Microcatheters are medical devices that can snake through the body’s blood vessels to deliver lifesaving therapies—for example to treat clogged arteries, or to stop bleeding. They can also be used to cut off blood flow to a tumor or deliver highly targeted chemotherapy.

Until now, interventional neuroradiologists have used guidewires to painstakingly ease microcatheters around blood vessels’ tortuous twists and turns using a time-consuming push-pull-torque technique, which risks damage to vessel walls. But even these instruments are too large to reach the furthest and most highly branched blood vessels in the brain, which can be smaller than 150 microns in diameter—about the size of a human hair.