Abstract
Collagen implants of dehydrated bovine pericardium have been developed as biodegradable materials for the surgical repair of cranial dura mater defects. However, the knowledge of the mechanical properties of the allograft is necessary to assess the reliability of the tissue reconstruction, since it is expected to withstand the functional loading in situ while the natural tissue heals. Tensile and stress-relaxation tests were performed on six rectangular samples of dehydrated bovine pericardium (DBP) graft (Tutogen Medical GmbH, Germany). In order to account for the anisotropic fiber architecture, the tests were run along two perpendicular directions of each graft, aligned to the sample edges. The stress-strain curves were non-linear, with fast stiffening at increasing strains. The stiffness in the transverse direction of the graft was only 1.5 times the one in the longitudinal direction, and for clinical purposes the xenograft can be considered as isotropic. The amount of stress relaxation was affected neither by the magnitude of the applied strain nor by the direction of stretching. The properties of the DBP were compared to the ones of native dura mater. Both the strength and the stiffness of cranial dura mater were well matched by the xenograft, but the graft material exhibited about twice the extensibility: the linear region of the stress-strain curve is attained at larger extension, although the slope of the curve in this region is similar to the native dura one. Pre-tensioning the graft in situ at surgery would reduce this slack strain; and therefore, improve compliance matching with the native tissue.