NEW YORK: Scientists have developed wirelessly powered bug-shaped robots that are able to walk, survive harsh environments, and are tiny enough to be injected through an ordinary hypodermic needle . The researchers at Cornell University in the US created a multistep nanofabrication technique that turns a four-inch specialised silicon wafer into a million microscopic robots in just weeks.Each 70 micron long -- about the width of a very thin human hair -- the robots' bodies are formed from a superthin rectangular skeleton of glass topped with a thin layer of silicon.In the layer, the researchers etch its electronics control components and either two or four silicon solar cells -- the rudimentary equivalent of a brain and organs."The really high-level explanation of how we make them is we are taking technology developed by the semiconductor industry and using it to make tiny robots," said Marc Miskin, who developed the nanofabrication techniques.Each of a robot 's four legs is formed from a bilayer of platinum and titanium, or alternately, graphene . The platinum is applied using atomic layer deposition."It's like painting with atoms," Miskin said in a statement.The platinum-titanium layer is then cut into each robot's four 100-atom-thick legs."The legs are super strong. Each robot carries a body that is 1,000 times thicker and weighs roughly 8,000 times more than each leg," he said.The researchers shine a laser on one of a robot's solar cells to power it.This causes the platinum in the leg to expand, while the titanium remains rigid in turn, causing the limb to bend.The robot's gait is generated because each solar cell causes the alternate contraction or relaxing of the front or back legs.The current laser power source would limit the robot's control to a fingernail-width into tissue, researchers said.Miskin is thinking about new energy sources, including ultrasound and magnetic fields, that would enable these robots to make incredible journeys in the human body for missions such as drug delivery or mapping the brain.