An “off the shelf” vascular allograft supports angiogenic growth in three-dimensional tissue engineering

ObjectivesDense angiogenic sprouting occurs from arteriovenous loops (AVLs) incorporating autologous vein grafts inserted into empty plastic chambers in vivo. The purpose of this study was to determine if angiogenesis from the AVL was limited by substituting an “off the shelf” cold-stored allograft vein instead of an autologous vein.MethodsFour Sprague Dawley rat groups (two AVL configurations × two chamber types) were established for both 2-week and 6-week harvest. Control AVLs were autologous femoral vein grafts harvested from the left femoral vein that were surgically inserted between the cut femoral artery and vein on the right side. Experimental “allograft” AVLs were rat femoral veins cold-stored (4°C, sterile) for 4 to 7 weeks and then microsurgically interposed between the right femoral artery and vein of an unrelated rat. The two AVL types were inserted in one of two plastic chamber types – smooth or perforated. At harvest, the AVL constructs were checked for patency, weighed, their volume determined, and histology undertaken. Morphometric assessment of percent and absolute volume of major tissue components (including blood vessels) at 6 weeks was completed.ResultsThere were no significant differences between autograft and allograft groups in construct weight, volume, or morphology at 2 or 6 weeks. No statistical differences occurred in the percent or absolute vascular volume of AVLs incorporating a cold-stored allograft vs autologous vein grafts at 6 weeks regardless of the chamber type. However, perforated chambers caused significant increases in construct weight (P = .015), volume (P = .006), and percent and absolute connective tissue volume at 6 weeks (P = .001) compared to smooth chamber constructs, regardless of the graft type.ConclusionCold-stored small-caliber allografts interposed in AVLs do not inhibit microcirculatory development and can be used in composite tissue engineering.

Clinical RelevanceThe issue of providing a growing vascular network within three-dimensional tissue-engineered constructs presents a major challenge to scientists and surgeons working in this field. Previously, many cell/scaffold constructs have been implanted in vascular areas of the body and rely on neighboring capillaries at the implantation site to grow into the construct and provide vascularization – this relatively slow process has been termed extrinsic vascularization. As an alternative, our group has established an intrinsic vascularization model where larger three-dimensional constructs can be grown. A macrovascular arteriovenous loop (AVL) is created by anastomosing a fresh autologous vein between the cut ends of the femoral artery and vein. The AVL is placed in a plastic chamber and this construct spontaneously sprouts an extensive capillary network suitable for the implantation of progenitor cells. Clinically, a more attractive option is to use an “off the shelf” synthetic or biologically created vascular graft within the AVL. In this study, we have used cold-stored allograft veins as vascular grafts within the loop and demonstrated that the angiogenic network generated is not significantly different to that formed when a fresh autograft vein is anastomosed into the AVL. This result indicates that use of this vascular graft material will improve the options available to vascular surgeons who may be involved in creating large tissue constructs. The use of this “off the shelf” biological graft will shorten surgery times, operating costs, provide flexibility to the surgeon, and is a further significant advancement in composite tissue engineering.