Objectives: The major problem with heart valve bioprostheses made from chemically treated porcine aortic valves is their limited longevity caused by gradual deterioration, which has a causal link with valve tissue mechanical properties. To our best knowledge, there are no published studies on the mechanical properties of modern, commercially available bioprostheses comparing them to native human valves. The objective of this study is to determine the mechanical properties of St Jude Epic bioprostheses and to compare them with native human and porcine aortic valves.
Methods: Leaflets from eight porcine aortic valves and six Epic bioprostheses were analyzed using uni-axial tensile tests in radial and circumferential directions. Mechanical properties of human valves have been previously published by our group. Results are represented as mean values+/-S.D.
Results: Circumferential direction. Modulus of elasticity of Epic bioprostheses in circumferential direction at the level of stress 1.0 MPa is 101.99+/-58.24 MPa, 42.3+/-4.96 MPa for native porcine and 15.34+/-3.84 MPa for human aortic valves. Ultimate stress is highest for Epic bioprostheses 5.77+/-1.94 MPa, human valves have ultimate stress of 1.74+/-0.29 MPa and porcine 1.58+/-0.26 MPa. Ultimate strain in circumferential direction is highest for human valves 18.35+/-7.61% followed by 7.26+/-0.69% for porcine valves and 5.95+/-1.54% for Epic bioprostheses. Radial direction. Modulus of elasticity in radial direction is 9.18+/-1.81 MPa for Epic bioprostheses, 5.33+/-0.61 MPa for native porcine, and 1.98+/-0.15 MPa for human aortic valve leaflets. In the radial direction ultimate stress is highest for Epic bioprostheses 0.7+/-0.21 MPa followed by native porcine valves 0.55+/-0.11 MPa and 0.32+/-0.04 MPa for human valves. For human valves ultimate strain is 23.92+/-4.87%, for native porcine valves 8.57+/-0.8% and 7.92+/-1.74% for Epic bioprostheses.
Conclusions: Epic bioprostheses have non-linear stress-strain behavior similar to native valve tissue, but they are significantly stiffer and hence less elastic compared to native porcine and human aortic valves. These differences in mechanical properties may cause variations in stress distribution within leaflets of the bioprosthetic valves and accelerate their deterioration.