Progress in developing a living human tissue-engineered tri-leaflet heart valve assembled from tissue produced by the self-assembly approach

Progress of organoid platform in cardiovascular research

Cardiovascular disease is a significant cause of death in humans. Various models are necessary for the study of cardiovascular diseases, but once cellular and animal models have some defects, such as insufficient fidelity. As a new technology, organoid has certain advantages and has been used in many applications in the study of cardiovascular diseases. This article aims to summarize the application of organoid platforms in cardiovascular diseases, including organoid construction schemes, modeling, and application of cardiovascular organoids. Advances in cardiovascular organoid research have provided many models for different cardiovascular diseases in a variety of areas, including myocardium, blood vessels, and valves. Physiological and pathological models of different diseases, drug research models, and methods for evaluating and promoting the maturation of different kinds of organ tissues are provided for various cardiovascular diseases, including cardiomyopathy, myocardial infarction, and atherosclerosis. This article provides a comprehensive overview of the latest research progress in cardiovascular organ tissues, including construction protocols for cardiovascular organoid tissues and their evaluation system, different types of disease models, and applications of cardiovascular organoid models in various studies. The problems and possible solutions in organoid development are summarized.

The Human Neonatal Skin Fibroblast, an Available Cell Source for Tissue Production and Transplantation, Exhibits Low Risk of Immunogenicity In Vitro

The immunogenicity of allogeneic skin fibroblasts in transplantation has been controversial. Whether this controversy comes from a natural heterogeneity among fibroblast subsets or species-specific differences between human and mouse remains to be addressed. In this study, we sought to investigate whether fibroblasts derived from either adult or neonatal human skin tissues could induce different immune responses toward phagocytosis and T cell activation using in vitro co-culture models. Our results indicate that both phagocytosis and T cell proliferation are reduced in the presence of neonatal skin fibroblasts compared to adult skin fibroblasts. We also show that neonatal skin fibroblasts secrete paracrine factors that are responsible for reduced T cell proliferation. In addition, we show that neonatal skin fibroblasts express less class II human leukocyte antigen (HLA) molecules than adult skin fibroblasts after interferon gamma priming, which might also contribute to reduced T cell proliferation. In conclusion, this study supports the use of allogeneic neonatal skin fibroblasts as a readily available cell source for tissue production and transplantation to treat patients with severe injuries.

Preparation of nanofibrous poly (L-lactic acid) scaffolds using the thermally induced phase separation technique in dioxane/polyethylene glycol solution

Porous nanofibrous poly (L-lactic acid) (PLLA) scaffolds were fabricated in combination with a thermally induced phase separation technique using a dioxane/polyethylene glycol (PEG) system. The effect of factors such as molecular weight of PEG, aging treatment, aging or gelation temperature, and the ratio of PEG to dioxane were investigated. The results revealed that all scaffolds had high porosity, and had a significant impact on the formation of nanofibrous structures. The decrease in the molecular weight and aging or gelation temperature leads to a thinner and more uniform fibrous structure.

Strategies for Development of Synthetic Heart Valve Tissue Engineering Scaffolds

The current clinical solutions, including mechanical and bioprosthetic valves for valvular heart diseases, are plagued by coagulation, calcification, nondurability, and the inability to grow with patients. The tissue engineering approach attempts to resolve these shortcomings by producing heart valve scaffolds that may deliver patients a life-long solution. Heart valve scaffolds serve as a three-dimensional support structure made of biocompatible materials that provide adequate porosity for cell infiltration, and nutrient and waste transport, sponsor cell adhesion, proliferation, and differentiation, and allow for extracellular matrix production that together contributes to the generation of functional neotissue. The foundation of successful heart valve tissue engineering is replicating native heart valve architecture, mechanics, and cellular attributes through appropriate biomaterials and scaffold designs. This article reviews biomaterials, the fabrication of heart valve scaffolds, and their in-vitro and in-vivo evaluations applied for heart valve tissue engineering.

Inter-donor variability of extracellular matrix production in long-term cultures of human fibroblasts

Several tissue engineering approaches are based on the ability of mesenchymal cells to endogenously synthesize an extracellular matrix (ECM) in vitro, which can be seen as a form of biomaterial. Accordingly, the inter-donor variability of cell-assembled extracellular matrix (CAM) production is a key parameter to understand in order to progress towards clinical applications, especially for autologous strategies. In this study, CAMs were produced, under good manufacturing process conditions, from skin fibroblasts of 21 patients as part of a clinical trial to evaluate a tissue-engineered vascular graft. The inter-donor variability of CAM strength, thickness, hydroxyproline, and glycosaminoglycan was substantial (coefficient of variability of 33%, 19%, 24%, and 19%, respectively), but a significant correlation was observed between all four properties (Pearson r: 0.43 to 0.70; p-value ≤ 0.05). A CAM matrisome analysis, performed by mass spectrometry, revealed the presence of 70 ECM-related proteins. Our study shows that the relative abundance of 16 proteins (15 non-collagenous) correlated with CAM thickness. These proteins also correlated with CAM hydroxyproline content, as well as 21 other proteins that included fibrillar collagens and non-collagenous proteins. However, data demonstrated that only the relative abundance of type I collagen subunit alpha-1 was correlated to CAM strength. This study is the most extensive evaluation of CAM inter-donor variability to date and will help tissue engineers working with this type of biomaterial to design strategies that take into account this variability, especially for autologous tissue manufacturing.

Several tissue engineering approaches are based on the ability of mesenchymal cells to endogenously synthesize an extracellular matrix (ECM) in vitro, which can be seen as a form of biomaterial.

The Human Tissue-Engineered Cornea (hTEC): Recent Progress

Each day, about 2000 U.S. workers have a job-related eye injury requiring medical treatment. Corneal diseases are the fifth cause of blindness worldwide. Most of these diseases can be cured using one form or another of corneal transplantation, which is the most successful transplantation in humans. In 2012, it was estimated that 12.7 million people were waiting for a corneal transplantation worldwide. Unfortunately, only 1 in 70 patients received a corneal graft that same year. In order to provide alternatives to the shortage of graftable corneas, considerable progress has been achieved in the development of living corneal substitutes produced by tissue engineering and designed to mimic their in vivo counterpart in terms of cell phenotype and tissue architecture. Most of these substitutes use synthetic biomaterials combined with immortalized cells, which makes them dissimilar from the native cornea. However, studies have emerged that describe the production of tridimensional (3D) tissue-engineered corneas using untransformed human corneal epithelial cells grown on a totally natural stroma synthesized by living corneal fibroblasts, that also show appropriate histology and expression of both extracellular matrix (ECM) components and integrins. This review highlights contributions from laboratories working on the production of human tissue-engineered corneas (hTECs) as future substitutes for grafting purposes. It overviews alternative models to the grafting of cadaveric corneas where cell organization is provided by the substrate, and then focuses on their 3D counterparts that are closer to the native human corneal architecture because of their tissue development and cell arrangement properties. These completely biological hTECs are therefore very promising as models that may help understand many aspects of the molecular and cellular mechanistic response of the cornea toward different types of diseases or wounds, as well as assist in the development of novel drugs that might be promising for therapeutic purposes.

State of the Art: Tissue Engineering in Congenital Heart Surgery

Congenital heart disease is the leading cause of death secondary to congenital abnormalities in the United States and the incidence has increased significantly over the last 50 years. For those defects requiring surgical repair, bioprosthetic xenografts, allografts, and synthetic materials have traditionally been used. However, none of these modalities offer the potential for growth and accommodation within the pediatric population. Tissue engineering has been an area of great interest in a variety of cardiac applications as an innovative solution to create a product that can grow and regenerate within the body over time. Over the last 30 years, the original tissue engineering paradigm of a scaffold seeded with cells and cultured in a bioreactor has been expanded upon to include innovative methods of decellularization and production of "off-the-shelf" tissue-engineered products capable of in situ host cell repopulation. Despite progress in conceptual design and promising clinical results, widespread use of tissue-engineered products remains limited due to both regulatory and ongoing scientific challenges. Here, we describe the current state of the art with regards to in vitro, in vivo, and in situ tissue engineering as applicable within the field of congenital heart surgery and provide a brief overview of challenges and future directions.

Spatial Regulation of Valve Interstitial Cell Phenotypes within Three-Dimensional Micropatterned Hydrogels

Calcific aortic valve disease (CAVD) is the third leading cause of cardiovascular disease. CAVD exhibits progressive disruption of the normally highly organized and aligned extracellular matrix (ECM) structure within the valve leaflets simultaneously with myofibroblastic and/or osteogenic differentiation of indigenous endogenous valve interstitial cells (VIC). It is unclear how the alignment of VIC within their 3D microenvironment drives VIC phenotype or how alignment affects cellular responses to biochemical cues in physiological or pathological conditions. In this study, we implement a photolithographic technique to control the alignment and elongation of both normal and diseased human aortic VIC (HAVIC) within microengineered 3D hydrogels consisting of methacrylated hyaluronic acid and methacrylated gelatin. Stripe micropatterning created distinct alignment of HAVIC within a 3D culture system, which promoted spreading and enhanced their activation and osteogenic differentiation in pro-osteogenic conditions. HAVIC from a patient with CAVD exhibited greater susceptibility to myofibroblastic and osteogenic differentiation in culture. The roles of conjugated basic fibroblastic growth factor (bFGF) and RhoA/ROCK pathway in regulating HAVIC phenotypes were also investigated in the presence of aligned microtopography. The addition of bFGF was preventative to osteogenic differentiation for healthy HAVIC; however, it promoted osteogenic differentiation in diseased HAVIC. Inhibition of the ROCK pathway only decreased osteogenic differentiation for diseased HAVIC in the aligned formation. Collectively, these results improve our knowledge of the effects that VIC alignment has on VIC phenotypes and valve disease progression. The cell culture platform also enables a better understanding of the interplay between topography, biochemical cues, and VIC differentiation and provides information useful for directing differentiation as well as valve tissue regeneration.

Behavior of valvular interstitial cells on trilayered nanofibrous substrate mimicking morphologies of heart valve leaflet

Heart valve tissue engineering could be an alternative to the current bioprosthetic heart valve that faces limitations especially in pediatric patients. However, heart valve tissue engineering has remained challenging because leaflets - the primary component of a heart valve - have three layers with three diverse orientations - circumferential, random and radial, respectively. In order to mimic the orientations, we first designed three novel collectors to fabricate three nanofibrous layers with those orientations from a polymeric biomaterial in an electrospinning system. Then, we devised a novel direct electrospinning technique to develop a unified trilayered nanofibrous (TN) substrate comprising those oriented layers. The TN substrate supported the growth and orientations of seeded porcine valvular interstitial cells (PVICs) and their deposited collagen fibrils. After one month culture, the obtained trilayered tissue construct (TC) exhibited increased tensile properties over its TN substrate. Most importantly, the developed TC did not show any sign of shrinkage. Gene expression pattern of the PVICs indicated the developing stage of the TC. Their protein expression pattern was quite similar to that of leaflets. STATEMENT OF SIGNIFICANCE: This manuscript talks about development of a novel trilayered nanofibrous substrate mimicking the morphologies of a heart valve leaflet. It also describes culturing of valvular interstitial cells that reside in a leaflet, in the substrate and compares the behavior of the cultured cells with that in native leaflets in terms cell morphology, protein deposition and its orientation, and molecular signature. This study builds the groundwork for our future trilayered, tissue-engineered leaflet development. This research article would be of great interest to investigators and researchers in the field of cardiovascular tissue engineering especially in cardiac valve tissue engineering through biomaterial-based tissue engineering.

Engineering Tissues without the Use of a Synthetic Scaffold: A Twenty-Year History of the Self-Assembly Method

Twenty years ago, Dr. François A. Auger, the founder of the Laboratory of Experimental Organogenesis (LOEX), introduced the self-assembly technique. This innovative technique relies on the ability of dermal fibroblasts to produce and assemble their own extracellular matrix, differing from all other tissue-engineering techniques that use preformed synthetic scaffolds. Nevertheless, the use of the self-assembly technique was limited for a long time due to its main drawbacks: time and cost. Recent scientific breakthroughs have addressed these limitations. New protocol modifications that aim at increasing the rate of extracellular matrix formation have been proposed to reduce the production costs and laboratory handling time of engineered tissues. Moreover, the introduction of vascularization strategies in vitro permits the formation of capillary-like networks within reconstructed tissues. These optimization strategies enable the large-scale production of inexpensive native-like substitutes using the self-assembly technique. These substitutes can be used to reconstruct three-dimensional models free of exogenous materials for clinical and fundamental applications.

Paediatric nanofibrous bioprosthetic heart valve

The search for an optimal aortic valve implant with durability, calcification resistance, excellent haemodynamic parameters and ability to withstand mechanical loading is yet to be met. Thus, there has been struggled to fabricate bio-prosthetics heart valve using bioengineering. The consequential product must be resilient with suitable mechanical features, biocompatible and possess the capacity to grow. Defective heart valves replacement by surgery is now common, this improves the value and survival of life for a lot of patients. The recent paediatric heart valve implant is suboptimal due to their inability of somatic growth. They usually have multiple surgeries to change outgrown valves. Short-lived valve bio-prostheses occurring in older patients and younger ones who more usually need the replacement of its damaged heart with prosthesis led to a new invasive surgical interventions with an improved quality of life. The authors propose that nanofibre scaffold for paediatric tissue-engineered heart valve will meet most of these conditions, most particularly those related to somatic growth, and, as the nanofibre scaffold is eroded, new valve is produced, the valve matures in the child until adulthood.

The future of heart valve replacement: recent developments and translational challenges for heart valve tissue engineering

Heart valve replacement is often the only solution for patients suffering from valvular heart disease. However, currently available valve replacements require either life-long anticoagulation or are associated with valve degeneration and calcification. Moreover, they are suboptimal for young patients, because they do not adapt to the somatic growth. Tissue-engineering has been proposed as a promising approach to fulfil the urgent need for heart valve replacements with regenerative and growth capacity. This review will start with an overview on the currently available valve substitutes and the techniques for heart valve replacement. The main focus will be on the evolution of and different approaches for heart valve tissue engineering, namely the in vitro, in vivo and in situ approaches. More specifically, several heart valve tissue-engineering studies will be discussed with regard to their shortcomings or successes and their possible suitability for novel minimally invasive implantation techniques. As in situ heart valve tissue engineering based on cell-free functionalized starter materials is considered to be a promising approach for clinical translation, this review will also analyse the techniques used to tune the inflammatory response and cell recruitment upon implantation in order to stir a favourable outcome: controlling the blood-material interface, regulating the cytokine release, and influencing cell adhesion and differentiation. In the last section, the authors provide their opinion about the future developments and the challenges towards clinical translation and adaptation of heart valve tissue engineering for valve replacement. Copyright © 2016 John Wiley & Sons, Ltd.

Biological and mechanical evaluation of a Bio-Hybrid scaffold for autologous valve tissue engineering

Major challenge in heart valve tissue engineering for paediatric patients is the development of an autologous valve with regenerative capacity. Hybrid tissue engineering approach is recently gaining popularity to design scaffolds with desired biological and mechanical properties that can remodel post implantation. In this study, we fabricated aligned nanofibrous Bio-Hybrid scaffold made of decellularized bovine pericardium: polycaprolactone-chitosan with optimized polymer thickness to yield the desired biological and mechanical properties. CD44⁺, αSMA⁺, Vimentin⁺ and CD105^- human valve interstitial cells were isolated and seeded on these Bio-Hybrid scaffolds. Subsequent biological evaluation revealed interstitial cell proliferation with dense extra cellular matrix deposition that indicated the viability for growth and proliferation of seeded cells on the scaffolds. Uniaxial mechanical tests along axial direction showed that the Bio-Hybrid scaffolds has at least 20 times the strength of the native valves and its stiffness is nearly 3 times more than that of native valves. Biaxial and uniaxial mechanical studies on valve interstitial cells cultured Bio-Hybrid scaffolds revealed that the response along the axial and circumferential direction was different, similar to native valves. Overall, our findings suggest that Bio-Hybrid scaffold is a promising material for future development of regenerative heart valve constructs in children.

Collagen and Elastin Biomaterials for the Fabrication of Engineered Living Tissues

Collagen and elastin represent the two most predominant proteins in the body and are responsible for modulating important biological and mechanical properties. Thus, the focus of this review is the use of collagen and elastin as biomaterials for the fabrication of living tissues. Considering the importance of both biomaterials, we first propose the notion that many tissues in the human body represent a reinforced composite of collagen and elastin. In the rest of the review, collagen and elastin biosynthesis and biophysics, as well as molecular sources and biomaterial fabrication methodologies, including casting, fiber spinning, and bioprinting, are discussed. Finally, we summarize the current attempts to fabricate a subset of living tissues and, based on biochemical and biomechanical considerations, suggest that future tissue-engineering efforts consider direct incorporation of collagen and elastin biomaterials.

Bioengineered living cardiac and venous valve replacements: current status and future prospects

Valvular heart disease remains to be a major cause of death worldwide with increasing prevalence, mortality, and morbidity. Current heart valve replacements are associated with several limitations due to their nonviable nature. In this regard, heart valve tissue engineering has shown to represent a promising concept in order to overcome these limitations and replace diseased cardiac valves with living, autologous constructs. These bioengineered valves hold potential for in situ remodeling, growth, and repair throughout the patient's lifetime without the risk of thromboembolic complications and adverse immune responses. For the fabrication of tissue-engineered heart valves, several concepts have been established, the "classical" in vitro tissue engineering approach, the in situ tissue engineering approach, and alternative approaches including three-dimensional printing and electrospinning. Besides first attempts have been conducted in order to produce a tissue-engineered venous valve for the treatment of deep venous valve insufficiency. Here we review basic principals and current scientific status of valvular tissue engineering, including a critical discussion and outlook for the future.

Heart valve regeneration: the need for systems approaches

Tissue-engineered heart valves are promising alternatives to address the limitations of current valve replacements, particularly for growing children. Current heart valve tissue engineering strategies involve the selection of biomaterial scaffolds, cell types, and often in vitro culture conditions aimed at regenerating a valve for implantation and subsequent maturation in vivo. However, identifying optimal combinations of cell sources, biomaterials, and/or bioreactor conditions to produce functional, durable valve tissue remains a challenge. Despite some short-term success in animal models, attempts to recapitulate aspects of the native heart valve environment based on 'best guesses' of a limited number of regulatory factors have not proven effective. Better outcomes for valve tissue regeneration will likely require a systems-level understanding of the relationships between multiple interacting regulatory factors and their effects on cell function and tissue formation. Until recently, conventional culture methods have not allowed for multiple design parameters to be considered at once. Emerging microtechnologies are well suited to systematically probe multiple inputs, in combination, in high throughput and with great precision. When combined with statistical and network systems analyses, these microtechnologies have excellent potential to define multivariate signal-response relationships and reveal key regulatory pathways for robust functional tissue regeneration.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Generation and Assessment of Functional Biomaterial Scaffolds for Applications in Cardiovascular Tissue Engineering and Regenerative Medicine

Current clinically applicable tissue and organ replacement therapies are limited in the field of cardiovascular regenerative medicine. The available options do not regenerate damaged tissues and organs, and, in the majority of the cases, show insufficient restoration of tissue function. To date, anticoagulant drug-free heart valve replacements or growing valves for pediatric patients, hemocompatible and thrombus-free vascular substitutes that are smaller than 6 mm, and stem cell-recruiting delivery systems that induce myocardial regeneration are still only visions of researchers and medical professionals worldwide and far from being the standard of clinical treatment. The design of functional off-the-shelf biomaterials as well as automatable and up-scalable biomaterial processing methods are the focus of current research endeavors and of great interest for fields of tissue engineering and regenerative medicine. Here, various approaches that aim to overcome the current limitations are reviewed, focusing on biomaterials design and generation methods for myocardium, heart valves, and blood vessels. Furthermore, novel contact- and marker-free biomaterial and extracellular matrix assessment methods are highlighted.

Scaffold and scaffold-free self-assembled systems in regenerative medicine

Self-assembly in tissue engineering refers to the spontaneous chemical or biological association of components to form a distinct functional construct, reminiscent of native tissue. Such self-assembled systems have been widely used to develop platforms for the delivery of therapeutic and/or bioactive molecules and various cell populations. Tissue morphology and functional characteristics have been recapitulated in several self-assembled constructs, designed to incorporate stimuli responsiveness and controlled architecture through spatial confinement or field manipulation. In parallel, owing to substantial functional properties, scaffold-free cell-assembled devices have aided in the development of functional neotissues for various clinical targets. Herein, we discuss recent advancements and future aspirations in scaffold and scaffold-free self-assembled devices for regenerative medicine purposes. Biotechnol. Bioeng. 2016;113: 1155-1163. © 2015 Wiley Periodicals, Inc.

Preparation and characterization of directed, one-day-self-assembled millimeter-size spheroids of adipose-derived mesenchymal stem cells

Three-dimensional cell spheroids prepared without using any artificial scaffold materials are desirable for cell-based transplants. However, conventional cell culture systems are inefficient for rapid, large-scale and non-cytotoxic generation of size-controlled spheroids (>1 mm diameter) that are required for tissue regenerative therapy application. In this study, we prepared millimeter-order spheroids of adipose-derived mesenchymal stem cells (ADSCs) by controlling the spheroid size (diameter range: 0.4-2.5 mm). Notably, spheroid generation required only one day of culture on charged culture dishes. Almost all spheroid-derived ADSCs were viable and produced adhesion molecules and growth factors, which play an important role in tissue regeneration. Moreover, spheroid-derived ADSCs could infiltrate and recellularize collagenous tissue membranes in vitro. The ADSC spheroids developed in this study could be directly (without additional processing) used for cell-based tissue regeneration therapy. Furthermore, the rapid scale-up process and noncytotoxic generation of spheroids would also enable other applications such as use as screening models for drug discovery.

Microfluidic Organ-on-a-Chip Technology for Advancement of Drug Development and Toxicology

In recent years, the exploitation of phenomena surrounding microfluidics has seen an increase in popularity, as researchers have found a way to use their unique properties to create superior design alternatives. One such application is representing the properties and functions of different organs on a microscale chip for the purpose of drug testing or tissue engineering. With the introduction of "organ-on-a-chip" systems, researchers have proposed various methods on various organ-on-a-chip systems to mimic their in vivo counterparts. In this article, a systematic approach is taken to review current technologies pertaining to organ-on-a-chip systems. Design processes with attention to the particular instruments, cells, and materials used are presented.

Current progress in tissue engineering of heart valves: multiscale problems, multiscale solutions

INTRODUCTION

Heart valve disease is an increasingly prevalent and clinically serious condition. There are no clinically effective biological diagnostics or treatment strategies. The only recourse available is replacement with a prosthetic valve, but the inability of these devices to grow or respond biologically to their environments necessitates multiple resizing surgeries and life-long coagulation treatment, especially in children. Tissue engineering has a unique opportunity to impact heart valve disease by providing a living valve conduit, capable of growth and biological integration.

AREAS COVERED

This review will cover current tissue engineering strategies in fabricating heart valves and their progress towards the clinic, including molded scaffolds using naturally derived or synthetic polymers, decellularization, electrospinning, 3D bioprinting, hybrid techniques, and in vivo engineering.

EXPERT OPINION

Whereas much progress has been made to create functional living heart valves, a clinically viable product is not yet realized. The next leap in engineered living heart valves will require a deeper understanding of how the natural multi-scale structural and biological heterogeneity of the tissue ensures its efficient function. Related, improved fabrication strategies must be developed that can replicate this de novo complexity, which is likely instructive for appropriate cell differentiation and remodeling whether seeded with autologous stem cells in vitro or endogenously recruited cells.