User blog comment:Inferno Pendragon/World Building 1 : Tech Levels/@comment-1070010-20160302154645

Another technology I planned on introducing at some point were cybercytes- basically, nanomachines that functioned identically to human cells, but with all of the added strengths of being, well, machines. They don't decay or die, are temperature-resistant, physically tougher, etc.

The idea was that they were originally intended for prosthetics, organ-replacement, etc... but if they could be used to replace any part of the human body, then, theoretically, there could be an entire functioning human body built solely out of cybercytes.