Quantification of the fiber architecture and biaxial mechanical behavior of porcine intestinal submucosa.

Porcine small intestinal submucosa (SIS) has been shown to serve as a remodelable tissue scaffold in a wide range of applications. Despite the large number of experimental studies, there is a lack of fundamental information on SIS anisotropic mechanical behavior and how this behavior changes postimplantation. As a first step in our study of remodeling biomaterials, we performed biaxial mechanical testing to quantify the anisotropic mechanical behavior and used small-angle light scattering (SALS) to quantify the gross fiber structure of fresh, unimplanted SIS. Structural results indicate that SIS displays primarily a single, continuous preferred fiber direction oriented parallel to the long axis of the intestine. Occasionally, two distinct fiber populations oriented at approximately +/-28 degrees with respect to the longitudinal axis could be distinguished. Consistent with this structure, SIS exhibited a nonlinear, anisotropic mechanical response with higher stresses along the longitudinal axis. Further, the circumferential stress-strain response was strongly affected by the maximum longitudinal strain level, but the maximum circumferential strain level only weakly affected the longitudinal stress-strain response. This asymmetric mechanical coupling suggests strong mechanical interactions on a fiber level. SIS stress-strain response also was similar to glutaraldehyde-treated bovine pericardium, attesting to the substantial strength of SIS in the fresh, untreated state. The results of this study will provide a basis for a future analysis of the structural and mechanical changes during the remodeling process.