## 5 Conclusions  
In conclusion, acellular TEVGs are considered an effective type of small-diameter vascular grafts that can lead to in situ regeneration. However, long-term patency is still the core problem associated with vascular grafts. Different scaffold materials, fabrication methods, and surface modification methods have been investigated with the aim of improving the mechanical properties, biocompatibility, and degradability of TEVGs (Figure 5). Moreover, many in vivo tests have been performed in the hope of showing long-term patency. However, as a result of the complicated process of in situ regeneration, it is difficult to judge which degradation rates are most appropriate. In addition, the question of the ideal mechanical properties of the scaffold is still open to debate. More research on the subject is needed, but undoubtedly, ideal TEVGs are gradually becoming a reality.  
Figure 5: Recent progress regarding TEVGs. (**a**) The scaffold of the TEVG was fabricated by co-electrospinning, which combined different types of materials. (**b**) The multilayered structure of the scaffold was constructed by combining different types of fabrication methods.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Year** & **Manufacturing Method and Structure of Scaffold** & **Animal Model** & **Duration (Week)** & **Patency** & **Reference** \\ \hline
2019 & small intestinal submuc (SIS) functionalized with & & & & \\  & heparin/vascular endothelial growth factor (VEGF) & mice & 4 & 100\% & [36] \\ \hline
2018 & decellularized film tissue obtained by implanting a mold in vivo in dog or goat & dogs and goats & 12 & - & [35] \\ \hline
2018 & electrospinning of poly-caprolactone (PCL) and gelatin & rats & 4 & 100\% & [19] \\  & surface modification with heparin & & & & \\ \hline
2018 & electrospinningning of PCL for inner layer 3D printing of & & & & \\  & polydopamine (PDA) for outer layer immobilization of VEGF & rats & 4 & 100\% & [29] \\ \hline  & electrospinningning of a & & & & \\  & poly(\(\epsilon\)-caprolactone)-pol/pol  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Year** & **Manufacturing Method and Structure of Scaffold** & **Animal Model** & **Duration (Week)** & **Patency** & **Reference** \\ \hline
2017 & electrospinningning of polyurethane (PU) surface modification of stromal cell-derived factor-1\(\alpha\) and VEGF & dogs & 24 & 62.5\% (5/8) & [44] \\ \hline
2017 & electrospinning of polycarbonate polyurethane (PCV) surface modification of NH\({}_{3}\) plasma and heparin & rabbits & 4 & - & [45] \\ \hline
2016 & 3D printing of poly(propylene fumarate) (PFE) & mice & 24 & 100\% & [27] \\ \hline  & decellularized film tissue obtained by implanting a mold in vivo in pigs for inner layer electrospinningning of PCL for outer layer & pigs & 4 & 87.5\% (7/8) & [46] \\ \hline  & comprising collagen fiber networks and elastin-like protein polymers & rats & 2 & 100\% & [47] \\ \hline
2012 & electrospinningning of PU & dogs & 24 & 83\% (5/6) & [48] \\ \hline
2008 & electrospinningning of PCL & rats & 24 & 100\% & [49] \\ \hline \end{tabular}
\end{table}
Table 1: _Cont._  
**Author Contributions:** [PERSON] and [PERSON] proposed the idea; [PERSON], [PERSON], and [PERSON] conceived and designed the structure of this review; [PERSON] contributed the materials, figures, and tables for this review; [PERSON] wrote the paper.  
**Funding:** This research was partially supported by Beijing Municipal Science and Technology Commission (Grant No. Z141100000214012).  
**Conflicts of Interest:** The authors declare no conflict of interest.