Precisely which kind, and what it must do, remains unknown and unstated, for both good and bad reasons.
Biotechnology counts as one kind of nanotechnology, and at present remains by far the most advanced.
However one major idea, that future biotechnology will prove unable to carry out many repairs needed because it cannot work at cryogenic temperatures, has remained almost a premise in speculations about repair. Regarded coolly, the latter possibility seems unlikely. The basic point raised by this article is that enzymes can also work in solvents other than water. Not only can they work, but some industrial uses for enzymes in non-water, organic solvents already exist. Yes, so far these enzymes are less active in such solvents than in water, but they can still be many orders of magnitude more active than other catalysts.