Other coatings such as drug eluting vascular grafts have been designed to slowly release bioactive substances into the bloodstream. Synthetic drugs that release reactive-oxygen-induced antiplatelet ethyl salicylate have been shown to prevent blood clotting. More recently, a decellularized tissue engineered vascular graft coated with a hyaluronic acid hydrogel revealed antithrombogenic protection and promotion of endothelium, due to protection of the underlying collagen layer. There were fewer adherent platelets and less fibrinogen and fibrin formation on coated grafts than on uncoated grafts. Furthermore, in vitro studies showed inhibition of macrophage adhesion due to the strongly hydrophilic nature of hyaluronic acid. Studies in vivo in rat and dog models showed reendothelialization after 5 weeks (Figure ). These finding pave the way for an "off-the shelf" tissue engineered vascular graft for small diameter applications. 30 b,i-iv) Nitric oxide-releasing polymer coating on prosthetic vascular grafts. i) Schematic illustration of nitric oxide release from polyvinyl chloride biomaterial upon contact with water. ii) Photographs of explanted and longitudinally opened polyurethane vascular grafts displaying luminal thrombus on uncoated (top) and coated (bottom) grafts. iii-iv) SEM images showing platelet adhesion and thrombus accumulation from arterial anastomoses on iii) coated and iv) uncoated grafts (Magnification ×1000). c,i) Design and synthesis of the zwitterionic polymer, MPC, depicting its phospholipid rich cell membrane and phosphocholine functional groups. ii-iii) SEM images assessing the thrombogenicity after exposure to ovine blood on ii) uncoated vascular graft showing platelet aggregates and iii) MPC coated vascular graft free of platelet depositions. iv-v) Histology assessment post a 24-week period in vivo of the MPC coated vascular graft, depicting i) a section of a native rat abdominal aorta prior to the proximal anastomosis of the graft and ii) section taken in proximity of the distal anastomosis. d,i-iv) Hyaluronic acid modified surface coating on decellularized TEVGs vascular graft. i) Depiction of hyaluronic acid coating on vascular graft. ii) Transmission electron microscopy (TEM) images of the coating morphology of uncoated and coated hyaluronic acid coated tissue engineered vascular graft. iii) Comparison of the inner diameter of the uncoated and coated allografts in rat aortic implants at 32 days (n = 6, *p < 0.05, **p < 0.01, by unpaired, two-sided t-test with Welch's correction). iv) Images of hematoxylin & eosin stained clotted, uncoated tissue engineered vascular grafts and coated graft at both the b) mid-graft and c) anastomosis regions of canine explants.