 stimulated interleukin-6 (IL-6) secretion that promoted monocytic THP-1 polarization into M2-like macrophages to increase TNBC cell invasiveness. In addition, MCT-1 elevated the soluble IL-6 receptor levels, and thus, IL-6R antibodies antagonized the effect of MCT-1 on promoting M2-like polarization and cancer cell invasion. Notably, MCT-1 increased the features of BCSCs, which were further advanced by IL-6 but prevented by tocilizumab, a humanized IL-6R antibody, thus MCT-1 knockdown and tocilizumab synergistically inhibited TNBC stemness. Tumor suppressor miR-34a was induced upon MCT-1 knockdown that inhibited IL-6R expression and activated M1 polarization. CONCLUSIONS: The MCT-1 pathway is a novel and promising therapeutic target for TNBC.

Widefield frequency domain fluorescence lifetime imaging microscopy (FD-FLIM) for accurate measurement of oxygen gradients within microfluidic devices.

An oxygen gradient is a key variable influencing various biological activities in vivo, such as tissue repair and tumor growth. To study the phenomenon, in vitro cell studies using microfluidic devices capable of generating oxygen gradients have been developed recently. However, it is challenging to accurately measure the gradient profiles in devices. The traditional fluorescence intensity-based method suffers from the difficulty of accurate measurement due to background fluorescence artefacts. In addition, it is hard to obtain accurate calibration conditions because of the difficulties to achieve a fully depleted and saturated oxygen concentrations in the devices. To overcome these difficulties, a widefield frequency domain fluorescence imaging microscopy (FD-FLIM) system was constructed and utilized to accurately measure oxygen gradient profiles in a microfluidic device in this paper. Since lifetime-based measurements do not solely depend on intensity variations, oxygen calibration processes are amiable and the measured oxygen concentrations can be more accurate. The performance of the FD-FLIM system was validated by comparing the experimental and simulation results in microfluidic devices with different geometries. The experimental results show that the oxygen gradients generated from the chemical reaction method can provide more hypoxic oxygen conditions compared to the gradients created by the gas flowing method. Owing to the advantages provided by the widefield microscopy technique, the image acquisition time can be significantly reduced resulting in less photobleaching for time-lapsed imaging applications. Consequently, the measurement technique developed in this paper is an efficient tool, which can greatly help scientists to better study biological activities under various oxygen conditions.

Electrofluidic Circuit-Based Microfluidic Viscometer for Analysis of Newtonian and Non-Newtonian Liquids under Different Temperatures.

This paper reports a microfluidic viscometer with an integrated pressure sensor based on electrofluidic circuits, which are electrical circuits constructed by ionic liquid-filled microfluidic channels. The electrofluidic circuit provides a pressure-sensing scheme with great long-term and thermal stability. The viscosity of the tested fluidic sample is estimated by its flow resistance, which is a function of pressure drop, flow rate, and the geometry of the microfluidic channel. The viscometer can be exploited to measure viscosity of either Newtonian or non-Newtonian power-law fluid under various shear rates (3-500 1/s) and temperatures (4-70 °C) with small sample volume (less than 400 µL). The developed sensor-integrated microfluidic viscometer is made of poly(dimethylsiloxane) (PDMS) with transparent electrofluidic circuit, which makes it feasible to simultaneously image samples under tests. In addition, the entire device is disposable to prevent cross-contamination between samples, which is desired for various chemical and biomedical applications. In the experiments, viscosities of Newtonian fluids, glycerol water solutions with different concentrations and a mixture of pyrogallol and sodium hydroxide (NaOH), and non-Newtonian fluids, xanthan gum solutions and human blood samples, have been characterized. The results demonstrate that the developed microfluidic viscometer provides a convenient and useful platform for practical viscosity characterization of fluidic samples for a wide variety of applications.

Polydimethylsiloxane SlipChip for mammalian cell culture applications.

This paper reports a polydimethylsiloxane (PDMS) SlipChip for in vitro cell culture applications, multiple-treatment assays, cell co-cultures, and cytokine detection assays. The PDMS SlipChip is composed of two PDMS layers with microfluidic channels on each surface that are separated by a thin silicone fluid (Si-fluid) layer. The integration of Si-fluid enables the two PDMS layers to be slid to different positions; therefore, the channel patterns can be re-arranged for various applications. The SlipChip design significantly reduces the complexity of sample handling, transportation, and treatment processes. To apply the developed SlipChip for cell culture applications, human lung adenocarcinoma epithelial cells (A549) and lung fibroblasts (MRC-5) were cultured to examine the biocompatibility of the developed PDMS SlipChip. Moreover, embryonic pluripotent stem cells (ES-D3) were also cultured in the device to evaluate the retention of their stemness in the device. The experimental results show that cell morphology, viability and proliferation are not affected when the cells are cultured in the SlipChip, indicating that the device is highly compatible with mammalian cell culture. In addition, the stemness of the ES-D3 cells was highly retained after they were cultured in the device, suggesting the feasibility of using the SlipChip for stem cell research. Various cell experiments, such as simultaneous triple staining of cells and co-culture of MRC-5 with A549 cells, were also performed to demonstrate the functionalities of the PDMS SlipChip. Furthermore, we used a cytokine detection assay to evaluate the effect of endotoxin (lipopolysaccharides, LPS) treatment on the cytokine secretion of A549 cells using the SlipChip. The developed PDMS SlipChip provides a straightforward and effective platform for various on-chip in vitro cell cultures and consequent analysis, which is promising for a number of cell biology studies and biomedical applications.

Characterization of Single-Spheroid Oxygen Consumption Using a Microfluidic Platform and Fluorescence Lifetime Imaging Microscopy.

Oxygen consumption has been used to evaluate various cellular activities. In addition, three-dimensional (3D) spheroids have been broadly exploited as advanced in vitro cell models for various biomedical studies due to their capability of mimicking 3D in vivo microenvironments and cell arrangements. However, monitoring the oxygen consumption of live 3D spheroids poses challenges because existing invasive methods cause structural and cell damage. In contrast, optical methods using fluorescence labeling and microscopy are non-invasive, but they suffer from technical limitations like high cost, tedious procedures, and poor signal-to-noise ratios. To address these challenges, we developed a microfluidic platform for uniform-sized spheroid formation, handling, and culture. The platform is further integrated with widefield frequency domain fluorescence lifetime imaging microscopy (FD-FLIM) to efficiently characterize the lifetime of an oxygen-sensitive dye filling the platform for oxygen consumption characterization. In the experiments, osteosarcoma (MG-63) cells are exploited as the spheroid model and for the oxygen consumption analysis. The results demonstrate the functionality of the developed approach and show the accurate characterization of the oxygen consumption of the spheroids in response to drug treatments. The developed approach possesses great potential to advance spheroid metabolism studies with single-spheroid resolution and high sensitivity.

Rapid Tissue Perfusion Using Sacrificial Percolation of Anisotropic Networks.

Tissue engineering has long sought to rapidly generate perfusable vascularized tissues with vessel sizes spanning those seen in humans. Current techniques such as biological 3D printing (top-down) and cellular self-assembly (bottom-up) are resource intensive and have not overcome the inherent tradeoff between vessel resolution and assembly time, limiting their utility and scalability for engineering tissues. We present a flexible and scalable technique termed SPAN - Sacrificial Percolation of Anisotropic Networks, where a network of perfusable channels is created throughout a tissue in minutes, irrespective of its size. Conduits with length scales spanning arterioles to capillaries are generated using pipettable alginate fibers that interconnect above a percolation density threshold and are then degraded within constructs of arbitrary size and shape. SPAN is readily used within common tissue engineering processes, can be used to generate endothelial cell-lined vasculature in a multi-cell type construct, and paves the way for rapid assembly of perfusable tissues.

Indocyanine-Green-Loaded Liposomes for Photodynamic and Photothermal Therapies: Inducing Apoptosis and Ferroptosis in Cancer Cells with Implications beyond Oral Cancer.

Oral cancer represents a global health burden, necessitating novel therapeutic strategies. Photodynamic and photothermal therapies using indocyanine green (ICG) have shown promise due to their distinctive near-infrared (NIR) light absorption characteristics and FDA-approved safety profiles. This study develops ICG-loaded liposomes (Lipo-ICGs) to further explore their potential in oral cancer treatments. We synthesized and characterized the Lipo-ICGs, conducted in vitro cell culture experiments to assess cellular uptake and photodynamic/photothermal effects, and performed in vivo animal studies to evaluate their therapeutic efficacy. Quantitative cell apoptosis and gene expression variation were further characterized using flow cytometry and RNA sequencing, respectively. Lipo-ICGs demonstrated a uniform molecular weight distribution among particles. The in vitro studies showed a successful internalization of Lipo-ICGs into the cells and a significant photodynamic treatment effect. The in vivo studies confirmed the efficient delivery of Lipo-ICGs to tumor sites and successful tumor growth inhibition following photodynamic therapy. Moreover, light exposure induced a time-sensitive photothermal effect, facilitating the further release of ICG, and enhancing the treatment efficacy. RNA sequencing data showed significant changes in gene expression patterns upon Lipo-ICG treatment, suggesting the activation of apoptosis and ferroptosis pathways. The findings demonstrate the potential of Lipo-ICGs as a therapeutic tool for oral cancer management, potentially extending to other cancer types.

Gradient conducting polymer surfaces with netrin-1-conjugation promote axon guidance and neuron transmission of human iPSC-derived retinal ganglion cells.

Major advances have been made in utilizing human-induced pluripotent stem cells (hiPSCs) for regenerative medicine. Nevertheless, the delivery and integration of hiPSCs into target tissues remain significant challenges, particularly in the context of retinal ganglion cell (RGC) restoration. In this study, we introduce a promising avenue for providing directional guidance to regenerated cells in the retina. First, we developed a technique for construction of gradient interfaces based on functionalized conductive polymers, which could be applied with various functionalized ehthylenedioxythiophene (EDOT) monomers. Using a tree-shaped channel encapsulated with a thin PDMS and a specially designed electrochemical chamber, gradient flow generation could be converted into a functionalized-PEDOT gradient film by cyclic voltammetry. The characteristics of the successfully fabricated gradient flow and surface were analyzed using fluorescent labels, time of flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). Remarkably, hiPSC-RGCs seeded on PEDOT exhibited improvements in neurite outgrowth, axon guidance and neuronal electrophysiology measurements. These results suggest that our novel gradient PEDOT may be used with hiPSC-based technologies as a potential biomedical engineering scaffold for functional restoration of RGCs in retinal degenerative diseases and optic neuropathies.

Efficient single-cell oxygen consumption rate characterization based on frequency domain fluorescence lifetime imaging microscopy measurement and microfluidic platform.

Cell metabolism is critical in regulating normal cell functions to maintain energy homeostasis. In order to monitor cell metabolism, the oxygen consumption rate (OCR) of cells has been characterized as an important factor. In conventional cell analysis, the cells are characterized in bulk due to technical limitations. However, the heterogeneity between the cells cannot be identified. Therefore, single-cell analysis has been proposed to reveal cellular functions and their heterogeneity. In this research, an approach integrating a microfluidic device and widefield frequency domain fluorescence imaging lifetime microscopy (FD-FLIM) for single-cell OCR characterization in an efficient manner is developed. The microfluidic device provides an efficient platform to trap and isolate single cells in microwells with the buffer saline containing an oxygen-sensitive phosphorescent dye. The oxygen tension variation within the microwells can be efficiently estimated by measuring the fluorescence lifetime change using the FD-FLIM, and the OCR values of the single cells can then be calculated. In the experiments, breast cancer (MCF-7) cells are exploited for the OCR measurement. The results demonstrate the functionality of the developed approach and show the heterogeneity among the cells. The developed approach possesses great potential to advance cellular metabolism studies with single-cell resolution.

Studying sprouting angiogenesis under combination of oxygen gradients and co-culture of fibroblasts using microfluidic cell culture model.

Sprouting angiogenesis is an essential process for expanding vascular systems under various physiological and pathological conditions. In this paper, a microfluidic device capable of integrating a hydrogel matrix for cell culture and generating stable oxygen gradients is developed to study the sprouting angiogenesis of endothelial cells under combinations of oxygen gradients and co-culture of fibroblast cells. The endothelial cells can be cultured as a monolayer endothelium inside the device to mimic an existing blood vessel, and the hydrogel without or with fibroblast cells cultured in it provides a matrix next to the formed endothelium for three-dimensional sprouting of the endothelial cells. Oxygen gradients can be stably established inside the device for cell culture using the spatially-confined chemical reaction method. Using the device, the sprouting angiogenesis under combinations of oxygen gradients and co-culture of fibroblast cells is systematically studied. The results show that the oxygen gradient and the co-culture of fibroblast cells in the hydrogel can promote sprouting of the endothelial cells into the hydrogel matrix by altering cytokines in the culture medium and the physical properties of the hydrogel. The developed device provides a powerful in vitro model to investigate sprouting angiogenesis under various in vivo-like microenvironments.

A 3D culture system for evaluating the combined effects of cisplatin and anti-fibrotic drugs on the growth and invasion of lung cancer cells co-cultured with fibroblasts.

Fibrosis and fibroblast activation usually occur in the tissues surrounding a malignant tumor; therefore, anti-fibrotic drugs are used in addition to chemotherapy. A reliable technique for evaluating the combined effects of anti-fibrotic drugs and anticancer drugs would be beneficial for the development of an appropriate treatment strategy. In this study, we manufactured a three-dimensional (3D) co-culture system of fibroblasts and lung cancer cell spheroids in Matrigel supplemented with fibrin (fibrin/Matrigel) that simulated the tissue microenvironment around a solid tumor. We compared the efficacy of an anticancer drug (cisplatin) with or without pretreatments of two anti-fibrotic drugs, nintedanib and pirfenidone, on the growth and invasion of cancer cells co-cultured with fibroblasts. The results showed that the addition of nintedanib improved cisplatin's effects on suppressing the growth of cancer cell spheroids and the invasion of cancer cells. In contrast, pirfenidone did not enhance the anticancer activity of cisplatin. Nintedanib also showed higher efficacy than pirfenidone in reducing the expression of four genes in fibroblasts associated with cell adhesion, invasion, and extracellular matrix degradation. This study demonstrated that the 3D co-cultures in fibrin/Matrigel would be useful for assessing the effects of drug combinations on tumor growth and invasion.

Extracellular Matrix-Derived Biophysical Cues Mediate Interstitial Flow-Induced Sprouting Angiogenesis.

Sprouting angiogenesis is orchestrated by an intricate balance of biochemical and mechanical cues in the local tissue microenvironment. Interstitial flow has been established as a potent regulator of angiogenesis. Similarly, extracellular matrix (ECM) physical properties, such as stiffness and microarchitecture, have also emerged as important mediators of angiogenesis. However, the interplay between interstitial flow and ECM physical properties in the initiation and control of angiogenesis is poorly understood. Using a three-dimensional (3D) microfluidic tissue analogue of angiogenic sprouting with defined interstitial flow superimposed over ECM with well-characterized physical properties, we found that the addition of hyaluronan (HA) to collagen-based matrices significantly enhances sprouting induced by interstitial flow compared to responses in collagen-only hydrogels. We confirmed that both the stiffness and matrix pore size of collagen-only hydrogels were increased by the addition of HA. Interestingly, interstitial flow-potentiated sprouting responses in collagen/HA matrices were not affected when functionally blocking the HA receptor CD44. In contrast, enzymatic depletion of HA in collagen/HA matrices with hyaluronidase (HAdase) resulted in decreased stiffness, pore size, and interstitial flow-mediated sprouting to the levels observed in collagen-only matrices. Taken together, these results suggest that HA enhances interstitial flow-mediated angiogenic sprouting through its alterations to collagen ECM stiffness and pore size.

Micro-ring structures stabilize microdroplets to enable long term spheroid culture in 384 hanging drop array plates.

Using stereolithography, 20 different structural variations comprised of millimeter diameter holes surrounded by trenches, plateaus, or micro-ring structures were prepared and tested for their ability to stably hold arrays of microliter sized droplets within the structures over an extended period of time. The micro-ring structures were the most effective in stabilizing droplets against mechanical and chemical perturbations. After confirming the importance of micro-ring structures using rapid prototyping, we developed an injection molding tool for mass production of polystyrene 3D cell culture plates with an array of 384 such micro-ring surrounded through-hole structures. These newly designed and injection molded polystyrene 384 hanging drop array plates with micro-rings were stable and robust against mechanical perturbations as well as surface fouling-facilitated droplet spreading making them capable of long term cell spheroid culture of up to 22 days within the droplet array. This is a significant improvement over previously reported 384 hanging drop array plates which are susceptible to small mechanical shocks and could not reliably maintain hanging drops for longer than a few days. With enhanced droplet stability, the hanging drop array plates with micro-ring structures provide better platforms and open up new opportunities for high-throughput preparation of microscale 3D cell constructs for drug screening and cell analysis.

384 hanging drop arrays give excellent Z-factors and allow versatile formation of co-culture spheroids.

We previously reported the development of a simple, user-friendly, and versatile 384 hanging drop array plate for 3D spheroid culture and the importance of utilizing 3D cellular models in anti-cancer drug sensitivity testing. The 384 hanging drop array plate allows for high-throughput capabilities and offers significant improvements over existing 3D spheroid culture methods. To allow for practical 3D cell-based high-throughput screening and enable broader use of the plate, we characterize the robustness of the 384 hanging drop array plate in terms of assay performance and demonstrate the versatility of the plate. We find that the 384 hanging drop array plate performance is robust in fluorescence- and colorimetric-based assays through Z-factor calculations. Finally, we demonstrate different plate capabilities and applications, including: spheroid transfer and retrieval for Janus spheroid formation, sequential addition of cells for concentric layer patterning of different cell types, and culture of a wide variety of cell types.

Study Hypoxic Response under Cyclic Oxygen Gradients Generated in Microfluidic Devices Using Real-Time Fluorescence Imaging.

Oxygen plays important roles in regulating various biological activities under physiological and pathological conditions. However, the response of cells facing temporal variation in oxygen microenvironments has seldom been studied due to technical limitations. In this paper, an integrated approach to studying hypoxic response under cyclic oxygen gradients is developed. In the experiments, a cell culture system based on a microfluidic device is constructed to generate cyclic oxygen gradients with desired periods by alternately introducing gases with specific compositions into the microfluidic channels next to the cell culture channel separated by thin channel walls. Observation of the hypoxic responses is performed using real-time fluorescence imaging of dyes sensitive to extra- and intracellular oxygen tensions as well as intracellular calcium concentrations. Cellular hypoxic responses of human aortic smooth muscle cells (AoSMCs) and lung carcinoma epithelium (A549) cells, including intracellular oxygen and calcium levels, are measured. The results show that the two types of cells have different hypoxic responses to the applied cyclic oxygen gradients. With the capability of real-time cellular response monitoring under cyclic oxygen gradients, the developed approach provides a useful scheme to investigate hypoxic responses in vitro under microenvironments mimicking various in vivo physiological and pathological conditions.

Revealing anisotropic elasticity of endothelium under fluid shear stress.

Endothelium lining interior surface of blood vessels experiences various physical stimulations in vivo. Its physical properties, especially elasticity, play important roles in regulating the physiological functions of vascular systems. In this paper, an integrated approach is developed to characterize the anisotropic elasticity of the endothelium under physiological-level fluid shear stress. A pressure sensor-embedded microfluidic device is developed to provide fluid shear stress on the perfusion-cultured endothelium and to measure transverse in-plane elasticities in the directions parallel and perpendicular to the flow direction. Biological atomic force microscopy (Bio-AFM) is further exploited to measure the vertical elasticity of the endothelium in its out-of-plane direction. The results show that the transverse elasticity of the endothelium in the direction parallel to the perfusion culture flow direction is about 70% higher than that in the direction perpendicular to the flow direction. Moreover, the transverse elasticities of the endothelium are estimated to be approximately 120 times larger than the vertical one. The results indicate the effects of fluid shear stress on the transverse elasticity anisotropy of the endothelium, and the difference between the elasticities in transverse and vertical directions. The quantitative measurement of the endothelium anisotropic elasticity in different directions at the tissue level under the fluid shear stress provides biologists insightful information for the advanced vascular system studies from biophysical and biomaterial viewpoints. STATEMENT OF SIGNIFICANCE: In this paper, we take advantage an integrated approach combining microfluidic devices and biological atomic force microscopy (Bio-AFM) to characterize anisotropic elasticities of endothelia with and without fluidic shear stress application. The microfluidic devices are exploited to conduct perfusion cell culture of the endothelial cells, and to estimate the in-plane elasticities of the endothelium in the direction parallel and perpendicular to the shear stress. In addition, the Bio-AFM is utilized for characterization of the endothelium morphology and vertical elasticity. The measurement results demonstrate the very first anisotropic elasticity quantification of the endothelia. Furthermore, the study provides insightful information bridging the microscopic sing cell and macroscopic organ level studies, which can greatly help to advance vascular system research from material perspective.

Comparison of Hydrogen Peroxide Secretion From Living Cells Cultured in Different Formats Using Hydrogel-Based LSPR Substrates.

Reactive oxygen species (ROS), a number of reactive molecules and free radicals derived from molecular oxygen, are generated as by-products during mitochondrial electron transport within cells. Physiologically, cells are capable of metabolizing the ROS exploiting specific mechanisms. However, if excessive ROS accumulate inside the cells, it will cause the cells apoptosis or necrosis. Hydrogen peroxide (H2O2) is one of the essential ROS often participating in chemical reactions in organisms and regulating homeostasis in the body. Therefore, rapid and sensitive detection of H2O2 is a significant task in cell biology research. Furthermore, it has been found that cells cultured in different formats can result in different cellular responses and biological activities. In order to investigate the H2O2 secretion from the cells cultured in different formats, a hydrogel-based substrate is exploited to separate relatively large molecular (e.g., proteins) for direct measurement of H2O2 secreted from living cells in complete cell culture medium containing serum. The substrate takes advantage of the localized surface plasmon resonance (LSPR) method based on enzyme immunoprecipitation. In addition, the H2O2 secreted from the cells cultured in different dimensions (suspension of single cells and three-dimensional cell spheroids) treated with identical drugs is measured and compared. The spheroid samples can be prepared with ample amount using a designed microfluidic device with precise control of size. The results show that the H2O2 secretion from the cells are great affected by their culture formats.