Engineering cardiac microphysiological systems to model pathological extracellular matrix remodeling

Model construction and clinical therapeutic potential of engineered cardiac organoids for cardiovascular diseases

Cardiovascular diseases cause significant morbidity and mortality worldwide. Engineered cardiac organoids are being developed and used to replicate cardiac tissues supporting cardiac morphogenesis and development. These organoids have applications in drug screening, cardiac disease models and regenerative medicine. Therefore, a thorough understanding of cardiac organoids and a comprehensive overview of their development are essential for cardiac tissue engineering. This review summarises different types of cardiac organoids used to explore cardiac function, including those based on co-culture, aggregation, scaffolds, and geometries. The self-assembly of monolayers, multilayers and aggravated cardiomyocytes forms biofunctional cell aggregates in cardiac organoids, elucidating the formation mechanism of scaffold-free cardiac organoids. In contrast, scaffolds such as decellularised extracellular matrices, three-dimensional hydrogels and bioprinting techniques provide a supportive framework for cardiac organoids, playing a crucial role in cardiac development. Different geometries are engineered to create cardiac organoids, facilitating the investigation of intrinsic communication between cardiac organoids and biomechanical pathways. Additionally, this review emphasises the relationship between cardiac organoids and the cardiac system, and evaluates their clinical applications. This review aims to provide valuable insights into the study of three-dimensional cardiac organoids and their clinical potential.

Optically Active, Paper-Based Scaffolds for 3D Cardiac Pacing

In this work, we report the design and fabrication of a light-addressable, paper-based nanocomposite scaffold for optical pacing and read-out of in vitro grown cardiac tissue. The scaffold consists of paper cellulose microfibers functionalized with gold nanorods (GNRs) and semiconductor quantum dots (QDs), embedded in a cell-permissive collagen matrix. The GNRs enable cardiomyocyte activity modulation through local temperature gradients induced by modulated near-infrared (NIR) laser illumination, with the local temperature changes reported by temperature-dependent QD photoluminescence (PL). The micrometer-sized paper fibers promote the tubular organization of HL-1 cardiac muscle cells, while the NIR plasmonic stimulation modulates reversibly their activity. Given the nanoscale spatial resolution and facile fabrication, paper-based nanocomposite scaffolds with NIR modulation offer excellent alternatives to electrode-based or optogenetic methods for cell activity modulation, at the single cell level, and are compatible with 3D tissue constructs. Such paper-based optical platforms can provide new possibilities for the development of in vitro drug screening assays and heart disease modeling.

Programmed spontaneously beating cardiomyocytes in regenerative cardiology

Stem cells have gained attention as a promising therapeutic approach for damaged myocardium, and there have been efforts to develop a protocol for regenerating cardiomyocytes (CMs). Certain cells have showed a greater aptitude for yielding beating CMs, such as induced pluripotent stem cells, embryonic stem cells, adipose-derived stromal vascular fraction cells and extended pluripotent stem cells. The approach for generating CMs from stem cells differs across studies, although there is evidence that Wnt signaling, chemical additives, electrical stimulation, co-culture, biomaterials and transcription factors triggers CM differentiation. Upregulation of Gata4, Mef2c and Tbx5 transcription factors has been correlated with successfully induced CMs, although Mef2c may potentially play a more prominent role in the generation of the beating phenotype, specifically. Regenerative research provides a possible candidate for cardiac repair; however, it is important to identify factors that influence their differentiation. Altogether, the spontaneously beating CMs would be monumental for regenerative research for cardiac repair.

Steering cell orientation through light-based spatiotemporal modulation of the mechanical environment

The anisotropic organization of cells and the extracellular matrix (ECM) is essential for the physiological function of numerous biological tissues, including the myocardium. This organization changes gradually in space and time, during disease progression such as myocardial infarction. The role of mechanical stimuli has been demonstrated to be essential in obtaining, maintaining and de-railing this organization, but the underlying mechanisms are scarcely known. To enable the study of the mechanobiological mechanisms involved,in vitrotechniques able to spatiotemporally control the multiscale tissue mechanical environment are thus necessary. Here, by using light-sensitive materials combined with light-illumination techniques, we fabricated 2D and 3Din vitromodel systems exposing cells to multiscale, spatiotemporally resolved stiffness anisotropies. Specifically, spatial stiffness anisotropies spanning from micron-sized (cellular) to millimeter-sized (tissue) were achieved. Moreover, the light-sensitive materials allowed to introduce the stiffness anisotropies at defined timepoints (hours) after cell seeding, facilitating the study of their temporal effects on cell and tissue orientation. The systems were tested using cardiac fibroblasts (cFBs), which are known to be crucial for the remodeling of anisotropic cardiac tissue. We observed that 2D stiffness micropatterns induced cFBs anisotropic alignment, independent of the stimulus timing, but dependent on the micropattern spacing. cFBs exhibited organized alignment also in response to 3D stiffness macropatterns, dependent on the stimulus timing and temporally followed by (slower) ECM co-alignment. In conclusion, the developed model systems allow improved fundamental understanding of the underlying mechanobiological factors that steer cell and ECM orientation, such as stiffness guidance and boundary constraints.

Detergent-Based Decellularization for Anisotropic Cardiac-Specific Extracellular Matrix Scaffold Generation

Cell-derived extracellular matrix (ECM) has become increasingly popular in tissue engineering applications due to its ability to provide tailored signals for desirable cellular responses. Anisotropic cardiac-specific ECM scaffold decellularized from human induced pluripotent stem cell (hiPSC)-derived cardiac fibroblasts (hiPSC-CFs) mimics the native cardiac microenvironment and provides essential biochemical and signaling cues to hiPSC-derived cardiomyocytes (hiPSC-CMs). The objective of this study was to assess the efficacy of two detergent-based decellularization methods: (1) a combination of ethylenediaminetetraacetic acid and sodium dodecyl sulfate (EDTA + SDS) and (2) a combination of sodium deoxycholate and deoxyribonuclease (SD + DNase), in preserving the composition and bioactive substances within the aligned ECM scaffold while maximumly removing cellular components. The decellularization effects were evaluated by characterizing the ECM morphology, quantifying key structural biomacromolecules, and measuring preserved growth factors. Results showed that both treatments met the standard of cell removal (less than 50 ng/mg ECM dry weight) and substantially preserved major ECM biomacromolecules and growth factors. The EDTA + SDS treatment was more time-efficient and has been determined to be a more efficient method for generating an anisotropic ECM scaffold from aligned hiPSC-CFs. Moreover, this cardiac-specific ECM has demonstrated effectiveness in supporting the alignment of hiPSC-CMs and their expression of mature structural and functional proteins in in vitro cultures, which is crucial for cardiac tissue engineering.

Biomimetic Approaches in Cardiac Tissue Engineering: Replicating the Native Heart Microenvironment

Cardiovascular diseases, including heart failure, pose significant challenges in medical practice, necessitating innovative approaches for cardiac repair and regeneration. Cardiac tissue engineering has emerged as a promising solution, aiming to develop functional and physiologically relevant cardiac tissue constructs. Replicating the native heart microenvironment, with its complex and dynamic milieu necessary for cardiac tissue growth and function, is crucial in tissue engineering. Biomimetic strategies that closely mimic the natural heart microenvironment have gained significant interest due to their potential to enhance synthetic cardiac tissue functionality and therapeutic applicability. Biomimetic approaches focus on mimicking biochemical cues, mechanical stimuli, coordinated electrical signaling, and cell-cell/cell-matrix interactions of cardiac tissue. By combining bioactive ligands, controlled delivery systems, appropriate biomaterial characteristics, electrical signals, and strategies to enhance cell interactions, biomimetic approaches provide a more physiologically relevant environment for tissue growth. The replication of the native cardiac microenvironment enables precise regulation of cellular responses, tissue remodeling, and the development of functional cardiac tissue constructs. Challenges and future directions include refining complex biochemical signaling networks, paracrine signaling, synchronized electrical networks, and cell-cell/cell-matrix interactions. Advancements in biomimetic approaches hold great promise for cardiovascular regenerative medicine, offering potential therapeutic strategies and revolutionizing cardiac disease modeling. These approaches contribute to the development of more effective treatments, personalized medicine, and improved patient outcomes. Ongoing research and innovation in biomimetic approaches have the potential to revolutionize regenerative medicine and cardiac disease modeling by replicating the native heart microenvironment, advancing functional cardiac tissue engineering, and improving patient outcomes.

3D-bioprinted cardiac tissues and their potential for disease modeling

Heart diseases cause over 17.9 million total deaths globally, making them the leading source of mortality. The aim of this review is to describe the characteristic mechanical, chemical and cellular properties of human cardiac tissue and how these properties can be mimicked in 3D bioprinted tissues. Furthermore, the authors review how current healthy cardiac models are being 3D bioprinted using extrusion-, laser- and inkjet-based printers. The review then discusses the pathologies of cardiac diseases and how bioprinting could be used to fabricate models to study these diseases and potentially find new drug targets for such diseases. Finally, the challenges and future directions of cardiac disease modeling using 3D bioprinting techniques are explored.

Culturing of Cardiac Fibroblasts in Engineered Heart Matrix Reduces Myofibroblast Differentiation but Maintains Their Response to Cyclic Stretch and Transforming Growth Factor β1

Isolation and culturing of cardiac fibroblasts (CF) induces rapid differentiation toward a myofibroblast phenotype, which is partly mediated by the high substrate stiffness of the culture plates. In the present study, a 3D model of Engineered Heart Matrix (EHM) of physiological stiffness (Youngs modulus ~15 kPa) was developed using primary adult rat CF and a natural hydrogel collagen type 1 matrix. CF were equally distributed, viable and quiescent for at least 13 days in EHM and the baseline gene expression of myofibroblast-markers alfa-smooth muscle actin (Acta2), and connective tissue growth factor (Ctgf) was significantly lower, compared to CF cultured in 2D monolayers. CF baseline gene expression of transforming growth factor-beta1 (Tgfβ1) and brain natriuretic peptide (Nppb) was higher in EHM-fibers compared to the monolayers. EHM stimulation by 10% cyclic stretch (1 Hz) increased the gene expression of Nppb (3.0-fold), Ctgf (2.1-fold) and Tgfβ1 (2.3-fold) after 24 h. Stimulation of EHM with TGFβ1 (1 ng/mL, 24 h) induced Tgfβ1 (1.6-fold) and Ctgf (1.6-fold). In conclusion, culturing CF in EHM of physiological stiffness reduced myofibroblast marker gene expression, while the CF response to stretch or TGFβ1 was maintained, indicating that our novel EHM structure provides a good physiological model to study CF function and myofibroblast differentiation.

Visible-Light Stiffness Patterning of GelMA Hydrogels Towards In Vitro Scar Tissue Models

Variations in mechanical properties of the extracellular matrix occurs in various processes, such as tissue fibrosis. The impact of changes in tissue stiffness on cell behaviour are studied in vitro using various types of biomaterials and methods. Stiffness patterning of hydrogel scaffolds, through the use of stiffness gradients for instance, allows the modelling and studying of cellular responses to fibrotic mechanisms. Gelatine methacryloyl (GelMA) has been used extensively in tissue engineering for its inherent biocompatibility and the ability to precisely tune its mechanical properties. Visible light is now increasingly employed for crosslinking GelMA hydrogels as it enables improved cell survival when performing cell encapsulation. We report here, the photopatterning of mechanical properties of GelMA hydrogels with visible light and eosin Y as the photoinitiator using physical photomasks and projection with a digital micromirror device. Using both methods, binary hydrogels with areas of different stiffnesses and hydrogels with stiffness gradients were fabricated. Their mechanical properties were characterised using force indentation with atomic force microscopy, which showed the efficiency of both methods to spatially pattern the elastic modulus of GelMA according to the photomask or the projected pattern. Crosslinking through projection was also used to build constructs with complex shapes. Overall, this work shows the feasibility of patterning the stiffness of GelMA scaffolds, in the range from healthy to pathological stiffness, with visible light. Consequently, this method could be used to build in vitro models of healthy and fibrotic tissue and study the cellular behaviours involved at the interface between the two.

IGFBP-4 Proteolysis by PAPP-A in a Primary Culture of Rat Neonatal Cardiomyocytes under Normal and Hypertrophic Conditions

Cardiovascular diseases (CVD) are among the leading causes of death and disability worldwide. Pregnancy-associated plasma protein-A (PAPP-A) is a matrix metalloprotease localized on the cell surface. One of the substrates that PAPP-A cleaves is the insulin-like growth factor binding protein-4 (IGFBP-4), a member of the family of proteins that bind insulin-like growth factor (IGF). Proteolysis of IGFBP-4 by PAPP-A occurs at a specific site resulting in formation of two proteolytic fragments - N-terminal IGFBP-4 (NT-IGFBP-4) and C-terminal IGFBP-4 (CT-IGFBP-4), and leads to the release of IGF activating various cellular processes including migration, proliferation, and cell growth. Increased levels of the proteolytic IGFBP-4 fragments correlate with the development of CVD complications and increased risk of death in patients with the coronary heart disease, acute coronary syndrome, and heart failure. However, there is no direct evidence that PAPP-A specifically cleaves IGFBP-4 in the cardiac tissue under normal and pathological conditions. In the present study, using a primary culture of rat neonatal cardiomyocytes as a model, we have demonstrated that: 1) proteolysis of IGFBP-4 by PAPP-A occurs in the conditioned medium of cardiomyocytes, 2) PAPP-A-specific IGFBP-4 proteolysis is increased when cardiomyocytes are transformed to a hypertrophic state. Thus, it can be assumed that the enhancement of IGFBP-4 cleavage by PAPP-A and hypertrophic changes in cardiomyocytes accompanying CVD are interrelated, and PAPP-A appears to be one of the activators of the IGF-dependent processes in normal and hypertrophic-state cardiomyocytes.

Modeling Cardiomyopathies in a Dish: State-of-the-Art and Novel Perspectives on hiPSC-Derived Cardiomyocytes Maturation

The stem cell technology and the induced pluripotent stem cells (iPSCs) production represent an excellent alternative tool to study cardiomyopathies, which overcome the limitations associated with primary cardiomyocytes (CMs) access and manipulation. CMs from human iPSCs (hiPSC-CMs) are genetically identical to patient primary cells of origin, with the main electrophysiological and mechanical features of CMs. The key issue to be solved is to achieve a degree of structural and functional maturity typical of adult CMs. In this perspective, we will focus on the main differences between fetal-like hiPSC-CMs and adult CMs. A viewpoint is given on the different approaches used to improve hiPSC-CMs maturity, spanning from long-term culture to complex engineered heart tissue. Further, we outline limitations and future developments needed in cardiomyopathy disease modeling.

Engineering the Cellular Microenvironment of Post-infarct Myocardium on a Chip

Myocardial infarctions are one of the most common forms of cardiac injury and death worldwide. Infarctions cause immediate necrosis in a localized region of the myocardium, which is followed by a repair process with inflammatory, proliferative, and maturation phases. This repair process culminates in the formation of scar tissue, which often leads to heart failure in the months or years after the initial injury. In each reparative phase, the infarct microenvironment is characterized by distinct biochemical, physical, and mechanical features, such as inflammatory cytokine production, localized hypoxia, and tissue stiffening, which likely each contribute to physiological and pathological tissue remodeling by mechanisms that are incompletely understood. Traditionally, simplified two-dimensional cell culture systems or animal models have been implemented to elucidate basic pathophysiological mechanisms or predict drug responses following myocardial infarction. However, these conventional approaches offer limited spatiotemporal control over relevant features of the post-infarct cellular microenvironment. To address these gaps, Organ on a Chip models of post-infarct myocardium have recently emerged as new paradigms for dissecting the highly complex, heterogeneous, and dynamic post-infarct microenvironment. In this review, we describe recent Organ on a Chip models of post-infarct myocardium, including their limitations and future opportunities in disease modeling and drug screening.

Cardiac Organoids to Model and Heal Heart Failure and Cardiomyopathies

Cardiac tissue engineering aims at creating contractile structures that can optimally reproduce the features of human cardiac tissue. These constructs are becoming valuable tools to model some of the cardiac functions, to set preclinical platforms for drug testing, or to alternatively be used as therapies for cardiac repair approaches. Most of the recent developments in cardiac tissue engineering have been made possible by important advances regarding the efficient generation of cardiac cells from pluripotent stem cells and the use of novel biomaterials and microfabrication methods. Different combinations of cells, biomaterials, scaffolds, and geometries are however possible, which results in different types of structures with gradual complexities and abilities to mimic the native cardiac tissue. Here, we intend to cover key aspects of tissue engineering applied to cardiology and the consequent development of cardiac organoids. This review presents various facets of the construction of human cardiac 3D constructs, from the choice of the components to their patterning, the final geometry of generated tissues, and the subsequent readouts and applications to model and treat cardiac diseases.

Bioengineering approaches to mature induced pluripotent stem cell-derived atrial cardiomyocytes to model atrial fibrillation

Induced pluripotent stem cells (iPSCs) serve as a robust platform to model several human arrhythmia syndromes including atrial fibrillation (AF). However, the structural, molecular, functional, and electrophysiological parameters of patient-specific iPSC-derived atrial cardiomyocytes (iPSC-aCMs) do not fully recapitulate the mature phenotype of their human adult counterparts. The use of physiologically inspired microenvironmental cues, such as postnatal factors, metabolic conditioning, extracellular matrix (ECM) modulation, electrical and mechanical stimulation, co-culture with non-parenchymal cells, and 3D culture techniques can help mimic natural atrial development and induce a more mature adult phenotype in iPSC-aCMs. Such advances will not only elucidate the underlying pathophysiological mechanisms of AF, but also identify and assess novel mechanism-based therapies towards supporting a more 'personalized' (i.e. patient-specific) approach to pharmacologic therapy of AF.

In Vitro Methods to Model Cardiac Mechanobiology in Health and Disease

In vitro cardiac modeling has taken great strides in the past decade. While most cell and engineered tissue models have focused on cell and tissue contractile function as readouts, mechanobiological cues from the cell environment that affect this function, such as matrix stiffness or organization, are less well explored. In this study, we review two-dimensional (2D) and three-dimensional (3D) models of cardiac function that allow for systematic manipulation or precise control of mechanobiological cues under simulated (patho)physiological conditions while acquiring multiple readouts of cell and tissue function. We summarize the cell types used in these models and highlight the importance of linking 2D and 3D models to address the multiscale organization and mechanical behavior. Finally, we provide directions on how to advance in vitro modeling for cardiac mechanobiology using next generation hydrogels that mimic mechanical and structural environmental features at different length scales and diseased cell types, along with the development of new tissue fabrication and readout techniques. Impact statement Understanding the impact of mechanobiology in cardiac (patho)physiology is essential for developing effective tissue regeneration and drug discovery strategies and requires detailed cause-effect studies. The development of three-dimensional in vitro models allows for such studies with high experimental control, while integrating knowledge from complementary cell culture models and in vivo studies for this purpose. Complemented by the use of human-induced pluripotent stem cells, with or without predisposed genetic diseases, these in vitro models will offer promising outlooks to delineate the impact of mechanobiological cues on human cardiac (patho)physiology in a dish.

Pathophysiological Basis for Nutraceutical Supplementation in Heart Failure: A Comprehensive Review

There is evidence demonstrating that heart failure (HF) occurs in 1-2% of the global population and is often accompanied by comorbidities which contribute to increasing the prevalence of the disease, the rate of hospitalization and the mortality. Although recent advances in both pharmacological and non-pharmacological approaches have led to a significant improvement in clinical outcomes in patients affected by HF, residual unmet needs remain, mostly related to the occurrence of poorly defined strategies in the early stages of myocardial dysfunction. Nutritional support in patients developing HF and nutraceutical supplementation have recently been shown to possibly contribute to protection of the failing myocardium, although their place in the treatment of HF requires further assessment, in order to find better therapeutic solutions. In this context, the Optimal Nutraceutical Supplementation in Heart Failure (ONUS-HF) working group aimed to assess the optimal nutraceutical approach to HF in the early phases of the disease, in order to counteract selected pathways that are imbalanced in the failing myocardium. In particular, we reviewed several of the most relevant pathophysiological and molecular changes occurring during the early stages of myocardial dysfunction. These include mitochondrial and sarcoplasmic reticulum stress, insufficient nitric oxide (NO) release, impaired cardiac stem cell mobilization and an imbalanced regulation of metalloproteinases. Moreover, we reviewed the potential of the nutraceutical supplementation of several natural products, such as coenzyme Q10 (CoQ10), a grape seed extract, Olea Europea L.-related antioxidants, a sodium-glucose cotransporter (SGLT2) inhibitor-rich apple extract and a bergamot polyphenolic fraction, in addition to their support in cardiomyocyte protection, in HF. Such an approach should contribute to optimising the use of nutraceuticals in HF, and the effect needs to be confirmed by means of more targeted clinical trials exploring the efficacy and safety of these compounds.

Engineering Shape-Controlled Microtissues on Compliant Hydrogels with Tunable Rigidity and Extracellular Matrix Ligands

In vitro models that recapitulate key aspects of native tissue architecture and the physical microenvironment are emerging systems for modeling development and disease. For example, the myocardium consists of layers of aligned and coupled cardiac myocytes that are interspersed with supporting cells and embedded in a compliant extracellular matrix (ECM). These cell-cell and cell-matrix interactions are known to be important regulators of tissue physiology and pathophysiology. In this protocol, we describe a method for mimicking the alignment, cell-cell interactions, and rigidity of the myocardium by engineering an array of square, aligned cardiac microtissues on polyacrylamide hydrogels. This entails three key methods: (1) fabricating elastomer stamps with a microtissue pattern; (2) preparing polyacrylamide hydrogel culture substrates with tunable elastic moduli; and (3) transferring ECM proteins onto the surface of the hydrogels using microcontact printing. These hydrogels can then be seeded with cardiac myocytes or mixtures of cardiac myocytes and fibroblasts to adjust cell-cell interactions. Overall, this approach is advantageous because shape-controlled microtissues encompass both cell-cell and cell-matrix adhesions in a form factor that is relatively reproducible and scalable. Furthermore, polyacrylamide hydrogels are compatible with the traction force microscopy assay for quantifying contractility, a critical function of the myocardium. Although cardiac microtissues are the example presented in this protocol, the techniques are relatively versatile and could have many applications in modeling other tissue systems.

Maladaptive Contractility of 3D Human Cardiac Microtissues to Mechanical Nonuniformity

Cardiac tissues are able to adjust their contractile behavior to adapt to the local mechanical environment. Nonuniformity of the native tissue mechanical properties contributes to the development of heart dysfunctions, yet the current in vitro cardiac tissue models often fail to recapitulate the mechanical nonuniformity. To address this issue, a 3D cardiac microtissue model is developed with engineered mechanical nonuniformity, enabled by 3D-printed hybrid matrices composed of fibers with different diameters. When escalating the complexity of tissue mechanical environments, cardiac microtissues start to develop maladaptive hypercontractile phenotypes, demonstrated in both contractile motion analysis and force-power analysis. This novel hybrid system could potentially facilitate the establishment of "pathologically-inspired" cardiac microtissue models for deeper understanding of heart pathology due to nonuniformity of the tissue mechanical environment.

Extracellular matrix in cardiovascular pathophysiology

The extracellular matrix (ECM) actively participates in diverse aspects of cardiovascular development and physiology as well as during disease development and progression. ECM roles are determined by its physical and mechanical properties and by its capacity to both release bioactive signals and activate cell signaling pathways. The ECM serves as a storage depot for a wide variety of molecules released in response to injury or with aging. Indeed, there is a plethora of examples describing how cells react to or modify ECM stiffness, how cells initiate intracellular signaling pathways, and how cells respond to the ECM. This Perspectives article reviews the contributions of 21 articles published in the American Journal of Physiology-Heart and Circulatory Physiology in response to a Call for Papers on this topic. Here, we summarize the contributions of these studies focused on the cardiac and vascular ECM. We highlight the translational importance of these studies and conclude that the ECM is a critical component of both the heart and vasculature. Readers are urged to examine and learn from this special Call for Papers.