De novo generation of axially vascularized tissue in a large animal model.

De novo generation of axially vascularized tissue with clinically relevant dimensions in a large animal model and implementation of clinically established imaging modalities for in vivo evaluation of vascularization. To be used for reconstruction of tissue defects, engineered grafts need to be axially vascularized to enable transplantation without graft loss due to hypoxia. Limitations to dimensions in small animal models had not yet been overcome, which is necessary to yield clinical relevance. Anatomical studies of groin and axillary regions in eight merino sheep were followed by microsurgical creation of an arteriovenous loop (AV-loop), embedded in an isolation chamber filled with fibrin matrix. Constructs were implanted in the groin of six sheep for up to 6 weeks. Course of vascularization in de novo forming tissue was assessed by sequential computed tomography angiography (CTA) and magnetic resonance angiography (MRA) in vivo, as well as by postexplantational micro-computed tomography and histology. A vascular axis was constantly found epifascially at the medial aspect of all sheep's thighs, which was used for AV-loop creation. Patency of AV-loop could be visualized by CTA and MRA scans during 1-6 weeks. Complex 3D-vessel-reconstruction revealed increasing axial vascularization of the fibrin matrix and growing connective tissue within the isolation chamber, which was confirmed by micro-computed tomography and histology postexplantation. De novo formation of axially vascularized tissue was demonstrated for the first time ever in a large animal model, paving the way for the first application of tissue engineering vascularized grafts with clinically relevant dimensions.