Heart valve replacement or repair has become an increasingly popular surgical intervention for chronic heart valve disease. The mitral valve's complex geometry and integration into the left ventricle make repair to the valve's parts more attractive than total valve replacement. This study investigated the deformations of the mitral valve using mathematical models. The calculated deformation will be used to optimise bioreactors used in the creation of tissue engineered replacement mitral valve parts. The constitutive make up of the valve was investigated at both the micro-scale using histological techniques and at the macro-scale using uniaxial tensile tests. This investigation showed that collagen fibres were mainly aligned circumferentially and that elastin fibres were aligned both radially and circumferentially in the leaflets which had the effect of making the leaflets less extensible in the circumferential direction. The chordae showed axial collagen fibre alignment with thinner chordae exhibiting less extensibility. The leaflet materials were modelled using a strain energy formulation for two fibre families. This formulation showed a better fit to experimental data for biaxial tests (May- Newman & Yin 1995; Grashow et al 2006) when compared to available constitutive models in LSDYNA. The complex 3D geometry of the valve was captured using micro-computed tomography in conjunction with geometry extraction codes written in MATLAB (MathWorks) and computer aided design package SolidWorks (Dassault Systeme). The reconstructed geometry highlighted the asymmetrical nature of chordae origins and insertions, along with the asymmetry of the leaflets free edge. The geometry and the constitutive model was brought together in a finite element model. The annular deformation was then modelled using an elastic boundary method to obtain 15% and 25% saddle height ratios (SVR). With the 25% SVR model showing reduced strains in the anterior leaflet at peak systole. Finally the strains for the central regions of the anterior leaflet were compared to the strains generated in a model of a pericardium patch bioreactor. It was shown that the 5th and 8th bioreactor settings came closest to replicating the strains reported in the mitral valve finite element models.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:581949 |
| Date | January 2011 |
| Creators | Roberts, Nicholas |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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