Extensive experiments were required on rats in preparation for the current rabbit penis triumph. In 90 rats, Atala’s team surgically cut the cavernosal nerves which are the two bundles of nerves innervating the penis. They then implanted either a graft of the rats’ own nerves or a graft made from collagen. Follow-up studies three months later showed that the rats’ own nerve cells had regenerated and infiltrated the collagen “scaffolding” material. “We used the body’s own healing abilities to create the tissue,” Atala said. The degree of nerve regeneration with the collagen grafts was equal to both the normal, undamaged nerves and the grafts consisting of the rats’ own nerves.