Decellularized tissue-engineered blood vessel as an arterial conduit

Abstract

Arterial tissue-engineering techniques that have been reported previously typically involve long waiting times of several months while cells from the recipient are cultured to create the engineered vessel. In this study, we developed a different approach to arterial tissue engineering that can substantially reduce the waiting time for a graft. Tissue-engineered vessels (TEVs) were grown from banked porcine smooth muscle cells that were allogeneic to the intended recipient, using a biomimetic perfusion system. The engineered vessels were then decellularized, leaving behind the mechanically robust extracellular matrix of the graft wall. The acellular grafts were then seeded with cells that were derived from the intended recipient-either endothelial progenitor cells (EPC) or endothelial cell (EC)-on the graft lumen. TEV were then implanted as end-toside grafts in the porcine carotid artery, which is a rigorous testbed due to its tendency for graft occlusion. The EPC-and EC-seeded TEV all remained patent for 30 d in this study, whereas the contralateral control vein grafts were patent in only 3/8 implants. Going along with the improved patency, the cell-seeded TEV demonstrated less neointimal hyperplasia and fewer proliferating cells than did the vein grafts. Proteins in the mammalian target of rapamycin signaling pathway tended to be decreased in TEV compared with vein grafts, implicating this pathway in the TEV's resistance to occlusion from intimal hyperplasia. These results indicate that a readily available, decellularized tissue-engineered vessel can be seeded with autologous endothelial progenitor cells to provide a biological vascular graft that resists both clotting and intimal hyperplasia. In addition, these results show that engineered connective tissues can be grown from banked cells, rendered acellular, and then used for tissue regeneration in vivo.bypass graft | collagen | mechanical conditioning

Implantation of Completely Biological Engineered Grafts Following Decellularization into the Sheep Femoral Artery

“…1 Various approaches have been used to fabricate TEVG, [3][4][5][6][7][8][9] recently reviewed. 3 Most notably in terms of clinical promise, TEVGs derived from rolling a fibroblastproduced ''cell sheet'' into a tube 5,7,8,10 and from smooth muscle cells (SMCs) seeded onto a degradable synthetic polymer tube 4,6,9 have resulted in successful implantation. In contrast to these approaches, our approach utilizes the biopolymer fibrin (in hydrogel form) as the starting scaffold, 11 which eliminates risk of any adverse host reaction to residual synthetic material.…”

Endothelial Outgrowth Cells: Function and Performance in Vascular Grafts

“…In one example, smooth muscle cells were cultured on a biodegradable polyglycolic acid rod for 10 weeks in a bioreactor, allowing the smooth muscle cells to generate a tubular extracellular matrix. 42 After decellularizing the scaffold, the mechanical properties were comparable to a human saphenous vein. The decellularized scaffolds were then seeded with autologous EOCs, preconditioned with 15 dyn/ cm 2 shear stress for 24 h, and implanted in porcine carotid arteries as end-to-side grafts to mimic clinical bypass grafts.…”

“…40,41 EOCs express the fundamental proteins used by ECs to regulate thrombosis, including tissue factor, thrombomodulin, endothelial Protein C receptor, tPA, and von Willebrand factor. 26,27,35,36,[42][43][44][45][46][47][48] Regulation of thrombus formation by EOCs has been suggested in vitro by studies demonstrating reduced platelet adhesion on EOC-lined materials and the generation of the anticoagulant activated Protein C. 45,46,48 In addition, in response to pro-thrombotic stimuli, EOCs increase their expression of tissue factor, decrease plasma clotting time, and increase tPA expression. 36 A number of strategies have been used in an attempt to improve EOCs' thromboprotective function before graft implantation.…”

“…46 Compared with ECs, EOCs have an increased production of thrombomodulin and corresponding Protein C activation, but do not increase tissue factor expression after steady fluid shear stress, indicating a superior thromboprotective phenotype in arterial flow conditions. 46,60 Steady shear causes EOCs to increase eNOS gene expression 37,42,60 and NO production, suggesting an improved capacity to limit intimal hyperplasia. 37,58,61,75 Models that incorporate both fluid shear stress and inflammatory cytokines enable a better characterization of how these factors interact to influence EOC behavior.…”

“…To ensure complete coverage of the tubular graft lumen, seeding is generally performed using multiple inoculations with manual or automated rotation, or by perfusing a cell suspension through the graft wall. 35,36,42,66,[79][80][81] …”