Key points from article :
Tt's been difficult to make microscopic robot move by themselves partly because of a lack of micrometre-scale actuators.
UoP has developed a new type of actuator made of an extremely thin layer of platinum.
Each robot uses four of them, connected to solar cells on its back.
The robots are smaller than a tenth of a millimetre and is only visible under a microscope.
Enable the legs to bend in response to laser light and propel their square metallic bodies forwards.
Movement directed by hitting the solar cells in sequence with a laser.
Team mass-produced more than a million of the microrobots using a process similar to creating circuit boards.
The next step will be to incorporate additional functions, e.g. sensing capabilities, programmability.
They are small enough to be injected through a hypodermic needle and are made from biocompatible materials.
Could potentially be developed to roam inside the human body.
Research by University of Pennsylvania published in Nature.