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

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

Semi-Automated Construction of Patient-Specific Aortic Valves from Computed Tomography Images.

This paper presents a semi-automatic method for the construction of volumetric models of the aortic valve using computed tomography angiography images. Although the aortic valve typically cannot be segmented directly from a computed tomography angiography image, the method described herein uses manually selected samples of an aortic segmentation derived from this image to inform the construction. These samples capture certain physiologic landmarks and are used to construct a volumetric valve model. As a demonstration of the capabilities of this method, valve models for 25 pediatric patients are created. A selected valve anatomy is used to perform fluid-structure interaction simulations using the immersed finite element/difference method with physiologic driving and loading conditions. Simulation results demonstrate this method creates a functional valve that opens and closes normally and generates pressure and flow waveforms that are similar to those observed clinically.

Current state of the art in hypoplastic left heart syndrome.

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart condition in which a neonate is born with an underdeveloped left ventricle and associated structures. Without palliative interventions, HLHS is fatal. Treatment typically includes medical management at the time of birth to maintain patency of the ductus arteriosus, followed by three palliative procedures: most commonly the Norwood procedure, bidirectional cavopulmonary shunt, and Fontan procedures. With recent advances in surgical management of HLHS patients, high survival rates are now obtained at tertiary treatment centers, though adverse neurodevelopmental outcomes remain a clinical challenge. While surgical management remains the standard of care for HLHS patients, innovative treatment strategies continue to be developing. Important for the development of new strategies for HLHS patients is an understanding of the genetic basis of this condition. Another investigational strategy being developed for HLHS patients is the injection of stem cells within the myocardium of the right ventricle. Recent innovations in tissue engineering and regenerative medicine promise to provide important tools to both understand the underlying basis of HLHS as well as provide new therapeutic strategies. In this review article, we provide an overview of HLHS, starting with a historical description and progressing through a discussion of the genetics, surgical management, post-surgical outcomes, stem cell therapy, hemodynamics and tissue engineering approaches.

Congenital Heart Disease: An Immunological Perspective.

Congenital heart disease (CHD) poses a significant global health and economic burden-despite advances in treating CHD reducing the mortality risk, globally CHD accounts for approximately 300,000 deaths yearly. Children with CHD experience both acute and chronic cardiac complications, and though treatment options have improved, some remain extremely invasive. A challenge in addressing these morbidity and mortality risks is that little is known regarding the cause of many CHDs and current evidence suggests a multifactorial etiology. Some studies implicate an immune contribution to CHD development; however, the role of the immune system is not well-understood. Defining the role of the immune and inflammatory responses in CHD therefore holds promise in elucidating mechanisms underlying these disorders and improving upon current diagnostic and treatment options. In this review, we address the current knowledge coinciding CHDs with immune and inflammatory associations, emphasizing conditions where this understanding would provide clinical benefit, and challenges in studying these mechanisms.

The Immune and Inflammatory Basis of Acquired Pediatric Cardiac Disease.

Children with acquired heart disease face significant health challenges, including a lifetime of strict medical management, multiple cardiac surgeries, and a high mortality risk. Though the presentation of these conditions is diverse, a unifying factor is the role of immune and inflammatory responses in their development and/or progression. For example, infectious agents have been linked to pediatric cardiovascular disease, leading to a large health burden that disproportionately affects low-income areas. Other implicated mechanisms include antibody targeting of cardiac proteins, infection of cardiac cells, and inflammation-mediated damage to cardiac structures. These changes can alter blood flow patterns, change extracellular matrix composition, and induce cardiac remodeling. Therefore, understanding the relationship between the immune system and cardiovascular disease can inform targeted diagnostic and treatment approaches. In this review, we discuss the current understanding of pediatric immune-associated cardiac diseases, challenges in the field, and areas of research with potential for clinical benefit.

Current State of the Art in Ventricle Tissue Engineering.

The field of ventricle tissue engineering is focused on bioengineering highly functioning left ventricles that can be used as model systems for basic cardiology research and for cardiotoxicity testing. In this article, we review the current state of the art in the field of ventricle tissue engineering and discuss different strategies that have been used to bioengineer ventricles. Based on this body of literature, there are now common themes in the field that provide guidance for future directives, also presented in this article.

Tissue engineering solutions to replace contractile function during pediatric heart surgery.

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

The Role of an IL-10/Hyaluronan Axis in Dermal Wound Healing.

Scar formation is the typical endpoint of postnatal dermal wound healing, which affects more than 100 million individuals annually. Not only do scars cause a functional burden by reducing the biomechanical strength of skin at the site of injury, but they also significantly increase healthcare costs and impose psychosocial challenges. Though the mechanisms that dictate how dermal wounds heal are still not completely understood, they are regulated by extracellular matrix (ECM) remodeling, neovascularization, and inflammatory responses. The cytokine interleukin (IL)-10 has emerged as a key mediator of the pro- to anti-inflammatory transition that counters collagen deposition in scarring. In parallel, the high molecular weight (HMW) glycosaminoglycan hyaluronan (HA) is present in the ECM and acts in concert with IL-10 to block pro-inflammatory signals and attenuate fibrotic responses. Notably, high concentrations of both IL-10 and HMW HA are produced in early gestational fetal skin, which heals scarlessly. Since fibroblasts are responsible for collagen deposition, it is critical to determine how the concerted actions of IL-10 and HA drive their function to potentially control fibrogenesis. Beyond their independent actions, an auto-regulatory IL-10/HA axis may exist to modulate the magnitude of CD4+ effector T lymphocyte activation and enhance T regulatory cell function in order to reduce scarring. This review underscores the pathophysiological impact of the IL-10/HA axis as a multifaceted molecular mechanism to direct primary cell responders and regulators toward either regenerative dermal tissue repair or scarring.

A methodological nine-step process to bioengineer heart muscle tissue.

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

3D Bioprinting the Cardiac Purkinje System Using Human Adipogenic Mesenchymal Stem Cell Derived Purkinje Cells.

PURPOSE: The objective of this study was to reprogram human adipogenic mesenchymal stem cells (hADMSCs) to form Purkinje cells and to use the reprogrammed Purkinje cells to bioprint Purkinje networks. METHODS: hADMSCs were reprogrammed to form Purkinje cells using a multi-step process using transcription factors ETS2 and MESP1 to first form cardiac progenitor stem cells followed by SHOX2 and TBX3 to form Purkinje cells. A novel bioprinting method was developed based on Pluronic acid as the sacrificial material and type I collagen as the structural material. The reprogrammed Purkinje cells were used in conjunction with the novel bioprinting method to bioprint Purkinje networks. Printed constructs were evaluated for retention of functional protein connexin 40 (Cx40) and ability to undergo membrane potential changes in response to physiologic stimulus. RESULTS: hADMSCs were successfully reprogrammed to form Purkinje cells based on the expression pattern of IRX3, IRX5, SEMA and SCN10. Reprogrammed purkinje cells were incorporated into a collagen type-1 bioink and the left ventricular Purkinje network was printed using anatomical images of the bovine Purkinje system as reference. Optimization studies demonstrated that 1.8 mg/mL type-I collagen at a seeding density of 300,000 cells per 200 µL resulted in the most functional bioprinted Purkinje networks. Furthermore, bioprinted Purkinje networks formed continuous syncytium, retained expression of vital functional gap junction protein Cx40 post-print, and exhibited membrane potential changes in response to electric stimulation and acetylcholine evaluated by DiBAC4(5), an electrically responsive dye. CONCLUSION: Based on the results of this study, hADMSCs were successfully reprogrammed to form Purkinje cells and bioprinted to form Purkinje networks.

3D bioprinting and its potential impact on cardiac failure treatment: An industry perspective.

3D printing technologies are emerging as a disruptive innovation for the treatment of patients in cardiac failure. The ability to create custom devices, at the point of care, will affect both the diagnosis and treatment of cardiac diseases. The introduction of bioinks containing cells and biomaterials and the development of new computer assisted design and computer assisted manufacturing systems have ushered in a new technology known as 3D bioprinting. Small scale 3D bioprinting has successfully created cardiac tissue microphysiological systems. 3D bioprinting provides an opportunity to evaluate the assembly of specific parts of the heart and most notably heart valves. With the continuous development of instrumentation and bioinks and a complete understanding of cardiac tissue development, it is proposed that 3D bioprinting may permit the assembly of a heart described as a total biofabricated heart.

A Highly Conductive 3D Cardiac Patch Fabricated Using Cardiac Myocytes Reprogrammed from Human Adipogenic Mesenchymal Stem Cells.

PURPOSE: The objective of this study was to bioengineer 3D patches from cardiac myocytes that have been reprogrammed from human adipogenic mesenchymal stem cells (hADMSCs). METHODS: Human adipogenic mesenchymal stem cells (hADMSCs) were reprogrammed to form cardiac myocytes using transcription factors ETS2 and MESP1. Reprogrammed cardiac myocytes were cultured in a fibrin gel to bioengineer 3D patch patches. The effect of initial plating density (1-25 million cells per patch), time (28-day culture period) and treatment with 1 µM isoproterenol and 1 µM epinephrine were evaluated. RESULTS: 3D patches were fabricated using cardiac myocytes that have been reprogrammed from hADMSCs. Based on optimization studies, it was determined that 10 million cells were needed to bioengineer a single patch, that measured 2 × 2 cm2. Furthermore, 3D patches fabricated 10 million cells were stable in culture for up to 28 days. Treatment of 3D patches with 1 µM isoproterenol and 1 µM epinephrine resulted in an increase in the electrical properties, as measured by electrical impulse amplitude and frequency. An increase in the expression of mTOR, KCNV1, GJA5, KCNJ16, CTNNT2, KCNV2, MYO3, FOXO1 and KCND2 was noted in response to treatment of 3D patches with isoproterenol and epinephrine. CONCLUSION: Based on the results of this study, there is evidence to support the successful fabrication of a highly functional 3D patches with measurable electrical activity using cardiac myocytes reprogrammed from hADMSCs. 3D patches fabricated using optimal conductions described in this study can be used to improve the functional properties of failing hearts. Predominantly, in case of the infarcted hearts with partial loss of electrical activity, the electrical properties of the 3D patches may restore the electrical activity of the heart.

Bioengineering Cardiac Tissue Constructs With Adult Rat Cardiomyocytes.

Bioengineering cardiac tissue constructs with adult cardiomyocytes may help treat adult heart defects and injury. In this study, we fabricated cardiac tissue constructs by seeding adult rat cardiomyocytes on a fibrin gel matrix and analyzed the electromechanical properties of the formed cardiac tissue constructs. Adult rat cardiomyocytes were isolated with a collagenase type II buffer using an optimized Langendorff perfusion system. Cardiac tissue constructs were fabricated using either indirect plating with cardiomyocytes that were cultured for 1 week and dedifferentiated or with freshly isolated cardiomyocytes. The current protocol generated (3.1 ± 0.5) × 10 (n = 5 hearts) fresh cardiomyocytes from a single heart. Tissue constructs obtained by both types of plating contracted up to 30 days, and electrogram (ECG) signals and contractile twitch forces were detected. The constructs bioengineered by indirect plating of dedifferentiated cardiomyocytes produced an ECG R wave amplitude of 15.1 ± 5.2 µV (n = 7 constructs), a twitch force of 70-110 µN, and a spontaneous contraction rate of about 390 bpm. The constructs bioengineered by direct plating of fresh cardiomyocytes generated an ECG R wave amplitude of 6.3 ± 2.5 µV (n = 8 constructs), a twitch force of 40-60 µN, and a spontaneous contraction rate of about 230 bpm. This study successfully bioengineered three-dimensional cardiac tissue constructs using primary adult cardiomyocytes.

The Bioengineered Cardiac Left Ventricle.

Left ventricle and aortic valve underdevelopment are presentations in the congenital cardiac condition hypoplastic left heart syndrome (HLHS); current clinical treatments involve right ventricle refunctionalization. Cardiac organoid models provide simplified open chambers engineered into a flow loop, to ameliorate ventricle-type function. Complete bioengineered ventricle development presents a significant advancement in cardiac organoids. This study provides the foundation for bioengineered complete ventricle (BECV) fabrication. Bioengineered trileaflet valve (BETV) molds and chitosan scaffolds were developed to emulate human neonate aortic valve geometry. Bioengineered complete ventricle were fabricated by fitting BETV into a bioengineered open ventricle (BEOV); the chamber was cellularized using a two-stage cellularization strategy, and BETV were passively seeded with rat neonatal cardiac fibroblasts and perfusion cultured for 3 days. Average pressure generated ranged from 0.06 to 0.12 mm Hg; average biopotential output was 1.02 mV. Histologic assessment displayed syncytial-type cardiomyocyte aggregates at the BECV chamber surface; BETV displayed randomly oriented, diffusely distributed cardiac fibroblasts. The fabrication of this novel BECV may aid in developing a functional engineered left ventricle for clinical application in HLHS.

16-Channel Flexible System to Measure Electrophysiological Properties of Bioengineered Hearts.

As tissue engineering continues to mature, it is necessary to develop new technologies that bring insight into current paradigms and guide improvements for future experiments. To this end, we have developed a system to characterize our bioartificial heart model and compare them to functional native structures. In the present study, the hearts of adult Sprague-Dawley were decellularized resulting in a natural three-dimensional cardiac scaffold. Neonatal rat primary cardiac cells were then cultured within a complex 3D fibrin gel, forming a 3-dimensional cardiac construct, which was sutured to the acellular scaffold and suspended in media for 24-48 h. The resulting bioartificial hearts (BAHs) were then affixed with 16 electrodes, in different configurations to evaluate not only the electrocardiographic characteristics of the cultured tissues, but to also test the system's consistency. Histological evaluation showed cellularization and cardiac tissue formation. The BAHs and native hearts were then evaluated with our 16-channel flexible system to acquire the metrics associated with their respective electrophysiological properties. Time delays between the native signals were in the range of 0-95 ms. As well, color maps revealed a trend in impulse propagation throughout the native hearts. After evaluation of the normal rat QRS complex we found the average amplitude of the R-wave to be 5351.48 ± 44.92 µV and the average QRS duration was found to be 10.61 ± 0.18 ms. In contrast, BAHs exhibited more erratic and non-uniform activity that garnered no appreciable quantification. The data collected in this study proves our system's efficacy for EKG data procurement.

Electrical Stimulation of Artificial Heart Muscle: A Look Into the Electrophysiologic and Genetic Implications.

Development of tissue-engineered hearts for treatment of myocardial infarction or biologic pacemakers has been hindered by the production of mostly arrhythmic or in-synergistic constructs. Electrical stimulation (ES) of these constructs has been shown to produce tissues with greater twitch force and better adrenergic response. To further our understanding of the mechanisms underlying the effect of ES, we fabricated a bioreactor capable of delivering continuous or intermittent waveforms of various types to multiple constructs simultaneously. In this study, we examined the effect of an intermittent biphasic square wave on our artificial heart muscle (AHM) composed of neonatal rat cardiac cells and fibrin gel. Twitch forces, spontaneous contraction rates, biopotentials, gene expression profiles, and histologic observations were examined for the ES protocol over a 12 day culture period. We demonstrate improved consistency between samples for twitch force and contraction rate, and higher normalized twitch force amplitudes for electrically stimulated AHMs. Improvements in electrophysiology within the AHM were noted by higher conduction velocities and lower latency in electrical response for electrically stimulated AHMs. Genes expressing key electrophysiologic and structural markers peaked at days 6 and 8 of culture, only a few days after the initiation of ES. These results may be used for optimization strategies to establish protocols for producing AHMs capable of replacing damaged heart tissue in either a contractile or electrophysiologic capacity. Optimized AHMs can lead to alternative treatments to heart failure and alleviate the limited donor supply crisis.

The design and fabrication of a three-dimensional bioengineered open ventricle.

Current treatments in hypoplastic left heart syndrome (HLHS) include multiple surgeries to refunctionalize the right ventricle and/or transplant. The development of a tissue-engineered left ventricle (LV) would provide a therapeutic option to overcome the inefficiencies and limitations associated with current treatment options. This study provides a foundation for the development and fabrication of the bioengineered open ventricle (BEOV) model. BEOV molds were developed to emulate the human LV geometry; molds were used to produce chitosan scaffolds. BEOV were fabricated by culturing 30 million rat neonatal cardiac cells on the chitosan scaffold. The model demonstrated 57% cell retention following 4days culture. The average biopotential output for the model was 1615 µV. Histological assessment displayed the presence of localized cell clusters, with intercellular and cell-scaffold interactions. The BEOV provides a novel foundation for the development of a 3D bioengineered LV for application in HLHS. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2206-2217, 2017.

Optimizing a spontaneously contracting heart tissue patch with rat neonatal cardiac cells on fibrin gel.

Engineered cardiac tissues have been constructed with primary or stem cell-derived cardiac cells on natural or synthetic scaffolds. They represent a tremendous potential for the treatment of injured areas through the addition of tensional support and delivery of sufficient cells. In this study, 1-6 million (M) neonatal cardiac cells were seeded on fibrin gels to fabricate cardiac tissue patches, and the effects of culture time and cell density on spontaneous contraction rates, twitch forces and paced response frequencies were measured. Electrocardiograms and signal volume index of connexin 43 were also analysed. Patches of 1-6 M cell densities exhibited maximal contraction rates in the range 305-410 beats/min (bpm) within the first 4 days after plating; low cell density (1-3 M) patches sustained rhythmic contraction longer than high cell density patches (4-6 M). Patches with 1-6 M cell densities generated contractile forces in the range 2.245-14.065 mN/mm3 on days 4-6. Upon patch formation, a paced response frequency of approximately 6 Hz was obtained, and decreased to approximately 3 Hz after 6 days of culture. High cell density patches contained a thicker real cardiac tissue layer, which generated higher R-wave amplitudes; however, low-density patches had a greater signal volume index of connexin 43. In addition, all patches manifested endothelial cell growth and robust nuclear division. The present study demonstrates that the proper time for in vivo implantation of this cardiac construct is just at patch formation, and patches with 3-4 M cell densities are the best candidates. Copyright © 2014 John Wiley & Sons, Ltd.

Pulsatile flow conditioning of three-dimensional bioengineered cardiac ventricle.

Current physical stimuli mechanical stretch bioreactor studies focus on conditioning planar and/or tubular engineered cardiac constructs. The current 3D bioreactor models in cardiac tissue engineering use differential pressure loading for structural support as opposed to conditioning. The development of the pulsatile flow conditioned ventricle (PFCV) provides a 3D mechanical stretch conditioning method to generate pump function in the engineered cardiac left ventricle. The study utilizes a chitosan bioengineered open ventricle scaffold, to produce the in vitro PFCV model. PFCV were fabricated by wrapping the outer scaffold surface with a 3D fibrin gel artificial heart muscle patch, followed by pulsatile flow conditioning for 20 h. The average contractile frequency was 57 bpm. The average pressure generated, under maintained flow, post-conditioning, was 3.1633 mmHg. The average biopotential output was 0.4881 mV. Histologically, the PFCV displayed a more disseminated presence of intercellular interactions and sarcomeric organization. The results of this study clearly demonstrate the effectiveness of pulsatile flow conditioning to improve the function of our engineered left ventricle.

Optimizing cell seeding and retention in a three-dimensional bioengineered cardiac ventricle: The two-stage cellularization model.

Current cell seeding techniques focus on passively directing cells to a scaffold surface with the addition of dynamic culture to encourage cell permeation. In 3D tissue engineered constructs, cell retention efficiency is dependent on the cell delivery method, and biomaterial properties. Passive cell delivery relies on cell migration to the scaffold surface; biomaterial surface properties and porosity determine cell infiltration capacity. As a result, cell retention efficiencies remain low. The development of an effective two-stage cell seeding technique, coupled with perfusion culture, provides the potential to improve cellularization efficiency, and retention. This study, uses a chitosan bioengineered open ventricle (BEOV) scaffold to produce a two-stage perfusion cultured ventricle (TPCV). TPCV were fabricated by direct injection of 10 million primary rat neonatal cardiac cells, followed by wrapping of the outer scaffold surface with a 3D fibrin gel artificial heart muscle patch; TPCV were perfusion cultured for 3 days. The average biopotential output was 1.731 mV. TPCV cell retention following culture was approximately 5%. Cardiac cells were deposited on the scaffold surface and formed intercellular connections. Histological assessment displayed localized cell clusters, with some dissemination, and validated the observed presence of intercellular and gap-junction interactions. The study demonstrates initial effectiveness of our two-stage cell delivery concept, based on function and biological metrics. Biotechnol. Bioeng. 2016;113: 2275-2285. © 2016 Wiley Periodicals, Inc.