We engineered implantable small-diameter blood vessels based on ovine smooth muscle and endothelial cells embedded in fibrin gels. Cylindrical tissue constructs remodeled the fibrin matrix and exhibited considerable reactivity in response to receptor-and nonreceptor-mediated vasoconstrictors and dilators. Aprotinin, a protease inhibitor of fibrinolysis, was added at varying concentrations and affected the development and functionality of tissue-engineered blood vessels (TEVs) in a concentration-dependent manner. Interestingly, at moderate concentrations, aprotinin increased mechanical strength but decreased vascular reactivity, indicating a possible relationship between matrix degradation/remodeling, vasoreactivity, and mechanical properties. TEVs developed considerable mechanical strength to withstand interpositional implantation in jugular veins of lambs. Implanted TEVs integrated well with the native vessel and demonstrated patency and similar blood flow rates as the native vessels. At 15 wk postimplantation, TEVs exhibited remarkable matrix remodeling with production of collagen and elastin fibers and orientation of smooth muscle cells perpendicular to the direction of blood flow. Implanted vessels gained significant mechanical strength and reactivity that were comparable to those of native veins. Our work demonstrates that fibrin-based TEVs hold significant promise for treatment of vascular disease and as a biological model for studying vascular development and pathophysiology. matrix degradation/remodeling; vascular disease; vascular reactivity; vascular tissue engineering; smooth muscle; endothelial cells MANY APPROACHES HAVE BEEN taken to replace diseased or damaged blood vessels. Synthetic conduits of polytetra-flouroethylene (Teflon, ePTFE) or polyethylene terephthalate (Dacron) have been used extensively with a great degree of success in replacement of large-diameter (Ͼ6 mm) vessels (9). However, small-diameter synthetic grafts displayed high failure rates due to thrombus and plaque formation. Adsorption of proteins or endothelial cells to the luminal surface of the grafts decreased thrombogenicity but did not restore vasoreactivity and long-term patency (8,9,11,26,37). Allogeneic grafts demonstrated long-term patency and reactivity, but their clinical use is prevented by high immunogenicity. Autografts, predominantly from saphenous veins or radial arteries, are the most widely used for small-diameter vessel replacement procedures such as coronary artery bypass. Although autologous grafts are currently the gold standard, limited availability, especially for repeat grafting procedures, and the pain and discomfort associated with the donor site necessitate the development of alternative technologies.Tissue engineering approaches that use natural or synthetic biomaterials as three-dimensional scaffolds for cell growth have been proposed. Natural biomaterials, derived from decellularized tissues, demonstrated successful infiltration of host cells and near physiological level of vasoreactivity after longte...

The large number of coronary artery bypass procedures necessitates development of off-the-shelf vascular grafts that do not require cell or tissue harvest from patients. However, immediate thrombus formation after implantation due to the absence of a healthy endothelium is very likely. Here we present the successful development of an Acellular Tissue Engineered Vessel (A-TEV) based on small intestinal submucosa that was functionalized sequentially with heparin and VEGF. A-TEVs were implanted into the carotid artery of an ovine model demonstrating high patency rates and significant host cell infiltration as early as one week post-implantation. At one month, a confluent and functional endothelium was present and the vascular wall showed significant infiltration of host smooth muscle cells exhibiting vascular contractility in response to vaso-agonists. After three months the endothelium aligned in the direction of flow and the medial layer comprised of circumferentially aligned smooth muscle cells. A-TEVs demonstrated high elastin and collagen content as well as impressive mechanical properties and vascular contractility comparable to native arteries. This is the first demonstration of successful endothelialization, remodeling, and development of vascular function of a cell-free vascular graft that was implanted in the arterial circulation of a pre-clinical animal model.

Our results suggest that BM-SMPC may be useful in studying SMC differentiation and have high potential for development of cell therapies for the treatment of cardiovascular disease.

Accumulating evidence suggests that the mechanical and biochemical signals originating from cell-cell adhesion are critical for stem cell lineage specification. In this review, we focus on the role of cadherin mediated signaling in development and stem cell differentiation, with emphasis on two well-known cadherins, cadherin-2 (CDH2) (N-cadherin) and cadherin-11 (CDH11) (OB-cadherin). We summarize the existing knowledge regarding the role of CDH2 and CDH11 during development and differentiation in vivo and in vitro. We also discuss engineering strategies to control stem cell fate decisions by fine-tuning the extent of cell-cell adhesion through surface chemistry and microtopology. These studies may be greatly facilitated by novel strategies that enable monitoring of stem cell specification in real time. We expect that better understanding of how intercellular adhesion signaling affects lineage specification may impact biomaterial and scaffold design to control stem cell fate decisions in three-dimensional context with potential implications for tissue engineering and regenerative medicine.