Bioengineering Human Myocardium on Native Extracellular Matrix

Progress of organoid platform in cardiovascular research

Cardiovascular disease is a significant cause of death in humans. Various models are necessary for the study of cardiovascular diseases, but once cellular and animal models have some defects, such as insufficient fidelity. As a new technology, organoid has certain advantages and has been used in many applications in the study of cardiovascular diseases. This article aims to summarize the application of organoid platforms in cardiovascular diseases, including organoid construction schemes, modeling, and application of cardiovascular organoids. Advances in cardiovascular organoid research have provided many models for different cardiovascular diseases in a variety of areas, including myocardium, blood vessels, and valves. Physiological and pathological models of different diseases, drug research models, and methods for evaluating and promoting the maturation of different kinds of organ tissues are provided for various cardiovascular diseases, including cardiomyopathy, myocardial infarction, and atherosclerosis. This article provides a comprehensive overview of the latest research progress in cardiovascular organ tissues, including construction protocols for cardiovascular organoid tissues and their evaluation system, different types of disease models, and applications of cardiovascular organoid models in various studies. The problems and possible solutions in organoid development are summarized.

Two Decades of Advances and Limitations in Organ Recellularization

The recellularization of tissues after decellularization is a relatively new technology in the field of tissue engineering (TE). Decellularization involves removing cells from a tissue or organ, leaving only the extracellular matrix (ECM). This can then be recellularized with new cells to create functional tissues or organs. The first significant mention of recellularization in decellularized tissues can be traced to research conducted in the early 2000s. One of the landmark studies in this field was published in 2008 by Ott, where researchers demonstrated the recellularization of a decellularized rat heart with cardiac cells, resulting in a functional organ capable of contraction. Since then, other important studies have been published. These studies paved the way for the widespread application of recellularization in TE, demonstrating the potential of decellularized ECM to serve as a scaffold for regenerating functional tissues. Thus, although the concept of recellularization was initially explored in previous decades, these studies from the 2000s marked a major turning point in the development and practical application of the technology for the recellularization of decellularized tissues. The article reviews the historical advances and limitations in organ recellularization in TE over the last two decades.

Human Chorionic Membrane-derived Tunable Hydrogels for Vascular Tissue Engineering Strategies

One of the foremost targets in the advancement of biomaterials to engineer vascularized tissues is not only to replicate the composition of the intended tissue but also to create thicker structures incorporating a vascular network for adequate nutrients and oxygen supply. For the first time, to the best of current knowledge, a clinically relevant biomaterial is developed, demonstrating that hydrogels made from the human decellularized extracellular matrix can exhibit robust mechanical properties (in the kPa range) and angiogenic capabilities simultaneously. These properties enable the culture and organization of human umbilical vein endothelial cells into tubular structures, maintaining their integrity for 14 days in vitro without the need for additional polymers or angiogenesis-related factors. This is achieved by repurposing the placenta chorionic membrane (CM), a medical waste with an exceptional biochemical composition, into a valuable resource for bioengineering purposes. After decellularization, the CM underwent chemical modification with methacryloyl groups, giving rise to methacrylated CM (CMMA). CMMA preserved key proteins, as well as glycosaminoglycans. The resulting hydrogels rapidly photopolymerize and have enhanced strength and customizable mechanical properties. Furthermore, they demonstrate angio-vasculogenic competence in vitro and in vivo, holding significant promise as a humanized platform for the engineering of vascularized tissues.

Natural Hydrogels Support Kidney Organoid Generation and Promote In Vitro Angiogenesis

To date, strategies aiming to modulate cell to extracellular matrix (ECM) interactions during organoid derivation remain largely unexplored. Here renal decellularized ECM (dECM) hydrogels are fabricated from porcine and human renal cortex as biomaterials to enrich cell-to-ECM crosstalk during the onset of kidney organoid differentiation from human pluripotent stem cells (hPSCs). Renal dECM-derived hydrogels are used in combination with hPSC-derived renal progenitor cells to define new approaches for 2D and 3D kidney organoid differentiation, demonstrating that in the presence of these biomaterials the resulting kidney organoids exhibit renal differentiation features and the formation of an endogenous vascular component. Based on these observations, a new method to produce kidney organoids with vascular-like structures is achieved through the assembly of hPSC-derived endothelial-like organoids with kidney organoids in 3D. Major readouts of kidney differentiation and renal cell morphology are assessed exploiting these culture platforms as new models of nephrogenesis. Overall, this work shows that exploiting cell-to-ECM interactions during the onset of kidney differentiation from hPSCs facilitates and optimizes current approaches for kidney organoid derivation thereby increasing the utility of these unique cell culture platforms for personalized medicine.

Fabrication of heart tubes from iPSC derived cardiomyocytes and human fibrinogen by rotating mold technology

Due to its structural and functional complexity the heart imposes immense physical, physiological and electromechanical challenges on the engineering of a biological replacement. Therefore, to come closer to clinical translation, the development of a simpler biological assist device is requested. Here, we demonstrate the fabrication of tubular cardiac constructs with substantial dimensions of 6 cm in length and 11 mm in diameter by combining human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and human foreskin fibroblast (hFFs) in human fibrin employing a rotating mold technology. By centrifugal forces employed in the process a cell-dense layer was generated enabling a timely functional coupling of iPSC-CMs demonstrated by a transgenic calcium sensor, rhythmic tissue contractions, and responsiveness to electrical pacing. Adjusting the degree of remodeling as a function of hFF-content and inhibition of fibrinolysis resulted in stable tissue integrity for up to 5 weeks. The rotating mold device developed in frame of this work enabled the production of tubes with clinically relevant dimensions of up to 10 cm in length and 22 mm in diameter which-in combination with advanced bioreactor technology for controlled production of functional iPSC-derivatives-paves the way towards the clinical translation of a biological cardiac assist device.

Engineered heart tissue: Design considerations and the state of the art

Originally developed more than 20 years ago, engineered heart tissue (EHT) has become an important tool in cardiovascular research for applications such as disease modeling and drug screening. Innovations in biomaterials, stem cell biology, and bioengineering, among other fields, have enabled EHT technologies to recapitulate many aspects of cardiac physiology and pathophysiology. While initial EHT designs were inspired by the isolated-trabecula culture system, current designs encompass a variety of formats, each of which have unique strengths and limitations. In this review, we describe the most common EHT formats, and then systematically evaluate each aspect of their design, emphasizing the rational selection of components for each application.

Distinct cellular microenvironment with cytotypic effects regulates orderly regeneration of vascular tissues

Regeneration of the architecturally complex blood vascular system requires precise temporal and spatial control of cell behaviours. Additional components must be integrated into the structure to achieve clinical success for in situ tissue engineering. Consequently, this study proposed a universal method for including any substrate type in vascular cell extracellular matrices (VCEM) via regulating selective adhesion to promote vascular tissue regeneration. The results uncovered that the VCEM worked as cell adhesion substrates, exhibited cell type specificity, and functioned as an address signal for recognition by vascular cells, which resulted in matching with the determined cells. The qPCR and immunofluorescence results revealed that a cell type-specific VCEM could be designed to promote or inhibit cell adhesion, consistenting with the expression patterns of eyes absent 3 (Eya3). In addition, a 3D vascular graft combined with VCEM which could recapitulate the vascular cell-like microenvironment was fabricated. The vascular graft revealed a prospective role for cellular microenvironment in the establishment of vascular cell distribution and tissue architecture, and potentiated the orderly regeneration and functional recovery of vascular tissues in vivo. The findings demonstrate that differential adhesion between cell types due to the cellular microenvironment is sufficient to drive the complex assembly of engineered blood vessel functional units, and underlies hierarchical organization during vascular regeneration.

Advancements in tissue engineering for cardiovascular health: a biomedical engineering perspective

Myocardial infarction (MI) stands as a prominent contributor to global cardiovascular disease (CVD) mortality rates. Acute MI (AMI) can result in the loss of a large number of cardiomyocytes (CMs), which the adult heart struggles to replenish due to its limited regenerative capacity. Consequently, this deficit in CMs often precipitates severe complications such as heart failure (HF), with whole heart transplantation remaining the sole definitive treatment option, albeit constrained by inherent limitations. In response to these challenges, the integration of bio-functional materials within cardiac tissue engineering has emerged as a groundbreaking approach with significant potential for cardiac tissue replacement. Bioengineering strategies entail fortifying or substituting biological tissues through the orchestrated interplay of cells, engineering methodologies, and innovative materials. Biomaterial scaffolds, crucial in this paradigm, provide the essential microenvironment conducive to the assembly of functional cardiac tissue by encapsulating contracting cells. Indeed, the field of cardiac tissue engineering has witnessed remarkable strides, largely owing to the application of biomaterial scaffolds. However, inherent complexities persist, necessitating further exploration and innovation. This review delves into the pivotal role of biomaterial scaffolds in cardiac tissue engineering, shedding light on their utilization, challenges encountered, and promising avenues for future advancement. By critically examining the current landscape, we aim to catalyze progress toward more effective solutions for cardiac tissue regeneration and ultimately, improved outcomes for patients grappling with cardiovascular ailments.

Versatile human cardiac tissues engineered with perfusable heart extracellular microenvironment for biomedical applications

Engineered human cardiac tissues have been utilized for various biomedical applications, including drug testing, disease modeling, and regenerative medicine. However, the applications of cardiac tissues derived from human pluripotent stem cells are often limited due to their immaturity and lack of functionality. Therefore, in this study, we establish a perfusable culture system based on in vivo-like heart microenvironments to improve human cardiac tissue fabrication. The integrated culture platform of a microfluidic chip and a three-dimensional heart extracellular matrix enhances human cardiac tissue development and their structural and functional maturation. These tissues are comprised of cardiovascular lineage cells, including cardiomyocytes and cardiac fibroblasts derived from human induced pluripotent stem cells, as well as vascular endothelial cells. The resultant macroscale human cardiac tissues exhibit improved efficacy in drug testing (small molecules with various levels of arrhythmia risk), disease modeling (Long QT Syndrome and cardiac fibrosis), and regenerative therapy (myocardial infarction treatment). Therefore, our culture system can serve as a highly effective tissue-engineering platform to provide human cardiac tissues for versatile biomedical applications.

The Future of Microsurgery: Vascularized Composite Allotransplantation and Engineering Vascularized Tissue

Background

Microsurgical techniques have revolutionized the field of reconstructive surgery and are the mainstay for complex soft tissue reconstruction. However, their limitations have promoted the development of viable alternatives. This article seeks to explore technologies that have the potential of revolutionizing microsurgical reconstruction as it is currently known, reflect on current and future vascularized composite allotransplantation (VCA) practices, as well as describe the basic science within emerging technologies and their potential translational applications.

Methods

A literature review was performed of the technologies that may represent the future of microsurgery: vascularized tissue engineering (VCA) and flap-specific tissue engineering.

Results

VCA has shown great promise and has already been employed in the clinical setting (especially in face and limb transplantation). Immunosuppression, logistics, cost, and regulatory pathways remain barriers to overcome to make it freely available. Vascularized and flap-specific tissue engineering remain a laboratory reality but have the potential to supersede VCA. The capability of creating an off-the-shelf free flap matching the required tissue, size, and shape is a significant advantage. However, these technologies are still at the early stage and require significant advancement before they can be translated into the clinical setting.

Conclusion

VCA, vascularized tissue engineering, and flap-specific bioengineering represent possible avenues for the evolution of current microsurgical techniques. The next decade will elucidate which of these three strategies will evolve into a tangible translational option and hopefully bring a paradigm shift of reconstructive surgery.

Ameliorating impaired cardiac function in myocardial infarction using exosome-loaded gallic-acid-containing polyurethane scaffolds

Myocardial infarction (MI) can be tackled by implanting cardiac patches which provide mechanical support to the heart. However, most tissue-engineered scaffolds face difficulty in attenuating oxidative stress, maintaining mechanical stability, and regenerating damaged cardiomyocytes. Here, we fabricated elastic cryogels using polyurethane modified with antioxidant gallic acid in its backbone (PUGA) and further coated them with decellularized extracellular matrix (dECM) to improve adhesiveness, biocompatibility and hemocompatibility. The scaffold was functionalized with exosomes (EXO) isolated from adipose-derived stem cells having regenerative potential. PUGA-dECM + EXO was tested in a rat model with induced MI where echocardiography after 8 weeks of implantation showed significant recovery in treatment group. Histological analysis revealed a decrease in fibrosis after application of patch and promotion of angiogenesis with reduced oxidative stress was shown by immunostaining. Expression of cardiac tissue contractile function marker was also observed in treatment groups. Thus, the proposed biomaterial has a promising application to be utilized as a patch for cardiac regeneration. More detailed studies with larger animal species are needed for using these observations for specific applications.

An overview of the production of tissue extracellular matrix and decellularization process

Thousands of patients need an organ transplant yearly, while only a tiny percentage have this chance to receive a tissue/organ transplant. Nowadays, decellularized animal tissue is one of the most widely used methods to produce engineered scaffolds for transplantation. Decellularization is defined as physically or chemically removing cellular components from tissues while retaining structural and functional extracellular matrix (ECM) components and creating an ECM-derived scaffold. Then, decellularized scaffolds could be reseeded with different cells to fabricate an autologous graft. Effective decellularization methods preserve ECM structure and bioactivity through the application of the agents and techniques used throughout the process. The most valuable agents for the decellularization process depend on biological properties, cellular density, and the thickness of the desired tissue. ECM-derived scaffolds from various mammalian tissues have been recently used in research and preclinical applications in tissue engineering. Many studies have shown that decellularized ECM-derived scaffolds could be obtained from tissues and organs such as the liver, cartilage, bone, kidney, lung, and skin. This review addresses the significance of ECM in organisms and various decellularization agents utilized to prepare the ECM. Also, we describe the current knowledge of the decellularization of different tissues and their applications.

The sinoatrial node extracellular matrix promotes pacemaker phenotype and protects automaticity in engineered heart tissues from cyclic strain

The composite material-like extracellular matrix (ECM) in the sinoatrial node (SAN) supports the native pacemaking cardiomyocytes (PCMs). To test the roles of SAN ECM in the PCM phenotype and function, we engineered reconstructed-SAN heart tissues (rSANHTs) by recellularizing porcine SAN ECMs with hiPSC-derived PCMs. The hiPSC-PCMs in rSANHTs self-organized into clusters resembling the native SAN and displayed higher expression of pacemaker-specific genes and a faster automaticity compared with PCMs in reconstructed-left ventricular heart tissues (rLVHTs). To test the protective nature of SAN ECMs under strain, rSANHTs and rLVHTs were transplanted onto the murine thoracic diaphragm to undergo constant cyclic strain. All strained-rSANHTs preserved automaticity, whereas 66% of strained-rLVHTs lost their automaticity. In contrast to the strained-rLVHTs, PCMs in strained-rSANHTs maintained high expression of key pacemaker genes (HCN4, TBX3, and TBX18). These findings highlight the promotive and protective roles of the composite SAN ECM and provide valuable insights for pacemaking tissue engineering.

A typical method for decellularization of plants as biomaterials

Decellularization is a process by which cells are removed from tissues or organs, leaving behind the extracellular matrix (ECM) structure. This process has gained interest in the fields of tissue engineering and regenerative medicine as a way to prepare suitable scaffolds for tissue reconstruction. Although the initial efforts come with the animal tissues, this technique can also be applied to various plant tissues with simple modifications, as plant-derived biomaterials have the benefit of being biocompatible and serving as a safe, all-natural substitute for synthetic or animal originated materials. Additionally, plant-derived biomaterials may help cells grow and differentiate, creating a three-dimensional environment for tissue regeneration and repair. Here we demonstrate a general method for plant tissue decellularization, including already experienced approaches and techniques.•Exhibit the basic steps for plant decellularization, which may be applied to several other plant tissues.•The proposed approach may be optimized considering various intended uses.•Gives basic information for the determination of decellularization efficiency.

Mimicking Transmural Helical Cardiomyofibre Orientation Using Bouligand-like Pore Structures in Ice-Templated Collagen Scaffolds

The helical arrangement of cardiac muscle fibres underpins the contractile properties of the heart chamber. Across the heart wall, the helical angle of the aligned fibres changes gradually across the range of 90-180°. It is essential to recreate this structural hierarchy in vitro for developing functional artificial tissue. Ice templating can achieve single-oriented pore alignment via unidirectional ice solidification with a flat base mould design. We hypothesise that the orientation of aligned pores can be controlled simply via base topography, and we propose a scalable base design to recapitulate the transmural fibre orientation. We have utilised finite element simulations for rapid testing of base designs, followed by experimental confirmation of the Bouligand-like orientation. X-ray microtomography of experimental samples showed a gradual shift of 106 ± 10°, with the flexibility to tailor pore size and spatial helical angle distribution for personalised medicine.

Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

Recent advances in soluble decellularized extracellular matrix for heart tissue engineering and organ modeling

Despite the advent of tissue engineering (TE) for the remodeling, restoring, and replacing damaged cardiovascular tissues, the progress is hindered by the optimal mechanical and chemical properties required to induce cardiac tissue-specific cellular behaviors including migration, adhesion, proliferation, and differentiation. Cardiac extracellular matrix (ECM) consists of numerous structural and functional molecules and tissue-specific cells, therefore it plays an important role in stimulating cell proliferation and differentiation, guiding cell migration, and activating regulatory signaling pathways. With the improvement and modification of cell removal methods, decellularized ECM (dECM) preserves biochemical complexity, and bio-inductive properties of the native matrix and improves the process of generating functional tissue. In this review, we first provide an overview of the latest advancements in the utilization of dECM in in vitro model systems for disease and tissue modeling, as well as drug screening. Then, we explore the role of dECM-based biomaterials in cardiovascular regenerative medicine (RM), including both invasive and non-invasive methods. In the next step, we elucidate the engineering and material considerations in the preparation of dECM-based biomaterials, namely various decellularization techniques, dECM sources, modulation, characterizations, and fabrication approaches. Finally, we discuss the limitations and future directions in fabrication of dECM-based biomaterials for cardiovascular modeling, RM, and clinical translation.

Evaluation of Porcine Psoas Major as a Scaffold Material for Engineered Heart Tissues

Decellularized porcine myocardium is commonly used as scaffolding for engineered heart tissues (EHTs). However, structural and mechanical heterogeneity in the myocardium complicate production of mechanically consistent tissues. In this study, we evaluate the porcine psoas major muscle (tenderloin) as an alternative scaffold material. Head-to-head comparison of decellularized tenderloin and ventricular scaffolds showed only minor differences in mean biomechanical characteristics, but tenderloin scaffolds were less variable and less dependent on the region of origin than ventricular samples. The active contractile behavior of EHTs made by seeding tenderloin versus ventricular scaffolds with human-induced pluripotent stem cell-derived cardiomyocytes was also comparable, with only minor differences observed. Collectively, the data reveal that the behavior of EHTs produced from decellularized porcine psoas muscle is almost identical to those made from porcine left ventricular myocardium, with the advantages of being more homogeneous, biomechanically consistent, and readily obtainable.

Application of locally responsive design of biomaterials based on microenvironmental changes in myocardial infarction

Morbidity and mortality caused by acute myocardial infarction (AMI) are on the rise, posing a grave threat to the health of the general population. Up to now, interventional, surgical, and pharmaceutical therapies have been the main treatment methods for AMI. Effective and timely reperfusion therapy decreases mortality, but it cannot stimulate myocardial cell regeneration or reverse ventricular remodeling. Cell therapy, gene therapy, immunotherapy, anti-inflammatory therapy, and several other techniques are utilized by researchers to improve patients' prognosis. In recent years, biomaterials for AMI therapy have become a hot spot in medical care. Biomaterials furnish a microenvironment conducive to cell growth and deliver therapeutic factors that stimulate cell regeneration and differentiation. Biomaterials adapt to the complex microenvironment and respond to changes in local physical and biochemical conditions. Therefore, environmental factors and material properties must be taken into account when designing biomaterials for the treatment of AMI. This article will review the factors that need to be fully considered in the design of biological materials.

A novel allogeneic acellular matrix scaffold for porcine cartilage regeneration

BACKGROUND

Cartilage defects are common sports injuries without significant treatment. Articular cartilage with inferior regenerative potential resulted in the poor formation of hyaline cartilage in defects. Acellular matrix scaffolds provide a microenvironment and biochemical properties similar to those of native tissues and are widely used for tissue regeneration. Therefore, we aimed to design a novel acellular cartilage matrix scaffold (ACS) for cartilage regeneration and hyaline-like cartilage formation.

METHODS

Four types of cartilage injury models, including full-thickness cartilage defects (6.5 and 8.5 mm in diameter and 2.5 mm in depth) and osteochondral defects (6.5 and 8.5 mm in diameter and 5 mm in depth), were constructed in the trochlear groove of the right femurs of pigs (n = 32, female, 25-40 kg). The pigs were divided into 8 groups (4 in each group) based on post-surgery treatment differences. was assessed by macroscopic appearance, magnetic resonance imaging (MRI), micro-computed tomography (micro-CT), and histologic and immunohistochemistry tests.

RESULTS

At 6 months, the ACS-implanted group exhibited better defect filling and a greater number of chondrocyte-like cells in the defect area than the blank groups. MRI and micro-CT imaging evaluations revealed that ACS implantation was an effective treatment for cartilage regeneration. The immunohistochemistry results suggested that more hyaline-like cartilage was generated in the defects of the ACS-implanted group.

CONCLUSIONS

ACS implantation promoted cartilage repair in full-thickness cartilage defects and osteochondral defects with increased hyaline-like cartilage formation at the 6-month follow-up.

Cardiac organoid: multiple construction approaches and potential applications

The human cardiac organoid (hCO) is three-dimensional tissue model that is similar to an in vivo organ and has great potential on heart development biology, disease modeling, drug screening and regenerative medicine. However, the construction of hCO presents a unique challenge compared with other organoids such as the lung, small intestine, pancreas, liver. Since heart disease is the dominant cause of death and the treatment of such disease is one of the most unmet medical needs worldwide, developing technologies for the construction and application of hCO is a critical task for the scientific community. In this review, we discuss the current classification and construction methods of hCO. In addition, we describe its applications in drug screening, disease modeling, and regenerative medicine. Finally, we propose the limitations of the cardiac organoid and future research directions. A detailed understanding of hCO will provide ways to improve its construction and expand its applications.

Human pluripotent stem cell-based models of heart development and disease

The heart is a complex organ composed of distinct cell types, such as cardiomyocytes, cardiac fibroblasts, endothelial cells, smooth muscle cells, neuronal cells and immune cells. All these cell types contribute to the structural, electrical and mechanical properties of the heart. Genetic manipulation and lineage tracing studies in mice have been instrumental in gaining critical insights into the networks regulating cardiac cell lineage specification, cell fate and plasticity. Such knowledge has been of fundamental importance for the development of efficient protocols for the directed differentiation of pluripotent stem cells (PSCs) in highly specialized cardiac cell types. In this review, we summarize the evolution and current advances in protocols for cardiac subtype specification, maturation, and assembly in cardiac microtissues and organoids.

Construction of cardiac fibrosis for biomedical research

Cardiac remodeling is critical for effective tissue recuperation, nevertheless, excessive formation and deposition of extracellular matrix components can result in the onset of cardiac fibrosis. Despite the emergence of novel therapies, there are still no lifelong therapeutic solutions for this issue. Understanding the detrimental cardiac remodeling may aid in the development of innovative treatment strategies to prevent or reverse fibrotic alterations in the heart. Further combining the latest understanding of disease pathogenesis with cardiac tissue engineering has provided the conversion of basic laboratory studies into the therapy of cardiac fibrosis patients as an increasingly viable prospect. This review presents the current main mechanisms and the potential tissue engineering of cardiac fibrosis. Approaches using biomedical materials-based cardiac constructions are reviewed to consider key issues for simulating in vitro cardiac fibrosis, outlining a future perspective for preclinical applications.

Biotechnological advances and applications of human pluripotent stem cell-derived heart models

In recent years, significant biotechnological advancements have been made in engineering human cardiac tissues and organ-like models. This field of research is crucial for both basic and translational research due to cardiovascular disease being the leading cause of death in the developed world. Additionally, drug-associated cardiotoxicity poses a major challenge for drug development in the pharmaceutical and biotechnological industries. Progress in three-dimensional cell culture and microfluidic devices has enabled the generation of human cardiac models that faithfully recapitulate key aspects of human physiology. In this review, we will discuss 3D pluripotent stem cell (PSC)-models of the human heart, such as engineered heart tissues and organoids, and their applications in disease modeling and drug screening.

Decellularized Extracellular Matrix: The Role of This Complex Biomaterial in Regeneration

Organ transplantation is understood as a technique where an organ from a donor patient is transferred to a recipient patient. This practice gained strength in the 20th century and ensured advances in areas of knowledge such as immunology and tissue engineering. The main problems that comprise the practice of transplants involve the demand for viable organs and immunological aspects related to organ rejection. In this review, we address advances in tissue engineering for reversing the current challenges of transplants, focusing on the possible use of decellularized tissues in tissue engineering. We address the interaction of acellular tissues with immune cells, especially macrophages and stem cells, due to their potential use in regenerative medicine. Our goal is to exhibit data that demonstrate the use of decellularized tissues as alternative biomaterials that can be applied clinically as partial or complete organ substitutes.

Tissue-engineered anterior segment eye cultures demonstrate hallmarks of conventional organ culture

BACKGROUND

Glaucoma is a blinding disease largely caused by dysregulation of outflow through the trabecular meshwork (TM), resulting in elevated intraocular pressure (IOP). We hypothesized that transplanting TM cells into a decellularized, tissue-engineered anterior segment eye culture could restore the outflow structure and function.

METHODS

Porcine eyes were decellularized with freeze-thaw cycles and perfusion of surfactant. We seeded control scaffolds with CrFK cells transduced with lentiviral vectors to stably express eGFP and compared them to scaffolds seeded with primary TM cells as well as to normal, unaltered eyes. We tracked the repopulation behavior, performed IOP maintenance challenges, and analyzed the histology.

RESULTS

Transplanted cells localized to the TM and progressively infiltrated the extracellular matrix, reaching a distribution comparable to normal, unaltered eyes. After a perfusion rate challenge to mimic a glaucomatous pressure elevation, transplanted and normal eyes reestablished a normal intraocular pressure (transplanted = 16.5 ± 0.9 mmHg, normal = 16.9 ± 0.9). However, eyes reseeded with eGFP-expressing CrFK cells could not regulate IOP, remaining high and unstable (27.0 ± 6.2 mmHg) instead.

CONCLUSION

Tissue-engineered anterior segment scaffolds can serve as readily available, scalable ocular perfusion cultures. This could reduce dependency on scarce donor globes in outflow research and may allow engineering perfusion cultures with specific geno- and phenotypes.

Current status and future directions in the development and optimization of thoracic and abdominal artificial organs

INTRODUCTION

Artificial organs are engineered devices with the capacity to be implanted or integrated into a living body to replace a failing organ, or to duplicate or augment one or multiple functions of the diseased organ.

AREAS COVERED

We evaluate the present landscape and future possibilities of artificial organ engineering by exploring the spectrum of four distinguishable device features: mobility, compatibility, functionality, and material composition. These mechanical and functional differences provide the framework through which we examine the current status and future possibilities of the abdominal and thoracic artificial organs.

EXPERT OPINION

Transforming the artificial organs landscape in ways that expand the scope of existing device capabilities and improve the clinical utility of artificial organs will require making improvements upon existing technologies and multidisciplinary cooperation to create and discover new capacities.

Development and evaluation of a novel combined perfusion decellularization heart-lung model for tissue engineering of bioartificial heart-lung scaffolds

BACKGROUND

Bioengineered transplantable heart-lung scaffolds could be potentially lifesaving in a large number of congenital and acquired cardiothoracic disorders including terminal heart-lung disease.

METHODS

We decellularized heart-lung organ-blocks from rats (n = 10) by coronary and tracheal perfusion with ionic detergents in a modified Langendorff circuit.

RESULTS

In the present project, we were able to achieve complete decellularization of the heart-lung organ-block. Decellularized heart-lung organ-blocks lacked intracellular components but maintained structure of the cellular walls with collagen and elastic fibers.

CONCLUSIONS

We present a novel model of combined perfusion and decellularization of heart-lung organ-blocks. This model is the first step on the pathway to creating bioengineered transplantable heart-lung scaffolds. We believe that further development of this technology could provide a life-saving conduit, significantly reducing the risks of heart-lung failure surgery and improving postoperative quality of life.

Current approaches for the recreation of cardiac ischaemic environment in vitro

Myocardial ischaemia is one of the leading dead causes worldwide. Although animal experiments have historically provided a wealth of information, animal models are time and money consuming, and they usually miss typical human patient's characteristics associated with ischemia prevalence, including aging and comorbidities. Generating reliable in vitro models that recapitulate the human cardiac microenvironment during an ischaemic event can boost the development of new drugs and therapeutic strategies, as well as our understanding of the underlying cellular and molecular events, helping the optimization of therapeutic approaches prior to animal and clinical testing. Although several culture systems have emerged for the recreation of cardiac physiology, mimicking the features of an ischaemic heart tissue in vitro is challenging and certain aspects of the disease process remain poorly addressed. Here, current in vitro cardiac culture systems used for modelling cardiac ischaemia, from self-aggregated organoids to scaffold-based constructs and heart-on-chip platforms are described. The advantages of these models to recreate ischaemic hallmarks such as oxygen gradients, pathological alterations of mechanical strength or fibrotic responses are highlighted. The new models represent a step forward to be considered, but unfortunately, we are far away from recapitulating all complexity of the clinical situations.

Whole-Heart Tissue Engineering and Cardiac Patches: Challenges and Promises

Despite all the advances in preventing, diagnosing, and treating cardiovascular disorders, they still account for a significant part of mortality and morbidity worldwide. The advent of tissue engineering and regenerative medicine has provided novel therapeutic approaches for the treatment of various diseases. Tissue engineering relies on three pillars: scaffolds, stem cells, and growth factors. Gene and cell therapy methods have been introduced as primary approaches to cardiac tissue engineering. Although the application of gene and cell therapy has resulted in improved regeneration of damaged cardiac tissue, further studies are needed to resolve their limitations, enhance their effectiveness, and translate them into the clinical setting. Scaffolds from synthetic, natural, or decellularized sources have provided desirable characteristics for the repair of cardiac tissue. Decellularized scaffolds are widely studied in heart regeneration, either as cell-free constructs or cell-seeded platforms. The application of human- or animal-derived decellularized heart patches has promoted the regeneration of heart tissue through in vivo and in vitro studies. Due to the complexity of cardiac tissue engineering, there is still a long way to go before cardiac patches or decellularized whole-heart scaffolds can be routinely used in clinical practice. This paper aims to review the decellularized whole-heart scaffolds and cardiac patches utilized in the regeneration of damaged cardiac tissue. Moreover, various decellularization methods related to these scaffolds will be discussed.

Biological Scaffolds for Congenital Heart Disease

Congenital heart disease (CHD) is the most predominant birth defect and can require several invasive surgeries throughout childhood. The absence of materials with growth and remodelling potential is a limitation of currently used prosthetics in cardiovascular surgery, as well as their susceptibility to calcification. The field of tissue engineering has emerged as a regenerative medicine approach aiming to develop durable scaffolds possessing the ability to grow and remodel upon implantation into the defective hearts of babies and children with CHD. Though tissue engineering has produced several synthetic scaffolds, most of them failed to be successfully translated in this life-endangering clinical scenario, and currently, biological scaffolds are the most extensively used. This review aims to thoroughly summarise the existing biological scaffolds for the treatment of paediatric CHD, categorised as homografts and xenografts, and present the preclinical and clinical studies. Fixation as well as techniques of decellularisation will be reported, highlighting the importance of these approaches for the successful implantation of biological scaffolds that avoid prosthetic rejection. Additionally, cardiac scaffolds for paediatric CHD can be implanted as acellular prostheses, or recellularised before implantation, and cellularisation techniques will be extensively discussed.

Zwitterionic coating assisted by dopamine with metal-phenolic networks loaded on titanium with improved biocompatibility and antibacterial property for artificial heart

Introduction: Titanium (Ti) and Ti-based alloy materials are commonly used to develop artificial hearts. To prevent bacterial infections and thrombus in patients with implanted artificial hearts, long-term prophylactic antibiotics and anti-thrombotic drugs are required, and this may lead to health complications. Therefore, the development of optimized antibacterial and antifouling surfaces for Ti-based substrate is especially critical when designing artificial heart implants. Methods: In this study, polydopamine and poly-(sulfobetaine methacrylate) polymers were co-deposited to form a coating on the surface of Ti substrate, a process initiated by Cu²⁺ metal ions. The mechanism for the fabrication of the coating was investigated by coating thickness measurements as well as Ultraviolet-visible and X-ray Photoelectron (XPS) spectroscopy. Characterization of the coating was observed by optical imaging, scanning electron microscope (SEM), XPS, atomic force microscope (AFM), water contact angle and film thickness. In addition, antibacterial property of the coating was tested using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as model strains, while the material biocompatibility was assessed by the antiplatelet adhesion test using platelet-rich plasma and in vitro cytotoxicity tests using human umbilical vein endothelial cells and red blood cells. Results and discussion: Optical imaging, SEM, XPS, AFM, water contact angle, and film thickness tests demonstrated that the coating was successfully deposited on the Ti substrate surface. The biocompatibility and antibacterial assays showed that the developed surface holds great potential for improving the antibacterial and antiplatelet adhesion properties of Ti-based heart implants.

Engineering approaches for cardiac organoid formation and their characterization

Cardiac organoids are 3-dimensional (3D) structures composed of tissue or niche-specific cells, obtained from diverse sources, encapsulated in either a naturally derived or synthetic, extracellular matrix scaffold, and include exogenous biochemical signals such as essential growth factors. The overarching goal of developing cardiac organoid models is to establish a functional integration of cardiomyocytes with physiologically relevant cells, tissues, and structures like capillary-like networks composed of endothelial cells. These organoids used to model human heart anatomy, physiology, and disease pathologies in vitro have the potential to solve many issues related to cardiovascular drug discovery and fundamental research. The advent of patient-specific human-induced pluripotent stem cell-derived cardiovascular cells provide a unique, single-source approach to study the complex process of cardiovascular disease progression through organoid formation and incorporation into relevant, controlled microenvironments such as microfluidic devices. Strategies that aim to accomplish such a feat include microfluidic technology-based approaches, microphysiological systems, microwells, microarray-based platforms, 3D bioprinted models, and electrospun fiber mat-based scaffolds. This article discusses the engineering or technology-driven practices for making cardiac organoid models in comparison with self-assembled or scaffold-free methods to generate organoids. We further discuss emerging strategies for characterization of the bio-assembled cardiac organoids including electrophysiology and machine-learning and conclude with prospective points of interest for engineering cardiac tissues in vitro.

Differentiating Human Pluripotent Stem Cells to Cardiomyocytes Using Purified Extracellular Matrix Proteins

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) can be differentiated into cardiomyocytes (hESC-CMs and iPSC-CMs, respectively), which hold great promise for cardiac regenerative medicine and disease modeling efforts. However, the most widely employed differentiation protocols require undefined substrates that are derived from xenogeneic (animal) products, contaminating resultant hESC- and iPSC-CM cultures with xenogeneic proteins and limiting their clinical applicability. Additionally, typical hESC- and iPSC-CM protocols produce CMs that are significantly contaminated by non-CMs and that are immature, requiring lengthy maturation procedures. In this review, we will summarize recent studies that have investigated the ability of purified extracellular matrix (ECM) proteins to support hESC- and iPSC-CM differentiation, with a focus on commercially available ECM proteins and coatings to make such protocols widely available to researchers. The most promising of the substrates reviewed here include laminin-521 with laminin-221 together or Synthemax (a synthetic vitronectin-based peptide coating), which both resulted in highly pure CM cultures. Future efforts are needed to determine whether combinations of specific purified ECM proteins or derived peptides could further improve CM maturation and culture times, and significantly improve hESC- and iPSC-CM differentiation protocols.

Early-Phase Clinical Trials of Bio-Artificial Organ Technology: A Systematic Review of Ethical Issues

Regenerative medicine has emerged as a novel alternative solution to organ failure which circumvents the issue of organ shortage. In preclinical research settings bio-artificial organs are being developed. It is anticipated that eventually it will be possible to launch first-in-human transplantation trials to test safety and efficacy in human recipients. In early-phase transplantation trials, however, research participants could be exposed to serious risks, such as toxicity, infections and tumorigenesis. So far, there is no ethical guidance for the safe and responsible design and conduct of early-phase clinical trials of bio-artificial organs. Therefore, research ethics review committees will need to look to related adjacent fields of research, including for example cell-based therapy, for guidance. In this systematic review, we examined the literature on early-phase clinical trials in these adjacent fields and undertook a thematic analysis of relevant ethical points to consider for early-phase clinical trials of transplantable bio-artificial organs. Six themes were identified: cell source, risk-benefit assessment, patient selection, trial design, informed consent, and oversight and accountability. Further empirical research is needed to provide insight in patient perspectives, as this may serve as valuable input in determining the conditions for ethically responsible and acceptable early clinical development of bio-artificial organs.

Decellularized Extracellular Matrix Scaffolds for Cardiovascular Tissue Engineering: Current Techniques and Challenges

Cardiovascular diseases are the leading cause of global mortality. Over the past two decades, researchers have tried to provide novel solutions for end-stage heart failure to address cardiac transplantation hurdles such as donor organ shortage, chronic rejection, and life-long immunosuppression. Cardiac decellularized extracellular matrix (dECM) has been widely explored as a promising approach in tissue-regenerative medicine because of its remarkable similarity to the original tissue. Optimized decellularization protocols combining physical, chemical, and enzymatic agents have been developed to obtain the perfect balance between cell removal, ECM composition, and function maintenance. However, proper assessment of decellularized tissue composition is still needed before clinical translation. Recellularizing the acellular scaffold with organ-specific cells and evaluating the extent of cardiomyocyte repopulation is also challenging. This review aims to discuss the existing literature on decellularized cardiac scaffolds, especially on the advantages and methods of preparation, pointing out areas for improvement. Finally, an overview of the state of research regarding the application of cardiac dECM and future challenges in bioengineering a human heart suitable for transplantation is provided.

Modeling the human heart ex vivo-current possibilities and strive for future applications

The high organ specification of the human heart is inversely proportional to its functional recovery after damage. The discovery of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) has accelerated research in human heart regeneration and physiology. Nevertheless, due to the immaturity of iPSC-CMs, they are far from being an representative model of the adult heart physiology. Therefore, number of laboratories strive to obtain a heart tissues by engineering methods by structuring iPSC-CMs into complex and advanced platforms. By using the iPSC-CMs and arranging them in 3D cultures it is possible to obtain a human heart muscle with physiological capabilities potentially similar to the adult heart, while remaining in vitro. Here, we attempt to describe existing examples of heart muscle either in vitro or ex vivo models and discuss potential options for the further development of such structures. This will be a crucial step for ultimate derivation of complete heart tissue-mimicking organs and their future use in drug development, therapeutic approaches testing, pre-clinical studies, and clinical applications. This review particularly aims to compile available models of advanced human heart tissue for scientists considering which model would best fit their research needs.

Healing the Broken Hearts: A Glimpse on Next Generation Therapeutics

Cardiovascular diseases are the leading cause of death worldwide, accounting for 32% of deaths globally and thus representing almost 18 million people according to WHO. Myocardial infarction, the most prevalent adult cardiovascular pathology, affects over half a million people in the USA according to the last records of the AHA. However, not only adult cardiovascular diseases are the most frequent diseases in adulthood, but congenital heart diseases also affect 0.8–1.2% of all births, accounting for mild developmental defects such as atrial septal defects to life-threatening pathologies such as tetralogy of Fallot or permanent common trunk that, if not surgically corrected in early postnatal days, they are incompatible with life. Therefore, both congenital and adult cardiovascular diseases represent an enormous social and economic burden that invariably demands continuous efforts to understand the causes of such cardiovascular defects and develop innovative strategies to correct and/or palliate them. In the next paragraphs, we aim to briefly account for our current understanding of the cellular bases of both congenital and adult cardiovascular diseases, providing a perspective of the plausible lines of action that might eventually result in increasing our understanding of cardiovascular diseases. This analysis will come out with the building blocks for designing novel and innovative therapeutic approaches to healing the broken hearts.

Cell-Based and Selected Cell-Free Therapies for Myocardial Infarction: How Do They Compare to the Current Treatment Options?

Because of cardiomyocyte death or dysfunction frequently caused by myocardial infarction (MI), heart failure is a leading cause of morbidity and mortality in modern society. Paradoxically, only limited and non-curative therapies for heart failure or MI are currently available. As a result, over the past two decades research has focused on developing cell-based approaches promoting the regeneration of infarcted tissue. Cell-based therapies for myocardial regeneration include powerful candidates, such as multipotent stem cells (mesenchymal stem cells (MSCs), bone-marrow-derived stem cells, endothelial progenitor cells, and hematopoietic stem cells) and induced pluripotent stem cells (iPSCs). These possess unique properties, such as potency to differentiate into desired cell types, proliferation capacity, and patient specificity. Preclinical and clinical studies have demonstrated modest improvement in the myocardial regeneration and reduced infarcted areas upon transplantation of pluripotent or multipotent stem cells. Another cell population that need to be considered as a potential source for cardiac regeneration are telocytes found in different organs, including the heart. Their therapeutic effect has been studied in various heart pathologies, such as MI, arrhythmias, or atrial amyloidosis. The most recent cell-free therapeutic tool relies on the cardioprotective effect of complex cargo carried by small membrane-bound vesicles-exosomes-released from stem cells via exocytosis. The MSC/iPSC-derived exosomes could be considered a novel exosome-based therapy for cardiovascular diseases thanks to their unique content. There are also other cell-free approaches, e.g., gene therapy, or acellular cardiac patches. Therefore, our review provides the most recent insights into the novel strategies for myocardial repair based on the regenerative potential of different cell types and cell-free approaches.

A Review on Bioinks and their Application in Plant Bioprinting

In recent years, the characterization and fabrication methods concerning new bioinks have received much attention, largely because the absence of bioprintable materials has been identified as one of the most rudimentary challenges for rapid advancement in the field of three-dimensional (3D) printing. Bioinks for printing mammalian organs have been rapidly produced, but bioinks in the field of plant science remain sparse. Thus, 3D fabrication of plant parts is still in its infancy due to the lack of appropriate bioink materials, and aside from that, the difficulty in recreating sophisticated microarchitectures that accurately and safely mimic natural biological activities is a concern. Therefore, this review article is designed to emphasize the significance of bioinks and their applications in plant bioprinting.

Transcriptomic Profile of Genes Regulating the Structural Organization of Porcine Atrial Cardiomyocytes during Primary In Vitro Culture

Numerous cardiovascular diseases (CVD) eventually lead to severe myocardial dysfunction, which is the most common cause of death worldwide. A better understanding of underlying molecular mechanisms of cardiovascular pathologies seems to be crucial to develop effective therapeutic options. Therefore, a worthwhile endeavor is a detailed molecular characterization of cells extracted from the myocardium. A transcriptomic profile of atrial cardiomyocytes during long-term primary cell culture revealed the expression patterns depending on the duration of the culture and the heart segment of origin (right atrial appendage and right atrium). Differentially expressed genes (DEGs) were classified as involved in ontological groups such as: “cellular component assembly”, “cellular component organization”, “cellular component biogenesis”, and “cytoskeleton organization”. Transcriptomic profiling allowed us to indicate the increased expression of COL5A2, COL8A1, and COL12A1, encoding different collagen subunits, pivotal in cardiac extracellular matrix (ECM) structure. Conversely, genes important for cellular architecture, such as ABLIM1, TMOD1, XIRP1, and PHACTR1, were downregulated during in vitro culture. The culture conditions may create a favorable environment for reconstruction of the ECM structures, whereas they may be suboptimal for expression of some pivotal transcripts responsible for the formation of intracellular structures.

A Progress Report and Roadmap for Microphysiological Systems and Organ-On-A-Chip Technologies to Be More Predictive Models in Human (Knee) Osteoarthritis

Osteoarthritis (OA), a chronic debilitating joint disease affecting hundreds of million people globally, is associated with significant pain and socioeconomic costs. Current treatment modalities are palliative and unable to stop the progressive degeneration of articular cartilage in OA. Scientific attention has shifted from the historical view of OA as a wear-and-tear cartilage disorder to its recognition as a whole-joint disease, highlighting the contribution of other knee joint tissues in OA pathogenesis. Despite much progress in the field of microfluidic systems/organs-on-a-chip in other research fields, current in vitro models in use do not yet accurately reflect the complexity of the OA pathophenotype. In this review, we provide: 1) a detailed overview of the most significant recent developments in the field of microsystems approaches for OA modeling, and 2) an OA-pathophysiology-based bioengineering roadmap for the requirements of the next generation of more predictive and authentic microscale systems fit for the purpose of not only disease modeling but also of drug screening to potentially allow OA animal model reduction and replacement in the near future.

Is a Bioengineered Heart From Recipient Tissues the Answer to the Shortage of Donors in Heart Transplantation?

With the increase in life expectancy worldwide, end-organ failure is becoming more prevalent. In addition, improving post-transplant outcomes has contributed to soaring demand for organs. Unfortunately, thousands have died waiting on the transplant list due to the critical shortage of organs. The success of bioengineered hearts may eventually lead to the production of limitless organs using the patient’s own cells that can be transplanted into them without the need for immunosuppressive medications. Despite being in its infancy, scientists are making tremendous strides in “growing” an artificial heart in the lab. We discuss these processes involved in bioengineering a human-compatible heart in this review. The components of a functional heart must be replicated in a bioengineered heart to make it viable. This review aims to discuss the advances that have already been made and the future challenges of bioengineering a human heart suitable for transplantation.

An Edible, Decellularized Plant Derived Cell Carrier for Lab Grown Meat

Rapidly expanding skeletal muscle satellite cells with cost-effective methods have been presented as a solution for meeting the growing global demand for meat. A common strategy for scaling cell proliferation employs microcarriers, small beads designed to support anchorage-dependent cells in suspension-style bioreactors. No carrier has yet been marketed for the cultivation of lab-grown meat. The objective of this study was to demonstrate a rapid, food safe, decellularization procedure to yield cell-free extracellular matrix scaffolds and evaluate them as cell carriers for lab grown meat. Broccoli florets were soaked in SDS, Tween-20, and bleach for 48 h. The decellularization process was confirmed via histology, which showed an absence of cell nuclei, and DNA quantification (0.0037 ± 0.00961 μg DNA/mg tissue). Decellularized carriers were sorted by cross sectional area (7.07 ± 1.74 mm2, 3.03 ± 1.15 mm2, and 0.49 ± 0.3 mm2) measured for eccentricity (0.73 ± 0.16). Density measurements of decellularized carriers (1.01 ± 0.01 g/cm) were comparable to traditional microcarriers. Primary bovine satellite cells were inoculated into and cultured within a reactor containing decellularized carriers. Cell adhesion was observed and cell death was limited to 2.55 ± 1.09%. These studies suggested that broccoli florets may serve as adequate edible carrier scaffolds for satellite cells.

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.

Cardiac Organoids: A 3D Technology for Modeling Heart Development and Disease

Cardiac organoids (COs) are miniaturized and simplified organ structures that can be used in heart development biology, drug screening, disease modeling, and regenerative medicine. This cardiac organoid (CO) model is revolutionizing our perspective on answering major cardiac physiology and pathology issues. Recently, many research groups have reported various methods for modeling the heart in vitro. However, there are differences in methodologies and concepts. In this review, we discuss the recent advances in cardiac organoid technologies derived from human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), with a focus on the summary of methods for organoid generation. In addition, we introduce CO applications in modeling heart development and cardiovascular diseases and discuss the prospects for and common challenges of CO that still need to be addressed. A detailed understanding of the development of CO will help us design better methods, explore and expand its application in the cardiovascular field.

Three decades of heart transplantation: experience and long-term outcome

Objectives. Heart transplantation (HTx) has become an established treatment option in patients with end-stage heart failure. The aim of this study was to report on long-term outcome over the past three decades. Design. Consecutive adult patients receiving first-time and isolated HTx from October 3, 1990, to November 2, 2020, at Rigshospitalet, Copenhagen, Denmark, were retrospectively evaluated. Data were obtained from the Scandinavian Transplant Registry and patient medical records. Recipients were grouped by time of transplantation (early era: 1990-1999; mid era: 2000-2009; recent era: 2010-2020). Results. A total of 384 recipients (77% men, median age 50 [IQR: 40-57]) were included. Median number of HTx procedures per year was 12 (10-14). Overall, 22% of patients were bridged to HTx with a mechanical circulatory support device. Median survival for the whole cohort was 13.8 years and improved numerically from the early era (12.6 years) to the mid era (14.9 years). Median survival conditional on survival to 1-year follow-up after HTx was 16.1 years. Survival probability by Kaplan-Meier method improved significantly from the mid to the recent era (log-rank p = .02). Conclusions. Heart transplantation remains an excellent treatment for selected patients with end-stage heart failure and long-term outcome has improved significantly over the past decades.

Structural and Functional Support by Left Atrial Appendage Transplant to the Left Ventricle after a Myocardial Infarction

The left atrial appendage (LAA) of the adult heart has been shown to contain cardiac and myeloid progenitor cells. The resident myeloid progenitor population expresses an array of pro-regenerative paracrine factors. Cardiac constructs have been shown to inhibit deleterious remodeling of the heart using physical support. Due to these aspects, LAA holds promise as a regenerative transplant. LAAs from adult mT/mG mice were transplanted to the recipient 129X1-SvJ mice simultaneously as myocardial infarction (MI) was performed. A decellularized LAA patch was implanted in the control group. Two weeks after MI, the LAA patch had integrated to the ventricular wall, and migrated cells were seen in the MI area. The cells had two main phenotypes: small F4/80+ cells and large troponin C+ cells. After follow-up at 8 weeks, the LAA patch remained viable, and the functional status of the heart improved. Cardiac echo demonstrated that, after 6 weeks, the mice in the LAA-patch-treated group showed an increasing and statistically significant improvement in cardiac performance when compared to the MI and MI + decellularized patch controls. Physical patch-support (LAA and decellularized LAA patch) had an equal effect on the inhibition of deleterious remodeling, but only the LAA patch inhibited the hypertrophic response. Our study demonstrates that the LAA transplantation has the potential for use as a treatment for myocardial infarction. This method can putatively combine cell therapy (regenerative effect) and physical support (inhibition of deleterious remodeling).

Decellularization of Full Heart—Optimizing the Classical Sodium-Dodecyl-Sulfate-Based Decellularization Protocol

Compared to cell therapy, where cells are injected into a defect region, the treatment of heart infarction with cells seeded in a vascularized scaffold bears advantages, such as an immediate nutrient supply or a controllable and persistent localization of cells. For this purpose, decellularized native tissues are a preferable choice as they provide an in vivo-like microenvironment. However, the quality of such scaffolds strongly depends on the decellularization process. Therefore, two protocols based on sodium dodecyl sulfate or sodium deoxycholate were tailored and optimized for the decellularization of a porcine heart. The obtained scaffolds were tested for their applicability to generate vascularized cardiac patches. Decellularization with sodium dodecyl sulfate was found to be more suitable and resulted in scaffolds with a low amount of DNA, a highly preserved extracellular matrix composition, and structure shown by GAG quantification and immunohistochemistry. After seeding human endothelial cells into the vasculature, a coagulation assay demonstrated the functionality of the endothelial cells to minimize the clotting of blood. Human-induced pluripotent-stem-cell-derived cardiomyocytes in co-culture with fibroblasts and mesenchymal stem cells transferred the scaffold into a vascularized cardiac patch spontaneously contracting with a frequency of 25.61 ± 5.99 beats/min for over 16 weeks. The customized decellularization protocol based on sodium dodecyl sulfate renders a step towards a preclinical evaluation of the scaffolds.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.