A new material derived from pig's intestines could be the basis of an improved treatment for knee injuries. The material, called SIS (small-intestinal submucosa), is derived from the middle layers of the small intestine of pigs. When disinfected and processed into forms such as tubes, sheets, or fibers, the material becomes a scaffold for the regeneration of damaged tissues, such as torn ligaments or tendons. The result is a new ligament-like structure of collagen infiltrated with cells that strengthens over time. SIS is anchored to bones through small holes drilled for the purpose. The material was developed through a partnership between Purdue University, West Lafayette Ind. and DePuy Orthopaedics Inc., Warsaw, Ind. The company began Phase I clinical trials in December. The first 12 surgeries will be carried out at Valley Presbyterian Hospital in Van Nuys, Calif. and Aspen Valley Hospital in Aspen, Colo.