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Objective:
To determine the evolving mechanical properties and histologic features of tissue engineered vascular grafts (TEVGs) implanted in the arterial circulation.
Design:
Basic Science.
Setting:
Academic Medical Center.
Patients:
None.
Interventions:
TEVGs composed of sheets of nonwoven polylactic acid and sealed into a tube with a 50:50 copolymer solution of ε-caprolactone and L-lactide were implanted as interpositional grafts in the infrarenal abdominal aorta of C57BL/6 mice (n=50).
Main Outcome Measures:
TEVGs were evaluated in vivo with Doppler ultrasound. At 3 months and 7 months TEVGs were explanted and underwent mechanical testing as well as histologic and immunohistochemical analysis. After mechanical testing grafts were treated with elastase or collagenase and retested in order to determine the mechanical contribution of elastin and collagen respectively.
Results:
TEVG failure occurred in 14 mice (28%) within 6 weeks of implantation primarily due to rupture along the seam line. Doppler ultrasound revealed no significant dilation or change in wall thickness in the 36 surviving mice. Mechanical testing demonstrated reduced axial stretch ratio in TEVGs versus proximal artery at 3 months (CI -0.5940 to 0.5300; n = 10) and 7 months (CI -0.6845 to -0.6215; n = 5), as well as reduced compliance during pressurization. Histologic and immunohistochemical analysis showed development of smooth muscle cell layers and endothelial cell layer in addition to deposition of collagen and elastin within TEVGs. Treatment with elastase resulted in no significant change in graft compliance, but partial collagenase treatment resulted in a modest increase in graft compliance.
Conclusions:
Mechanical testing is a reliable method for evaluating TEVG properties. Despite promising histologic findings TEVGs demonstrate a lack of axial stretch and compliance at 3 and 7 months.