Since 1995, strategies have been developed to treat animal tissues to prevent immunogenic and inflammatory responses after human implantation.  These tissues do not contain living cells but the natural structure of the tissue fibers are preseved and remain intact.  After implantation, the tissues maintain functional strength for long periods without eliciting a breakdown process.  This allows a very slow infiltration of host cells into the tissues so intergration and rebuilding can take place.  Eventually, the infiltrated host cells convert the implanted material into a living tissue indistinguishable from the recipient's own tissue.