The effects of collagen fiber orientation on the flexural properties of pericardial heterograft biomaterials

Improving cardiac valve bioprostheses (BHV) utilizing heterograft biomaterials requires a better understanding of their mechanical behavior. Flexure is a major mode of deformation for BHV leaflets during valve operation, inducing more complex deformation patterns within the tissue compared to tensile loads. In this study, we investigated the relation between collagen fiber preferred direction and the resulting flexural properties of native and glutaraldehyde-treated bovine pericardium. 20 mm×4 mm strips were cut from the presorted sheets of bovine pericardium and divided into four groups: two directions of collagen fiber orientation in two groups of native and chemically treated specimens. Specimens were flexed in two different directions using a three-point bending technique (ASAIO J. 45(1999)59) and their flexural mechanical response compared. Results indicated that: (1) the relationship between the applied flexing moment and change of curvature of specimens was non-linear in both native and chemically fixed groups, (2) there were no directional differences in flexural properties when the bovine pericardium is flexed towards either the epi-pericardial or visceral surfaces in both native and chemically fixed specimens, (3) native and chemically fixed bovine pericardium were stiffer when flexed perpendicular to local preferred collagen fiber direction, and (4) chemical fixation increased the flexural rigidity of bovine pericardium. Results of this study indicate that the flexural properties of bovine pericardium are dominated by inter-fiber cross-links as opposed to the stiffness of the collagen fibers themselves. These findings can be used to guide the development of novel chemical treatment methods that seek to optimize biomechanical properties of heterograft biomaterials.