A Microfluidic Chip for Cell Patterning Utilizing Paired Microwells and Protein Patterns

Simple methodology to score micropattern quality and effectiveness

Micropatterns (MPs) are widely used as a powerful tool to control cell morphology and phenotype. However, methods for determining the effectiveness of how well cells are controlled by the shape of MPs have been inconsistently used and studies rarely report on this topic, indicating lack of standardization. We introduce an evaluation score that quantitatively assesses the MP fabrication quality and effectiveness, which can be broadly used in conjunction with all currently available MP design types. This score uses four simple and quick steps: (i) scoring MP and (ii) background fabrication quality, (iii) defining the type(s) of MP of interest, and (iv) assigning so-called efficiency descriptors describing cell behavior. These steps are based on visual inspection and quick categorization of various aspects of MP fabrication quality and cell behaviour, presented in illustrations and microscopy image examples intended to serve as a reference "atlas". To illustrate the advantage of using this score, we determined differences in cell morphology and F-actin intensity between scored vs. non-scored cells. These measurements, which could be different in other studies, were chosen because both are understood as markers of cell phenotype and function. We combined intensity-calibrated immunofluorescence microscopy and image-based single cell protein analysis. Importantly, significant differences in cell morphology and cytoskeletal protein content between scored vs. non-scored cells were noted: the unconditional inclusion of all experimental read-outs (i.e., all MP data regardless of MP quality and effectiveness) into the final results significantly misjudged the experimental readouts vs. only including experimental read-outs of quality-controlled and effective MPs, identified by scoring. Specifically, non-scoring underestimated the F-actin intensity per cell and quantitative cellular morphometric descriptors circularity and solidity and overestimated aspect ratio. Scoring improved the precision of cellular readouts, advocating the use of a MP quality and efficiency score as a quantitative decision-supporting tool in deciding whether or not particular MPs should be used for experiments, saving time and money. This simple scoring methodology can be used for improving MP fabrication, comparing results across studies, benefiting basic science studies and potential future clinical use of MPs by introducing standardization.

A facile single-cell patterning strategy based on harbor-like microwell microfluidics

Single-cell analysis is an effective method for conducting comprehensive heterogeneity studies ranging from cell phenotype to gene expression. The ability to arrange different cells in a predetermined pattern at single-cell resolution has a wide range of applications in cell-based analysis and plays an important role in facilitating interdisciplinary research by researchers in various fields. Most existing microfluidic microwell chips is a simple and straightforward method, which typically use small-sized microwells to accommodate single cells. However, this method imposes certain limitations on cells of various sizes, and the single-cell capture efficiency is relatively low without the assistance of external forces. Moreover, the microwells limit the spatiotemporal resolution of reagent replacement, as well as cell-to-cell communication. In this study, we propose a new strategy to prepare a single-cell array on a planar microchannel based on microfluidic flip microwells chip platform with large apertures (50 μm), shallow channels (50 μm), and deep microwells (50 μm). The combination of three configuration characteristics contributes to multi-cell trapping and a single-cell array within microwells, while the subsequent chip flipping accomplishes the transfer of the single-cell array to the opposite planar microchannel for cells adherence and growth. Further assisted by protein coating of bovine serum albumin and fibronectin on different layers, the single-cell capture efficiency in microwells is achieved at 92.1% ± 1%, while ultimately 85% ± 3.4% on planar microchannel. To verify the microfluidic flip microwells chip platform, the real-time and heterogeneous study of calcium release and apoptosis behaviours of single cells is carried out. To our knowledge, this is the first time that high-efficiency single-cell acquisition has been accomplished using a circular-well chip design that combines shallow channel, large aperture and deep microwell together. The chip is effective in avoiding the shearing force of high flow rates on cells, and the large apertures better allows cells to sedimentation. Therefore, this strategy owns the advantages of easy preparation and user-friendliness, which is especially valuable for researchers from different fields.

Reversible bonding of microfluidics: Review and applications

With the development of microfluidic technology, new materials and fabrication methods have been constantly invented in the field of microfluidics. Bonding is one of the key steps for the fabrication of enclosed-channel microfluidic chips, which have been extensively explored by researchers globally. The main purpose of bonding is to seal/enclose fabricated microchannels for subsequent fluid manipulations. Conventional bonding methods are usually irreversible, and the forced detachment of the substrate and cover plate may lead to structural damage to the chip. Some of the current microfluidic applications require reversible bonding to reuse the chip or retrieve the contents inside the chip. Therefore, it is essential to develop reversible bonding methods to meet the requirements of various applications. This review introduces the most recent developments in reversible bonding methods in microfluidics and their corresponding applications. Finally, the perspective and outlook of reversible bonding technology were discussed in this review.

Sub-wavelength acoustic stencil for tailored micropatterning

Acoustofluidic devices are ideal for biomedical micromanipulation applications, with high biocompatibility and the ability to generate force gradients down to the scale of cells. However, complex and designed patterning at the microscale remains challenging. In this work we report an acoustofluidic approach to direct particles and cells within a structured surface in arbitrary configurations. Wells, trenches and cavities are embedded in this surface. Combined with a half-wavelength acoustic field, together these form an 'acoustic stencil' where arbitrary cell and particle arrangements can be reversibly generated. Here a bulk-wavemode lithium niobate resonator generates multiplexed parallel patterning via a multilayer resonant geometry, where cell-scale resolution is accomplished via structured sub-wavelength microfeatures. Uniquely, this permits simultaneous manipulation in a unidirectional, device-spanning single-node field across scalable ∼cm² areas in a microfluidic device. This approach is demonstrated via patterning of 5, 10 and 15 μm particles and 293-F cells in a variety of arrangements, where these activities are enabling for a range of cell studies and tissue engineering applications via the generation of highly complex and designed acoustic patterns at the microscale.

Advances in Microfluidics for Single Red Blood Cell Analysis

The utilizations of microfluidic chips for single RBC (red blood cell) studies have attracted great interests in recent years to filter, trap, analyze, and release single erythrocytes for various applications. Researchers in this field have highlighted the vast potential in developing micro devices for industrial and academia usages, including lab-on-a-chip and organ-on-a-chip systems. This article critically reviews the current state-of-the-art and recent advances of microfluidics for single RBC analyses, including integrated sensors and microfluidic platforms for microscopic/tomographic/spectroscopic single RBC analyses, trapping arrays (including bifurcating channels), dielectrophoretic and agglutination/aggregation studies, as well as clinical implications covering cancer, sepsis, prenatal, and Sickle Cell diseases. Microfluidics based RBC microarrays, sorting/counting and trapping techniques (including acoustic, dielectrophoretic, hydrodynamic, magnetic, and optical techniques) are also reviewed. Lastly, organs on chips, multi-organ chips, and drug discovery involving single RBC are described. The limitations and drawbacks of each technology are addressed and future prospects are discussed.

Translational Nanomedicines Across Human Reproductive Organs Modeling on Microfluidic Chips: State-of-the-Art and Future Prospects

Forecasting the consequence of nanoparticles (NPs) and therapeutically significant molecules before materializing for human clinical trials is a mainstay for drug delivery and screening processes. One of the noteworthy obstacles that has prevented the clinical translation of NP-based drug delivery systems and novel drugs is the lack of effective preclinical platforms. As a revolutionary technology, the organ-on-a-chip (OOC), a coalition of microfluidics and tissue engineering, has surfaced as an alternative to orthodox screening platforms. OOC technology recapitulates the structural and physiological features of human organs along with intercommunications between tissues on a chip. The current review discusses the concept of microfluidics and confers cutting-edge fabrication processes for chip designing. We also outlined the advantages of microfluidics in analyzing NPs in terms of characterization, transport, and degradation in biological systems. The review further elaborates the scope and research on translational nanomedicines in human reproductive organs (testis, placenta, uterus, and menstrual cycle) by taking the advantages offered by microfluidics and shedding light on their potential future implications. Finally, we accentuate the existing challenges for clinical translation and scale-up dynamics for microfluidics chips and emphasize its future perspectives.

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.

Micro-patterned cell populations as advanced pharmaceutical drugs with precise functional control

Human cells are both advanced pharmaceutical drugs and 'drug deliverers'. However, functional control prior to or after cell implantation remains challenging. Micro-patterning cells through geometrically defined adhesion sites allows controlling morphogenesis, polarity, cellular mechanics, proliferation, migration, differentiation, stemness, cell-cell interactions, collective cell behavior, and likely immuno-modulatory properties. Consequently, generating micro-patterned therapeutic cells is a promising idea that has not yet been realized and few if any steps have been undertaken in this direction. This review highlights potential therapeutic applications, summarizes comprehensively the many cell functions that have been successfully controlled through micro-patterning, details the established micro-pattern designs, introduces the available fabrication technologies to the non-specialized reader, and suggests a quality evaluation score. Such a broad review is not yet available but would facilitate the manufacturing of therapeutically patterned cell populations using micro-patterned cell-instructive biomaterials for improved functional control as drug delivery systems in the context of cells as pharmaceutical products.

Novel Quick Cell Patterning Using Light-Responsive Gas-Generating Polymer and Fluorescence Microscope

Conventional cell patterning methods are mainly based on hydrophilic/hydrophobic differences or chemical coating for cell adhesion/non-adhesion with wavering strength as it varies with the substrate surface conditions, including the cell type and the extracellular matrix components (ECMs) coating; thus, the versatility and stability of cell patterning methods must be improved. In this study, we propose a new cell patterning method using a light-responsive gas-generating polymer (LGP) and a conventional fluorescence microscope. Herein, cells and cellular tissues are easily released from the substrate surface by the nitrogen gas bubbles generated from LGP by the excitation light for fluorescence observation without harming the cells. The LGP-implanted chip was fabricated by packing LGP into a polystyrene (PS) microarray chip with a concave pattern. HeLa cells were spread on the LGP-implanted chips coated with three different ECMs (fibronectin, collagen, and poly-D-lysine), and all HeLa cells on the three LGP patterns were released. The pattern error between the LGP pattern and the remaining HeLa cells was 8.81 ± 4.24 μm, less than single-cell size. In addition, the LGP-implanted chip method can be applied to millimeter-scale patterns, with less than 30 s required for cell patterning. Therefore, the proposed method is a simple and rapid cell patterning method with high cell patterning accuracy of less than the cell size error, high scalability, versatility, and stability unaffected by the cell type or the ECM coating.

Facile cell patterning induced by combined surface topography and chemistry on polydopamine-defined nanosubstrates

Cell patterning holds significant implications for cell-based analysis and high-throughput screening. The challenge and key factor for formation of cell patterns is to precisely modulate the interaction between cells and substrate surfaces. Many nanosubstrates have been developed to control cell adhesion and patterning, however, requirements of complicated fabrication procedures, harsh reaction conditions, and delicate manipulation are not routinely feasible. Here, we developed a hierarchical polydimethylsiloxane nanosubstrate (HPNS) coated with mussel-inspired polydopamine (PDA) micropatterns for effective cell patterning, depending on both surface topography and chemistry. HPNSs obtained by facile template-assisted replication brought enhanced topographic interaction between cells and substrates, but they were innately hydrophobic and cell-repellent. The hydrophobic nanosubstrates were converted to be hydrophilic after PDA coatings formed via spontaneous self-polymerization, which greatly facilitated cell adhesion. As such, without resorting to any external forces or physical constraints, cells selectively adhered and spread on spatially defined PDA regions with high efficiency, and well-defined cell microarrays could be formed within 20 min. Therefore, this easy-to-fabricate nanosubstrate with no complex chemical modification will afford a facile yet effective platform for rapid cell patterning.

Reversible Bonding of Thermoplastic Elastomers for Cell Patterning Applications

In this paper, we present a simple, versatile method that creates patterns for cell migration studies using thermoplastic elastomer (TPE). The TPE material used here can be robustly, but reversibly, bonded to a variety of plastic substrates, allowing patterning of cultured cells in a microenvironment. We first examine the bonding strength of TPE to glass and polystyrene substrates and com-pare it to thermoset silicone-based PDMS under various conditions and demonstrate that the TPE can be strongly and reversibly bonded on commercially available polystyrene culture plates. In cell migration studies, cell patterns are templated around TPE features cored from a thin TPE film. We show that the significance of fibroblast cell growth with fetal bovine serum (FBS)-cell culture media compared to the cells cultured without FBS, analyzed over two days of cell culture. This simple approach allows us to generate cell patterns without harsh manipulations like scratch assays and to avoid damaging the cells. We also confirm that the TPE material is non-toxic to cell growth and supports a high viability of fibroblasts and breast cancer cells. We anticipate this TPE-based patterning approach can be further utilized for many other cell patterning applications such as in cell-to-cell communication studies.

Visualization and Measurements of Blood Cells Flowing in Microfluidic Systems and Blood Rheology: A Personalized Medicine Perspective

Hemorheological alterations in the majority of metabolic diseases are always connected with blood rheology disturbances, such as the increase of blood and plasma viscosity, cell aggregation enhancement, and reduction of the red blood cells (RBCs) deformability. Thus, the visualizations and measurements of blood cells deformability flowing in microfluidic devices (point-of-care devices) can provide vital information to diagnose early symptoms of blood diseases and consequently to be used as a fast clinical tool for early detection of biomarkers. For instance, RBCs rigidity has been correlated with myocardial infarction, diabetes mellitus, hypertension, among other blood diseases. In order to better understand the blood cells behavior in microfluidic devices, rheological properties analysis is gaining interest by the biomedical committee, since it is strongly dependent on the interactions and mechanical cells proprieties. In addition, the development of blood analogue fluids capable of reproducing the rheological properties of blood and mimic the RBCs behavior at in vitro conditions is crucial for the design, performance and optimization of the microfluidic devices frequently used for personalized medicine. By combining the unique features of the hemorheology and microfluidic technology for single-cell analysis, valuable advances in personalized medicine for new treatments and diagnosis approach can be achieved.

Time-resolved microwell cell-pairing array reveals multiple T cell activation profiles

The differences in behaviour between individual cells in a large population are often important, yet are masked in bulk analyses where only average parameters are measured. One unresolved question in the field of immunology is the extent to which important immunological phenomena such as immunodominance to cancer antigens correlates with the average activity of a population of antigen-specific T lymphocytes, or with the activity of individual "outlier" cells. Despite progress in single cell technologies, few platforms are available that can deliver time-resolved, functional analysis at single cell resolution, for these investigations. We have developed an accessible high-throughput platform to measure single T cell signalling in real time following time-controlled stimulation by live antigen presenting cells. The cell-trap array consists of thousands of individual microwells cast in an agarose block, which is biocompatible and permeable to nutrients. Single T cells are isolated in wells via passive sedimentation and size exclusion, achieving up to 90% occupancy. The device enables simultaneous activation of thousands of single CD8⁺ cells. Stimulation with soluble reagents (ionomycin, anti-CD3 antibodies) or antigen presenting cells leads to changes in intracellular calcium concentrations which were measured using calcium-chelating fluorophore dyes. The platform was used to demonstrate a range of activation profiles among individual cells of a cloned, antigen specific CD8⁺ T cell hybridoma in response to both nonspecific stimuli and specific, physiologically relevant antigen stimulation. The presence of two different activation profiles was demonstrated, together with rare outlier behaviour among cells that are essentially clonal.

Effects of Processing Parameters of 3D Bioprinting on the Cellular Activity of Bioinks

In this review, few established cell printing techniques along with their parameters that affect the cell viability during bioprinting are considered. 3D bioprinting is developed on the principle of additive manufacturing using biomaterial inks and bioinks. Different bioprinting methods impose few challenges on cell printing such as shear stress, mechanical impact, heat, laser radiation, etc., which eventually lead to cell death. These factors also cause alteration of cells phenotype, recoverable or irrecoverable damages to the cells. Such challenges are not addressed in detail in the literature and scientific reports. Hence, this review presents a detailed discussion of several cellular bioprinting methods and their process-related impacts on cell viability, followed by probable mitigation techniques. Most of the printable bioinks encompass cells within hydrogel as scaffold material to avoid the direct exposure of the harsh printing environment on cells. However, the advantages of printing with scaffold-free cellular aggregates over cell-laden hydrogels have emerged very recently. Henceforth, optimal and favorable crosslinking mechanisms providing structural rigidity to the cell-laden printed constructs with ideal cell differentiation and proliferation, are discussed for improved understanding of cell printing methods for the future of organ printing and transplantation.

A micropore array-based solid lift-off method for highly efficient and controllable cell alignment and spreading

Interpretation of cell-cell and cell-microenvironment interactions is critical for both advancing knowledge of basic biology and promoting applications of regenerative medicine. Cell patterning has been widely investigated in previous studies. However, the reported methods cannot simultaneously realize precise control of cell alignment and adhesion/spreading with a high efficiency at a high throughput. Here, a novel solid lift-off method with a micropore array as a shadow mask was proposed. Efficient and precise control of cell alignment and adhesion/spreading are simultaneously achieved via an ingeniously designed shadow mask, which contains large micropores (capture pores) in central areas and small micropores (spreading pores) in surrounding areas contributing to capture/alignment and adhesion/spreading control, respectively. The solid lift-off functions as follows: (1) protein micropattern generates through both the capture and spreading pores, (2) cell capture/alignment control is realized through the capture pores, and (3) cell adhesion/spreading is controlled through previously generated protein micropatterns after lift-off of the shadow mask. High-throughput (2.4-3.2 × 10⁴ cells/cm²) cell alignments were achieved with high efficiencies (86.2 ± 3.2%, 56.7 ± 9.4% and 51.1 ± 4.0% for single-cell, double-cell, and triple-cell alignments, respectively). Precise control of cell spreading and applications for regulating cell skeletons and cell-cell junctions were investigated and verified using murine skeletal muscle myoblasts. To the best of our knowledge, this is the first report to demonstrate highly efficient and controllable multicell alignment and adhesion/spreading simultaneously via a simple solid lift-off operation. This study successfully fills a gap in literatures and promotes the effective and reproducible application of cell patterning in the fields of both basic mechanism studies and applied medicine.

Micropatterning Method for Porous Materials Using the Difference of the Glass Transition Temperature between Exposed and Unexposed Areas of a Thick-Photoresist

A cell culture on a scaffold has the advantages of functionality and easy handling, because the geometry of the cellular tissue is controlled by designing the scaffold. To create complex cellular tissue, scaffolds should be complex two-dimensional (2D) and three-dimensional (3D) structures. However, it is difficult to fabricate a scaffold with a 2D and 3D structure because the shape, size, and fabrication processes of a 2D structure in creating a cell layer, and a 3D structure containing cells, are different. In this research, we propose a micropatterning method for porous materials using the difference of the glass transition temperature between exposed and unexposed areas of a thick-photoresist. Since the proposed method does not require a vacuum, high temperature, or high voltage, it can be used for fabricating various structures with a wide range of scales, regardless of the materials used. Additionally, the patterning area can be fabricated accurately by photolithography. To evaluate the proposed method, a membrane integrated scaffold (MIS) with a 2D porous membrane and 3D porous material was fabricated. The MIS had a porous membrane with a pore size of 4 μm or less, which was impermeable to cells, and a porous material which was capable of containing cells. By seeding HUVECs and HeLa cells on each side of the MIS, the cellular tissue was formed with the designed geometry.

A Micropatterning Strategy to Study Nuclear Mechanotransduction in Cells

Micropatterning techniques have been widely used in biology, particularly in studies involving cell adhesion and proliferation on different substrates. Cell micropatterning approaches are also increasingly employed as in vitro tools to investigate intracellular mechanotransduction processes. In this report, we examined how modulating cellular shapes on two-dimensional rectangular fibronectin micropatterns of different widths influences nuclear mechanotransduction mediated by emerin, a nuclear envelope protein implicated in Emery-Dreifuss muscular dystrophy (EDMD). Fibronectin microcontact printing was tested onto glass coverslips functionalized with three different silane reagents (hexamethyldisilazane (HMDS), (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GPTMS)) using a vapor-phase deposition method. We observed that HMDS provides the most reliable printing surface for cell micropatterning, notably because it forms a hydrophobic organosilane monolayer that favors the retainment of surface antifouling agents on the coverslips. We showed that, under specific mechanical cues, emerin-null human skin fibroblasts display a significantly more deformed nucleus than skin fibroblasts expressing wild type emerin, indicating that emerin plays a crucial role in nuclear adaptability to mechanical stresses. We further showed that proper nuclear responses to forces involve a significant relocation of emerin from the inner nuclear envelope towards the outer nuclear envelope and the endoplasmic reticulum membrane network. Cell micropatterning by fibronectin microcontact printing directly on HMDS-treated glass represents a simple approach to apply steady-state biophysical cues to cells and study their specific mechanobiology responses in vitro.

Plasma-induced covalent immobilization and patterning of bioactive species in microfluidic devices

Here, we present a straightforward technique to create bio-functional microfluidic channels using CO2 plasma to induce both carboxylic and hydroxyl groups onto the channel surface. Consequently, not only does the surface allow for irreversible covalent bonding to an oxygen plasma treated PDMS for microfluidic device fabrication, but it also provides functionality for biomolecular immobilization. Furthermore, we demonstrate integration of this technique with microcontact printing to covalently micropattern functional biomolecules inside microfluidic channels. The bio-functionality and efficacy of the microcontact printed antibodies is demonstrated for both bioassays as well as patterning and culturing different cell lines. Results show that the introduced method can be an excellent candidate for cell culture studies in microfluidics. With the new printing method, full cell confluency (∼400 cells per mm2) was achieved after incubation for only 1 day, which is significantly greater than other conventional cell culture techniques inside microfluidic devices. As a proof of concept, we demonstrated the endothelial cells functionality by stimulating von Willebrand Factor secretion under shear stress. This is done via perfusion of histamine through the channel and performing immunofluorescence labeling to observe the inflammatory response of the cells. The developed method eliminates the need for wet chemistry and significantly simplifies producing bio-functional chips which can be used for biosensing, organs-on-chips and tissue engineering applications.

Recent advances in microfluidic platforms for single-cell analysis in cancer biology, diagnosis and therapy

Understanding molecular, cellular, genetic and functional heterogeneity of tumors at the single-cell level has become a major challenge for cancer research. The microfluidic technique has emerged as an important tool that offers advantages in analyzing single-cells with the capability to integrate time-consuming and labour-intensive experimental procedures such as single-cell capture into a single microdevice at ease and in a high-throughput fashion. Single-cell manipulation and analysis can be implemented within a multi-functional microfluidic device for various applications in cancer research. Here, we present recent advances of microfluidic devices for single-cell analysis pertaining to cancer biology, diagnostics, and therapeutics. We first concisely introduce various microfluidic platforms used for single-cell analysis, followed with different microfluidic techniques for single-cell manipulation. Then, we highlight their various applications in cancer research, with an emphasis on cancer biology, diagnosis, and therapy. Current limitations and prospective trends of microfluidic single-cell analysis are discussed at the end.

Polarity Induced in Human Stem Cell Derived Motoneurons on Patterned Self-Assembled Monolayers

The control of polarized human neurite/axon development at the single neuron level is critical in geographically directing signal propagation in engineered neural networks, for both in vitro and in vivo applications. While there is an increasing need to exert control over axonal growth for the successful development and establishment of integrative and functional in vitro systems, controlled, polarized distribution of either human-derived neurons or motoneurons in vitro has yet to be reported. In this study, we established the polarized distribution of stem cell derived human motoneurons, using a patterned surface, and maintained the cells in a serum-free system. A surface pattern with defined polarity was developed using self-assembled monolayers (SAMs). A cell permissive SAM, DETA (trimethoxysilyl propyldiethylenetri-amine), combined with photolithography and a nonpermissive fluorinated silane, 13F (tridecafluoro-1,1,2,2-tetrahydroctyl-1-dimethylchloro-silane), generated a surface where neurons only adhered to the designed attachment sites and did so with preferred orientation. In addition, 75% of the cells attached to the patterns were motoneurons compared to their percentage in the standard unpatterned surface which was used as a control condition (20%), demonstrating the preference of these human motoneurons in adhering to the patterns. The ability to dictate the distribution and polarity of human motoneurons will be essential to the engineering of human-based functional in vitro systems in which the control of signal propagation is necessary but more importantly for cell implantation studies. Such systems will greatly benefit the study of motor function as well as aid the development of high-throughput systems for drug screening and test beds for use in preclinical studies related to conditions such as spinal cord injury, ALS, and muscular dystrophy.

Low Cost and Lithography-free Stamp fabrication for Microcontact Printing

Microcontact printing (µCP) is a commonly used technique for patterning proteins of interest on substrates. The cells take the shape of these printed patterns. This technique is used to explore the effect of cellular morphology on their various functions such as survival, differentiation, migration, etc. An essential step for µCP is to fabricate a stamp from a silicon mould, prepared using lithography. Lithography is cost intensive and needs a high level of expertise to handle the instrumentation. Also, one stamp can be used to print patterns of one size and shape. Here, to overcome these limitations, we devised a low-cost fabrication technique using readily available objects such as injection needles and polystyrene beads. We patterned the C2C12, myoblasts cells on the shapes printed using lithography-free fabricated stamps. We further exploited the surface curvature of the stamp to vary the size of the print either by changing the applied load and/or the substrate stiffness. We showed that the print dimension could be predicted well by using JKR theory of contact mechanics. Moreover, some innovative improvisations enabled us to print complex shapes, which would be otherwise difficult with conventional lithography technique. We envisage that this low cost and easy to fabricate method will allow many research laboratories with limited resources to perform exciting research which is at present out of their reach.

Expanding the flexibility of dynamics simulation on different size particle-particle interactions by dielectrophoresis

In this paper, we perform flexible and reliable dynamics simulations on different sizes of two or more particles' interactive motions, where they encounter positive or negative dielectrophoresis (DEP) forces. The particles with identical or non-identical size are in close proximity suspended freely in a solution under a homogeneous electric field. According to the description of classic dipole moment, DEP forces make the particles form a straight chain. Therefore, dynamics simulation based on Newton's laws is utilized to understand AC DEP phenomena among multiple particles. To solve the relevant governing equations, Stokes drag and repulsive forces (including wall and particles) are combined with DEP forces to obtain the trajectories of particles. Results show that particles with the same sign of the Clausius-Mossotti (CM) factor revolve clockwise or counterclockwise to attract each other parallel to the electric field direction. Conversely, the particle chain is perpendicular to the field. This programmable advantage is of great benefit to the study of three or four particle motions. Meanwhile, the pearl chain consisting of three or four particles is related not only to an individual CM factor but also to initial spatial configuration. Both the cluster and short chain are dependent on symmetry between the geometric distribution and electric field, while it implies different size particles easily cause the chain structure with less time.

Methods of Micropatterning and Manipulation of Cells for Biomedical Applications

Micropatterning and manipulation of mammalian and bacterial cells are important in biomedical studies to perform in vitro assays and to evaluate biochemical processes accurately, establishing the basis for implementing biomedical microelectromechanical systems (bioMEMS), point-of-care (POC) devices, or organs-on-chips (OOC), which impact on neurological, oncological, dermatologic, or tissue engineering issues as part of personalized medicine. Cell patterning represents a crucial step in fundamental and applied biological studies in vitro, hence today there are a myriad of materials and techniques that allow one to immobilize and manipulate cells, imitating the 3D in vivo milieu. This review focuses on current physical cell patterning, plus chemical and a combination of them both that utilizes different materials and cutting-edge micro-nanofabrication methodologies.

Observation Interface of PDMS Membrane in a Microfluidic Chip Based on One-Step Molding

Nowadays, researchers are focusing on sorting, characterizing and detecting micron or submicron particles or bacteria in microfluidic chips. However, some contradictions hinder the applications of conventional microfluidic chips, including the low working distance of high resolving power microscopy and the low light transmittance of conventional microfluidic chips. In this paper, a rapid and readily accessible microfluidic fabrication method is presented to realize observation with high magnification microscopy. With the one-step molding process, the interconnections, the thin observation interface of polydimethylsiloxane (PDMS) membrane and microfluidic channels were integrated into an intact PDMS replica. Three kinds of PDMS replicas with different auxiliary beams were designed and optimized by leakage experiments and analytical software. The observation interfaces of a 170 μm thickness PDMS membrane enlarges the application domain of microfluidic chips. By adopting a solution of high magnification observation, microfluidic devices could be applied widely in medical science, biology and material science.