Cell culture on MEMS platforms: a review

Customizable Collagen Vitrigel Membranes and Preliminary Results in Corneal Engineering

Corneal opacities are a leading cause of visual impairment that affect 4.2 million people annually. The current treatment is corneal transplantation, which is limited by tissue donor shortages. Corneal engineering aims to develop membranes that function as scaffolds in corneal cell transplantation. Here, we describe a method for producing transplantable corneal constructs based on a collagen vitrigel (CVM) membrane and corneal endothelial cells (CECs). The CVMs were produced using increasing volumes of collagen type I: 1X (2.8 μL/mm²), 2X, and 3X. The vitrification process was performed at 40% relative humidity (RH) and 40 °C using a matryoshka-like system consisting of a shaking-oven harboring a desiccator with a saturated K₂CO₃ solution. The CVMs were characterized via SEM microscopy, cell adherence, FTIR, and manipulation in an ex vivo model. A pilot transplantation of the CECs/CVM construct in rabbits was also carried out. The thickness of the CVMs was 3.65–7.2 µm. The transparency was superior to a human cornea (92.6% = 1X; 94% = 2X; 89.21% = 3X). SEM microscopy showed a homogenous surface and laminar organization. The cell concentration seeded over the CVM increased threefold with no significant difference between 1X, 2X, and 3X (p = 0.323). The 2X-CVM was suitable for surgical manipulation in the ex vivo model. Constructs using the CECs/2X-CVM promoted corneal transparency restoration.

A Review - Biodegradable Polymers and their Applications

Polymers have an endless scope in the recent era due to their flexibility, amendment, and insertion of organic and inorganic active components into the polymer backbone. There is strong competition between natural and synthetic biodegradable polymers in the sense of biodegradability and compatibility with modern technology. Biodegradable polymers play a significant role in sustaining mankind on the earth due to non-environment hazards. These polymers play a crucial role in the area of biomedicine technology such as tissues engineering, preparation of different scaffolds, drug delivery systems, industrial, agriculture, and food packaging. Here, we probed on an assortment of types of applications, challenges, and limitations of biodegradable polymers in life.

Recent Advances in Cardiac Tissue Engineering for the Management of Myocardium Infarction

Myocardium Infarction (MI) is one of the foremost cardiovascular diseases (CVDs) causing death worldwide, and its case numbers are expected to continuously increase in the coming years. Pharmacological interventions have not been at the forefront in ameliorating MI-related morbidity and mortality. Stem cell-based tissue engineering approaches have been extensively explored for their regenerative potential in the infarcted myocardium. Recent studies on microfluidic devices employing stem cells under laboratory set-up have revealed meticulous events pertaining to the pathophysiology of MI occurring at the infarcted site. This discovery also underpins the appropriate conditions in the niche for differentiating stem cells into mature cardiomyocyte-like cells and leads to engineering of the scaffold via mimicking of native cardiac physiological conditions. However, the mode of stem cell-loaded engineered scaffolds delivered to the site of infarction is still a challenging mission, and yet to be translated to the clinical setting. In this review, we have elucidated the various strategies developed using a hydrogel-based system both as encapsulated stem cells and as biocompatible patches loaded with cells and applied at the site of infarction.

Microfluidics for Drug Development: From Synthesis to Evaluation

Drug development is a long process whose main content includes drug synthesis, drug delivery, and drug evaluation. Compared with conventional drug development procedures, microfluidics has emerged as a revolutionary technology in that it offers a miniaturized and highly controllable environment for bio(chemical) reactions to take place. It is also compatible with analytical strategies to implement integrated and high-throughput screening and evaluations. In this review, we provide a comprehensive summary of the entire microfluidics-based drug development system, from drug synthesis to drug evaluation. The challenges in the current status and the prospects for future development are also discussed. We believe that this review will promote communications throughout diversified scientific and engineering communities that will continue contributing to this burgeoning field.

Self-detachable UV-curable polymers for open-access microfluidic platforms

This study presents an ultraviolet (UV)-curable polymer which is applicable to open-access microfluidic platforms. The UV-curable polymer was prepared by mixing trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), polyethylene glycol-diacrylate (PEG-DA), and Irgacure 184. The polymer resin is optically transparent before and after UV-assisted curing and showed good biocompatibility when culturing multiple types of cells on the nanopatterned polymer substrate. The polymer has good adhesion with poly(dimethylsiloxane) (PDMS) even under large deformation and showed a low swelling ratio when exposed to water, suggesting a possibility to be used as a substrate for an organ on a chip. Furthermore, because the polymers have controllable hydrolysis ability depending on the composition, long-term 3D cell culture and subsequent biological analysis with harvested cells are possible. The self-detachable synthesized UV-curable polymer may help the advancement of biomedical studies using in vitro cell culture.

Nanoparticle Deposition of Fluoropolymer CYTOP via Holographic Femtosecond Laser Processing and Its Biochip Application

The fundamental characteristics of nanoparticle (NP) deposition of the fluoropolymer CYTOP using a femtosecond (fs) laser were investigated. In previous studies, we have demonstrated the microfluidic fabrication of CYTOP, which enables clear microscopic observation of the fluid boundary because of its low refractive index, as well as that of water. In the present work, we generated CYTOP NPs using holographic fs laser processing with a spatial light modulator to demonstrate the capabilities of this functional polymer. We established a deposition technique via five-dot parallel fs laser beam irradiation for fibrous network and monolayer structures composed of CYTOP NPs on the surface of glass slides by manipulating the various fundamental laser processing parameters. The network structure on the glass surface exhibits superhydrophobic behavior, while the monolayer structure performs almost the same wettability as that of CYTOP thin film. After an investigation of the surface features of the NPs deposited onto the glass, the combination of the holographic fs laser deposition and the removal of CYTOP NPs was used to selectively pattern CYTOP NPs on the glass slide for HeLa cell culturing. Consequently, cells were selectively cultured on the glass surface where the laser removal of deposited NPs was carried out.

Proliferation and Cluster Analysis of Neurons and Glial Cell Organization on Nanocolumnar TiN Sub-Strates

Biomaterials employed for neural stimulation, as well as brain/machine interfaces, offer great perspectives to combat neurodegenerative diseases, while application of lab-on-a-chip devices such as multielectrode arrays is a promising alternative to assess neural function in vitro. For bioelectronic monitoring, nanostructured microelectrodes are required, which exhibit an increased surface area where the detection sensitivity is not reduced by the self-impedance of the electrode. In our study, we investigated the interaction of neurons (SH-SY5Y) and glial cells (U-87 MG) with nanocolumnar titanium nitride (TiN) electrode materials in comparison to TiN with larger surface grains, gold, and indium tin oxide (ITO) substrates. Glial cells showed an enhanced proliferation on TiN materials; however, these cells spread evenly distributed over all the substrate surfaces. By contrast, neurons proliferated fastest on nanocolumnar TiN and formed large cell agglomerations. We implemented a radial autocorrelation function of cellular positions combined with various clustering algorithms. These combined analyses allowed us to quantify the largest cluster on nanocolumnar TiN; however, on ITO and gold, neurons spread more homogeneously across the substrates. As SH-SY5Y cells tend to grow in clusters under physiologic conditions, our study proves nanocolumnar TiN as a potential bioactive material candidate for the application of microelectrodes in contact with neurons. To this end, the employed K-means clustering algorithm together with radial autocorrelation analysis is a valuable tool to quantify cell-surface interaction and cell organization to evaluate biomaterials' performance in vitro.

PDMS Nano-Modified Scaffolds for Improvement of Stem Cells Proliferation and Differentiation in Microfluidic Platform

Microfluidics cell-based assays require strong cell-substrate adhesion for cell viability, proliferation, and differentiation. The intrinsic properties of PDMS, a commonly used polymer in microfluidics systems, regarding cell-substrate interactions have limited its application for microfluidics cell-based assays. Various attempts by previous researchers, such as chemical modification, plasma-treatment, and protein-coating of PDMS revealed some improvements. These strategies are often reversible, time-consuming, short-lived with either cell aggregates formation, not cost-effective as well as not user- and eco-friendly too. To address these challenges, cell-surface interaction has been tuned by the modification of PDMS doped with different biocompatible nanomaterials. Gold nanowires (AuNWs), superparamagnetic iron oxide nanoparticles (SPIONs), graphene oxide sheets (GO), and graphene quantum dot (GQD) have already been coupled to PDMS as an alternative biomaterial enabling easy and straightforward integration during microfluidic fabrication. The synthesized nanoparticles were characterized by corresponding methods. Physical cues of the nanostructured substrates such as Young’s modulus, surface roughness, and nanotopology have been carried out using atomic force microscopy (AFM). Initial biocompatibility assessment of the nanocomposites using human amniotic mesenchymal stem cells (hAMSCs) showed comparable cell viabilities among all nanostructured PDMS composites. Finally, osteogenic stem cell differentiation demonstrated an improved differentiation rate inside microfluidic devices. The results revealed that the presence of nanomaterials affected a 5- to 10-fold increase in surface roughness. In addition, the results showed enhancement of cell proliferation from 30% (pristine PDMS) to 85% (nano-modified scaffolds containing AuNWs and SPIONs), calcification from 60% (pristine PDMS) to 95% (PDMS/AuNWs), and cell surface marker expression from 40% in PDMS to 77% in SPION- and AuNWs-PDMS scaffolds at 14 day. Our results suggest that nanostructured composites have a very high potential for stem cell studies and future therapies.

Pulsatile Flow in Microfluidic Systems

This review describes the current knowledge and applications of pulsatile flow in microfluidic systems. Elements of fluid dynamics at low Reynolds number are first described in the context of pulsatile flow. Then the practical applications in microfluidic processes are presented: the methods to generate a pulsatile flow, the generation of emulsion droplets through harmonic flow rate perturbation, the applications in mixing and particle separation, and the benefits of pulsatile flow for clog mitigation. The second part of the review is devoted to pulsatile flow in biological applications. Pulsatile flows can be used for mimicking physiological systems, to alter or enhance cell cultures, and for bioassay automation. Pulsatile flows offer unique advantages over a steady flow, especially in microfluidic systems, but also require some new physical insights and more rigorous investigation to fully benefit future applications.

High-Repetition-Rate Femtosecond Laser Processing of Acrylic Intra-Ocular Lenses

The study of laser processing of acrylic intra-ocular lenses (IOL) by using femtosecond laser pulses delivered at high-repetition rate is presented in this work. An ultra-compact air-cooled femtosecond diode laser (HighQ2-SHG, Spectra-Physics) delivering 250 fs laser pulses at the fixed wavelength of 520 nm with a repetition rate of 63 MHz was used to process the samples. Laser inscription of linear periodic patterns on the surface and inside the acrylic substrates was studied as a function of the processing parameters as well as the optical absorption characteristics of the sample. Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Spectroscopy (EDX), and micro-Raman Spectroscopy were used to evaluate the compositional and microstructural changes induced by the laser radiation in the processed areas. Diffractive characterization was used to assess 1st-order efficiency and the refractive index change.

Cell Culture Platforms with Controllable Stiffness for Chick Embryonic Cardiomyocytes

For several years, cell culture techniques have been physiologically relevant to understand living organisms both structurally and functionally, aiming at preserving as carefully as possible the in vivo integrity and function of the cells. However, when studying cardiac cells, glass or plastic Petri dishes and culture-coated plates lack important cues that do not allow to maintain the desired phenotype, especially for primary cell culture. In this work, we show that microscaffolds made with polydimethylsiloxane (PDMS) enable modulating the stiffness of the surface of the culture substrate and this originates different patterns of adhesion, self-organization, and synchronized or propagated activity in the culture of chick embryonic cardiomyocytes. Thanks to the calcium imaging technique, we found that the substrate stiffness affected cardiomyocyte adhesion, as well as the calcium signal propagation in the formed tissue. The patterns of activity shown by the calcium fluorescence variations are reliable clues of the functional organization achieved by the cell layers. We found that PDMS substrates with a stiffness of 25 kPa did not allow the formation of cell layers and therefore the optimal propagation of the intracellular calcium signals, while softer PDMS substrates with Young’s modulus within the physiological in vivo reported range did permit synchronized and coordinated contractility and intracellular calcium activity. This type of methodology allows us to study phenomena such as arrhythmias. For example, the occurrence of synchronized activity or rotors that can initiate or maintain cardiac arrhythmias can be reproduced on different substrates for study, so that replacement tissues or patches can be better designed.

Bioinspired Engineering of Organ-on-Chip Devices

The human body can be viewed as an organism consisting of a variety of cellular and non-cellular materials interacting in a highly ordered manner. Its complex and hierarchical nature inspires the multi-level recapitulation of the human body in order to gain insights into the inner workings of life. While traditional cell culture models have led to new insights into the cellular microenvironment and biological control in vivo, deeper understanding of biological systems and human pathophysiology requires the development of novel model systems that allow for analysis of complex internal and external interactions within the cellular microenvironment in a more relevant organ context. Engineering organ-on-chip systems offers an unprecedented opportunity to unravel the complex and hierarchical nature of human organs. In this chapter, we first highlight the advances in microfluidic platforms that enable engineering of the cellular microenvironment and the transition from cells-on-chips to organs-on-chips. Then, we introduce the key features of the emerging organs-on-chips and their proof-of-concept applications in biomedical research. We also discuss the challenges and future outlooks of this state-of-the-art technology.

Gas Partial Pressure in Cultured Cells: Patho-Physiological Importance and Methodological Approaches

Gas partial pressures within the cell microenvironment are one of the key modulators of cell pathophysiology. Indeed, respiratory gases (O2 and CO2) are usually altered in respiratory diseases and gasotransmitters (CO, NO, H2S) have been proposed as potential therapeutic agents. Investigating the pathophysiology of respiratory diseases in vitro mandates that cultured cells are subjected to gas partial pressures similar to those experienced by each cell type in its native microenvironment. For instance, O2 partial pressures range from ∼13% in the arterial endothelium to values as low as 2-5% in cells of other healthy tissues and to less than 1% in solid tumor cells, clearly much lower values than those used in conventional cell culture research settings (∼19%). Moreover, actual cell O2 partial pressure in vivo changes with time, at considerably different timescales as illustrated by tumors, sleep apnea, or mechanical ventilation. Unfortunately, the conventional approach to modify gas concentrations at the above culture medium precludes the tight and exact control of intra-cellular gas levels to realistically mimic the natural cell microenvironment. Interestingly, well-controlled cellular application of gas partial pressures is currently possible through commercially available silicone-like material (PDMS) membranes, which are biocompatible and have a high permeability to gases. Cells are seeded on one side of the membrane and tailored gas concentrations are circulated on the other side of the membrane. Using thin membranes (50-100 μm) the value of gas concentration is instantaneously (<0.5 s) transmitted to the cell microenvironment. As PDMS is transparent, cells can be concurrently observed by conventional or advanced microscopy. This procedure can be implemented in specific-purpose microfluidic devices and in settings that do not require expensive or complex technologies, thus making the procedure readily implementable in any cell biology laboratory. This review describes the gas composition requirements for a cell culture in respiratory research, the limitations of current experimental settings, and also suggests new approaches to better control gas partial pressures in a cell culture.

A durable and biocompatible ascorbic acid-based covalent coating method of polydimethylsiloxane for dynamic cell culture

Polydimethylsiloxane (PDMS) is widely used in dynamic biological microfluidic applications. As a highly hydrophobic material, native PDMS does not support cell attachment and culture, especially in dynamic conditions. Previous covalent coating methods use glutaraldehyde (GA) which, however, is cytotoxic. This paper introduces a novel and simple method for binding collagen type I covalently on PDMS using ascorbic acid (AA) as a cross-linker instead of GA. We compare the novel method against physisorption and GA cross-linker-based methods. The coatings are characterized by immunostaining, contact angle measurement, atomic force microscopy and infrared spectroscopy, and evaluated in static and stretched human adipose stem cell (hASC) cultures up to 13 days. We found that AA can replace GA as a cross-linker in the covalent coating method and that the coating is durable after sonication and after 6 days of stretching. Furthermore, we show that hASCs attach and proliferate better on AA cross-linked samples compared with physisorbed or GA-based methods. Thus, in this paper, we provide a new PDMS coating method for studying cells, such as hASCs, in static and dynamic conditions. The proposed method is an important step in the development of PDMS-based devices in cell and tissue engineering applications.

Biocompatibility of polymer-based biomaterials and medical devices – regulations,in vitroscreening and risk-management

Biomaterials play an increasing role in modern health care systems.

Superior Robust Ultrathin Single-Crystalline Silicon Carbide Membrane as a Versatile Platform for Biological Applications

Micromachined membranes are promising platforms for cell culture thanks to their miniaturization and integration capabilities. Possessing chemical inertness, biocompatibility, and integration, silicon carbide (SiC) membranes have attracted great interest toward biological applications. In this paper, we present the batch fabrication, mechanical characterizations, and cell culture demonstration of robust ultrathin epitaxial deposited SiC membranes. The as-fabricated ultrathin SiC membranes, with an ultrahigh aspect ratio (length/thickness) of up to 20 000, possess high a fracture strength up to 2.95 GPa and deformation up to 50 μm. A high optical transmittance of above 80% at visible wavelengths was obtained for 50 nm membranes. The as-fabricated membranes were experimentally demonstrated as an excellent substrate platform for bio-MEMS/NEMS cell culture with the cell viability rate of more than 92% after 72 h. The ultrathin SiC membrane is promising for in vitro observations/imaging of bio-objects with an extremely short optical access.

A perfusion incubator liver chip for 3D cell culture with application on chronic hepatotoxicity testing

Liver chips have been developed to recapitulate in vivo physiological conditions to enhance hepatocyte functions for assessing acute responses to drugs. To develop liver chips that can assess repeated dosing chronic hepatotoxicity, we need to ensure that hepatocyte functions be maintained at constant values over two weeks in stable culture conditions of sterility, temperature, pH, fluidic-flow of culture media and drugs. We have designed a perfusion-incubator-liver-chip (PIC) for 3D cell culture, that assures a tangential flow of the media over the spheroids culture. Rat hepatocyte spheroids constrained between a cover glass and a porous-ultrathin Parylene C membrane experienced optimal mass transfer and limited shear stress from the flowing culture media; maintained cell viability over 24 days. Hepatocyte functions were significantly improved and maintained at constant values (urea, albumin synthesis, and CYP450 enzyme activities) for 14 days. The chip act as an incubator, having 5% CO₂ pressure-driven culture-media flow, on-chip heater and active debubbler. It operates in a biosafety cabinet, thus minimizing risk of contamination. The chronic drug response to repeated dosing of Diclofenac and Acetaminophen evaluated in PIC were more sensitive than the static culture control.

Multiwell capillarity-based microfluidic device for the study of 3D tumour tissue-2D endothelium interactions and drug screening in co-culture models

The tumour microenvironment is very complex, and essential in tumour development and drug resistance. The endothelium is critical in the tumour microenvironment: it provides nutrients and oxygen to the tumour and is essential for systemic drug delivery. Therefore, we report a simple, user-friendly microfluidic device for co-culture of a 3D breast tumour model and a 2D endothelium model for cross-talk and drug delivery studies. First, we demonstrated the endothelium was functional, whereas the tumour model exhibited in vivo features, e.g., oxygen gradients and preferential proliferation of cells with better access to nutrients and oxygen. Next, we observed the endothelium structure lost its integrity in the co-culture. Following this, we evaluated two drug formulations of TRAIL (TNF-related apoptosis inducing ligand): soluble and anchored to a LUV (large unilamellar vesicle). Both diffused through the endothelium, LUV-TRAIL being more efficient in killing tumour cells, showing no effect on the integrity of endothelium. Overall, we have developed a simple capillary force-based microfluidic device for 2D and 3D cell co-cultures. Our device allows high-throughput approaches, patterning different cell types and generating gradients without specialised equipment. We anticipate this microfluidic device will facilitate drug screening in a relevant microenvironment thanks to its simple, effective and user-friendly operation.

Microchip-based 3D-Cell Culture Using Polymer Nanofibers Generated by Solution Blow Spinning

Polymer nano/micro fibers have found many applications including 3D cell culture and the creation of wound dressings. The fibers can be produced by a variety of techniques that include electrospinning, the primary disadvantage of which include the requirement for a high voltage supply (which may cause issues such as polymer denaturation) and lack of portability. More recently, solution blow spinning, where a high velocity sheath gas is used instead of high voltage, has been used to generate polymer fibers. In this work, we used blow spinning to create nano/microfibers for microchip-based 3D cell culture. First, we thoroughly investigated fiber generation from a 3D printed gas sheath device using two polymers that are amenable to cell culture (polycaprolactone, PCL and polystyrene, PS) as well as the parameters that can affect PCL and PS fiber quality. Using the 3D printed sheath device, it was found that the pressure of the sheath N2 and the concentration of polymer solutions determine if fibers can be produced as well as the resulting fiber morphology. In addition, we showed how these fibers can be used for 3D cell culture by directly depositing PCL fibers in petri dishes and well plates. It is shown the fibers have good compatibility with RAW 264.7 macrophages and the PCL fiber scaffold can be as thick as 178 ± 14 μm. PCL fibers created from solution blow spinning (with the 3D printed sheath device) were then integrated with a microfluidic device for the first time to fabricate a 3D cell culture scaffold with a flow component. After culturing and stimulating macrophages on the fluidic device, it was found that the integrated 3D fibrous scaffold is a better mimic of the extracellular matrix (as opposed to a flat, 2D substrate), with enhanced nitrite accumulation (product of nitric oxide release) from macrophages stimulated with lipopolysaccharide. PS fibers were also made and integrated in a microfluidic device for 3D culture of endothelial cells, which stayed viable for at least 72 hours (48 hours under the flowing conditions). This approach will be useful for future studies involving more realistic microchip-based culture models for studying cell-to-cell communication.

Stem cell therapies for ischemic stroke: current animal models, clinical trials and biomaterials

We report the facilitation of stem cell therapy in stroke by tissue engineering and applications of biomaterials.

Microfluidics-based 3D cell culture models: Utility in novel drug discovery and delivery research

The implementation of microfluidic devices within life sciences has furthered the possibilities of both academic and industrial applications such as rapid genome sequencing, predictive drug studies, and single cell manipulation. In contrast to the preferred two‐dimensional cell‐based screening, three‐dimensional (3D) systems have more in vivo relevance as well as ability to perform as a predictive tool for the success or failure of a drug screening campaign. 3D cell culture has shown an adaptive response to the recent advancements in microfluidic technologies which has allowed better control over spheroid sizes and subsequent drug screening studies. In this review, we highlight the most significant developments in the field of microfluidic 3D culture over the past half‐decade with a special focus on their benefits and challenges down the lane. With the newer technologies emerging, implementation of microfluidic 3D culture systems into the drug discovery pipeline is right around the bend.

Cell response on the biomimetic scaffold of silicon nano- and micro-topography

Silicon scaffolds were synthesized in a low-pressure furnace via a vapor–liquid–solid (VLS) mechanism.

Surface modification on polydimethylsiloxane-based microchannels with fragmented poly(l-lactic acid) nanosheets

Surface modification is a critical issue in various applications of polydimethylsiloxane (PDMS)-based microfluidic devices. Here, we describe a novel method through which PDMS-based microchannels were successfully modified with fragmented poly(l-lactic acid) (PLLA) nanosheets through a simple patchwork technique that exploited the high level of adhesiveness of PLLA nanosheets. Compared with other surface modification methods, our method required neither complicated chemical modifications nor the use of organic solvents that tend to cause PDMS swelling. The experimental results indicated that the modified PDMS exhibited excellent capacity for preventing the adhesion and activation of platelets. This simple yet efficient method can be used to fabricate the special PDMS microfluidic devices for biological, medical, and even hematological purposes.

Micro 3D cell culture systems for cellular behavior studies: Culture matrices, devices, substrates, and in-situ sensing methods

Microfabricated systems equipped with 3D cell culture devices and in-situ cellular biosensing tools can be a powerful bionanotechnology platform to investigate a variety of biomedical applications. Various construction substrates such as plastics, glass, and paper are used for microstructures. When selecting a construction substrate, a key consideration is a porous microenvironment that allows for spheroid growth and mimics the extracellular matrix (ECM) of cell aggregates. Various bio-functionalized hydrogels are ideal candidates that mimic the natural ECM for 3D cell culture. When selecting an optimal and appropriate microfabrication method, both the intended use of the system and the characteristics and restrictions of the target cells should be carefully considered. For highly sensitive and near-cell surface detection of excreted cellular compounds, SERS-based microsystems capable of dual modal imaging have the potential to be powerful tools; however, the development of optical reporters and nanoprobes remains a key challenge. We expect that the microsystems capable of both 3D cell culture and cellular response monitoring would serve as excellent tools to provide fundamental cellular behavior information for various biomedical applications such as metastasis, wound healing, high throughput screening, tissue engineering, regenerative medicine, and drug discovery and development.

Wax-Impregnated Cotton Fabrics as Cell Culture Platform

Microwell plates are widely used in various cell-based assay and drug screening. Usually these plates are made from non-biodegradable materials such as polystyrene or polyethylene. In this report, we propose the use of wax-impregnated cotton fabrics as an alternative microwell plate that is easy to fabricate, simple to use, sustainable and environmentally friendlier. Several researchers recently used soft lithography and photolithography technique to fabricate various cell culture platforms. Our proposed method consists instead of simple dipping and drying process. The platform is made of a series of fabrics being stacked and held together with various wax formulations. With the exception of the base layer, each fabric layer has a circular hole opening with increasing diameter towards the top layer; thereby forming a well where cells are cultured at its flat bottom. We characterized the chemical and physical properties of the platform surface which affect cells attachment and proliferation. These properties include the surface chemistry, hydrophobicity and roughness. We cultured human skin fibroblast (HSF 1184 Cell Line) on the platform as our preliminary proof of concept. We observed proliferation of the cells after 24 hours. The result indicates the potential use of the platform for future cell-based assay applications.

Making a big thing of a small cell--recent advances in single cell analysis

Single cell analysis is an emerging field requiring a high level interdisciplinary collaboration to provide detailed insights into the complex organisation, function and heterogeneity of life. This review is addressed to life science researchers as well as researchers developing novel technologies. It covers all aspects of the characterisation of single cells (with a special focus on mammalian cells) from morphology to genetics and different omics-techniques to physiological, mechanical and electrical methods. In recent years, tremendous advances have been achieved in all fields of single cell analysis: (1) improved spatial and temporal resolution of imaging techniques to enable the tracking of single molecule dynamics within single cells; (2) increased throughput to reveal unexpected heterogeneity between different individual cells raising the question what characterizes a cell type and what is just natural biological variation; and (3) emerging multimodal approaches trying to bring together information from complementary techniques paving the way for a deeper understanding of the complexity of biological processes. This review also covers the first successful translations of single cell analysis methods to diagnostic applications in the field of tumour research (especially circulating tumour cells), regenerative medicine, drug discovery and immunology.

Microplatforms for gradient field generation of various properties and biological applications

Well-designed microfluidic platforms can be excellent tools to eliminate bottleneck problems or issues that have arisen in biological fields by providing unprecedented high-resolution control of mechanical and chemical microenvironments for cell culture. Among such microtechnologies, the precise generation of biochemical concentration gradients has been highly regarded in the biorelated scientific fields; even today, the principles and mechanisms for gradient generation continue to be refined, and the number of applications for this technique is growing. Here, we review the current status of the concentration gradient generation technologies achieved in various microplatforms and how they have been and will be applied to biological issues, particularly those that have arisen from cancer research, stem cell research, and tissue engineering. We also provide information about the advances and future challenges in the technological aspects of microscale concentration gradient generation.

Fabrication of polyHEMA grids by micromolding in capillaries for cell patterning and single-cell arrays

Control of cell adhesion and growth by microfabrication technology and surface chemistry is important in an increasing number of applications in biotechnology and medicine. In this study, we developed a method to fabricate (2-hydroxyethyl methacrylate) (polyHEMA) grids on glass by micromolding in capillaries (MIMIC). As a non-fouling biomaterial, polyHEMA was used to inhibit the nonspecific bonding of cells, whereas the glass surface provided a cell adhesive background. The polyHEMA chemical barrier was directly obtained using MIMIC without surface modification, and the microchannel networks used for capillarity were easily achieved by reversibly bonding the polydimethylsiloxane (PDMS)mold and the glass. After fabrication of the polyHEMA micropattern, individual cytophilic microwells surrounded by cytophobic sidewalls were presented on the glass surface. The polyHEMA micropattern proved effective in controlling the shape and spreading of cells, and square-shaped mouse osteoblast MC3T3-E1 cells were obtained in microwell arrays after incubation for 3 days. Moreover, the widths of the microwells in this micropattern were optimized for use as single-cell arrays. The proposed method could be a convenient tool in the field of drug screening, stem cell research, and tissue engineering.

Development of a three-dimensional cell culture system based on microfluidics for nuclear magnetic resonance and optical monitoring

A new microfluidic cell culture device compatible with real-time nuclear magnetic resonance (NMR) is presented here. The intended application is the long-term monitoring of 3D cell cultures by several techniques. The system has been designed to fit inside commercially available NMR equipment to obtain maximum readout resolution when working with small samples. Moreover, the microfluidic device integrates a fibre-optic-based sensor to monitor parameters such as oxygen, pH, or temperature during NMR monitoring, and it also allows the use of optical microscopy techniques such as confocal fluorescence microscopy. This manuscript reports the initial trials culturing neurospheres inside the microchamber of this device and the preliminary images and spatially localised spectra obtained by NMR. The images show the presence of a necrotic area in the interior of the neurospheres, as is frequently observed in histological preparations; this phenomenon appears whenever the distance between the cells and fresh nutrients impairs the diffusion of oxygen. Moreover, the spectra acquired in a volume of 8 nl inside the neurosphere show an accumulation of lactate and lipids, which are indicative of anoxic conditions. Additionally, a basis for general temperature control and monitoring and a graphical control software have been developed and are also described. The complete platform will allow biomedical assays of therapeutic agents to be performed in the early phases of therapeutic development. Thus, small quantities of drugs or advanced nanodevices may be studied long-term under simulated living conditions that mimic the flow and distribution of nutrients.

Continuous microcarrier-based cell culture in a benchtop microfluidic bioreactor

Microfluidic bioreactors are expected to impact cell therapy and biopharmaceutical production due to their ability to control cellular microenvironments. This work presents a novel approach for continuous cell culture in a microfluidic system. Microcarriers (i.e., microbeads) are used as growth support for anchorage-dependent mammalian cells. This approach eases the manipulation of cells within the system and enables harmless extraction of cells. Moreover, the microbioreactor uses a perfusion function based on the biocompatible integration of a porous membrane to continuously feed the cells. The perfusion rate is optimized through simulations to provide a stable biochemical environment. Thermal management is also addressed to ensure a homogeneous bioreactor temperature. Eventually, incubator-free cell cultures of Drosophila S2 and PC3 cells are achieved over the course of a week using this bioreactor. In future applications, a more efficient alternative to harvesting cells from microcarriers is also anticipated as suggested by our positive results from the microcarrier digestion experiments.

Reconstruction of vascular structure with multicellular components using cell transfer printing methods

Natural vessel has three types of concentric cell layers that perform their specific functions. Here, the fabrication of vascular structure is reported by transfer printing of three different cell layers using thermosensitive hydrogels. Tetronic-tyramine and RGD peptide are co-crosslinked to prepare cell adhesive and thermosensitive hydrogels. The hydrogel increases its diameter by 1.26 times when the temperature reduces from 37 °C to 4 °C. At optimized seeding density, three types of cells form monolayers on the hydrogel, which is then transferred to the target surface within 3 min. Three monolayers are simultaneously transferred on one substrate with controlled shape and arrangement. The same approach is applied onto nanofiber scaffolds that are cultured for more than 5 d. Every type of monolayer shows proliferation and migration on nanofiber scaffolds, and the formation of robust cell-cell contact is revealed by CD31 staining in endothelial cell layer. A vascular structure with multicellular components is fabricated by transfer of three monolayers on nanofibers that are manually rolled with the diameter and length of the tube being approximately 3 mm and 12 mm, respectively. Collectively, it is concluded that the tissue transfer printing is a useful tool for constructing a vascular structure and mimicking natural structure of different types of tissues.

Advantages and challenges of microfluidic cell culture in polydimethylsiloxane devices

Culture of cells using various microfluidic devices is becoming more common within experimental cell biology. At the same time, a technological radiation of microfluidic cell culture device designs is currently in progress. Ultimately, the utility of microfluidic cell culture will be determined by its capacity to permit new insights into cellular function. Especially insights that would otherwise be difficult or impossible to obtain with macroscopic cell culture in traditional polystyrene dishes, flasks or well-plates. Many decades of heuristic optimization have gone into perfecting conventional cell culture devices and protocols. In comparison, even for the most commonly used microfluidic cell culture devices, such as those fabricated from polydimethylsiloxane (PDMS), collective understanding of the differences in cellular behavior between microfluidic and macroscopic culture is still developing. Moving in vitro culture from macroscopic culture to PDMS based devices can come with unforeseen challenges. Changes in device material, surface coating, cell number per unit surface area or per unit media volume may all affect the outcome of otherwise standard protocols. In this review, we outline some of the advantages and challenges that may accompany a transition from macroscopic to microfluidic cell culture. We focus on decisive factors that distinguish macroscopic from microfluidic cell culture to encourage a reconsideration of how macroscopic cell culture principles might apply to microfluidic cell culture.

Graphene-based patterning and differentiation of C2C12 myoblasts

This study aims at generating highly aligned functional myotubes using graphene as the underlying scaffold. Graphene not only supports the growth of C2C12 muscle cells but also enhances its differentiation and leads to spontaneous patterning of myotubes.

Multiscale tissue engineering for liver reconstruction

The liver is a target of in vitro tissue engineering despite its capability to regenerate in vivo. The construction of liver tissues in vitro remains challenging. In this review, conventional 3D cultures of hepatocytes are first discussed. Recent advances in the 3D culturing of liver cells are then summarized in the context of in vitro liver tissue reconstruction at the micro- and macroscales. The application of microfluidics technology to liver tissue engineering has been introduced as a bottom-up approach performed at the microscale, whereas whole-organ bioengineering technology was introduced as a top-down approach performed at the macroscale. Mesoscale approaches are also discussed in considering the integration of micro- and macroscale approaches. Multiple parallel multiscale liver tissue engineering studies are ongoing; however, no tissue-engineered liver that is appropriate for clinical use has yet been realized. The integration of multiscale tissue engineering studies is essential for further understanding of liver reconstruction strategies.

Fabricated micro-nano devices for in vivo and in vitro biomedical applications

In recent years, the innovative use of microelectromechanical systems (MEMSs) and nanoelectromechanical systems (NEMSs) in biomedical applications has opened wide opportunities for precise and accurate human diagnostics and therapeutics. The introduction of nanotechnology in biomedical applications has facilitated the exact control and regulation of biological environments. This ability is derived from the small size of the devices and their multifunctional capabilities to operate at specific sites for selected durations of time. Researchers have developed wide varieties of unique and multifunctional MEMS/NEMS devices with micro and nano features for biomedical applications (BioMEMS/NEMS) using the state of the art microfabrication techniques and biocompatible materials. However, the integration of devices with the biological milieu is still a fundamental issue to be addressed. Devices often fail to operate due to loss of functionality, or generate adverse toxic effects inside the body. The in vitro and in vivo performance of implantable BioMEMS such as biosensors, smart stents, drug delivery systems, and actuation systems are researched extensively to understand the interaction of the BioMEMS devices with physiological environments. BioMEMS developed for drug delivery applications include microneedles, microreservoirs, and micropumps to achieve targeted drug delivery. The biocompatibility of BioMEMS is further enhanced through the application of tissue and smart surface engineering. This involves the application of nanotechnology, which includes the modification of surfaces with polymers or the self-assembly of monolayers of molecules. Thereby, the adverse effects of biofouling can be reduced and the performance of devices can be improved in in vivo and in vitro conditions.

Microfluidic Paper-Based Analytical Devices (μPADs) and Micro Total Analysis Systems (μTAS): Development, Applications and Future Trends

Microfluidic paper-based analytical devices and micro total analysis systems are relatively new group of analytical tools, capable of analyzing complex biochemical samples containing macromolecules, proteins, nucleic acids, toxins, cells or pathogens. Within one analytical run, fluidic manipulations like transportation, sorting, mixing or separation are available. Recently, microfluidic devices are a subject of extensive research, mostly for fast and non-expensive biochemical analysis but also for screening of medical samples and forensic diagnostics. They are used for neurotransmitter detection, cancer diagnosis and treatment, cell and tissue culture growth and amplification, drug discovery and determination, detection and identification of microorganisms. This review summarizes development history, basic fabrication methods, applications and also future development trends for production of such devices.

Advances in microfluidics-based experimental methods for neuroscience research

The application of microfluidics to neuroscience applications has always appealed to neuroscientists because of the capability to control the cellular microenvironment in both a spatial and temporal manner. Recently, there has been rapid development of biological micro-electro-mechanical systems (BioMEMS) for both fundamental and applied neuroscience research. In this review, we will discuss the applications of BioMEMS to various topics in the field of neuroscience. The purpose of this review is to summarise recent advances in the components and design of the BioMEMS devices, in vitro disease models, electrophysiology and neural stem cell research. We envision that microfluidics will play a key role in future neuroscience research, both fundamental and applied research.

Synthetic and bio-artificial tactile sensing: a review

This paper reviews the state of the art of artificial tactile sensing, with a particular focus on bio-hybrid and fully-biological approaches. To this aim, the study of physiology of the human sense of touch and of the coding mechanisms of tactile information is a significant starting point, which is briefly explored in this review. Then, the progress towards the development of an artificial sense of touch are investigated. Artificial tactile sensing is analysed with respect to the possible approaches to fabricate the outer interface layer: synthetic skin versus bio-artificial skin. With particular respect to the synthetic skin approach, a brief overview is provided on various technologies and transduction principles that can be integrated beneath the skin layer. Then, the main focus moves to approaches characterized by the use of bio-artificial skin as an outer layer of the artificial sensory system. Within this design solution for the skin, bio-hybrid and fully-biological tactile sensing systems are thoroughly presented: while significant results have been reported for the development of tissue engineered skins, the development of mechanotransduction units and their integration is a recent trend that is still lagging behind, therefore requiring research efforts and investments. In the last part of the paper, application domains and perspectives of the reviewed tactile sensing technologies are discussed.

Poly(dimethylsiloxane) (PDMS) affects gene expression in PC12 cells differentiating into neuronal-like cells

Introduction

Microfluidics systems usually consist of materials like PMMA - poly(methyl methacrylate) and PDMS - poly(dimethylsiloxane) and not polystyrene (PS), which is usually used for cell culture. Cellular and molecular responses in cells grown on PS are well characterized due to decades of accumulated research. In contrast, the experience base is limited for materials used in microfludics chip fabrication.

Methods

The effect of different materials (PS, PMMA and perforated PMMA with a piece of PDMS underneath) on the growth and differentiation of PC12 (adrenal phaeochromocytoma) cells into neuronal-like cells was investigated using cell viability, cell cycle distribution, morphology, and gene expression analysis.

Results/Conclusions

After differentiation, the morphology, viability and cell cycle distribution of PC12 cells grown on PS, PMMA with and without PDMS underneath was the same. By contrast, 41 genes showed different expression for PC12 cells differentiating on PMMA as compared to on PS. In contrast, 677 genes showed different expression on PMMA with PDMS underneath as compared with PC12 cells on PS. The differentially expressed genes are involved in neuronal cell development and function. However, there were also many markers for neuronal cell development and functions that were expressed similarly in cells differentiating on PS, PMMA and PMMA with PDMS underneath. In conclusion, it was shown that PMMA has a minor impact and PDMS a major impact on gene expression in PC12 cells.