Tiny robots guided stem cells. The severed spine healed.

A mouse with a completely severed spinal cord walked normally again after engineers at ETH Zurich treated it with stem cells steered by magnetic micro-robots, according to a study published in Nature Materials. The team built what they call NPCbots, combining therapeutic cells derived from a skin sample with nanoparticles that respond to magnetic fields and convert that response into electrical signals. The cells and particles fuse in about thirty minutes in a culture medium one square centimeter wide. Once injected, the particles can be guided to the exact site of injury and switched on to accelerate repair. After 28 days, the severed nerve cells at each end of the mouse's spinal column reconnected, and its gait and coordination steadily returned. The treatment caused no adverse reactions. Before any human trials, the researchers still need to answer a quieter question first. "We first need to test which magnetic fields work best in humans," said senior scientist Hao Ye.