# Artificial Heart Valve Scaffold Based on Electrospun PCL/PU Three-Layer Composite Fibers
## 3 Results and Analysis
### Mechanical Properties and Young's Modulus  
The electrospun heart valve samples had a three-layer polymer structure, which was similar to the structure of native heart valves. Because the internal structure of the natural valve changes with strain, involving the extension of the highly coiled collagen fibers and the rotation of the fibers to the tensile axis, the mechanical properties of the valve leaflet are relatively complex, and the durability of the material has a great relationship with the tensile resistance of the material after opening and closing millions of times. Among the various components of the sample, the one with the best tensile properties needs to be selected for the following biological experiments. The experimental results are shown in Figure 7a. Figure 7a shows that for the PCL/PU = 1:2 sample, the valve axial mechanical property of the valve leaflet is the best. Through data processing, the formula for calculating [PERSON]'s modulus is given by E = \(\sigma/\varepsilon\), with E being Young's modulus in MPa, \(\sigma\) denoting stress in kPa, and \(\varepsilon\) representing strain in %. Figure 7b gives the calculated Young's modulus for the five samples. For PCL/PU = 1:2 sample, the axial Young's modulus of the valve leaflet was the highest, at 14.70 MPa. For native heart valve leaflets, axial forces are much greater than radial forces. The axial elastic modulus of native aortic valve leaflets is about 5-15 MPa depending on the individual, genetics, sex, race, blood, blood pressure, etc. [28]. As shown in Figure 7b, the Young's moduli of the electrospun heart valves were basically within the normal interval. Figure 6: A linear plot of the contact angle of the ordered layer at the initial time point as a function of the PCL/PU ratio. After reviewing the literature, a table summarizing the Young's moduli of heart valves made of different materials was compiled, as shown in Table 1:  
As can be seen, compared to artificial heart valves made from other materials, the PCL/PU composite heart valve has a higher Young's modulus, which proves its excellent mechanical properties. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Polymer** & **Concentration** & **Mechanical Properties** & **Diameter of Fiber** & **Reserve Note** & **Reference** \\ \hline  & & & & It has high cell capture & \\  & & & & and growth promotion & \\  & & & & ability. & \\ PDO/PEUU & 1.24 g/cm\({}^{3}\) & 3.9 \(\pm\) 0.2 MPa & 1068 \(\pm\) 235 nm & PDO nanofibers and & [29] \\  & & & & PEUU nanofibers showed & \\  & & & & significant antioxidant & \\  & & & & properties. & \\  & & Modulus of elasticity & & & \\  & & & PGS/PCL 2:1 & PGS/PCL (2:1) & \\ PGs/PCL & 33\% \(w/v\) & 8.5 \(\pm\) 1.6 MPa & 4.0 \(\pm\) 0.11 \(\upmu\)m. & Improve biocompatibility. & [30] \\  & & & PGS/PCL 3:1 & PGS/PCL (3:1) & \\  & & & 8.6 \(\pm\) 1.3 MPa & 6.1 \(\pm\) 0.17 \(\upmu\)m & \\  & & & Modulus of elasticity & & \\  & & & 10.7 MPa & & \\ APS-co- & & & Ultimate tensile strength & & \\
25 PEG/ & 17.5\% \(w/v\) & 8.36 MPa & 300 nm & The thrombotic effect was & \\ PCL & & & 8.36 MPa & 300 nm & small due to the presence & \\  & & & Toughness & & of PEG \\  & & & 12.0 MPa & & \\  & & & Modulus of elasticity & & \\ PCL & 14\% \(w/v\) & 6.4 MPa & & & \\  & & & Coefficient of poisson & & \\  & & & 0.45 & & \\  & & & Outer PCL fibers & A three-layer-structure & \\  & & & 0.47 \(\upmu\)m \(\pm\) 0.17 \(\upmu\)m & heart valve is similar to & \\ PCL/PU & 20\% \(w/v\) & Modulus of elasticity & PCL/PU middle & natural valves and & This work \\  & & & 14.70 MPa & ordered layer & belongs to a biomimetic & \\  & & & 0.46 \(\upmu\)m \(\pm\) 0.14 \(\upmu\)m & construction & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of polymer materials used in electrospun heart valves in recent years. Figure 7: (**a**) Tensile test curves of the fiber membranes (leaflet blade part of the valve scaffold) prepared by electrospinningning. (**b**) The bar graph of the Young’s modulus of the samples. * stands for Comparison of the maximum and minimum values.