Living Heart Valve Research Articles

Storage, preservation, and rehabilitation of living heart valves to treat congenital heart disease

Heart valve disease patients undergo multiple surgeries to replace structurally degraded valve prostheses, highlighting the need for valve replacements with growth and self-repair capacity. Given allogeneic valve transplantation's promise in meeting these goals by delivering a living valve replacement, we propose a framework for preserving and rehabilitating living valves exvivo.

Electrospun Scaffolds are Not Necessarily Always Made of Nanofibers as Demonstrated by Polymeric Heart Valves for Tissue Engineering.

In the last 30 years, there are ≈60000 publications about electrospun nanofibers, but it is still unclear whether nanoscale fibers are really necessary for electrospun tissue engineering scaffolds. The present report puts forward this argument and reveals that compared with electrospun nanofibers, microfibers with diameter of ≈3 µm (named as "oligo-micro fiber") are more appropriate for tissue engineering scaffolds owing to their better cell infiltration ability caused by larger pores with available nuclear deformation. To further increase pore sizes, electrospun poly(ε-caprolactone) (PCL) scaffolds are fabricated using latticed collectors with meshes. Fiber orientation leads to sufficient mechanical strength albeit increases porosity. The latticed scaffolds exhibit good biocompatibility and improve cell infiltration. Under aortic conditions in vitro, the performances of latticed scaffolds are satisfactory in terms of the acute systolic hemodynamic functionality, except for the higher regurgitation fraction caused by the enlarged pores. This hierarchical electrospun scaffold with sparse fibers in macropores and oligo-micro fibers in filaments provides new insights into the design of tissue engineering scaffolds, and tissue engineering may provide living heart valves with regenerative capabilities for patients with severe valve disease in the future.

Valvulogenesis of a living, innervated pulmonary root induced by an acellular scaffold

Heart valve disease is a major cause of mortality and morbidity worldwide with no effective medical therapy and no ideal valve substitute emulating the extremely sophisticated functions of a living heart valve. These functions influence survival and quality of life. This has stimulated extensive attempts at tissue engineering “living” heart valves. These attempts utilised combinations of allogeneic/ autologous cells and biological scaffolds with practical, regulatory, and ethical issues. In situ regeneration depends on scaffolds that attract, house and instruct cells and promote connective tissue formation. We describe a surgical, tissue-engineered, anatomically precise, novel off-the-shelf, acellular, synthetic scaffold inducing a rapid process of morphogenesis involving relevant cell types, extracellular matrix, regulatory elements including nerves and humoral components. This process relies on specific material characteristics, design and “morphodynamism”.

How Smart are Smart Materials? A Conceptual and Ethical Analysis of Smart Lifelike Materials for the Design of Regenerative Valve Implants.

It may soon become possible not just to replace, but to re-grow healthy tissues after injury or disease, because of innovations in the field of Regenerative Medicine. One particularly promising innovation is a regenerative valve implant to treat people with heart valve disease. These implants are fabricated from so-called 'smart', 'lifelike' materials. Implanted inside a heart, these implants stimulate re-growth of a healthy, living heart valve. While the technological development advances, the ethical implications of this new technology are still unclear and a clear conceptual understanding of the notions 'smart' and 'lifelike' is currently lacking. In this paper, we explore the conceptual and ethical implications of the development of smart lifelike materials for the design of regenerative implants, by analysing heart valve implants as a showcase. In our conceptual analysis, we show that the materials are considered 'smart' because they can communicate with human tissues, and 'lifelike' because they are structurally similar to these tissues. This shows that regenerative valve implants become intimately integrated in the living tissues of the human body. As such, they manifest the ontological entanglement of body and technology. In our ethical analysis, we argue this is ethically significant in at least two ways: It exacerbates the irreversibility of the implantation procedure, and it might affect the embodied experience of the implant recipient. With our conceptual and ethical analysis, we aim to contribute to responsible development of smart lifelike materials and regenerative implants.

How Smart are Smart Materials? A Conceptual and Ethical Analysis

"Today, a person can receive a hip implant to replace a deformed, swollen hip joint or a pacemaker to sustain the beating rhythm of their heart. Thanks to Regenerative Medicine, soon, it may become possible not just to replace, but to re-grow healthy tissues after injury or disease. To this end, tissue engineers are designing ‘smart’, ‘life-like’ biomaterial implants to activate the inherent regenerative capacity of the human body. Such a smart life-like biomaterial may for example stimulate re-growth of a fresh, living heart valve after implantation in a patient’s heart. However, the meaning of the smartness and lifelikeness of these synthetic biomaterials is conceptually unclear. Therefore, in this paper, we first aim to unravel the meaning of the terms ‘smart’ and ‘life-like’, and next, analyse what ethical and societal implications are associated with this new generation of biomaterial implants as a result. Our conceptual analysis reveals that the biomaterials are considered ‘smart’ because they can communicate with human tissues and ‘life-like’ because they are structurally similar to these tissues. Moreover, the biomaterial artifacts are designed to integrate to a high degree with the living tissue of the human body. While these characteristics provide the biomaterials with their therapeutic potential, we argue that it complicates a) the irreversibility of the implantation process, b) questions of ownership regarding the biomaterial implant, and c) the sense of embodiment of the receiver of the implant. Overall, timely anticipation and consideration of these ethical challenges will promote responsible development of biomaterials in Regenerative Medicine. "

Recent investigation on biomaterial based tissue engineered heart valve (TEHV)

In recent years the concept of tissue-engineered heart valves provides advanced treatment for creating a living heart valve replacing the failed one. Valvular Heart Disease (VHD) is the most common disease in failing one or more valves in the heart, for those people from various countries are being affected in a huge number. This may be due to valvular stenosis (abnormal narrowing in valves of the heart), valvular prolapse and regurgitation (backflow of blood or due to leakage). This study was designed to overcome the failure faced by the present bioprosthetic heart valves as well as tissue-engineered heart valves by bringing in an optimized advanced material using the present biopolymers. The main reason for the usage of biopolymers in this study is due to its good physiochemical and mechanical properties as compared to other existing materials which is been used in the manufacturing of heart valves. A crucial factor of this methodology is to solve problems like calcification at the surface of the material, thrombosis, degeneration, and others. Bio polymeric materials generally possess good resistance towards oxidation and hydrolysis with good stability. As there are many existing materials available to manufacture heart valves, in this review the materials that are investigated are Polyurethane (PU), Polydimethyl Siloxane (PDMS) - Polyhexamethylene Oxide (PHMO) PU, and POSS-PCU Nanocomposite (Polyhedral Oligomeric Silsesquioxane - Polycarbonate Urethane). These biopolymer materials exhibit long term stability, resulting in good mechanical properties and enhanced resistance towards hydrolysis, oxidation. These materials also result in reduced calcification and thrombosis.

What Is the Potential of Tissue-Engineered Pulmonary Valves in Children?

As a living heart valve substitute with growth potential and improved durability, tissue-engineered heart valves (TEHVs) may prevent reinterventions that are currently often needed in children withcongenital heart disease. We performed early healthtechnology assessment to assess the potential cost-effectiveness of TEHVs in children requiring right ventricular outflow tract reconstruction (RVOTR). A systematic review and meta-analysis was conducted of studies reporting clinical outcome after RVOTR with existing heart valve substitutes in children (mean age ≤12 years or maximum age ≤21 years) published between January 1, 2000, and May 2, 2018. Using a patient-level simulation model, costs and effects of RVOTR with TEHVs compared with existing heart valve substitutes were assessed from a health care perspective applying a 10-year time horizon. Improvements in performance of TEHVs, divided in durability, thrombogenicity, and infection resistance, were explored to estimate quality-adjusted life year (QALY) gain, cost reduction, headroom, and budget impact associated with TEHVs. Five-year freedom from reintervention after RVOTR with existing heart valve substitutes was 46.1% in patients less than or equal to 2 years of age and 81.1% in patients greater than 2 years of age. Improvements in durability had the highest impact on QALYs and costs. In the improved TEHV performance scenario (durability ≥5 years and -50% other valve-related events), QALY gain was 0.074 and cost reduction was €10,378 per patient, translating to maximum additional costs of €11,856 per TEHV compared with existing heart valve substitutes. This study showed that there is room for improvement in clinical outcomes in children requiring RVOTR. If TEHVs result in improved clinical outcomes, they are expected to be cost-effective compared with existing heart valve substitutes.

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.

In situ heart valve tissue engineering using a bioresorbable elastomeric implant – From material design to 12 months follow-up in sheep

The creation of a living heart valve is a much-wanted alternative for current valve prostheses that suffer from limited durability and thromboembolic complications. Current strategies to create such valves, however, require the use of cells for invitro culture, or decellularized human- or animal-derived donor tissue for in situ engineering. Here, we propose and demonstrate proof-of-concept of in situ heart valve tissue engineering using a synthetic approach, in which a cell-free, slow degrading elastomeric valvular implant is populated by endogenous cells to form new valvular tissue inside the heart. We designed a fibrous valvular scaffold, fabricated from a novel supramolecular elastomer, that enables endogenous cells to enter and produce matrix. Orthotopic implantations as pulmonary valve in sheep demonstrated sustained functionality up to 12 months, while the implant was gradually replaced by a layered collagen and elastic matrix in pace with cell-driven polymer resorption. Our results offer new perspectives for endogenous heart valve replacement starting from a readily-available synthetic graft that is compatible with surgical and transcatheter implantation procedures.

Living nano-micro fibrous woven fabric/hydrogel composite scaffolds for heart valve engineering.

Heart valve-related disease is an important clinical problem, with over 300,000 surgical repairs performed annually. Tissue engineering offers a promising strategy for heart valve repair and regeneration. In this study, we developed and tissue engineered living nano-micro fibrous woven fabric/hydrogel composite scaffolds by using textile technique combined with bioactive hydrogel formation. The novelty of our technique is that the composite scaffolds can mimic physical structure anisotropy and the mechanical strength of natural aortic valve leaflet. Moreover, the composite scaffolds prevented the matrix shrinkage, which is major problem that causes the failure of TEHV, and better maintained physiological fibroblastic phenotype in both normal and diseased HAVIC. This work marks the first report of a combination composite scaffold using 3D hydrogel enhanced by nano-micro fibrous woven fabric, and represents a promising tissue engineering strategy to treat heart valve injury.

2015 4thTERMIS World CongressBoston, MassachusettsSeptember 8–11, 2015

2015 4^thTERMIS World CongressBoston, MassachusettsSeptember 8–11, 2015

Development Of A Conceptual Model For Early Health Technology Assessment Of Tissue-Engineered Heart Valves

Objectives: In-situ tissue-engineering provides a promising method to create living heart valves with the potential to grow, repair and last a lifetime. The objective of the present study is to develop a conceptual model (CM) that can be used to investigate the requirements for tissue-engineered heart valves (TEHV) to become cost-effective compared to current surgical and transcatheter heart valve substitutes (HVS). Methods: The development of the CM was based on recommendations from the ISPOR-SMDM Modeling Good Research Practices Task Force-2. After scoping the decision problem, a draft CM was developed based on clinical guidelines and discussion within a small workgroup. This model was compared with existing models for cost-effectiveness of HVS, found by systematic literature search. It was further discussed with a Delphi panel of cardio-thoracic surgeons, cardiologists and a biomedical scientist (n= 10). Delphi panelists were first interviewed individually to discuss the CM structure. Thereafter, they completed online surveys in order to reach consensus between panelists. Results: Health states included in the CM are ‘alive without complications’, cerebrovascular accident, myocardial infarction, vascular complication, bleeding, acute kidney injury, atrial fibrillation, pacemaker implantation, prosthetic valve dysfunction, prosthetic valve thrombosis, prosthetic valve endocarditis, ‘alive after complications’ and dead. Predictors of transition probabilities between the health states are included; age, gender, NYHA functional class, left ventricular function, renal impairment, and diabetes. Relevant outcome measures included health-related quality of life, event occurrence, event-free survival, mortality and costs. Conclusions: The CM provides the foundation of a microsimulation model that will be used to estimate the cost-effectiveness of TEHV compared with current HVS. The results will be used to inform stakeholders about the requirements for TEHV to become cost-effective. This information can help bio-tech companies to decide about further development of TEHV, focus on the most promising target groups, set realistic performance-price goals, and design and manage a reimbursement strategy.

Tissue-engineered heart valve with a tubular leaflet design for minimally invasive transcatheter implantation.

Transcatheter aortic valve implantation of (nonviable) bioprosthetic valves has been proven a valid alternative to conventional surgical implantation in patients at high or prohibitive mortality risk. In this study we present the in vitro proof-of-principle of a newly developed tissue-engineered heart valve for minimally invasive implantation, with the ultimate aim of adding the unique advantages of a living tissue with regeneration capabilities to the continuously developing transcatheter technologies. The tube-in-stent is a fibrin-based tissue-engineered valve with a tubular leaflet design. It consists of a tubular construct sewn into a self-expandable nitinol stent at three commissural attachment points and along a circumferential line so that it forms three coaptating leaflets by collapsing under diastolic back pressure. The tubular constructs were molded with fibrin and human umbilical vein cells. After 3 weeks of conditioning in a bioreactor, the valves were fully functional with unobstructed opening (systolic phase) and complete closure (diastolic phase). Tissue analysis showed a homogeneous cell distribution throughout the valve's thickness and deposition of collagen types I and III oriented along the longitudinal direction. Immunohistochemical staining against CD31 and scanning electron microscopy revealed a confluent endothelial cell layer on the surface of the valves. After harvesting, the valves underwent crimping for 20 min to simulate the catheter-based delivery. This procedure did not affect the valvular functionality in terms of orifice area during systole and complete closure during diastole. No influence on the extracellular matrix organization, as assessed by immunohistochemistry, nor on the mechanical properties was observed. These results show the potential of combining tissue engineering and minimally invasive implantation technology to obtain a living heart valve with a simple and robust tubular design for transcatheter delivery. The effect of the in vivo remodeling on the functionality of the tube-in-stent valve remains to be tested.

Effect of biodegradation and de novo matrix synthesis on the mechanical properties of valvular interstitial cell-seeded polyglycerol sebacate–polycaprolactone scaffolds

The development of living heart valves that grow with the patient is a promising strategy for heart valve replacements in pediatric patients. Despite active research in the field of tissue engineered heart valves there have been limited efforts to optimize the balance between biodegradation of the scaffolds and de novo extracellular matrix (ECM) synthesis by cells and study their consequences on the mechanical properties of the cell-seeded construct. This study investigates the effect of in vitro degradation and ECM secretion on the mechanical properties of hybrid polyester scaffolds. The scaffolds were synthesized from blends of fast degrading polyglycerol sebacate (PGS) and slowly degrading polycaprolactone (PCL). PGS–PCL scaffolds were electrospun using a 2:1 ratio of PGS to PCL. Accelerated hydrolytic degradation in 0.1mM sodium hydroxide revealed 2-fold faster degradation of PGS–PCL scaffolds compared with PCL scaffolds. Thermal analysis and scanning electron microscopy demonstrated marginal change in PCL scaffold properties, while PGS–PCL scaffolds showed preferential mass loss of PGS and thinning of the individual fibers during degradation. Consequently, the mechanical properties of PGS–PCL scaffolds decreased gradually with no significant change for PCL scaffolds during accelerated degradation. Valvular interstitial cells (VICs) seeded on PGS–PCL scaffolds showed higher ECM protein secretion compared with PCL. Thus the mechanical properties of the cell-seeded PCL scaffolds did not change significantly compared with acellular scaffolds, probably due to slower degradation and ECM deposition by VICs. In contrast, the PGS–PCL scaffolds exhibited a gradual decrease in the mechanical properties of the acellular scaffolds due to degradation, which was compensated for by new matrix secreted by VICs seeded on the scaffolds. Our study demonstrated that the faster degrading PGS component of PGS–PCL accelerated the degradation rate of the scaffolds. VICs, on the other hand, were able to remodel the synthetic scaffold, depositing new matrix proteins and maintaining the mechanical properties of the scaffolds.

Stem Cell–Based Transcatheter Aortic Valve Implantation: First Experiences in a Pre-Clinical Model

This study sought to investigate the combination of transcatheter aortic valve implantation and a novel concept of stem cell-based, tissue-engineered heart valves (TEHV) comprising minimally invasive techniques for both cell harvest and valve delivery. TAVI represents an emerging technology for the treatment of aortic valve disease. The used bioprostheses are inherently prone to calcific degeneration and recent evidence suggests even accelerated degeneration resulting from structural damage due to the crimping procedures. An autologous, living heart valve prosthesis with regeneration and repair capacities would overcome such limitations. Within a 1-step intervention, trileaflet TEHV, generated from biodegradable synthetic scaffolds, were integrated into self-expanding nitinol stents, seeded with autologous bone marrow mononuclear cells, crimped and transapically delivered into adult sheep (n = 12). Planned follow-up was 4 h (Group A, n = 4), 48 h (Group B, n = 5) or 1 and 2 weeks (Group C, n = 3). TEHV functionality was assessed by fluoroscopy, echocardiography, and computed tomography. Post-mortem analysis was performed using histology, extracellular matrix analysis, and electron microscopy. Transapical implantation of TEHV was successful in all animals (n = 12). Follow-up was complete in all animals of Group A, three-fifths of Group B, and two-thirds of Group C (1 week, n = 1; 2 weeks, n = 1). Fluoroscopy and echocardiography displayed TEHV functionality demonstrating adequate leaflet mobility and coaptation. TEHV showed intact leaflet structures with well-defined cusps without signs of thrombus formation or structural damage. Histology and extracellular matrix displayed a high cellularity indicative for an early cellular remodeling and in-growth after 2 weeks. We demonstrate the principal feasibility of a transcatheter, stem cell-based TEHV implantation into the aortic valve position within a 1-step intervention. Its long-term functionality proven, a stem cell-based TEHV approach may represent a next-generation heart valve concept.

Wharton's jelly derived mesenchymal stem cells: regenerative medicine beyond umbilical cord blood

Wharton's jelly derived mesenchymal stem cells: regenerative medicine beyond umbilical cord blood

Transapical Aortic Implantation of Autologous Marrow Stromal Cell-Based Tissue-Engineered Heart Valves: First Experiences in the Systemic Circulation

Within 1 procedure, tissue-engineered, living heart valves (TEHVs), fabricated from biodegradable scaffolds seeded with autologous bone marrow–derived mononuclear cells ([Fig. 1][1]A), were integrated into self-expanding nitinol stents (20 mm × 30 mm) and transapically delivered into the

A completely autologous valved conduit prepared in the open form of trileaflets (type VI biovalve): Mold design and valve function in vitro

In-body tissue, architecture technology represents a promising approach for the development of living heart valve replacements and preparation of a series of biovalves. To reduce the degree of regurgitation and increase the orifice ratio, we designed a novel mold for a type VI biovalve. The mold had an outer diameter of 14 mm for implantation in beagles, and it was prepared by assembling two silicone rods with a small aperture (1 mm) between them. One rod had three protrusions of the sinus of Valsalva, whereas the other was almost cylindrical. When the molds were embedded in the subcutaneous pouches of beagles for 1 month, the native connective tissues that subsequently developed covered the entire outer surface of the molds and migrated into the aperture between the rods. The mold from both sides of the harvested cylindrical implant was removed, and homogenous well-balanced trileaflets were found to be separately formed in the open form with a small aperture at the three commissure parts inside the developed conduit, which had a thick homogenous wall even in the sinus of Valsalva. Exposure of the obtained biovalves to physiological aortic valve flow in beagles revealed proper opening motion with a wide orifice area. The closure dynamics were suboptimal, probably due to the reduction in the size of the sinus of Valsalva. The mechanical behavior of this biovalve might allow its use as a living aortic valve replacement.

Injectable living marrow stromal cell-based autologous tissue engineered heart valves: first experiences with a one-step intervention in primates

A living heart valve with regeneration capacity based on autologous cells and minimally invasive implantation technology would represent a substantial improvement upon contemporary heart valve prostheses. This study investigates the feasibility of injectable, marrow stromal cell-based, autologous, living tissue engineered heart valves (TEHV) generated and implanted in a one-step intervention in non-human primates. Trileaflet heart valves were fabricated from non-woven biodegradable synthetic composite scaffolds and integrated into self-expanding nitinol stents. During the same intervention autologous bone marrow-derived mononuclear cells were harvested, seeded onto the scaffold matrix, and implanted transapically as pulmonary valve replacements into non-human primates (n = 6). The transapical implantations were successful in all animals and the overall procedure time from cell harvest to TEHV implantation was 118 ± 17 min. In vivo functionality assessed by echocardiography revealed preserved valvular structures and adequate functionality up to 4 weeks post implantation. Substantial cellular remodelling and in-growth into the scaffold materials resulted in layered, endothelialized tissues as visualized by histology and immunohistochemistry. Biomechanical analysis showed non-linear stress-strain curves of the leaflets, indicating replacement of the initial biodegradable matrix by living tissue. Here, we provide a novel concept demonstrating that heart valve tissue engineering based on a minimally invasive technique for both cell harvest and valve delivery as a one-step intervention is feasible in non-human primates. This innovative approach may overcome the limitations of contemporary surgical and interventional bioprosthetic heart valve prostheses.

Lectin and antibody-based histochemical techniques for cardiovascular tissue engineering

Tissue engineering holds immense potential for treatment of cardiovascular diseases by creating living structures to replace diseased blood vessels, heart valves, and cardiac muscle. In a traditional approach, scaffolds are seeded with stem cells and subjected to stimuli in bioreactors that mimic physiologic conditions or are directly implanted into target sites in animal models. The expected results are significant cell changes, extensive remodeling of the scaffolds and creation of surrogate structures that would be deemed acceptable for tissue regeneration. Histochemical techniques are increasingly becoming essential tools in tissue engineering research. In our studies, we used lectin and antibody-based techniques to characterize novel collagen and elastin scaffolds and to ensure efficient removal of xenoantigens. Scaffolds were implanted in animals and infiltrated host cells were identified using antibodies to activated fibroblasts, macrophages, and lymphocytes. Stem cell-seeded scaffolds were subjected to mechanical strains and tested for differentiation into cardiovascular cells using antibody-based double immunofluorescence methods. Finally, living heart valves were constructed from scaffolds and stem cells, subjected to conditioning in a bioreactor and stem cell differentiation evaluated by immunofluorescence. Overall, these techniques have proven to be outstanding companions to biochemical, molecular biology and cell analysis methods used in tissue engineering research and development.