Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Bioengineering

Advisor

Vyavahare, Naren R.

Committee Member

LaBerge , Martine

Committee Member

Nagatomi , Jiro

Committee Member

Ramamurthi , Anand

Abstract

The native heart valve will open and close an astonishing 3 billion times in the average lifetime, implicating immense biomechanical ramifications that necessitate near-flawless structure and functional behavior. Deviations from this idyllic function as a result of heart valve disease (HVD) affect millions of individuals worldwide and result in over 275,000 heart valve replacements worldwide every year. Glutaraldehyde (GLUT) cross-linked porcine aortic heart valves, a common type of bioprosthetic heart valve (BHV), are used frequently in these valve replacement surgeries. The native valve leaflets entail a tri-composite design of type I collagen, elastin and glycosaminoglycans (GAGs), each of which are important structural and functional biomechanical components.
Our group has previously characterized the loss of GAGs from BHVs due to the inability of GLUT crosslinking to stabilize these structures during in-vitro storage, fatigue, enzymatic degradation, and in-vivo implantation. Consequences of GAG loss include, but are not limited to, decreased hydration, loss of tissue compliancy, altered leaflet morphology and possible compromise of collagen organization and mechanical integrity.
This study explicitly examines the ability of neomycin to enhance glutaraldehyde crosslinking (NG) and stabilize GAGs. Evidence for enhanced crosslinking using neomycin was supported by increased resistance to enzymatic collagen and elastin degradation compared to that of standard GLUT crosslinking, and by a small but significant increase in collagen denaturation temperature as measured using differential scanning calorimetry. NG also exhibited a slightly diminished hydration capacity compared to GLUT crosslinking, indicating potentially adverse biomechanical effects. However, biaxial tensile testing revealed no significant alterations in compliancy in NG versus GLUT crosslinking. NG-cross-linked leaflets subjected to storage, accelerated cyclic fatigue and enzyme-mediated GAG degradation revealed improved GAG stabilization versus standard GLUT-fixed valves, which sustained substantial decreases in GAG content. Lastly, ultrastructural analysis using transmission electron microscopy qualitatively assessed preservation of GAGs in NG leaflets and yielded insight into their morphological preservation utilizing NG crosslinking. Thus, we hypothesized that preservation of the GAG matrix using NG crosslinking may help maintain biomechanical function and ultimately improve BHV tissue durability.

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