J Michael Lee

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Bioprosthetic vardiac valves are constructed from chemically-treated tissue, the most popular valves being made from aldehyde-treated porcine aortic valves, aldehyde-treated bovine pericardium, and glycerol-treated human dura mater. While the chemical treatments were originally used to sterilize the tissue, and to suppress immunological reaction, it is now appreciated that the treatment also affects the mechanical function of the valve and its fatigue lifetime. This thesis is a study of the tensile viscoelastic properties of each tissue and the effect of each chemical treatment on those properties.;I have examined: (1) the effect of fixation (with or without pressure) in 0.625% glutaraldehyde and 4% formaldehyde on 109 strips of aortic valve leaflets from 47 pigs; (2) the effect of fixation in 0.5% glutaraldehyde and 4% formaldehyde on 98 strips on pericardium from 17 calves; and (3) the effect of storage in 98% glycerol on 54 strips of human dura mater from 13 patients.;The study of fresh pericardium was extended to examination of 76 strips of pericardium from 19 dogs, 37 strips of pericardium from 10 patients with healthy pericardia, and 12 strips of pericardium from 3 patients with pericardial disease. These studies were aimed at the normal physiological function of the pericardium, the applicability of canine data to humans, and the mechanical nature of pericardial disease.;Mechanical tests were conducted on an Instron testing machine. The tissue strips were tested in Hanks solution at 37(DEGREES)C for response to cyclic loading (preconditioning), hysteresis, stress-strain relations, stress relaxation, creep, and fracture. Scanning electron microscopy of torn samples was used to provide structural correlates to the mechanical properties. Each tissue was examined as a pliant fiber-reinforced composite, and its mechanical response examined using the phenomenological theory of viscoelasticity.;Canine and human pericardium showed nonlinear stress-strain curves which provice ventricular volume coupling and limitation during rapid expansions. The viscoelastic properties of stress relaxation and creep allow the stress-strain curve to shift, accomodating greater volumes without plasticity. Pericardium has a crossed-fibrillar structure which correlates with its mechanical isotropy. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI



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