Magnetic Microrobots Guide Stem Cells to Repair Spinal Cords in Mice and Zebrafish

Microscopic Robots Deliver Stem Cells Directly to Spinal Injuries

A team of researchers in Zurich has engineered tiny biohybrid devices that can transport therapeutic stem cells straight to a damaged spinal cord, using magnetic fields to guide and stimulate the cells.

Why Conventional Treatments Fall Short

Injuries to the spinal cord often lead to permanent loss of function because nerve cells rarely regenerate on their own and scar tissue blocks the growth of new fibers. Current approaches that rely on implanted electrodes to electrically stimulate stem cells face challenges such as invasive hardware and inconsistent cell survival.

Designing a Magnetically Guided Bio‑Robot

The scientists combined neural progenitor cells derived from induced pluripotent stem cells with specially engineered magnetoelectric nanoparticles. The nanoparticles feature an inner magnetic layer and an outer layer that converts magnetic activity into electrical signals. When merged with the progenitor cells, the resulting constructs—dubbed NPCbots—measure about six micrometres each.

Production occurs on a one‑square‑centimetre lab‑on‑chip platform. “We place a reservoir in the centre where we trap the cells, then we inject the nanoparticles and wait for the two components to bind,” says Professor Salvador Pané i Vidal of ETH Zurich’s Multi‑Scale Robotics Lab. Within thirty minutes the NPCbots are ready for deployment. Scaling up involves running multiple chips in parallel, allowing the team to generate hundreds of thousands of robots for cell‑based tests and several million for animal studies, according to senior scientist Hao Ye, the study’s first author.

Testing in Regenerative Fish Model

The team first evaluated the NPCbots in zebrafish larvae that had sustained spinal cord lesions. Microrobots were injected directly into the injury site, and external electromagnetic fields were applied. The fish regained near‑normal swimming and exploratory behaviour within three days. “Stephan Neuhauss and Jingjing Zang at the University of Zurich performed essential work that let us show how quickly cells differentiate using our method,” notes Professor Pané i Vidal.

Promising Results in Mammalian Subjects

In a separate experiment, mice with completely transected spinal cords received NPCbot injections. After twenty‑eight days, nerve fibers reconnected across the lesion, and the animals displayed marked improvements in gait, stride length, coordination and exploratory activity. Unlike the fish, the mouse spinal cord does not naturally regenerate, making the outcome particularly noteworthy. The treatment was well tolerated, with no detectable immune reactions.

How Magnetic Stimulation Drives Repair

The magnetoelectric nanoparticles translate the applied magnetic field into localized electrical impulses that accelerate stem‑cell differentiation. This eliminates the need for implanted electrodes, a critical advantage given the spinal cord’s sensitivity. Once the progenitor cells mature into neurons, the NPCbots dissolve within the tissue. Their barium titanate coating is expected to remain stable and minimally reactive, though future work will assess long‑term degradation or excretion pathways.

Next Steps Toward Clinical Translation

Before human trials can begin, researchers must identify the optimal magnetic field parameters and stimulation durations for patients. “We first need to test which magnetic fields work best in humans and determine the optimal stimulation duration,” says Hao Ye. The scalable lab‑on‑chip production method also suggests broader biomedical uses, ranging from cardiac repair to oncology and wound healing, according to Professor Pané i Vidal.