SALS-ing is believing: Determining dominant fibre orientation in pericardium using visual inspection and Small Angle Light Scattering (SALS)

Porcine pericardium and bovine pericardium are commonly used materials in medical devices, most notably in the leaflets of bioprosthetic valves. The mechanical and fatigue behaviour of pericardium is influenced primarily by its collagen fibre architecture. Multiple methods exist in the literature for determining the collagen fibre architecture of pericardium, including inspecting the tissue by eye using a light source. However, visual inspection of pericardium has not yet been established to be repeatable or accurate for providing information on mechanically relevant fibre orientations. This study aims to establish the reliability of this visual inspection method. To do this a ‘ground truth’ for fibre architecture was defined using small angle light scattering (SALS). SALS repeatability was demonstrated by imaging porcine pericardium in four different positions and the ability to determine mechanically relevant tissue fibre orientations by SALS was correlated by uniaxial tensile testing. The repeatability and accuracy of visual inspection using a light source was then investigated, with six researchers identifying by eye the dominant fibre orientation of porcine pericardium in the same four positions from a bank of images. SALS was found to be highly repeatable in determining fibre alignment and the mechanically dominant fibre orientation, regardless of tissue orientation or the surface imaged. Visual inspection was found to be unrepeatable and inaccurate for all six researchers. Based on the data presented in this study, small angle light scattering, and not visual inspection, is recommended for the non-destructive repeatable determination of the mechanically dominant fibre orientation in pericardium.