Mice with completely severed spinal cords. Six-micrometre stem-cell microrobots steered in by magnetic field, then stimulated wirelessly. 28 days later, nerve cells reconnected at the lesion and gait improved.

This is one of the more exciting things I've read in regenerative medicine this year. ETH Zurich built microrobots, each one a human stem cell paired with a magnetoelectric nanoparticle, about six micrometres across. An external magnetic field steers it to a spinal cord injury, then a second field switches it on wirelessly so the cell turns into neurons. It needs no implanted electrodes or cables, which is what the older stimulation methods relied on.

In mice with completely severed cords, which don't regenerate on their own, nerve cells reconnected at the injury after 28 days and the animals moved close to normally again. The treatment was well tolerated, with no adverse effects or immune reaction. In zebrafish the recovery was even faster: near-normal swimming within three days.

It's also built to scale. The bots are made on a lab-on-a-chip in about thirty minutes, the particles are designed to dissolve into the tissue once they've done the work, and the same platform could one day carry stem cells for things like cardiology or wound healing.

Out now in Nature Materials. It's early and these are animal models, but the direction looks real.