Cyborgs

A cyborg is a human or other life form who has been modified with machinery and metal for better functioning. These mechanical enhancements can include cybernetic replacements for missing organs or body parts, metal skin for extra protection, and weapons installed somewhere in the body.

Cyborgs in One Piece
In One Piece cyborgs are rare, as the technology required for their creation is somewhat advanced. Those who are cyborgs often have an advantage in battle, as they are more powerful than regular humans in both offense and defense.

Though they have mechanical parts, so long as their brain is not altered in any way, these cyborgs maintain their free will. As shown with Bartholomew Kuma, cyborgs with their brains modified lose their free will. This leaves them "dead", reducing them to being nothing more than a tool. It is also claimed by Doflamingo that such cyborgs have no memories or recollections of their past lives. Indeed, Kuma has become obedient to the words of the World Government he once hated so much. In an earlier instance when Nami hears a heartless remark from Franky she asks him if he replaced his heart to which he apologizes in metaphoric terms that he "never meant to go that far". This confirms Franky, unlike Kuma, has not lost his humanity.

List of Cyborgs

 * Franky - maintains humanity
 * Bartholomew Kuma - lost his humanity
 * Pacifista - never had humanity to begin with
 * Taroimo
 * Several inhabitants of Karakuri Island