NANOTECHNOLOGY UPDATE: This sounds promising:

Human bones can shatter in accidents, or they can disintegrate when ravaged by disease and time. But scientists may have a new weapon in the battle against forces that damage the human skeleton.

Carbon nanotubes, incredibly strong molecules just billionths of a meter wide, can function as scaffolds for bone regrowth, according to researchers led by Robert Haddon at the University of California at Riverside. They have found a way to create a stronger and safer frame than the artificial bone scaffolds currently in use.

This isn’t molecular manufacturing, of course, but it’s important early work.