Ironically enough, while the Jedi only had marginal success in finding any connection between the Force and droids, mostly through the observation of the instinctual tendencies some Jedi such as Cay Qel-Droma and Anakin Solo exhibited toward fixing machinery, the first real proof of a correlation between the Force and droids came from the Sith. It is believed that through their bizarre alchemies, the Sith somehow stumbled upon the ability to manipulate mechanicals of complex nature through the Force: ships, computers, and, indeed, even droids. This power, known as mechu-deru, was responsible for the creation of Belia Darzu's infamous Technobeasts, which were capable of rewriting an organism's entire genetic code.
Needless to say, the idea that droids could only be touched by the Force through dark magicks discouraged the majority of Jedi from further researching the issue. It also didn't help that 'borgs -- sentients that had been fitted with extensive prosthetics or cybernetic enhancements -- such as the Clone Wars veteran Kligson and the bounty hunter Gorm the Dissolver, often exhibited explicitly deviant social behaviors. It was also a matter of record that Force-sensitive "cybered" beings generally demonstrated added difficulty in accessing the light side of the Force, at least initially, and often demonstrated a greater susceptibility to the dark side. Many a Jedi, including Even Piell and Tenel Ka, in part rejected prosthetics for these reasons. Doctors and Jedi Masters postulated that cybernetics made one "less human," reducing a person's empathy, but the accuracy of this theory was plagued by the gaps that persist in A.S. understanding, not to mention the omnipresence of droid prejudice. Certainly, great Jedi like King Empatojayos Brand and Daye Azur-Jamin would have much to say against this accusation of reduced humanity -- both lost more than half their organic selves, but a more just monarch and conscientious man are not easily found.
2. New Advances
Many things changed with the coming of Palpatine's New Order, to put it mildly, among them the Jedi taboo against researching the connection between the Force and mechanicals. The Emperor needed tools, tools that could be used to locate and detain the Jedi. Many Jedi had long maintained that the Force could not be empirically measured, nor synthetically manufactured. They were in a sense quite wrong, and this proved detrimental, as the effects of the Jedi Purge show. Perhaps because they could not see the Force, Palpatine's scientists could not be blinded by its wondrous light. They dissected the Force, treating it not as a supernatural phenomenon, but reducing it to its mere physical components: midi-chlorians and energy. With the morality of light and darkness no longer at issue, a cadre of Palpatine's super-scientists that included Umak Leth, Borborygmus Gog, and Lord Cronal sought to bridge the gap between technology and the Force with an aggression and reckless abandon never before applied. The result was three of the instruments most dreaded by the Jedi: the Essence Stealer, the Universal Energy Cage, and the Force Detector.
Procuring a Ssi-ruuvi battle droid vessel at an exorbitant price from rare ship collector Raith Sienar, Borborygmus Gog feverishly worked to discover the secrets of Ssi-ruuvi entechment -- a process by which a being's life-force could be stripped from his or her body and transferred to a mechanical construct (for the Ssi-ruuk, typically a droid ship). Gog succeeded in creating a soul-stealing machine able to rip the life-essence from a being and contain it within a giant computer-linked crystal matrix, while the comatose bodies were put in cryostasis in adjacent transparisteel containers. Setting the machine up within the old Jedi library on the abandoned Nespis VIII space station, Gog had hoped to trap the spirit of a Jedi for study. Yet, while his machine ensnared many life-forces, Gog was unable to capture a Force-sensitive, or at least not for long -- the Jedi he caught invariably willed themselves to die rather than partake in the evil experiment. No matter. Jedi philosophers had long stated that the Force was generated by all living things to a greater or lesser degree, and the Emperor's scientists found this to be true of the life-forces they captured.
The Essence Stealer was eventually destroyed during the Rebellion by the young Zak and Tash Arranda, who went on to become great Jedi in their own right. The freed spirits returned to their bodies if they were still preserved, and the rest went on to become one with the Force. It is suspected, however, that this particular machine was but one of several that were set up by Gog.
Building on the work of the demented researcher Jenna Zan Arbor, the scientists were able to study the trapped spirits endlessly, harnessing the energy field they created, and testing it. Its power was incredible. No energy source could rival it. A curiosity they did notice was the relation between the field and the incredibly durable Mandalorian iron: they found that the metal could not be affected by the Force energy field, this effect peculiar only to iron from Mandalore and not "normal" iron. The scientists mistakenly believed then that this odd iron could actually suppress the Force energy field. This proved untrue, though the metal did make for effective Jedi containment devices, as seen with Imperial Dungeon ships and Mandalorian handcuffs. However, it is suspected that the ysalamiri of Myrkr, creatures known for their ability to dampen the Force, could owe their unique gift to their ability to process the great quantities of Mandalorian iron to be found in the trees that serve as both home and nutrition for the creatures. It is suspected that the trees were transplanted at some point from Mandalore.