Fabrication and in-vitro characterization of a polymeric aortic valve for minimally invasive valve replacement

Recent advancements in polymeric heart valves: From basic research to clinical trials

Valvular heart diseases (VHDs) have become one of the most prevalent heart diseases worldwide, and prosthetic valve replacement is one of the effective treatments. With the fast development of minimal invasive technology, transcatheter valves replacement has been exploring in recent years, such as transcatheter aortic valve replacement (TAVR) technology. In addition, basic research on prosthetic valves has begun to shift from traditional mechanical valves and biological valves to the development of polymeric heart valves. The polymeric heart valves (PHVs) have shown a bright future due to their advantages of longer durability, better biocompatibility and reduced cost. This review gives a brief history of the development of polymeric heart valves, provides a summary of the types of polymer materials suitable for heart leaflets and the emerging processing/preparation methods for polymeric heart valves in the basic research. Besides, we facilitate a deeper understanding of polymeric heart valve products that are currently in preclinical/clinical studies, also summary the limitations of the present researches as well as the future development trends. Hence, this review will provide a holistic understanding for researchers working in the field of prosthetic valves, and will offer ideas for the design and research of valves with better durability and biocompatibility.

3D printing of heart valves

3D printing technologies have the potential to revolutionize the manufacture of heart valves through the ability to create bespoke, complex constructs. In light of recent technological advances, we review the progress made towards 3D printing of heart valves, focusing on studies that have utilised these technologies beyond manufacturing patient-specific moulds. We first overview the key requirements of a heart valve to assess functionality. We then present the 3D printing technologies used to engineer heart valves. By referencing International Organisation for Standardisation (ISO) Standard 5840 (Cardiovascular implants - Cardiac valve prostheses), we provide insight into the achieved functionality of these valves. Overall, 3D printing promises to have a significant positive impact on the creation of artificial heart valves and potentially unlock full complex functionality.

Design, manufacturing and testing of a green non-isocyanate polyurethane prosthetic heart valve

The sole effective treatment for most patients with heart valve disease is valve replacement by implantation of mechanical or biological prostheses. However, mechanical valves represent high risk of thromboembolism, and biological prostheses are prone to early degeneration. In this work, we aim to determine the potential of novel environmentally-friendly non-isocyanate polyurethanes (NIPUs) for manufacturing synthetic prosthetic heart valves. Polyhydroxyurethane (PHU) NIPUs are synthesized via an isocyanate-free route, tested in vitro, and used to produce aortic valves. PHU elastomers reinforced with a polyester mesh show mechanical properties similar to native valve leaflets. These NIPUs do not cause hemolysis. Interestingly, both platelet adhesion and contact activation-induced coagulation are strongly reduced on NIPU surfaces, indicating low thrombogenicity. Fibroblasts and endothelial cells maintain normal growth and shape after indirect contact with NIPUs. Fluid-structure interaction (FSI) allows modeling of the ideal valve design, with minimal shear stress on the leaflets. Injection-molded valves are tested in a pulse duplicator and show ISO-compliant hydrodynamic performance, comparable to clinically-used bioprostheses. Poly(tetrahydrofuran) (PTHF)-NIPU patches do not show any evidence of calcification over a period of 8 weeks. NIPUs are promising sustainable biomaterials for the manufacturing of improved prosthetic valves with low thrombogenicity.

Design of an aortic polymeric valve with asymmetric leaflets and evaluation of its performance by finite element method

BACKGROUND

The geometry of leaflets plays a significant role in prosthetic valves' (PVs) performance. Typically, natural aortic valves have three unequal leaflets, which differ in size. The present study aims to design an asymmetric tri-leaflet polymeric valve with one large and two small leaflets based on commissure lengths and leaflet eccentricities.

METHODS

Eccentricity was related to commissure lengths based on the deformation of the free margins for the fully-opened state of leaflets. The polystyrene-block-polyethylene-polypropylene-block-polystyrene polymer characterized the material properties of the leaflets. The Finite Element Method (FEM) was used to evaluate performance parameters, including maximum geometric orifice area (GOA), average GOA, maximum von Mises stress, and leaflet's coaptation surface area (CSA).

RESULTS

Asymmetric valves with no eccentricity provided a low level of GOA because the asymmetric form of small leaflets caused them to close faster than the large leaflet, leading to a sudden drop in the GOA during systole. As the radial curve tends towards a straight line, an undesirable coaptation occurs, and peak stress increases despite higher GOAs. A new radial curve consisting of two straight lines connected by an arc that provided 25.64 mm² coaptation surface area (CAS) and 117.54 mm² average GOA, was proposed to improve coaptation and GOA.

CONCLUSION

The radial curve of leaflets affects the valve's performance more than other geometric parameters. The combination of straight lines and arcs for radial curves was selected as the reference model for asymmetric valves with one large and two small leaflets.

Transcatheter Heart Valves: A Biomaterials Perspective

Heart valve disease is prevalent throughout the world, and the number of heart valve replacements is expected to increase rapidly in the coming years. Transcatheter heart valve replacement (THVR) provides a safe and minimally invasive means for heart valve replacement in high-risk patients. The latest clinical data demonstrates that THVR is a practical solution for low-risk patients. Despite these promising results, there is no long-term (>20 years) durability data on transcatheter heart valves (THVs), raising concerns about material degeneration and long-term performance. This review presents a detailed account of the materials development for THVRs. It provides a brief overview of THVR, the native valve properties, the criteria for an ideal THV, and how these devices are tested. A comprehensive review of materials and their applications in THVR, including how these materials are fabricated, prepared, and assembled into THVs is presented, followed by a discussion of current and future THVR biomaterial trends. The field of THVR is proliferating, and this review serves as a guide for understanding the development of THVs from a materials science and engineering perspective.