Biology on a chip: microfabrication for studying the behavior of cultured cells

Recent Progress and Challenges of Implantable Biodegradable Biosensors

Implantable biosensors have evolved to the cutting-edge technology of personalized health care and provide promise for future directions in precision medicine. This is the reason why these devices stand to revolutionize our approach to health and disease management and offer insights into our bodily functions in ways that have never been possible before. This review article tries to delve into the important developments, new materials, and multifarious applications of these biosensors, along with a frank discussion on the challenges that the devices will face in their clinical deployment. In addition, techniques that have been employed for the improvement of the sensitivity and specificity of the biosensors alike are focused on in this article, like new biomarkers and advanced computational and data communicational models. A significant challenge of miniaturized in situ implants is that they need to be removed after serving their purpose. Surgical expulsion provokes discomfort to patients, potentially leading to post-operative complications. Therefore, the biodegradability of implants is an alternative method for removal through natural biological processes. This includes biocompatible materials to develop sensors that remain in the body over longer periods with a much-reduced immune response and better device longevity. However, the biodegradability of implantable sensors is still in its infancy compared to conventional non-biodegradable ones. Sensor design, morphology, fabrication, power, electronics, and data transmission all play a pivotal role in developing medically approved implantable biodegradable biosensors. Advanced material science and nanotechnology extended the capacity of different research groups to implement novel courses of action to design implantable and biodegradable sensor components. But the actualization of such potential for the transformative nature of the health sector, in the first place, will have to surmount the challenges related to biofouling, managing power, guaranteeing data security, and meeting today's rules and regulations. Solving these problems will, therefore, not only enhance the performance and reliability of implantable biodegradable biosensors but also facilitate the translation of laboratory development into clinics, serving patients worldwide in their better disease management and personalized therapeutic interventions.

Cost-Effective Laboratory Matrix Projection Micro-Lithography System

This paper presents a home-built projection lithographer designed to transfer the image from a DLP (digital light processing) projector MEMS matrix onto the microscope objective's field of view, where a photoresist-covered substrate is placed. The photoresist is exposed using blue light with a wavelength of 450 nm. To calibrate the device and adjust focal lengths, we utilize a red light that does not affect the photoresist. The substrate is located on a movable platform, allowing the exposure field to be shifted, enabling the exposure of designs with lateral sizes of 1 × 1 cm2 at a resolution of a few micrometers. Our setup showcases a 2 μm resolution for the single frame 200 × 100 μm2, and a 5 μm resolution for 1 × 1 cm2 with field stitching. The exposure speed, approximately 1 mm2/100 s, proves to be sufficient for a variety of laboratory prototyping needs. This system offers a significant advantage due to its utilization of easily accessible and budget-friendly components, thereby enhancing its accessibility for a broader user base. The exposure speed and resolution meet the requirements for laboratory prototyping in the fields of 2D materials, quantum optics, superconducting microelectronics, microfluidics, and biology.

Engineered cell culture microenvironments for mechanobiology studies of brain neural cells

The biomechanical properties of the brain microenvironment, which is composed of different neural cell types, the extracellular matrix, and blood vessels, are critical for normal brain development and neural functioning. Stiffness, viscoelasticity and spatial organization of brain tissue modulate proliferation, migration, differentiation, and cell function. However, the mechanical aspects of the neural microenvironment are largely ignored in current cell culture systems. Considering the high promises of human induced pluripotent stem cell- (iPSC-) based models for disease modelling and new treatment development, and in light of the physiological relevance of neuromechanobiological features, applications of in vitro engineered neuronal microenvironments should be explored thoroughly to develop more representative in vitro brain models. In this context, recently developed biomaterials in combination with micro- and nanofabrication techniques 1) allow investigating how mechanical properties affect neural cell development and functioning; 2) enable optimal cell microenvironment engineering strategies to advance neural cell models; and 3) provide a quantitative tool to assess changes in the neuromechanobiological properties of the brain microenvironment induced by pathology. In this review, we discuss the biological and engineering aspects involved in studying neuromechanobiology within scaffold-free and scaffold-based 2D and 3D iPSC-based brain models and approaches employing primary lineages (neural/glial), cell lines and other stem cells. Finally, we discuss future experimental directions of engineered microenvironments in neuroscience.

The Development of Biomimetic Aligned Skeletal Muscles in a Fully 3D Printed Microfluidic Device

Human skeletal muscles are characterized by a unique aligned microstructure of myotubes which is important for their function as well as for their homeostasis. Thus, the recapitulation of the aligned microstructure of skeletal muscles is crucial for the construction of an advanced biomimetic model aimed at drug development applications. Here, we have developed a 3D printed micropatterned microfluid device (3D-PMMD) through the employment of a fused deposition modeling (FDM)-based 3D printer and clear filaments made of biocompatible polyethylene terephthalate glycol (PETG). We could fabricate micropatterns through the adjustment of the printing deposition heights of PETG filaments, leading to the generation of aligned half-cylinder-shaped micropatterns in a dimension range from 100 µm to 400 µm in width and from 60 µm to 150 µm in height, respectively. Moreover, we could grow and expand C2C12 mouse myoblast cells on 3D-PMMD where cells could differentiate into aligned bundles of myotubes with respect to the dimension of each micropattern. Furthermore, our platform was applicable with the electrical pulses stimulus (EPS) modality where we noticed an improvement in myotubes maturation under the EPS conditions, indicating the potential use of the 3D-PMMD for biological experiments as well as for myogenic drug development applications in the future.

Biomimicked hierarchical 2D and 3D structures from natural templates: applications in cell biology

Intricate structures of natural surfaces and materials have amazed people over the ages. The unique properties of various surfaces also created interest and curiosity in researchers. In the recent past, with the advent of superior microscopy techniques, we have started to understand how these complex structures provide superior properties. With that knowledge, scientists have developed various biomimicked and bio-inspired surfaces for different non-biological applications. In the last two decades, we have also started to learn how structures of the tissue microenvironment influence cell function and behaviour, both in physiological and pathological conditions. Hence, it became essential to decipher the role and importance of structural hierarchy in the cellular context. With advances in microfabricated techniques, such complex structures were made by superimposing features of different dimensions. However, the fabricated topographies are far from matching the complexities presentin vivo. Hence, the need of biomimicking the natural surfaces for cellular applications was felt. In this review, we discuss a few examples of hierarchical surfaces found in plants, insects, and vertebrates. Such structures have been widely biomimicked for various applications but rarely studied for cell-substrate interaction and cellular response. Here, we discuss the research work wherein 2D hierarchical substrates were prepared using biomimicking to understand cellular functions such as adhesion, orientation, differentiation, and formation of spheroids. Further, we also present the status of ongoing research in mimicking 3D tissue architecture using de-cellularized plant-based and tissue/organ-based scaffolds. We will also discuss 3D printing for fabricating 2D and 3D hierarchical structures. The review will end by highlighting the various advantages and research challenges in this approach. The biomimickedin-vivolike substrate can be used to better understand cellular physiology, and for tissue engineering.

Microfabricated Devices for Confocal Microscopy on Biological Samples

Microfabricated devices have found applications in a range of biomedical research problems in recent years, with thousands of research papers published and multiple commercial devices now available. This chapter is intended to provide an overview of the available options for devices compatible with confocal microscopy, including an overview of fabrication techniques and some examples of device use. Although there are times when off-the-shelf devices are well suited for the problem at hand, in some cases customized devices are necessary or more convenient. Protocols for researchers who wish to make their own devices are outlined below; although fabricating templates for devices requires some specialized equipment, making PDMS or hydrogel devices from templates can be done in a standard laboratory setting.

Lithography Technology for Micro- and Nanofabrication

Micro and nanofabrication technologies are integral to the development of miniaturized systems. Lithography plays a key role in micro and nanofabrication techniques. Since high functional miniaturized systems are required in various fields, such as the development of a semiconductor, chemical and biological analysis, and biomedical researches, lithography techniques have been developed and applied for their appropriate purpose. Lithography can be classified into conventional and unconventional lithography, or top-down and bottom-up, or with mask and mask-less approaches. In this chapter, various lithography techniques are categorized and classified into conventional and unconventional lithography. In the first part, photolithography, electron beam, and focused-ion beam lithography are introduced as conventional lithography techniques. The second part introduces nanoimprint lithography, deformation lithography, and colloidal lithography as unconventional lithography techniques. In the last part, the pros and cons of each lithography are discussed for an appropriate design of fabrication processes.

Microfluidic and Microscale Assays to Examine Regenerative Strategies in the Neuro Retina

Bioengineering systems have transformed scientific knowledge of cellular behaviors in the nervous system (NS) and pioneered innovative, regenerative therapies to treat adult neural disorders. Microscale systems with characteristic lengths of single to hundreds of microns have examined the development and specialized behaviors of numerous neuromuscular and neurosensory components of the NS. The visual system is comprised of the eye sensory organ and its connecting pathways to the visual cortex. Significant vision loss arises from dysfunction in the retina, the photosensitive tissue at the eye posterior that achieves phototransduction of light to form images in the brain. Retinal regenerative medicine has embraced microfluidic technologies to manipulate stem-like cells for transplantation therapies, where de/differentiated cells are introduced within adult tissue to replace dysfunctional or damaged neurons. Microfluidic systems coupled with stem cell biology and biomaterials have produced exciting advances to restore vision. The current article reviews contemporary microfluidic technologies and microfluidics-enhanced bioassays, developed to interrogate cellular responses to adult retinal cues. The focus is on applications of microfluidics and microscale assays within mammalian sensory retina, or neuro retina, comprised of five types of retinal neurons (photoreceptors, horizontal, bipolar, amacrine, retinal ganglion) and one neuroglia (Müller), but excludes the non-sensory, retinal pigmented epithelium.

100th Anniversary of Macromolecular Science Viewpoint: Re-Engineering Cellular Interfaces with Synthetic Macromolecules Using Metabolic Glycan Labeling

Cell-surface functionality is largely programmed by genetically encoded information through modulation of protein expression levels, including glycosylation enzymes. Genetic tools enable control over protein-based functionality, but are not easily adapted to recruit non-native functionality such as synthetic polymers and nanomaterials to tune biological responses and attach therapeutic or imaging payloads. Similar to how polymer-protein conjugation evolved from nonspecific PEGylation to site-selective bioconjugates, the same evolution is now occurring for polymer-cell conjugation. This Viewpoint discusses the potential of using metabolic glycan labeling to install bio-orthogonal reactive cell-surface anchors for the recruitment of synthetic polymers and nanomaterials to cell surfaces, exploring the expanding therapeutic and diagnostic potential. Comparisons to conventional approaches that target endogenous membrane components, such as hydrophobic, protein coupling and electrostatic conjugation, as well as enzymatic and genetic tools, have been made to highlight the huge potential of this approach in the emerging cellular engineering field.

Large-Scale, High-Resolution Microelectrode Arrays for Interrogation of Neurons and Networks

High-density microelectrode arrays (HD-MEAs) are increasingly being used for the observation and manipulation of neurons and networks in vitro. Large-scale electrode arrays allow for long-term extracellular recording of the electrical activity from thousands of neurons simultaneously. Beyond population activity, it has also become possible to extract information of single neurons at subcellular level (e.g., the propagation of action potentials along axons). In effect, HD-MEAs have become an electrical imaging platform for label-free extraction of the structure and activation of cells in cultures and tissues. The quality of HD-MEA data depends on the resolution of the electrode array and the signal-to-noise ratio. In this chapter, we begin with an introduction to HD-MEA signals. We provide an overview of the developments on complementary metal-oxide-semiconductor or CMOS-based HD-MEA technology. We also discuss the factors affecting the performance of HD-MEAs and the trending application requirements that drive the efforts for future devices. We conclude with an outlook on the potential of HD-MEAs for advancing basic neuroscience and drug discovery.

Microfluidic Cell Trapping for Single-Cell Analysis

The single-cell capture microfluidic chip has many advantages, including low cost, high throughput, easy manufacturing, integration, non-toxicity and good stability. Because of these characteristics, the cell capture microfluidic chip is increasingly becoming an important carrier on the study of life science and pharmaceutical analysis. Important promises of single-cell analysis are the paring, fusion, disruption and analysis of intracellular components for capturing a single cell. The capture, which is based on the fluid dynamics method in the field of micro fluidic chips is an important way to achieve and realize the operations mentioned above. The aim of this study was to compare the ability of three fluid dynamics-based microfluidic chip structures to capture cells. The effects of cell growth and distribution after being captured by different structural chips and the subsequent observation and analysis of single cells on the chip were compared. It can be seen from the experimental results that the microfluidic chip structure most suitable for single-cell capture is a U-shaped structure. It enables single-cell capture as well as long-term continuous culture and the single-cell observation of captured cells. Compared to the U-shaped structure, the cells captured by the microcavity structure easily overlapped during the culture process and affected the subsequent analysis of single cells. The flow shortcut structure can also be used to capture and observe single cells, however, the shearing force of the fluid caused by the chip structure is likely to cause deformation of the cultured cells. By comparing the cell capture efficiency of the three chips, the reagent loss during the culture process and the cell growth state of the captured cells, we are provided with a theoretical support for the design of a single-cell capture microfluidic chip and a reference for the study of single-cell capture in the future.

Regulating positioning and orientation of mitotic spindles via cell size and shape

Proper location of the mitotic spindle is critical for chromosome segregation and the selection of the cell division plane. However, how mitotic spindles sense cell size and shape to regulate their own position and orientation is still largely unclear. To investigate this question systematically, we used a general model by considering chromosomes, microtubule dynamics, and forces of various molecular motors. Our results show that in cells of various sizes and shapes, spindles can always be centered and oriented along the long axis robustly in the absence of other specified mechanisms. We found that the characteristic time of positioning and orientation processes increases with cell size. Spindles sense the cell size mainly by the cortical force in small cells and by the cytoplasmic force in large cells. In addition to the cell size, the cell shape mainly influences the orientation process. We found that more slender cells have a faster orientation process, and the final orientation is not necessarily along the longest axis but is determined by the radial profile and the symmetry of the cell shape. Finally, our model also reproduces the separation and repositioning of the spindle poles during the anaphase. Therefore, our work provides a general tool for studying the mitotic spindle across the whole mitotic phase.

Microfluidics: innovative approaches for rapid diagnosis of antibiotic-resistant bacteria

The emergence of antibiotic-resistant bacteria has become a major global health concern. Rapid and accurate diagnostic strategies to determine the antibiotic susceptibility profile prior to antibiotic prescription and treatment are critical to control drug resistance. The standard diagnostic procedures for the detection of antibiotic-resistant bacteria, which rely mostly on phenotypic characterization, are time consuming, insensitive and often require skilled personnel, making them unsuitable for point-of-care (POC) diagnosis. Various molecular techniques have therefore been implemented to help speed up the process and increase sensitivity. Over the past decade, microfluidic technology has gained great momentum in medical diagnosis as a series of fluid handling steps in a laboratory can be simplified and miniaturized on to a small platform, allowing marked reduction of sample amount, high portability and tremendous possibility for integration with other detection technologies. These advantages render the microfluidic system a great candidate to be developed into an easy-to-use sample-to-answer POC diagnosis suitable for application in remote clinical settings. This review provides an overview of the current development of microfluidic technologies for the nucleic acid based and phenotypic-based detections of antibiotic resistance.

A Microfabricated 96-Well 3D Assay Enabling High-Throughput Quantification of Cellular Invasion Capabilities

This paper presents a 96-well microfabricated assay to study three-dimensional (3D) invasion of tumor cells. A 3D cluster of tumor cells was first generated within each well by seeding cells onto a micro-patterned surface consisting of a central fibronectin-coated area that promotes cellular attachment, surrounded by a poly ethylene glycol (PEG) coated area that is resistant to cellular attachment. Following the formation of the 3D cell clusters, a 3D collagen extracellular matrix was formed in each well by thermal-triggered gelation. Invasion of the tumor cells into the extracellular matrix was subsequently initiated and monitored. Two modes of cellular infiltration were observed: A549 cells invaded into the extracellular matrix following the surfaces previously coated with PEG molecules in a pseudo-2D manner, while H1299 cells invaded into the extracellular matrix in a truly 3D manner including multiple directions. Based on the processing of 2D microscopic images, a key parameter, namely, equivalent invasion distance (the area of invaded cells divided by the circumference of the initial cell cluster) was obtained to quantify migration capabilities of these two cell types. These results validate the feasibility of the proposed platform, which may function as a high-throughput 3D cellular invasion assay.

Microfluidic System for Automated Cell-based Assays

Microfluidic cell culture is a promising technology for applications in the drug screening industry. Key benefits include improved biological function, higher quality cell-based data, reduced reagent consumption, and lower cost. In this work, we demonstrate how a microfluidic cell culture design was adapted to be compatible with the standard 96-well plate format. Key design features include the elimination of tubing and connectors, the ability to maintain long term continuous perfusion cell culture using a passive gravity driven pump, and direct analysis on the outlet wells of the microfluidic plate. A single microfluidic culture plate contained 8 independent flow units, each with 10(4) cells at a flow rate of 50 μl/day (6 minute residence time). The cytotoxicity of the anti-cancer drug etoposide was measured on HeLa cells cultured in this format, using a commercial lactate dehydrogenase (LDH) plate reader assay. The integration of microfluidic cell culture methods with commercial automation capabilities offers an exciting opportunity for improved cell-based screening.

An open-chamber flow-focusing device for focal stimulation of micropatterned cells

Microfluidic devices can deliver soluble factors to cell and tissue culture microenvironments with precise spatiotemporal control. However, enclosed microfluidic environments often have drawbacks such as the need for continuous culture medium perfusion which limits the duration of experiments, incongruity between microculture and macroculture, difficulty in introducing cells and tissues, and high shear stress on cells. Here, we present an open-chamber microfluidic device that delivers hydrodynamically focused streams of soluble reagents to cells over long time periods (i.e., several hours). We demonstrate the advantage of the open chamber by using conventional cell culture techniques to induce the differentiation of myoblasts into myotubes, a process that occurs in 7-10 days and is difficult to achieve in closed chamber microfluidic devices. By controlling the flow rates and altering the device geometry, we produced sharp focal streams with widths ranging from 36 μm to 187 μm. The focal streams were reproducible (∼12% variation between units) and stable (∼20% increase in stream width over 10 h of operation). Furthermore, we integrated trenches for micropatterning myoblasts and microtraps for confining single primary myofibers into the device. We demonstrate with finite element method (FEM) simulations that shear stresses within the cell trench are well below values known to be deleterious to cells, while local concentrations are maintained at ∼22% of the input concentration. Finally, we demonstrated focused delivery of cytoplasmic and nuclear dyes to micropatterned myoblasts and myofibers. The open-chamber microfluidic flow-focusing concept combined with micropatterning may be generalized to other microfluidic applications that require stringent long-term cell culture conditions.

Changes in Cell Adhesiveness and Physicochemical Properties of Cross-Linked Albumin Films after Ultraviolet Irradiation

We discovered the unique cell adhesive properties of ultraviolet (UV)-irradiated albumin films. Albumin films prepared using a cross-linking reagent with epoxy groups maintained native albumin properties, such as resistance to cell adhesion. Interestingly, the cell adhesive properties of films varied depending upon the UV irradiation time; specifically, cell adhesiveness increased until 2 h of UV irradiation, when the cell number attached to the film was similar to that of culture dishes, and then cell adhesiveness decreased until 20 h of UV irradiation, after which the surface returned to the initial non-adhesive state. To elucidate the molecular mechanisms underlying this phenomenon, we examined the effect of UV irradiation on albumin film properties. The following changes occurred in response to UV irradiation: decreased α-helical structure, cleavage of albumin peptide bonds, and increased hydrophilicity and oxygen content of the albumin film surface. In addition, we found a positive correlation between the degree of cell adhesion and the amount of fibronectin adsorbed on the film. Taken together, UV-induced changes in films highly affect the amount of cell adhesion proteins adsorbed on the films depending upon the irradiation time, which determines cell adhesion behavior.

Use of high concentrations of dimethyl sulfoxide for cryopreservation of HepG2 cells adhered to glass and polydimethylsiloxane matrices

Animal cells are generally cryopreserved in cryovials in a cell suspension state containing 5%-10% v/v dimethyl sulfoxide (DMSO) used as a cryoprotective agent. However, cryopreservation of cells in an attached state has not been intensively studied, and the effective freezing solution remains unknown. Here we determined the suitable DMSO concentration for the cryopreservation of human hepatoma HepG2 cells attached to glass and polydimethylsiloxane (PDMS) matrices coated with poly-l-lysine. With the use of the glass matrix, the rate of cell adhesion increased with the DMSO concentration up to 30% v/v in the freezing solution. In contrast, the cell-adhesion rate remained constant in the case of the PDMS matrix irrespective of the DMSO concentration between 10% v/v and 30% v/v. The viability of post-thawed cells attached to glass or PDMS matrix was also investigated. The viability was highest at the DMSO concentration of 20% v/v in the freezing solution. The DMSO concentration of 30% v/v, however, had a cytotoxic effect on the cell viability. Thus, the 20% v/v DMSO concentration was found to be most suitable for the cryopreservation of HepG2 cells in the attached state. This dose is high compared to the DMSO concentration used for the cryopreservation of cells in the suspended state.

Co-fabrication of chitosan and epoxy photoresist to form microwell arrays with permeable hydrogel bottoms

Microfabrication technology offers the potential to create biological platforms with customizable patterns and surface chemistries, allowing precise control over the biochemical microenvironment to which a cell or group of cells is exposed. However, most microfabricated platforms grow cells on impermeable surfaces. This report describes the co-fabrication of a micropatterned epoxy photoresist film with a chitosan film to create a freestanding array of permeable, hydrogel-bottomed microwells. These films possess optical properties ideal for microscopy applications, and the chitosan layers are semi-permeable with a molecular exclusion of 9.9 ± 2.1 kDa. By seeding cells into the microwells, overlaying inert mineral oil, and supplying media via the bottom surface, this hybrid film permits cells to be physically isolated from one another but maintained in culture for at least 4 days. Arrays co-fabricated using these materials reduce both large-molecular-weight biochemical crosstalk between cells and mixing of different clonal populations, and will enable high-throughput studies of cellular heterogeneity with increased ability to customize dynamic interrogations compared to materials in currently available technologies.

Biomimetic collagen I and IV double layer Langmuir-Schaefer films as microenvironment for human pluripotent stem cell derived retinal pigment epithelial cells

The environmental cues received by the cells from synthetic substrates in vitro are very different from those they receive in vivo. In this study, we applied the Langmuir-Schaefer (LS) deposition, a variant of Langmuir-Blodgett technique, to fabricate a biomimetic microenvironment mimicking the structure and organization of native Bruch's membrane for the production of the functional human embryonic stem cell derived retinal pigment epithelial (hESC-RPE) cells. Surface pressure-area isotherms were measured simultaneously with Brewster angle microscopy to investigate the self-assembly of human collagens type I and IV on air-subphase interface. Furthermore, the structure of the prepared collagen LS films was characterized with scanning electron microscopy, atomic force microscopy, surface plasmon resonance measurements and immunofluorescent staining. The integrity of hESC-RPE on double layer LS films was investigated by measuring transepithelial resistance and permeability of small molecular weight substance. Maturation and functionality of hESC-RPE cells on double layer collagen LS films was further assessed by RPE-specific gene and protein expression, growth factor secretion, and phagocytic activity. Here, we demonstrated that the prepared collagen LS films have layered structure with oriented fibers corresponding to architecture of the uppermost layers of Bruch's membrane and result in increased barrier properties and functionality of hESC-RPE cells as compared to the commonly used dip-coated controls.

Revealing neuronal function through microelectrode array recordings

Microelectrode arrays and microprobes have been widely utilized to measure neuronal activity, both in vitro and in vivo. The key advantage is the capability to record and stimulate neurons at multiple sites simultaneously. However, unlike the single-cell or single-channel resolution of intracellular recording, microelectrodes detect signals from all possible sources around every sensor. Here, we review the current understanding of microelectrode signals and the techniques for analyzing them. We introduce the ongoing advancements in microelectrode technology, with focus on achieving higher resolution and quality of recordings by means of monolithic integration with on-chip circuitry. We show how recent advanced microelectrode array measurement methods facilitate the understanding of single neurons as well as network function.

Physical-level synthesis for digital lab-on-a-chip considering variation, contamination, and defect

Microfluidic lab-on-a-chips have been widely utilized in biochemical analysis and human health studies due to high detection accuracy, high timing efficiency, and low cost. The increasing design complexity of lab-on-a-chips necessitates the computer-aided design (CAD) methodology in contrast to the classical manual design methodology. A key part in lab-on-a-chip CAD is physical-level synthesis. It includes the lab-on-a-chip placement and routing, where placement is to determine the physical location and the starting time of each operation and routing is to transport each droplet from the source to the destination. In the lab-on-a-chip design, variation, contamination, and defect need to be considered. This work designs a physical-level synthesis flow which simultaneously considers variation, contamination, and defect of the lab-on-a-chip design. It proposes a maze routing based, variation, contamination, and defect aware droplet routing technique, which is seamlessly integrated into an existing placement technique. The proposed technique improves the placement solution for routing and achieves the placement and routing co-optimization to handle variation, contamination, and defect. The simulation results demonstrate that our technique does not use any defective/contaminated grids, while the technique without considering contamination and defect uses 17.0% of the defective/contaminated grids on average. In addition, our routing variation aware technique significantly improves the average routing yield by 51.2% with only 3.5% increase in completion time compared to a routing variation unaware technique.

Programmable patterning of protein bioactivity by visible light

The simple and quick patterning of functional proteins on engineered surfaces affords an opportunity to fabricate protein microarrays in lab-on-chip systems. We report on the programmable patterning of proteins as well as the local activation of enzymes by visible light. We successfully generated functional protein patterns with different geometries in situ and demonstrated the specific patterning of multiple kinds of proteins side-by-side without the need for specific linker molecules or elaborate surface preparation.

Characterization of cell seeding and specific capture of B cells in microbubble well arrays

Development of micro-well array systems for use in high-throughput screening of rare cells requires a detailed understanding of the factors that impact the specific capture of cells in wells and the distribution statistics of the number of cells deposited into wells. In this study we investigate the development of microbubble (MB) well array technology for sorting antigen-specific B-cells. Using Poisson statistics we delineate the important role that the fractional area of MB well opening and the cell seeding density have on determining cell seeding distribution in wells. The unique architecture of the MB well hinders captured cells from escaping the well and provides a unique microenvironmental niche that enables media changes as needed for extended cell culture. Using cell lines and primary B and T cells isolated from human peripheral blood we demonstrate the use of affinity capture agents coated in the MB wells to enrich for the selective capture of B cells. Important differences were noted in the efficacy of bovine serum albumin to block the nonspecific adsorption of primary cells relative to cell lines as well as the efficacy of the capture coatings using mixed primary B and T cells samples. These results emphasize the importance of using primary cells in technology development and suggest the need to utilize B cell capture agents that are insensitive to cell activation.

Neural circuits with long-distance axon tracts for determining functional connectivity

The cortical circuitry in the brain consists of structurally and functionally distinct neuronal assemblies with reciprocal axon connections. To generate cell culture-based systems that emulate axon tract systems of an in vivo neural network, we developed a living neural circuit consisting of compartmentalized neuronal populations connected by arrays of two millimeter-long axon tracts that are integrated on a planar multi-electrode array (MEA). The millimeter-scale node-to-node separation allows for pharmacological and electrophysiological manipulations to simultaneously target multiple neuronal populations. The results show controlled selectivity of dye absorption by neurons in different compartments. MEA-transmitted electrical stimulation of targeted neurons shows ∼46% increase of intracellular calcium levels with 20 Hz stimulation, but ∼22% decrease with 2k Hz stimulation. The unique feature of long distance axons promotes in vivo-like fasciculation. These axon tracts are determined to be inhibitory afferents by showing increased action potential firing of downstream node upon selective application of γ-aminobutyric acid (GABA) to the upstream node. Together, this model demonstrates integrated capabilities for assessing multiple endpoints including axon tract tracing, calcium influx, network architecture and activities. This system can be used as a multi-functional platform for studying axon tract-associated CNS disorders in vitro, such as diffuse axonal injury after brain trauma.

Cell chips as new tools for cell biology--results, perspectives and opportunities

Cell culture technologies were initially developed as research tools for studying cell functions, but nowadays they are essential for the biotechnology industry, with rapidly expanding applications requiring more and more advancements with respect to traditional tools. Miniaturization and integration of sensors and microfluidic components with cell culture techniques open the way to the development of cellomics as a new field of research targeting innovative analytic platforms for high-throughput studies. This approach enables advanced cell studies under controllable conditions by providing inexpensive, easy-to-operate devices. Thanks to their numerous advantages cell-chips have become a hotspot in biosensors and bioelectronics fields and have been applied to very different fields. In this review exemplary applications will be discussed, for cell counting and detection, cytotoxicity assays, migration assays and stem cell studies.

Micropatterning of ECM Proteins on Glass Substrates to Regulate Cell Attachment and Proliferation

BACKGROUND

Micropatterning is becoming a powerful tool for studying cells in vitro. This method not only uses very small amount of material but also mimic the microenvironment structure present in living tissues better than flask culturing techniques. In previous studies using micropatterning of extracellular matrix proteins on glass surfaces, the rate of protein detachment from the surface was so high that the proteins and the cultivated cells detached after 3 three days of cell seeding.

METHODS

Here we optimized the glass surface modification method to fulfill the requirement of most in vitro studies.

RESULTS

In our study we showed that the optimum time for glass surface modification reaction is 1.5 hr, and the cells could be tracked in vitro for over 15 days after cell seeding which is enough for the most in vitro studies. As a model, we cultivated HEK 293T and HepG2 cells on the collagen micro-patterns and showed that they have normal growth and morphology on these micropatterns. The HEK cells also transfected with pmaxGFP plasmid vector to show that the cells on collagen micropatterns could also used in transfection studies.

CONCLUSION

Taking these together, this novel method is promising for efficient cell culture studies on micropatterened surfaces in the future.

Charting microbial phenotypes in multiplex nanoliter batch bioreactors

High-throughput growth phenotyping is receiving great attention for establishing the genotype-phenotype map of sequenced organisms owing to the ready availability of complete genome sequences. To date, microbial growth phenotypes have been investigated mostly by the conventional method of batch cultivation using test tubes, Erlenmeyer flasks, or the recently available microwell plates. However, the current batch cultivation methods are time- and labor-intensive and often fail to consider sophisticated environmental changes. The implementation of batch cultures at the nanoliter scale has been difficult because of the quick evaporation of the culture medium inside the reactors. Here, we report a microfluidic system that allows independent cell cultures in evaporation-free multiplex nanoliter reactors under different culture conditions to assess the behavior of cells. The design allows three experimental replicates for each of eight culture environments in a single run. We demonstrate the versatility of the device by performing growth curve experiments with Escherichia coli and microbiological assays of antibiotics against the opportunistic pathogen Pseudomonas aeruginosa. Our study highlights that the microfluidic system can effectively replace the traditional batch culture methods with nanoliter volumes of bacterial cultivations, and it may be therefore promising for high-throughput growth phenotyping as well as for single-cell analyses.

WITHDRAWN: Neural circuits with long-distance axon tracts for determining functional connectivity

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Skeletal muscle-derived cell cultures as potent models in regenerative medicine research

Cell cultures have been used extensively by many scientists in recent decades to study various cell and tissue mechanisms. The use of cell cultures has many advantages over use of in vivo experimental models, but there are also limitations. As skeletal muscle-derived cell cultures become more commonly utilized in studies of muscle regeneration processes the question of their relevance in experimentation is highlighted with regard to in vivo experimental models. This article reviews studies that have been performed simultaneously in in vivo and in vitro experiments on skeletal muscle and assesses the correlation of results. Although they seem to correlate, no such studies on humans have been performed so far.

Nanotechnology meets electrophysiology

Recording of electrical signals from electrogenic cells is an essential aspect to many areas, ranging from fundamental biophysical studies of the function of the brain and heart, through medical monitoring and intervention. Over the past decades, these studies have been primarily carried out by various well-established techniques that have greatly advanced the field, yet pose handicapping technical limitations. Nanotechnology allows the fabrication of devices small enough to enable recording of single cells, and even single neurites. The rise in knowledge in controlling nanostructures allows their tailoring to match cellular components, thus offering high level of interfacing to single cells. We will cover the latest developments in electrophysiology, applying new nanotechnology-based approaches for cellular electrical recordings, both extracellularly and intracellularly.

Accumulation and detection of secreted proteins from single cells for reporter gene assays using a local redox cycling-based electrochemical (LRC-EC) chip device

A lab-on-a-chip device is described for the electrochemical detection of alkaline phosphatase (ALP) secreted by transformed single HeLa cells. Detection on the chip device is based on local redox cycling at 256 individually addressable sensor points. Ring-disk electrodes (generator/collector) are arranged at individual sensor points to amplify the signal due to redox-cycling with only 32 connector pads. The surface of each sensor point is modified with antibodies for secreted alkaline phosphatase (SEAP) immobilization, which facilitates separation and detection of SEAP. Separation of SEAP from HeLa cells enables elimination of endogenous ALP and prevents HeLa cells from damage due to exposure to high level pH used during electrochemical detection. The large number of sensor points enables the simultaneous analysis of a large amount of single cells using the chip. The system is useful for gene reporter assays and for the detection of several types of secreted proteins.

Microwell regulation of pluripotent stem cell self-renewal and differentiation

The fates of pluripotent stem cells (PSCs), including survival, self-renewal, and differentiation, are regulated by chemical and mechanical cues presented in the three-dimensional (3D) microenvironment. Most PSC studies have been performed on two-dimensional substrates. However, 3D culture systems have demonstrated the importance of intercellular interactions in regulating PSC self-renewal and differentiation. Microwell culture systems have been developed to generate homogenous PSC colonies of defined sizes and shapes and to study how colony morphology affects cell fate. Using microwells, researchers have demonstrated that PSCs remain in a self-renewing undifferentiated state as a result of autocrine and paracrine signaling. Other studies have shown that microwell regulation of embryoid body size affects lineage commitment during differentiation via cell-cell contact and expression of soluble signals. In this review, we discuss recent advances in the design and utilization of 3D microwell platforms for studying intercellular regulation of PSC cell fate decisions and the underlying molecular mechanisms.

Highly ordered large-scale neuronal networks of individual cells - toward single cell to 3D nanowire intracellular interfaces

The use of artificial, prepatterned neuronal networks in vitro is a promising approach for studying the development and dynamics of small neural systems in order to understand the basic functionality of neurons and later on of the brain. The present work presents a high fidelity and robust procedure for controlling neuronal growth on substrates such as silicon wafers and glass, enabling us to obtain mature and durable neural networks of individual cells at designed geometries. It offers several advantages compared to other related techniques that have been reported in recent years mainly because of its high yield and reproducibility. The procedure is based on surface chemistry that allows the formation of functional, tailormade neural architectures with a micrometer high-resolution partition, that has the ability to promote or repel cells attachment. The main achievements of this work are deemed to be the creation of a large scale neuronal network at low density down to individual cells, that develop intact typical neurites and synapses without any glia-supportive cells straight from the plating stage and with a relatively long term survival rate, up to 4 weeks. An important application of this method is its use on 3D nanopillars and 3D nanowire-device arrays, enabling not only the cell bodies, but also their neurites to be positioned directly on electrical devices and grow with registration to the recording elements underneath.

Matrix nanotopography as a regulator of cell function

The architecture of the extracellular matrix (ECM) directs cell behavior by providing spatial and mechanical cues to which cells respond. In addition to soluble chemical factors, physical interactions between the cell and ECM regulate primary cell processes, including differentiation, migration, and proliferation. Advances in microtechnology and, more recently, nanotechnology provide a powerful means to study the influence of the ECM on cell behavior. By recapitulating local architectures that cells encounter in vivo, we can elucidate and dissect the fundamental signal transduction pathways that control cell behavior in critical developmental, physiological, and pathological processes.

Nano/microstructural effect of hydroxyapatite nanocrystals on hepatocyte cell aggregation and adhesion

Hepatocyte cell aggregation and adhesion to HAp nanocrystals covered with SU-8 polymer micropatterns by nano/microfabrication techniques is demonstrated. The surface roughness and wettability of the HAp nanocrystals are significantly different from those of the SU-8 polymer. QCM-D and microscopic observation clearly reveal that the cells realize the surface properties to form aggregation and preferentially adhere to the HAp nanocrystals at 2 h after seeding, indicating the importance of the microstructures as well as the interfacial phenomena at a nanometer scale.

Bioassisted capture and release of nanoparticles on nanolithographed ZnO films

Using an artificial peptide library, we have identified a peptide that has strict selective affinity for ZnO surfaces. The binding affinity of the peptide on the ZnO surface can be controlled simply through changes in phosphate concentration at constant pH and temperature. In this study, we functionalized inorganic nanoparticles by orderly conjugating ZnO-binding peptides (ZnOBPs) on the surface of cadmium selenide (CdSe) nanoparticles and performed spontaneous and reversible nanopatterning of ZnOBP-displayed nanoparticles on lithographed ZnO films. Conjugation of ZnOBPs on CdSe nanoparticles caused spontaneous adsorption of the nanoparticles on a ZnO film, and fluorescence and cathodoluminescence images clearly showed specific adsorption of nanoparticles on the ZnO films lithographed on nano- and micrometer scales. The selectively bound nanoparticles on ZnO films were completely released by changing the phosphate concentration in solution; such release did not require heat or mechanical applications. Repeated capture and release of nanoparticles were achieved on the micrometer scale. Our results show the potential of material-binding peptides for nanopatterning and dynamic microarrays.

Engineering systems for the generation of patterned co-cultures for controlling cell-cell interactions

BACKGROUND

Inside the body, cells lie in direct contact or in close proximity to other cell types in a tightly controlled architecture that often regulates the resulting tissue function. Therefore, tissue engineering constructs that aim to reproduce the architecture and the geometry of tissues will benefit from methods of controlling cell-cell interactions with microscale resolution.

SCOPE OF THE REVIEW

We discuss the use of microfabrication technologies for generating patterned co-cultures. In addition, we categorize patterned co-culture systems by cell type and discuss the implications of regulating cell-cell interactions in the resulting biological function of the tissues.

MAJOR CONCLUSIONS

Patterned co-cultures are a useful tool for fabricating tissue engineered constructs and for studying cell-cell interactions in vitro, because they can be used to control the degree of homotypic and heterotypic cell-cell contact. In addition, this approach can be manipulated to elucidate important factors involved in cell-matrix interactions.

GENERAL SIGNIFICANCE

Patterned co-culture strategies hold significant potential to develop biomimetic structures for tissue engineering. It is expected that they would create opportunities to develop artificial tissues in the future. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

MEMS Sensors and Microsystems for Cell Mechanobiology

Forces generated by cells play a vital role in many cellular processes like cell spreading, motility, differentiation and apoptosis. Understanding the mechanics of single cells is essential to delineate the link between cellular force generation/sensing and function. MEMS sensors, because of their small size and fine force/displacement resolution, are ideal for force and displacement sensing at the single cell level. In addition, the amenability of MEMS sensors to batch fabrication methods allows the study of large cell populations simultaneously, leading to robust statistical studies. In this review, we discuss various microsystems used for studying cell mechanics and the insights on cell mechanical behavior that have resulted from their use. The advantages and limitations of these microsystems for biological studies are also outlined.

Microwell device for targeting single cells to electrochemical microelectrodes for high-throughput amperometric detection of quantal exocytosis

Electrochemical microelectrodes are commonly used to detect spikes of amperometric current that correspond to exocytosis of oxidizable transmitter from individual vesicles, i.e., quantal exocytosis. We are developing transparent multielectrochemical electrode arrays on microchips in order to automate measurement of quantal exocytosis. Here, we report development of an improved device to target individual cells to each microelectrode in an array. Efficient targeting (~75%) is achieved using cell-sized microwell traps fabricated in SU-8 photoresist together with patterning of poly(l-lysine) in register with electrodes to promote cell adhesion. The surface between electrodes is made resistant to cell adhesion using poly(ethylene glycol) in order to facilitate movement of cells to electrode "docking sites". We demonstrate the activity of the electrodes using the test analyte ferricyanide and perform recordings of quantal exocytosis from bovine adrenal chromaffin cells on the device. Multiple cell recordings on a single device demonstrate the consistency of spike measurements, and multiple recordings from the same electrodes demonstrate that the device can be cleaned and reused without degradation of performance. The new device will enable high-throughput studies of quantal exocytosis and may also find application in rapidly screening drugs or toxins for effects on exocytosis.

A high-throughput microfluidic assay to study neurite response to growth factor gradients

Studying neurite guidance by diffusible or substrate bound gradients is challenging with current techniques. In this study, we present the design, fabrication and utility of a microfluidic device to study neurite guidance under chemogradients. Experimental and computational studies demonstrated the establishment of a steep gradient of guidance cue within 30 min and stable for up to 48 h. The gradient was found to be insensitive to external perturbations such as media change and movement of device. The effects of netrin-1 (0.1-10 µg mL(-1)) and brain pulp (0.1 µL mL(-1)) were evaluated for their chemoattractive potential on neurite turning, while slit-2 (62.5 or 250 ng mL(-1)) was studied for its chemorepellant properties. Hippocampal or dorsal root ganglion (DRG) neurons were seeded into a micro-channel and packed onto the surface of a 3D collagen gel. Neurites grew into the matrix in three dimensions, and a gradient of guidance cue was created orthogonal to the direction of neurite growth to impact guidance. The average turning angle of each neurite was measured and averaged across multiple devices cultured under similar conditions to quantify the effect of guidance cue gradient. Significant positive turning towards gradient was measured in the presence of brain pulp and netrin-1 (1 µg mL(-1)), relative to control cultures which received no external guidance cue (p < 0.001). Netrin-1 released from transfected fibroblasts had the most positive turning effect of all the chemoattractive cues tested (p < 0.001). Slit-2 exhibited strong chemorepellant characteristics on both hippocampal and DRG neurite guidance at 250 ng mL(-1) concentration. Slit-2 also showed similar behavior on DRG neuron invasion into 3D collagen gel (p < 0.01 relative to control cultures). Taken together, the results suggest the utility of this microfluidic device to generate stable chemogradients for studying neurobiology, cell migration and proliferation, matrix remodeling and co-cultures with other cell lines, with potential applications in cancer biology, tissue engineering and regenerative medicine.