Magnetic screw robot drills through sheep brain tissue in lab tests

A magnet outside the body turns a tiny screw-shaped robot, and in laboratory tests the device has drilled through sheep brain tissue without a tether. Researchers from UT and Radboudumc also made it retrace the channel it had created, a small but concrete step toward reaching deep brain lesions without opening the skull.

The robot advances by spinning like a screw. The challenge is knowing when the tissue will make it lose the magnet’s command. That point, called the step-out frequency, arrives when the magnet turns faster than the robot can follow: the device slips, stalls or begins moving erratically.

The team’s model links the robot’s size and magnetic strength with the stiffness of the tissue. In soft tissue, the robot kept pace for roughly 30 rotations per second. In the stiffest tissue tested, that fell to less than one rotation per second. After one calibration measurement in tissue with known stiffness, the model predicted how the same robot design would behave in other tissues, and the researchers validated it across four designs in gelatin before testing real sheep brain tissue.

The biological setting made control harder. Without blood flow, the robot stayed synchronized with the magnet up to about 1.8 rotations per second. When blood was pumped through the vessels to mimic a living brain, the threshold dropped below 0.45 rotations per second. The robot drilled forward at 0.2 millimeters per second, then moved back through its existing channel at 2.9 millimeters per second, because it no longer had to cut a new path. In a soft gel model, camera tracking guided it to selected targets with accuracy of less than a millimeter in some trials.

And then what, concretely? The model could give engineers a clearer operating envelope before they test a robot in more complex tissue: how fast to spin the magnet and when the robot will lose synchronization. The researchers envision using the approach for clots after a stroke, tumors and vascular malformations deep in the brain, but the reported work is still a laboratory test in sheep tissue and gel—not a treatment in patients. The study was published in Advanced Science.