  Micro motors that could run in liquid environment is very important for a
variety of practices such as serving as pipeline robot, soft machine, drug
delivery, or microfluidics system etc. However, fabrication of such tiny motors
is generally rather time and cost consumptive and has been a tough issue due to
involve too many complicated procedures and tools. Here, we show a
straightforward injectable way for spontaneously generating autonomously
running soft motors in large quantity. A basic fabrication strategy thus
enabled is established and illustrated. It was found that, injecting the GaIn
alloy pre-fueled with aluminum into electrolyte would automatically split in
seconds into tremendous droplet motors swiftly running here and there. The
driving force originated from the galvanic cell reaction among alloy, aluminum
and surrounding electrolyte which offers interior electricity and hydrogen gas
as motion power. This finding opens the possibility to develop injectable
tiny-robots, droplet machines or microfluidic elements. It also raised
important scientific issues regarding characterizing the complicated fluid
mechanics stimulated by the quick running of the soft metal droplet and the
gases it generated during the traveling.
