Online Analysis of Drug Toxicity to Cells with Shear Stress on an Integrated Microfluidic Chip

Mechanical deformation and death of circulating tumor cells in the bloodstream

The circulation of tumor cells through the bloodstream is a significant step in tumor metastasis. To better understand the metastatic process, circulating tumor cell (CTC) survival in the circulation must be explored. While immune interactions with CTCs in recent decades have been examined, research has yet to sufficiently explain some CTC behaviors in blood flow. Studies related to CTC mechanical responses in the bloodstream have recently been conducted to further study conditions under which CTCs might die. While experimental methods can assess the mechanical properties and death of CTCs, increasingly sophisticated computational models are being built to simulate the blood flow and CTC mechanical deformation under fluid shear stresses (FSS) in the bloodstream.Several factors contribute to the mechanical deformation and death of CTCs as they circulate. While FSS can damage CTC structure, diverse interactions between CTCs and blood components may either promote or hinder the next metastatic step-extravasation at a remote site. Overall understanding of how these factors influence the deformation and death of CTCs could serve as a basis for future experiments and simulations, enabling researchers to predict CTC death more accurately. Ultimately, these efforts can lead to improved metastasis-specific therapeutics and diagnostics specific in the future.

Integrating machine learning and biosensors in microfluidic devices: A review

Microfluidic devices are increasingly widespread in the literature, being applied to numerous exciting applications, from chemical research to Point-of-Care devices, passing through drug development and clinical scenarios. Setting up these microenvironments, however, introduces the necessity of locally controlling the variables involved in the phenomena under investigation. For this reason, the literature has deeply explored the possibility of introducing sensing elements to investigate the physical quantities and the biochemical concentration inside microfluidic devices. Biosensors, particularly, are well known for their high accuracy, selectivity, and responsiveness. However, their signals could be challenging to interpret and must be carefully analysed to carry out the correct information. In addition, proper data analysis has been demonstrated even to increase biosensors' mentioned qualities. To this regard, machine learning algorithms are undoubtedly among the most suitable approaches to undertake this job, automatically learning from data and highlighting biosensor signals' characteristics at best. Interestingly, it was also demonstrated to benefit microfluidic devices themselves, in a new paradigm that the literature is starting to name "intelligent microfluidics", ideally closing this benefic interaction among these disciplines. This review aims to demonstrate the advantages of the triad paradigm microfluidics-biosensors-machine learning, which is still little used but has a great perspective. After briefly describing the single entities, the different sections will demonstrate the benefits of the dual interactions, highlighting the applications where the reviewed triad paradigm was employed.

Loss of Hormone Receptor Expression after Exposure to Fluid Shear Stress in Breast Cancer Cell Lines

Following metastatic spread, many hormone receptor positive (HR+) patients develop a more aggressive phenotype with an observed loss of the HRs estrogen receptor (ER) and progesterone receptor (PR). During metastasis, breast cancer cells are exposed to high magnitudes of fluid shear stress (FSS). Unfortunately, the role for FSS on the regulation of HR expression and function during metastasis is not fully understood. This study was designed to elucidate the impact of FSS on HR+ breast cancer. Utilizing a microfluidic platform capable of exposing breast cancer cells to FSS that mimics in situ conditions, we demonstrate the impact of FSS exposure on representative HR+ breast cancer cell lines through protein and gene expression analysis. Proteomics results demonstrated that 540 total proteins and 1473 phospho-proteins significantly changed due to FSS exposure and pathways of interest included early and late estrogen response. The impact of FSS on response to 17β-estradiol (E2) was next evaluated and gene expression analysis revealed repression of ER and E2-mediated genes (PR and SDF1) following exposure to FSS. Western blot demonstrated enhanced phosphorylation of mTOR following exposure to FSS. Taken together, these studies provide initial insight into the effects of FSS on HR signaling in metastatic breast cancer.

Lab-on-a-chip: an advanced technology for the modernization of traditional Chinese medicine

Benefiting from the complex system composed of various constituents, medicament portions, species, and places of origin, traditional Chinese medicine (TCM) possesses numerous customizable and adaptable efficacies in clinical practice guided by its theories. However, these unique features are also present challenges in areas such as quality control, screening active ingredients, studying cell and organ pharmacology, and characterizing the compatibility between different Chinese medicines. Drawing inspiration from the holistic concept, an integrated strategy and pattern more aligned with TCM research emerges, necessitating the integration of novel technology into TCM modernization. The microfluidic chip serves as a powerful platform for integrating technologies in chemistry, biology, and biophysics. Microfluidics has given rise to innovative patterns like lab-on-a-chip and organoids-on-a-chip, effectively challenging the conventional research paradigms of TCM. This review provides a systematic summary of the nature and advanced utilization of microfluidic chips in TCM, focusing on quality control, active ingredient screening/separation, pharmaceutical analysis, and pharmacological/toxicological assays. Drawing on these remarkable references, the challenges, opportunities, and future trends of microfluidic chips in TCM are also comprehensively discussed, providing valuable insights into the development of TCM.

Effects of Mechanical Stress on Endothelial Cells In Situ and In Vitro

Endothelial cells lining blood vessels are essential for maintaining vascular homeostasis and mediate several pathological and physiological processes. Mechanical stresses generated by blood flow and other biomechanical factors significantly affect endothelial cell activity. Here, we review how mechanical stresses, both in situ and in vitro, affect endothelial cells. We review the basic principles underlying the cellular response to mechanical stresses. We also consider the implications of these findings for understanding the mechanisms of mechanotransducer and mechano-signal transduction systems by cytoskeletal components.

Recent Advances on Cell Culture Platforms for In Vitro Drug Screening and Cell Therapies: From Conventional to Microfluidic Strategies

The clinical translations of drugs and nanomedicines depend on coherent pharmaceutical research based on biologically accurate screening approaches. Since establishing the 2D in vitro cell culture method, the scientific community has improved cell-based drug screening assays and models. Those advances result in more informative biochemical assays and the development of 3D multicellular models to describe the biological complexity better and enhance the simulation of the in vivo microenvironment. Despite the overall dominance of conventional 2D and 3D cell macroscopic culture methods, they present physicochemical and operational challenges that impair the scale-up of drug screening by not allowing a high parallelization, multidrug combination, and high-throughput screening. Their combination and complementarity with microfluidic platforms enable the development of microfluidics-based cell culture platforms with unequivocal advantages in drug screening and cell therapies. Thus, this review presents an updated and consolidated view of cell culture miniaturization's physical, chemical, and operational considerations in the pharmaceutical research scenario. It clarifies advances in the field using gradient-based microfluidics, droplet-based microfluidics, printed-based microfluidics, digital-based microfluidics, SlipChip, and paper-based microfluidics. Finally, it presents a comparative analysis of the performance of cell-based methods in life research and development to achieve increased precision in the drug screening process.

Replicating endothelial shear stress in organ-on-a-chip for predictive hypericin photodynamic efficiency

Photodynamic therapy using Hypericin (Hy-PDT) is an alternative non-invasive treatment that enables selective tumor inhibition and angiogenesis derived from the differential recruitment of endothelial cells in the tumor microenvironment. Most PDT studies were performed on in vitro models without vascular biomechanical simulation. Our work strives to develop a microchip that generates a constant shear stress force to investigate the Hy-PDT efficiency on human umbilical vein endothelial cells (HUVECs). The microchip with a single straight microchannel was composed of the bottom layer (polystyrene), the middle layer (double-sided biocompatible adhesive tape), and the top layer (polyester film) and could produce shear stress in the range of 1.4 - 7.0 dyn cm^-2. The quantification of vascular endothelial growth factor (VEGF), cell viability, and activities of caspases 3 and 7 were assayed to validate the microchip and Hy-PDT efficacy. After the endothelization, static and dynamic cell incubations with Hy were conducted in microchips. Compared to static systems, the shear stress displayed its effect on the increasing release of VEGF and promoted more cell damage and cell death via necrosis during Hy-PDT. In conclusion, the expressive shear stress-dependent manner during PDT treatments suggests that the microchip could be an essential approach in preclinical tests to evaluate the therapeutic outcome considering the endothelial shear stress microenvironment.

Fluid shear stress affects the metabolic and toxicological response of the rainbow trout gill cell line RTgill-W1

The Rainbow trout gill cell-line (RTgill-W1) has been accepted by the Organisation for Economic Co-operation and Development (OECD TG249) as a replacement for fish in acute toxicity tests. In these tests cells are exposed under static conditions. In contrast, in vivo, water moves over fish gills generating fluid shear stress (FSS) that alters cell physiology and response to toxicants. The current study uses a specialised 3D printed chamber designed to house inserts and allows for the flow (0.2 dynes cm²) of water over the cells. This system was used to assess RTgill-W1 cell responses to FSS in the absence and presence of copper (Cu) over 24 h. FSS caused increased gene expression of mechanosensitive channel peizo1 and the Cu-transporter atp7a, elevated reactive oxygen species generation and increased expression of superoxidase dismutase. Cell metabolism was unaffected by Cu (0.163 μM to 2.6 μM Cu) under static conditions but significantly reduced by FSS + Cu above 1.3 μM. Differential expression of metallothionein (mt) a and b was observed with increased expression of mta under static conditions and mtb under FSS on exposure to Cu. These findings highlight toxicologically relevant mechanosensory responses by RTgill-W1 to FSS that may influence toxicological responses.

A single-cell surgery microfluidic device for transplanting tumor cytoplasm into dendritic cells without nuclei mixing

This study aimed to demonstrate the feasibility of generating tumor cell vaccine models by single-cell surgery in a microfluidic device that integrates one-to-one electrofusion, shear flow reseparation, and on-device culture. The device was microfabricated from polydimethylsiloxane (PDMS) and consisted of microorifices (aperture size: ∼3 μm) for one-to-one fusion, and microcages for on-device culture. Using the device, we could achieve one-to-one electrofusion of leukemic plasmacytoid dendritic cells (DC-like cells) and Jurkat cells with a fusion efficiency of ∼ 80%. Fusion via the narrow microorifices allowed DC-like cells to acquire cytoplasmic contents of the Jurkat cells while preventing nuclei mixing. After fusion, the DC-like cells were selectively reseparated from the Jurkat cells by shear flow application to generate tumor nuclei-free antigen-recipient DC-like (tarDC-like) cells. When cultured as single cells on the device, these cells could survive under gentle medium perfusion with a median survival time of 11.5 h, although a few cells could survive longer than 36 h. Overall, this study demonstrates single-cell surgery in a microfluidic device for potential generation of dendritic cell vaccines which are uncontaminated with tumor nucleic materials. We believe that this study will inspire the generation of safer tumor cell vaccines for cancer immunotherapy.

Size-dependent neurotoxicity of micro- and nanoplastics in flowing condition based on an in vitro microfluidic study

With the widespread presence of plastic wastes, knowledge about the potential environmental risks and bioavailability of micro- or nanoplastics fragmented from large analogs is of utmost importance. As the particle size matters in mediating endocytic mechanism and particle internalization, we first studied the effects of polystyrene microparticles (PS-MPs, 1 μm) and polystyrene nanoparticles (PS-NPs, 100 nm) of two different sizes at varying concentrations of 5, 25 and 75 μg/mL on the mouse hippocampal neuronal HT22 cells. The in vitro study showed efficient cellular uptake of PS-MPs and PS-NPs of both sizes. The adverse effects of cellular metabolic activity as reflective of excess Reactive Oxygen Species (ROS) and cell cycle S phase arresting were observed especially at the greater concentration of smaller-sized PS particles, consequently leading to mild cytotoxicity. We further evaluated the dynamic particle-cell interaction with a continuous supply of PS particles using a microfluidic device. By recapitulating the in vivo mechanical microenvironments while allowing homogeneous distribution of PS particles, the dynamic exposure to PS particles of both sizes under flowing conditions resulted in much lesser viability of neural cells than the traditional static exposure. As the flowing dynamics may avoid the gravitational settling of particles and allow more efficient cellular uptake, the size distribution, together with the exposure configurations, contributed significantly to the determination of the PS particle cytotoxicity. The on-chip investigation and a better understanding of particle translocation mechanisms would offer very much to the risk assessment of PS particles on human health.

A high-throughput integrated biofilm-on-a-chip platform for the investigation of combinatory physicochemical responses to chemical and fluid shear stress

Physicochemical conditions play a key role in the development of biofilm removal strategies. This study presents an integrated, double-layer, high-throughput microfluidic chip for real-time screening of the combined effect of antibiotic concentration and fluid shear stress (FSS) on biofilms. Biofilms of Escherichia coli LF82 and Pseudomonas aeruginosa were tested against gentamicin and streptomycin to examine the time dependent effects of concentration and FSS on the integrity of the biofilm. A MatLab image analysis method was developed to measure the bacterial surface coverage and total fluorescent intensity of the biofilms before and after each treatment. The chip consists of two layers. The top layer contains the concentration gradient generator (CGG) capable of diluting the input drug linearly into four concentrations. The bottom layer contains four expanding FSS chambers imposing three different FSSs on cultured biofilms. As a result, 12 combinatorial states of concentration and FSS can be investigated on the biofilm simultaneously. Our proof-of-concept study revealed that the reduction of E. coli biofilms was directly dependent upon both antibacterial dose and shear intensity, whereas the P. aeruginosa biofilms were not impacted as significantly. This confirmed that the effectiveness of biofilm removal is dependent on bacterial species and the environment. Our experimental system could be used to investigate the physicochemical responses of other biofilms or to assess the effectiveness of biofilm removal methods.

A Review of Functional Analysis of Endothelial Cells in Flow Chambers

The vascular endothelial cells constitute the innermost layer. The cells are exposed to mechanical stress by the flow, causing them to express their functions. To elucidate the functions, methods involving seeding endothelial cells as a layer in a chamber were studied. The chambers are known as parallel plate, T-chamber, step, cone plate, and stretch. The stimulated functions or signals from endothelial cells by flows are extensively connected to other outer layers of arteries or organs. The coculture layer was developed in a chamber to investigate the interaction between smooth muscle cells in the middle layer of the blood vessel wall in vascular physiology and pathology. Additionally, the microfabrication technology used to create a chamber for a microfluidic device involves both mechanical and chemical stimulation of cells to show their dynamics in in vivo microenvironments. The purpose of this study is to summarize the blood flow (flow inducing) for the functions connecting to endothelial cells and blood vessels, and to find directions for future chamber and device developments for further understanding and application of vascular functions. The relationship between chamber design flow, cell layers, and microfluidics was studied.

The impact of microfluidics in high-throughput drug-screening applications

Drug discovery is an expensive and lengthy process. Among the different phases, drug discovery and preclinical trials play an important role as only 5-10 of all drugs that begin preclinical tests proceed to clinical trials. Indeed, current high-throughput screening technologies are very expensive, as they are unable to dispense small liquid volumes in an accurate and quick way. Moreover, despite being simple and fast, drug screening assays are usually performed under static conditions, thus failing to recapitulate tissue-specific architecture and biomechanical cues present in vivo even in the case of 3D models. On the contrary, microfluidics might offer a more rapid and cost-effective alternative. Although considered incompatible with high-throughput systems for years, technological advancements have demonstrated how this gap is rapidly reducing. In this Review, we want to further outline the role of microfluidics in high-throughput drug screening applications by looking at the multiple strategies for cell seeding, compartmentalization, continuous flow, stimuli administration (e.g., drug gradients or shear stresses), and single-cell analyses.

Comparative study of the transcriptomes of Caco-2 cells cultured under dynamic vs. static conditions following exposure to titanium dioxide and zinc oxide nanomaterials

Due to the widespread application of food-relevant inorganic nanomaterials, the gastrointestinal tract is potentially exposed to these materials. Gut-on-chip in vitro systems are proposed for the investigation of compound toxicity as they better recapitulate the in vivo human intestinal environment than static models, due to the added shear stresses associated with the flow of the medium. We aimed to compare cellular responses of intestinal epithelial Caco-2 cells at the gene expression level upon TiO₂ (E171) and ZnO (NM110) nanomaterial exposure when cultured under dynamic and conventionally applied static conditions. Whole-genome transcriptome analyses upon exposure of the cells to TiO₂ and ZnO nanomaterials revealed differentially expressed genes and related biological processes that were culture condition specific. The total number of differentially expressed genes (p < 0.01) and affected pathways (p < 0.05 and FDR < 0.25) after nanomaterial exposure was higher under dynamic culture conditions than under static conditions for both nanomaterials. The observed increase in nanomaterial-induced responses in the gut-on-chip model indicates that shear stress might be a major factor in cell susceptibility. This is the first report on the application of a gut-on-chip system in which gene expression responses upon TiO₂ and ZnO nanomaterial exposure are evaluated and compared to a static system. It extends current knowledge on nanomaterial toxicity assessment and the influence of a dynamic environment on cellular responses. Application of the gut-on-chip system resulted in higher sensitivity of the cells and might thus be an attractive system for use in the toxicological hazard characterization of nanomaterials.

Recent advances of integrated microfluidic suspension cell culture system

Microfluidic devices with superior microscale fluid manipulation ability and large integration flexibility offer great advantages of high throughput, parallelisation and multifunctional automation. Such features have been extensively utilised to facilitate cell culture processes such as cell capturing and culturing under controllable and monitored conditions for cell-based assays. Incorporating functional components and microfabricated configurations offered different levels of fluid control and cell manipulation strategies to meet diverse culture demands. This review will discuss the advances of single-phase flow and droplet-based integrated microfluidic suspension cell culture systems and their applications for accelerated bioprocess development, high-throughput cell selection, drug screening and scientific research to insight cell biology. Challenges and future prospects for this dynamically developing field are also highlighted.

A Simple and Low-Cost Method for Fabrication of Polydimethylsiloxane Microfludic Chips

The conventional fabrication methods for enrichment microfluidic devices require cleanroom, which are costly and time-consuming. Developing a facile and low-cost method to fabricate microfluidic chips could stimulate the progress of the applications of those chips. Here, we present an easy method for fabrication of a complete PDMS (Polydimethylsiloxane) microfluidic chip used for ion and protein enrichment. The method consists of three main fabrication steps: PDMS microchannels ablation by co₂ laser, nation membrane deposition, and oxygen plasma assist bonding under pressure. To fabricate a desired microchannel, the laser ablation parameters, containing laser power and ablation speed, were analyzed. The parameters for oxygen plasma assist bonding were also investigated to improve the bonding quality of the chips (low dimension loss and high bonding strength). The following Rhodamine B enrichment tests demonstrate that the presented method allows fabrication of microfluidic chips with precise dimensions and leakage free.

A high-resolution real-time quantification of astrocyte cytokine secretion under shear stress for investigating hydrocephalus shunt failure

It has been hypothesized that physiological shear forces acting on medical devices implanted in the brain significantly accelerate the rate to device failure in patients with chronically indwelling neuroprosthetics. In hydrocephalus shunt devices, shear forces arise from cerebrospinal fluid flow. The shunt's unacceptably high failure rate is mostly due to obstruction with adherent inflammatory cells. Astrocytes are the dominant cell type bound directly to obstructing shunts, rapidly manipulating their activation via shear stress-dependent cytokine secretion. Here we developed a total internal reflection fluorescence microscopy combined with a microfluidic shear device chip (MSDC) for quantitative analysis and direct spatial-temporal mapping of secreted cytokines at the single-cell level under physiological shear stress to identify the root cause for shunt failure. Real-time secretion imaging at 1-min time intervals enabled successful detection of a significant increase of astrocyte IL-6 cytokine secretion under shear stress greater than 0.5 dyne/cm2, validating our hypothesis and highlighting the importance of reducing shear stress activation of cells.

Development of Skin-On-A-Chip Platforms for Different Utilizations: Factors to Be Considered

There is increasing interest in miniaturized technologies in diagnostics, therapeutic testing, and biomedicinal fundamental research. The same is true for the dermal studies in topical drug development, dermatological disease pathology testing, and cosmetic science. This review aims to collect the recent scientific literature and knowledge about the application of skin-on-a-chip technology in drug diffusion studies, in pharmacological and toxicological experiments, in wound healing, and in fields of cosmetic science (ageing or repair). The basic mathematical models are also presented in the article to predict physical phenomena, such as fluid movement, drug diffusion, and heat transfer taking place across the dermal layers in the chip using Computational Fluid Dynamics techniques. Soon, it can be envisioned that animal studies might be at least in part replaced with skin-on-a-chip technology leading to more reliable results close to study on humans. The new technology is a cost-effective alternative to traditional methods used in research institutes, university labs, and industry. With this article, the authors would like to call attention to a new investigational family of platforms to refresh the researchers’ theranostics and preclinical, experimental toolbox.

Cell Analysis on Microfluidics Combined with Mass Spectrometry

Cell analysis is of great significance for the exploration of human diseases and health. However, there are not many techniques for high-throughput cell analysis in the simulated cell microenvironment. The high designability of the microfluidic chip enables multiple kinds of cells to be co-cultured on the chip, with other functions such as sample preprocessing and cell manipulation. Mass spectrometry (MS) can detect a large number of biomolecules without labelling. Therefore, the application of the microfluidic chip coupled with MS has represented a major branch of cell analysis over the past decades. Here, we concisely introduce various microfluidic devices coupled with MS used for cell analysis. The main functions of microfluidic devices are described first, followed by introductions of different interfaces with different types of MS. Then, their various applications in cell analysis are highlighted, with an emphasis on cell metabolism, drug screening, and signal transduction. Current limitations and prospective trends of microfluidics coupled with MS are discussed at the end.

A Fluidic Isolation-Assisted Homogeneous-Flow-Pressure Chip-Solid Phase Extraction-Mass Spectrometry System for Online Dynamic Monitoring of 25-Hydroxyvitamin D3 Biotransformation in Cells

It is well known that cell can response to various chemical and mechanical stimuli. Therefore, flow pressure variation induced by sample loading and elution should be small enough to ignore the physical impact on cells when we use a Chip-SPE-MS system for cells. However, most existent Chip-SPE-MS systems ignored the pressure alternation because it is extremely difficult to develop a homogeneous-flow-pressure hyphenated module. Herein, we developed an interesting fluidic isolation-assisted homogeneous-flow-pressure Chip-SPE-MS system and demonstrated that it is adequate for online high-throughput determination and quantification of the 25-hydroxyvitamin D₃ (25(OH)D₃) biotransformation in different cells. Briefly, the homogeneous ambient flow pressure is achieved by fluidic isolation between the cell culture channel and the SPE column, and an automatic sampling probe could accomplish the sample loading and dispensing to fulfill online pretreatment of the sample. Through this new system, the expression levels of 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃) can be determined in real time with a detection limit of 2.54 nM. In addition, the results revealed that 25(OH)D₃ metabolic activity differed significantly between normal L-02 cells and cancerous HepG2 cells. Treatment of L-02 cells with a high dose of 25(OH)D₃ was found to increase significant formation of 24,25(OH)₂D₃, but this change was not apparent in HepG2 cells. The presented system promises to be a versatile tool for online accurate molecule biotransformation investigation and drug screening processes.

Endothelial cell polarization and orientation to flow in a novel microfluidic multimodal shear stress generator

Endothelial cells (EC) respond to shear stress to maintain vascular homeostasis, and a disrupted response is associated with cardiovascular diseases. To understand how different shear stress modalities affect EC morphology and behavior, we developed a microfluidic device that concurrently generates three different levels of uniform wall shear stress (WSS) and six different WSS gradients (WSSG). In this device, human umbilical vein endothelial cells (HUVECs) exhibited a rapid and robust response to WSS, with the relative positioning of the Golgi and nucleus transitioning from a non-polarized to polarized state in a WSS magnitude- and gradient-dependent manner. By contrast, polarized HUVECs oriented their Golgi and nucleus polarity to the flow vector in a WSS magnitude-dependent manner, with positive WSSG inhibiting and negative WSSG promoting upstream orientation. Having validated this device, this chip can now be used to dissect the mechanisms underlying EC responses to different WSS modalities, including shear stress gradients, and to investigate the influence of flow on a diverse range of cells during development, homeostasis and disease.

MechanoBioTester: A Decoupled Multistimulus Cell Culture Device for Studying Complex Microenvironments In Vitro

Increasingly being recognized is the role of the complex microenvironment to regulate cell phenotype; however, the cell culture systems used to study these effects in vitro are lagging. The complex microenvironment is host to a combination of biological interactions, chemical factors, and mechanical stimuli. Many devices have been designed to probe the effects of one mechanical stimulus, but few are capable of systematically interrogating all combinations of mechanical stimuli with independent control. To address this gap, we have developed the MechanoBioTester platform, a decoupled, multi-stimulus cell culture model for studying the cellular response to complex microenvironments in vitro. The system uses an engineered elastomeric chamber with a specially defined region for incorporating different target materials to act as the cell culture substrate. We have tested the system with several target materials including: polydimethylsiloxane elastomer, polyacrylamide gel, poly(1,8-octanediol citrate) elastomer, and type I collagen gel for both 2D and 3D co-culture. Additionally, when the chamber is connected to a flow circuit and our stretching device, stimuli in the form of fluid flow, cyclic stretch, and hydrostatic pressure are able to be imparted with independent control. We validated the device using experimental and computational methods to define a range of capabilities relevant to physiological microenvironments. The MechanoBioTester platform promises to function as a model system for mechanobiology, biomaterial design, and drug discovery applications that focus on probing the impact of a complex microenvironment in an in vitro setting. The protocol described within provides the details characterizing the MechanoBioTester system, the steps for fabricating the MechanoBioTester chamber, and the procedure for operating the MechanoBioTester system to stimulate cells.

Integrating Biophysics in Toxicology

Integration of biophysical stimulation in test systems is established in diverse branches of biomedical sciences including toxicology. This is largely motivated by the need to create novel experimental setups capable of reproducing more closely in vivo physiological conditions. Indeed, we face the need to increase predictive power and experimental output, albeit reducing the use of animals in toxicity testing. In vivo, mechanical stimulation is essential for cellular homeostasis. In vitro, diverse strategies can be used to model this crucial component. The compliance of the extracellular matrix can be tuned by modifying the stiffness or through the deformation of substrates hosting the cells via static or dynamic strain. Moreover, cells can be cultivated under shear stress deriving from the movement of the extracellular fluids. In turn, introduction of physical cues in the cell culture environment modulates differentiation, functional properties, and metabolic competence, thus influencing cellular capability to cope with toxic insults. This review summarizes the state of the art of integration of biophysical stimuli in model systems for toxicity testing, discusses future challenges, and provides perspectives for the further advancement of in vitro cytotoxicity studies.

Single-cell patterning technology for biological applications

Single-cell patterning technology has revealed significant contributions of single cells to conduct basic and applied biological studies in vitro such as the understanding of basic cell functions, neuronal network formation, and drug screening. Unlike traditional population-based cell patterning approaches, single-cell patterning is an effective technology of fully understanding cell heterogeneity by precisely controlling the positions of individual cells. Therefore, much attention is currently being paid to this technology, leading to the development of various micro-nanofabrication methodologies that have been applied to locate cells at the single-cell level. In recent years, various methods have been continuously improved and innovated on the basis of existing ones, overcoming the deficiencies and promoting the progress in biomedicine. In particular, microfluidics with the advantages of high throughput, small sample volume, and the ability to combine with other technologies has a wide range of applications in single-cell analysis. Here, we present an overview of the recent advances in single-cell patterning technology, with a special focus on current physical and physicochemical methods including stencil patterning, trap- and droplet-based microfluidics, and chemical modification on surfaces via photolithography, microcontact printing, and scanning probe lithography. Meanwhile, the methods applied to biological studies and the development trends of single-cell patterning technology in biological applications are also described.

Responses of Cellular Adhesion Strength and Stiffness to Fluid Shear Stress during Tumor Cell Rolling Motion

Biochemical and physical factors affect the rolling of tumor cells across the blood vessel. The biochemical factors have been well studied, while the influence of physical factors such as fluid shear stress (FSS) remains poorly understood. Here, human glioma cells (U87 cells) in a straight microfluidic channel were exposed to FSS (0.12, 1.2, and 1.8 dyn/cm²); and their locomotion behaviors from crawling-to-rolling and changes in cellular morphology (concave, elongated, less elongated, and round) were observed. The adhesion strength and stiffness of the cells of different morphologies were analyzed using a live single-cell extractor and atomic force microscopy, respectively. In general, the FSS stimulated cells showed stronger adhesion strength than the cells not exposed to FSS. The cell not exposed to FSS always exhibited greater nuclear stiffness than cortex stiffness, while after FSS treatment the cortex hardened and nucleus softened, where the round-shaped cell had a cortex that was more rigid than its nucleus. These results indicated that FSS influenced the biomechanics of circulating tumor cells, and elucidation of the mechanical responses to FSS might provide a deeper insight for cancer metastasis.