Current State of the Art in Myocardial Tissue Engineering

Current Strategies for Engineered Vascular Grafts and Vascularized Tissue Engineering

Blood vessels not only transport oxygen and nutrients to each organ, but also play an important role in the regulation of tissue regeneration. Impaired or occluded vessels can result in ischemia, tissue necrosis, or even life-threatening events. Bioengineered vascular grafts have become a promising alternative treatment for damaged or occlusive vessels. Large-scale tubular grafts, which can match arteries, arterioles, and venules, as well as meso- and microscale vasculature to alleviate ischemia or prevascularized engineered tissues, have been developed. In this review, materials and techniques for engineering tubular scaffolds and vasculature at all levels are discussed. Examples of vascularized tissue engineering in bone, peripheral nerves, and the heart are also provided. Finally, the current challenges are discussed and the perspectives on future developments in biofunctional engineered vessels are delineated.

Recent advances in modified poly (lactic acid) as tissue engineering materials

As an emerging science, tissue engineering and regenerative medicine focus on developing materials to replace, restore or improve organs or tissues and enhancing the cellular capacity to proliferate, migrate and differentiate into different cell types and specific tissues. Renewable resources have been used to develop new materials, resulting in attempts to produce various environmentally friendly biomaterials. Poly (lactic acid) (PLA) is a biopolymer known to be biodegradable and it is produced from the fermentation of carbohydrates. PLA can be combined with other polymers to produce new biomaterials with suitable physicochemical properties for tissue engineering applications. Here, the advances in modified PLA as tissue engineering materials are discussed in light of its drawbacks, such as biological inertness, low cell adhesion, and low degradation rate, and the efforts conducted to address these challenges toward the design of new enhanced alternative biomaterials.

The role of major immune cells in myocardial infarction

Myocardial infarction (MI) is a cardiovascular disease (CVD) with high morbidity and mortality worldwide, often leading to adverse cardiac remodeling and heart failure, which is a serious threat to human life and health. The immune system makes an important contribution to the maintenance of normal cardiac function. In the disease process of MI, necrotic cardiomyocytes release signals that activate nonspecific immunity and trigger the action of specific immunity. Complex immune cells play an important role in all stages of MI progression by removing necrotic cardiomyocytes and tissue and promoting the healing of damaged tissue cells. With the development of biomaterials, cardiac patches have become an emerging method of repairing MI, and the development of engineered cardiac patches through the construction of multiple animal models of MI can help treat MI. This review introduces immune cells involved in the development of MI, summarizes the commonly used animal models of MI and the newly developed cardiac patch, so as to provide scientific reference for the accurate diagnosis and effective treatment of MI.

Microphysiological stem cell models of the human heart

Models of heart disease and drug responses are increasingly based on human pluripotent stem cells (hPSCs) since their ability to capture human heart (dys-)function is often better than animal models. Simple monolayer cultures of hPSC-derived cardiomyocytes, however, have shortcomings. Some of these can be overcome using more complex, multi cell-type models in 3D. Here we review modalities that address this, describe efforts to tailor readouts and sensors for monitoring tissue- and cell physiology (exogenously and in situ) and discuss perspectives for implementation in industry and academia.

From arteries to capillaries: approaches to engineering human vasculature

From micro-scaled capillaries to millimeter-sized arteries and veins, human vasculature spans multiple scales and cell types. The convergence of bioengineering, materials science, and stem cell biology has enabled tissue engineers to recreate the structure and function of different hierarchical levels of the vascular tree. Engineering large-scale vessels has been pursued over the past thirty years to replace or bypass damaged arteries, arterioles, and venules, and their routine application in the clinic may become a reality in the near future. Strategies to engineer meso- and microvasculature have been extensively explored to generate models to study vascular biology, drug transport, and disease progression, as well as for vascularizing engineered tissues for regenerative medicine. However, bioengineering of large-scale tissues and whole organs for transplantation, have failed to result in clinical translation due to the lack of proper integrated vasculature for effective oxygen and nutrient delivery. The development of strategies to generate multi-scale vascular networks and their direct anastomosis to host vasculature would greatly benefit this formidable goal. In this review, we discuss design considerations and technologies for engineering millimeter-, meso-, and micro-scale vessels. We further provide examples of recent state-of-the-art strategies to engineer multi-scale vasculature. Finally, we identify key challenges limiting the translation of vascularized tissues and offer our perspective on future directions for exploration.

Reduced graphene oxide foam templated by nickel foam for organ-on-a-chip engineering of cardiac constructs

Myocardial tissue engineering has attracted increasing awareness for heart failure, and researchers are committed to developing an appropriate biological material to reconstruct myocardial tissues. Here, we applied a simple and high-throughput method to fabricate a three-dimensional (3D) partially reduced graphene oxide (PRGO) foam chip, whose structure, properties and biocompatibility confirmed that it is a suitable material for myocardial tissue engineering. The PRGO foam was produced based on a reduction reaction that occurred at the interface between the graphene oxide (GO) solution and Ni foam; as the Ni foam scaffold was dissolved in an HCl solution, the PRGO foam was harvested. After the PRGO foam was freeze-dried, its elasticity property was evaluated, and primary cardiomyocytes obtained from 2-day-old SD rats were cultured in the 3D foam. The results demonstrated good cell adherence, spreading, activity, organization and beating function in the PRGO foam during the long-term culturing process, which proved that the PRGO foam obtained by this method had application potential for myocardial tissue engineering.

Myocardial tissue engineering strategies for heart repair: current state of the art

The current state-of-the-art treatment for heart failure patients is aimed at delaying disease progression, relieving symptoms, reducing morbidity and improving survival. Cardiac regeneration of the injured heart, however, is not achieved. Currently, numerous alternative treatment approaches aiming at cardiac regeneration are under investigation. Myocardial tissue engineering strategies follow the idea of in vitro generation of myocardium-like structures for epicardial transplantation. Recently, this field has made tremendous advances regarding in vitro optimization of tissue-engineered constructs, and valuable data have been generated in small animal models. This review summarizes the technical aspects of engineered human myocardium generation, lessons learned from preclinical in vitro and in vivo studies and the current state of this approach on its way to clinical translation.

Contact guidance for cardiac tissue engineering using 3D bioprinted gelatin patterned hydrogel

Here, we have developed a 3D bioprinted microchanneled gelatin hydrogel that promotes human mesenchymal stem cell (hMSC) myocardial commitment and supports native cardiomyocytes (CMs) contractile functionality. Firstly, we studied the effect of bioprinted microchanneled hydrogel on the alignment, elongation, and differentiation of hMSC. Notably, the cells displayed well defined F-actin anisotropy and elongated morphology on the microchanneled hydrogel, hence showing the effects of topographical control over cell behavior. Furthermore, the aligned stem cells showed myocardial lineage commitment, as detected using mature cardiac markers. The fluorescence-activated cell sorting analysis also confirmed a significant increase in the commitment towards myocardial tissue lineage. Moreover, seeded CMs were found to be more aligned and demonstrated synchronized beating on microchanneled hydrogel as compared to the unpatterned hydrogel. Overall, our study proved that microchanneled hydrogel scaffold produced by 3D bioprinting induces myocardial differentiation of stem cells as well as supports CMs growth and contractility. Applications of this approach may be beneficial for generating in vitro cardiac model systems to physiological and cardiotoxicity studies as well as in vivo generating custom designed cell impregnated constructs for tissue engineering and regenerative medicine applications.

Poly(3-hydroxyoctanoate), a promising new material for cardiac tissue engineering

Cardiac tissue engineering (CTE) is currently a prime focus of research because of an enormous clinical need. In the present work, a novel functional material, poly(3-hydroxyoctanoate), P(3HO), a medium chain-length polyhydroxyalkanoate (PHA), produced using bacterial fermentation, was studied as a new potential material for CTE. Engineered constructs with improved mechanical properties, crucial for supporting the organ during new tissue regeneration, and enhanced surface topography, to allow efficient cell adhesion and proliferation, were fabricated. Results showed that the mechanical properties of the final patches were close to that of cardiac muscle. Biocompatibility of neat P(3HO) patches, assessed using neonatal ventricular rat myocytes (NVRM), showed that the polymer was as good as collagen in terms of cell viability, proliferation and adhesion. Enhanced cell adhesion and proliferation properties were observed when porous and fibrous structures were incorporated into the patches. In addition, no deleterious effect was observed on adult cardiomyocyte contraction when cardiomyocytes were seeded on the P(3HO) patches. Hence, P(3HO)-based multifunctional cardiac patches are promising constructs for efficient CTE. This work will have a positive impact on the development of P(3HO) and other PHAs as a novel new family of biodegradable functional materials with huge potential in a range of different biomedical applications, particularly CTE, leading to further interest and exploitation of these materials. Copyright © 2016 John Wiley & Sons, Ltd.

Establishing Early Functional Perfusion and Structure in Tissue Engineered Cardiac Constructs

Myocardial infarction (MI) causes massive heart muscle death and remains a leading cause of death in the world. Cardiac tissue engineering aims to replace the infarcted tissues with functional engineered heart muscles or revitalize the infarcted heart by delivering cells, bioactive factors, and/or biomaterials. One major challenge of cardiac tissue engineering and regeneration is the establishment of functional perfusion and structure to achieve timely angiogenesis and effective vascularization, which are essential to the survival of thick implants and the integration of repaired tissue with host heart. In this paper, we review four major approaches to promoting angiogenesis and vascularization in cardiac tissue engineering and regeneration: delivery of pro-angiogenic factors/molecules, direct cell implantation/cell sheet grafting, fabrication of prevascularized cardiac constructs, and the use of bioreactors to promote angiogenesis and vascularization. We further provide a detailed review and discussion on the early perfusion design in nature-derived biomaterials, synthetic biodegradable polymers, tissue-derived acellular scaffolds/whole hearts, and hydrogel derived from extracellular matrix. A better understanding of the current approaches and their advantages, limitations, and hurdles could be useful for developing better materials for future clinical applications.

Nano-Enabled Approaches for Stem Cell-Based Cardiac Tissue Engineering

Cardiac diseases are the most prevalent causes of mortality in the world, putting a major economic burden on global healthcare system. Tissue engineering strategies aim at developing efficient therapeutic approaches to overcome the current challenges in prolonging patients survival upon cardiac diseases. The integration of advanced biomaterials and stem cells has offered enormous promises for regeneration of damaged myocardium. Natural or synthetic biomaterials have been extensively used to deliver cells or bioactive molecules to the site of injury in heart. Additionally, nano-enabled approaches (e.g., nanomaterials, nanofeatured surfaces) have been instrumental in developing suitable scaffolding biomaterials and regulating stem cells microenvironment to achieve functional therapeutic outcomes. This review article explores tissue engineering strategies, which have emphasized on the use of nano-enabled approaches in combination with stem cells for regeneration and repair of injured myocardium upon myocardial infarction (MI). Primarily a wide range of biomaterials, along with different types of stem cells, which have utilized in cardiac tissue engineering will be presented. Then integration of nanomaterials and surface nanotopographies with biomaterials and stem cells for myocardial regeneration will be presented. The advantages and challenges of these approaches will be reviewed and future perspective will be discussed.

Cardiomyocyte behavior on biodegradable polyurethane/gold nanocomposite scaffolds under electrical stimulation

Following a myocardial infarction (MI), cardiomyocytes are replaced by scar tissue, which decreases ventricular contractile function. Tissue engineering is a promising approach to regenerate such damaged cardiomyocyte tissue. Engineered cardiac patches can be fabricated by seeding a high density of cardiac cells onto a synthetic or natural porous polymer. In this study, nanocomposite scaffolds made of gold nanotubes/nanowires incorporated into biodegradable castor oil-based polyurethane were employed to make micro-porous scaffolds. H9C2 cardiomyocyte cells were cultured on the scaffolds for one day, and electrical stimulation was applied to improve cell communication and interaction in neighboring pores. Cells on scaffolds were examined by fluorescence microscopy and scanning electron microscopy, revealing that the combination of scaffold design and electrical stimulation significantly increased cell confluency of H9C2 cells on the scaffolds. Furthermore, we showed that the gene expression levels of Nkx2.5, atrial natriuretic peptide (ANF) and natriuretic peptide precursor B (NPPB), which are functional genes of the myocardium, were up-regulated by the incorporation of gold nanotubes/nanowires into the polyurethane scaffolds, in particular after electrical stimulation.

Three-dimensional extracellular matrix scaffolds by microfluidic fabrication for long-term spontaneously contracted cardiomyocyte culture

To repair damaged cardiac tissue, the important principle of in vitro cell culture is to mimic the in vivo cell growth environment. Thus, micro-sized cells are more suitably cultured in three-dimensional (3D) than in two-dimensional (2D) microenvironments (ex: culture dish). With the matching dimensions of works produced by microfluidic technology, chemical engineering and biochemistry applications have used this technology extensively in cellular works. The 3D scaffolds produced in our investigation has essential properties, such has high mass transfer efficiency, and variable pore sizes, to adapt to various needs of different cell types. In addition to the malleability of these innovative scaffolds, fabrication procedure was effortless and fast. Primary neonatal mice cardiomyocytes were successfully harvested and cultured in 3D scaffolds made of gelatin and collagen. Gelatin and gelatin-collagen scaffold were produced by the formation of microbubbles through a microfluidic device, and the mechanical properties of gelatin scaffold and gelatin-collagen scaffold were measured. Cellular properties in the microbubbles were also monitored. Fluorescence staining results assured that cardiomyocytes could maintain in vivo morphology in 3D gelatin scaffold. In addition, it was found that 3D scaffold could prolong the contraction behavior of cardiomyocytes compared with a conventional 2D culture dish. Spontaneously contracted behavior was maintained for the longest (about 1 month) in the 3D gelatin scaffold, about 19 days in the 3D gelatin-collagen scaffold. To sum up, this 3D platform for cell culture has promising potential for myocardial tissue engineering.

Heart regeneration with engineered myocardial tissue

Heart disease is the leading cause of morbidity and mortality worldwide, and regenerative therapies that replace damaged myocardium could benefit millions of patients annually. The many cell types in the heart, including cardiomyocytes, endothelial cells, vascular smooth muscle cells, pericytes, and cardiac fibroblasts, communicate via intercellular signaling and modulate each other's function. Although much progress has been made in generating cells of the cardiovascular lineage from human pluripotent stem cells, a major challenge now is creating the tissue architecture to integrate a microvascular circulation and afferent arterioles into such an engineered tissue. Recent advances in cardiac and vascular tissue engineering will move us closer to the goal of generating functionally mature tissue. Using the biology of the myocardium as the foundation for designing engineered tissue and addressing the challenges to implantation and integration, we can bridge the gap from bench to bedside for a clinically tractable engineered cardiac tissue.

Tropoelastin: a versatile, bioactive assembly module

Elastin provides structural integrity, biological cues and persistent elasticity to a range of important tissues, including the vasculature and lungs. Its critical importance to normal physiology makes it a desirable component of biomaterials that seek to repair or replace these tissues. The recent availability of large quantities of the highly purified elastin monomer, tropoelastin, has allowed for a thorough characterization of the mechanical and biological mechanisms underpinning the benefits of mature elastin. While tropoelastin is a flexible molecule, a combination of optical and structural analyses has defined key regions of the molecule that directly contribute to the elastomeric properties and control the cell interactions of the protein. Insights into the structure and behavior of tropoelastin have translated into increasingly sophisticated elastin-like biomaterials, evolving from classically manufactured hydrogels and fibers to new forms, stabilized in the absence of incorporated cross-linkers. Tropoelastin is also compatible with synthetic and natural co-polymers, expanding the applications of its potential use beyond traditional elastin-rich tissues and facilitating finer control of biomaterial properties and the design of next-generation tailored bioactive materials.

Highly Elastic Micropatterned Hydrogel for Engineering Functional Cardiac Tissue

Heart failure is a major international health issue. Myocardial mass loss and lack of contractility are precursors to heart failure. Surgical demand for effective myocardial repair is tempered by a paucity of appropriate biological materials. These materials should conveniently replicate natural human tissue components, convey persistent elasticity, promote cell attachment, growth and conformability to direct cell orientation and functional performance. Here, microfabrication techniques are applied to recombinant human tropoelastin, the resilience-imparting protein found in all elastic human tissues, to generate photocrosslinked biological materials containing well-defined micropatterns. These highly elastic substrates are then used to engineer biomimetic cardiac tissue constructs. The micropatterned hydrogels, produced through photocrosslinking of methacrylated tropoelastin (MeTro), promote the attachment, spreading, alignment, function, and intercellular communication of cardiomyocytes by providing an elastic mechanical support that mimics their dynamic mechanical properties in vivo. The fabricated MeTro hydrogels also support the synchronous beating of cardiomyocytes in response to electrical field stimulation. These novel engineered micropatterned elastic gels are designed to be amenable to 3D modular assembly and establish a versatile, adaptable foundation for the modeling and regeneration of functional cardiac tissue with potential for application to other elastic tissues.

Natural ECM as biomaterial for scaffold based cardiac regeneration using adult bone marrow derived stem cells

Cellular therapy using stem cells for cardiac diseases has recently gained much interest in the scientific community due to its potential in regenerating damaged and even dead tissue and thereby restoring the organ function. Stem cells from various sources and origin are being currently used for regeneration studies directly or along with differentiation inducing agents. Long term survival and minimal side effects can be attained by using autologous cells and reduced use of inducing agents. Cardiomyogenic differentiation of adult derived stem cells has been previously reported using various inducing agents but the use of a potentially harmful DNA demethylating agent 5-azacytidine (5-azaC) has been found to be critical in almost all studies. Alternate inducing factors and conditions/stimulant like physical condition including electrical stimulation, chemical inducers and biological agents have been attempted by numerous groups to induce cardiac differentiation. Biomaterials were initially used as artificial scaffold in in vitro studies and later as a delivery vehicle. Natural ECM is the ideal biological scaffold since it contains all the components of the tissue from which it was derived except for the living cells. Constructive remodeling can be performed using such natural ECM scaffolds and stem cells since, the cells can be delivered to the site of infraction and once delivered the cells adhere and are not "lost". Due to the niche like conditions of ECM, stem cells tend to differentiate into tissue specific cells and attain several characteristics similar to that of functional cells even in absence of any directed differentiation using external inducers. The development of niche mimicking biomaterials and hybrid biomaterial can further advance directed differentiation without specific induction. The mechanical and electrical integration of these materials to the functional tissue is a problem to be addressed. The search for the perfect extracellular matrix for therapeutic applications including engineering cardiac tissue structures for post ischemic cardiac tissue regeneration continues.

Myocardial scaffold-based cardiac tissue engineering: application of coordinated mechanical and electrical stimulations

Recently, we developed an optimal decellularization protocol to generate 3D porcine myocardial scaffolds, which preserve the natural extracellular matrix structure, mechanical anisotropy, and vasculature templates and also show good cell recellularization and differentiation potential. In this study, a multistimulation bioreactor was built to provide coordinated mechanical and electrical stimulation for facilitating stem cell differentiation and cardiac construct development. The acellular myocardial scaffolds were seeded with mesenchymal stem cells (10(6) cells/mL) by needle injection and subjected to 5-azacytidine treatment (3 μmol/L, 24 h) and various bioreactor conditioning protocols. We found that after 2 days of culturing with mechanical (20% strain) and electrical stimulation (5 V, 1 Hz), high cell density and good cell viability were observed in the reseeded scaffold. Immunofluorescence staining demonstrated that the differentiated cells showed a cardiomyocyte-like phenotype by expressing sarcomeric α-actinin, myosin heavy chain, cardiac troponin T, connexin-43, and N-cadherin. Biaxial mechanical testing demonstrated that positive tissue remodeling took place after 2 days of bioreactor conditioning (20% strain + 5 V, 1 Hz); passive mechanical properties of the 2 day and 4 day tissue constructs were comparable to those of the tissue constructs produced by stirring reseeding followed by 2 weeks of static culturing, implying the effectiveness and efficiency of the coordinated simulations in promoting tissue remodeling. In short, the synergistic stimulations might be beneficial not only for the quality of cardiac construct development but also for patients by reducing the waiting time in future clinical scenarios.

Engineered cell-laden human protein-based elastomer

Elastic tissue equivalence is a vital requirement of synthetic materials proposed for many resilient, soft tissue engineering applications. Here we present a bioelastomer made from tropoelastin, the human protein that naturally facilitates elasticity and cell interactions in all elastic tissues. We combined this protein's innate versatility with fast non-toxic fabrication techniques to make highly extensible, cell compatible hydrogels. These hydrogels can be produced in less than a minute through photocrosslinking of methacrylated tropoelastin (MeTro) in an aqueous solution. The fabricated MeTro gels exhibited high extensibility (up to 400%) and superior mechanical properties that outperformed other photocrosslinkable hydrogels. MeTro gels were used to encapsulate cells within a flexible 3D environment and to manufacture highly elastic 2D films for cell attachment, growth, and proliferation. In addition, the physical properties of this fabricated bioelastomer such as elasticity, stiffness, and pore characteristics were tuned through manipulation of the methacrylation degree and protein concentration. This photocrosslinkable, functional tissue mimetic gel benefits from the innate biological properties of a human elastic protein and opens new opportunities in tissue engineering.

Impact of cardiac stem cell sheet transplantation on myocardial infarction

PURPOSE

Myocardial infarction (MI) remains a major cause of mortality because of the limited regenerative capacity of the myocardium. Transplantation of somatic tissue-derived cells into the heart has been shown to enhance the endogenous healing process, but the magnitude of its therapeutic effects is dependent upon the cell-source or cell-delivery method. We investigated the therapeutic effects of C-Kit positive cardiac cell (CSC) cell-sheet transplantation therapy in a rat model of MI.

METHODS AND RESULTS

CSCs of human origin were sorted and cultured to generate scaffold-free CSC cell-sheets. One-layered or 3-layered cell-sheets were transplanted into nude rats 1 h after left coronary artery ligation. We observed a significant increase in the left ventricular ejection fraction and a significant decrease in left ventricular systolic dimension at 2 and 4 weeks in the 3-layer group, but not in the 1-layer or sham groups. Consistently, there was less accumulation of interstitial fibrosis in the 3-layer group than in the 1-layer or sham groups. Moreover, capillary density was significantly greater in the 3-layer group than in the 1-layer or sham groups.

CONCLUSIONS

The 3-layered cell-sheet improved cardiac function associated with angiogenic and anti-fibrotic effects. Thus, CSC is a promising cell-source to use with the cell-sheet method for the treatment of cardiac failure, as long as a sufficient number of cells are delivered.

Biomimetic three-dimensional anisotropic geometries by uniaxial stretch of poly(ε-caprolactone) films for mesenchymal stem cell proliferation, alignment, and myogenic differentiation

Anisotropic geometries are critical for eliciting cell alignment to dictate tissue microarchitectures and biological functions. Current fabrication techniques are complex and utilize toxic solvents, hampering their applications for translational research. Here, we present a novel simple, solvent-free, and reproducible method via uniaxial stretching for incorporating anisotropic topographies on bioresorbable films with ambitions to realize stem cell alignment control. Uniaxial stretching of poly(ε-caprolactone) (PCL) films resulted in a three-dimensional micro-ridge/groove topography (inter-ridge-distance: ~6 μm; ridge-length: ~90 μm; ridge-depth: 200-900 nm) with uniform distribution and controllable orientation by the direction of stretch on the whole film surface. When stretch temperature (Ts) and draw ratio (DR) were increased, the inter-ridge-distance was reduced and ridge-length increased. Through modification of hydrolysis, increased surface hydrophilicity was achieved, while maintaining the morphology of PCL ridge/grooves. Upon seeding human mesenchymal stem cells (hMSCs) on uniaxial-stretched PCL (UX-PCL) films, aligned hMSC organization was obtained. Compared to unstretched films, hMSCs on UX-PCL had larger increase in cellular alignment (>85%) and elongation, without indication of cytotoxicity or reduction in cellular proliferation. This aligned hMSC organization was homogenous and stably maintained with controlled orientation along the ridges on the whole UX-PCL surface for over 2 weeks. Moreover, the hMSCs on UX-PCL had a higher level of myogenic genes' expression than that on the unstretched films. We conclude that uniaxial stretching has potential in patterning film topography with anisotropic structures. The UX-PCL in conjunction with hMSCs could be used as "basic units" to create tissue constructs with microscale control of cellular alignment and elongation for tissue engineering applications.

Cell therapies for heart function recovery: focus on myocardial tissue engineering and nanotechnologies

Cell therapies have gained increasing interest and developed in several approaches related to the treatment of damaged myocardium. The results of multiple clinical trials have already been reported, almost exclusively involving the direct injection of stem cells. It has, however, been postulated that the efficiency of injected cells could possibly be hindered by the mechanical trauma due to the injection and their low survival in the hostile environment. It has indeed been demonstrated that cell mortality due to the injection approaches 90%. Major issues still need to be resolved and bed-to-bench followup is paramount to foster clinical implementations. The tissue engineering approach thus constitutes an attractive alternative since it provides the opportunity to deliver a large number of cells that are already organized in an extracellular matrix. Recent laboratory reports confirmed the interest of this approach and already encouraged a few groups to investigate it in clinical studies. We discuss current knowledge regarding engineered tissue for myocardial repair or replacement and in particular the recent implementation of nanotechnological approaches.

Functional scaffold-free 3-D cardiac microtissues: a novel model for the investigation of heart cells

To bridge the gap between two-dimensional cell culture and tissue, various three-dimensional (3-D) cell culture approaches have been developed for the investigation of cardiac myocytes (CMs) and cardiac fibroblasts (CFs). However, several limitations still exist. This study was designed to develop a cardiac 3-D culture model with a scaffold-free technology that can easily and inexpensively generate large numbers of microtissues with cellular distribution and functional behavior similar to cardiac tissue. Using micromolded nonadhesive agarose hydrogels containing 822 concave recesses (800 μm deep × 400 μm wide), we demonstrated that neonatal rat ventricular CMs and CFs alone or in combination self-assembled into viable (Live/Dead stain) spherical-shaped microtissues. Importantly, when seeded simultaneously or sequentially, CMs and CFs self-sorted to be interspersed, reminiscent of their myocardial distribution, as shown by cell type-specific CellTracker or antibody labeling. Microelectrode recordings and optical mapping revealed characteristic triangular action potentials (APs) with a resting membrane potential of -66 ± 7 mV (n = 4) in spontaneously contracting CM microtissues. Under pacing, optically mapped AP duration at 90% repolarization and conduction velocity were 100 ± 30 ms and 18.0 ± 1.9 cm/s, respectively (n = 5 each). The presence of CFs led to a twofold AP prolongation in heterogenous microtissues (CM-to-CF ratio of 1:1). Importantly, Ba(2+)-sensitive inward rectifier K(+) currents and Ca(2+)-handling proteins, including sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a, were detected in CM-containing microtissues. Furthermore, cell type-specific adenoviral gene transfer was achieved, with no impact on microtissue formation or cell viability. In conclusion, we developed a novel scaffold-free cardiac 3-D culture model with several advancements for the investigation of CM and CF function and cross-regulation.

Substrates for cardiovascular tissue engineering

Cardiovascular tissue engineering aims to find solutions for the suboptimal regeneration of heart valves, arteries and myocardium by creating 'living' tissue replacements outside (in vitro) or inside (in situ) the human body. A combination of cells, biomaterials and environmental cues of tissue development is employed to obtain tissues with targeted structure and functional properties that can survive and develop within the harsh hemodynamic environment of the cardiovascular system. This paper reviews the up-to-date status of cardiovascular tissue engineering with special emphasis on the development and use of biomaterial substrates. Key requirements and properties of these substrates, as well as methods and readout parameters to test their efficacy in the human body, are described in detail and discussed in the light of current trends toward designing biologically inspired microenviroments for in situ tissue engineering purposes.

Tissue-engineered cardiac constructs for cardiac repair

Several recent basic research studies have described surgical methods for cardiac repair using tissue cardiomyoplasty. This review summarizes recent advances in cardiac repair using bioengineered tissue from the viewpoint of the cardiac surgeon. We conclude that the results of many basic and preclinical studies indicate that bioengineered tissue can be adapted to conventional surgical techniques. However, no clinical studies have yet proved bioengineered tissue is effective as a treatment for human heart failure. Today's cardiac surgeons can look forward to the advent of new techniques to benefit patients who respond poorly to existing treatment for heart failure.

Transplantation of cardiac progenitor cell sheet onto infarcted heart promotes cardiogenesis and improves function

AIMS

Cell-based therapy for myocardial infarction (MI) holds great promise; however, the ideal cell type and delivery system have not been established. Obstacles in the field are the massive cell death after direct injection and the small percentage of surviving cells differentiating into cardiomyocytes. To overcome these challenges we designed a novel study to deliver cardiac progenitor cells as a cell sheet.

METHODS AND RESULTS

Cell sheets composed of rat or human cardiac progenitor cells (cardiospheres), and cardiac stromal cells were transplanted onto the infarcted myocardium after coronary artery ligation in rats. Three weeks later, transplanted cells survived, proliferated, and differentiated into cardiomyocytes (14.6 +/- 4.7%). Cell sheet transplantation suppressed cardiac wall thinning and increased capillary density (194 +/- 20 vs. 97 +/- 24 per mm(2), P < 0.05) compared with the untreated MI. Cell migration from the sheet was observed along the necrotic trails within the infarcted area. The migrated cells were located in the vicinity of stromal-derived factor (SDF-1) released from the injured myocardium, and about 20% of these cells expressed CXCR4, suggesting that the SDF-1/CXCR4 axis plays, at least, a role in cell migration. Transplantation of cell sheets resulted in a preservation of cardiac contractile function after MI, as was shown by a greater ejection fraction and lower left ventricular end diastolic pressure compared with untreated MI.

CONCLUSION

The scaffold-free cardiosphere-derived cell sheet approach seeks to efficiently deliver cells and increase cell survival. These transplanted cells effectively rescue myocardium function after infarction by promoting not only neovascularization but also inducing a significant level of cardiomyogenesis.

Cellular cardiomyoplasty: what have we learned?

Restoring blood flow, improving perfusion, reducing clinical symptoms, and augmenting ventricular function are the goals after acute myocardial infarction. Other than cardiac transplantation, no standard clinical procedure is available to restore damaged myocardium. Since we first reported cellular cardiomyoplasty in 1989, successful outcomes have been confirmed by experimental and clinical studies, but definitive long-term efficacy requires large-scale placebo-controlled double-blind randomized trials. On meta-analysis, stem cell-treated groups had significantly improved left ventricular ejection fraction, reduced infarct scar size, and decreased left ventricular end-systolic volume. Fewer myocardial infarctions, deaths, readmissions for heart failure, and repeat revascularizations were additional benefits. Encouraging clinical findings have been reported using satellite or bone marrow stem cells, but understanding of the benefit mechanisms demands additional studies. Adult mammalian ventricular myocardium lacks adequate regeneration capability, and cellular cardiomyoplasty offers a new way to overcome this; the poor retention and engraftment rate and high apoptotic rate of the implanted stem cells limit outcomes. The ideal type and number of cells, optimal timing of cell therapy, and ideal cell delivery method depend on determining the beneficial mechanisms. Cellular cardiomyoplasty has progressed rapidly in the last decade. A critical review may help us to better plan the future direction.

Use of arginine-glycine-aspartic acid adhesion peptides coupled with a new collagen scaffold to engineer a myocardium-like tissue graft

BACKGROUND

Cardiac tissue engineering might be useful in treatment of diseased myocardium or cardiac malformations. The creation of functional, biocompatible contractile tissues, however, remains challenging. We hypothesized that coupling of arginine-glycine-aspartic acid-serine (RGD+) adhesion peptides would improve cardiomyocyte viability and differentiation and contractile performance of collagen-cell scaffolds.

METHODS

Clinically approved collagen scaffolds were functionalized with RGD+ cells and seeded with cardiomyocytes. Contractile performance, cardiomyocyte viability and differentiation were analyzed at days 1 and 8 and/or after culture for 1 month.

RESULTS

The method used for the RGD+ cell-collagen scaffold coupling enabled the following features: high coupling yields and complete washout of excess reagent and by-products with no need for chromatography; spectroscopic quantification of RGD+ coupling; a spacer arm of 36 A, a length reported as optimal for RGD+-peptide presentation and favorable for integrin-receptor clustering and subsequent activation. Isotonic and isometric mechanical parameters, either spontaneous or electrostimulated, exhibited good performance in RGD+ constructs. Cell number and viability was increased in RGD+ scaffolds, and we saw good organization of cell contractile apparatus with occurrence of cross-striation.

CONCLUSIONS

We report a novel method of engineering a highly effective collagen-cell scaffold based on RGD+ peptides cross-linked to a clinically approved collagen matrix. The main advantages were cell contractile performance, cardiomyocyte viability and differentiation.

Myocardial repair: from salvage to tissue reconstruction

Cardiac tissue reconstruction following myocardial infarction represents a major challenge in cardiovascular therapy, as current clinical approaches are limited in their ability to regenerate or replace damaged myocardium. Thus, different novel treatments have been introduced aimed at myocardial salvage and repair. Here, we present a review of recent advancements in cardiac cell, gene-based and tissue engineering therapies. Selected strategies in cell therapy and new tools for myocardial gene transfer are summarized. Finally, we consider novel approaches to myocardial tissue engineering as a platform for the integration of various modalities in an attempt to rejuvenate infarcted tissue in vivo.

Myocardial Assistance by Grafting a New Bioartificial Upgraded Myocardium (MAGNUM trial): clinical feasibility study

BACKGROUND

Cell transplantation for the regeneration of ischemic myocardium is limited by poor graft viability and low cell retention. In ischemic cardiomyopathy, the extracellular matrix is deeply altered; therefore, it could be important to associate a procedure aiming at regenerating myocardial cells and restoring the extracellular matrix function. We evaluated the feasibility and safety of intrainfarct cell therapy associated with a cell-seeded collagen scaffold grafted onto infarcted ventricles.

METHODS

In 20 consecutive patients presenting with left ventricular postischemic myocardial scars and indication for coronary artery bypass graft surgery, bone marrow cells were implanted during surgery. In the last 10 patients, we added a collagen matrix seeded with bone marrow cells, placed onto the scar.

RESULTS

There was no mortality and any related adverse events (follow-up 10 +/- 3.5 months). New York Heart Association functional class improved in both groups from 2.3 +/- 0.5 to 1.3 +/- 0.5 (matrix, p = 0.0002) versus 2.4 +/- 0.5 to 1.5 +/- 0.5 (no matrix, p = 0.001). Left ventricular end-diastolic volume evolved from 142.4 +/- 24.5 mL to 112.9 +/- 27.3 mL (matrix, p = 0.02) versus 138.9 +/- 36.1 mL to 148.7 +/- 41 mL (no matrix, p = 0.57), left ventricular filling deceleration time improved significantly in the matrix group from 162 +/- 7 ms to 198 +/- 9 ms (p = 0.01) versus the no-matrix group (from 159 +/- 5 ms to 167 +/- 8 ms, p = 0.07). Scar area thickness progressed from 6 +/- 1.4 to 9 mm +/- 1.1 mm (matrix, p = 0.005) versus 5 +/- 1.5 mm to 6 +/- 0.8 mm (no matrix, p = 0.09). Ejection fraction improved in both groups, from 25.3% +/- 7.3% to 32% +/- 5.4% (matrix, p = 0.03) versus 27.2% +/- 6.9% to 34.6% +/- 7.3% (no matrix, p = 0.031).

CONCLUSIONS

This tissue-engineered approach is feasible and safe and appears to improve the efficiency of cellular cardiomyoplasty. The cell-seeded collagen matrix increases the thickness of the infarct scar with viable tissue and helps to normalize cardiac wall stress in injured regions, thus limiting ventricular remodeling and improving diastolic function.

Myocardial tissue engineering

INTRODUCTION

Regeneration of the infarcted myocardium after a heart attack is one of the most challenging aspects in tissue engineering. Suitable cell sources and optimized biocompatible materials must be identified.

SOURCES OF DATA

In this review, we briefly discuss the current therapeutic options available to patients with heart failure post-myocardial infarction. We describe the various strategies currently proposed to encourage myocardial regeneration, with focus on the achievements in myocardial tissue engineering (MTE). We report on the current cell types, materials and methods being investigated for developing a tissue-engineered myocardial construct.

AREAS OF AGREEMENT

Generally, there is agreement that a 'vehicle' is required to transport cells to the infarcted heart to help myocardial repair and regeneration.

AREAS OF CONTROVERSY

Suitable cell source, biomaterials, cell environment and implantation time post-infarction remain obstacles in the field of MTE.

GROWING POINTS

Research is being focused on optimizing natural and synthetic biomaterials for tissue engineering. The type of cell and its origin (autologous or derived from embryonic stem cells), cell density and method of cell delivery are also being explored.

AREAS TIMELY FOR DEVELOPING RESEARCH

The possibility is being explored that materials may not only act as a support for the delivered cell implants, but may also add value by changing cell survival, maturation or integration, or by prevention of mechanical and electrical remodelling of the failing heart.