## 4 Conclusions  
This study investigated the uniaxial tensile tests and numerical theories of the samples extracted from the abdominal aorta in order to determine the material constants according to age in the numerical model. In addition, the numerical simulations were conducted under tensile loading for the axial and circumferential directions to observe the stress-stretch curve of the specimens, and the results were compared with experimental results to determine the reliability of the simulation method. From the numerical simulation and the experimental results, the stress of the specimen was examined according to age as well as the stress-stretch curve related to loading direction. Furthermore, the material parameters were determined according to age, and the formulae used in the material constants according to age were suggested. The results have the following general features:  
* According to the tensile test results with respect to direction, the samples on the circumferentially oriented strip was noted to have an average tensile strength value of 0.34 MPa, which is 14.3% higher than that on the axially oriented strip. In addition, from the stretch results, it can be seen that the sample on the axially oriented strip had more flexibility than the sample on the circumferentially oriented strip. Therefore, the arterial tissue can be confirmed to have different tensile stress and stretch depending on the fiber orientation. * Moreover, in this study, the failure stress and stretch from the uniaxial tensile test were examined according to age, and the trend lines of the average, maximum, and minimum values were  
Figure 9: Comparison between material constants ((**a**) \(C_{10}\). (**b**) \(k_{1}\), and (**c**) \(k_{2}\)) and formulae according to age. calculated based on the experimental results. The numerical simulations according to age were conducted based on the results for the trend lines. As a result, a maximum error rate of 0.0065 and 0.0129 and an average error rate of 0.0021 and 0.0031 were observed in the comparison study between the trend lines and the simulations. * In the parametric study, the material constants for age were estimated on the basis of the maximum and minimum trend lines. Regarding the correlation between material constants and age, they continuously increased overall as the age of the specimen increased. In particular, it can be seen that the values of the material constants, \(C_{10}\), \(k_{1,\min}\), and \(k_{2,\max}\), were nonlinearly related with age. * From these results, the formulae that associated the value of the material constant with age were proposed, and the proportion variance in the dependent variable that can be distinguished from the independent variable was examined. Consequently, it could be seen that the R-squared ranged from 0.9152 to 0.9979 in the correlation between the values of the material constant and the formulae. The results obtained in the present study are expected to be used in the design for the medical device in order to enhance further understanding of the soft tissue behaviors. In addition, based on the results obtained in this study, we propose that the solid mechanics of the soft tissue must be considered when choosing the medical device design. Conceptualization: C.-W.L., C.S.L., J.-P.W. and D.-M.R. ; methodology: U.H., C.-S.L., J.-P.W. and D.-M.R. ; software: J.-H.Y., K.-H.K., C.-H.S. and D.-M.R. ; validation: C.-W.L., J.-H.Y., C.-S.L. and D.-M.R. ; formal analysis: U.H., K.-H.K. and J.-P.W. ; investigation: C.-W.L., U.H., J.-H.Y., K.-H.K. and D.-M.R. ; writing--original draft preparation: J.-H.Y., C.-S.L. and D.-M.R. ; writing--review and editing: C.-W.L., U.H., C.-H.S., [PERSON]-[PERSON] and D.-M.R. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1C1B6007145). This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2018R1D1A1B07044567).