The mechanical properties of porcine small-intestinal submucosa as a vascular graft biomaterial

Each year, hundreds of thousands of small-diameter, arterial graft procedures are performed in the United States. While the autogenous saphenous vein is presently the only acceptable material for these procedures, many patients do not have suitable saphenous veins to transplant. Therefore, an acute need exists for a new biomaterial to aid these patients. Small-intestinal submucosa (SIS) is able to withstand the stresses of arterial blood pressure while stimulating the host to fashion a new vascular conduit in its place. The studies contained herein describe the mechanical properties of SIS--specifically, porosity, circumferential stress-strain, and changes which occur in these properties after implantation. Porosity of a graft material is thought to be very important in the host incorporation process. Specimens of SIS were porosity tested with a typical result of 0.52 ml/min/cm$\sp2$, which is much higher than polytetrafluoroethylene grafts and much lower than polyester grafts. The circumferential stress-strain curve for SIS is useful in predicting its performance in specific applications and was determined using pressurized air or water while measuring the outer diameter. This curve is a nonlinear, sigmoid shape which ends with burst at an approximate stress of 5.25 MPa, but the ultimate stress is source dependent with larger pigs producing stronger SIS. The sterilization methods of glutaraldehyde, peracetic acid, and gamma irradiation all decreased the strength of SIS, but the last study described herein proves that peracetic acid sterilized SIS is sufficiently strong to serve as an infrarenal aortic graft in the dog. Sterilized SIS grafts placed in this aortic position in dogs for 1 or 2 months transformed into new vascular conduits. The wall thickness of the grafts increased to over 1 mm from an original thickness of only 0.1 mm, and the overall strength of the 2-month graft explants was greater than that of the natural aorta. The overall stiffness of the graft explants and immunocyto-chemical staining show that a portion of the original SIS remains in the grafts at this time. Porcine SIS is a promising new biomaterial for vascular graft applications, and these studies provide new information concerning this material. SIS has a porosity that is suitable for rapid host incorporation, and a strength after peracetic acid sterilization that is sufficient for use in the infrarenal aortic position. Because of its remodelling characteristics, SIS is not only a potential alternative to autogenous saphenous vein but perhaps a general biomaterial for many soft tissue replacement applications