A Novel Small-Animal Model for Accelerated Investigation of Tissue-Engineered Aortic Valve Conduits

The objective of the study was to describe a novel small-animal model of tissue-engineered aortic valve conduits and to investigate biological processes in an accelerated and inexpensive fashion. An isogenic Lewis-to-Lewis rat model was used to exclude immunological factors of graft deterioration. U-shaped aortic valvular grafts were decellularized and characterized morphologically. Acellular conduits were repopulated with labeled isogenic cells in a bioreactor under flow conditions. Grafts were anastomosed to the recipient's abdominal aorta in an end-to-side manner (n = 7). Native rat aortas were implanted as a control group (n = 7). Grafts were explanted after 28 days and characterized. After treatment with trypsin-ethylenediaminetetraacetic acid, no residual cells were visualized in the scaffold. Mean DNA content decreased from 0.347 to 0 mu g/mg of DNA/tissue, and the content of collagenous connective tissue and proteoglycans appeared slightly reduced. Isolated aortic rat endothelial cells and myofibroblasts were repopulated on the acellularized scaffold, and florescent-labeled myofibroblasts were identified in the meshwork. Endothelial cells formed a monolayer on the luminal surface. Reseeded cells were viable as ascertained using a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. After implantation, Doppler and M-mode echography proved pulsatile cusp movement. All conduits were patent after 28 days. Examination of tissue-engineered explants revealed thickened aortic walls and incompetent valve function. Microscopically, aortic intima and media appeared normal, whereas the adventitia showed hyperproliferation of fibroblasts. Our new model leads to accelerated and reproducible results, suited to investigation of biological patterns of tissue engineering. The observed adventitial fibrosis emphasized the importance of careful selection of optimal cell types for repopulation in tissue-engineered constructs.