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Current heart valve prostheses represent a 50% reduction in life expectancy for young patients, especially children. The thromboembolic complications, which is the formation of blood clots that travel through the bloodstream that could block the arteries, and induce the formation of calcium deposits on the valve limit the durability of the device ending on an unavoidable replacement of the valve, inducing unnecessary stress on the patient, risking their life. The search for an ideal aortic valve substitute has been going on for more than fifty years. Nevertheless, the selection of a proper prosthesis for the pediatric patient can be challenging and controversial. Hereunder, different present-day biomaterials are described, which are used to reduce the mentioned complications and at the same time increase its durability.
Fig 1. Explant polyurethane valve viewed in situ immediately prior to explant. (a) Inflow surface; (b) outflow surface; (c) radiograph of explant porcine valve (Wheatley et al., 2000).
Polyurethane is an effective biomaterial for this application, due to its mechanical strength and durability. It’s also biocompatible and long-term in vitro durability has been achieved, especially textile polyurethane, which performed favorably in laboratory fatigue tests. The functionality of this biomaterial was compared with the performance of a porcine and a biomechanical valve, which have favorable results in terms of hemodynamic function, in other words, the cardiovascular function that includes the flowing blood and the solid structures (such as arteries) through which it flows. Polyurethane valves are as effective as mechanical valves, while the porcine valve is compromised with time (Wheatley et al., 2000), meaning that polyurethane does increase durability, see Figure 1.
In the same way, a group of specialists from different universities and disciplines, have developed a heart valve using a bioresorbable elastomeric implant. The heart valve consists of a tube made from a polycaprolactone bis-urea biomaterial (PC-BU, Figure 2), and a support ring generated by a computer-aided design software with a crown-like structure, made from a polyether ether ketone solid piece (PEEK). Long-term in vivo testing demonstrates sustained functionality and doesn’t present any sign of calcification or thromboembolic complications. Also, it has a proper elastic network which enhances the durability and functioning of the valve (Kluin et al, 2017).
Fig. 2 Fabrication and in vitro functionality of the polycarbonate bis-urea (PC-BU) valve (Kluin et al, 2017).
Similarly, another group of researchers have found good clinical outcomes of using expanded polytetrafluoroethylene (ePTFE) bi-leaflet valve substitutes for pulmonary valve replacement (PVR) in right ventricular outflow tract reconstruction (RVOT). In the case of pediatric patient, it is necessary to provide a useful reference to overcome the challenges on the aortic site (Zhu et al., 2019), however, for this valve design it is only analyzed the dynamic function which corresponds to the leaflets deformation during a full cardiac cycle and hemodynamic function such as energy loss of the cardiac cycle, pressure, regurgitant fraction of the valve, and flow rate. Therefore, various biocompatibility studies still need to be carried out.
Fig. 3 FEM model of bi-leaflet valves (Zhu et al., 2019).
Through the revision of the mentioned research papers, it was observed that bioresorbable elastomeric implant is the best option for enhancing durability, since it showed the best results by demonstrating a sustained functionality, with no sign of calcification or thromboembolic complications. The designed valves are manufactured by suturing the electrospun PC-BU tube on the PEEK supporting stent. As reported by the promising results, the approach of a bioresorbable polymer for heart valves, could represent a potential alternative for children who suffer from heart disease. If they manage to increase of the durability and reduction of common valve complications it could significantly reduce the need of a future valve replacement, increasing the life expectancy of the patients. It’s important to mention that the approximated budget for the creation of the valves is around $21,091.48 MXN, which makes it feasible. Nonetheless this budget considers the access to a laboratory, but if that is not the case, it may increase because of the necessary equipment (electrospinning apparatus and ethylene oxide sterilization).
As with any new technology, several challenges are yet to be overcome. The use of a PEEK supporting ring is still not optimal and could be replaced by a degrading ring or stent for future applications. Another challenge lies in the application of the current valve in the aortic position, since it was only tested in the pulmonary position. Finally, it would be important to look for the possibility of cell regeneration to increase the durability of the valves. Despite the several efforts that scientists have been doing, there is yet a lot to do to accomplish the desired durability, nonetheless the described technology has potential and represents a great advance into fulfilling that goal.
References
Kluin, J., Talacua, H., Smits, A., Emmert, M., Brugmans, M., Fioretta, E., Dijkman, P., Sontjens, S., Duijvelshoff, R., Dekker, S., Broek, J., Lintas, V., Vink, A., Hoerstrup,S., Janseen,H., Dankers,P., Baaijens,F., & Bouten, C. (2017). In situ heart valve tissue engineering using a bioresorbable elastomeric implant – From material design to 12 months follow-up in sheep, Biomaterials, 125, 101-117. https://doi.org/10.1016/j.biomaterials.2017.02.007
Wheatley, D., Raco, L., Bernacca, G., Sim, I., Belcher, P., & Boyd, J. (2000) Polyurethane: material for the next generation of heart valve prostheses? European Journal of Cardio-Thoracic Surgery, 17(4), 440–448. https://doi.org/10.1016/S1010-7940(00)00381-X
Zhu, G., Ismail, M., Nakao, M., Yuan, Q., & Yeo, J. (2019). Numerical and in-vitro experimental assessment of the performance of a novel designed expanded-polytetrafluoroethylene stentless bi-leaflet valve for aortic valve replacement. PLOS ONE. 14(1):e0210780. https://doi.org/10.1371/journal.pone.0210780
About the authors
Fatima Belen Palacios Magaña
8th semester student in Biomedical Engineering and Languages.
fatima.palaciosma@udlap.mx
Lizbeth Segura Romo
8th semester student in Biomedical Engineering, member of UDLAP’s Honors Program.
lizbeth.seguraro@udlap.mx
Dana Gabriela Jimenez Peña
8th semester student in Biomedical Engineering and Mechatronics Engineering, member of UDLAP’s Honors Program.
dana.jimenezpa@udlap.mx
Last modified: 14 mayo, 2021