Cell sheet, constructing vascular

There are generally three methods of constructing tissue engineered vascular grafts by applying collagen gel, cell-sheet and biodegradable polymer scaffolds. 

After resolving the issue of matrix design, the next step was to determine a desirable anatomical location. Several considerations were used in determining possible implant sites. The first is the size of the implant and the requirement that it be placed in juxtaposition to well-vascularized tissue. A transplant matrix constructed as a porous sheet-like structure could be at most 200 mm thick, based on estimates of nutrient transport limitations (66). The size of a device required to replace about 5% of the mass of an adult liver would then be about 0.5 m2. Surgical trauma must be avoided when implanting the device, because such trauma produces fibrin clots and hematoma formation around the wounded area, which creates a poor environment for cell survival. Also, the implant may behave better if supplied by the portal circulation rather than the systemic, because the portal circulation contains potential hepatotrophic factors. For these reasons, the mesentery—the vascularized membrane which secures the intestines—was selected as the best potential site (Fig. 15). 

Other attempts at tissue engineering blood vessels have been made by constructing the vessels ex vivo directly from the cellular components. This may be accomplished by culturing a sheet of human vascular smooth muscle cells in collagen and placing it within a lumenal support to produce tire media. A fibroblast sheet is then similarly cultured and placed about tire media to form the adventitia. Endothelial cells are later seeded into the lumen of the vessel, thus forming a mechanically soimd, three-dimensional vessel. 

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