Objective Autologous grafts are used to repair atherosclerotic cardiovascular diseases; however, many patients lack suitable donor graft tissue. Recently, tissue engineering techniques have emerged ...to make biologically active blood vessels. We applied this technique to produce arterial grafts using established biodegradable materials without cell seeding. The grafts were evaluated in vivo for vessel remodeling during 12 months. Methods Poly( l -lactide-co-ε-caprolactone) scaffolds reinforced by poly(lactic acid) (PLA) fiber were prepared as arterial grafts. Twenty-eight cell-free grafts were implanted as infrarenal aortic interposition grafts in 8-week-old female SCID/Bg mice. Serial ultrasound and micro computed tomography angiography were used to monitor grafts after implantation. Five grafts were harvested for histologic assessments and reverse transcription-quantitative polymerase chain reaction analysis at time points ranging from 4 months to 1 year after implantation. Results Micro computed tomography indicated that most implanted mice displayed aneurysmal changes (three of five mice at 4 months, four of five mice at 8 months, and two of five mice at 12 months). Histologic assessments demonstrated extensive tissue remodeling leading to the development of well-circumscribed neovessels with an endothelial inner lining, a neointima containing smooth muscle cells and elastin, and a collagen-rich extracellular matrix. There were a few observed calcified deposits, located around residual PLA fibers at 12 months after implantation. Macrophage infiltration into the scaffold, as evaluated by F4/80 immunohistochemical staining, remained after 12 months and was focused mostly around residual PLA fibers. Reverse transcription-quantitative polymerase chain reaction analysis revealed that gene expression of Itgam, a marker for macrophages, and of matrix metalloproteinase 9 was higher than in native aorta during the course of 12 months, indicating prolonged inflammation (Itgam at 8 months: 11.75 ± 0.99 vs native aorta, P < .01; matrix metalloproteinase 9 at 4 months: 4.35 ± 3.05 vs native aorta, P < .05). Conclusions In this study, we demonstrated well-organized neotissue of cell-free biodegradable arterial grafts. Although most grafts experienced aneurysmal change, such findings provide insight into the process of tissue-engineered vascular graft remodeling and should allow informed rational design of the next generation of arterial grafts.
Objectives The clinical translation of tissue-engineered vascular grafts has been demonstrated in children. The remodeling of biodegradable, cell-seeded scaffolds to functional neovessels has been ...partially attributed to matrix metalloproteinases. Noninvasive assessment of matrix metalloproteinase activity can indicate graft remodeling and elucidate the progression of neovessel formation. Therefore, matrix metalloproteinase activity was evaluated in grafts implanted in lambs using in vivo and ex vivo hybrid imaging. Graft growth and remodeling was quantified using in vivo x-ray computed tomography angiography. Methods Cell-seeded and unseeded scaffolds were implanted in 5 lambs as inferior vena cava interposition grafts. At 2 and 6 months after implantation, in vivo angiography was used to assess graft morphology. In vivo and ex vivo single photon emission tomography/computed tomography imaging was performed with a radiolabeled compound targeting matrix metalloproteinase activity at 6 months. The neotissue was examined at 6 months using qualitative histologic and immunohistochemical staining and quantitative biochemical analysis. Results The seeded grafts demonstrated significant luminal and longitudinal growth from 2 to 6 months. In vivo imaging revealed subjectively greater matrix metalloproteinase activity in grafts versus native tissue. Ex vivo imaging confirmed a quantitative increase in matrix metalloproteinase activity and demonstrated greater activity in unseeded versus seeded grafts. The glycosaminoglycan content was increased in seeded grafts versus unseeded grafts, without significant differences in collagen content. Conclusions Matrix metalloproteinase activity remained elevated in tissue-engineered grafts 6 months after implantation and could indicate remodeling. Optimization of in vivo imaging to noninvasively evaluate matrix metalloproteinase activity could assist in the serial assessment of vascular graft remodeling.
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