Date of Award
1987
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The glutaraldehyde-treated porcine xenograft has been successful in the short term ({dollar}<{dollar}3 years), but clinical reports indicate problems with long term durability. Cyclic bending stresses have been implicated in the calcification, disruption and tearing of the valve leaflets, yet calculations of flexural stresses are not possible because leaflet mechanics are not fully understood. Although tensile testing has quantified many of the elastic properties of the material, it has offered little insight into the mechanism of xenograft failure that may result from systolic leaflet bending.;This thesis therefore reports my examination of the bending mechanics of xenografts in comparison with the fresh tissue from natural pig aortic valves.;From 15 histologically-prepared thin sections of each type, I found that glutaraldehyde-treated tissue was much more susceptible to compressive buckling and delamination than fresh tissue (p {dollar}<{dollar} 0.005), especially when the natural curvature of the leaflet was reversed. Through mechanical testing of 35 specimens in a custom-built bending machine, I found the bending stiffness of both tissues to be influenced very little by applied stress (0.8 kPa to 40 kPa), although the glutaraldehyde-treated tissue was up to 4 times stiffer than fresh tissue of similar thickness (p {dollar}<{dollar} 0.001). Radial strips were significantly more pliable than circumferential (p {dollar}<{dollar} 0.001), a finding consistent with reported elastic moduli. Using polarized light microscopy, I found that glutaraldehyde-treated tissue shears less during bending than fresh tissue (3% vs. 10% mean shear strain on 7 specimens of each, p {dollar}<{dollar} 0.005), and located the neutral axis within the fibrosa, near the outer surface of the tissue. From this, I determined that during reverse bending, compressive strains were approximately 5 times greater than tensile strains indicating that the compressive modulus of fresh tissue was about 25 times lower than the tensile modulus. For treated tissue, the neutral axis was slightly deeper, suggesting that the xenograft material has a decreased compressibility.;These results indicate that the standard glutaraldehyde treatment process has detrimental effects on xenograft performance by increasing tissue stiffness, promoting compressive buckling and reducing internal shearing. Alternate concepts for tissue preparation and valve design are discussed.
Recommended Citation
Vesely, Ivan, "Analysis Of The Bending Behaviour Of Porcine Xenograft Leaflets And Of Natural Aortic Valve Tissue" (1987). Digitized Theses. 1672.
https://ir.lib.uwo.ca/digitizedtheses/1672