Design of well and groove microchannel bioreactors for cell culture

Step-by-step fabrication of heart-on-chip systems as models for cardiac disease modeling and drug screening

Cardiovascular diseases are caused by hereditary factors, environmental conditions, and medication-related issues. On the other hand, the cardiotoxicity of drugs should be thoroughly examined before entering the market. In this regard, heart-on-chip (HOC) systems have been developed as a more efficient and cost-effective solution than traditional methods, such as 2D cell culture and animal models. HOCs must replicate the biology, physiology, and pathology of human heart tissue to be considered a reliable platform for heart disease modeling and drug testing. Therefore, many efforts have been made to find the best methods to fabricate different parts of HOCs and to improve the bio-mimicry of the systems in the last decade. Beating HOCs with different platforms have been developed and techniques, such as fabricating pumpless HOCs, have been used to make HOCs more user-friendly systems. Recent HOC platforms have the ability to simultaneously induce and record electrophysiological stimuli. Additionally, systems including both heart and cancer tissue have been developed to investigate tissue-tissue interactions' effect on cardiac tissue response to cancer drugs. In this review, all steps needed to be considered to fabricate a HOC were introduced, including the choice of cellular resources, biomaterials, fabrication techniques, biomarkers, and corresponding biosensors. Moreover, the current HOCs used for modeling cardiac diseases and testing the drugs are discussed. We finally introduced some suggestions for fabricating relatively more user-friendly HOCs and facilitating the commercialization process.

Four-Arm Polymer-Guided Formation of Curcumin-Loaded Flower-Like Porous Microspheres as Injectable Cell Carriers for Diabetic Wound Healing

Stem cell injection is an effective approach for treating diabetic wounds; however, shear stress during injections can negatively affect their stemness and cell growth. Cell-laden porous microspheres can provide shelter for bone mesenchymal stem cells (BMSC). Herein, curcumin-loaded flower-like porous microspheres (CFPM) are designed by combining phase inversion emulsification with thermally induced phase separation-guided four-arm poly (l-lactic acid) (B-PLLA). Notably, the CFPM shows a well-defined surface topography and inner structure, ensuring a high surface area to enable the incorporation and delivery of a large amount of -BMSC and curcumin. The BMSC-carrying CFPM (BMSC@CFPM) maintains the proliferation, retention, and stemness of -BMSCs, which, in combination with their sustainable curcumin release, facilitates the endogenous production of growth/proangiogenic factors and offers a local anti-inflammatory function. An in vivo bioluminescence assay demonstrates that BMSC@CFPM can significantly increase the retention and survival of BMSC in wound sites. Accordingly, BMSC@CFPM, with no significant systemic toxicity, could significantly accelerate diabetic wound healing by promoting angiogenesis, collagen reconstruction, and M2 macrophage polarization. RNA sequencing further unveils the mechanisms by which BMSC@CFPM promotes diabetic wound healing by increasing -growth factors and enhancing angiogenesis through the JAK/STAT pathway. Overall, BMSC@CFPM represents a potential therapeutic tool for diabetic wound healing.

Low-Cost Laser Micromachining Super Hydrophilic-Super Hydrophobic Microgrooves for Robotic Capillary Micromanipulation of Microfibers

Capillary self-alignment technique can achieve highly accurate and fast alignment of micro components. Capillary self-alignment technique relies on the confinement of liquid droplets at receptor sites where hydrophobic–hydrophilic patterns are widely used. This paper reports a low-cost microsecond pulse laser micromachining method for fabrication of super hydrophilic–super hydrophobic grooves as receptor sites for capillary self-alignment of microfibers. We investigated the influence of major manufacturing parameters on groove sizes and wetting properties. The effects of the width (20 µm–100 µm) and depth (8 µm–36 µm) of the groove on the volume of water droplet contained inside the groove were also investigated. We show that by altering scanning speed, using a de-focused laser beam, we can modify the wetting properties of the microgrooves from 10° to 120° in terms of the contact angle. We demonstrated that different types of microfibers including natural and artificial microfibers can self-align to the size matching super hydrophilic–super hydrophobic microgrooves. The results show that super hydrophilic–super hydrophobic microgrooves have great potential in microfiber micromanipulation applications such as natural microfiber categorization, fiber-based microsensor construction, and fiber-enforced material development.

Evaluation of the Cross-Sectional Shape of μ-Grooves Produced in Stainless Steel 304 by Laser-Induced Etching Technique

The variation in cross-sectional profile of a microgroove fabricated with focused and diverging laser irradiation is demonstrated with ray tracing. To verify the result of ray tracing, stainless-steel 304 microgrooves were manufactured utilizing the conventional lens-based and optical fiber-based laser-induced etching techniques in phosphoric acid solution. Three distinctive groove geometries, i.e., a flat surface with no groove, an intermediate stage groove, and a fully developed V-groove, were rendered for numerical analysis. For focusing mode, the first and second reflections were caused by high laser intensity and the second reflected beam could lead to variation in the groove shape such as a U-shaped groove or a V-shaped groove in accordance with etchant concentration. On the contrary, a weak laser entirely distributed at the groove sidewall could not induce a chemical reaction, leading to a V-shaped groove. The effect of process variables such as laser power (intensity) and etchant concentration on the cross-sectional profiles of a groove are closely examined through the computed simulation results.

A novel dual-well array chip for efficiently trapping single-cell in large isolated micro-well without complicated accessory equipment

Conventional cell-sized well arrays have advantages of high occupancy, simple operation, and low cost for capturing single-cells. However, they have insufficient space for including reagents required for cell treatment or analysis, which restricts the wide application of cell-sized well arrays as a single-cell research tool alone. Here, we present a novel dual-well array chip, which integrates capture-wells (20 μm in diameter) with reaction-wells (100 μm in diameter) and describe a flow method for convenient single-cell analysis requiring neither complicated infra-structure nor high expenditure, while enabling highly efficient single cell trapping (75.8%) with only 11.3% multi-cells. Briefly, the cells are first loaded into the dual-wells by gravity and then multi-cells in the reaction-wells are washed out by phosphate buffer saline. Next, biochemical reagents are loaded into reaction-wells using the scraping method and the chip is packed as a sandwich structure. We thereby successfully measured intracellular β-galactosidase activity of K562 cells at the single-cell level. We also used computational simulations to illustrate the working principle of dual-well structure and found out a relationship between the wall shear stress distribution and the aspect ratio of the dual-well array chip which provides theoretical guidance for designing multi-wells chip for convenient single-cell analysis. Our work produced the first dual-well chip that can simultaneously provide a high occupancy rate for single cells and sufficient space for reagents, as well as being low in cost and simple to operate. We believe that the feasibility and convenience of our method will enhance its use as a practical single-cell research tool.

Predictions for optimal mitigation of paracrine inhibitory signalling in haemopoietic stem cell cultures

Introduction

Recent studies in the literature have highlighted the critical role played by cell signalling in determining haemopoietic stem cell (HSC) fate within ex vivo culture systems. Stimulatory signals can enhance proliferation and promote differentiation, whilst inhibitory signals can significantly limit culture output.

Methods

Numerical models of various mitigation strategies are presented and applied to determine effectiveness of these strategies toward mitigation of paracrine inhibitory signalling inherent in these culture systems. The strategies assessed include mixing, media-exchange, fed-batch and perfusion.

Results

The models predict that significant spatial concentration gradients exist in typical cell cultures, with important consequences for subsequent cell expansion. Media exchange is shown to be the most effective mitigation strategy, but remains labour intensive and difficult to scale-up for large culture systems. The fed-batch strategy is only effective at very small Peclet number, and its effect is diminished as the cell culture volume grows. Conversely, mixing is effective at high Peclet number, and ineffective at low Peclet number. The models predict that cell expansion in fed-batch cultures becomes independent of increasing dilution rate, consistent with experimental results previously reported in the literature. In contrast, the models predict that increasing the flow rate in perfused cultures will lead to increased cell expansion, indicating the suitability of perfusion for use as an automated, tunable strategy. The effect of initial cell seeding density is also investigated, with the model showing that perfusion outperforms dilution for all densities considered.

Conclusions

The models predict that the impact of inhibitory signalling in HSC cultures can be mitigated against using media manipulation strategies, with the optimal strategy dependent upon the protein diffusion time-scale relative to the media manipulation time-scale. The key messages from this study can be applied to any complex cell culture scenario where cell-cell interactions and paracrine signalling networks impact upon cell fate and cell expansion.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0048-7) contains supplementary material, which is available to authorized users.

Corrugated round fibers to improve cell adhesion and proliferation in tissue engineering scaffolds

Optimal cell interaction with biomaterial scaffolds is one of the important requirements for the development of successful in vitro tissue-engineered tissues. Fast, efficient and spatially uniform cell adhesion can improve the clinical potential of engineered tissue. Three-dimensional (3-D) solid free form fabrication is one widely used scaffold fabrication technique today. By means of deposition of polymer fibers, scaffolds with various porosity, 3-D architecture and mechanical properties can be prepared. These scaffolds consist mostly of solid round fibers. In this study, it was hypothesized that a corrugated fiber morphology enhances cell adhesion and proliferation and therefore leads to the development of successful in vitro tissue-engineered constructs. Corrugated round fibers were prepared and characterized by extruding poly(ethylene oxide terephthalate)-co-poly(butylene terephthalate) (300PEOT55PBT45) block co-polymer through specially designed silicon wafer inserts. Corrugated round fibers with 6 and 10 grooves on the fiber surface were compared with solid round fibers of various diameters. The culture of mouse pre-myoblast (C2C12) cells on all fibers was studied under static and dynamic conditions by means of scanning electron microscopy, cell staining and DNA quantification. After 7days of culturing under static conditions, the DNA content on the corrugated round fibers was approximately twice as high as that on the solid round fibers. Moreover, under dynamic culture conditions, the cells on the corrugated round fibers seemed to experience lower mechanical forces and therefore adhered better than on the solid round fibers. The results of this study show that the surface architecture of fibers in a tissue engineering scaffold can be used as a tool to improve the performance of the scaffold in terms of cell adhesion and proliferation.

Microfabricated modular scale-down device for regenerative medicine process development

The capacity of milli and micro litre bioreactors to accelerate process development has been successfully demonstrated in traditional biotechnology. However, for regenerative medicine present smaller scale culture methods cannot cope with the wide range of processing variables that need to be evaluated. Existing microfabricated culture devices, which could test different culture variables with a minimum amount of resources (e.g. expensive culture medium), are typically not designed with process development in mind. We present a novel, autoclavable, and microfabricated scale-down device designed for regenerative medicine process development. The microfabricated device contains a re-sealable culture chamber that facilitates use of standard culture protocols, creating a link with traditional small-scale culture devices for validation and scale-up studies. Further, the modular design can easily accommodate investigation of different culture substrate/extra-cellular matrix combinations. Inactivated mouse embryonic fibroblasts (iMEF) and human embryonic stem cell (hESC) colonies were successfully seeded on gelatine-coated tissue culture polystyrene (TC-PS) using standard static seeding protocols. The microfluidic chip included in the device offers precise and accurate control over the culture medium flow rate and resulting shear stresses in the device. Cells were cultured for two days with media perfused at 300 µl.h⁻¹ resulting in a modelled shear stress of 1.1×10⁻⁴ Pa. Following perfusion, hESC colonies stained positively for different pluripotency markers and retained an undifferentiated morphology. An image processing algorithm was developed which permits quantification of co-cultured colony-forming cells from phase contrast microscope images. hESC colony sizes were quantified against the background of the feeder cells (iMEF) in less than 45 seconds for high-resolution images, which will permit real-time monitoring of culture progress in future experiments. The presented device is a first step to harness the advantages of microfluidics for regenerative medicine process development.

Microfluidic 3D cell culture: potential application for tissue-based bioassays

Current fundamental investigations of human biology and the development of therapeutic drugs commonly rely on 2D monolayer cell culture systems. However, 2D cell culture systems do not accurately recapitulate the structure, function or physiology of living tissues, nor the highly complex and dynamic 3D environments in vivo. Microfluidic technology can provide microscale complex structures and well-controlled parameters to mimic the in vivo environment of cells. The combination of microfluidic technology with 3D cell culture offers great potential for in vivo-like tissue-based applications, such as the emerging organ-on-a-chip system. This article will review recent advances in the microfluidic technology for 3D cell culture and their biological applications.

Nanoporous membrane-sealed microfluidic devices for improved cell viability

Cell-laden microfluidic devices have broad potential in various biomedical applications, including tissue engineering and drug discovery. However, multiple difficulties encountered while culturing cells within devices affecting cell viability, proliferation, and behavior has complicated their use. While active perfusion systems have been used to overcome the diffusive limitations associated with nutrient delivery into microchannels to support longer culture times, these systems can result in non-uniform oxygen and nutrient delivery and subject cells to shear stresses, which can affect cell behavior. Additionally, histological analysis of cell cultures within devices is generally laborious and yields inconsistent results due to difficulties in delivering labeling agents in microchannels. Herein, we describe a simple, cost-effective approach to preserve cell viability and simplify labeling within microfluidic networks without the need for active perfusion. Instead of bonding a microfluidic network to glass, PDMS, or other solid substrate, the network is bonded to a semi-permeable nanoporous membrane. The membrane-sealed devices allow free exchange of proteins, nutrients, buffers, and labeling reagents between the microfluidic channels and culture media in static culture plates under sterile conditions. The use of the semi-permeable membrane dramatically simplifies microniche cell culturing while avoiding many of the complications which arise from perfusion systems.

Microwell perfusion array for high-throughput, long-term imaging of clonal growth

Continuous cell tracking by time-lapse microscopy has led to detailed study of cell differentiation pathways using single cell fate maps. There are a multitude of cell fate outcomes, so hundreds of clonal division histories are required to measure these stochastic branching processes. This study examines the principle of condensing cell imaging information into a relatively small region to maximize live cell imaging throughput. High throughput clonal analysis of non-adherent cells by continuous live cell tracking was possible using a microwell perfusion array with an internal volume of 16 μl and 600 microwells at the base. This study includes examination of biocompatibility of buffer systems, connecting tubing, cell culture substrates, and media degradation. An intermittent perfusion protocol was selected for long-term time-lapse imaging of KG1a cells in the microwell array; 1500 clones were simultaneously cultured and scanned every 3 min at 100 × magnifications for 6 days. The advantages of perfusion microwell culture are continuous long-term cell tracking, higher cell imaging throughput, and greater control over cell microenvironment. Microwell devices facilitate high throughput analysis of cell lineage development and measurement of the probability distribution for cell life events such as mitosis.

Microfluidic platforms for hepatocyte cell culture: new technologies and applications

In this article, we summarize the key elements of microfluidic platforms for mimicking in vivo hepatocyte cell culture and the major recent advances in this area. Specifically, we will give brief background and rationale for key design requirements for mimicking in vivo hepatocyte cell culture, and then summarize findings, applications, and limitations from microfluidic platforms that addressed these design requirements. Although no ideal microfluidic platform has so far been developed for fully mimicking in vivo hepatocyte cell culture, some approaches and designs have demonstrated great potential in this area.

Micro- and nanoengineering for stem cell biology: the promise with a caution

Current techniques used in stem cell research only crudely mimic the physiological complexity of the stem cell niches. Recent advances in the field of micro- and nanoengineering have brought an array of in vitro cell culture models that have enabled development of novel, highly precise and standardized tools that capture physiological details in a single platform, with greater control, consistency, and throughput. In this review, we describe the micro- and nanotechnology-driven modern toolkit for stem cell biologists to design novel experiments in more physiological microenvironments with increased precision and standardization, and caution them against potential challenges that the modern technologies might present.

A microfluidic traps system supporting prolonged culture of human embryonic stem cells aggregates

The unlimited proliferative and differentiative capacities of embryonic stem cells (ESCs) are tightly regulated by their microenvironment. Local concentrations of soluble factors, cell-cell interactions and extracellular matrix signaling are just a few variables that influence ESC fate. A common method employed to induce ESC differentiation involves the formation of cell aggregates called embryoid bodies (EBs), which recapitulate early stages of embryonic development. EBs are normally formed in suspension cultures, producing heterogeneously shaped and sized aggregates. The present study demonstrates the usage of a microfluidic traps system which supports prolonged EB culturing. The traps are uniquely designed to facilitate cell capture and aggregation while offering efficient gas/nutrients exchange. A finite element simulation is presented with emphasis on several aspects critical to appropriate design of such bioreactors for ESC culture. Finally, human ESC, mouse Nestin-GFP ESC and OCT4-EGFP ESCs were cultured using this technique and demonstrated extended viability for more than 5 days. In addition, EBs developed and maintained a polarized differentiation pattern, possibly as a result of the nutrient gradients imposed by the traps bioreactor. The novel microbioreactor presented here can enhance future embryogenesis research by offering tight control of culturing conditions.

Integration of single oocyte trapping, in vitro fertilization and embryo culture in a microwell-structured microfluidic device

In vitro fertilization (IVF) therapy is an important treatment for human infertility. However, the methods for clinical IVF have only changed slightly over decades: culture medium is held in oil-covered drops in Petri dishes and manipulation occurs by manual pipetting. Here we report a novel microwell-structured microfluidic device that integrates single oocyte trapping, fertilization and subsequent embryo culture. A microwell array was used to capture and hold individual oocytes during the flow-through process of oocyte and sperm loading, medium substitution and debris cleaning. Different microwell depths were compared by computational modeling and flow washing experiments for their effectiveness in oocyte trapping and debris removal. Fertilization was achieved in the microfluidic devices with similar fertilization rates to standard oil-covered drops in Petri dishes. Embryos could be cultured to blastocyst stages in our devices with developmental status individually monitored and tracked. The results suggest that the microfluidic device may bring several advantages to IVF practices by simplifying oocyte handling and manipulation, allowing rapid and convenient medium changing, and enabling automated tracking of any single embryo development.

A computational and experimental study inside microfluidic systems: the role of shear stress and flow recirculation in cell docking

In this paper, microfluidic devices containing microwells that enabled cell docking were investigated. We theoretically assessed the effect of geometry on recirculation areas and wall shear stress patterns within microwells and studied the relationship between the computational predictions and experimental cell docking. We used microchannels with 150 microm diameter microwells that had either 20 or 80 microm thickness. Flow within 80 microm deep microwells was subject to extensive recirculation areas and low shear stresses (<0.5 mPa) near the well base; whilst these were only presented within a 10 microm peripheral ring in 20 microm thick microwells. We also experimentally demonstrated that cell docking was significantly higher (p < 0.01) in 80 microm thick microwells as compared to 20 microm thick microwells. Finally, a computational tool which correlated physical and geometrical parameters of microwells with their fluid dynamic environment was developed and was also experimentally confirmed.

Lab-on-a-chip devices as an emerging platform for stem cell biology

The advent of stem cell based therapies has brought regenerative medicine into an increased focus as a part of the modern medicine practice, with a potential to treat a myriad of intractable diseases in the future. Stem cells reside in a complex microenvironment presenting them with a multitude of potential cues that are chemical, physical, and mechanical in nature. Conventional techniques used for experiments involving stem cells can only poorly mimic the physiological context, and suffer from imprecise spatial and temporal control, low throughput, lack of scalability and reproducibility, and poor representation of the mechanical and physical cell microenvironment. Novel lab-on-a-chip platforms, on the other hand, can much better mimic the complexity of in vivo tissue milieu and provide a greater control of the parameter variation in a high throughput and scalable manner. This capability may be especially important for understanding the biology and cementing the clinical potential of stem cell based therapies. Here we review microfabrication- and microfluidics-based approaches to investigating the complex biology of stem cell responses to changes in the local microenvironment. In particular, we categorize each method based on the types of controlled inputs it can have on stem cells, including soluble biochemical factors, extracellular matrix interactions, homotypic and heterotypic cell-cell signaling, physical cues (e.g. oxygen tension, pH, temperature), and mechanical forces (e.g. shear, topography, rigidity). Finally, we outline the methods to perform large scale observations of stem cell phenotypes and high-throughput screening of cellular responses to a combination of stimuli, and many new emerging technologies that are becoming available specifically for stem cell applications.

A microfluidic hepatic coculture platform for cell-based drug metabolism studies

Within the global pharmaceutical and biotech industries, there is significant interest in identifying in vitro screening systems that are more human-relevant-i.e., that offer greater utility in predicting subcellular and cellular physiological responses in humans in vivo-and that thereby allow investigators to reduce the incidence of costly late-stage failures during pharmaceutical clinical trials, as well as to reduce the use of animals in drug testing. Currently incumbent in vitro screening methods, such as culturing human hepatocytes in suspension, while useful, are limited by a lack of long term cellular function. In order to address this limitation, we have established an integrated, microfluidic, in vitro platform that combines the patented HmuREL((R)) microdevice with a hepatic coculture system. In the present report, we use this platform to study clearance and metabolite generation of a battery of molecular entities. The results show that the flow-based coculture system is capable of clearing, with improved resolution and predictive value, compounds with high, medium, and low clearance values. In addition, when coculture is coupled with flow, higher metabolite production rates are obtained than in static systems.