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Summary of Materials and Manufacturing Perspectives in Engineering Heart Valves conclusion

Valvular heart diseases (VHD) that cause stenosis and regurgitation in heart valves, such as congenital, rheumatic, and degenerative heart illnesses, require constant clinical monitoring.

  • Summary of Materials and Manufacturing Perspectives in Engineering Heart Valves

Valvular heart diseases (VHD) that cause stenosis and regurgitation in heart valves, such as congenital, rheumatic, and degenerative heart illnesses, require constant clinical monitoring. Aortic or pulmonary valve anomalies are responsible for 33% of congenital heart disorders. Although patients with VHD have received transcatheter therapies and minimally invasive operations, the bulk of valve replacement surgeries still use open-heart techniques. The folded design of transcatheter valves necessitates a large reduction in thickness, which would pose a durability difficulty. Only mechanical and bioprosthetic valves have been employed in clinical trials to date, and they have frequently caused discomfort and difficulties due to anticoagulant intake, immune-driven calcification, and deterioration. Novel materials with mechanical and hemodynamic qualities similar to native heart valves are desirable. 

The methods employed with sample size (N) were aortic valve replacement, pulmonary valve replacement, and right posterior leaflet of the pulmonary valve replacement (N). After 12 hours (N=1), and after 4 weeks (N=5), there was a significant outcome. Early cellular infiltration and ingrowth into the substance; development of multilayer endothelialized tissues; sufficient leaflet mobility Up to 8 weeks, the valve worked perfectly (4 weeks beyond the half-life of suture strength). One-day follow-up (N=2), 8-week follow-up (N=2), 16-week follow-up (N=4), and 24-week follow-up (N=4). After week 8, there was mild central regurgitation, which progressed to moderate regurgitation by week 24. 

PTFE is a crystalline polymer (40–70%) having nonlinear mechanical properties such as modulus and yield stress that are temperature and rate-dependent. PTFE has Young's modulus of 1 GPa, the yield stress of 10 MPa, the ultimate stress of 160 MPa, and a strain at break of 150 percent at ambient temperature. Despite their high hemodynamic properties, both PTFE and ePTFE have limited thromboembolism and calcification resistance. As a result, polyesters are commonly employed to make absorbable scaffolds for heart valves that include fibroblasts and endothelial cells. In one experiment, P4HB was used to coat nonwoven poly(glycolic acid) (PGA) mesh to create an absorbable trileaflet heart valve scaffold for myofibroblasts and endothelial cells. Depending on their network topology and chemical structure of polymer backbones, the mechanical properties of hydrogels range from brittle with low fracture energies to extremely tough with fracture energies similar to those of rubbers. The swollen network of hydrogels allows for rapid diffusion of nutrients and oxygen.  

The multi-step molding process may include opening and closing the mold multiple times, resulting in potential problems and manufacturing discrepancies, which are undesirable. Furthermore, while molding can be used to create multi-component structures, each material phase will have isotropic qualities. The natural heart valves, on the other hand, are multi-component and anisotropic in each phase. 

Electrospinning of ester-based polyurethane on precisely constructed collecting electrodes with insulating and conductive patterns, for example, has been used to create various geometries of heart valve leaflets. The control variables for artificial valve leaflets emulating native tricuspid, aortic, mitral, and pulmonary valves were the 3D geometry of electrodes and their insulating/conductive patterns, as well as the deposition time. This method enables prosthetic heart valves to be designed with the desired macroscopic shape and size, mechanical properties, heterogeneity, and microstructure. 
Extrusion printing can handle a far broader range of materials, including thermoplastics, hydrogels, gels, and cell-laden mediums with viscosities ranging from 30 to 102 Pa sec-1. Polyethylene glycol (PEG) and polypropylene glycol (PPG) derivatives, alginate, gelatin derivatives such as gelatin methacrylate (GelMA), agarose, collagen, fibrin, silk, and hyaluronic acid are all common hydrogel-based materials used in ink preparation for extrusion printing (HA). Because of the freedom in ink design for gel extrusion printing, multi-material complexes such as 3D vascularized structures have been created. 
Because of their heterogeneous construction at various scales, heart valves have very anisotropic mechanical properties. Any possible material for the manufacture of new heart valves must, in fact, be able to endure long-term dynamic deformations under biological conditions. As a result, understanding the tensile properties of the artificial heart valve's constituent materials is critical for manufacture. The strain rate dependency was reduced in both circumferential and radial directions by performing a large number of load/unload cycles on native heart valve tissues. Understanding the complicated stress regime that will be imposed on a mechanical heart valve is critical for improved design and engineering. 
Fluid-structure interaction models, in particular, can be highly valuable in the design and evaluation of artificial heart valve mechanical performance. The simulation will then let researchers and engineers evaluate the performance of the prosthetic heart valves prior to in vivo testing. 

The platelet activation of xSIBS valves and native tissue did not differ significantly in an in vitro hemodynamical evaluation of trileaflet valves produced from xSIBS. 

For extremely swollen hydrogels with more than 96 percent water content, maximum strength could approach 800 kPa depending on the ratio of collagen and poly(ethylene glycol) networks. When the highest shear stress experienced in the fluid goes from 20 kPa to 760 kPa, the percentage of viable cells decreases by more than 38%, according to Nair et al. Within the 3D printed tissues, both cell types had greater than 80% vitality and encapsulated VIC expressed enhanced vimentin, whereas SMC expressed elevated alpha-smooth muscle actin (-SMA). 

Conclusion 

Alternative heart valves are urgently needed to address the long-term durability and biocompatibility difficulties associated with prosthetic heart valves. The high mechanical and biological demands of valves, the complicated and anisotropic geometries of valves, and the absence of self-recovery in artificial materials all contribute to the delayed advancement in this domain. It is expected that, in the future, new inks can be designed to make use of additive manufacturing to manufacture individualized heart valves with anisotropic features, in light of recent advances in materials sciences, robust and processable hydrogels. Highly intricate and hybrid constructions approximating the geometry of heart valves can be created using innovative electrospinning technologies. Material engineers will confront a major problem in developing novel, processable, self-healing materials with acceptable mechanical characteristics for highly "dynamic" biological settings. While several self-healing materials have been discovered, none have yet been used to manufacture heart valves. In the case of congenital heart disease, creating a build that allows for size adoption to reduce the number of surgical operations for young patients would be excellent.
 

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