Heart valve tissue engineering: concepts, approaches, progress, and challenges

Preservation of human heart valves for replacement in children with heart valve disease: past, present and future

Valvular heart disease affects 30% of the new-borns with congenital heart disease. Valve replacement of semilunar valves by mechanical, bioprosthetic or donor allograft valves is the main treatment approach. However, none of the replacements provides a viable valve that can grow and/or adapt with the growth of the child leading to re-operation throughout life. In this study, we review the impact of donor valve preservation on moving towards a more viable valve alternative for valve replacements in children or young adults.

Mechanical modeling of the maturation process for tissue-engineered implants: Application to biohybrid heart valves

The development of tissue-engineered cardiovascular implants can improve the lives of large segments of our society who suffer from cardiovascular diseases. Regenerative tissues are fabricated using a process called tissue maturation. Furthermore, it is highly challenging to produce cardiovascular regenerative implants with sufficient mechanical strength to withstand the loading conditions within the human body. Therefore, biohybrid implants for which the regenerative tissue is reinforced by standard reinforcement material (e.g. textile or 3d printed scaffold) can be an interesting solution. In silico models can significantly contribute to characterizing, designing, and optimizing biohybrid implants. The first step towards this goal is to develop a computational model for the maturation process of tissue-engineered implants. This paper focuses on the mechanical modeling of textile-reinforced tissue-engineered cardiovascular implants. First, an energy-based approach is proposed to compute the collagen evolution during the maturation process. Then, the concept of structural tensors is applied to model the anisotropic behavior of the extracellular matrix and the textile scaffold. Next, the newly developed material model is embedded into a special solid-shell finite element formulation with reduced integration. Finally, our framework is used to compute two structural problems: a pressurized shell construct and a tubular-shaped heart valve. The results show the ability of the model to predict collagen growth in response to the boundary conditions applied during the maturation process. Consequently, the model can predict the implant's mechanical response, such as the deformation and stresses of the implant.

Ozaki procedure-re-construction of aortic valve leaflets using autologous pericardial tissue: a review

The Ozaki procedure has emerged as a valuable option for treating various aortic valve pathologies. This review article delves into the intricacies of this innovative surgical approach by exploring its adaptation to the complex anatomy and physiology of the aortic root. The diverse etiologies of aortic valve diseases, ranging from congenital anomalies to degenerative changes, make treatment selection a complex challenge. Aortic valve replacement has traditionally been the gold standard, but emerging evidence supports valve repair techniques, emphasizing the importance of preserving native tissue. Nevertheless, issues like lifelong anticoagulation with mechanical valves and patient-prosthetic mismatch remain. The Ozaki procedure offers a compelling alternative by utilizing autologous pericardium or a tissue substitute to construct new aortic valve leaflets. This technique, standardized by Dr. Ozaki in 2007, provides a customizable and adaptable solution. The article highlights the anatomy of the aortic root, emphasizing the critical role of the sinus of Valsalva and interleaflet triangles in maintaining proper valve function. The procedure's unique adaptation to aortic root dynamics allows for reduced mechanical stress during systole and diastole, mimicking the natural valve's behavior. Furthermore, Ozaki leaflets exhibit promising hemodynamics and reduced risks of complications, such as permanent pacemaker implantation and patient-prosthetic mismatch. The use of autologous pericardium in the Ozaki procedure presents advantages, including enhanced tissue strength, minimal immunogenicity, and reduced risk of immune-mediated calcification. These factors contribute to the longevity and resilience of the reconstructed valve. This comprehensive review aims to shed light on the procedure's intricacies, its alignment with aortic root anatomy and physiology, and its potential as a valuable tool in the armamentarium of aortic surgeons.

Biofunctionalized Decellularized Tissue-Engineered Heart Valve with Mesoporous Silica Nanoparticles for Controlled Release of VEGF and RunX2-siRNA against Calcification

The goal of tissue-engineered heart valves (TEHV) is to replace normal heart valves and overcome the shortcomings of heart valve replacement commonly used in clinical practice. However, calcification of TEHV is the major bottleneck to break for both clinical workers and researchers. Endothelialization of TEHV plays a crucial role in delaying valve calcification by reducing platelet adhesion and covering the calcified spots. In the present study, we loaded RunX2-siRNA and VEGF into mesoporous silica nanoparticles and investigated the properties of anti-calcification and endothelialization in vitro. Then, the mesoporous silica nanoparticle was immobilized on the decellularized porcine aortic valve (DPAV) by layer self-assembly and investigated the anti-calcification and endothelialization. Our results demonstrated that the mesoporous silica nanoparticles delivery vehicle demonstrated good biocompatibility, and a stable release of RunX2-siRNA and VEGF. The hybrid decellularized valve exhibited a low hemolysis rate and promoted endothelial cell proliferation and adhesion while silencing RunX2 gene expression in valve interstitial cells, and the hybrid decellularized valve showed good mechanical properties. Finally, the in vivo experiment showed that the mesoporous silica nanoparticles delivery vehicle could enhance the endothelialization of the hybrid valve. In summary, we constructed a delivery system based on mesoporous silica to biofunctionalized TEHV scaffold for endothelialization and anti-calcification.

Biomimetic Scaffolds for Tendon Tissue Regeneration

Tendon tissue connects muscle to bone and plays crucial roles in stress transfer. Tendon injury remains a significant clinical challenge due to its complicated biological structure and poor self-healing capacity. The treatments for tendon injury have advanced significantly with the development of technology, including the use of sophisticated biomaterials, bioactive growth factors, and numerous stem cells. Among these, biomaterials that the mimic extracellular matrix (ECM) of tendon tissue would provide a resembling microenvironment to improve efficacy in tendon repair and regeneration. In this review, we will begin with a description of the constituents and structural features of tendon tissue, followed by a focus on the available biomimetic scaffolds of natural or synthetic origin for tendon tissue engineering. Finally, we will discuss novel strategies and present challenges in tendon regeneration and repair.

Three-dimensional analysis of hydrogel-imbedded aortic valve interstitial cell shape and its relation to contractile behavior

Cell-shape is a conglomerate of mechanical, chemical, and biological mechanisms that reflects the cell biophysical state. In a specific application, we consider aortic valve interstitial cells (AVICs), which maintain the structure and function of aortic heart valve leaflets. Actomyosin stress fibers help determine AVIC shape and facilitate processes such as adhesion, contraction, and mechanosensing. However, detailed 3D assessment of stress fiber architecture and function is currently impractical. Herein, we assessed AVIC shape and contractile behaviors using hydrogel-based 3D traction force microscopy to intuit the orientation and behavior of AVIC stress fibers. We utilized spherical harmonics (SPHARM) to quantify AVIC geometries through three days of incubation, which demonstrated a shift from a spherical shape to forming substantial protrusions. Furthermore, we assessed changes in post-three day AVIC shape and contractile function within two testing regimes: (1) normal contractile level to relaxation (cytochalasin D), and (2) normal contractile level to hyper-contraction (endothelin-1). In both scenarios, AVICs underwent isovolumic shape changes and produced complex displacement fields within the hydrogel. AVICs were more elongated when relaxed and more spherical in hyper-contraction. Locally, AVIC protrusions contracted along their long axis and expanded in their circumferential direction, indicating predominately axially aligned stress fibers. Furthermore, the magnitude of protrusion displacements was correlated with protrusion length and approached a consistent displacement plateau at a similar critical length across all AVICs. This implied that stress fiber behavior is conserved, despite great variations in AVIC shapes. We anticipate our findings will bolster future investigations into AVIC stress fiber architecture and function. STATEMENT OF SIGNIFICANCE: Within the aortic valve there exists a population of aortic valve interstitial cells, which orchestrate the turnover, secretion, and remodeling of its extracellular matrix, maintaining tissue integrity and ultimately sustaining the proper mechanical function. Alterations in these processes are thought to underlie diseases of the aortic valve, which affect hundreds of thousands domestically and world-wide. Yet, to date, there are no non-surgical treatments for aortic heart valve disease, in part due to our limited understanding of the underlying disease processes. In the present study, we built upon our previous study to include a full 3D analysis of aortic valve interstitial cell shapes at differing contractile levels. The resulting detailed shape and deformation analysis provided insight into the underlying stress-fiber structures and mechanical behaviors.

Structural and biomechanical characterizations of acellular porcine mitral valve scaffolds: anterior leaflets, posterior leaflets, and chordae tendineae

Mitral valve (MV) tissue engineering is still in its early stage, and one major challenge in MV tissue engineering is to identify appropriate scaffold materials. With the potential of acellular MV scaffolds being demonstrated recently, it is important to have a full understanding of the biomechanics of the native MV components and their acellular scaffolds. In this study, we have successfully characterized the structural and mechanical properties of porcine MV components, including anterior leaflet (AL), posterior leaflet (PL), strut chordae, and basal chordae, before and after decellularization. Quantitative DNA assay showed more than 90% reduction in DNA content, and Griffonia simplicifolia (GS) lectin immunohistochemistry confirmed the complete lack of porcine α-Gal antigen in the acellular MV components. In the acellular AL and PL, the atrialis, spongiosa, and fibrosa trilayered structure, along with its ECM constitutes, i.e., collagen fibers, elastin fibers, and portion of GAGs, were preserved. Nevertheless, the ECM of both AL and PL experienced a certain degree of disruption, exhibiting a less dense, porous ECM morphology. The overall anatomical morphology of the strut and basal chordae were also maintained after decellularization, with longitudinal morphology experiencing minimum disruption, but the cross-sectional morphology exhibiting evenly-distributed porous structure. In the acellular AL and PL, the nonlinear anisotropic biaxial mechanical behavior was overall preserved; however, uniaxial tensile tests showed that the removal of cellular content and the disruption of structural ECM did result in small decreases in maximum tensile modulus, tissue extensibility, failure stress, and failure strain for both MV leaflets and chordae.

Natural Polymers in Heart Valve Tissue Engineering: Strategies, Advances and Challenges

In the history of biomedicine and biomedical devices, heart valve manufacturing techniques have undergone a spectacular evolution. However, important limitations in the development and use of these devices are known and heart valve tissue engineering has proven to be the solution to the problems faced by mechanical and prosthetic valves. The new generation of heart valves developed by tissue engineering has the ability to repair, reshape and regenerate cardiac tissue. Achieving a sustainable and functional tissue-engineered heart valve (TEHV) requires deep understanding of the complex interactions that occur among valve cells, the extracellular matrix (ECM) and the mechanical environment. Starting from this idea, the review presents a comprehensive overview related not only to the structural components of the heart valve, such as cells sources, potential materials and scaffolds fabrication, but also to the advances in the development of heart valve replacements. The focus of the review is on the recent achievements concerning the utilization of natural polymers (polysaccharides and proteins) in TEHV; thus, their extensive presentation is provided. In addition, the technological progresses in heart valve tissue engineering (HVTE) are shown, with several inherent challenges and limitations. The available strategies to design, validate and remodel heart valves are discussed in depth by a comparative analysis of in vitro, in vivo (pre-clinical models) and in situ (clinical translation) tissue engineering studies.

Cardiovascular tissue engineering and regeneration: A plead for further knowledge convergence

Cardiovascular tissue engineering and regeneration strive to provide long-term, effective solutions for a growing group of patients in need of myocardial repair, vascular (access) grafts, heart valves, and regeneration of organ microcirculation. In the past two decades, ongoing convergence of disciplines and multidisciplinary collaborations between cardiothoracic surgeons, cardiologists, bioengineers, material scientists, and cell biologists have resulted in better understanding of the problems at hand and novel regenerative approaches. As a side effect, however, the field has become strongly organized and differentiated around topical areas at risk of reinvention of technologies and repetition of approaches and across the areas. A better integration of knowledge and technologies from the individual topical areas and regenerative approaches and technologies may pave the way towards faster and more effective treatments to cure the cardiovascular system. This review summarizes the evolution of research and regenerative approaches in the areas of myocardial regeneration, heart valve and vascular tissue engineering, and regeneration of microcirculations and discusses previous and potential future integration of these individual areas and developed technologies for improved clinical impact. Finally, it provides a perspective on the further integration of research organization, knowledge implementation, and valorization as a contributor to advancing cardiovascular tissue engineering and regenerative medicine.

Generation of individualized immunocompatible endothelial cells from HLA-I-matched human pluripotent stem cells

BACKGROUND

Endothelial cells (ECs) derived from human-induced pluripotent stem cell (iPSC) are a valuable cell resource for cardiovascular regeneration. To avoid time-consuming preparation from primary autologous cells, the allogeneic iPSC-ECs are being expected to become "off-the-shelf" cell products. However, allorejection caused by HLA mismatching is a major barrier for this strategy. Although the "hypoimmunogenic" iPSCs could be simply generated by inhibition of HLA-I expression via β-2 microglobulin knockout (B2M KO), the deletion of HLA-I expression will activate natural killer (NK) cells, which kill the HLA-I negative cells. To inhibit NK activation, we proposed to generate HLA-matched iPSCs based on patient's HLA genotyping by HLA exchanging approach to express the required HLA allele.

METHODS

To establish a prototype of HLA exchanging system, the expression of HLA-I molecules of iPSCs was inhibited by CRISPR/Cas9-mediated B2M KO, and then HLA-A*11:01 allele, as a model molecule, was introduced into B2M KO iPSCs by lentiviral gene transfer. HLA-I-modified iPSCs were tested for their pluripotency and ability to differentiate into ECs. The stimulation of iPSC-EC to allogeneic T and NK cells was detected by respective co-culture of PBMC-EC and NK-EC. Finally, the iPSC-ECs were used as the seeding cells to re-endothelialize the decellularized valves.

RESULTS

We generated the iPSCs only expressed one HLA-A allele (HLA-A *11:01) by B2M KO plus HLA gene transfer. These HLA-I-modified iPSCs maintained pluripotency and furthermore were successfully differentiated into functional ECs assessed by tube formation assay. Single HLA-A*11:01-matched iPSC-ECs significantly less induced the allogeneic response of CD8+ T cell and NK cells expressing matched HLA-A*11:01 and other HLA-A,-B and -C alleles. These cells were successfully used to re-endothelialize the decellularized valves.

CONCLUSIONS

In summary, a simple HLA-I exchanging system has been created by efficient HLA engineering of iPSCs to evade both of the alloresponse of CD8+ T cells and the activation of NK cells. This technology has been applied to generate iPSC-ECs for the engineering of cellular heart valves. Our strategy should be extremely useful if the "off-the-shelf" and "non-immunogenic" allogeneic iPSCs were created for the common HLA alleles.

Enhenced cell adhesion on collagen I treated parylene-C microplates

On account of unique mechanical property and inertia, parylene-C has become a promising material for microdevices especially in three-dimensional microstructures loaded with cells. However, parylene-C is not favorable for cell adhesion, and a routine procedure is to modify it with a new adhesive layer. Herein, the parylene-C substrates with or without collagen Ӏ (Col-I) coating were adopted to estimate the influence of micro-environment change on cell attachment and spreading. After modification with Col-I, cauliflower-like particles presented on the substrate surface. Contact angle was significantly decreased after Col-I modification, which suggested the surface hydrophilicity was enhanced. Furthermore, cells cultured on parylene-C surface with Col-I treatment showed increased proliferation rate and spreading areas. In order to test the adhesion strength, a series of fixed size parylene-C microplates was fabricated, and cell suspension concentration was adjusted to culture a single cell on one microplate. The microplate was folded by the autogenous shrinkage force of cell. The folding angles of parylene-C microplates with Col-I treatment exhibited higher folding angle (112.6 ± 15.6°) than untreated samples (46.7 ± 5.9°). The work proved the existence of Col-I layer was particularly important, especially in analysis of cells mechanics using parylene-C microplate as a substrate.

Pathology of the Aorta and Aorta as Homograft

The aorta is not a rigid tube, it is an “organ” with lamellar units, consisting of elastic fibers, extracellular matrix and smooth muscle cells in between as parenchyma. Several diseases may occur in the natural history of the aorta, requiring replacement of both semilunar cusps and ascending aorta. They may be congenital defects, such as bicuspid aortic valve and isthmal coarctation with aortopathy; genetically determined, such as Marfan and William syndromes; degenerative diseases, such as atherosclerosis and medial necrosis with aortic dilatation, valve incompetence and dissecting aneurysm; inflammatory diseases such as Takayasu arteritis, syphilis, giant cell and IgM4 aortitis; neoplasms; and trauma. Aortic homografts from cadavers, including both the sinus portion with semilunar cusps and the tubular portion, are surgically employed to replace a native sick ascending aorta. However, the antigenicity of allograft cells, in the lamellar units and interstitial cells in the cusps, is maintained. Thus, an immune reaction may occur, limiting durability. After proper decellularization and 6 months’ implantation in sheep, endogenous cell repopulation was shown to occur in both the valve and aortic wall, including the endothelium, without evidence of inflammation and structural deterioration/calcification in the mid-term. The allograft was transformed into an autograft.

Porcine Umbilical Cord Perivascular Cells for Preclinical Testing of Tissue-Engineered Heart Valves

Many children born with congenital heart disease need a heart valve repair or replacement. Currently available repair materials and valve replacements are incapable of growth, repair, and adaptation, rendering them inadequate for growing children. Heart valve tissue engineering (HVTE) aims to develop living replacement valves that can meet these needs. Among numerous cell sources for in vitro HVTE, umbilical cord perivascular cells (UCPVCs) are particularly attractive because they are autologous, readily available, and have excellent regenerative capacity. As an essential step toward preclinical testing of heart valves engineered from UCPVCs, the goal of this study was to establish methods to isolate, expand, and promote extracellular matrix (ECM) synthesis by UCPVCs from pigs (porcine umbilical cord perivascular cells [pUCPVCs]), as a relevant preclinical model. We determined that Dulbecco's modified Eagle's medium with 20% fetal bovine serum supported isolation and substantial expansion of pUCPVCs, whereas media designed for human mesenchymal stromal cell (MSC) expansion did not. We further demonstrated the capacity of pUCPVCs to synthesize the main ECM components of heart valves (collagen type I, elastin, and glycosaminoglycans), with maximal collagen and elastin per-cell production occurring in serum-free culture conditions using StemMACS™ MSC Expansion Media. Altogether, these results establish protocols that enable the use of pUCPVCs as a viable cell source for preclinical testing of engineered heart valves. Impact statement This study establishes methods to successfully isolate, expand, and promote the synthesis of the main extracellular matrix components of heart valves (collagen type I, elastin, and glycosaminoglycans) by porcine umbilical cord perivascular cells (pUCPVCs). These protocols enable further evaluation of pUCPVCs as an autologous, readily available, and clinically relevant cell source for preclinical testing of pediatric tissue-engineered heart valves.

Histological assessment of the human heart valves and its relationship with age

The human heart valves are complex anatomical structures consisting of leaflets with many supporting structures. With advancing age, the microstructure of the components of the valves can change. Knowledge and understanding of the anatomical relationships between the different components of the heart valve structures and their relationship with age is crucial for the development and progression of treatment of valvular disease. The purpose of this study was to determine histological changes of the components of the heart valves and their relationship with age. Fifty hearts taken from cadavers were included to examine the histology of the tricuspid, mitral, pulmonary, and aortic valves. All specimens were stained with Elastic Van Gieson, and picrosirius red to enable the evaluation of elastic and collagen fibers, respectively. There was a gradual increase in elastic and collagen fibers with advancing age, particularly over 40 years, in all valve types. In the case of tricuspid and mitral valves increases in collagen and elastic fibers were observed starting in the fifth decade. Elastic fiber fragmentation was observed in specimens over 50 years. In the case of the pulmonary and the aortic valves, collagen fibers were denser and more irregular in the sixth to seventh decades when compared to younger ages while elastic fibers were significantly increased in the sixth decade. In addition, an increase in fat deposition had an association with aging. These findings provide additional basic knowledge in age-related morphological changes of the heart valves and will increase understanding concerning valvular heart diseases and treatment options.

Next-generation tissue-engineered heart valves with repair, remodelling and regeneration capacity

Valvular heart disease is a major cause of morbidity and mortality worldwide. Surgical valve repair or replacement has been the standard of care for patients with valvular heart disease for many decades, but transcatheter heart valve therapy has revolutionized the field in the past 15 years. However, despite the tremendous technical evolution of transcatheter heart valves, to date, the clinically available heart valve prostheses for surgical and transcatheter replacement have considerable limitations. The design of next-generation tissue-engineered heart valves (TEHVs) with repair, remodelling and regenerative capacity can address these limitations, and TEHVs could become a promising therapeutic alternative for patients with valvular disease. In this Review, we present a comprehensive overview of current clinically adopted heart valve replacement options, with a focus on transcatheter prostheses. We discuss the various concepts of heart valve tissue engineering underlying the design of next-generation TEHVs, focusing on off-the-shelf technologies. We also summarize the latest preclinical and clinical evidence for the use of these TEHVs and describe the current scientific, regulatory and clinical challenges associated with the safe and broad clinical translation of this technology.

Challenges in Perioperative Animal Care for Orthotopic Implantation of Tissue-Engineered Pulmonary Valves in the Ovine Model

BACKGROUND

Development of valvular substitutes meeting the performance criteria for surgical correction of congenital heart malformations is a major research challenge. The sheep is probably the most widely used animal model in heart valves regenerative medicine. Although the standard cardiopulmonary bypass (CPB) technique and various anesthetic and surgical protocols are reported to be feasible and safe, they are associated with significant morbidity and mortality rates. The premise of this paper is that the surgical technique itself, especially the perioperative animal care and management protocol, is essential for successful outcomes and survival.

METHODS

Ten juvenile and adult female sheep aged 7.8-37.5 months and weighing 32.0-58.0 kg underwent orthotopic implantation of tissue-engineered pulmonary valve conduits on beating heart under normothermic CPB. The animals were followed-up for 6 months before scheduled euthanasia.

RESULTS

Based on our observations, we established a guide for perioperative care, follow-up, and treatment containing information regarding the appropriate clinical, biological, and ultrasound examinations and recommendations for feasible and safe anesthetic, surgical, and euthanasia protocols. Specific recommendations were also included for perioperative care of juvenile versus adult sheep.

CONCLUSION

The described surgical technique was feasible, with a low mortality rate and minimal surgical complications. The proposed anesthetic protocol was safe and effective, ensuring both adequate sedation and analgesia as well as rapid recovery from anesthesia without significant complications. The established guide for postoperative care, follow-up and treatment in sheep after open-heart surgery may help other research teams working in the field of heart valves tissue regeneration.

The time has come to extend the expiration limit of cryopreserved allograft heart valves

Despite the wide choice of commercial heart valve prostheses, cryopreserved semilunar allograft heart valves (C-AHV) are required, and successfully transplanted in selected groups of patients. The expiration limit (EL) criteria have not been defined yet. Most Tissue Establishments (TE) use the EL of 5 years. From physiological, functional, and surgical point of view, the morphology and mechanical properties of aortic and pulmonary roots represent basic features limiting the EL of C-AHV. The aim of this work was to review methods of AHV tissue structural analysis and mechanical testing from the perspective of suitability for EL validation studies. Microscopic structure analysis of great arterial wall and semilunar leaflets tissue should clearly demonstrate cells as well as the extracellular matrix components by highly reproducible and specific histological staining procedures. Quantitative morphometry using stereological grids has proved to be effective, as the exact statistics was feasible. From mechanical testing methods, tensile test was the most suitable. Young's moduli of elasticity, ultimate stress and strain were shown to represent most important AHV tissue mechanical characteristics, suitable for exact statistical analysis. C-AHV are prepared by many different protocols, so as each TE has to work out own EL for C-AHV.

Differential microRNAs expression in calcified versus rheumatic aortic valve disease

BACKGROUND

The aortic valve (AV) is the most commonly affected valve in valvular heart diseases (VHDs). The objective of the study is to identify microRNA (miRNA) molecules expressed in VHDs and the differential expression patterns of miRNA in AVs with either calcification or rheumatism etiologies.

METHODS

Human AVs were collected during valve replacement surgery. RNA was extracted and miRNA containing libraries were prepared and sequenced using the next generation sequencing (NGS) approach. miRNAs identified as differentially expressed between the two etiologies were validated by quantitative real-time polymerase chain reaction (qPCR). The receiver operating characteristic (ROC) curve analysis was performed to examine the ability of relevant miRNA to differentiate between calcification and rheumatism etiologies.

RESULTS

Rheumatic and calcified AV samples were prepared for the NGS and were successfully sequenced. The expression was validated by the qPCR approach in 46 AVs, 13 rheumatic, and 33 calcified AVs, confirming that miR-145-5p, miR-199a-5p, and miR-5701 were significantly higher in rheumatic AVs as compared with calcified AVs. ROC curve analysis revealed that miR-145-5p had a sensitivity of 76.92% and a specificity of 94.12%, area under the curve (AUC) = 0.88 (P = .0001), and miR-5701 had a sensitivity of 84.62% and a specificity of 76.47%, AUC = 0.78 (P = .0001), whereas miR-199a-5p had a sensitivity of 84.62%, and a specificity of 57.58%, AUC = 0.73 (P = .0083).

CONCLUSION

We documented differential miRNA expression between AV disease etiologies. The miRNAs identified in this study advance our understanding of the mechanisms underlining AV disease.

Cardiac Progenitor Cells from Stem Cells: Learning from Genetics and Biomaterials

Cardiac Progenitor Cells (CPCs) show great potential as a cell resource for restoring cardiac function in patients affected by heart disease or heart failure. CPCs are proliferative and committed to cardiac fate, capable of generating cells of all the cardiac lineages. These cells offer a significant shift in paradigm over the use of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes owing to the latter’s inability to recapitulate mature features of a native myocardium, limiting their translational applications. The iPSCs and direct reprogramming of somatic cells have been attempted to produce CPCs and, in this process, a variety of chemical and/or genetic factors have been evaluated for their ability to generate, expand, and maintain CPCs in vitro. However, the precise stoichiometry and spatiotemporal activity of these factors and the genetic interplay during embryonic CPC development remain challenging to reproduce in culture, in terms of efficiency, numbers, and translational potential. Recent advances in biomaterials to mimic the native cardiac microenvironment have shown promise to influence CPC regenerative functions, while being capable of integrating with host tissue. This review highlights recent developments and limitations in the generation and use of CPCs from stem cells, and the trends that influence the direction of research to promote better application of CPCs.

Disease-inspired tissue engineering: Investigation of cardiovascular pathologies

Once focused exclusively on the creation of tissues to repair or replace diseased or damaged organs, the field of tissue engineering has undergone an important evolution in recent years. Namely, tissue engineering techniques are increasingly being applied to intentionally generate pathological conditions. Motivated in part by the wide gap between 2D cultures and animal models in the current disease modeling continuum, disease-inspired tissue-engineered platforms have numerous potential applications, and may serve to advance our understanding and clinical treatment of various diseases. This review will focus on recent progress toward generating tissue-engineered models of cardiovascular diseases, including cardiac hypertrophy, fibrosis, and ischemia reperfusion injury, atherosclerosis, and calcific aortic valve disease, with an emphasis on how these disease-inspired platforms can be used to decipher disease etiology. Each pathology is discussed in the context of generating both disease-specific cells as well as disease-specific extracellular environments, with an eye toward future opportunities to integrate different tools to yield more complex and physiologically relevant culture platforms. Ultimately, the development of effective disease treatments relies upon our ability to develop appropriate experimental models; as cardiovascular diseases are the leading cause of death worldwide, the insights yielded by improved in vitro disease modeling could have substantial ramifications for public health and clinical care.

Effect of cyclic deformation on xenogeneic heart valve biomaterials

Glutaraldehyde-fixed bovine pericardium is currently the most popular biomaterial utilized in the creation of bioprosthetic heart valves. However, recent studies indicate that glutaraldehyde fixation results in calcification and structural valve deterioration, limiting the longevity of bioprosthetic heart valves. Additionally, glutaraldehyde fixation renders the tissue incompatible with constructive recipient cellular repopulation, remodeling and growth. Use of unfixed xenogeneic biomaterials devoid of antigenic burden has potential to overcome the limitations of current glutaraldehyde-fixed biomaterials. Heart valves undergo billion cycles of opening and closing throughout the patient’s lifetime. Therefore, understanding the response of unfixed tissues to cyclic loading is crucial to these in a heart valve leaflet configuration. In this manuscript we quantify the effect of cyclic deformation on cycle dependent strain, structural, compositional and mechanical properties of fixed and unfixed tissues. Glutaraldehyde-fixed bovine pericardium underwent marked cyclic dependent strain, resulting from significant changes in structure, composition and mechanical function of the material. Conversely, unfixed bovine pericardium underwent minimal strain and maintained its structure, composition and mechanical integrity. This manuscript demonstrates that unfixed bovine pericardium can withstand cyclic deformations equivalent to 6 months of in vivo heart valve leaflet performance.

Preclinical Assessment of Cardiac Valve Substitutes: Current Status and Considerations for Engineered Tissue Heart Valves

Tissue engineered heart valve (TEHV) technology may overcome deficiencies of existing available heart valve substitutes. The pathway by which TEHVs will undergo development and regulatory approval has several challenges. In this communication, we review: (1) the regulatory framework for regulation of medical devices in general and substitute heart valves in particular; (2) the special challenges of preclinical testing using animal models for TEHV, emphasizing the International Standards Organization (ISO) guidelines in document 5840; and (3) considerations that suggest a translational roadmap to move TEHV forward from pre-clinical to clinical studies and clinical implementation.

Ectopic mineralization in heart valves: new insights from in vivo and in vitro procalcific models and promising perspectives on noncalcifiable bioengineered valves

Ectopic calcification of native and bioprosthetic heart valves represents a major public health problem causing severe morbidity and mortality worldwide. Valve procalcific degeneration is known to be caused mainly by calcium salt precipitation onto membranes of suffering non-scavenged cells and dead-cell-derived products acting as major hydroxyapatite nucleators. Although etiopathogenesis of calcification in native valves is still far from being exhaustively elucidated, it is well known that bioprosthesis mineralization may be primed by glutaraldehyde-mediated toxicity for xenografts, cryopreservation-related damage for allografts and graft immune rejection for both. Instead, mechanical valves, which are free from calcification, are extremely thrombogenic, requiring chronic anticoagulation therapies for transplanted patients. Since surgical substitution of failed valves is still the leading therapeutic option, progressive improvements in tissue engineering techniques are crucial to attain readily available valve implants with good biocompatibility, proper functionality and long-term durability in order to meet the considerable clinical demand for valve substitutes. Bioengineered valves obtained from acellular non-valvular scaffolds or decellularized native valves are proving to be a compelling alternative to mechanical and bioprosthetic valve implants, as they appear to permit repopulation by the host's own cells with associated tissue remodelling, growth and repair, besides showing less propensity to calcification and adequate hemodynamic performances. In this review, insights into valve calcification onset as revealed by in vivo and in vitro procalcific models are updated as well as advances in the field of valve bioengineering.

Collagen type I and hyaluronic acid based hybrid scaffolds for heart valve tissue engineering

Tissue engineers have achieved limited success so far in designing an ideal scaffold for aortic valve; scaffolds lack in mechanical compatibility, appropriate degradation rate, and microstructural similarity. This paper, therefore, has demonstrated a carbodiimide-based sequential crosslinking technique to prepare aortic valve extracellular matrix mimicking (ECM) hybrid scaffolds from collagen type I and hyaluronic acid (HA), the building blocks of heart valve ECM, with tailorable crosslinking densities. Swelling studies revealed that crosslinking densities of parent networks increased with increasing the concentration of the crosslinking agents whereas crosslinking densities of hybrid scaffolds averaged from those of parent collagen and HA networks. Hybrid scaffolds also offered a wide range of pore size (66-126 μm) which fulfilled the criteria for valvular tissue regeneration. Scanning electron microscopy and images of Alcian blue-Periodic acid Schiff stained samples suggested that our crosslinking technique yielded an ECM mimicking microstructure with interlaced bands of collagen and HA in the hybrid scaffolds. The mutually reinforcing networks of collagen and HA also resulted in increased bending moduli up to 1660 kPa which spanned the range of natural aortic valves. Cardio sphere-derived cells (CDCs) from rat hearts showed that crosslinking density affected the available cell attachment sites on the surface of the scaffold. Increased bending moduli of CDCs seeded scaffolds up to two folds (2-6 kPa) as compared to the non-seeded scaffolds (1 kPa) suggested that an increase in crosslinking density of the scaffolds could not only increase the in vitro bending modulus but also prevented its disintegration in the cell culture medium.

Gross age-related changes and diseases in human heart valves

Cardiac valves are highly complex structures optimizing their function during the cardiac cycle. They open and close directed by blood flow under different pressure conditions in the dynamic environment in the heart. It is acknowledged that the aging process affects the structure and functions of the heart valves. With regard to morphometry, age-related changes of the heart valve can be found in valve circumference, thickness of the leaflet, luminal area at the sinotubular junction, valve diameter, orifice area, and leaflet size in circumferential and radial direction. In addition, there are differences between male and female hearts in some features. Moreover, there are studies the qualitative and quantitative assessment of histological compositions, echocardiography study to investigate the annular circumference and diameter in the human heart valves related with age. Studies into the detailed anatomy of the changes in heart valves with age are important and the correlation between valve morphology and age may be used as an age indicator. This study reviews the basic anatomical structure of the heart valves, age-related changes of valve morphometry, heart valve diseases, and general treatment of valvular diseases in humans. Detailed knowledge of the anatomical features of the morphology of the human heart valve is useful for any treatments of valve pathology.

Comparing the Role of Mechanical Forces in Vascular and Valvular Calcification Progression

Calcification is a prevalent disease in most fully developed countries and is predominantly observed in heart valves and nearby vasculature. Calcification of either tissue leads to deterioration and, ultimately, failure causing poor quality of life and decreased overall life expectancy in patients. In valves, calcification presents as Calcific Aortic Valve Disease (CAVD), in which the aortic valve becomes stenotic when calcific nodules form within the leaflets. The initiation and progression of these calcific nodules is strongly influenced by the varied mechanical forces on the valve. In turn, the addition of calcific nodules creates localized disturbances in the tissue biomechanics, which affects extracellular matrix (ECM) production and cellular activation. In vasculature, atherosclerosis is the most common occurrence of calcification. Atherosclerosis exhibits as calcific plaque formation that forms in juxtaposition to areas of low blood shear stresses. Research in these two manifestations of calcification remain separated, although many similarities persist. Both diseases show that the endothelial layer and its regulation of nitric oxide is crucial to calcification progression. Further, there are similarities between vascular smooth muscle cells and valvular interstitial cells in terms of their roles in ECM overproduction. This review summarizes valvular and vascular tissue in terms of their basic anatomy, their cellular and ECM components and mechanical forces. Calcification is then examined in both tissues in terms of disease prediction, progression, and treatment. Highlighting the similarities and differences between these areas will help target further research toward disease treatment.

The effect of heparin hydrogel embedding on glutaraldehyde fixed bovine pericardial tissues: Mechanical behavior and anticalcification potential

Heart valve diseases remain common in industrialized countries. Bioprosthetic heart valves, introduced as free of anticoagulation therapy alternatives to mechanical substitutes. Still they suffer from long term failure due to calcification. Different treatment methods introduced to inhibit calcification, have so far been limited in success. Glycosaminoglycans (GAGs) possess properties including high negative charge, anticoagulation and anti-inflammatory activity that make them a potential solution for calcification problem. In this study, heparin hydrogel was prepared and characterized both chemically and mechanically. After that, heparin hydrogel embedded bovine pericardial tissues, fixed with glutaraldehyde, were produced and tested for their mechanical behavior and anticalcifcation potential in vitro using the constant composition model. In the calcification experiments, tissues were divided into three groups: a) Controls without treatment, b) Hydrogel treated tissues and c) Tissues with raw heparin dissolved in the calcification solution. The results showed that embedding of tissue with hydrogel had no stiffening effect on its mechanical behavior. Calcification assessment showed a significant efficacy on inhibition of calcium phosphate deposition of hydrogel treated (second group) in comparison to untreated tissues (control, first group). Calcification inhibition potential was very similar in both the second and raw heparin (third group). Histological data confirmed the obtained results, suggesting that heparin treatment is a promising anticalcification agent.

Elastic materials for tissue engineering applications: Natural, synthetic, and hybrid polymers

Elastin and collagen are the two main components of elastic tissues and provide the tissue with elasticity and mechanical strength, respectively. Whereas collagen is adequately produced in vitro, production of elastin in tissue-engineered constructs is often inadequate when engineering elastic tissues. Therefore, elasticity has to be artificially introduced into tissue-engineered scaffolds. The elasticity of scaffold materials can be attributed to either natural sources, when native elastin or recombinant techniques are used to provide natural polymers, or synthetic sources, when polymers are synthesized. While synthetic elastomers often lack the biocompatibility needed for tissue engineering applications, the production of natural materials in adequate amounts or with proper mechanical strength remains a challenge. However, combining natural and synthetic materials to create hybrid components could overcome these issues. This review explains the synthesis, mechanical properties, and structure of native elastin as well as the theories on how this extracellular matrix component provides elasticity in vivo. Furthermore, current methods, ranging from proteins and synthetic polymers to hybrid structures that are being investigated for providing elasticity to tissue engineering constructs, are comprehensively discussed.

STATEMENT OF SIGNIFICANCE

Tissue engineered scaffolds are being developed as treatment options for malfunctioning tissues throughout the body. It is essential that the scaffold is a close mimic of the native tissue with regards to both mechanical and biological functionalities. Therefore, the production of elastic scaffolds is of key importance to fabricate tissue engineered scaffolds of the elastic tissues such as heart valves and blood vessels. Combining naturally derived and synthetic materials to reach this goal proves to be an interesting area where a highly tunable material that unites mechanical and biological functionalities can be obtained.

Use of sucrose to diminish pore formation in freeze-dried heart valves

Freeze-dried storage of decellularized heart valves provides easy storage and transport for clinical use. Freeze-drying without protectants, however, results in a disrupted histoarchitecture after rehydration. In this study, heart valves were incubated in solutions of various sucrose concentrations and subsequently freeze-dried. Porosity of rehydrated valves was determined from histological images. In the absence of sucrose, freeze-dried valves were shown to have pores after rehydration in the cusp, artery and muscle sections. Use of sucrose reduced pore formation in a dose-dependent manner, and pretreatment of the valves in a 40% (w/v) sucrose solution prior to freeze-drying was found to be sufficient to completely diminish pore formation. The presence of pores in freeze-dried valves was found to coincide with altered biomechanical characteristics, whereas biomechanical parameters of valves freeze-dried with enough sucrose were not significantly different from those of valves not exposed to freeze-drying. Multiphoton imaging, Fourier transform infrared spectroscopy, and differential scanning calorimetry studies revealed that matrix proteins (i.e. collagen and elastin) were not affected by freeze-drying.

Sheep-Specific Immunohistochemical Panel for the Evaluation of Regenerative and Inflammatory Processes in Tissue-Engineered Heart Valves

The creation of living heart valve replacements via tissue engineering is actively being pursued by many research groups. Numerous strategies have been described, aimed either at culturing autologous living valves in a bioreactor (in vitro) or inducing endogenous regeneration by the host via resorbable scaffolds (in situ). Whereas a lot of effort is being invested in the optimization of heart valve scaffold parameters and culturing conditions, the pathophysiological in vivo remodeling processes to which tissue-engineered heart valves are subjected upon implantation have been largely under-investigated. This is partly due to the unavailability of suitable immunohistochemical tools specific to sheep, which serves as the gold standard animal model in translational research on heart valve replacements. Therefore, the goal of this study was to comprise and validate a comprehensive sheep-specific panel of antibodies for the immunohistochemical analysis of tissue-engineered heart valve explants. For the selection of our panel we took inspiration from previous histopathological studies describing the morphology, extracellular matrix composition and cellular composition of native human heart valves throughout development and adult stages. Moreover, we included a range of immunological markers, which are particularly relevant to assess the host inflammatory response evoked by the implanted heart valve. The markers specifically identifying extracellular matrix components and cell phenotypes were tested on formalin-fixed paraffin-embedded sections of native sheep aortic valves. Markers for inflammation and apoptosis were tested on ovine spleen and kidney tissues. Taken together, this panel of antibodies could serve as a tool to study the spatiotemporal expression of proteins in remodeling tissue-engineered heart valves after implantation in a sheep model, thereby contributing to our understanding of the in vivo processes which ultimately determine long-term success or failure of tissue-engineered heart valves.

Biomechanical and morphological stability of acellular scaffolds for tissue-engineered heart valves depends on different storage conditions

Currently available bioprosthetic heart valves have been successfully used clinically; however, they have several limitations. Alternatively, tissue-engineering techniques can be used. However, there are limited data concerning the impact of storage conditions of scaffolds on their biomechanics and morphology. The aim of this study was to determine the effect of different storage conditions on the biomechanics and morphology of pulmonary valve dedicated for the acellular scaffold preparation to achieve optimal conditions to obtain stable heart valve prostheses. Scaffold can then be used for the construction of tissue-engineered heart valve, for this reason evaluation of these parameters can determine the success of the clinical application this type of bioprosthesis. Pulmonary heart valves were collected from adult porcines. Materials were divided into five groups depending on the storage conditions. Biomechanical tests were performed, both the static tensile test, and examination of viscoelastic properties. Extracellular matrix morphology was evaluated using transmission electron microscopy and immunohistochemistry. Tissue stored at 4 °C exhibited a higher modulus of elasticity than the control (native) and fresh acellular, which indicated the stiffening of the tissue and changes of the viscoelastic properties. Such changes were not observed in the radial direction. Percent strain was not significantly different in the study groups. The storage conditions affected the acellularization efficiency and tissue morphology. To the best of our knowledge, this study is the first that attributes the mechanical properties of pulmonary valve tissue to the biomechanical changes in the collagen network due to different storage conditions. Storage conditions of scaffolds for tissue-engineered heart valves may have a significant impact on the haemodynamic and clinical effects of the used bioprostheses.

Human iPSC-derived mesenchymal stem cells encapsulated in PEGDA hydrogels mature into valve interstitial-like cells

Despite recent advances in tissue engineered heart valves (TEHV), a major challenge is identifying a cell source for seeding TEHV scaffolds. Native heart valves are durable because valve interstitial cells (VICs) maintain tissue homeostasis by synthesizing and remodeling the extracellular matrix. This study demonstrates that induced pluripotent stem cells (iPSC)-derived mesenchymal stem cells (iMSCs) can be derived from iPSCs using a feeder-free protocol and then further matured into VICs by encapsulation within 3D hydrogels. The differentiation efficiency was characterized using flow cytometry, immunohistochemistry staining, and trilineage differentiation. Using our feeder-free differentiation protocol, iMSCs were differentiated from iPSCs and had CD90+, CD44+, CD71+, αSMA+, and CD45- expression. Furthermore, iMSCs underwent trilineage differentiation when cultured in induction media for 21 days. iMSCs were then encapsulated in poly(ethylene glycol)diacrylate (PEGDA) hydrogels grafted with adhesion peptide (RGDS) to promote remodeling and further maturation into VIC-like cells. VIC phenotype was assessed by the expression of alpha-smooth muscle actin (αSMA), vimentin, and collagen production after 28 days. When MSC-derived cells were encapsulated in PEGDA hydrogels that mimic the leaflet modulus, a decrease in αSMA expression and increase in vimentin was observed. In addition, iMSCs synthesized collagen type I after 28 days in 3D hydrogel culture. Thus, the results from this study suggest that iMSCs may be a promising cell source for TEHV.

STATEMENT OF SIGNIFICANCE

Developing a suitable cell source is a critical component for the success and durability of tissue engineered heart valves. The significance of this study is the generation of iPSCs-derived mesenchymal stem cells (iMSCs) that have the capacity to mature into valve interstitial-like cells when introduced into a 3D cell culture designed to mimic the layers of the valve leaflet. iMSCs were generated using a feeder-free protocol, which is one major advantage over other methods, as it is more clinically relevant. In addition to generating a potential new cell source for heart valve tissue engineering, this study also highlights the importance of a 3D culture environment to influence cell phenotype and function.

A sterilization method for decellularized xenogeneic cardiovascular scaffolds

Decellularized xenogeneic scaffolds have shown promise to be employed as compatible and functional cardiovascular biomaterials. However, one of the main barriers to their clinical exploitation is the lack of appropriate sterilization procedures. This study investigated the efficiency of a two-step sterilization method, antibiotics/antimycotic (AA) cocktail and peracetic acid (PAA), on porcine and bovine decellularized pericardium. In order to assess the efficiency of the method, a sterilization assessment protocol was specifically designed, comprising: i) controlled contamination with a known amount of bacteria; ii) sterility test; iii) identification of contaminants through MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight) mass spectrometry and iv) quantification by the Most Probable Number (MPN) method. This sterilization assessment protocol proved to be a successful tool to monitor and optimize the proposed sterilization method. The treatment with AA + PAA method provided sterile scaffolds while preserving the structural integrity and biocompatibility of the decellularized porcine and bovine tissues. However, surface properties and cellular adhesion resulted slightly impaired on porcine pericardium. This work developed a sterilization method suitable for decellularized pericardial scaffolds that could be adopted for in vivo tissue engineering. Together with the proposed sterilization assessment protocol, this decontamination method will foster the clinical translation of decellularized xenogeneic substitutes.

STATEMENT OF SIGNIFICANCE

Clinical application of functional and compatible xenogeneic decellularized scaffolds has been delayed due to the lack of appropriate sterilization methodologies. In this study, it was investigated an effective sterilization method optimized for porcine and bovine decellularized pericardia, based on the use of antibiotics/antimycotics followed by peracetic acid treatment. This treatment effectively sterilizes both species scaffolds, proves to maintain tissue overall structure and components, preserves biocompatibility and biomechanical properties. Furthermore, it was also developed a sterilization assessment protocol used to monitor and validate the previous method, consisting in three main parts: i) controlled contamination; ii) sterility test, and iii) identification and quantification of contaminants. Both methodologies were optimized for the tissues in study but can be applied to other scaffolds and accelerate their clinical translation.

Heart valve tissue engineering: an overview of heart valve decellularization processes

Despite recent advances in medicine and surgery, many people still suffer from cardiovascular diseases, which affect their life span and morbidity. Regenerative medicine and tissue engineering are novel approaches based on restoring or replacing injured tissues and organs with scaffolds, cells and growth factors. Scaffolds are acquired from two major sources, synthetic materials and naturally derived scaffolds. Biological scaffolds derived from native tissues and cell-derived matrix offer many advantages. They are more biocompatible with a higher affinity to cells, which facilitate tissue reconstruction. Interestingly, xenogeneic recipients generally tolerate their components. Therefore, heart valve tissue engineering is increasingly benefiting from naturally derived scaffolds. In this review, we investigated the different protocols and methods that have been used for heart valve decellularization.

Improving the biological function of decellularized heart valves through integration of protein tethering and three-dimensional cell seeding in a bioreactor

Decellularized xenogeneic heart valves (DHVs) are promising products for valve replacement. However, the widespread clinical application of such products is limited due to the risk of immune reaction, progressive degeneration, inflammation, and calcification. Here, we have developed an optimized decellularization protocol for a xenogeneic heart valve. We improved the biological function of DHVs by protein tethering onto DHV and three-dimensional (3D) cell seeding in a bioreactor. Our results showed that heart valves treated with a Triton X-100 and sodium deoxycholate-based protocol were completely cell-free, with preserved biochemical and biomechanical properties. The immobilization of stromal derived factor-1α (SDF-1α) and basic fibroblast growth factor on DHV significantly improved recellularization with endothelial progenitor cells under the 3D culture condition in the bioreactor compared to static culture conditions. Cell phenotype analysis showed higher fibroblast-like cells and less myofibroblast-like cells in both protein-tethered DHVs. However, SDF-DHV significantly enhanced recellularization both in vitro and in vivo compared to basic fibroblast growth factor DHV and demonstrated less inflammatory cell infiltration. SDF-DHV had less calcification and platelet adhesion. Altogether, integration of SDF-1α immobilization and 3D cell seeding in a bioreactor might provide a novel, promising approach for production of functional heart valves.

Developing a Clinically Relevant Tissue Engineered Heart Valve-A Review of Current Approaches

Tissue engineered heart valves (TEHVs) have the potential to address the shortcomings of current implants through the combination of cells and bioactive biomaterials that promote growth and proper mechanical function in physiological conditions. The ideal TEHV should be anti-thrombogenic, biocompatible, durable, and resistant to calcification, and should exhibit a physiological hemodynamic profile. In addition, TEHVs may possess the capability to integrate and grow with somatic growth, eliminating the need for multiple surgeries children must undergo. Thus, this review assesses clinically available heart valve prostheses, outlines the design criteria for developing a heart valve, and evaluates three types of biomaterials (decellularized, natural, and synthetic) for tissue engineering heart valves. While significant progress has been made in biomaterials and fabrication techniques, a viable tissue engineered heart valve has yet to be translated into a clinical product. Thus, current strategies and future perspectives are also discussed to facilitate the development of new approaches and considerations for heart valve tissue engineering.

Novel Approach Toward the Generation of Tissue Engineered Heart Valve by Using Combination of Antioxidant and Detergent: A Potential Therapy in Cardiovascular Tissue Engineering

To develop decellularized heart valve scaffold from porcine for heart valve regeneration. Porcine heart valves were decellularized with unique optimized approach by using 1% sodium dodecyl sulfate solution and 5% dimethyl sulfoxide for the first time. Effect of decellularization process on scaffold were characterized by hematoxylin-eosin, 4',6-diamidino-2-phenylindole, Masson's trichrome, alcian blue staining and scanning electron microscopy for extracellular matrix (ECM) analysis in scaffold. The results showed that developed protocol for decellularization of heart valve scaffold shown complete removal of all cellular components, without changing the properties of ECM. The developed protocol was successfully used for heart valve ECM scaffolds development from porcine. The developed protocol seems to be promising solution for the heart valve tissue engineering application.

Congenital aortic valve repair using CorMatrix® : A histologic evaluation

BACKGROUND

The reconstruction of heart valves provides substantial benefits, particularly in the pediatric population. We present our experience using decellularized extracellular matrix (dECM, CorMatrix^® ) for aortic valve procedures.

METHODS

We retrospectively reviewed the case histories of 6 patients (aged from 2 months - 14 years) who underwent surgery for severe aortic valve stenosis (n = 4) or regurgitation (n = 2). Aortic valve repair was performed on all patients using dECM as a leaflet replacement or leaflet extension. Follow-ups were performed using echocardiography. Reoperation was necessary in 4 cases, and the dECM was explanted and examined histologically and immunohistochemically.

RESULTS

The early post-operative period was uneventful, and the scaffold fulfilled the mechanical requirements. Significant valve insufficiency developed in 5 patients during the post-operative period (119-441 days postoperatively). In all specimens, only a migration of inflammatory cells was identified, which induced structural and functional changes caused by the chronic inflammatory response.

CONCLUSIONS

Our results suggest a mixed immunological response of remodeling and inflammation following the implantation. The expected process of seeding/migration and remodeling of the bioscaffold into the typical 3-layered architecture were not observed in our explanted specimens.

3D bioprint me: a socioethical view of bioprinting human organs and tissues

In this article, we review the extant social science and ethical literature on three-dimensional (3D) bioprinting. 3D bioprinting has the potential to be a 'game-changer', printing human organs on demand, no longer necessitating the need for living or deceased human donation or animal transplantation. Although the technology is not yet at the level required to bioprint an entire organ, 3D bioprinting may have a variety of other mid-term and short-term benefits that also have positive ethical consequences, for example, creating alternatives to animal testing, filling a therapeutic need for minors and avoiding species boundary crossing. Despite a lack of current socioethical engagement with the consequences of the technology, we outline what we see as some preliminary practical, ethical and regulatory issues that need tackling. These relate to managing public expectations and the continuing reliance on technoscientific solutions to diseases that affect high-income countries. Avoiding prescribing a course of action for the way forward in terms of research agendas, we do briefly outline one possible ethical framework 'Responsible Research Innovation' as an oversight model should 3D bioprinting promises are ever realised. 3D bioprinting has a lot to offer in the course of time should it move beyond a conceptual therapy, but is an area that requires ethical oversight and regulation and debate, in the here and now. The purpose of this article is to begin that discussion.

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.

JetValve: Rapid manufacturing of biohybrid scaffolds for biomimetic heart valve replacement

Tissue engineered scaffolds have emerged as a promising solution for heart valve replacement because of their potential for regeneration. However, traditional heart valve tissue engineering has relied on resource-intensive, cell-based manufacturing, which increases cost and hinders clinical translation. To overcome these limitations, in situ tissue engineering approaches aim to develop scaffold materials and manufacturing processes that elicit endogenous tissue remodeling and repair. Yet despite recent advances in synthetic materials manufacturing, there remains a lack of cell-free, automated approaches for rapidly producing biomimetic heart valve scaffolds. Here, we designed a jet spinning process for the rapid and automated fabrication of fibrous heart valve scaffolds. The composition, multiscale architecture, and mechanical properties of the scaffolds were tailored to mimic that of the native leaflet fibrosa and assembled into three dimensional, semilunar valve structures. We demonstrated controlled modulation of these scaffold parameters and show initial biocompatibility and functionality in vitro. Valves were minimally-invasively deployed via transapical access to the pulmonary valve position in an ovine model and shown to be functional for 15 h.