Bioacoustic-enabled patterning of human iPSC-derived cardiomyocytes into 3D cardiac tissue

Comparing fabrication techniques for engineered cardiac tissue

Tissue engineering can provide in vitro models for drug testing, disease modeling, and perhaps someday, tissue/organ replacements. For building 3D heart tissue, the alignment of cardiac cells or cardiomyocytes (CMs) is important in generating a synchronously contracting tissue. To that end, researchers have generated several fabrication methods for building heart tissue, but direct comparisons of pros and cons using the same cell source is lacking. Here, we derived cardiomyocytes (CMs) from human induced pluripotent stem cells (hiPSCs) and compare the assembly of these cells using three fabrication methods: cardiospheres, muscle rings, and muscle strips. All three protocols successfully generated compacted tissue comprised of hiPSC-derived CMs stable for at least 2 weeks. The percentage of aligned cells was greatest in the muscle strip (55%) and the muscle ring (50%) compared with the relatively unaligned cardiospheres (35%). The iPSC-derived CMs within the muscle strip also exhibited the greatest elongation, with elongation factor at 2.0 compared with 1.5 for the muscle ring and 1.2 for the cardiospheres. This is the first direct comparison of various fabrication techniques using the same cell source.

FSTL-1 loaded 3D bioprinted vascular patch regenerates the ischemic heart tissue

Cardiac patch strategies are developed as a promising approach to regenerate the injured heart after myocardial infarction (MI). This study integrated 3D bioprinting and cardioprotective paracrine signaling to fabricate vascular patch devices containing endothelial cells (ECs) and the regenerative follistatin-like 1 (FSTL1) peptide. Engineered patch supported the 3D culture of ECs in both static and dynamic culture, forming a uniform endothelium on the printed channels. Implantation of vascular patch onto a rat model of acute MI resulted in significant reduction of scar formation, left ventricle dilation, and wall thinning, as well as enhanced ejection fraction. Furthermore, increased vascularization and proliferation of cardiomyocytes were observed in hearts treated with patches. These findings highlight the remarkable capacity of 3D bioprinted vascular patch to augment the endogenous regenerative capacity of mammalian heart, together with the exogenous cardioprotective function, to serve as a robust therapeutic device to treat acute MI.

Multidirectional Filamented Light Biofabrication Creates Aligned and Contractile Cardiac Tissues

Biofabricating 3D cardiac tissues that mimic the native myocardial tissue is a pivotal challenge in tissue engineering. In this study, we fabricate 3D cardiac tissues with controlled, multidirectional cellular alignment and directed or twisting contractility. We show that multidirectional filamented light can be used to biofabricate high-density (up to 60 × 106 cells mL-1) tissues, with directed uniaxial contractility (3.8x) and improved cell-to-cell connectivity (1.6x gap junction expression). Furthermore, by using multidirectional light projection, we can partially overcome cell-induced light attenuation, and fabricate larger tissues with multidirectional cellular alignment. For example, we fabricate a tri-layered myocardium-like tissue and a bi-layered tissue with torsional contractility. The approach provides a new strategy to rapidly fabricate aligned cardiac tissues relevant to regenerative medicine and biohybrid robotics.

Human induced pluripotent stem cell-derived cardiac muscle rings for biohybrid self-beating actuator

Cardiac muscle, a subtype of striated muscle composing our heart, has garnered attention as a source of autonomously driven actuators due to its inherent capability for spontaneous contraction. However, conventional cardiac biohybrid robots have utilized planar (2D) cardiac tissue consisting of a thin monolayer of cardiac myotubes with a thickness of 3-5 μm, which can generate a limited contractile force per unit footprint. In this study, 3D cardiac muscle rings were proposed as robotic actuator units. These units not only exhibit higher contractile force per unit footprint compared to their 2D counterparts due to their increased height, but they can also be integrated into desired 3D configurations. We fabricated cardiac muscle rings from human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), evaluated their driving characteristics, and verified the actuation effects by integrating them with artificial components. After the 10th day from culture, the cardiac muscle rings exhibited rhythmic spontaneous contraction and increased contractile force in response to stretching stimuli. Furthermore, after constructing a centimeter-sized biohybrid self-beating actuator with an antagonistic pair structure of cardiac muscle rings, the periodic antagonistic beating motion at its tail portion was confirmed. We believe that 3D cardiac muscle rings, possessing high contractile force and capable of being positioned within limited 3D space, can be used as potent biohybrid robotic actuators.

Biofabrication of Tissue-Engineered Cartilage Constructs Through Faraday Wave Bioassembly of Cell-Laden Gelatin Microcarriers

Acoustic biofabrication is an emerging strategy in tissue engineering due to its mild and fast manufacturing process. Herein, tissue-engineered cartilage constructs with high cell viability are fabricated from cell-laden gelatin microcarriers (GMs) through Faraday wave bioassembly, a typical acoustic "bottom-up" manufacturing process. Assembly modules are first prepared by incorporating cartilage precursor cells, the chondrogenic cell line ATDC5, or bone marrow-derived mesenchymal stem cells (BMSCs), into GMs. Patterned structures are formed by Faraday wave bioassembly of the cell-laden GMs. Due to the gentle and efficient assembly process and the protective effects of microcarriers, cells in the patterned structures maintain high activity. Subsequently, tissue-engineered cartilage constructs are obtained by inducing cell differentiation of the patterned structures. Comprehensive evaluations are conducted to verify chondrocyte differentiation and the formation of cartilage tissue constructs in terms of cell viability, morphological analysis, gene expression, and matrix production. Finally, implantation studies with a rat cartilage defect model demonstrate that these tissue-engineered cartilage constructs are beneficial for the repair of articular cartilage damage in vivo. This study provides the first biofabrication of cartilage tissue constructs using Faraday wave bioassembly, extending its application to engineering tissues with a low cell density.

Lactate- and immunomagnetic-purified hiPSC-derived cardiomyocytes generate comparable engineered cardiac tissue constructs

Three-dimensional engineered cardiac tissue (ECT) using purified human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) has emerged as an appealing model system for the study of human cardiac biology and disease. A recent study reported widely used metabolic (lactate) purification of monolayer hiPSC-CM cultures results in an ischemic cardiomyopathy-like phenotype compared with magnetic antibody-based cell sorting (MACS) purification, complicating the interpretation of studies using lactate-purified hiPSC-CMs. Herein, our objective was to determine if use of lactate relative to MACS-purified hiPSC-CMs affects the properties of resulting hiPSC-ECTs. Therefore, hiPSC-CMs were differentiated and purified using either lactate-based media or MACS. Global proteomics revealed that lactate-purified hiPSC-CMs displayed a differential phenotype over MACS hiPSC-CMs. hiPSC-CMs were then integrated into 3D hiPSC-ECTs and cultured for 4 weeks. Structurally, there was no significant difference in sarcomere length between lactate and MACS hiPSC-ECTs. Assessment of isometric twitch force and Ca2+ transient measurements revealed similar functional performance between purification methods. High-resolution mass spectrometry-based quantitative proteomics showed no significant difference in protein pathway expression or myofilament proteoforms. Taken together, this study demonstrates that lactate- and MACS-purified hiPSC-CMs generate ECTs with comparable structural, functional, and proteomic features, and it suggests that lactate purification does not result in an irreversible change in a hiPSC-CM phenotype.

Construction of millimeter-scale vascularized engineered myocardial tissue using a mixed gel

Engineering myocardium has shown great clinal potential for repairing permanent myocardial injury. However, the lack of perfusing blood vessels and difficulties in preparing a thick-engineered myocardium result in its limited clinical use. We prepared a mixed gel containing fibrin (5 mg/ml) and collagen I (0.2 mg/ml) and verified that human umbilical vein endothelial cells (HUVECs) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) could form microvascular lumens and myocardial cell clusters by harnessing the low-hardness and hyperelastic characteristics of fibrin. hiPSC-CMs and HUVECs in the mixed gel formed self-organized cell clusters, which were then cultured in different media using a three-phase approach. The successfully constructed vascularized engineered myocardial tissue had a spherical structure and final diameter of 1-2 mm. The tissue exhibited autonomous beats that occurred at a frequency similar to a normal human heart rate. The internal microvascular lumen could be maintained for 6 weeks and showed good results during preliminary surface re-vascularization in vitro and vascular remodeling in vivo. In summary, we propose a simple method for constructing vascularized engineered myocardial tissue, through phased cultivation that does not rely on high-end manufacturing equipment and cutting-edge preparation techniques. The constructed tissue has potential value for clinical use after preliminary evaluation.

Ultrasound standing wave spatial patterning of human umbilical vein endothelial cells for 3D micro-vascular networks formation

Generating functional and perfusable micro-vascular networks is an important goal for the fabrication of large and three-dimensional tissues. Up to now, the fabrication of micro-vascular networks is a complicated multitask involving several different factors such as time consuming, cells survival, micro-diameter vasculature and strict alignment. Here, we propose a technique combining multi-material extrusion and ultrasound standing wave forces to create a network structure of human umbilical vein endothelial cells within a mixture of calcium alginate and decellularized extracellular matrix. The functionality of the matured microvasculature networks was demonstrated through the enhancement of cell-cell adhesion, angiogenesis process, and perfusion tests with microparticles, FITC-dextran, and whole mouse blood. Moreover, animal experiments exhibited the implantability including that the pre-existing blood vessels of the host sprout towards the preformed vessels of the scaffold over time and the microvessels inside the implanted scaffold matured from empty tubular structures to functional blood-carrying microvessels in two weeks.

Sound-based assembly of three-dimensional cellularized and acellularized constructs

Herein we show an accessible technique based on Faraday waves that assist the rapid assembly of osteoinductive β-Tricalcium phosphate (β-TCP) particles as well as human osteoblast pre-assembled in spheroids. The hydrodynamic forces originating at 'seabed' of the assembly chamber can be used to tightly aggregate inorganic and biological entities at packing densities that resemble those of native tissues. Additionally, following a layer-by-layer assembly procedure, centimeter scaled osteoinductive three-dimensional and cellularized constructs have been fabricated. We showed that the intimate connection between biological building blocks is essential in engineering living system able of localized mineral deposition. Our results demonstrate, for the first time, the possibility to obtain three-dimensional cellularized and acellularized anisotropic constructs using Faraday waves.

In vivo acoustic patterning of endothelial cells for tissue vascularization

Strategies to fabricate microvascular networks that structurally and functionally mimic native microvessels are needed to address a host of clinical conditions associated with tissue ischemia. The objective of this work was to advance a novel ultrasound technology to fabricate complex, functional microvascular networks directly in vivo. Acoustic patterning utilizes forces within an ultrasound standing wave field (USWF) to organize cells or microparticles volumetrically into defined geometric assemblies. A dual-transducer system was developed to generate USWFs site-specifically in vivo through interference of two ultrasound fields. The system rapidly patterned injected cells or microparticles into parallel sheets within collagen hydrogels in vivo. Acoustic patterning of injected endothelial cells within flanks of immunodeficient mice gave rise to perfused microvessels within 7 days of patterning, whereas non-patterned cells did not survive. Thus, externally-applied ultrasound fields guided injected endothelial cells to self-assemble into perfused microvascular networks in vivo. These studies advance acoustic patterning towards in vivo tissue engineering by providing the first proof-of-concept demonstration that non-invasive, ultrasound-mediated cell patterning can be used to fabricate functional microvascular networks directly in vivo.

Cardiac regeneration - Past advancements, current challenges, and future directions

Cardiovascular disease is the leading cause of mortality and morbidity worldwide. Despite improvements in the standard of care for patients with heart diseases, including innovation in pharmacotherapy and surgical interventions, none have yet been proven effective to prevent the progression to heart failure. Cardiac transplantation is the last resort for patients with severe heart failure, but donor shortages remain a roadblock. Cardiac regenerative strategies include cell-based therapeutics, gene therapy, direct reprogramming of non-cardiac cells, acellular biologics, and tissue engineering methods to restore damaged hearts. Significant advancements have been made over the past several decades within each of these fields. This review focuses on the advancements of: 1) cell-based cardiac regenerative therapies, 2) the use of noncoding RNA to induce endogenous cell proliferation, and 3) application of bioengineering methods to promote retention and integration of engrafted cells. Different cell sources have been investigated, including adult stem cells derived from bone marrow and adipose cells, cardiosphere-derived cells, skeletal myoblasts, and pluripotent stem cells. In addition to cell-based transplantation approaches, there have been accumulating interest over the past decade in inducing endogenous CM proliferation for heart regeneration, particularly with the use of noncoding RNAs such as miRNAs and lncRNAs. Bioengineering applications have focused on combining cell-transplantation approaches with fabrication of a porous, vascularized scaffold using biomaterials and advanced bio-fabrication techniques that may offer enhanced retention of transplanted cells, with the hope that these cells would better engraft with host tissue to improve cardiac function. This review summarizes the present status and future challenges of cardiac regenerative therapies.

Laser-guided programmable construction of cell-laden hydrogel microstructures forin vitrodrug evaluation

Cell-laden hydrogel microstructures have been used in broad applications in tissue engineering, translational medicine, and cell-based assays for pharmaceutical research. However, the construction of cell-laden hydrogel microstructuresin vitroremains challenging. The technologies permitting generation of multicellular structures with different cellular compositions and spatial distributions are needed. Herein, we propose a laser-guided programmable hydrogel-microstructures-construction platform, allowing controllable and heterogeneous assembly of multiple cellular spheroids into spatially organized multicellular structures with good bioactivity. And the cell-laden hydrogel microstructures could be further leveraged forin vitrodrug evaluation. We demonstrate that cells within hydrogels exhibit significantly higher half-maximal inhibitory concentration values against doxorubicin compared with traditional 2D plate culture. Moreover, we reveal the differences in drug responses between heterogeneous and homogeneous cell-laden hydrogel microstructures, providing valuable insight intoin vitrodrug evaluation.

One Billion hiPSC-Cardiomyocytes: Upscaling Engineered Cardiac Tissues to Create High Cell Density Therapies for Clinical Translation in Heart Regeneration

Despite the overwhelming use of cellularized therapeutics in cardiac regenerative engineering, approaches to biomanufacture engineered cardiac tissues (ECTs) at clinical scale remain limited. This study aims to evaluate the impact of critical biomanufacturing decisions-namely cell dose, hydrogel composition, and size-on ECT formation and function-through the lens of clinical translation. ECTs were fabricated by mixing human induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) and human cardiac fibroblasts into a collagen hydrogel to engineer meso-(3 × 9 mm), macro- (8 × 12 mm), and mega-ECTs (65 × 75 mm). Meso-ECTs exhibited a hiPSC-CM dose-dependent response in structure and mechanics, with high-density ECTs displaying reduced elastic modulus, collagen organization, prestrain development, and active stress generation. Scaling up, cell-dense macro-ECTs were able to follow point stimulation pacing without arrhythmogenesis. Finally, we successfully fabricated a mega-ECT at clinical scale containing 1 billion hiPSC-CMs for implantation in a swine model of chronic myocardial ischemia to demonstrate the technical feasibility of biomanufacturing, surgical implantation, and engraftment. Through this iterative process, we define the impact of manufacturing variables on ECT formation and function as well as identify challenges that must still be overcome to successfully accelerate ECT clinical translation.

Lactate and Immunomagnetic-purified iPSC-derived Cardiomyocytes Generate Comparable Engineered Cardiac Tissue Constructs

Three-dimensional engineered cardiac tissue (ECT) using purified human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) has emerged as an appealing model system for the study of human cardiac biology and disease. A recent study reported widely-used metabolic (lactate) purification of monolayer hiPSC-CM cultures results in an ischemic cardiomyopathy-like phenotype compared to magnetic antibody-based cell sorting (MACS) purification, complicating the interpretation of studies using lactate-purified hiPSC-CMs. Herein, our objective was to determine if use of lactate relative to MACs-purified hiPSC-CMs impacts the properties of resulting hiPSC-ECTs. Therefore, hiPSC-CMs were differentiated and purified using either lactate-based media or MACS. After purification, hiPSC-CMs were combined with hiPSC-cardiac fibroblasts to create 3D hiPSC-ECT constructs maintained in culture for four weeks. There were no structural differences observed, and there was no significant difference in sarcomere length between lactate and MACS hiPSC-ECTs. Assessment of isometric twitch force, Ca 2+ transients, and β-adrenergic response revealed similar functional performance between purification methods. High-resolution mass spectrometry (MS)-based quantitative proteomics showed no significant difference in any protein pathway expression or myofilament proteoforms. Taken together, this study demonstrates lactate- and MACS-purified hiPSC-CMs generate ECTs with comparable molecular and functional properties, and suggests lactate purification does not result in an irreversible change in hiPSC-CM phenotype.

From rectangular to diamond shape: on the three-dimensional and size-dependent transformation of patterns formed by single particles trapped in microfluidic acoustic tweezers

Generally, the pattern formed by individual particles trapped inside a microfluidic chamber by a two-dimensional standing acoustic wave field has been considered only the result of the acoustic radiation force. Previous studies showed that particles can be trapped at the local minima and maxima of the first-order pressure and velocity fields. Thus, either a rectangular or a diamond pattern can be formed solely depending on the particle size, when the acoustic field is unchanged, and the material properties of the particles and the fluid are fixed. In this paper, we report about the co-existence of different patterns with particles of the same size. The actual shape of the patterns depends mainly on the ratio between particle diameter and wavelength. In addition, particles were found to be trapped at locations that coincide with the position of antinodes, even though the particles have a positive acoustic contrast factor. These phenomena imply that the trapping of individual particles cannot be described by the acoustic radiation force solely. Hence, further research is required, taking the viscous drag force caused by the fluid flow induced by the acoustic streaming effect into account.

Acoustic Trapping: An Emerging Tool for Microfabrication Technology

The high throughput deposition of microscale objects with precise spatial arrangement represents a key step in microfabrication technology. This can be done by creating physical boundaries to guide the deposition process or using printing technologies; in both approaches, these microscale objects cannot be further modified after they are formed. The utilization of dynamic acoustic fields offers a novel approach to facilitate real-time reconfigurable miniaturized systems in a contactless manner, which can potentially be used in physics, chemistry, biology, as well as materials science. Here, the physical interactions of microscale objects in an acoustic pressure field are discussed and how to fabricate different acoustic trapping devices and how to tune the spatial arrangement of the microscale objects are explained. Moreover, different approaches that can dynamically modulate microscale objects in acoustic fields are presented, and the potential applications of the microarrays in biomedical engineering, chemical/biochemical sensing, and materials science are highlighted alongside a discussion of future research challenges.

Acoustofluidics - changing paradigm in tissue engineering, therapeutics development, and biosensing

For more than 70 years, acoustic waves have been used to screen, diagnose, and treat patients in hundreds of medical devices. The biocompatible nature of acoustic waves, their non-invasive and contactless operation, and their compatibility with wide visualization techniques are just a few of the many features that lead to the clinical success of sound-powered devices. The development of microelectromechanical systems and fabrication technologies in the past two decades reignited the spark of acoustics in the discovery of unique microscale bio applications. Acoustofluidics, the combination of acoustic waves and fluid mechanics in the nano and micro-realm, allowed researchers to access high-resolution and controllable manipulation and sensing tools for particle separation, isolation and enrichment, patterning of cells and bioparticles, fluid handling, and point of care biosensing strategies. This versatility and attractiveness of acoustofluidics have led to the rapid expansion of platforms and methods, making it also challenging for users to select the best acoustic technology. Depending on the setup, acoustic devices can offer a diverse level of biocompatibility, throughput, versatility, and sensitivity, where each of these considerations can become the design priority based on the application. In this paper, we aim to overview the recent advancements of acoustofluidics in the multifaceted fields of regenerative medicine, therapeutic development, and diagnosis and provide researchers with the necessary information needed to choose the best-suited acoustic technology for their application. Moreover, the effect of acoustofluidic systems on phenotypic behavior of living organisms are investigated. The review starts with a brief explanation of acoustofluidic principles, the different working mechanisms, and the advantages or challenges of commonly used platforms based on the state-of-the-art design features of acoustofluidic technologies. Finally, we present an outlook of potential trends, the areas to be explored, and the challenges that need to be overcome in developing acoustofluidic platforms that can echo the clinical success of conventional ultrasound-based devices.

Bisymmetric coherent acoustic tweezers based on modulation of surface acoustic waves for dynamic and reconfigurable cluster manipulation of particles and cells

Acoustic tweezers based on surface acoustic waves (SAWs) have raised great interest in the fields of tissue engineering, targeted therapy, and drug delivery. Generally, the complex structure and array layout design of interdigital electrodes would restrict the applications of acoustic tweezers. Here, we present a novel approach by using bisymmetric coherent acoustic tweezers to modulate the shape of acoustic pressure fields with high flexibility and accuracy. Experimental tests were conducted to perform the precise, contactless, and biocompatible cluster manipulation of polystyrene microparticles and yeast cells. Stripe, dot, quadratic lattice, hexagonal lattice, interleaved stripe, oblique stripe, and many other complex arrays were achieved by real-time modulation of amplitudes and phase relations of coherent SAWs to demonstrate the capability of the device for the cluster manipulation of particles and cells. Furthermore, rapid switching among various arrays, shape regulation, geometric parameter modulation of array units, and directional translation of microparticles and cells were implemented. This study demonstrated a favorable technique for flexible and versatile manipulation and patterning of cells and biomolecules, and it has the advantages of high manipulation accuracy and adjustability, thus it is expected to be utilized in the fields of targeted cellular assembly, biological 3D printing, and targeted release of drugs.

Rapid Assembly of Cellulose Microfibers into Translucent and Flexible Microfluidic Paper-Based Analytical Devices via Wettability Patterning

Microfluidic paper-based analytical devices (μPADs) are emerging as powerful analytical platforms in clinical diagnostics, food safety, and environmental protection because of their low cost and favorable substrate properties for biosensing. However, the existing top-down fabrication methods of paper-based chips suffer from low resolution (>200 μm). Additionally, papers have limitations in their physical properties (e.g., thickness, transmittance, and mechanical flexibility). Here, we demonstrate a bottom-up approach for the rapid fabrication of heterogeneously controlled paper-based chip arrays. We simply print a wax-patterned microchip with wettability contrasts, enabling automatic and selective assembly of cellulose microfibers to construct predefined paper-based microchip arrays with controllable thickness. This paper-based microchip printing technology is feasible for various substrate materials ranging from inorganic glass to organic polymers, providing a versatile platform for the full range of applications including transparent devices and flexible health monitoring. Our bottom-up printing technology using cellulose microfibers as the starting material provides a lateral resolution down to 42 ± 3 μm and achieves the narrowest channel barrier down to 33 ± 2 μm. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 μL of sample for testing.

Advances in three-dimensional bioprinted stem cell-based tissue engineering for cardiovascular regeneration

Three-dimensional (3D) bioprinting of cellular or biological components are an emerging field to develop tissue structures that mimic the spatial, mechanochemical and temporal characteristics of cardiovascular tissues. 3D multi-cellular and multi-domain organotypic biological constructs can better recapitulate in vivo physiology and can be utilized in a variety of applications. Such applications include in vitro cellular studies, high-throughput drug screening, disease modeling, biocompatibility analysis, drug testing and regenerative medicine. A major challenge of 3D bioprinting strategies is the inability of matrix molecules to reconstitute the complexity of the extracellular matrix and the intrinsic cellular morphologies and functions. An important factor is the inclusion of a vascular network to facilitate oxygen and nutrient perfusion in scalable and patterned 3D bioprinted tissues to promote cell viability and functionality. In this review, we summarize the new generation of 3D bioprinting techniques, the kinds of bioinks and printing materials employed for 3D bioprinting, along with the current state-of-the-art in engineered cardiovascular tissue models. We also highlight the translational applications of 3D bioprinting in engineering the myocardium cardiac valves, and vascular grafts. Finally, we discuss current challenges and perspectives of designing effective 3D bioprinted constructs with native vasculature, architecture and functionality for clinical translation and cardiovascular regeneration.

An Insight of Nanomaterials in Tissue Engineering from Fabrication to Applications

Tissue engineering is a research domain that deals with the growth of various kinds of tissues with the help of synthetic composites. With the culmination of nanotechnology and bioengineering, tissue engineering has emerged as an exciting domain. Recent literature describes its various applications in biomedical and biological sciences, such as facilitating the growth of tissue and organs, gene delivery, biosensor-based detection, etc. It deals with the development of biomimetics to repair, restore, maintain and amplify or strengthen several biological functions at the level of tissue and organs. Herein, the synthesis of nanocomposites based on polymers, along with their classification as conductive hydrogels and bioscaffolds, is comprehensively discussed. Furthermore, their implementation in numerous tissue engineering and regenerative medicine applications is also described. The limitations of tissue engineering are also discussed here. The present review highlights and summarizes the latest progress in the tissue engineering domain directed at functionalized nanomaterials.

Current methods for fabricating 3D cardiac engineered constructs

3D cardiac engineered constructs have yielded not only the next generation of cardiac regenerative medicine but also have allowed for more accurate modeling of both healthy and diseased cardiac tissues. This is critical as current cardiac treatments are rudimentary and often default to eventual heart transplants. This review serves to highlight the various cell types found in cardiac tissues and how they correspond with current advanced fabrication methods for creating cardiac engineered constructs capable of shedding light on various pathologies and providing the therapeutic potential for damaged myocardium. In addition, insight is given toward the future direction of the field with an emphasis on the creation of specialized and personalized constructs that model the region-specific microtopography and function of native cardiac tissues.

PPARdelta activation induces metabolic and contractile maturation of human pluripotent stem cell-derived cardiomyocytes

Pluripotent stem-cell-derived cardiomyocytes (PSC-CMs) provide an unprecedented opportunity to study human heart development and disease, but they are functionally and structurally immature. Here, we induce efficient human PSC-CM (hPSC-CM) maturation through metabolic-pathway modulations. Specifically, we find that peroxisome-proliferator-associated receptor (PPAR) signaling regulates glycolysis and fatty acid oxidation (FAO) in an isoform-specific manner. While PPARalpha (PPARa) is the most active isoform in hPSC-CMs, PPARdelta (PPARd) activation efficiently upregulates the gene regulatory networks underlying FAO, increases mitochondrial and peroxisome content, enhances mitochondrial cristae formation, and augments FAO flux. PPARd activation further increases binucleation, enhances myofibril organization, and improves contractility. Transient lactate exposure, which is frequently used for hPSC-CM purification, induces an independent cardiac maturation program but, when combined with PPARd activation, still enhances oxidative metabolism. In summary, we investigate multiple metabolic modifications in hPSC-CMs and identify a role for PPARd signaling in inducing the metabolic switch from glycolysis to FAO in hPSC-CMs.

Synthetic developmental biology: Engineering approaches to guide multicellular organization

Multicellular organisms of various complexities self-organize in nature. Organoids are in vitro 3D structures that display important aspects of the anatomy and physiology of their in vivo counterparts and that develop from pluripotent or tissue-specific stem cells through a self-organization process. In this review, we describe the multidisciplinary concept of “synthetic developmental biology” where engineering approaches are employed to guide multicellular organization in an experimental setting. We introduce a novel classification of engineering approaches based on the extent of microenvironmental manipulation applied to organoids. In the final section, we discuss how engineering tools might help overcome current limitations in organoid construction.

Concentration of Microparticles Using Flexural Acoustic Wave in Sessile Droplets

Acoustic manipulation of microparticles and cells has attracted growing interest in biomedical applications. In particular, the use of acoustic waves to concentrate particles plays an important role in enhancing the detection process by biosensors. Here, we demonstrated microparticle concentration within sessile droplets placed on the hydrophobic surface using the flexural wave. The design benefits from streaming flow induced by the Lamb wave propagated in the glass waveguide to manipulate particles in the droplets. Microparticles will be concentrated at the central area of the droplet adhesion plane based on the balance among the streaming drag force, gravity, and buoyancy at the operating frequency. We experimentally demonstrated the concentration of particles of various sizes and tumor cells. Using numerical simulation, we predicted the acoustic pressure and streaming flow pattern within the droplet and characterized the underlying physical mechanisms for particle motion. The design is more suitable for micron-sized particle preparation, and it can be valuable for various biological, chemical, and medical applications.

Bioengineering approaches to treat the failing heart: from cell biology to 3D printing

Successfully engineering a functional, human, myocardial pump would represent a therapeutic alternative for the millions of patients with end-stage heart disease and provide an alternative to animal-based preclinical models. Although the field of cardiac tissue engineering has made tremendous advances, major challenges remain, which, if properly resolved, might allow the clinical implementation of engineered, functional, complex 3D structures in the future. In this Review, we provide an overview of state-of-the-art studies, challenges that have not yet been overcome and perspectives on cardiac tissue engineering. We begin with the most clinically relevant cell sources used in this field and discuss the use of topological, biophysical and metabolic stimuli to obtain mature phenotypes of cardiomyocytes, particularly in relation to organized cytoskeletal and contractile intracellular structures. We then move from the cellular level to engineering planar cardiac patches and discuss the need for proper vascularization and the main strategies for obtaining it. Finally, we provide an overview of several different approaches for the engineering of volumetric organs and organ parts - from whole-heart decellularization and recellularization to advanced 3D printing technologies.

Engineering Biological Tissues from the Bottom-Up: Recent Advances and Future Prospects

Tissue engineering provides a powerful solution for current organ shortages, and researchers have cultured blood vessels, heart tissues, and bone tissues in vitro. However, traditional top-down tissue engineering has suffered two challenges: vascularization and reconfigurability of functional units. With the continuous development of micro-nano technology and biomaterial technology, bottom-up tissue engineering as a promising approach for organ and tissue modular reconstruction has gradually developed. In this article, relevant advances in living blocks fabrication and assembly techniques for creation of higher-order bioarchitectures are described. After a critical overview of this technology, a discussion of practical challenges is provided, and future development prospects are proposed.

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.

Recapitulating pancreatic cell-cell interactions through bioengineering approaches: the momentous role of non-epithelial cells for diabetes cell therapy

Over the past few years, extensive efforts have been made to generate in-vitro pancreatic micro-tissue, for disease modeling or cell replacement approaches in pancreatic related diseases such as diabetes mellitus. To obtain these goals, a closer look at the diverse cells participating in pancreatic development is necessary. Five major non-epithelial pancreatic (pN-Epi) cell populations namely, pancreatic endothelium, mesothelium, neural crests, pericytes, and stellate cells exist in pancreas throughout its development, and they are hypothesized to be endogenous inducers of the development. In this review, we discuss different pN-Epi cells migrating to and existing within the pancreas and their diverse effects on pancreatic epithelium during organ development mediated via associated signaling pathways, soluble factors or mechanical cell-cell interactions. In-vivo and in-vitro experiments, with a focus on N-Epi cells' impact on pancreas endocrine development, have also been considered. Pluripotent stem cell technology and multicellular three-dimensional organoids as new approaches to generate pancreatic micro-tissues have also been discussed. Main challenges for reaching a detailed understanding of the role of pN-Epi cells in pancreas development in utilizing for in-vitro recapitulation have been summarized. Finally, various novel and innovative large-scale bioengineering approaches which may help to recapitulate cell-cell interactions and are crucial for generation of large-scale in-vitro multicellular pancreatic micro-tissues, are discussed.

Strategies for constructing pluripotent stem cell- and progenitor cell-derived three-dimensional cardiac micro-tissues

Three-dimensional (3D) cardiac micro-tissue is a promising model for simulating the structural and functional features of heart in vitro. This scientific achievement provides a platform for exploration about the mechanisms on the development, damage, and regeneration of tissue, hence, paving a way toward development of novel therapies for heart diseases. However, 3D micro-tissue technology is still in its infant stages faced with many challenges such as incompleteness of the tissue microarchitecture, loss of the resident immune cells, poor reproducibility, and deficiencies in continuously feeding the nutrients and removing wastes during micro-tissue culturing. There is an urgent need to optimize the construction of 3D cardiac micro-tissue and improve functions of the involved cells. Therefore, scaffolds and cell resources for building 3D cardiac micro-tissues, strategies for inducing the maturation and functionalization of pluripotent stem cell- or cardiac progenitor cell-derived cardiomyocytes, and the major challenges were reviewed in this writing to enable future fabrication of 3D cardiac micro-tissues or organoids for drug screening, disease modeling, regeneration treatment, and so on.

Directed Assembly of Particles for Additive Manufacturing of Particle-Polymer Composites

Particle-polymer dispersions are ubiquitous in additive manufacturing (AM), where they are used as inks to create composite materials with applications to wearable sensors, energy storage materials, and actuation elements. It has been observed that directional alignment of the particle phase in the polymer dispersion can imbue the resulting composite material with enhanced mechanical, electrical, thermal or optical properties. Thus, external field-driven particle alignment during the AM process is one approach to tailoring the properties of composites for end-use applications. This review article provides an overview of externally directed field mechanisms (e.g., electric, magnetic, and acoustic) that are used for particle alignment. Illustrative examples from the AM literature show how these mechanisms are used to create structured composites with unique properties that can only be achieved through alignment. This article closes with a discussion of how particle distribution (i.e., microstructure) affects mechanical properties. A fundamental description of particle phase transport in polymers could lead to the development of AM process control for particle-polymer composite fabrication. This would ultimately create opportunities to explore the fundamental impact that alignment has on particle-polymer composite properties, which opens up the possibility of tailoring these materials for specific applications.

Patient-Specific 3D Bioprinted Models of Developing Human Heart

The heart is the first organ to develop in the human embryo through a series of complex chronological processes, many of which critically rely on the interplay between cells and the dynamic microenvironment. Tight spatiotemporal regulation of these interactions is key in heart development and diseases. Due to suboptimal experimental models, however, little is known about the role of microenvironmental cues in the heart development. This study investigates the use of 3D bioprinting and perfusion bioreactor technologies to create bioartificial constructs that can serve as high-fidelity models of the developing human heart. Bioprinted hydrogel-based, anatomically accurate models of the human embryonic heart tube (e-HT, day 22) and fetal left ventricle (f-LV, week 33) are perfused and analyzed both computationally and experimentally using ultrasound and magnetic resonance imaging. Results demonstrate comparable flow hemodynamic patterns within the 3D space. We demonstrate endothelial cell growth and function within the bioprinted e-HT and f-LV constructs, which varied significantly in varying cardiac geometries and flow. This study introduces the first generation of anatomically accurate, 3D functional models of developing human heart. This platform enables precise tuning of microenvironmental factors, such as flow and geometry, thus allowing the study of normal developmental processes and underlying diseases.

Reversible Design of Dynamic Assemblies at Small Scales

Emerging bottom-up fabrication methods have enabled the assembly of synthetic colloids, microrobots, living cells, and organoids to create intricate structures with unique properties that transcend their individual components. This review provides an access point to the latest developments in externally driven assembly of synthetic and biological components. In particular, we emphasize reversibility, which enables the fabrication of multiscale systems that would not be possible under traditional techniques. Magnetic, acoustic, optical, and electric fields are the most promising methods for controlling the reversible assembly of biological and synthetic subunits since they can reprogram their assembly by switching on/off the external field or shaping these fields. We feature capabilities to dynamically actuate the assembly configuration by modulating the properties of the external stimuli, including frequency and amplitude. We describe the design principles which enable the assembly of reconfigurable structures. Finally, we foresee that the high degree of control capabilities offered by externally driven assembly will enable broad access to increasingly robust design principles towards building advanced dynamic intelligent systems.

The waves that make the pattern: a review on acoustic manipulation in biomedical research

Novel approaches, combining technology, biomaterial design, and cutting-edge cell culture, have been increasingly considered to advance the field of tissue engineering and regenerative medicine. Within this context, acoustic manipulation to remotely control spatial cellular organization within a carrier matrix has arisen as a particularly promising method during the last decade. Acoustic or sound-induced manipulation takes advantage of hydrodynamic forces exerted on systems of particles within a liquid medium by standing waves. Inorganic or organic particles, cells, or organoids assemble within the nodes of the standing wave, creating distinct patterns in response to the applied frequency and amplitude. Acoustic manipulation has advanced from micro- or nanoparticle arrangement in 2D to the assembly of multiple cell types or organoids into highly complex in vitro tissues. In this review, we discuss the past research achievements in the field of acoustic manipulation with particular emphasis on biomedical application. We survey microfluidic, open chamber, and high throughput devices for their applicability to arrange non-living and living units in buffer or hydrogels. We also investigate the challenges arising from different methods, and their prospects to gain a deeper understanding of in vitro tissue formation and application in the field of biomedical engineering.

•

Work on sound waves to spatially control particulate systems is reviewed.

•

Classification of surface acoustic waves, bulk acoustic waves, and Faraday waves.

•

Sound can be used to arrange, separate, or filter polymer particles.

•

Sound can pattern cells in 3D to induce morphogenesis.

•

Long-term applied sound induces differentiation and tissue formation.

Engineering Human Cardiac Muscle Patch Constructs for Prevention of Post-infarction LV Remodeling

Tissue engineering combines principles of engineering and biology to generate living tissue equivalents for drug testing, disease modeling, and regenerative medicine. As techniques for reprogramming human somatic cells into induced pluripotent stem cells (iPSCs) and subsequently differentiating them into cardiomyocytes and other cardiac cells have become increasingly efficient, progress toward the development of engineered human cardiac muscle patch (hCMP) and heart tissue analogs has accelerated. A few pilot clinical studies in patients with post-infarction LV remodeling have been already approved. Conventional methods for hCMP fabrication include suspending cells within scaffolds, consisting of biocompatible materials, or growing two-dimensional sheets that can be stacked to form multilayered constructs. More recently, advanced technologies, such as micropatterning and three-dimensional bioprinting, have enabled fabrication of hCMP architectures at unprecedented spatiotemporal resolution. However, the studies working on various hCMP-based strategies for in vivo tissue repair face several major obstacles, including the inadequate scalability for clinical applications, poor integration and engraftment rate, and the lack of functional vasculature. Here, we review many of the recent advancements and key concerns in cardiac tissue engineering, focusing primarily on the production of hCMPs at clinical/industrial scales that are suitable for administration to patients with myocardial disease. The wide variety of cardiac cell types and sources that are applicable to hCMP biomanufacturing are elaborated. Finally, some of the key challenges remaining in the field and potential future directions to address these obstacles are discussed.

Emerging biofabrication approaches for gastrointestinal organoids towards patient specific cancer models

Tissue engineered organoids are simple biomodels that can emulate the structural and functional complexity of specific organs. Here, we review developments in three-dimensional (3D) artificial cell constructs to model gastrointestinal dynamics towards cancer diagnosis. We describe bottom-up approaches to fabricate close-packed cell aggregates, from the use of biochemical and physical cues to guide the self-assembly of organoids, to the use of engineering approaches, including 3D printing/additive manufacturing and external field-driven protocols. Finally, we outline the main challenges and possible risks regarding the potential translation of gastrointestinal organoids from laboratory settings to patient-specific models in clinical applications.

Toward rapid infectious disease diagnosis with advances in surface-enhanced Raman spectroscopy

In a pandemic era, rapid infectious disease diagnosis is essential. Surface-enhanced Raman spectroscopy (SERS) promises sensitive and specific diagnosis including rapid point-of-care detection and drug susceptibility testing. SERS utilizes inelastic light scattering arising from the interaction of incident photons with molecular vibrations, enhanced by orders of magnitude with resonant metallic or dielectric nanostructures. While SERS provides a spectral fingerprint of the sample, clinical translation is lagged due to challenges in consistency of spectral enhancement, complexity in spectral interpretation, insufficient specificity and sensitivity, and inefficient workflow from patient sample collection to spectral acquisition. Here, we highlight the recent, complementary advances that address these shortcomings, including (1) design of label-free SERS substrates and data processing algorithms that improve spectral signal and interpretability, essential for broad pathogen screening assays; (2) development of new capture and affinity agents, such as aptamers and polymers, critical for determining the presence or absence of particular pathogens; and (3) microfluidic and bioprinting platforms for efficient clinical sample processing. We also describe the development of low-cost, point-of-care, optical SERS hardware. Our paper focuses on SERS for viral and bacterial detection, in hopes of accelerating infectious disease diagnosis, monitoring, and vaccine development. With advances in SERS substrates, machine learning, and microfluidics and bioprinting, the specificity, sensitivity, and speed of SERS can be readily translated from laboratory bench to patient bedside, accelerating point-of-care diagnosis, personalized medicine, and precision health.

Biofabrication of a Functional Tubular Construct from Tissue Spheroids Using Magnetoacoustic Levitational Directed Assembly

In traditional tissue engineering, synthetic or natural scaffolds are usually used as removable temporal support, which involves some biotechnology limitations. The concept of "scaffield" approach utilizing the physical fields instead of biomaterial scaffold has been proposed recently. In particular, a combination of intense magnetic and acoustic fields can enable rapid levitational bioassembly of complex-shaped 3D tissue constructs from tissue spheroids at low concentration of paramagnetic agent (gadolinium salt) in the medium. In the current study, the tissue spheroids from human bladder smooth muscle cells (myospheres) are used as building blocks for assembling the tubular 3D constructs. Levitational assembly is accomplished at low concentrations of gadolinium salts in the high magnetic field at 9.5 T. The biofabricated smooth muscle constructs demonstrate contraction after the addition of vasoconstrictive agent endothelin-1. Thus, hybrid magnetoacoustic levitational bioassembly is considered as a new technology platform in the emerging field of formative biofabrication. This novel technology of scaffold-free, nozzle-free, and label-free bioassembly opens a unique opportunity for rapid biofabrication of 3D tissue and organ constructs with complex geometry.

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.

Reconfigurable Particle Swarm Robotics Powered by Acoustic Vibration Tweezer

Inspired by natural swarms such as bees and ants, various types of swarm robotic systems have been developed to work together to complete tasks that transcend individual capabilities. Autonomous robots controlled by collective algorithm and colloidal swarms energized by external field have been designed in an attempt to emulate collective behaviors in nature. However, either sophisticated hardware designs or active agents with special electromagnetic properties and microstructural designs are needed. Here, for the first time, we create a swarm robotic system that can make any granular materials an active swarm robot by acoustic vibration tweezer. It should be noted that the particles energized by only one vibration generator are ordinary sand without any microstructural design. Therefore, it is the simplest and lowest cost swarm robot. Particles can display a solid-like aggregate, which is capable of robustly carrying and transporting an object that is about 1 million times heavier than a single particle. Moreover, through the cooperation of two swarm robots, we can achieve cooperative transport of a stick with a length of 1000 times the diameter of a single particle. The particle robot can move in a fluid-like amorphous group, which can change its own shape to adapt to the surrounding environment, thus having a strong environmental adaptability. Besides, it can move quickly (about 600 times the particle diameter per second) in a discrete state. Within one certain particle system, the particle swarm robot can emulate diverse biomimetic collective behaviors through navigated locomotion, multimode transformation, and cooperative transport.

Medical Micro/Nanorobots in Precision Medicine

Advances in medical robots promise to improve modern medicine and the quality of life. Miniaturization of these robotic platforms has led to numerous applications that leverages precision medicine. In this review, the current trends of medical micro and nanorobotics for therapy, surgery, diagnosis, and medical imaging are discussed. The use of micro and nanorobots in precision medicine still faces technical, regulatory, and market challenges for their widespread use in clinical settings. Nevertheless, recent translations from proof of concept to in vivo studies demonstrate their potential toward precision medicine.

Strategies and Challenges to Improve Cellular Programming-Based Approaches for Heart Regeneration Therapy

Limited adult cardiac cell proliferation after cardiovascular disease, such as heart failure, hampers regeneration, resulting in a major loss of cardiomyocytes (CMs) at the site of injury. Recent studies in cellular reprogramming approaches have provided the opportunity to improve upon previous techniques used to regenerate damaged heart. Using these approaches, new CMs can be regenerated from differentiation of iPSCs (similar to embryonic stem cells), the direct reprogramming of fibroblasts [induced cardiomyocytes (iCMs)], or induced cardiac progenitors. Although these CMs have been shown to functionally repair infarcted heart, advancements in technology are still in the early stages of development in research laboratories. In this review, reprogramming-based approaches for generating CMs are briefly introduced and reviewed, and the challenges (including low efficiency, functional maturity, and safety issues) that hinder further translation of these approaches into a clinical setting are discussed. The creative and combined optimal methods to address these challenges are also summarized, with optimism that further investigation into tissue engineering, cardiac development signaling, and epigenetic mechanisms will help to establish methods that improve cell-reprogramming approaches for heart regeneration.

Acoustofluidic multi-well plates for enrichment of micro/nano particles and cells

Controllable enrichment of micro/nanoscale objects plays a significant role in many biomedical and biochemical applications, such as increasing the detection sensitivity of assays, or improving the structures of bio-engineered tissues. However, few techniques can perform concentrations of micro/nano objects in multi-well plates, a very common laboratory vessel. In this work, we develop an acoustofluidic multi-well plate, which adopts an array of simple, low-cost and commercially available ring-shaped piezoelectric transducers for rapid and robust enrichment of micro/nanoscale particles/cells in each well of the plate. The enrichment mechanism is validated and characterized through both numerical simulations and experiments. We observe that the ring-shaped piezoelectric transducer can generate circular standing flexural waves in the substrate of each well, and that the vibrations can induce acoustic streaming near the interface between the substrate and a fluid droplet placed within the well; this streaming can drive micro/nanoscale objects to the center of the droplet for enrichment. Moreover, the acoustofluidic multi-well plate can realize simultaneous and consistent enrichment of biological cells in each well of the plate. With merits such as simplicity, controllability, low cost, and excellent compatibility with other downstream analysis tools, the developed acoustofluidic multi-well plate could be a versatile tool for many applications such as micro/nano fabrication, self-assembly, biomedical/biochemical sensing, and tissue engineering.

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.

Recent advancements of human iPSC derived cardiomyocytes in drug screening and tissue regeneration

Myocardial infarction together with subsequent heart failures are among the main reasons for death related to cardiovascular diseases (CVD). Restoring cardiac function and replacing scar tissue with healthy regenerated cardiomyocytes (CMs) is a hopeful therapy for heart failure. Human-induced pluripotent stem cell (hiPSC) derived CMs (hiPSC-CMs) offer the advantages of not having significant ethical issues and having negligible immunological rejection compared to other myocardial regeneration methods. hiPSCs can also produce an unlimited number of human CMs, another advantage they have compared with other cell sources for cardiac regeneration. Numerous researchers have focused their work on promoting the functional maturity of hiPSC-CMs, as well as finding out the precise regulatory mechanisms of each differentiation stage together with the economical and practical methods of acquisition and purification. However, the clinical applications of hiPSC-CMs in drug discovery and cardiac regeneration therapy have yet to be achieved. In this review, we present an overview of various methods for improving the differentiation efficiency of hiPSC-CMs and discuss the differences of electrophysiological characteristics between hiPSC-CMs and matured native CMs. We also introduce approaches for obtaining a large quantity of iPSC-CMs, which are needed to achieve biomanufacturing strategies for building biomimetic three-dimensional tissue constructs using combinations of biomaterials and advanced microfabrication techniques. Recent advances in specific iPSC technology-based drug screening platforms and regeneration therapies can suggest future directions for personalized medicine in biomedical applications.

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.