Tissue Engineered Vascular Grafts (TEVGs)
The development of functional TEVGs using tissue engineering techniques and engineering principles has the potential to tremendously affect on coronary and peripheral artery bypass surgeries. One of the most significant limitations for vessel patency is restenosis due to vascular injury from the previous bypass surgery. Since anastamoses may create injury to the endothelium, this damage is essentially responsible for the mechanism of restenosis in the graft. Many people also have multiple bypass surgeries because of such occlusions that form or many sites of plaque formation, yet the amount of autografts available is still a limiting factor. Allografts are often not used because of the high probability of a significant immune response to the foreign body. Therefore, the development of functional TEVGs may significantly change how treatments for CAD are performed as well how many. Currently, there are no TEVGs that are available for clinical use, and only a handful has reached clinical trials.
Requirements for TEVGs
Academic research has had the most success with the development of functional TEVGs in animal models. However, there are still many parameters that must be optimized to better mimic the native vessels of interest. First, the endothelium of the vascular graft must be confluent, adherent, and must maintain a contractile phenotype to prevent and resist the development of thrombosis in vivo. Second, the mechanical properties of the vascular graft must match the mechanical properties of the native vessels. Specifically, the graft must have a highly organized collagen matrix that will provide the required mechanical support along with an elastin network that will provide the adequate compliance and recoil to prevent permanent deformation (Mitchell, 2003).
3 Approaches to Tissue Engineering Vascular Grafts
Currently, there are three general tissue engineering strategies that have been used to develop TEVGs in academia:
1. Sheet-based Graft: Cellular sheets are fabricated for self-assembly of the graft (does not use any
external scaffold)
2. Biodegradable Polymer-based Graft: Cells are seeded into a biodegradable synthetic scaffold
material
3. Naturally-Derived Graft (Decellularized tissues): Desired tissue removed from xenogenic or
allogenic source and chemically treated to remove everything but the ECM.
In the following pages, each approach will be explained along with a supplementary study by three lab groups.