The Importance of Cyborg Engineering
There's one very crucial hurdle to implanting artificial components and replacement parts into the human body: how to integrate implants with living tissue at the smallest scales. One could make a good argument that it is this barrier, over and above anything else, that has prevented advances in prosthetic replacements to match advances in materials science. All barriers fall eventually, however: "scientists describe how they took an elastic scaffold (the material that gives the artificial graft its shape) of compliant poly(carbonate-urea)urethane and incorporated human vascular smooth muscle cells and epithelial cells from umbilical cords. Then they took the artificial grafts and simulated blood flow in the laboratory to test their durability. They found that as the pulsing fluid flow slowly increased, the artificial graft's performance actually improved. ... The notion that any body part could be engineered in a lab, attach to existing tissue 'naturally,' and grow stronger as it is being used is something thought completely impossible just 20 years ago. It is only a matter of time before human tissues can be engineered to be at least as good as the originals, and this study moves us toward that reality." Prosthetics might still give tissue engineering a run for its money when it comes to building replacement organs.
Link: http://www.eurekalert.org/pub_releases/2008-06/foas-sd060308.php