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Heng et al. Vessel Plus 2023;7:31 https://dx.doi.org/10.20517/2574-1209.2023.97 Page 9 of 14

Figure 3. Evolution of external vein graft stent design. (A) Knitted fabric stent of polyethylene, polypropylene, and Teflon [20] . (B)
Polytetrafluoroethylene (PTFE) sheath applied to proximal rabbit jugular vein graft [17] . (C) Loose-fitting external polyester stent (above)
and polyglactin (Vicryl) sheath (below) [22] . (D) Expandable braided cobalt-chromium alloy stent [33] . (E) Poly L-lactide-ε-caprolactone
(75/25) copolymer (P (LA/CL)) mesh [34] . (F) Electrospun poly(ester urethane)urea (PEUU) stent [36] . (G) Extent (Vascutek Ltd,
Inchinnan, Scotland) external Dacron stent [47] . (H) Knitted nitinol eSVS mesh (Kips Bay Medical Inc, Minneapolis, MN, USA) [48] . (I)
[50]
Braided cobalt-chromium VEST (Vascular Graft Solutions Ltd, Tel Aviv, Israel) . Photographs adapted from respective references.

Finally, woven mesh materials including soft polyester, Monocryl, and Vicryl have been fashioned into
“appropriate fit” external supports that closely appose vessel walls while still allowing neoadventitial
vascularization between mesh fibers [22,32,37] . Together, these innovations in external stent design and
production aim to overcome previous limitations of early stent devices and enhance long-term vein graft
patency in CABG.

In light of increasing awareness of the molecular signaling pathways contributing to vein graft failure,
researchers have also explored peri-adventitial treatments targeting these pathways as an alternative to
external stent usage. For instance, periadventitial applications of elastomer gels containing
diethylenetriamine nitric oxide (NO) adduct have been explored as a way to suppress platelet aggregation
and restore endothelial dysfunction from downregulation of eNOS after vein grafting . Adventitial
[38]
administration of gene transfer vectors and nanoparticles have also been studied to deliver platelet-derived
endothelial cell growth factor (PD-ECGF) thymidine phosphorylase (TP) and microRNA-145 (miR-145)-
[39]
loaded poly(lactic-co-glycolic acid) (PLGA) to modulate SMC chemotaxis and phenotype from
[40]
proliferative to contractile states. Fibrin sealants such as cyanoacrylate [41,42] , anti-adhesive agents such as
hyaluronic acid-carboxymethyl cellulose (HA/CMC) , and collagen cross-linking with photoactive tissue
[43]
passivation have also been investigated as methods of providing mechanical offloading to vein grafts
[44]
without sheath implants. As with external vein graft stents, the long-term effects of these adventitial
treatments remain to be seen and will remain a subject of future investigation.