[dmm]

JurijD:
Thanks, lots of good points.

The immune system certainly is a nuisance! (Not one I want to do without, though.) I think that you are right to be pessimistic about replacement parts that are anywhere close to the original equipment. But I think that some primitive stuff is not quite as far off as you imply. For instance, one expt on replacement retinas worked well enough for the patients to distinguish between circles and rectangles. They couldn't leave it in -- it was too big, and the immune system would have rejected it anyway. But it did show that interfacing to the optic nerve was sufficient -- you don't have to interface to the brain directly.

Repairing severed hands....always makes me think of the ST episode where McCoy suddenly loses his alien-machine-induced knowledge right in the middle of the operation to re-attach Spock's brain. "My God, Jim, there are millions of connections! Nobody can re-attach a brain!" But they are making progress with "scaffolding" that encourages various kinds of cells to grow.

Certainly you are right that the problem is not so simple as we often think.

dmm