Researchers at ETH Zurich developed tiny, magnetically steerable gel capsules that deliver clot‑dissolving drugs directly to stroke-causing blockages. The beads contain iron oxide for magnetic control and tantalum for X‑ray visibility, and they dissolve after releasing medication. Bench and animal tests showed reliable steering through vessel models and 95% target accuracy in pigs, suggesting the approach could lower systemic drug doses and reduce bleeding risks, though human trials are still required.
Tiny Magnetic Beads Steered Through Blood to Deliver Clot‑Busting Drugs for Stroke
Researchers at ETH Zurich developed tiny, magnetically steerable gel capsules that deliver clot‑dissolving drugs directly to stroke-causing blockages. The beads contain iron oxide for magnetic control and tantalum for X‑ray visibility, and they dissolve after releasing medication. Bench and animal tests showed reliable steering through vessel models and 95% target accuracy in pigs, suggesting the approach could lower systemic drug doses and reduce bleeding risks, though human trials are still required.
07:48 AM, 11/14/2025Health
Tiny magnetic beads steered through blood to treat strokes
Researchers at ETH Zurich have developed microscopic, magnetically steerable gel capsules designed to deliver clot‑dissolving drugs directly to blocked vessels in the brain. These spherical delivery agents are not autonomous robots in the traditional sense; they are tiny, soluble beads loaded with thrombolytic medication and a small amount of radioactive tracer so clinicians can image and track their progress.
How the beads work
The capsules contain iron oxide nanoparticles that make them responsive to external magnetic fields, and tantalum nanoparticles to make them visible on X‑ray imaging. The gel is degradable, so after the capsule reaches its target and releases its payload, it dissolves.
"The vessels in the human brain are extremely small, so the capsule must be tiny. The technical hurdle was ensuring such a small capsule still has adequate magnetic properties," said Fabian Landers, a robotics researcher and coauthor of the study.
Magnetic navigation strategies
Controlling a microrobotic bead through the circulatory system is challenging because blood flow speed varies widely by location. The team combined three complementary magnetic control strategies to navigate the head's vascular network reliably. Using a rotating magnetic field, they could propel and steer capsules precisely at speeds up to 4 millimetres per second. In another configuration, a shifting magnetic field gradient pulled the bead along the stronger field direction, allowing it to move even against blood flow; in some trials the device reached velocities as high as 20 centimetres per second.
"Magnetic fields and their gradients are ideal for minimally invasive procedures because they penetrate deeply into tissue and—at the strengths and frequencies we use—do not harm the body," said microrobotics expert Bradley Nelson, coauthor of the study.
Testing and results
Initial bench tests used silicone models of human and animal blood vessels. The microrobot was deployed from a catheter that includes an internal guidewire and a polymer gripper to release the capsule. After encouraging bench results, the team progressed to animal trials. In pig experiments the microrobot delivered thrombolytic medication to the intended target in 95% of scenarios. The approach also performed well in trials involving sheep cerebrospinal fluid, suggesting potential applications beyond stroke therapy.
Potential benefits and limitations
By focusing drug delivery directly at a clot, this technology could reduce the systemic doses currently required and lower the risk of serious side effects such as internal bleeding. However, more testing is needed to confirm safety and effectiveness in humans, to scale manufacturing, and to integrate real‑time imaging and clinical workflows. The complexity of human vascular anatomy and variability in blood flow will require further optimization and regulatory evaluation before clinical use.
Next steps: larger preclinical safety studies, refined imaging and control systems, and eventual clinical trials to evaluate efficacy and safety in people with ischemic stroke.