Microfluidic perfusion culture of human induced pluripotent stem cells under fully defined culture conditions

Quantitative assessment of cardiomyocyte mechanobiology through high-throughput cantilever-based functional well plate systems

Proper regulation of the in vitro cell culture environment is essential for disease modelling and drug toxicity screening. The main limitation of well plates used for cell culture is that they cannot accurately maintain energy sources and compounds needed during cell growth. Herein, to understand the importance of perfusion in cardiomyocyte culture, changes in contractile force and heart rate during cardiomyocyte growth are systematically investigated, and the results are compared with those of a perfusion-free system. The proposed perfusion system consists of a Peltier refrigerator, a peristaltic pump, and a functional well plate. A functional well plate with 12 wells is made through injection moulding, with two tubes integrated in the cover for each well to continuously circulate the culture medium. The contractile force of cardiomyocytes growing on the cantilever surface is analysed through changes in cantilever displacement. The maturation of cardiomyocytes is evaluated through fluorescence staining and western blot; cardiomyocytes cultured in the perfusion system show greater maturity than those cultured in a manually replaced culture medium. The pH of the culture medium manually replaced at intervals of 3 days decreases to 6.8, resulting in an abnormal heartbeat, while cardiomyocytes cultured in the perfusion system maintained at pH 7.4 show improved contractility and a uniform heart rate. Two well-known ion channel blockers, verapamil and quinidine, are used to measure changes in the contractile force of cardiomyocytes from the two systems. Cardiomyocytes in the perfusion system show greater stability during drug toxicity screening, proving that the perfusion system provides a better environment for cell growth.

Artificial Intelligence in Regenerative Medicine: Applications and Implications

The field of regenerative medicine is constantly advancing and aims to repair, regenerate, or substitute impaired or unhealthy tissues and organs using cutting-edge approaches such as stem cell-based therapies, gene therapy, and tissue engineering. Nevertheless, incorporating artificial intelligence (AI) technologies has opened new doors for research in this field. AI refers to the ability of machines to perform tasks that typically require human intelligence in ways such as learning the patterns in the data and applying that to the new data without being explicitly programmed. AI has the potential to improve and accelerate various aspects of regenerative medicine research and development, particularly, although not exclusively, when complex patterns are involved. This review paper provides an overview of AI in the context of regenerative medicine, discusses its potential applications with a focus on personalized medicine, and highlights the challenges and opportunities in this field.

The differentiation of human induced pluripotent stem cells into hematopoietic stem cells on 3D bone scaffold in a dynamic culture system

Hematopoietic stem cell transplantation is used for cell-based therapy for many hematological disorders. However, difficulty in finding proper donors has limited this source of stem cells. For clinical application, the generation of these cells from induced pluripotent stem cells (iPSs) is a fascinating and endless source. One of the experimental methods to generate HSCs from iPSs is the mimicking of the hematopoietic niche. In the current study, as the first phase of differentiation, embryoid bodies were formed from iPSs. They were then cultured in different dynamic conditions in order to determine the appropriate settings for their differentiation into HSCs. The dynamic culture was composed of DBM Scaffold with or without growth factor. After ten days, the specific HSC markers (CD34, CD133, CD31 and CD45) were assessed using flow-cytometry. Our findings demonstrated that the dynamic conditions were significantly suitable than static ones. In addition, in 3D scaffold and dynamic system the expression of CXCR4, as a homing marker, was increased. These results suggest that the 3D culture bioreactor with DBM scaffold could provide a new approach for differentiation of iPSs into HSCs. Moreover, this system could provide maximum mimicry of bone marrow niche.

Gravity-driven microfluidic device placed on a slow-tilting table enables constant unidirectional perfusion culture of human induced pluripotent stem cells

Gravity-driven microfluidics, which utilizes gravity force to drive liquid flow, offers portability and multi-condition setting flexibility because they do not require pumps or connection tubes to drive the flow. However, because the flow rate decreases with time in gravity-driven microfluidics, it is not suitable for stem cell experiments, which require long-term (at least a day) stability. In this study, gravity-driven microfluidics and a slow-tilting table were developed to culture cells under constant unidirectional perfusion. The microfluidic device was placed on a slow-tilting table, which tilts unidirectionally at a rate of approximately 7° per day to compensate for the reduction in the flow rate. Computational simulations showed that the pulsation of the flow arising from the stepwise movement of the table was less than 0.2%, and the flow was laminar. Hydrophilization of the tanks increased the flow rate, which is consistent with the theoretical values. We showed that vitronectin is better than laminin 511 fragments as a coating material for adhering human induced pluripotent stem cells on a microchamber made of polydimethylsiloxane, and succeeded in culturing the cells for 3 days. It is believed that the system offers easy-to-use cell culture tools, such as conventional multiwell culture vessels, and enables the control of the cell microenvironment.

Sounding a New Era in Biomechanics with Acoustic Force Spectroscopy

The acoustic force spectroscopy (AFS) tool was recently introduced as a novel tool for probing mechanical properties of biomolecules, expanding the application of sound waves to high-throughput quantification of the mechanical properties of single cells. By using controlled acoustic forces in the piconewton to nanonewton range, tens to hundreds of cells functionalized by attached microspheres can simultaneously be stretched and tracked in real-time with sub millisecond time response. Since its first application, several studies have demonstrated the potential and versatility of the AFS for high-throughput measurements of force-induced molecular mechanisms, revealing insight into cellular biomechanics and mechanobiology at the molecular level. In this chapter, we describe the operation of the AFS starting with the underlying physical principles, followed by a run-down of experimental considerations, and finally leading to applications in molecular and cellular biology.

Micro/nanoengineered technologies for human pluripotent stem cells maintenance and differentiation

Human pluripotent stem cells (hPSCs) are a promising source of cells for cell replacement-based therapies as well as modeling human development and diseases in vitro. However, achieving fate control of hPSC with a high yield and specificity remains challenging. The fate specification of hPSCs is regulated by biochemical and biomechanical cues in their environment. Driven by this knowledge, recent exciting advances in micro/nanoengineering have been leveraged to develop a broad range of tools for the generation of extracellular biomechanical and biochemical signals that determine the behavior of hPSCs. In this review, we summarize such micro/nanoengineered technologies for controlling hPSC fate and highlight the role of biochemical and biomechanical cues such as substrate rigidity, surface topography, and cellular confinement in the hPSC-based technologies that are on the horizon.

Microfluidic Devices as Process Development Tools for Cellular Therapy Manufacturing

Cellular therapies are creating a paradigm shift in the biomanufacturing industry. Particularly for autologous therapies, small-scale processing methods are better suited than the large-scale approaches that are traditionally employed in the industry. Current small-scale methods for manufacturing personalized cell therapies, however, are labour-intensive and involve a number of 'open events'. To overcome these challenges, new cell manufacturing platforms following a GMP-in-a-box concept have recently come on the market (GMP: Good Manufacturing Practice). These are closed automated systems with built-in pumps for fluid handling and sensors for in-process monitoring. At a much smaller scale, microfluidic devices exhibit many of the same features as current GMP-in-a-box systems. They are closed systems, fluids can be processed and manipulated, and sensors integrated for real-time detection of process variables. Fabricated from polymers, they can be made disposable, i.e. single-use. Furthermore, microfluidics offers exquisite spatiotemporal control over the cellular microenvironment, promising both reproducibility and control of outcomes. In this chapter, we consider the challenges in cell manufacturing, highlight recent advances of microfluidic devices for each of the main process steps, and summarize our findings on the current state of the art. As microfluidic cell culture devices have been reported for both adherent and suspension cell cultures, we report on devices for the key process steps, or unit operations, of both stem cell therapies and cell-based immunotherapies.

Highly parallelized human embryonic stem cell differentiation to cardiac mesoderm in nanoliter chambers on a microfluidic chip

Human stem cell-derived cells and tissues hold considerable potential for applications in regenerative medicine, disease modeling and drug discovery. The generation, culture and differentiation of stem cells in low-volume, automated and parallelized microfluidic chips hold great promise to accelerate the research in this domain. Here, we show that we can differentiate human embryonic stem cells (hESCs) to early cardiac mesodermal cells in microfluidic chambers that have a volume of only 30 nanoliters, using discontinuous medium perfusion. 64 of these chambers were parallelized on a chip which contained integrated valves to spatiotemporally isolate the chambers and automate cell culture medium exchanges. To confirm cell pluripotency, we tracked hESC proliferation and immunostained the cells for pluripotency markers SOX2 and OCT3/4. During differentiation, we investigated the effect of different medium perfusion frequencies on cell reorganization and the expression of the early cardiac mesoderm reporter MESP1mCherry by live-cell imaging. Our study demonstrates that microfluidic technology can be used to automatically culture, differentiate and study hESC in very low-volume culture chambers even without continuous medium perfusion. This result is an important step towards further automation and parallelization in stem cell technology.

A microfluidic platform for dissociating clinical scale tissue samples into single cells

The advancement of sample preparation techniques is essential for the field of cell-based therapeutics. To obtain cells suited for clinical applications, the entire process starting from acquiring donor tissue biopsy, all through cell transplantation into the recipient, should occur in an integrated, safe, and efficient system. The current laboratory approach for solid tissue-to-cell isolation is invasive and involves multiple incoherent manual procedures running in an open operator-dependent system. Such an approach provides a chain of events for systematic cell loss that would be unfavorable for rare cell populations such as adult and cancer stem cells. A few lab-on-chip platforms were proposed to process biological tissues, however, they were limited to partial tissue dissociation and required additional processing off-chip. Here, we report the first microfluidic platform that can dissociate native biological tissue into ready-to-use single cells. The platform can merge the successive steps of tissue dissociation, debris filtration, cell sieving, washing, and staining in one streamlined process. Performance of the platform was tested with diverse biological tissues and it could yield viable cells that were ready for on or off-chip cell culture without further processing. Microfluidic tissue dissociation using this platform produced a higher number of viable single cells (an average of 2262 cells/ml per milligram of tissue compared to 1233.25 cells/ml/mg with conventional dissociation).

Microfluidics-enabled 96-well perfusion system for high-throughput tissue engineering and long-term all-optical electrophysiology

This work demonstrates a novel high-throughput (HT) microfluidics-enabled uninterrupted perfusion system (HT-μUPS) and validates its use with chronic all-optical electrophysiology in human excitable cells. HT-μUPS consists of a soft multichannel microfluidic plate cover which could button on a commercial HT 96-well plate. Herein, we demonstrate the manufacturing process of the system and its usages in acute and chronic all-optical electrophysiological studies of human induced pluripotent stem-cell-derived cardiomyocytes (iPSC-CM) and engineered excitable (spiking HEK) cells. HT-μUPS perfusion maintained functional voltage and calcium responses in iPSC-CM and spiking HEK cells under spontaneous conditions and under optogenetic pacing. Long-term culture with HT-μUPS improved cell viability and optogenetically-tracked calcium responses in spiking HEK cells. The simplicity of this design and its compatibility with HT all-optical electrophysiology can empower cell-based assays for personalized medicine using patient-derived cells.

Hydrogel-based sealed microchamber arrays for rapid medium exchange and drug testing of cell spheroids

Culturing cell spheroids in microchamber arrays is a widely used method in regenerative medicine and drug discovery while it requires laborious procedures during medium exchange and drug administration. Here, we report a simple method for the medium exchange and drug testing using a hydrogel-based sealed microchamber arrays. Owing to the high molecular permeability of poly(vinyl alcohol) hydrogel, the sealed microchamber allows nutrients and drugs in outer medium to pass through. Thus, automatic medium exchange and drug testing for all the cell spheroids inside the microchamber arrays are achieved by simply transferring the microchamber from old medium to fresh medium. Cell spheroids of human induced pluripotent stem cell-derived cardiomyocytes were cultured inside the sealed microchambers, and it was confirmed that the spheroids were stably positioned inside the microchamber even after transferring 10 times. The cell spheroids showed high viability after culturing for 7 days in the sealed microchamber with the transfer-based medium exchange, which allowed cardiac maturation by simultaneous electrical stimulation. Isoproterenol, a model cardiac drug, was administrated from outside the sealed microchamber to demonstrate the feasibility of drug testing by the rapid transfer method.

Progress, obstacles, and limitations in the use of stem cells in organ-on-a-chip models

In recent years, drug development costs have soared, primarily due to the failure of preclinical animal and cell culture models, which do not directly translate to human physiology. Organ-on-a-chip (OOC) is a burgeoning technology with the potential to revolutionize disease modeling, drug discovery, and toxicology research by strengthening the relevance of culture-based models while reducing costly animal studies. Although OOC models can incorporate a variety of tissue sources, the most robust and relevant OOC models going forward will include stem cells. In this review, we will highlight the benefits of stem cells as a tissue source while considering current limitations to their complete and effective implementation into OOC models.

Caring for cells in microsystems: principles and practices of cell-safe device design and operation

Microfluidic device designers and users continually question whether cells are 'happy' in a given microsystem or whether they are perturbed by micro-scale technologies. This issue is normally brought up by engineers building platforms, or by external reviewers (academic or commercial) comparing multiple technological approaches to a problem. Microsystems can apply combinations of biophysical and biochemical stimuli that, although essential to device operation, may damage cells in complex ways. However, assays to assess the impact of microsystems upon cells have been challenging to conduct and have led to subjective interpretation and evaluation of cell stressors, hampering development and adoption of microsystems. To this end, we introduce a framework that defines cell health, describes how device stimuli may stress cells, and contrasts approaches to measure cell stress. Importantly, we provide practical guidelines regarding device design and operation to minimize cell stress, and recommend a minimal set of quantitative assays that will enable standardization in the assessment of cell health in diverse devices. We anticipate that as microsystem designers, reviewers, and end-users enforce such guidelines, we as a community can create a set of essential principles that will further the adoption of such technologies in clinical, translational and commercial applications.

Random migration of induced pluripotent stem cell-derived human gastrulation-stage mesendoderm

Gastrulation is the initial systematic deformation of the embryo to form germ layers, which is characterized by the placement of appropriate cells in their destined locations. Thus, gastrulation, which occurs at the beginning of the second month of pregnancy, is a critical stage in human body formation. Although histological analyses indicate that human gastrulation is similar to that of other amniotes (birds and mammals), much of human gastrulation dynamics remain unresolved due to ethical and technical limitations. We used human induced pluripotent stem cells (hiPSCs) to study the migration of mesendodermal cells through the primitive streak to form discoidal germ layers during gastrulation. Immunostaining results showed that hiPSCs differentiated into mesendodermal cells and that epithelial–mesenchymal transition occurred through the activation of the Activin/Nodal and Wnt/beta-catenin pathways. Single-cell time-lapse imaging of cells adhered to cover glass showed that mesendodermal differentiation resulted in the dissociation of cells and an increase in their migration speed, thus confirming the occurrence of epithelial–mesenchymal transition. These results suggest that mesendodermal cells derived from hiPSCs may be used as a model system for studying migration during human gastrulation in vitro. Using random walk analysis, we found that random migration occurred for both undifferentiated hiPSCs and differentiated mesendodermal cells. Two-dimensional random walk simulation showed that homogeneous dissociation of particles may form a discoidal layer, suggesting that random migration might be suitable to effectively disperse cells homogeneously from the primitive streak to form discoidal germ layers during human gastrulation.

In Vitro Microscale Models for Embryogenesis

Embryogenesis is a highly regulated developmental process requiring complex mechanical and biochemical microenvironments to give rise to a fully developed and functional embryo. Significant efforts have been taken to recapitulate specific features of embryogenesis by presenting the cells with developmentally relevant signals. The outcomes, however, are limited partly due to the complexity of this biological process. Microtechnologies such as micropatterned and microfluidic systems, along with new emerging embryonic stem cell-based models, could potentially serve as powerful tools to study embryogenesis. The aim of this article is to review major studies involving the culturing of pluripotent stem cells using different geometrical patterns, microfluidic platforms, and embryo/embryoid body-on-a-chip modalities. Indeed, new research opportunities have emerged for establishing in vitro culture for studying human embryogenesis and for high-throughput pharmacological testing platforms and disease models to prevent defects in early stages of human development.

High cell density suppresses BMP4-induced differentiation of human pluripotent stem cells to produce macroscopic spatial patterning in a unidirectional perfusion culture chamber

Spatial pattern formation is a critical step in embryogenesis. Bone morphogenetic protein 4 (BMP4) and its inhibitors are major factors for the formation of spatial patterns during embryogenesis. However, spatial patterning of the human embryo is unclear because of ethical issues and isotropic culture environments resulting from conventional culture dishes. Here, we utilized human pluripotent stem cells (hiPSCs) and a simple anisotropic (unidirectional perfusion) culture chamber, which creates unidirectional conditions, to measure the cell community effect. The influence of cell density on BMP4-induced differentiation was explored during static culture using a conventional culture dish. Immunostaining of the early differentiation marker SSEA-1 and the mesendoderm marker BRACHYURY revealed that high cell density suppressed differentiation, with small clusters of differentiated and undifferentiated cells formed. Addition of five-fold higher concentration of BMP4 showed similar results, suggesting that suppression was not caused by depletion of BMP4 but rather by high cell density. Quantitative RT-PCR array analysis showed that BMP4 induced multi-lineage differentiation, which was also suppressed under high-density conditions. We fabricated an elongated perfusion culture chamber, in which proteins were transported unidirectionally, and hiPSCs were cultured with BMP4. At low density, the expression was the same throughout the chamber. However, at high density, SSEA-1 and BRACHYURY were expressed only in upstream cells, suggesting that some autocrine/paracrine factors inhibited the action of BMP4 in downstream cells to form the spatial pattern. Human iPSCs cultured in a perfusion culture chamber might be useful for studying in vitro macroscopic pattern formation in human embryogenesis.

Transfection in perfused microfluidic cell culture devices: A case study

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Automated chemical transfection in a microfluidic device for long-term homogeneous cell culture.

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Transfection reagent mixture uniformly exposed to cells growing in the device.

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Embryonic stem cells transfected with GFP show improved efficiency and an increased median fluorescence intensity on-chip relative to 24 well plate.

Automated microfluidic devices are a promising route towards a point-of-care autologous cell therapy. The initial steps of induced pluripotent stem cell (iPSC) derivation involve transfection and long term cell culture. Integration of these steps would help reduce the cost and footprint of micro-scale devices with applications in cell reprogramming or gene correction. Current examples of transfection integration focus on maximising efficiency rather than viable long-term culture. Here we look for whole process compatibility by integrating automated transfection with a perfused microfluidic device designed for homogeneous culture conditions. The injection process was characterised using fluorescein to establish a LabVIEW-based routine for user-defined automation. Proof-of-concept is demonstrated by chemically transfecting a GFP plasmid into mouse embryonic stem cells (mESCs). Cells transfected in the device showed an improvement in efficiency (34%, n = 3) compared with standard protocols (17.2%, n = 3). This represents a first step towards microfluidic processing systems for cell reprogramming or gene therapy.

Current Strategies and Challenges for Purification of Cardiomyocytes Derived from Human Pluripotent Stem Cells

Cardiomyocytes (CMs) derived from human pluripotent stem cells (hPSCs) are considered a most promising option for cell-based cardiac repair. Hence, various protocols have been developed for differentiating hPSCs into CMs. Despite remarkable improvement in the generation of hPSC-CMs, without purification, these protocols can only generate mixed cell populations including undifferentiated hPSCs or non-CMs, which may elicit adverse outcomes. Therefore, one of the major challenges for clinical use of hPSC-CMs is the development of efficient isolation techniques that allow enrichment of hPSC-CMs. In this review, we will discuss diverse strategies that have been developed to enrich hPSC-CMs. We will describe major characteristics of individual hPSC-CM purification methods including their scientific principles, advantages, limitations, and needed improvements. Development of a comprehensive system which can enrich hPSC-CMs will be ultimately useful for cell therapy for diseased hearts, human cardiac disease modeling, cardiac toxicity screening, and cardiac tissue engineering.

Stem cell culture and differentiation in microfluidic devices toward organ-on-a-chip

Microfluidic lab-on-a-chip provides a new platform with unique advantages to mimic complex physiological microenvironments in vivo and has been increasingly exploited to stem cell research. In this review, we highlight recent advances of microfluidic devices for stem cell culture and differentiation toward the development of organ-on-a-chip, especially with an emphasis on vital innovations within the last 2 years. Various aspects for improving on-chip stem-cell culture and differentiation, particularly toward organ-on-a-chip, are discussed, along with microenvironment control, surface modification, extracellular scaffolds, high throughput and stimuli. The combination of microfluidic technologies and stem cells hold great potential toward versatile systems of ‘organ-on-a-chip’ as desired.

Adapted with permission from [1–8].

Stem cells, capable of self-renewing and differentiating into cells of various tissue types, are drawing more and more attention for their enormous potential in many clinically associated applications that include drug screening, disease modeling and regenerative medicine. Conventional cell culture methods, however, have proven to be difficult to mimic in vivo like microenvironments and to provide a number of well-controlled stimuli that are critical for stem cell culture and differentiation. In contrast, microfluidic devices offer new capacities and unique advantages to mimic complex physiological microenvironments in vivo, and has been increasingly applied to stem cell research.

Compartmentalized microfluidic perfusion system to culture human induced pluripotent stem cell aggregates

Microfluidic perfusion systems enable small-volume cell cultures under precisely controlled microenvironments, and are typically developed for cell-based high-throughput screening. However, most such systems are designed to manipulate dissociated single cells, not cell aggregates, and are thus unsuitable to induce differentiation in human induced pluripotent stem cells (hiPSCs), which is conventionally achieved by using cell aggregates to increase cell-cell interactions. We have now developed a compartmentalized microfluidic perfusion system with large flow channels to load, culture, and observe cell aggregates. Homogeneously sized cell aggregates to be loaded into the device were prepared by shredding flat hiPSC colonies into squares. These aggregates were then seeded into microchambers coated with fibronectin and bovine serum albumin (BSA) to establish adherent and floating cultures, respectively, both of which are frequently used to differentiate hiPSCs. However, the number of aggregates loaded in fibronectin-coated microchambers was much lower than in BSA-coated microchambers, suggesting that fibronectin traps cell aggregates before they reach the chambers. Accordingly, hiPSCs that reached the microchambers subsequently adhered. In contrast, BSA-coated microchambers did not allow cell aggregates to adhere, but were sufficiently deep to prevent cell aggregates from flowing out during perfusion of media. Immunostaining for markers of undifferentiated cells showed that cultures on both fibronectin- and BSA-coated microchambers were successfully established. Notably, we found that floating aggregates eventually adhered to surfaces coated with BSA upon differentiation, and that differentiation depends on the initial size of aggregates. Collectively, these results suggest that the microfluidic system is suitable for manipulating hiPSC aggregates in compartmentalized microchambers.

Biological Effects of Culture Substrates on Human Pluripotent Stem Cells

In recent years, as human pluripotent stem cells (hPSCs) have been commonly cultured in feeder-free conditions, a number of cell culture substrates have been applied or developed. However, the functional roles of these substrates in maintaining hPSC self-renewal remain unclear. Here in this review, we summarize the types of these substrates and their effect on maintaining hPSC self-renewal. Endogenous extracellular matrix (ECM) protein expression has been shown to be crucial in maintaining hPSC self-renewal. These ECM molecules interact with integrin cell-surface receptors and transmit their cellular signaling. We discuss the possible effect of integrin-mediated signaling pathways on maintaining hPSC self-renewal. Activation of integrin-linked kinase (ILK), which transmits ECM-integrin signaling to AKT (also known as protein kinase B), has been shown to be critical in maintaining hPSC self-renewal. Also, since naïve pluripotency has been widely recognized as an alternative pluripotent state of hPSCs, we discuss the possible effects of culture substrates and integrin signaling on naïve hPSCs based on the studies of mouse embryonic stem cells. Understanding the role of culture substrates in hPSC self-renewal and differentiation enables us to control hPSC behavior precisely and to establish scalable or microfabricated culture technologies for regenerative medicine and drug development.

Advances in microfluidic platforms for analyzing and regulating human pluripotent stem cells

Microfluidic devices employ submillimeter length scale control of flow to achieve high-resolution spatial and temporal control over the microenvironment, providing powerful tools to elucidate mechanisms of human pluripotent stem cell (hPSC) regulation and to elicit desired hPSC fates. In addition, microfluidics allow control of paracrine and juxtracrine signaling, thereby enabling fabrication of microphysiological systems comprised of multiple cell types organized into organs-on-a-chip. Microfluidic cell culture systems can also be integrated with actuators and sensors, permitting construction of high-density arrays of cell-based biosensors for screening applications. This review describes recent advances in using microfluidics to understand mechanisms by which the microenvironment regulates hPSC fates and applications of microfluidics to realize the potential of hPSCs for in vitro modeling and screening applications.

Clinical-scale purification of pluripotent stem cell derivatives for cell-based therapies

Human pluripotent stem cells (hPSCs) have the potential to revolutionize cell-replacement therapies because of their ability to self renew and differentiate into nearly every cell type in the body. However, safety concerns have delayed the clinical translation of this technology. One cause for this is the capacity that hPSCs have to generate tumors after transplantation. Because of the challenges associated with achieving complete differentiation into clinically relevant cell types, the development of safe and efficient strategies for purifying committed cells is essential for advancing hPSC-based therapies. Several purification strategies have now succeeded in generating non-tumorigenic and homogeneous cell-populations. These techniques typically enrich for cells by either depleting early committed populations from teratoma-initiating hPSCs or by positively selecting cells after differentiation. Here we review the working principles behind separation methods that have facilitated the safe and controlled application of hPSC-derived cells in laboratory settings and pre-clinical research. We underscore the need for improving and integrating purification strategies within differentiation protocols in order to unlock the therapeutic potential of hPSCs.

Functional maintenance of differentiated embryoid bodies in microfluidic systems: a platform for personalized medicine

Hormone replacement therapies have become important for treating diseases such as premature ovarian failure or menopausal complications. The clinical use of bioidentical hormones might significantly reduce some of the potential risks reportedly associated with the use of synthetic hormones. In the present study, we demonstrate the utility and advantage of a microfluidic chip culture system to enhance the development of personalized, on-demand, treatment modules using embryoid bodies (EBs). Functional EBs cultured on microfluidic chips represent a platform for personalized, patient-specific treatment cassettes that can be cryopreserved until required for treatment. We assessed the viability, differentiation, and functionality of EBs cultured and cryopreserved in this system. During extended microfluidic culture, estradiol, progesterone, testosterone, and anti-müllerian hormone levels were measured, and the expression of differentiated steroidogenic cells was confirmed by immunocytochemistry assay for the ovarian tissue markers anti-müllerian hormone receptor type II, follicle-stimulating hormone receptor, and inhibin β-A and the estrogen biosynthesis enzyme aromatase. Our studies showed that under microfluidic conditions, differentiated steroidogenic EBs continued to secrete estradiol and progesterone at physiologically relevant concentrations (30-120 pg/ml and 150-450 pg/ml, respectively) for up to 21 days. Collectively, we have demonstrated for the first time the feasibility of using a microfluidic chip system with continuous flow for the differentiation and extended culture of functional steroidogenic stem cell-derived EBs, the differentiation of EBs into cells expressing ovarian antigens in a microfluidic system, and the ability to cryopreserve this system with restoration of growth and functionality on thawing. These results present a platform for the development of a new therapeutic system for personalized medicine.

Enzyme-free passage of human pluripotent stem cells by controlling divalent cations

Enzymes used for passaging human pluripotent stem cells (hPSCs) digest cell surface proteins, resulting in cell damage. Moreover, cell dissociation using divalent cation-free solutions causes apoptosis. Here we report that Mg²⁺ and Ca²⁺ control cell-fibronectin and cell-cell binding of hPSCs, respectively, under feeder- and serum-free culture conditions without enzyme. The hPSCs were detached from fibronectin-, vitronectin- or laminin-coated dishes in low concentrations of Mg²⁺ and remained as large colonies in high concentrations of Ca²⁺. Using enzyme-free solutions containing Ca²⁺ without Mg²⁺, we successfully passaged hPSCs as large cell clumps that showed less damage than cells passaged using a divalent cation-free solution or dispase. Under the same conditions, the undifferentiated and early-differentiated cells could also be harvested as a cell sheet without being split off. Our enzyme-free passage of hPSCs under a serum- and feeder-free culture condition reduces cell damage and facilitates easier and safer cultures of hPSCs.

Control of adhesion of human induced pluripotent stem cells to plasma-patterned polydimethylsiloxane coated with vitronectin and γ-globulin

Human induced pluripotent stem cells (hiPSCs) are a promising source of cells for medical applications. Recently, the development of polydimethylsiloxane (PDMS) microdevices to control the microenvironment of hiPSCs has been extensively studied. PDMS surfaces are often treated with low-pressure air plasma to facilitate protein adsorption and cell adhesion. However, undefined molecules present in the serum and extracellular matrix used to culture cells complicate the study of cell adhesion. Here, we studied the effects of vitronectin and γ-globulin on hiPSC adhesion to plasma-treated and untreated PDMS surfaces under defined culture conditions. We chose these proteins because they have opposite properties: vitronectin mediates hiPSC attachment to hydrophilic siliceous surfaces, whereas γ-globulin is adsorbed by hydrophobic surfaces and does not mediate cell adhesion. Immunostaining showed that, when applied separately, vitronectin and γ-globulin were adsorbed by both plasma-treated and untreated PDMS surfaces. In contrast, when PDMS surfaces were exposed to a mixture of the two proteins, vitronectin was preferentially adsorbed onto plasma-treated surfaces, whereas γ-globulin was adsorbed onto untreated surfaces. Human iPSCs adhered to the vitronectin-rich plasma-treated surfaces but not to the γ-globulin-rich untreated surfaces. On the basis of these results, we used perforated masks to prepare plasma-patterned PDMS substrates, which were then used to pattern hiPSCs. The patterned hiPSCs expressed undifferentiated-cell markers and did not escape from the patterned area for at least 7 days. The patterned PDMS could be stored for up to 6 days before hiPSCs were plated. We believe that our results will be useful for the development of hiPSC microdevices.