Restoration of left ventricular geometry and improvement of left ventricular function in a rodent model of chronic ischemic cardiomyopathy

The Current State of Extracellular Matrix Therapy for Ischemic Heart Disease

The extracellular matrix (ECM) is a three-dimensional, acellular network of diverse structural and nonstructural proteins embedded within a gel-like ground substance composed of glycosaminoglycans and proteoglycans. The ECM serves numerous roles that vary according to the tissue in which it is situated. In the myocardium, the ECM acts as a collagen-based scaffold that mediates the transmission of contractile signals, provides means for paracrine signaling, and maintains nutritional and immunologic homeostasis. Given this spectrum, it is unsurprising that both the composition and role of the ECM has been found to be modulated in the context of cardiac pathology. Myocardial infarction (MI) provides a familiar example of this; the ECM changes in a way that is characteristic of the progressive phases of post-infarction healing. In recent years, this involvement in infarct pathophysiology has prompted a search for therapeutic targets: if ECM components facilitate healing, then their manipulation may accelerate recovery, or even reverse pre-existing damage. This possibility has been the subject of numerous efforts involving the integration of ECM-based therapies, either derived directly from biologic sources or bioengineered sources, into models of myocardial disease. In this paper, we provide a thorough review of the published literature on the use of the ECM as a novel therapy for ischemic heart disease, with a focus on biologically derived models, of both the whole ECM and the components thereof.

Hydrogels for Cardiac Restorative Support: Relevance of Gelation Mechanisms for Prospective Clinical Use

PURPOSE OF REVIEW

Cardiac tissue regenerative strategies have gained much traction over the years, in particular those utilizing hydrogels. With our review, and with special focus on supporting post-myocardial infarcted tissue, we aim to provide insights in determining crucial design considerations of a hydrogel and the implications these could have for future clinical use.

RECENT FINDINGS

To date, two hydrogel delivery strategies are being explored, cardiac injection or patch, to treat myocardial infarction. Recent advances have demonstrated that the mechanism by which a hydrogel is gelated (i.e., physically or chemically cross-linked) not only impacts the biocompatibility, mechanical properties, and chemical structure, but also the route of delivery of the hydrogel and thus its effect on cardiac repair. With regard to cardiac regeneration, various hydrogels have been developed with the ability to function as a delivery system for therapeutic strategies (e.g., drug and stem cells treatments), as well as a scaffold to guide cardiac tissue regeneration following myocardial infarction. However, these developments remain within the experimental and pre-clinical realm and have yet to transition towards the clinical setting.

Reduced graphene oxide coated alginate scaffolds: potential for cardiac patch application

BACKGROUND

Cardiovascular diseases, particularly myocardial infarction (MI), are the leading cause of death worldwide and a major contributor to disability. Cardiac tissue engineering is a promising approach for preventing functional damage or improving cardiac function after MI. We aimed to introduce a novel electroactive cardiac patch based on reduced graphene oxide-coated alginate scaffolds due to the promising functional behavior of electroactive biomaterials to regulate cell proliferation, biocompatibility, and signal transition.

METHODS

The fabrication of novel electroactive cardiac patches based on alginate (ALG) coated with different concentrations of reduced graphene oxide (rGO) using sodium hydrosulfite is described here. The prepared scaffolds were thoroughly tested for their physicochemical properties and cytocompatibility. ALG-rGO scaffolds were also tested for their antimicrobial and antioxidant properties. Subcutaneous implantation in mice was used to evaluate the scaffolds' ability to induce angiogenesis.

RESULTS

The Young modulus of the scaffolds was increased by increasing the rGO concentration from 92 ± 4.51 kPa for ALG to 431 ± 4.89 kPa for ALG-rGO-4 (ALG coated with 0.3% w/v rGO). The scaffolds' tensile strength trended similarly. The electrical conductivity of coated scaffolds was calculated in the semi-conductive range (~ 10-4 S/m). Furthermore, when compared to ALG scaffolds, human umbilical vein endothelial cells (HUVECs) cultured on ALG-rGO scaffolds demonstrated improved cell viability and adhesion. Upregulation of VEGFR2 expression at both the mRNA and protein levels confirmed that rGO coating significantly boosted the angiogenic capability of ALG against HUVECs. OD620 assay and FE-SEM observation demonstrated the antibacterial properties of electroactive scaffolds against Escherichia coli, Staphylococcus aureus, and Streptococcus pyogenes. We also showed that the prepared samples possessed antioxidant activity using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assay and UV-vis spectroscopy. Histological evaluations confirmed the enhanced vascularization properties of coated samples after subcutaneous implantation.

CONCLUSION

Our findings suggest that ALG-rGO is a promising scaffold for accelerating the repair of damaged heart tissue.

Angiogenesis induction as a key step in cardiac tissue Regeneration: From angiogenic agents to biomaterials

Cardiovascular diseases are the leading cause of death worldwide. After myocardial infarction, the vascular supply of the heart is damaged or blocked, leading to the formation of scar tissue, followed by several cardiac dysfunctions or even death. In this regard, induction of angiogenesis is considered as a vital process for supplying nutrients and oxygen to the cells in cardiac tissue engineering. The current review aims to summarize different approaches of angiogenesis induction for effective cardiac tissue repair. Accordingly, a comprehensive classification of induction of pro-angiogenic signaling pathways through using engineered biomaterials, drugs, angiogenic factors, as well as combinatorial approaches is introduced as a potential platform for cardiac regeneration application. The angiogenic induction for cardiac repair can enhance patient treatment outcomes and generate economic prospects for the biomedical industry. The development and commercialization of angiogenesis methods often involves collaboration between academic institutions, research organizations, and biomedical companies.

Research Advances of Injectable Functional Hydrogel Materials in the Treatment of Myocardial Infarction

Myocardial infarction (MI) has become one of the serious diseases threatening human life and health. However, traditional treatment methods for MI have some limitations, such as irreversible myocardial necrosis and cardiac dysfunction. Fortunately, recent endeavors have shown that hydrogel materials can effectively prevent negative remodeling of the heart and improve the heart function and long-term prognosis of patients with MI due to their good biocompatibility, mechanical properties, and electrical conductivity. Therefore, this review aims to summarize the research progress of injectable hydrogel in the treatment of MI in recent years and to introduce the rational design of injectable hydrogels in myocardial repair. Finally, the potential challenges and perspectives of injectable hydrogel in this field will be discussed, in order to provide theoretical guidance for the development of new and effective treatment strategies for MI.

Electroconductive biomaterials for cardiac tissue engineering

Myocardial infarction (MI) is still the leading cause of mortality worldwide. The success of cell-based therapies and tissue engineering strategies for treatment of injured myocardium have been notably hindered due to the limitations associated with the selection of a proper cell source, lack of engraftment of engineered tissues and biomaterials with the host myocardium, limited vascularity, as well as immaturity of the injected cells. The first-generation approaches in cardiac tissue engineering (cTE) have mainly relied on the use of desired cells (e.g., stem cells) along with non-conductive natural or synthetic biomaterials for in vitro construction and maturation of functional cardiac tissues, followed by testing the efficacy of the engineered tissues in vivo. However, to better recapitulate the native characteristics and conductivity of the cardiac muscle, recent approaches have utilized electroconductive biomaterials or nanomaterial components within engineered cardiac tissues. This review article will cover the recent advancements in the use of electrically conductive biomaterials in cTE. The specific emphasis will be placed on the use of different types of nanomaterials such as gold nanoparticles (GNPs), silicon-derived nanomaterials, carbon-based nanomaterials (CBNs), as well as electroconductive polymers (ECPs) for engineering of functional and electrically conductive cardiac tissues. We will also cover the recent progress in the use of engineered electroconductive tissues for in vivo cardiac regeneration applications. We will discuss the opportunities and challenges of each approach and provide our perspectives on potential avenues for enhanced cTE. STATEMENT OF SIGNIFICANCE: Myocardial infarction (MI) is still the primary cause of death worldwide. Over the past decade, electroconductive biomaterials have increasingly been applied in the field of cardiac tissue engineering. This review article provides the readers with the leading advances in the in vitro applications of electroconductive biomaterials for cTE along with an in-depth discussion of injectable/transplantable electroconductive biomaterials and their delivery methods for in vivo MI treatment. The article also discusses the knowledge gaps in the field and offers possible novel avenues for improved cardiac tissue engineering.

A deep dive into the darning effects of biomaterials in infarct myocardium: current advances and future perspectives

Myocardial infarction (MI) occurs due to the obstruction of coronary arteries, a major crux that restricts blood flow and thereby oxygen to the distal part of the myocardium, leading to loss of cardiomyocytes and eventually, if left untreated, leads to heart failure. MI, a potent cardiovascular disorder, requires intense therapeutic interventions and thereby presents towering challenges. Despite the concerted efforts, the treatment strategies for MI are still demanding, which has paved the way for the genesis of biomaterial applications. Biomaterials exhibit immense potentials for cardiac repair and regeneration, wherein they act as extracellular matrix replacing scaffolds or as delivery vehicles for stem cells, protein, plasmids, etc. This review concentrates on natural, synthetic, and hybrid biomaterials; their function; and interaction with the body, mechanisms of repair by which they are able to improve cardiac function in a MI milieu. We also provide focus on future perspectives that need attention. The cognizance provided by the research results certainly indicates that biomaterials could revolutionize the treatment paradigms for MI with a positive impact on clinical translation.

Biotherapeutic-loaded injectable hydrogels as a synergistic strategy to support myocardial repair after myocardial infarction

Myocardial infarction (MI) has been considered as the leading cause of cardiovascular-related deaths worldwide. Although traditional therapeutic agents including various bioactive species such as growth factors, stem cells, and nucleic acids have demonstrated somewhat usefulness for the restoration of cardiac functions, the therapeutic efficiency remains unsatisfactory most likely due to the off-target-associated side effects and low localized retention of the used therapeutic agents in the infarcted myocardium, which constitutes a substantial barrier for the effective treatment of MI. Injectable hydrogels are regarded as a minimally invasive technology that can overcome the clinical and surgical limitations of traditional stenting by a modulated sol-gel transition and localized transport of a variety of encapsulated cargoes, leading to enhanced therapeutic efficiency and improved patient comfort and compliance. However, the design of injectable hydrogels for myocardial repair and the mechanism of action of bioactive substance-loaded hydrogels for MI repair remain unclear. To elucidate these points, we summarized the recent progresses made on the use of injectable hydrogels for encapsulation of various therapeutic substances for MI treatment with an emphasis on the mechanism of action of hydrogel systems for myocardial repair. Specifically, the pathogenesis of MI and the rational design of injectable hydrogels for myocardial repair were presented. Next, the mechanisms of various biotherapeutic substance-loaded injectable hydrogels for myocardial repair was discussed. Finally, the potential challenges and future prospects for the use of injectable hydrogels for MI treatment were proposed for the purpose of drawing theoretical guidance on the development of novel therapeutic strategies for efficient treatment of MI.

Histologic evaluation of therapeutic responses in ischemic myocardium elicited by dual growth factor delivery from composite glycosaminoglycan hydrogels

In this project, the ability of dual growth factor-preloaded, silk-reinforced, composite hyaluronic acid-based hydrogels to elicit advantageous histologic responses when secured to ischemic myocardium was evaluated in vivo. Reinforced hydrogels containing both Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF) were prepared by crosslinking chemically modified hyaluronic acid and heparin with poly(ethylene glycol)-diacrylate around a reinforcing silk mesh. Composite patches were sutured to the ventricular surface of ischemic myocardium in Sprague-Dawley rats, and the resulting angiogenic response was followed for 28 days. The gross appearance of treated hearts showed significantly reduced ischemic area and fibrous deposition compared to untreated control hearts. Histologic evaluation showed growth factor delivery to restore myofiber orientation to pre-surgical levels and to significantly increase elicited microvessel density and maturity by day 28 in infarcted myocardial tissue (p < 0.05). In addition, growth factor delivery reduced cell apoptosis and decreased the density of elicited mast cells and both CD68+ and anti-inflammatory CD163+ macrophages. These findings suggest that HA-based, dual growth factor-loaded hydrogels can successfully induce a series of beneficial responses in ischemic myocardium, and offer the potential for therapeutic improvement of ischemic myocardial remodeling.

Application of Cell, Tissue, and Biomaterial Delivery in Cardiac Regenerative Therapy

Cardiovascular diseases (CVD) are the leading cause of death around the world, being responsible for 31.8% of all deaths in 2017 (Roth, G. A. et al. The Lancet 2018, 392, 1736-1788). The leading cause of CVD is ischemic heart disease (IHD), which caused 8.1 million deaths in 2013 (Benjamin, E. J. et al. Circulation 2017, 135, e146-e603). IHD occurs when coronary arteries in the heart are narrowed or blocked, preventing the flow of oxygen and blood into the cardiac muscle, which could provoke acute myocardial infarction (AMI) and ultimately lead to heart failure and death. Cardiac regenerative therapy aims to repair and refunctionalize damaged heart tissue through the application of (1) intramyocardial cell delivery, (2) epicardial cardiac patch, and (3) acellular biomaterials. In this review, we aim to examine these current approaches and challenges in the cardiac regenerative therapy field.

Natural Biomaterials for Cardiac Tissue Engineering: A Highly Biocompatible Solution

Cardiovascular diseases (CVD) constitute a major fraction of the current major global diseases and lead to about 30% of the deaths, i.e., 17.9 million deaths per year. CVD include coronary artery disease (CAD), myocardial infarction (MI), arrhythmias, heart failure, heart valve diseases, congenital heart disease, and cardiomyopathy. Cardiac Tissue Engineering (CTE) aims to address these conditions, the overall goal being the efficient regeneration of diseased cardiac tissue using an ideal combination of biomaterials and cells. Various cells have thus far been utilized in pre-clinical studies for CTE. These include adult stem cell populations (mesenchymal stem cells) and pluripotent stem cells (including autologous human induced pluripotent stem cells or allogenic human embryonic stem cells) with the latter undergoing differentiation to form functional cardiac cells. The ideal biomaterial for cardiac tissue engineering needs to have suitable material properties with the ability to support efficient attachment, growth, and differentiation of the cardiac cells, leading to the formation of functional cardiac tissue. In this review, we have focused on the use of biomaterials of natural origin for CTE. Natural biomaterials are generally known to be highly biocompatible and in addition are sustainable in nature. We have focused on those that have been widely explored in CTE and describe the original work and the current state of art. These include fibrinogen (in the context of Engineered Heart Tissue, EHT), collagen, alginate, silk, and Polyhydroxyalkanoates (PHAs). Amongst these, fibrinogen, collagen, alginate, and silk are isolated from natural sources whereas PHAs are produced via bacterial fermentation. Overall, these biomaterials have proven to be highly promising, displaying robust biocompatibility and, when combined with cells, an ability to enhance post-MI cardiac function in pre-clinical models. As such, CTE has great potential for future clinical solutions and hence can lead to a considerable reduction in mortality rates due to CVD.

Reduced graphene oxide facilitates biocompatibility of alginate for cardiac repair

The benefits of combined cell/material therapy appear promising for myocardial infarction treatment. The safety of alginate, along with its excellent biocompatibility and biodegradability, has been extensively investigated for cardiac tissue engineering. Among graphene-based nanomaterials, reduced graphene oxide has been considered as a promising candidate for cardiac treatment due to its unique physicochemical properties. In this study, the reduced graphene oxide incorporation effect within alginate hydrogels was investigated for cardiac repair application. Reduced graphene oxide reinforced alginate properties, resulting in an increase in gel stiffness. The cytocompatibility of the hydrogels prepared with human bone marrow–derived mesenchymal stem cells was assessed by the 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide) assay. Following reduced graphene oxide addition, alginate-reduced graphene oxide retained significantly higher cell viability compared to that of alginate and cells cultured on tissue culture plates. Acridine orange/propidium iodide staining was also used to identify both viable and necrotic human bone marrow–derived mesenchymal stem cells within the prepared hydrogels. After a 72-h culture, the percentage of viable cells was twice as much as those cultured on either alginate or tissue culture plate, reaching approximately 80%. Quantitative reverse transcription polymerase chain reaction analysis was performed to assess gene expression of neonatal rat cardiac cells encapsulated on hydrogels for TrpT-2, Conx43, and Actn4 after 7 days. The expression of all genes in alginate-reduced graphene oxide increased significantly compared to that in alginate or tissue culture plate. The results obtained confirmed that the presence of reduced graphene oxide, as an electro-active moiety within alginate, could tune the physicochemical properties of this material, providing a desirable electroactive hydrogel for stem cell therapy in patients with ischemic heart disease.

Biomechanics of infarcted left Ventricle-A review of experiments

Myocardial infarction (MI) is one of leading diseases to contribute to annual death rate of 5% in the world. In the past decades, significant work has been devoted to this subject. Biomechanics of infarcted left ventricle (LV) is associated with MI diagnosis, understanding of remodelling, MI micro-structure and biomechanical property characterizations as well as MI therapy design and optimization, but the subject has not been reviewed presently. In the article, biomechanics of infarcted LV was reviewed in terms of experiments achieved in the subject so far. The concerned content includes experimental remodelling, kinematics and kinetics of infarcted LVs. A few important issues were discussed and several essential topics that need to be investigated further were summarized. Microstructure of MI tissue should be observed even carefully and compared between different methods for producing MI scar in the same animal model, and eventually correlated to passive biomechanical property by establishing innovative constitutive laws. More uniaxial or biaxial tensile tests are desirable on MI, border and remote tissues, and viscoelastic property identification should be performed in various time scales. Active contraction experiments on LV wall with MI should be conducted to clarify impaired LV pumping function and supply necessary data to the function modelling. Pressure-volume curves of LV with MI during diastole and systole for the human are also desirable to propose and validate constitutive laws for LV walls with MI.

Coadministration of an Adhesive Conductive Hydrogel Patch and an Injectable Hydrogel to Treat Myocardial Infarction

Over the past decade, tissue-engineering strategies, mainly involving injectable hydrogels and epicardial biomaterial patches, have been pursued to treat myocardial infarction. However, only limited therapeutic efficacy is achieved with a single means. Here, a combined therapy approach is proposed, that is, the coadministration of a conductive hydrogel patch and injectable hydrogel to the infarcted myocardium. The self-adhesive conductive hydrogel patch is fabricated based on Fe³⁺-induced ionic coordination between dopamine-gelatin (GelDA) conjugates and dopamine-functionalized polypyrrole (DA-PPy), which form a homogeneous network. The injectable and cleavable hydrogel is formed in situ via a Schiff base reaction between oxidized sodium hyaluronic acid (HA-CHO) and hydrazided hyaluronic acid (HHA). Compared with a single-mode system, injecting the HA-CHO/HHA hydrogel intramyocardially followed by painting a conductive GelDA/DA-PPy hydrogel patch on the heart surface results in a more pronounced improvement of the cardiac function in terms of echocardiographical, histological, and angiogenic outcomes.

Development of Injectable Amniotic Membrane Matrix for Postmyocardial Infarction Tissue Repair

Ischemic heart disease represents the leading cause of death worldwide. Heart failure following myocardial infarction (MI) is associated with severe fibrosis formation and cardiac remodeling. Recently, injectable hydrogels have emerged as a promising approach to repair the infarcted heart and improve heart function through minimally invasive administration. Here, a novel injectable human amniotic membrane (hAM) matrix is developed to enhance cardiac regeneration following MI. Human amniotic membrane is isolated from human placenta and engineered to be a thermoresponsive, injectable gel around body temperature. Ultrasound-guided injection of hAM matrix into rat MI hearts significantly improves cardiac contractility, as measured by ejection fraction (EF), and decrease fibrosis. The results of this study demonstrate the feasibility of engineering as an injectable hAM matrix and its efficacy in attenuating degenerative changes in cardiac function following MI, which may have broad applications in tissue regeneration.

The interstitium in cardiac repair: role of the immune-stromal cell interplay

Cardiac regeneration, that is, restoration of the original structure and function in a damaged heart, differs from tissue repair, in which collagen deposition and scar formation often lead to functional impairment. In both scenarios, the early-onset inflammatory response is essential to clear damaged cardiac cells and initiate organ repair, but the quality and extent of the immune response vary. Immune cells embedded in the damaged heart tissue sense and modulate inflammation through a dynamic interplay with stromal cells in the cardiac interstitium, which either leads to recapitulation of cardiac morphology by rebuilding functional scaffolds to support muscle regrowth in regenerative organisms or fails to resolve the inflammatory response and produces fibrotic scar tissue in adult mammals. Current investigation into the mechanistic basis of homeostasis and restoration of cardiac function has increasingly shifted focus away from stem cell-mediated cardiac repair towards a dynamic interplay of cells composing the less-studied interstitial compartment of the heart, offering unexpected insights into the immunoregulatory functions of cardiac interstitial components and the complex network of cell interactions that must be considered for clinical intervention in heart diseases.

An injectable sulfonated reversible thermal gel for therapeutic angiogenesis to protect cardiac function after a myocardial infarction

BACKGROUND

Cardiovascular disease and myocardial infarction are associated with high mortality and morbidity and a more effective treatment remains a major clinical need. The intramyocardial injection of biomaterials has been investigated as a potential treatment for heart failure by providing mechanical support to the myocardium and reducing stress on cardiomyocytes. Another treatment approach that has been explored is therapeutic angiogenesis that requires careful spatiotemporal control of angiogenic drug delivery. An injectable sulfonated reversible thermal gel composed of a polyurea conjugated with poly(N-isopropylacrylamide) and sulfonate groups has been developed for intramyocardial injection with angiogenic factors for the protection of cardiac function after a myocardial infarction.

RESULTS

The thermal gel allowed for the sustained, localized release of VEGF in vivo with intramyocardial injection after two weeks. A myocardial infarction reperfusion injury model was used to evaluate therapeutic benefits to cardiac function and vascularization. Echocardiography presented improved cardiac function, infarct size and ventricular wall thinning were reduced, and immunohistochemistry showed improved vascularization with thermal gel injections. The thermal gel alone showed cardioprotective and vascularization properties, and slightly improved further with the additional delivery of VEGF. An inflammatory response evaluation demonstrated the infiltration of macrophages due to the myocardial infarction was more significant compared to the foreign body inflammatory response to the thermal gel. Detecting DNA fragments of apoptotic cells also demonstrated potential anti-apoptotic effects of the thermal gel.

CONCLUSION

The intramyocardial injection of the sulfonated reversible thermal gel has cardioprotective and vascularization properties for the treatment of myocardial infarction.

Therapeutic neovascularization promoted by injectable hydrogels

The aim of therapeutic neovascularization is to repair ischemic tissues via formation of new blood vessels by delivery of angiogenic growth factors, stem cells or expansion of pre-existing cells. For efficient neovascularization, controlled release of growth factors is particularly necessary since bolus injection of molecules generally lead to a poor outcome due to inadequate retention within the injured site. In this regard, injectable hydrogels, made of natural, synthetic or hybrid biomaterials, have become a promising solution for efficient delivery of angiogenic factors or stem and progenitor cells for in situ tissue repair, regeneration and neovascularization. This review article will broadly discuss the state-of-the-art in the development of injectable hydrogels from natural and synthetic precursors, and their applications in ischemic tissue repair and wound healing. We will cover a wide range of in vitro and in vivo studies in testing the functionalities of the engineered injectable hydrogels in promoting tissue repair and neovascularization. We will also discuss some of the injectable hydrogels that exhibit self-healing properties by promoting neovascularization without the presence of angiogenic factors.

Delivery of progenitor cells with injectable shear-thinning hydrogel maintains geometry and normalizes strain to stabilize cardiac function after ischemia

OBJECTIVES

The ventricle undergoes adverse remodeling after myocardial infarction, resulting in abnormal biomechanics and decreased function. We hypothesize that tissue-engineered therapy could minimize postischemic remodeling through mechanical stress reduction and retention of tensile myocardial properties due to improved endothelial progenitor cell retention and intrinsic biomechanical properties of the hyaluronic acid shear-thinning gel.

METHODS

Endothelial progenitor cells were harvested from adult Wistar rats and resuspended in shear-thinning gel. The constructs were injected at the border zone of ischemic rat myocardium in an acute model of myocardial infarction. Myocardial remodeling, tensile properties, and hemodynamic function were analyzed: control (phosphate-buffered saline), endothelial progenitor cells, shear-thinning gel, and shear-thinning gel + endothelial progenitor cells. Novel high-resolution, high-sensitivity ultrasound with speckle tracking allowed for global strain analysis. Uniaxial testing assessed tensile biomechanical properties.

RESULTS

Shear-thinning gel + endothelial progenitor cell injection significantly increased engraftment and retention of the endothelial progenitor cells within the myocardium compared with endothelial progenitor cells alone. With the use of strain echocardiography, a significant improvement in left ventricular ejection fraction was noted in the shear-thinning gel + endothelial progenitor cell cohort compared with control (69.5% ± 10.8% vs 40.1% ± 4.6%, P = .04). A significant normalization of myocardial longitudinal displacement with subsequent stabilization of myocardial velocity with shear-thinning gel + endothelial progenitor cell therapy compared with control was also evident (0.84 + 0.3 cm/s vs 0.11 ± 0.01 cm/s, P = .03). A significantly positive and higher myocardial strain was observed in shear-thinning gel + endothelial progenitor cell (4.5% ± 0.45%) compared with shear-thinning gel (3.7% ± 0.24%), endothelial progenitor cell (3.5% ± 0.97%), and control (8.6% ± 0.3%, P = .05). A resultant reduction in dynamic stiffness was noted in the shear-thinning gel + endothelial progenitor cell cohort.

CONCLUSIONS

This novel injectable shear-thinning hyaluronic acid hydrogel demonstrates stabilization of border zone myocardium with reduction in adverse myocardial remodeling and preservation of myocardial biomechanics. The cellular construct provides a normalization of strain measurements and reduces left ventricular dilatation, thus resulting in improvement of left ventricular function.

Interventional Heart Failure and Hemodynamic Monitoring

Convergence of the fields of heart failure (HF) and interventional cardiology has led to the formation of a discipline referred to as interventional HF. Although the term may be applied to essentially any invasive procedure performed in patients with HF (eg, coronary angiography, percutaneous coronary intervention, invasive assessment of hemodynamics), it is more commonly reserved for the application of invasive diagnostic or therapeutic procedures to improve the clinical decision-making, functional status, and outcomes of HF patients. This article reviews developing modalities.

Tissue Engineering Strategies for Myocardial Regeneration: Acellular Versus Cellular Scaffolds?

Heart disease remains one of the leading causes of death in industrialized nations with myocardial infarction (MI) contributing to at least one fifth of the reported deaths. The hypoxic environment eventually leads to cellular death and scar tissue formation. The scar tissue that forms is not mechanically functional and often leads to myocardial remodeling and eventual heart failure. Tissue engineering and regenerative medicine principles provide an alternative approach to restoring myocardial function by designing constructs that will restore the mechanical function of the heart. In this review, we will describe the cellular events that take place after an MI and describe current treatments. We will also describe how biomaterials, alone or in combination with a cellular component, have been used to engineer suitable myocardium replacement constructs and how new advanced culture systems will be required to achieve clinical success.

Current Treatment Strategies for Heart Failure: Role of Device Therapy and LV Reconstruction

OPINION STATEMENT

Medical care of heart failure (HF) begins with the determination of the cause of the heart failure and diagnosing potential reversible causes (i.e., coronary heart disease, hyperthyroidism, etc.). Medical therapy includes pharmacological and nonpharmacological strategies that limit and/or reverse the signs and symptoms of HF. Initial behavior modification includes dietary sodium and fluid restriction to avoid weight gain; and encouraging physical activity when appropriate. Optimization of medical therapy is the first line of treatment that includes the use of diuretics, vasodilators (i.e., ACE inhibitors or ARBs), beta blockers, and potentially inotropic agents and anticoagulation depending on the patient's severity of heart failure and LV dysfunction. As heart failure advances despite optimized medical management, cardiac resynchronization therapy (CRT), and implantable cardioverter defibrillators (ICDs) are appropriate device therapies. The development of progressive end-stage HF, despite maximal medical therapy, necessitates the consideration of mechanical circulatory devices such as ventricular assist devices (VADs) either as a bridge to heart transplantation or as destination therapy. Despite the advances in the treatment of heart failure, there is still a large morbidity and mortality associated with HF, thus the need to develop newer strategies for the treatment of HF.

Biomaterial-Enhanced Cell and Drug Delivery: Lessons Learned in the Cardiac Field and Future Perspectives

Heart failure is a significant clinical issue. It is the cause of enormous healthcare costs worldwide and results in significant morbidity and mortality. Cardiac regenerative therapy has progressed considerably from clinical and preclinical studies delivering simple suspensions of cells, macromolecule, and small molecules to more advanced delivery methods utilizing biomaterial scaffolds as depots for localized targeted delivery to the damaged and ischemic myocardium. Here, regenerative strategies for cardiac tissue engineering with a focus on advanced delivery strategies and the use of multimodal therapeutic strategies are reviewed.

Transplantation Effectiveness of Induced Pluripotent Stem Cells Is Improved by a Fibrinogen Biomatrix in an Experimental Model of Ischemic Heart Failure

OBJECTIVES

The aim of this study was to investigate whether a fibrinogen biomatrix improves the transplantation effectiveness of induced pluripotent stem cells (iPSCs) in a model of myocardial infarction.

BACKGROUND

Early retention, engraftment, and cell proliferation are important factors for successful cardiac stem cell therapy. Common transplantation techniques involve the direction injection of cells in aqueous media. However, this approach yields low retention and variable cell biodistribution, leading to reduced grafts that are unable to sufficiently regenerate damaged myocardium. Biologically compatible scaffolds that improve the retention of injected cells can improve cardiac stem cell therapy.

METHODS

Murine iPSCs were transfected for luciferase reporter gene expression. First, in vitro experiments were performed comparing cell viability in fibrinogen and medium. Second, iPSCs were transplanted intramyocardially by direct injection into ischemic myocardium of immunodeficient mice, following permanent left coronary artery ligation. Cells were delivered in medium or fibrinogen. Follow-up included graft assessment by bioluminescence imaging, the evaluation of cardiac function by magnetic resonance imaging, and histology to evaluate graft size and determine the extent of myocardial scarring.

RESULTS

In vitro experiments showed proliferation of iPSCs in fibrinogen from 6.4×10(3)±8.0×10(2) after 24 h to 2.1×10(4)±3.2×10(3) after 72 h. Early cardiac cell amount in control group animals was low (23.7%±0.7%) with massive cell accumulation in the right (46.3%±1.0%) and the left lung (30.0%±0.6%). When iPSCs were injected applying the fibrinogen biomatrix, intramyocardial cell amount was increased (66.3%±0.9%) with demonstrable graft proliferation over the experimental time course. Left ventricle-function was higher in the fibrinogen group (42.9%±2.8%), also showing a higher fraction of refilled infarcted-area (66.9%±2.7%).

CONCLUSIONS

The fibrinogen biomatrix improved cardiac iPSc retention, sustaining functional improvement and cellular refill of infarcted myocardium. Therefore, fibrinogen can be considered an ideal biological scaffold for intramyocardial stem cell transplantations.

Myocardial infarction: stem cell transplantation for cardiac regeneration

It is estimated that by 2030, almost 23.6 million people will perish from cardiovascular disease, according to the WHO. The review discusses advances in stem cell therapy for myocardial infarction, including cell sources, methods of differentiation, expansion selection and their route of delivery. Skeletal muscle cells, hematopoietic cells and mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs)-derived cardiomyocytes have advanced to the clinical stage, while induced pluripotent cells (iPSCs) are yet to be considered clinically. Delivery of cells to the sites of injury and their subsequent retention is a major issue. The development of supportive scaffold matrices to facilitate stem cell retention and differentiation are analyzed. The review outlines clinical translation of conjugate stem cell-based cellular therapeutics post-myocardial infarction.

Current advances and future perspectives in extrusion-based bioprinting

Extrusion-based bioprinting (EBB) is a rapidly growing technology that has made substantial progress during the last decade. It has great versatility in printing various biologics, including cells, tissues, tissue constructs, organ modules and microfluidic devices, in applications from basic research and pharmaceutics to clinics. Despite the great benefits and flexibility in printing a wide range of bioinks, including tissue spheroids, tissue strands, cell pellets, decellularized matrix components, micro-carriers and cell-laden hydrogels, the technology currently faces several limitations and challenges. These include impediments to organ fabrication, the limited resolution of printed features, the need for advanced bioprinting solutions to transition the technology bench to bedside, the necessity of new bioink development for rapid, safe and sustainable delivery of cells in a biomimetically organized microenvironment, and regulatory concerns to transform the technology into a product. This paper, presenting a first-time comprehensive review of EBB, discusses the current advancements in EBB technology and highlights future directions to transform the technology to generate viable end products for tissue engineering and regenerative medicine.

The feasibility and safety of Algisyl-LVR™ as a method of left ventricular augmentation in patients with dilated cardiomyopathy: initial first in man clinical results

BACKGROUND

A tissue engineering approach to augment the left ventricular wall has been suggested as a means to treat patients with advanced heart failure. This study evaluated the safety and feasibility of Algisyl-LVR™ as a method of left ventricular augmentation in patients with dilated cardiomyopathy undergoing open-heart surgery.

METHODS AND RESULTS

Eleven male patients (aged 44 to 74years) with advanced heart failure (NYHA class 3 or 4), a left ventricular ejection fraction (LVEF) of <40% and requiring conventional heart surgery received Algisyl-LVR delivered into the LV myocardial free wall. Serial echocardiography, assessment of NYHA class, Kansas City Cardiomyopathy Questionnaire (KCCQ) and 24-hour Holter monitoring were obtained at baseline, days 3 and 8 (for echocardiography and Holter monitoring), and at 3, 6, 12, 18 and 24months. A total of 9 (81.8%) patients completed 24months of follow-up. Two patients withdrew consent after day 8 and at the 3month visit. Operative mortality was 0% (n=10 with 30day follow-up). There were no adverse events attributed to Algisyl-LVR. Mean LVEF improved from 27.1 (±7.3) % at screening to a mean LVEF of 34.8 (±18.6) % 24months post-discharge. Improvements of NYHA class were corroborated with improvements in KCCQ summary scores. Holter monitor data showed a significant decrease in the episodes of nonsustained ventricular tachycardia following administration of Algisyl-LVR.

CONCLUSIONS

Administration of Algisyl-LVR to patients with advanced HF at the time of cardiac surgery is feasible and safe; warranting continued development of Algisyl-LVR as a potential therapy in patients with advanced HF.

A prospective comparison of alginate-hydrogel with standard medical therapy to determine impact on functional capacity and clinical outcomes in patients with advanced heart failure (AUGMENT-HF trial)

Aims

AUGMENT-HF was an international, multi-centre, prospective, randomized, controlled trial to evaluate the benefits and safety of a novel method of left ventricular (LV) modification with alginate-hydrogel.

Methods

Alginate-hydrogel is an inert permanent implant that is directly injected into LV heart muscle and serves as a prosthetic scaffold to modify the shape and size of the dilated LV. Patients with advanced chronic heart failure (HF) were randomized (1 : 1) to alginate-hydrogel (n = 40) in combination with standard medical therapy or standard medical therapy alone (Control, n = 38). The primary endpoint of AUGMENT-HF was the change in peak VO₂ from baseline to 6 months. Secondary endpoints included changes in 6-min walk test (6MWT) distance and New York Heart Association (NYHA) functional class, as well as assessments of procedural safety.

Results

Enrolled patients were 63 ± 10 years old, 74% in NYHA functional class III, had a LV ejection fraction of 26 ± 5% and a mean peak VO₂ of 12.2 ± 1.8 mL/kg/min. Thirty-five patients were successfully treated with alginate-hydrogel injections through a limited left thoracotomy approach without device-related complications; the 30-day surgical mortality was 8.6% (3 deaths). Alginate-hydrogel treatment was associated with improved peak VO₂ at 6 months—treatment effect vs. Control: +1.24 mL/kg/min (95% confidence interval 0.26–2.23, P = 0.014). Also 6MWT distance and NYHA functional class improved in alginate-hydrogel-treated patients vs. Control (both P < 0.001).

Conclusion

Alginate-hydrogel in addition to standard medical therapy for patients with advanced chronic HF was more effective than standard medical therapy alone for improving exercise capacity and symptoms. The results of AUGMENT-HF provide proof of concept for a pivotal trial.

Trial Registration Number

NCT01311791.

Overview of hydrogel-based strategies for application in cardiac tissue regeneration

Cardiovascular diseases remain the leading cause of death globally. Since the adult heart lacks the capacity to regenerate, loss of myocardium following myocardial infarction is irreversible and ultimately leads to failure to maintain cardiac function. In order to repopulate the areas of cell loss in the damaged hearts for restoration of cardiac function, cell transplantation/replacement has been extensively investigated. Recently, biomaterials have emerged as an approach to improve delivery and viability of cells for the regeneration of the damaged heart. Here we review the most common approaches in hydrogel-based cardiac tissue regeneration with particular focus on the implementation of hydrogels to improve cell delivery.

Drug and cell delivery for cardiac regeneration

The spectrum of ischaemic cardiomyopathy, encompassing acute myocardial infarction to congestive heart failure is a significant clinical issue in the modern era. This group of diseases is an enormous source of morbidity and mortality and underlies significant healthcare costs worldwide. Cardiac regenerative therapy, whereby pro-regenerative cells, drugs or growth factors are administered to damaged and ischaemic myocardium has demonstrated significant potential, especially preclinically. While some of these strategies have demonstrated a measure of success in clinical trials, tangible clinical translation has been slow. To date, the majority of clinical studies and a significant number of preclinical studies have utilised relatively simple delivery methods for regenerative therapeutics, such as simple systemic administration or local injection in saline carrier vehicles. Here, we review cardiac regenerative strategies with a particular focus on advanced delivery concepts as a potential means to enhance treatment efficacy and tolerability and ultimately, clinical translation. These include (i) delivery of therapeutic agents in biomaterial carriers, (ii) nanoparticulate encapsulation, (iii) multimodal therapeutic strategies and (iv) localised, minimally invasive delivery via percutaneous transcatheter systems.

Injectable biodegradable hybrid hydrogels based on thiolated collagen and oligo(acryloyl carbonate)-poly(ethylene glycol)-oligo(acryloyl carbonate) copolymer for functional cardiac regeneration

Injectable biodegradable hybrid hydrogels were designed and developed based on thiolated collagen (Col-SH) and multiple acrylate containing oligo(acryloyl carbonate)-b-poly(ethylene glycol)-b-oligo(acryloyl carbonate) (OAC-PEG-OAC) copolymers for functional cardiac regeneration. Hydrogels were readily formed under physiological conditions (37°C and pH 7.4) from Col-SH and OAC-PEG-OAC via a Michael-type addition reaction, with gelation times ranging from 0.4 to 8.1 min and storage moduli from 11.4 to 55.6 kPa, depending on the polymer concentrations, solution pH and degrees of substitution of Col-SH. The collagen component in the hybrid hydrogels retained its enzymatic degradability against collagenase, and the degradation time of the hydrogels increased with increasing polymer concentration. In vitro studies showed that bone marrow mesenchymal stem cells (BMSCs) exhibited rapid cell spreading and extensive cellular network formation on these hybrid hydrogels. In a rat infarction model, the infarcted left ventricle was injected with PBS, hybrid hydrogels, BMSCs or BMSC-encapsulating hybrid hydrogels. Echocardiography demonstrated that the hybrid hydrogels and BMSC-encapsulating hydrogels could increase the ejection fraction at 28 days compared to the PBS control group, resulting in improved cardiac function. Histology revealed that the injected hybrid hydrogels significantly reduced the infarct size and increased the wall thickness, and these were further improved with the BMSC-encapsulating hybrid hydrogel treatment, probably related to the enhanced engraftment and persistence of the BMSCs when delivered within the hybrid hydrogel. Thus, these injectable hybrid hydrogels combining intrinsic bioactivity of collagen, controlled mechanical properties and enhanced stability provide a versatile platform for functional cardiac regeneration.

Augmentation of left ventricular wall thickness with alginate hydrogel implants improves left ventricular function and prevents progressive remodeling in dogs with chronic heart failure

OBJECTIVES

The study tested the hypothesis that augmentation of the left ventricular (LV) wall thickness with direct intramyocardial injections of alginate hydrogel implants (AHI) reduces LV cavity size, restores LV shape, and improves LV function in dogs with heart failure (HF).

BACKGROUND

Progressive LV dysfunction, enlargement, and chamber sphericity are features of HF associated with increased mortality and morbidity.

METHODS

Studies were performed in 14 dogs with HF produced by intracoronary microembolizations (LV ejection fraction [EF] <30%). Dogs were randomized to AHI treatment (n = 8) or to sham-operated control (n = 6). During an open-chest procedure, dogs received either intramyocardial injections of 0.25 to 0.35 ml of alginate hydrogel (Algisyl-LVR, LoneStar Heart, Inc., Laguna Hills, California) or saline. Seven injections were made ∼ 1.0 to 1.5 cm apart (total volume 1.8 to 2.1 ml) along the circumference of the LV free wall halfway between the apex and base starting from the anteroseptal groove and ending at the posteroseptal groove. Hemodynamic and ventriculographic measurements were made before treatment (PRE) and repeated post-surgery for up to 17 weeks (POST).

RESULTS

Compared to control, AHI significantly reduced LV end-diastolic and end-systolic volumes and improved LV sphericity. AHI treatment significantly increased EF (26 ± 0.4% at PRE to 31 ± 0.4% at POST; p < 0.05) compared to the decreased EF seen in control dogs (27 ± 0.3% at PRE to 24 ± 1.3% at POST; p < 0.05). AHI treatment was well tolerated and was not associated with increased LV diastolic stiffness.

CONCLUSIONS

In HF dogs, circumferential augmentation of LV wall thickness with AHI improves LV structure and function. The results support continued development of AHI for the treatment of patients with advanced HF.

Biomaterials in myocardial tissue engineering

Cardiovascular disease is the leading cause of death in the developed world, and as such there is a pressing need for treatment options. Cardiac tissue engineering emerged from the need to develop alternative sources and methods of replacing tissue damaged by cardiovascular diseases, as the ultimate treatment option for many who suffer from end-stage heart failure is a heart transplant. In this review we focus on biomaterial approaches to augmenting injured or impaired myocardium, with specific emphasis on: the design criteria for these biomaterials; the types of scaffolds - composed of natural or synthetic biomaterials or decellularized extracellular matrix - that have been used to develop cardiac patches and tissue models; methods to vascularize scaffolds and engineered tissue; and finally, injectable biomaterials (hydrogels) designed for endogenous repair, exogenous repair or as bulking agents to maintain ventricular geometry post-infarct. The challenges facing the field and obstacles that must be overcome to develop truly clinically viable cardiac therapies are also discussed.

Discrete microstructural cues for the attenuation of fibrosis following myocardial infarction

Chronic fibrosis caused by acute myocardial infarction (MI) leads to increased morbidity and mortality due to cardiac dysfunction. We have developed a therapeutic materials strategy that aims to mitigate myocardial fibrosis by utilizing injectable polymeric microstructures to mechanically alter the microenvironment. Polymeric microstructures were fabricated using photolithographic techniques and studied in a three-dimensional culture model of the fibrotic environment and by direct injection into the infarct zone of adult rats. Here, we show dose-dependent down-regulation of expression of genes associated with the mechanical fibrotic response in the presence of microstructures. Injection of this microstructured material into the infarct zone decreased levels of collagen and TGF-β, increased elastin deposition and vascularization in the infarcted region, and improved functional outcomes after six weeks. Our results demonstrate the efficacy of these discrete anti-fibrotic microstructures and suggest a potential therapeutic materials approach for combatting pathologic fibrosis.

Mesenchymal stem cell delivery strategies to promote cardiac regeneration following ischemic injury

Myocardial infarction (MI) is one of the leading causes of mortality worldwide and is associated with irreversible cardiomyocyte death and pathological remodeling of cardiac tissue. In the past 15 years, several animal models have been developed for pre-clinical testing to assess the potential of stem cells for functional tissue regeneration and the attenuation of left ventricular remodeling. The promising results obtained in terms of improved cardiac function, neo-angiogenesis and reduction in infarct size have motivated the initiation of clinical trials in humans. Despite the potential, the results of these studies have highlighted that the effective delivery and retention of viable cells within the heart remain significant challenges that have limited the therapeutic efficacy of cell-based therapies for treating the ischemic myocardium. In this review, we discuss key elements for designing clinically translatable cell-delivery approaches to promote myocardial regeneration. Key topics addressed include cell selection, with a focus on mesenchymal stem cells derived from the bone marrow (bMSCs) and adipose tissue (ASCs), including a discussion of their potential mechanisms of action. Natural and synthetic biomaterials that have been investigated as injectable cell delivery vehicles for cardiac applications are critically reviewed, including an analysis of the role of the biomaterials themselves in the therapeutic scheme.

Intramyocardial injection of a synthetic hydrogel with delivery of bFGF and IGF1 in a rat model of ischemic cardiomyopathy

It is increasingly appreciated that the properties of a biomaterial used in intramyocardial injection therapy influence the outcomes of infarcted hearts that are treated. In this report the extended in vivo efficacy of a thermally responsive material that can deliver dual growth factors while providing a slow degradation time and high mechanical stiffness is examined. Copolymers consisting of N-isopropylacrylamide, 2-hydroxyethyl methacrylate, and degradable methacrylate polylactide were synthesized. The release of bioactive basic fibroblast growth factor (bFGF) and insulin-like growth factor 1 (IGF1) from the gel and loaded poly(lactide-co-glycolide) microparticles was assessed. Hydrogel with or without loaded growth factors was injected into 2 week-old infarcts in Lewis rats and animals were followed for 16 weeks. The hydrogel released bioactive bFGF and IGF1 as shown by mitogenic effects on rat smooth muscle cells in vitro. Cardiac function and geometry were improved for 16 weeks after hydrogel injection compared to saline injection. Despite demonstrating that left ventricular levels of bFGF and IGF1 were elevated for two weeks after injection of growth factor loaded gels, both functional and histological assessment showed no added benefit to inclusion of these proteins. This result points to the complexity of designing appropriate materials for this application and suggests that the nature of the material alone, without exogenous growth factors, has a direct ability to influence cardiac remodeling.

In vivo response to dynamic hyaluronic acid hydrogels

Tissue-specific elasticity arises in part from developmental changes in extracellular matrix over time, e.g. ~10-fold myocardial stiffening in the chicken embryo. When this time-dependent stiffening has been mimicked in vitro with thiolated hyaluronic acid (HA-SH) hydrogels, improved cardiomyocyte maturation has been observed. However, host interactions, matrix polymerization, and the stiffening kinetics remain uncertain in vivo, and each plays a critical role in therapeutic applications using HA-SH. Hematological and histological analysis of subcutaneously injected HA-SH hydrogels showed minimal systemic immune response and host cell infiltration. Most importantly, subcutaneously injected HA-SH hydrogels exhibited time-dependent porosity and stiffness changes at a rate similar to hydrogels polymerized in vitro. When injected intramyocardially host cells begin to actively degrade HA-SH hydrogels within 1week post-injection, continuing this process while producing matrix to nearly replace the hydrogel within 1month post-injection. While non-thiolated HA did not degrade after injection into the myocardium, it also did not elicit an immune response, unlike HA-SH, where visible granulomas and macrophage infiltration were present 1month post-injection, likely due to reactive thiol groups. Altogether these data suggest that the HA-SH hydrogel responds appropriately in a less vascularized niche and stiffens as had been demonstrated in vitro, but in more vascularized tissues, in vivo applicability appears limited.

Reduction in left ventricular wall stress and improvement in function in failing hearts using Algisyl-LVR

Injection of Algisyl-LVR, a treatment under clinical development, is intended to treat patients with dilated cardiomyopathy. This treatment was recently used for the first time in patients who had symptomatic heart failure. In all patients, cardiac function of the left ventricle (LV) improved significantly, as manifested by consistent reduction of the LV volume and wall stress. Here we describe this novel treatment procedure and the methods used to quantify its effects on LV wall stress and function. Algisyl-LVR is a biopolymer gel consisting of Na(+)-Alginate and Ca(2+)-Alginate. The treatment procedure was carried out by mixing these two components and then combining them into one syringe for intramyocardial injections. This mixture was injected at 10 to 19 locations mid-way between the base and apex of the LV free wall in patients. Magnetic resonance imaging (MRI), together with mathematical modeling, was used to quantify the effects of this treatment in patients before treatment and at various time points during recovery. The epicardial and endocardial surfaces were first digitized from the MR images to reconstruct the LV geometry at end-systole and at end-diastole. Left ventricular cavity volumes were then measured from these reconstructed surfaces. Mathematical models of the LV were created from these MRI-reconstructed surfaces to calculate regional myofiber stress. Each LV model was constructed so that 1) it deforms according to a previously validated stress-strain relationship of the myocardium, and 2) the predicted LV cavity volume from these models matches the corresponding MRI-measured volume at end-diastole and end-systole. Diastolic filling was simulated by loading the LV endocardial surface with a prescribed end-diastolic pressure. Systolic contraction was simulated by concurrently loading the endocardial surface with a prescribed end-systolic pressure and adding active contraction in the myofiber direction. Regional myofiber stress at end-diastole and end-systole was computed from the deformed LV based on the stress-strain relationship.

Approach to assessing myocardial perfusion in rats using static [13N]-ammonia images and a small-animal PET

PURPOSE

Semi-quantitative, static positron emission tomography (PET) has been used to perform an initial approach to the assessment of [13N]-ammonia perfusion studies aimed to elucidating the effect of injecting human embryonic stem cell-derived (hES) hemangioblasts on infarcted rat hearts.

PROCEDURES

Female NIH nude rats underwent occlusion of the left anterior descending coronary artery for 30 min before reperfusion. Either one million hES-derived hemangioblasts (n = 5) or control media (n = 4) were injected into the site of the infarct 1 day post-myocardial infarction (MI) under high-resolution echocardiography guidance. PET imaging was performed 6 weeks after MI induction, and uptake polar maps were created by sampling the left ventricle at equidistant slices from the base to the apex and measuring the average myocardium value at three contiguous voxels to minimize partial volume effects. Statistical comparison between treatment and control groups was done with a Mann-Whitney U test.

RESULTS

Myocardium uptake ratios for treated and untreated subjects show statistically significant difference (98% certainty).

CONCLUSIONS

The straightforward procedure described here (similar to those commonly used in clinical routine) was sufficient to yield statistically significant perfusion differences between the treated and untreated animals despite the small sample size.

Minimally invasive cell-seeded biomaterial systems for injectable/epicardial implantation in ischemic heart disease

Myocardial infarction (MI) is characterized by heart-wall thinning, myocyte slippage, and ventricular dilation. The injury to the heart-wall muscle after MI is permanent, as after an abundant cell loss the myocardial tissue lacks the intrinsic capability to regenerate. New therapeutics are required for functional improvement and regeneration of the infarcted myocardium, to overcome harmful diagnosis of patients with heart failure, and to overcome the shortage of heart donors. In the past few years, myocardial tissue engineering has emerged as a new and ambitious approach for treating MI. Several left ventricular assist devices and epicardial patches have been developed for MI. These devices and acellular/cellular cardiac patches are employed surgically and sutured to the epicardial surface of the heart, limiting the region of therapeutic benefit. An injectable system offers the potential benefit of minimally invasive release into the myocardium either to restore the injured extracellular matrix or to act as a scaffold for cell delivery. Furthermore, intramyocardial injection of biomaterials and cells has opened new opportunities to explore and also to augment the potentials of this technique to ease morbidity and mortality rates owing to heart failure. This review summarizes the growing body of literature in the field of myocardial tissue engineering, where biomaterial injection, with or without simultaneous cellular delivery, has been pursued to enhance functional and structural outcomes following MI. Additionally, this review also provides a complete outlook on the tissue-engineering therapies presently being used for myocardial regeneration, as well as some perceptivity into the possible issues that may hinder its progress in the future.

Injectable hydrogel therapies and their delivery strategies for treating myocardial infarction

INTRODUCTION

Heart failure following myocardial infarction (MI) impacts millions of people each year in the US. The field of tissue engineering has developed several potential therapies for treating MI including injectable acellular hydrogels. These injectable biomaterials can either be synthetic or naturally derived, and have the potential to be delivered minimally invasively.

AREAS COVERED

This review covers the different methods of delivery and presents the initial work on the use of injectable biomaterial scaffolds alone to improve cardiac function post-MI. Several naturally derived materials including alginate, collagen, chitosan, decellularized tissues, fibrin, hyaluronic acid, keratin, and Matrigel, as well as a few synthetic materials have shown promise on their own without the addition of therapeutics such as cells or growth factors. These biomaterials can be potentially delivered via endocardial, epicardial, or intracoronary injections and some can even utilize current catheter technology, indicating a potential for avoiding invasive surgical procedures. Once injected into the wall of the heart, these hydrogels create a scaffold that provides biochemical and structural cues, and the ability for cellular infiltration and remodeling of the local environment.

EXPERT OPINION

Injectable biomaterials have several crucial challenges that should be over come to design optimal therapies for MI and heart failure, including optimizing material properties, methods of injection and understanding the mechanisms of action. But, studies in both small and large animals have shown significant improvement in important parameters including wall thickness, vascularization of the ischemic region, left ventricular volumes, and cardiac function. Thus, the application of injectable biomaterials shows promise for developing into new therapies to treat MI, potentially improving millions of lives.

Alginate scaffolds for mesenchymal stem cell cardiac therapy: influence of alginate composition

Despite the success of alginate scaffolds and mesenchymal stem cells (MSCs) therapy in cardiac failure treatment, the impact of the physicochemical environment provided by alginate matrices on cell behavior has never been investigated. The purpose of this work was double: to determine the alginate composition influence on (1) encapsulated rat MSC viability, paracrine activity, and phenotype in vitro and (2) cardiac implantability and in vivo biocompatibility of patch shape scaffolds. Two alginates, differing in composition and thus presenting different mechanical properties when hydrogels, were characterized. In both cases, encapsulated MSC viability was maintained at around 75%, and their secretion characteristics were retained 28 days postencapsulation. In vivo study revealed a high cardiac compatibility of the tested alginates: cardiac parameters were maintained, and rats did not present any sign of infection. Moreover, explanted hydrogels appeared surrounded by a vascularized tissue. However, scaffold implantability was highly dependent on alginate composition. G-type alginate patches, presenting higher elastic and Young moduli than M-type alginate patches, showed a better implantation easiness and were the only ones that maintained their shape and morphology in vivo. As a consequence of alginate chemical composition and resulting hydrogel structuration, G-type alginate hydrogels appear to be more adapted for cardiac implantation.