Cardiac Tissue Engineering Models of Inherited and Acquired Cardiomyopathies

A Novel In Vitro Pathological Model for Studying Neural Invasion in Non-Melanoma Skin Cancer

Neural Invasion (NI) is a key pathological feature of cancer in the colonization of distant tissues, and its underlying biological mechanisms are still scarcely known. The complex interactions between nerve and tumor cells, along with the stroma, make it difficult to reproduce this pathology in effective study models, which in turn has limited the understanding of NI pathogenesis. In this study, we have designed a three-dimensional model of NI squamous cell carcinoma combining human epidermoid carcinoma cells (hECCs) with a complete peripheral nerve segment encapsulated in a fibrine-agarose hydrogel. We recreated two vital processes of NI: a pre-invasive NI model in which hECCs were seeded on the top of the nerve-enriched stroma, and an invasive NI model in which cancer cells were immersed with the nerve in the hydrogel. Histological, histochemical and immunohistochemical analyses were performed to validate the model. Results showed that the integration of fibrin-agarose advanced hydrogel with a complete nerve structure and hECCs successfully generated an environment in which tumor cells and nerve components coexisted. Moreover, this model correctly preserved components of the neural extracellular matrix as well as allowing the proliferation and migration of cells embedded in hydrogel. All these results suggest the suitability of the model for the study of the mechanisms underlaying NI.

A Workflow to Produce a Low-Cost In Vitro Platform for the Electric-Field Pacing of Cellularised 3D Porous Scaffolds

Endogenous electrically mediated signaling is a key feature of most native tissues, the most notable examples being the nervous and the cardiac systems. Biomedical engineering often aims to harness and drive such activity in vitro, in bioreactors to study cell disease and differentiation, and often in three-dimensional (3D) formats with the help of biomaterials, with most of these approaches adopting scaffold-free self-assembling strategies to create 3D tissues. In essence, this is the casting of gels which self-assemble in response to factors such as temperature or pH and have capacity to harbor cells during this process without imparting toxicity. However, the use of materials that do not self-assemble but can support 3D encapsulation of cells (such as porous scaffolds) warrants consideration given the larger repertoire this would provide in terms of material physicochemical properties and microstructure. In this method and protocol paper, we detail and provide design codes and assembly instructions to cheaply create an electrical pacing bioreactor and a Rig for Stimulation of Sponge-like Scaffolds (R3S). This setup has also been engineered to simultaneously perform live optical imaging of the in vitro models. To showcase a pilot exploration of material physiochemistry (in this aspect material conductivity) and microstructure (isotropy versus anisotropy), we adopt isotropic and anisotropic porous scaffolds composed of collagen or poly(3,4-ethylene dioxythiophene):polystyrenesulfonate (PEDOT:PSS) for their contrasting conductivity properties yet similar in porosity and mechanical integrity. Electric field pacing of mouse C3H10 cells on anisotropic porous scaffolds placed in R3S led to increased metabolic activity and enhanced cell alignment. Furthermore, after 7 days electrical pacing drove C3H10 alignment regardless of material conductivity or anisotropy. This platform and its design, which we have shared, have wide suitability for the study of electrical pacing of cellularized scaffolds in 3D in vitro cultures.

Recent advances in biological pumps as a building block for bioartificial hearts

The field of biological pumps is a subset of cardiac tissue engineering and focused on the development of tubular grafts that are designed generate intraluminal pressure. In the simplest embodiment, biological pumps are tubular grafts with contractile cardiomyocytes on the external surface. The rationale for biological pumps is a transition from planar 3D cardiac patches to functional biological pumps, on the way to complete bioartificial hearts. Biological pumps also have applications as a standalone device, for example, to support the Fontan circulation in pediatric patients. In recent years, there has been a lot of progress in the field of biological pumps, with innovative fabrication technologies. Examples include the use of cell sheet engineering, self-organized heart muscle, bioprinting and in vivo bio chambers for vascularization. Several materials have been tested for biological pumps and included resected aortic segments from rodents, type I collagen, and fibrin hydrogel, to name a few. Multiple bioreactors have been tested to condition biological pumps and replicate the complex in vivo environment during controlled in vitro culture. The purpose of this article is to provide an overview of the field of the biological pumps, outlining progress in the field over the past several years. In particular, different fabrication methods, biomaterial platforms for tubular grafts and examples of bioreactors will be presented. In addition, we present an overview of some of the challenges that need to be overcome for the field of biological pumps to move forward.

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

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

Engineering spatial-organized cardiac organoids for developmental toxicity testing

Emerging technologies in stem cell engineering have produced sophisticated organoid platforms by controlling stem cell fate via biomaterial instructive cues. By micropatterning and differentiating human induced pluripotent stem cells (hiPSCs), we have engineered spatially organized cardiac organoids with contracting cardiomyocytes in the center surrounded by stromal cells distributed along the pattern perimeter. We investigated how geometric confinement directed the structural morphology and contractile functions of the cardiac organoids and tailored the pattern geometry to optimize organoid production. Using modern data-mining techniques, we found that pattern sizes significantly affected contraction functions, particularly in the parameters related to contraction duration and diastolic functions. We applied cardiac organoids generated from 600 μm diameter circles as a developmental toxicity screening assay and quantified the embryotoxic potential of nine pharmaceutical compounds. These cardiac organoids have potential use as an in vitro platform for studying organoid structure-function relationships, developmental processes, and drug-induced cardiac developmental toxicity.

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Micropattern-based geometric confinement directs cardiac organoid development

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Cardiac organoid structure-function relationships are guided by organoid size

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Cardiac organoids can be used as an in vitro embryotoxicity assessment tool

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

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

Engineering and Assessing Cardiac Tissue Complexity

Cardiac tissue engineering is very much in a current focus of regenerative medicine research as it represents a promising strategy for cardiac disease modelling, cardiotoxicity testing and cardiovascular repair. Advances in this field over the last two decades have enabled the generation of human engineered cardiac tissue constructs with progressively increased functional capabilities. However, reproducing tissue-like properties is still a pending issue, as constructs generated to date remain immature relative to native adult heart. Moreover, there is a high degree of heterogeneity in the methodologies used to assess the functionality and cardiac maturation state of engineered cardiac tissue constructs, which further complicates the comparison of constructs generated in different ways. Here, we present an overview of the general approaches developed to generate functional cardiac tissues, discussing the different cell sources, biomaterials, and types of engineering strategies utilized to date. Moreover, we discuss the main functional assays used to evaluate the cardiac maturation state of the constructs, both at the cellular and the tissue levels. We trust that researchers interested in developing engineered cardiac tissue constructs will find the information reviewed here useful. Furthermore, we believe that providing a unified framework for comparison will further the development of human engineered cardiac tissue constructs displaying the specific properties best suited for each particular application.

A methodological nine-step process to bioengineer heart muscle tissue

Research in the field of heart muscle tissue engineering is focused on the fabrication of heart muscle tissue which can be utilized to repair, replace and/or augment functionality of damaged and/or diseased tissue. In the simplest embodiment, bioengineering heart muscle tissue constructs involves culture of cardiomyocytes within natural or synthetic scaffolds. Functional integration of the cells with the scaffold and subsequent remodeling lead to the formation of 3D heart muscle tissue and physiological cues like mechanical stretch, electrical stimulation and perfusion are necessary to guide tissue maturation and development. Potential applications for bioengineered heart muscle include use as grafts to repair or replace damaged tissue, as models for basic research and as tools for high-throughput screening of pharmacological agents. In this article, we provide a methodological process to bioengineer functional 3D heart muscle tissue and discuss state of the art and potential challenges in each of the nine-step tissue fabrication process.

Tissue engineering solutions to replace contractile function during pediatric heart surgery

Pediatric heart surgery remains challenging due to the small size of the pediatric heart, the severity of congenital abnormalities and the unique characteristics of each case. New tools and technologies are needed to tackle this enormous challenge. Tissue engineering strategies are focused on fabricating contractile heart muscle, ventricles, Fontan pumps and whole hearts, and a transplantable tissue equivalent has tremendous implications in pediatric heart surgery to provide functional cardiac tissue. This technology will prove to be a game-changer in the field of pediatric heart surgery and provide a novel toolkit for pediatric heart surgeons. This review will provide insight into the potential applications of tissue engineering technologies to replace lost contractile function in pediatric patients with heart abnormalities.

Beyond Family: Modeling Non-hereditary Heart Diseases With Human Pluripotent Stem Cell-Derived Cardiomyocytes

Non-genetic cardiac pathologies develop as an aftermath of extracellular stress-conditions. Nevertheless, the response to pathological stimuli depends deeply on intracellular factors such as physiological state and complex genetic backgrounds. Without a thorough characterization of their in vitro phenotype, modeling of maladaptive hypertrophy, ischemia and reperfusion injury or diabetes in human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) has been more challenging than hereditary diseases with defined molecular causes. In past years, greater insights into hPSC-CM in vitro physiology and advancements in technological solutions and culture protocols have generated cell types displaying stress-responsive phenotypes reminiscent of in vivo pathological events, unlocking their application as a reductionist model of human cardiomyocytes, if not the adult human myocardium. Here, we provide an overview of the available literature of pathology models for cardiac non-genetic conditions employing healthy (or asymptomatic) hPSC-CMs. In terms of numbers of published articles, these models are significantly lagging behind monogenic diseases, which misrepresents the incidence of heart disease causes in the human population.

Adult human cardiac stem cell supplementation effectively increases contractile function and maturation in human engineered cardiac tissues

BACKGROUND

Delivery of stem cells to the failing heart is a promising therapeutic strategy. However, the improvement in cardiac function in animal studies has not fully translated to humans. To help bridge the gap between species, we investigated the effects of adult human cardiac stem cells (hCSCs) on contractile function of human engineered cardiac tissues (hECTs) as a species-specific model of the human myocardium.

METHODS

Human induced pluripotent stem cell-derived cardiomyoctes (hCMs) were mixed with Collagen/Matrigel to fabricate control hECTs, with an experimental group of hCSC-supplemented hECT fabricated using a 9:1 ratio of hCM to hCSC. Functional testing was performed starting on culture day 6, under spontaneous conditions and also during electrical pacing from 0.25 to 1.0 Hz, measurements repeated at days 8 and 10. hECTs were then frozen and processed for gene analysis using a Nanostring assay with a cardiac targeted custom panel.

RESULTS

The hCSC-supplemented hECTs displayed a twofold higher developed force vs. hCM-only controls by day 6, with approximately threefold higher developed stress and maximum rates of contraction and relaxation during pacing at 0.75 Hz. The spontaneous beat rate characteristics were similar between groups, and hCSC supplementation did not adversely impact beat rate variability. The increased contractility persisted through days 8 and 10, albeit with some decrease in the magnitude of the difference of the force by day 10, but with developed stress still significantly higher in hCSC-supplemented hECT; these findings were confirmed with multiple hCSC and hCM cell lines. The force-frequency relationship, while negative for both, control (- 0.687 Hz^- 1; p = 0.013 vs. zero) and hCSC-supplemented (- 0.233 Hz^- 1;p = 0.067 vs. zero) hECTs, showed a significant rectification in the regression slope in hCSC-supplemented hECT (p = 0.011 vs. control). Targeted gene exploration (59 genes) identified a total of 14 differentially expressed genes, with increases in the ratios of MYH7/MHY6, MYL2/MYL7, and TNNI3/TNNI1 in hCSC-supplemented hECT versus controls.

CONCLUSIONS

For the first time, hCSC supplementation was shown to significantly improve human cardiac tissue contractility in vitro, without evidence of proarrhythmic effects, and was associated with increased expression of markers of cardiac maturation. These findings provide new insights about adult cardiac stem cells as contributors to functional improvement of human myocardium.

Biomaterializing the promise of cardiac tissue engineering

During an average individual's lifespan, the human heart pumps nearly 200 million liters of blood delivered by approximately 3 billion heartbeats. Therefore, it is not surprising that native myocardium under this incredible demand is extraordinarily complex, both structurally and functionally. As a result, successful engineering of adult-mimetic functional cardiac tissues is likely to require utilization of highly specialized biomaterials representative of the native extracellular microenvironment. There is currently no single biomaterial that fully recapitulates the architecture or the biochemical and biomechanical properties of adult myocardium. However, significant effort has gone toward designing highly functional materials and tissue constructs that may one day provide a ready source of cardiac tissue grafts to address the overwhelming burden of cardiomyopathic disease. In the near term, biomaterial-based scaffolds are helping to generate in vitro systems for querying the mechanisms underlying human heart homeostasis and disease and discovering new, patient-specific therapeutics. When combined with advances in minimally-invasive cardiac delivery, ongoing efforts will likely lead to scalable cell and biomaterial technologies for use in clinical practice. In this review, we describe recent progress in the field of cardiac tissue engineering with particular emphasis on use of biomaterials for therapeutic tissue design and delivery.