Contractile force measurement of human induced pluripotent stem cell-derived cardiac cell sheet-tissue

Cardiac Tissue Engineering for Translational Cardiology: From In Vitro Models to Regenerative Therapies

Cardiovascular diseases (CVD) are the primary cause of death and disability around the world. Over the past decades, several conventional model systems based on two-dimensional (3D) monolayer cultures or experimental animals have been adopted to dissect and understand heart diseases in order to develop treatment modalities. However, traditional models exhibit several limitations in recapitulating human-specific key physiological and pathological characteristics, which highlights the necessity of developing physiologically relevant models. In recent years, tissue engineering approaches have been extensively employed to generate revolutionary three-dimensional (3D) cardiac models. In particular, the combined use of various bioengineering strategies and cellular reprogramming approaches has facilitated the development of various models. This review presents an overview of different approaches (bioprinting, scaffolding, and electrospinning) for creating bioengineered cardiac tissue models. Next, a broad survey of recent research related to the modeling of various cardiac diseases is presented. Finally, current challenges and future directions are proposed to foster further developments in the field of cardiac tissue engineering.

One-step fabrication of 3D-aligned human skeletal muscle tissue and measurement of contractile force for preclinical drug testing

Human muscle tissue models are critical to understanding the complex physiology of skeletal muscle in studies of drug discovery, development, and toxicity profiling in the human body. However, due to the challenges in in vitro maturation of human muscle cells, few research groups developing their own tissue engineering techniques have succeeded in producing contractile human muscle tissues. Moreover, a more sophisticated method is necessary to measure contractile forces generated by the muscle tissues for preclinical studies in muscle physiology and drug discovery. Although a few research groups have established their own tissue model systems that measure contractile force, they require multi-step fabrication processes to produce human muscle tissues sufficiently functional to be able to measure the contractile forces. To improve the usability of our tissue model system, this study focused on simplifying the tissue engineering approach to produce a practical muscle tissue model. In this study, muscle satellite cells were simply mixed with a combination of fibrinogen, thrombin, and Matrigel before gel formation. The presence of muscle satellite cells induces gel compaction and spontaneously induces unidirectional stretching of the gel, resulting in the muscle satellite cells being aligned three-dimensionally with the direction of stretching. Furthermore, this gel environment promotes the maturation of the human muscle progenitor cells into aligned myofibers, also provides the tissue with an elastic platform for muscle contraction, and allows the attachment of the muscle tissue to a device for measurement of contractile force. Therefore, this one-step tissue fabrication allowed us to produce 3D-aligned human muscle tissues and this tissue model is ready to use for the measurement of contractile forces. In fact, the muscle contractions created by electrical and chemical stimulation were quantitatively determined using our measurement system. In addition, the impact of some representative drugs on this muscle tissue were able to be monitored in real-time throughout the changes in contractile forces. In conclusion, our tissue model system, produced by a simple fabrication method, can be used for preclinical in vitro studies in muscle physiology and drug discovery.

FORCETRACKER: A versatile tool for standardized assessment of tissue contractile properties in 3D Heart-on-Chip platforms

Engineered heart tissues (EHTs) have shown great potential in recapitulating tissue organization, functions, and cell-cell interactions of the human heart in vitro. Currently, multiple EHT platforms are used by both industry and academia for different applications, such as drug discovery, disease modelling, and fundamental research. The tissues' contractile force, one of the main hallmarks of tissue function and maturation level of cardiomyocytes, can be read out from EHT platforms by optically tracking the movement of elastic pillars induced by the contractile tissues. However, existing optical tracking algorithms which focus on calculating the contractile force are customized and platform-specific, often not available to the broad research community, and thus hamper head-to-head comparison of the model output. Therefore, there is the need for robust, standardized and platform-independent software for tissues' force assessment. To meet this need, we developed ForceTracker: a standalone and computationally efficient software for analyzing contractile properties of tissues in different EHT platforms. The software uses a shape-detection algorithm to single out and track the movement of pillars' tips for the most common shapes of EHT platforms. In this way, we can obtain information about tissues' contractile performance. ForceTracker is coded in Python and uses a multi-threading approach for time-efficient analysis of large data sets in multiple formats. The software efficiency to analyze circular and rectangular pillar shapes is successfully tested by analyzing different format videos from two EHT platforms, developed by different research groups. We demonstrate robust and reproducible performance of the software in the analysis of tissues over time and in various conditions. ForceTracker's detection and tracking shows low sensitivity to common incidental defects, such as alteration of tissue shape or air bubbles. Detection accuracy is determined via comparison with manual measurements using the software ImageJ. We developed ForceTracker as a tool for standardized analysis of contractile performance in EHT platforms to facilitate research on disease modeling and drug discovery in academia and industry.

Rapid Video Analysis for Contraction Synchrony of Human Induced Pluripotent Stem Cells-Derived Cardiac Tissues

BACKGROUND

The contraction behaviors of cardiomyocytes (CMs), especially contraction synchrony, are crucial factors reflecting their maturity and response to drugs. A wider field of view helps to observe more pronounced synchrony differences, but the accompanied greater computational load, requiring more computing power or longer computational time.

METHODS

We proposed a method that directly correlates variations in optical field brightness with cardiac tissue contraction status (CVB method), based on principles from physics and photometry, for rapid video analysis in wide field of view to obtain contraction parameters, such as period and contraction propagation direction and speed.

RESULTS

Through video analysis of human induced pluripotent stem cell (hiPSC)-derived CMs labeled with green fluorescent protein (GFP) cultured on aligned and random nanofiber scaffolds, the CVB method was demonstrated to obtain contraction parameters and quantify the direction and speed of contraction within regions of interest (ROIs) in wide field of view. The CVB method required less computation time compared to one of the contour tracking methods, the Lucas-Kanade (LK) optical flow method, and provided better stability and accuracy in the results.

CONCLUSION

This method has a smaller computational load, is less affected by motion blur and out-of-focus conditions, and provides a potential tool for accurate and rapid analysis of cardiac tissue contraction synchrony in wide field of view without the need for more powerful hardware.

Induction of cardiac alternans in human iPS-derived cardiomyocytes through β-adrenergic receptor stimulation

Cardiac alternans (C-ALT) is a phenomenon of alternating strong and weak contractions in the heart and is considered a risk factor for the development of heart failure and arrhythmias. However, no model has been reported that can induce C-ALT in vitro using human cells, and the developmental mechanism of C-ALT has not been studied using human cells. In this study, we successfully induced C-ALT in vitro using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). By stimulating β-adrenergic receptor with isoproterenol on hiPSC-CMs cultured in atmospheric condition (with ~0.04% CO2), contractility and calcium transient were observed to alternately increase and decrease with each beat. In contrast, C-ALT was not induced in hiPSC-CMs cultured at 5% CO2 concentration. Since previous studies have linked C-ALT to problems with calcium regulation in the sarcoplasmic reticulum (SR), we exposed hiPSC-CMs to compounds that alter SR Ca2+ loading and analyzed their contractile responses. The results showed that exposure to verapamil, thapsigargin, and ryanodine either suppressed or eliminated C-ALT. In contrast, omecamtiv mecarbil and blebbistatin, which alter contractility without SR Ca2+ loading, did not induce or suppress C-ALT. These results suggest that C-ALT in hiPSC-CMs induced by isoproterenol may be due to abnormal regulation of the ryanodine receptor's opening and closing caused by excessive Ca2+ load in the SR from β-adrenergic receptor stimulation.

Design of an Innovative Method for Measuring the Contractile Behavior of Engineered Tissues

Hypertrophic scarring is a common complication in severely burned patients who undergo autologous skin grafting. Meshed skin grafts tend to contract during wound healing, increasing the risk of pathological scarring. Although various technologies have been used to study cellular contraction, current methods for measuring contractile forces at the tissue level are limited and do not replicate the complexity of native tissues. Self-assembled skin substitutes (SASSs) were developed at the "Centre de recherche en organogénèse expérimentale de l'Université Laval/LOEX" and are used as permanent full-thickness skin grafts. The autologous skin substitutes are produced using the self-assembly method, allowing the cultured cells to produce their extracellular matrix leading to a tissue-engineered substitute resembling the native skin. The level of contraction of the SASSs during the fabrication process is patient-dependent. Thus, because of its architecture and composition, SASS is an interesting model to study skin contraction in vitro. Unfortunately, standard measurement methods are unsuited for SASS contraction assessment, mainly due to incompatibilities between the SASS manufacturing process and the current contraction force measurement methods. Here, we present an innovative contraction measurement method specifically designed to quantify the contractile behavior of tissue-engineered substitutes, without disrupting the protocol of production. The method uses C-shape anchoring frames that close at different speeds and magnitudes according to the tissue contractile behavior. A finite element analysis model is then used to associate the frame deformation to a contractile force amplitude. This article shows that the method can be used to measure the contraction force of tissues produced with cells displaying different contractile properties, such as primary skin fibroblasts and myofibroblasts. It can also be used to study the effects of cell culture conditions on tissue contraction, such as serum concentration. This protocol can be easily and affordably applied and tuned to many regenerative medicine applications or contraction-related pathological studies. Impact Statement The protocol presented in this article is a new and simple method to quantify contraction forces present in tissue-engineered substitutes. Using finite element analysis, it allows for the measurement of a contraction force rather than a surface reduction as usually provided by other tissue contraction measurement methods. The results shown are in correlation with the current literature relevant to tissue contraction. It can be easily implemented, and hence, this method will open up new avenues to study tissue contraction of living substitutes engineered with various cell types and to optimize culture conditions.

Advances in the design, generation, and application of tissue-engineered myocardial equivalents

Due to the limited regenerative ability of cardiomyocytes, the disabling irreversible condition of myocardial failure can only be treated with conservative and temporary therapeutic approaches, not able to repair the damage directly, or with organ transplantation. Among the regenerative strategies, intramyocardial cell injection or intravascular cell infusion should attenuate damage to the myocardium and reduce the risk of heart failure. However, these cell delivery-based therapies suffer from significant drawbacks and have a low success rate. Indeed, cardiac tissue engineering efforts are directed to repair, replace, and regenerate native myocardial tissue function. In a regenerative strategy, biomaterials and biomimetic stimuli play a key role in promoting cell adhesion, proliferation, differentiation, and neo-tissue formation. Thus, appropriate biochemical and biophysical cues should be combined with scaffolds emulating extracellular matrix in order to support cell growth and prompt favorable cardiac microenvironment and tissue regeneration. In this review, we provide an overview of recent developments that occurred in the biomimetic design and fabrication of cardiac scaffolds and patches. Furthermore, we sift in vitro and in situ strategies in several preclinical and clinical applications. Finally, we evaluate the possible use of bioengineered cardiac tissue equivalents as in vitro models for disease studies and drug tests.

Cardiac cell sheet engineering for regenerative medicine and tissue modeling

Stem cell biology and tissue engineering are essential techniques for cardiac tissue construction. We have succeeded in fabricating human cardiac tissue using the mass production technology of human iPS cell-derived cardiomyocytes and cell sheet engineering, and we are developing regenerative medicine and tissue models to apply this tissue to heart disease research. Cardiac tissue fabrication and tissue functional evaluation technologies for contractile and electrophysiological function are indispensable, which lead to the functional improvement of bioengineered human cardiac tissue.

Membrane Remodeling of Human-Engineered Cardiac Tissue by Chronic Electric Stimulation

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) show immature features, but these are improved by integration into 3D cardiac constructs. In addition, it has been demonstrated that physical manipulations such as electrical stimulation (ES) are highly effective in improving the maturation of human-engineered cardiac tissue (hECT) derived from hiPSC-CMs. Here, we continuously applied an ES in capacitive coupling configuration, which is below the pacing threshold, to millimeter-sized hECTs for 1-2 weeks. Meanwhile, the structural and functional developments of the hECTs were monitored and measured using an array of assays. Of particular note, a nanoscale imaging technique, scanning ion conductance microscopy (SICM), has been used to directly image membrane remodeling of CMs at different locations on the tissue surface. Periodic crest/valley patterns with a distance close to the sarcomere length appeared on the membrane of CMs near the edge of the tissue after ES, suggesting the enhanced transverse tubulation network. The SICM observation is also supported by the fluorescence images of the transverse tubulation network and α-actinin. Correspondingly, essential cardiac functions such as calcium handling and contraction force generation were improved. Our study provides evidence that chronic subthreshold ES can still improve the structural and functional developments of hECTs.

Engineered Human Muscle Tissue from Multilayered Aligned Myofiber Sheets for Studies of Muscle Physiology and Predicting Drug Response

In preclinical drug testing, human muscle tissue models are critical to understanding the complex physiology, including drug effects in the human body. This study reports that a multilayering approach to cell sheet-based engineering produces an engineered human muscle tissue with sufficient contractile force suitable for measurement. A thermoresponsive micropatterned substrate regulates the biomimetic alignment of myofiber structures enabling the harvest of the aligned myofibers as a single cell sheet. The functional muscle tissue is produced by layering multiple myofiber sheets on a fibrin-based gel. This gel environment promotes myofiber maturation, provides the tissue an elastic platform for contraction, and allows the attachment of a measurement device. Since this multilayering approach is effective in enhancing the contractile ability of the muscle tissue, this muscle tissue generates a significantly high contractile force that can be measured quantitatively. The multilayered muscle tissue shows unidirectional contraction from electrical and chemical stimulation. In addition, their physiological responses to representative drugs can be determined quantitatively in real time by changes in contractile force and fatigue resistance. These physiological properties indicate that the engineered muscle tissue can become a promising tissue model for preclinical in vitro studies in muscle physiology and drug discovery.

Macromolecular crowding facilitates rapid fabrication of intact, robust cell sheets

OBJECTIVES

To develop a rapid and simple method to fabricate intact, robust cell sheets from common cell culture dishes by combination of a macromolecular crowding (MMC) reagent and vitamin C.

RESULTS

It was found that 3T3 fibroblasts or human bone marrow mesenchymal stem cells (hBMSCs) and their secreted cell derived extracellular matrices could be easily detached as intact cell sheets under gently pipetting after treated by MMC and vitamin C for 4 days. This method also allowed fabrication of functional multi-layered hepatic cell sheets by culturing 10 × 10⁴ cells/cm² HepG2 cells on top of confluent 3T3 fibroblast layers. What's more, MMC induced hBMSC cell sheets demonstrated 1.9 times larger area and 1.6 times greater cell number than that of cell sheets harvested from temperature-responsive cell culture dishes.

CONCLUSION

MMC based method make it possible to fabricate various types of cell sheets more conveniently, economically, and thus may facilitate wide application of cell sheet technology.

Development of appropriate fatty acid formulations to raise the contractility of constructed myocardial tissues

Introduction

Methods

Results

Conclusions

Integrins Increase Sarcoplasmic Reticulum Activity for Excitation-Contraction Coupling in Human Stem Cell-Derived Cardiomyocytes

Engagement of the sarcoplasmic reticulum (SR) Ca2+ stores for excitation-contraction (EC)-coupling is a fundamental feature of cardiac muscle cells. Extracellular matrix (ECM) proteins that form the extracellular scaffolding supporting cardiac contractile activity are thought to play an integral role in the modulation of EC-coupling. At baseline, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) show poor utilisation of SR Ca2+ stores, leading to inefficient EC-coupling, like developing or human CMs in cardiac diseases such as heart failure. We hypothesised that integrin ligand-receptor interactions between ECM proteins and CMs recruit the SR to Ca2+ cycling during EC-coupling. hiPSC-CM monolayers were cultured on fibronectin-coated glass before 24 h treatment with fibril-forming peptides containing the integrin-binding tripeptide sequence arginine-glycine-aspartic acid (2 mM). Micropipette application of 40 mM caffeine in standard or Na+/Ca2+-free Tyrode's solutions was used to assess the Ca2+ removal mechanisms. Microelectrode recordings were conducted to analyse action potentials in current-clamp. Confocal images of labelled hiPSC-CMs were analysed to investigate hiPSC-CM morphology and ultrastructural arrangements in Ca2+ release units. This study demonstrates that peptides containing the integrin-binding sequence arginine-glycine-aspartic acid (1) abbreviate hiPSC-CM Ca2+ transient and action potential duration, (2) increase co-localisation between L-type Ca2+ channels and ryanodine receptors involved in EC-coupling, and (3) increase the rate of SR-mediated Ca2+ cycling. We conclude that integrin-binding peptides induce recruitment of the SR for Ca2+ cycling in EC-coupling through functional and structural improvements and demonstrate the importance of the ECM in modulating cardiomyocyte function in physiology.

The Development of an Innovative Embedded Sensor for the Optical Measurement of Ex-Vivo Engineered Muscle Tissue Contractility

Tissue engineering is a multidisciplinary approach focused on the development of innovative bioartificial substitutes for damaged organs and tissues. For skeletal muscle, the measurement of contractile capability represents a crucial aspect for tissue replacement, drug screening and personalized medicine. To date, the measurement of engineered muscle tissues is rather invasive and not continuous. In this context, we proposed an innovative sensor for the continuous monitoring of engineered-muscle-tissue contractility through an embedded technique. The sensor is based on the calibrated deflection of one of the engineered tissue's supporting pins, whose movements are measured using a noninvasive optical method. The sensor was calibrated to return force values through the use of a step linear motor and a micro-force transducer. Experimental results showed that the embedded sensor did not alter the correct maturation of the engineered muscle tissue. Finally, as proof of concept, we demonstrated the ability of the sensor to capture alterations in the force contractility of the engineered muscle tissues subjected to serum deprivation.

Myocardial infarction from a tissue engineering and regenerative medicine point of view: A comprehensive review on models and treatments

In the modern world, myocardial infarction is one of the most common cardiovascular diseases, which are responsible for around 18 million deaths every year or almost 32% of all deaths. Due to the detrimental effects of COVID-19 on the cardiovascular system, this rate is expected to increase in the coming years. Although there has been some progress in myocardial infarction treatment, translating pre-clinical findings to the clinic remains a major challenge. One reason for this is the lack of reliable and human representative healthy and fibrotic cardiac tissue models that can be used to understand the fundamentals of ischemic/reperfusion injury caused by myocardial infarction and to test new drugs and therapeutic strategies. In this review, we first present an overview of the anatomy of the heart and the pathophysiology of myocardial infarction, and then discuss the recent developments on pre-clinical infarct models, focusing mainly on the engineered three-dimensional cardiac ischemic/reperfusion injury and fibrosis models developed using different engineering methods such as organoids, microfluidic devices, and bioprinted constructs. We also present the benefits and limitations of emerging and promising regenerative therapy treatments for myocardial infarction such as cell therapies, extracellular vesicles, and cardiac patches. This review aims to overview recent advances in three-dimensional engineered infarct models and current regenerative therapeutic options, which can be used as a guide for developing new models and treatment strategies.

Engineering stem cell therapeutics for cardiac repair

Cardiovascular disease is the leading cause of death in the world. Stem cell-based therapies have been widely investigated for cardiac regeneration in patients with heart failure or myocardial infarction (MI) and surged ahead on multiple fronts over the past two decades. To enhance cellular therapy for cardiac regeneration, numerous engineering techniques have been explored to engineer cells, develop novel scaffolds, make constructs, and deliver cells or their derivatives. This review summarizes the state-of-art stem cell-based therapeutics for cardiac regeneration and discusses the emerged bioengineering approaches toward the enhancement of therapeutic efficacy of stem cell therapies in cardiac repair. We cover the topics in stem cell source and engineering, followed by stem cell-based therapies such as cell aggregates and cell sheets, and biomaterial-mediated stem cell therapies such as stem cell delivery with injectable hydrogel, three-dimensional scaffolds, and microneedle patches. Finally, we discuss future directions and challenges of engineering stem cell therapies for clinical translation.

In vitro circulation model driven by tissue-engineered dome-shaped cardiac tissue

The heart is an essential organ for animals and humans. With the increased availability of pluripotent stem cells, the use of three-dimensional cardiac tissues consisting of cultured cardiomyocytes in in vitro drug evaluation has been widely studied. Several models have been proposed for the realization of the pump function, which is the original function of the heart. However, there are no models that simulate the human circulatory system using cultured cardiac tissue. This study shows that a dome-shaped cardiac tissue fabricated using the cell sheet stacking technique can achieve a heart-like pump function and circulate culture medium, there by mimicking the human circulatory system. Firstly, human induced pluripotent stem cells were differentiated into autonomously beating cardiomyocytes, and cardiomyocyte cell sheets were created using temperature-responsive culture dishes. A cardiomyocyte sheet and a human dermal fibroblast sheet were stacked using a cell sheet manipulator. This two-layered cell sheet was then inflated to create a dome-shaped cardiac tissue with a base diameter of 8 mm. The volume of the dome-shaped cardiac tissue changed according to the autonomous beating. The stroke volume increased with the culture period and reached 21 ± 8.9 μL (n = 6) on day 21. It also responded to β-stimulant and extracellular calcium concentrations. Internal pressure fluctuations were also recorded under isovolumetric conditions by dedicated culture devices. The peak heights of pulsatile pressure were 0.33 ± 0.048 mmHg (n = 3) under a basal pressure of 0.5 mmHg on day 19. When the tissue was connected to a flow path that had check valves applied, it drove a directional flow with an average flow rate of approximately 1 μL/s. Furthermore, pressure-volume (P-V) diagrams were created from the simultaneous measurement of changes in pressure and volume under three conditions of fluidic resistance. In conclusion, this cardiac model can potentially be used for biological pumps that drive multi-organ chips and for more accurate in vitro drug evaluation using P-V diagrams.

Contractility analysis of human engineered 3D heart tissues by an automatic tracking technique using a standalone application

The use of Engineered Heart Tissues (EHT) as in vitro model for disease modeling and drug screening has increased, as they provide important insight into the genetic mechanisms, cardiac toxicity or drug responses. Consequently, this has highlighted the need for a standardized, unbiased, robust and automatic way to analyze hallmark physiological features of EHTs. In this study we described and validated a standalone application to analyze physiological features of EHTs in an automatic, robust, and unbiased way, using low computational time. The standalone application “EHT Analysis” contains two analysis modes (automatic and manual) to analyzes the contractile properties and the contraction kinetics of EHTs from high speed bright field videos. As output data, the graphs of displacement, contraction force and contraction kinetics per file will be generated together with the raw data. Additionally, it also generates a summary file containing all the data from the analyzed files, which facilitates and speeds up the post analysis. From our study we highlight the importance of analyzing the axial stress which is the force per surface area (μN/mm²). This allows to have a readout overtime of tissue compaction, axial stress and leave the option to calculate at the end point of an experiment the physiological cross-section area (PSCA). We demonstrated the utility of this tool by analyzing contractile properties and compaction over time of EHTs made out of a double reporter human pluripotent stem cell (hPSC) line (NKX2.5^EGFP/+-COUP-TFII^mCherry/+) and different ratios of human adult cardiac fibroblasts (HCF). Our standalone application “EHT Analysis” can be applied for different studies where the physiological features of EHTs needs to be analyzed under the effect of a drug compound or in a disease model.

Functional Evaluation of Human Bioengineered Cardiac Tissue Using iPS Cells Derived from a Patient with Lamin Variant Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is caused by various gene variants and characterized by systolic dysfunction. Lamin variants have been reported to have a poor prognosis. Medical and device therapies are not sufficient to improve the prognosis of DCM with the lamin variants. Recently, induced pluripotent stem (iPS) cells have been used for research on genetic disorders. However, few studies have evaluated the contractile function of cardiac tissue with lamin variants. The aim of this study was to elucidate the function of cardiac cell sheet tissue derived from patients with lamin variant DCM. iPS cells were generated from a patient with lamin A/C (LMNA) -mutant DCM (LMNA p.R225X mutation). After cardiac differentiation and purification, cardiac cell sheets that were fabricated through cultivation on a temperature-responsive culture dish were transferred to the surface of the fibrin gel, and the contractile force was measured. The contractile force and maximum contraction velocity, but not the maximum relaxation velocity, were significantly decreased in cardiac cell sheet tissue with the lamin variant. A qRT-PCR analysis revealed that mRNA expression of some contractile proteins, cardiac transcription factors, Ca²⁺-handling genes, and ion channels were downregulated in cardiac tissue with the lamin variant.Human iPS-derived bioengineered cardiac tissue with the LMNA p.R225X mutation has the functional properties of systolic dysfunction and may be a promising tissue model for understanding the underlying mechanisms of DCM.

Systems for the functional evaluation of human heart tissues derived from pluripotent stem cells

Human pluripotent stem cells (hPSCs) are expected to be a promising cell source in regenerative medicine and drug discovery for the treatment of various intractable diseases. An approach for creating a three-dimensional (3D) structure from hPSCs that mimics human cardiac tissue functions has made it theoretically possible to conduct drug discovery and cardiotoxicity tests by assessing pharmacological responses in human cardiac tissues by a screening system using a compound library. The myocardium functions as a tissue composed of organized vascular networks, supporting stromal cells and cardiac muscle cells. Considering this, the reconstruction of tissue structure by various cells of cardiovascular lineages, such as vascular cells and cardiac muscle cells, is desirable for the ideal conformation of hPSC-derived cardiac tissues. Heart-on-a-chip, an organ-on-a-chip system to evaluate the physiological pump function of 3D cardiac tissues might hold promise in medical researches such as drug discovery and regenerative medicine. Here, we review various modalities to evaluate the function of human stem cell-derived cardiac tissues and introduce heart-on-a-chip systems that can recapitulate physiological parameters of hPSC-derived cardiac tissues.

Rat-Induced Pluripotent Stem Cells-Derived Cardiac Myocytes in a Cell Culture Dish

Induced pluripotent stem (iPS) cells are genetically reprogrammed somatic cells that exhibit embryonic stem cell-like characteristics such as self-renewal and pluripotency. These cells have broad differentiation capability to convert into diverse cell types that make up the primary germ layers during embryonic development. iPS cells can spontaneously differentiate and form cell aggregates termed embryoid bodies (EBs) in the absence of differentiation inhibitory factors. Unlike other methods used to generate EBs, "the hanging drop" method offers reproducibility and homogeneity from a set number of iPS cells. As such, we describe the differentiation of rat-induced pluripotent stem cells into cardiac myocytes in vitro using the hanging drop method. Both the confirmation and identification of the cardiac myocytes are done using immunocytochemistry, RT-PCR, Western Blot, and Flow Cytometry. Briefly, a specific number of iPS cells are placed in droplets on the lid of culture dishes and incubated for 2 days, yielding embryoid bodies, which are suspended and plated. Spontaneous beating of cardiomyocytes can be seen 7-14 days after the plating of EBs and specific cardiac markers can be observed through identification assays.

Defined Engineered Human Myocardium for Disease Modeling, Drug Screening, and Heart Repair

Different engineered heart muscle formats have been developed for applications in disease modeling, drug screening, and heart repair. The advantage of 3D engineered versus 2D monolayer and 3D aggregate cardiomyocyte cultures is a clearly advanced degree of maturation, which in many aspects resembles the postnatal rather than the embryonic or fetal heart, in the most advanced 3D culture formats. According to the desired in vitro (disease modeling or drug screening) and in vivo (heart repair) application, scale and geometry of tissue engineered heart muscle must be adapted. In this updated methods paper, we report a simple and scalable (up and down) collagen-based protocol for the construction of Engineered Human Myocardium (EHM) under defined, serum-free conditions.

Aligned human induced pluripotent stem cell-derived cardiac tissue improves contractile properties through promoting unidirectional and synchronous cardiomyocyte contraction

Alignment, as seen in the native myocardium, is crucial for the fabrication of functional cardiac tissue. However, it remains unclear whether the control of cardiomyocyte alignment influences cardiac function and the underlying mechanisms. We fabricated aligned human cardiac tissue using a micro-processed fibrin gel with inverted V-shaped ridges (MFG) and elucidated the effect of alignment control on contractile properties. When human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were seeded on MFG, hiPSC-CMs were aligned more uniformly than the control, and we succeeded in fabricating the aligned cardiac tissue. Assessing the contractile properties with the direct contractile measurement system, the contractile force, maximum contractile velocity, and relaxation velocity were significantly increased in aligned cardiac tissue compared with non-aligned cardiac tissue. However, gene expression profiles were not different between the two groups, suggesting that functional improvement of cardiac tissue through alignment control might not be dependent on cardiomyocyte maturation. Motion capture analysis revealed that the cardiomyocytes in the aligned cardiac tissues showed more unidirectional and synchronous contraction than the non-aligned cardiac tissues, indicating that cardiac tissue maturation involves electrical integration of cardiomyocytes. Herein, cardiomyocyte alignment control might improve the contractile properties of cardiac tissue through promoting unidirectional and synchronous cardiomyocyte contraction.

Recent advances on bioengineering approaches for fabrication of functional engineered cardiac pumps: A review

The field of cardiac tissue engineering has advanced over the past decades; however, most research progress has been limited to engineered cardiac tissues (ECTs) at the microscale with minimal geometrical complexities such as 3D strips and patches. Although microscale ECTs are advantageous for drug screening applications because of their high-throughput and standardization characteristics, they have limited translational applications in heart repair and the in vitro modeling of cardiac function and diseases. Recently, researchers have made various attempts to construct engineered cardiac pumps (ECPs) such as chambered ventricles, recapitulating the geometrical complexity of the native heart. The transition from microscale ECTs to ECPs at a translatable scale would greatly accelerate their translational applications; however, researchers are confronted with several major hurdles, including geometrical reconstruction, vascularization, and functional maturation. Therefore, the objective of this paper is to review the recent advances on bioengineering approaches for fabrication of functional engineered cardiac pumps. We first review the bioengineering approaches to fabricate ECPs, and then emphasize the unmatched potential of 3D bioprinting techniques. We highlight key advances in bioprinting strategies with high cell density as researchers have begun to realize the critical role that the cell density of non-proliferative cardiomyocytes plays in the cell-cell interaction and functional contracting performance. We summarize the current approaches to engineering vasculatures both at micro- and meso-scales, crucial for the survival of thick cardiac tissues and ECPs. We showcase a variety of strategies developed to enable the functional maturation of cardiac tissues, mimicking the in vivo environment during cardiac development. By highlighting state-of-the-art research, this review offers personal perspectives on future opportunities and trends that may bring us closer to the promise of functional ECPs.

Possible Treatment of Myocardial Infarct Based on Tissue Engineering Using a Cellularized Solid Collagen Scaffold Functionalized with Arg-Glyc-Asp (RGD) Peptide

Currently, the clinical impact of cell therapy after a myocardial infarction (MI) is limited by low cell engraftment due to low cell retention, cell death in inflammatory and poor angiogenic infarcted areas, secondary migration. Cells interact with their microenvironment through integrin mechanoreceptors that control their survival/apoptosis/differentiation/migration and proliferation. The association of cells with a three-dimensional material may be a way to improve interactions with their integrins, and thus outcomes, especially if preparations are epicardially applied. In this review, we will focus on the rationale for using collagen as a polymer backbone for tissue engineering of a contractile tissue. Contractilities are reported for natural but not synthetic polymers and for naturals only for: collagen/gelatin/decellularized-tissue/fibrin/Matrigel™ and for different material states: hydrogels/gels/solids. To achieve a thick/long-term contractile tissue and for cell transfer, solid porous compliant scaffolds are superior to hydrogels or gels. Classical methods to produce solid scaffolds: electrospinning/freeze-drying/3D-printing/solvent-casting and methods to reinforce and/or maintain scaffold properties by reticulations are reported. We also highlight the possibility of improving integrin interaction between cells and their associated collagen by its functionalizing with the RGD-peptide. Using a contractile patch that can be applied epicardially may be a way of improving ventricular remodeling and limiting secondary cell migration.

An organic transistor matrix for multipoint intracellular action potential recording

Electrode arrays are widely used for multipoint recording of electrophysiological activities, and organic electronics have been utilized to achieve both high performance and biocompatibility. However, extracellular electrode arrays record the field potential instead of the membrane potential itself, resulting in the loss of information and signal amplitude. Although much effort has been dedicated to developing intracellular access methods, their three-dimensional structures and advanced protocols prohibited implementation with organic electronics. Here, we show an organic electrochemical transistor (OECT) matrix for the intracellular action potential recording. The driving voltage of sensor matrix simultaneously causes electroporation so that intracellular action potentials are recorded with simple equipment. The amplitude of the recorded peaks was larger than that of an extracellular field potential recording, and it was further enhanced by tuning the driving voltage and geometry of OECTs. The capability of miniaturization and multiplexed recording was demonstrated through a 4 × 4 action potential mapping using a matrix of 5- × 5-μm² OECTs. Those features are realized using a mild fabrication process and a simple circuit without limiting the potential applications of functional organic electronics.

Contractile Force Measurement of Engineered Cardiac Tissues Derived from Human iPS Cells

Recent advances in stem cell technologies and tissue engineering are enabling the fabrication of dynamically beating cardiac tissues from human induced pluripotent stem cells. These engineered human cardiac tissues are expected to be used for cardiac regenerative therapies, in vitro drug testing, and pathological investigations. Here we describe the method to fabricate engineered cardiac tissues from human induced pluripotent stem cell-derived cardiomyocytes and to measure the contractile force.

Scaffold-based and scaffold-free cardiac constructs for drug testing

The safety and therapeutic efficacy of new drugs are tested in experimental animals. However, besides being a laborious, costly process, differences in drug responses between humans and other animals and potential cardiac adverse effects lead to the discontinued development of new drugs. Thus, alternative approaches to animal tests are needed. Cardiotoxicity and responses of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to drugs are conventionally evaluated by cell seeding and two-dimensional (2D) culture, which allows measurements of field potential duration and the action potentials of CMs using multielectrode arrays. However, 2D-cultured hiPSC-CMs lack 3D spatial adhesion, and have fewer intercellular and extracellular matrix interactions, as well as different contractile behavior from CMsin vivo. This issue has been addressed using tissue engineering to fabricate three-dimensional (3D) cardiac constructs from hiPSC-CMs culturedin vitro. Tissue engineering can be categorized as scaffold-based and scaffold-free. In scaffold-based tissue engineering, collagen and fibrin gel scaffolds comprise a 3D culture environment in which seeded cells exhibit cardiac-specific functions and drug responses, whereas 3D cardiac constructs fabricated by tissue engineering without a scaffold have high cell density and form intercellular interactions. This review summarizes the characteristics of scaffold-based and scaffold-free cardiac tissue engineering and discusses the applications of fabricated cardiac constructs to drug screening.

Perfusable System Using Porous Collagen Gel Scaffold Actively Provides Fresh Culture Media to a Cultured 3D Tissue

Culturing three-dimensional (3D) tissues with an appropriate microenvironment is a critical and fundamental technology in broad areas of cutting-edge bioengineering research. In addition, many technologies have engineered tissue functions. However, an effective system for transporting nutrients, waste, or oxygen to affect the functions of cell tissues has not been reported. In this study, we introduce a novel system that employs diffusion and convection to enhance transportation. To demonstrate the concept of the proposed system, three layers of normal human dermal fibroblast cell sheets are used as a model tissue, which is cultured on a general dish or porous collagen scaffold with perfusable channels for three days with and without the perfusion of culture media in the scaffold. The results show that the viability of the cell tissue was improved by the developed system. Furthermore, glucose consumption, lactate production, and oxygen transport to the tissues were increased, which might improve the viability of tissues. However, mechanical stress in the proposed system did not cause damage or unintentional functional changes in the cultured tissue. We believe that the introduced culturing system potentially suggests a novel standard for 3D cell cultures.

Next generation of heart regenerative therapies: progress and promise of cardiac tissue engineering

The adult heart is a vital and highly specialized organ of the human body, with limited capability of self-repair and regeneration in case of injury or disease. Engineering biomimetic cardiac tissue to regenerate the heart has been an ambition in the field of tissue engineering, tracing back to the 1990s. Increased understanding of human stem cell biology and advances in process engineering have provided an unlimited source of cells, particularly cardiomyocytes, for the development of functional cardiac muscle, even though pluripotent stem cell-derived cardiomyocytes poorly resemble those of the adult heart. This review outlines key biology-inspired strategies reported to improve cardiomyocyte maturation features and current biofabrication approaches developed to engineer clinically relevant cardiac tissues. It also highlights the potential use of this technology in drug discovery science and disease modeling as well as the current efforts to translate it into effective therapies that improve heart function and promote regeneration.

Genetically modified cell sheets in regenerative medicine and tissue engineering

Genetically modified cell sheet technology is emerging as a promising biomedical tool to deliver therapeutic genes for regenerative medicine and tissue engineering. Virus-based gene transfection and non-viral gene transfection have been used to fabricate genetically modified cell sheets. Preclinical and clinical studies have shown various beneficial effects of genetically modified cell sheets in the regeneration of bone, periodontal tissue, cartilage and nerves, as well as the amelioration of dental implant osseointegration, myocardial infarction, skeletal muscle ischemia and kidney injury. Furthermore, this technology provides a potential treatment option for various hereditary diseases. However, the method has several limitations, such as safety concerns and difficulties in controlling transgene expression. Therefore, recent studies explored efficient and safe gene transfection methods, prolonged and controllable transgene expression and their potential application in personalized and precision medicine. This review summarizes various types of genetically modified cell sheets, preparation procedures, therapeutic applications and possible improvements.

Drawing Inspiration from Developmental Biology for Cardiac Tissue Engineers

A sound understanding of developmental biology is part of the foundation of effective stem cell-derived tissue engineering. Here, the key concepts of cardiac development that are successfully applied in a bioinspired approach to growing engineered cardiac tissues, are reviewed. The native cardiac milieu is studied extensively from embryonic to adult phenotypes, as it provides a resource of factors, mechanisms, and protocols to consider when working toward establishing living tissues in vitro. It begins with the various cell types that constitute the cardiac tissue. It is discussed how myocytes interact with other cell types and their microenvironment and how they change over time from the embryonic to the adult states, with a view on how such changes affect the tissue function and may be used in engineered tissue models. Key embryonic signaling pathways that have been leveraged in the design of culture media and differentiation protocols are presented. The cellular microenvironment, from extracellular matrix chemical and physical properties, to the dynamic mechanical and electrical forces that are exerted on tissues is explored. It is shown that how such microenvironmental factors can inform the design of biomaterials, scaffolds, stimulation bioreactors, and maturation readouts, and suggest considerations for ongoing biomimetic advancement of engineered cardiac tissues and regeneration strategies for the future.

An Optical-Flow-Based Method to Quantify Dynamic Behavior of Human Pluripotent Stem Cell-Derived Cardiomyocytes in Disease Modeling Platforms

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) hold great promise for cardiovascular disease modeling, drug screening and personalized medicine. A crucial requirement to establish an hPSC-CM-based disease model is the availability of a reliable differentiation protocol and a functional assessment of phenotypic properties of CMs in a disease context. Characterization of relative changes in contractile behavior of CMs can provide insight not only about drug effects but into the pathogenesis of cardiovascular diseases. Image-based optical-flow analysis, which applies a speckle tracking algorithm to videomicroscopy of hPSC-CMs, is a noninvasive method to quantitatively assess the dynamics of mechanical contraction of the CMs. This method offers an efficient characterization of contractile cycles. It quantifies contraction velocity field, beat rate, contractile strain and contraction-relaxation strain rate profile, which are important phenotypic characteristics of CMs.

Assessment of human bioengineered cardiac tissue function in hypoxic and re-oxygenized environments to understand functional recovery in heart failure

Introduction

Myocardial recovery is one of the targets for heart failure treatment. A non-negligible number of heart failure with reduced ejection fraction (EF) patients experience myocardial recovery through treatment. Although myocardial hypoxia has been reported to contribute to the progression of heart failure even in non-ischemic cardiomyopathy, the relationship between contractile recovery and re-oxygenation and its underlying mechanisms remain unclear. The present study investigated the effects of hypoxia/re-oxygenation on bioengineered cardiac cell sheets-tissue function and the underlying mechanisms.

Methods

Bioengineered cardiac cell sheets-tissue was fabricated with human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) using temperature-responsive culture dishes. Cardiac tissue functions in the following conditions were evaluated with a contractile force measurement system: continuous normoxia (20% O₂) for 12 days; hypoxia (1% O₂) for 4 days followed by normoxia (20% O₂) for 8 days; or continuous hypoxia (1% O₂) for 8 days. Cell number, sarcomere structure, ATP levels, mRNA expressions and Ca²⁺ transients of hiPSC-CM in those conditions were also assessed.

Results

Hypoxia (4 days) elicited progressive decreases in contractile force, maximum contraction velocity, maximum relaxation velocity, Ca²⁺ transient amplitude and ATP level, but sarcomere structure and cell number were not affected. Re-oxygenation (8 days) after hypoxia (4 days) was associated with progressive increases in contractile force, maximum contraction velocity and relaxation time to the similar extent levels of continuous normoxia group, while maximum relaxation velocity was still significantly low even after re-oxygenation. Ca²⁺ transient magnitude, cell number, sarcomere structure and ATP level after re-oxygenation were similar to those in the continuous normoxia group. Hypoxia/re-oxygenation up-regulated mRNA expression of PLN.

Conclusions

Hypoxia and re-oxygenation condition directly affected human bioengineered cardiac tissue function. Further understanding the molecular mechanisms of functional recovery of cardiac tissue after re-oxygenation might provide us the new insight on heart failure with recovered ejection fraction and preserved ejection fraction.

Considerations for the Bioengineering of Advanced Cardiac In Vitro Models of Myocardial Infarction

Despite the latest advances in cardiovascular biology and medicine, myocardial infarction (MI) remains one of the major causes of deaths worldwide. While reperfusion of the myocardium is critical to limit the ischemic damage typical of a MI event, it causes detrimental morphological and functional changes known as "reperfusion injury." This complex scenario is poorly represented in currently available models of ischemia/reperfusion injury, leading to a poor translation of findings from the bench to the bedside. However, more recent bioengineered in vitro models of the human heart represent more clinically relevant tools to prevent and treat MI in patients. These include 3D cultures of cardiac cells, the use of patient-derived stem cells, and 3D bioprinting technology. This review aims at highlighting the major features typical of a heart attack while comparing current in vitro, ex vivo, and in vivo models. This information has the potential to further guide in developing novel advanced in vitro cardiac models of ischemia/reperfusion injury. It may pave the way for the generation of advanced pathophysiological cardiac models with the potential to develop personalized therapies.

Cardiac Tissues From Stem Cells: New Routes to Maturation and Cardiac Regeneration

The ability of human pluripotent stem cells to form all cells of the body has provided many opportunities to study disease and produce cells that can be used for therapy in regenerative medicine. Even though beating cardiomyocytes were among the first cell types to be differentiated from human pluripotent stem cell, cardiac applications have advanced more slowly than those, for example, for the brain, eye, and pancreas. This is, in part, because simple 2-dimensional human pluripotent stem cell cardiomyocyte cultures appear to need crucial functional cues normally present in the 3-dimensional heart structure. Recent tissue engineering approaches combined with new insights into the dialogue between noncardiomyocytes and cardiomyocytes have addressed and provided solutions to issues such as cardiomyocyte immaturity and inability to recapitulate adult heart values for features like contraction force, electrophysiology, or metabolism. Three-dimensional bioengineered heart tissues are thus poised to contribute significantly to disease modeling, drug discovery, and safety pharmacology, as well as provide new modalities for heart repair. Here, we review the current status of 3-dimensional engineered heart tissues.

Human iPSC-engineered cardiac tissue platform faithfully models important cardiac physiology

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CM) may provide an important bridge between animal models and the intact human myocardium. Fulfilling this potential is hampered by their relative immaturity, leading to poor physiological responsiveness. hiPSC-CMs grown in traditional two-dimensional (2D) culture lack a t-tubular system, have only rudimentary intracellular calcium-handling systems, express predominantly embryonic sarcomeric protein isoforms, and preferentially use glucose as an energy substrate. Culturing hiPSC-CM in a variety of three-dimensional (3D) environments and the addition of nutritional, pharmacological, and electromechanical stimuli have proven, to various degrees, to be beneficial for maturation. We present a detailed assessment of a novel model in which hiPSC-CMs and hiPSC-derived cardiac fibroblasts are cocultured in a 3D fibrin matrix to form engineered cardiac tissue constructs (hiPSC-ECTs). The hiPSC-ECTs are responsive to physiological stimuli, including stretch, frequency, and β-adrenergic stimulation, develop a t-tubular system, and demonstrate calcium-handling and contractile kinetics that compare favorably with ventricular human myocardium. Furthermore, transcript levels of various genes involved in calcium-handling and contraction are increased. These markers of maturation become more robust over a relatively short period of time in culture (6 wk vs. 2 wk in hiPSC-ECTs). A comparison of the hiPSC-ECT molecular and performance variables with those of human cardiac tissue and other available engineered tissue platforms is provided to aid selection of the most appropriate platform for the research question at hand. Important and noteworthy aspects of this human cardiac model system are its reliance on "off-the-shelf" equipment, ability to provide detailed physiological performance data, and the ability to achieve a relatively mature cardiac physiology without additional nutritional, pharmacological, and electromechanical stimuli that may elicit unintended effects on function.NEW & NOTEWORTHY This study seeks to provide an in-depth assessment of contractile performance of human iPSC-derived cardiomyocytes cultured together with fibroblasts in a 3-dimensional-engineered tissue and compares performance both over time as cells mature, and with corresponding measures found in the literature using alternative 3D culture configurations. The suitability of 3D-engineered human cardiac tissues to model cardiac function is emphasized, and data provided to assist in the selection of the most appropriate configuration based on the target application.

Fundamental Technologies and Recent Advances of Cell-Sheet-Based Tissue Engineering

Tissue engineering has attracted significant attention since the 1980s, and the applications of tissue engineering have been expanding. To produce a cell-dense tissue, cell sheet technology has been studied as a promising strategy. Fundamental techniques involving tissue engineering are mainly introduced in this review. First, the technologies to fabricate a cell sheet were reviewed. Although temperature-responsive polymer-based technique was a trigger to establish and spread cell sheet technology, other methodologies for cell sheet fabrication have also been reported. Second, the methods to improve the function of the cell sheet were investigated. Adding electrical and mechanical stimulation on muscle-type cells, building 3D structures, and co-culturing with other cell species can be possible strategies for imitating the physiological situation under in vitro conditions, resulting in improved functions. Finally, culture methods to promote vasculogenesis in the layered cell sheets were introduced with in vivo, ex vivo, and in vitro bioreactors. We believe the present review that shows and compares the fundamental technologies and recent advances for cell-sheet-based tissue engineering should promote further development of tissue engineering. The development of cell sheet technology should promote many bioengineering applications.

Making Cardiomyocytes from Pluripotent Stem Cells

The ability to differentiate pluripotent stem cells to cardiomyocyte lineages (PSC-CMs) has opened the door to new disease models and innovative drug and cell therapies for the heart. Nevertheless, further advances in the differentiation protocols are needed to fulfill the promise of PSC-CMs. Obstacles that remain include deriving PSC-CMs with proper electromechanical properties, coalescing them into functional tissue structures, and manipulating the genome to test the impact mutations have on arrhythmias and other heart disorders. This chapter gives a brief consideration of these challenges and outlines current methodologies that offer partial solutions.

Advances in Multidimensional Cardiac Biosensing Technologies: From Electrophysiology to Mechanical Motion and Contractile Force

Cardiovascular disease is currently a leading killer to human, while drug-induced cardiotoxicity remains the main cause of the withdrawal and attrition of drugs. Taking clinical correlation and throughput into account, cardiomyocyte is perfect as in vitro cardiac model for heart disease modeling, drug discovery, and cardiotoxicity assessment by accurately measuring the physiological multiparameters of cardiomyocytes. Remarkably, cardiomyocytes present both electrophysiological and biomechanical characteristics due to the unique excitation-contraction coupling, which plays a significant role in studying the cardiomyocytes. This review mainly focuses on the recent advances of biosensing technologies for the 2D and 3D cardiac models with three special properties: electrophysiology, mechanical motion, and contractile force. These high-performance multidimensional cardiac models are popular and effective to rebuild and mimic the heart in vitro. To help understand the high-quality and accurate physiologies, related detection techniques are highly demanded, from microtechnology to nanotechnology, from extracellular to intracellular recording, from multiple cells to single cell, and from planar to 3D models. Furthermore, the characteristics, advantages, limitations, and applications of these cardiac biosensing technologies, as well as the future development prospects should contribute to the systematization and expansion of knowledge.

Establishment of a heart-on-a-chip microdevice based on human iPS cells for the evaluation of human heart tissue function

Human iPS cell (iPSC)-derived cardiomyocytes (CMs) hold promise for drug discovery for heart diseases and cardiac toxicity tests. To utilize human iPSC-derived CMs, the establishment of three-dimensional (3D) heart tissues from iPSC-derived CMs and other heart cells, and a sensitive bioassay system to depict physiological heart function are anticipated. We have developed a heart-on-a-chip microdevice (HMD) as a novel system consisting of dynamic culture-based 3D cardiac microtissues derived from human iPSCs and microelectromechanical system (MEMS)-based microfluidic chips. The HMDs could visualize the kinetics of cardiac microtissue pulsations by monitoring particle displacement, which enabled us to quantify the physiological parameters, including fluidic output, pressure, and force. The HMDs demonstrated a strong correlation between particle displacement and the frequency of external electrical stimulation. The transition patterns were validated by a previously reported versatile video-based system to evaluate contractile function. The patterns are also consistent with oscillations of intracellular calcium ion concentration of CMs, which is a fundamental biological component of CM contraction. The HMDs showed a pharmacological response to isoproterenol, a β-adrenoceptor agonist, that resulted in a strong correlation between beating rate and particle displacement. Thus, we have validated the basic performance of HMDs as a resource for human iPSC-based pharmacological investigations.

Establishment of a heart-on-a-chip microdevice based on human iPS cells for the evaluation of human heart tissue function

Human iPS cell (iPSC)-derived cardiomyocytes (CMs) hold promise for drug discovery for heart diseases and cardiac toxicity tests. To utilize human iPSC-derived CMs, the establishment of three-dimensional (3D) heart tissues from iPSC-derived CMs and other heart cells, and a sensitive bioassay system to depict physiological heart function are anticipated. We have developed a heart-on-a-chip microdevice (HMD) as a novel system consisting of dynamic culture-based 3D cardiac microtissues derived from human iPSCs and microelectromechanical system (MEMS)-based microfluidic chips. The HMDs could visualize the kinetics of cardiac microtissue pulsations by monitoring particle displacement, which enabled us to quantify the physiological parameters, including fluidic output, pressure, and force. The HMDs demonstrated a strong correlation between particle displacement and the frequency of external electrical stimulation. The transition patterns were validated by a previously reported versatile video-based system to evaluate contractile function. The patterns are also consistent with oscillations of intracellular calcium ion concentration of CMs, which is a fundamental biological component of CM contraction. The HMDs showed a pharmacological response to isoproterenol, a β-adrenoceptor agonist, that resulted in a strong correlation between beating rate and particle displacement. Thus, we have validated the basic performance of HMDs as a resource for human iPSC-based pharmacological investigations.

Optimizing the Direction and Order of the Motion Unveiled the Ability of Conventional Monolayers of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes to Show Frequency-Dependent Enhancement of Contraction and Relaxation Motion

Contractility of the human heart increases as its beating rate is elevated, so-called positive force-frequency relationship; however, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been reported to exert a negative force-frequency relationship. We tested the hypothesis that the regulation of motion directions by electrical pacing and/or oxygen supply may improve the electro-mechanical properties of hiPSC-CMs monolayers. To better evaluate the spatial and temporal relationship between electrical excitation and contractile motion, we simultaneously observed the field potential and motion vector of hiPSC-CMs sheets. Under spontaneous contraction, although an electrical excitation originating from a region propagated unidirectionally over the cell sheet, contraction wave started from multiple sites, and relaxation wave was initiated from a geometric center of hiPSC-CMs sheet. During electrical pacing, contraction and relaxation waves were propagated from the stimulated site. Interestingly, the maximum contraction speed was more increased when the hiPSC-CMs sheet was stimulated at an area relaxation initiated under spontaneous condition. Furthermore, motion vector analysis demonstrated that "positive contraction velocity-frequency relationship" in contraction and "frequency-dependent enhancement of relaxation" were produced in the cell sheet by optimizing the direction and order of the contractile motion with pacing at the relaxation-initiating area. A close analysis of motion vectors along with field potential recording demonstrated that relaxation process consists of fast and slow phases, and suggest that intracellular Ca²⁺ dynamics may be closely related to functions of Ca²⁺-ATPase pump and Na⁺-Ca²⁺ exchangers. Namely, the slow relaxation phase occurred after the second peak of field potential, suggesting that the slow phase may be associated with extrusion of Ca²⁺ by Na⁺-Ca²⁺ exchangers during repolarization. Increase of oxygen concentration from 20 to 95% as well as β-adrenergic stimulation with isoproterenol accelerated the fast relaxation, suggesting that it could depend on Ca²⁺ uptake via Ca²⁺-ATPase during the depolarization phase. The ratio of maximum contraction speed to field potential duration was increased by the β-adrenergic stimulation, indicating the elevated contraction efficiency per Ca²⁺-influx. Thus, these findings revealed potential ability of conventional monolayers of hiPSC-CMs, which will help apply them to translational study filling the gap between physiological as well as pharmacological studies and clinical practice.

Measuring the Contractile Force of Multilayered Human Cardiac Cell Sheets

Three-dimensional (3D) cardiac tissue reconstruction using tissue engineering technology is a rapidly growing area of regenerative medicine and drug screening development. However, there remains an urgent need for the development of a method capable of accurately measuring the contractile force of physiologically relevant 3D myocardial tissues to facilitate the prediction of human heart tissue drug sensitivity. To this end, our laboratory has developed a novel drug screening model that measures the contractile force of cardiac cell sheets prepared using temperature-responsive culture dishes. To circumvent the difficulties that commonly arise during the stacking of cardiomyocyte sheets, we established a stacking method using centrifugal force, making it possible to measure 3D myocardial tissue. Human induced pluripotent stem cell-derived cardiomyocytes were seeded in a temperature-responsive culture dish and processed into a sheet. The cardiac cell sheets were multilayered to construct 3D cardiac tissue. Measurement of the contractile force and cross-sectional area of the multilayered 3D cardiac tissue were then obtained and used to determine the relationship between the cross-sectional area of the cardiac tissue and its contractile force. The contractile force of the 1-, 3-, and 5-layer tissues increased linearly in proportion to the cross-sectional area. A result of 6.4 mN/mm², accounting for one-seventh of the contractile force found in adult tissue, was obtained. However, with 7-layer tissues, there was a sudden drop in the contractile force, possibly because of limited oxygen and nutrient supply. In conclusion, we established a method wherein the thickness of the cell sheets was controlled through layering, thus enabling accurate evaluation of the cardiac contractile function. This method may enable comparisons with living heart tissue while providing information applicable to regenerative medicine and drug screening models.

Concise Review: Harnessing iPSC-derived Cells for Ischemic Heart Disease Treatment

Ischemic heart disease (IHD) is one of the most common cardiovascular diseases and is the leading cause of death worldwide. Stem cell therapy is a promising strategy to promote cardiac regeneration and myocardial function recovery. Recently, the generation of human induced pluripotent cells (hiPSCs) and their differentiation into cardiomyocytes and vascular cells offer an unprecedented opportunity for the IHD treatment. This review briefly summarizes hiPSCs and their differentiation, and presents the recent advances in hiPSC injection, engineered cardiac patch fabrication, and the application of hiPSC derived extracellular vesicle. Current challenges and further perspectives are also discussed to understand current risks and concerns, identify potential solutions, and direct future clinical trials and applications.