In a sterile Stanford lab, a tiny spinning tube with delicate fins whirred to life. The object, no larger than a grain of rice, might seem unassuming. But when placed in a model artery clogged with a blood clot, it performed something outstanding. Within seconds, the once-lethal blockage shrank to a fraction of its size. Blood flow, simulated with saline, resumed almost instantly.
This is the milli-spinner—a new mechanical device developed by researchers at Stanford University that could transform how doctors treat strokes and other deadly vascular blockages.
Thrombectomy 2.0
Every year, millions of people suffer strokes, heart attacks, and pulmonary embolisms due to blood clots. In ischemic strokes—the most common kind—a clot blocks blood flow to the brain. Every minute that passes without treatment kills about 2 million neurons.
Doctors can attempt to physically remove the clot using a technique called thrombectomy. But the tools at their disposal—tiny vacuums or mesh-like snares—often fall short. “Current technologies only successfully remove clots on the first try about 50% of the time,” said Dr. Jeremy Heit, co-author of the new study and chief of Neurointervention at Stanford. In tough cases, the failure rate can exceed 80%.
The milli-spinner offers a new approach. It doesn’t try to yank or tear the clot apart. Instead, it reshapes it, compressing and coiling the clot’s sticky threads until it’s compact enough to be suctioned out cleanly.
“For most cases, we’re more than doubling the efficacy of current technology,” Heit said. “And for the toughest clots—we’re only removing about 11% of the time with current devices—we’re getting the artery open on the first try 90% of the time. It’s unbelievable. This is a sea-change technology that will drastically improve our ability to help people.”
Clot Sculpting by Shear and Suction
At the heart of a blood clot is fibrin—a tough, web-like protein that tangles red blood cells into a sticky mass. Traditional thrombectomy devices stretch or rupture this network, risking the breakup of the clot and further blockages elsewhere.
“What’s unique about the milli-spinner is that it applies compression and shear forces to shrink the entire clot,” said Ruike Renee Zhao, a mechanical engineering professor at Stanford and senior author of the study published in Nature. “It works so well, for a wide range of clot compositions and sizes. Even for tough, fibrin-rich clots—which are impossible to treat with current technologies—our milli-spinner can treat them.”
The spinner enters the blood vessel through a catheter, just like existing tools. Once in place near the clot, it spins rapidly—up to 40,000 revolutions per minute. Slits and fins on the tube generate localized suction that gently presses the clot against its surface. Then, through spinning-induced shear, it compresses the fibrin fibers into a tight core—much like twirling loose cotton between your palms.
The red blood cells are released, the clot’s volume drops by up to 95%, and the dense fibrin ball is pulled into the spinner. “Honestly, it felt like magic,” Zhao said. “We didn’t fully understand the mechanism at the time.”
Medical Breakthrough
The discovery started from sheer exploration. Zhao’s lab designs “millirobots”—tiny, flexible devices that swim through the body to deliver medicine or perform diagnostics. While testing a new propulsion concept, the team noticed something strange: when the spinner touched a clot, it changed color and shrank.
That unexpected result sparked years of exploration, computational modeling, and design iteration. The team optimized the fins, added suction-enhancing slits, and tested the device in artificial arteries and eventually live animals.
In swine models, the milli-spinner removed clots in cerebral and renal arteries (vessels similar in size and complexity to those in the human brain) with near-perfect success. In more than 500 lab trials, including tortuous vessel models, the device achieved full revascularization nearly every time. In all cases where conventional treatment failed, the milli-spinner succeeded in rescuing the blocked artery.
The next step, of course, is to start human trials.
Clinical trials are expected to begin soon, with initial focus on stroke treatment. But Zhao believes the design has much broader potential. The spinner could help remove kidney stone fragments and there are even possibilities beyond medicine.
The work is supported by the Wu Tsai Neurosciences Institute, Stanford’s High Impact Technology Fund, and the National Institutes of Health. It’s also a reminder that curiosity, not just necessity, often drives the best medical breakthroughs.
If successful in human trials, the milli-spinner could rewrite the rules of thrombectomy—and offer new hope to millions affected by stroke and vascular disease.
