Mechanical testing of glutaraldehyde cross-linked mitral valves. Part two: Elastic and viscoelastic properties of chordae tendineae

Abstract

The aim of this study was to assess whether the mechanical properties of mitral valve chordae tendineae are sensitive to being cross-linked under load. A total 64 chordae were extracted from eight porcine hearts. Two chordae (posterior basal) from each heart were subjected to uniaxial ramp testing and six chordae (two strut, two anterior basal and two posterior basal) were subjected to dynamic mechanical analysis over frequencies between 0.5 and 10 Hz. Chordae were either cross-linked in tension or cross-linked in the absence of loading. Chordae cross-linked under load transitioned from high to low extension at a lower strain than cross-linked unloaded chordae (0.07 cf. 0.22), with greater pre-transitional (30.8 MPa cf. 5.78 MPa) and post-transitional (139 MPa cf. 74.1 MPa) moduli. The mean storage modulus of anterior strut chordae ranged from 48 to 54 MPa for cross-linked unloaded chordae, as compared to 53–61 MPa cross-linked loaded chordae. The mean loss modulus of anterior strut chordae ranged from 2.3 to 2.9 MPa for cross-linked unloaded chordae, as compared to 3.8–4.8 MPa cross-linked loaded chordae. The elastic and viscoelastic properties of chordae following glutaraldehyde cross-linking are dependent on the inclusion/exclusion of loading during the cross-linking process; with loading increasing the magnitude of the material properties measured.

Mechanical testing of glutaraldehyde cross-linked mitral valves. Part one: In vitro mechanical behaviour

“…9 Mechanical testing of chordae tendineae has been used to assess how glutaraldehyde cross-linking alters their material properties and is presented in full in Part-2 of this study. 19 SEM imaging revealed the loss of endothelium on the surface of the fixed valve leaflets exposing subendothelial fibrils. This is similar to the damage that occurs during rheumatic heart disease 34 and is in agreement with imaging from previous studies of glutaraldehyde-fixed valves.…”

“…9 Mechanical testing of chordae tendineae has been used to assess how glutaraldehyde cross-linking alters their material properties and is presented in full in Part-2 of this study. 19…”

“…Blue rectangles denote work reported in this current study; boxes with a black outline are reported in part-2 of this study. 19…”

“…Following both cycles of in vitro testing, chordae were dissected from the mitral valve for mechanical testing; reported elsewhere. 19 Mitral valve leaflets were dissected and prepared for examination using Scanning Electron Microscopy (SEM; section 2.4). For clarity, the experimental protocol is outlined in Figure 2.…”

“…Elastic and viscoelastic properties of chordae from the heart valves have also been characterised but are presented separately; as Part-2 of this study. 19 The material's testing data is reported separately because data obtained were not in broad agreement with expected results 20 ; therefore, they have been assessed in detail, aiming to account for the wider implications as regards tissue mechanics.…”