TECH – Researchers at ETH Zurich have engineered microscopic robots — less than two millimetres wide — that can be guided through blood vessels to deliver targeted medications, including treatments to dissolve stroke-causing clots. The development marks a significant advance in precision medicine, combining magnetic navigation, biocompatible materials, and controlled drug release.
The microrobot is structured around a spherical gel capsule that holds the therapeutic compound. Embedded in this gel are iron-oxide nanoparticles, which respond to externally applied magnetic fields. This design makes the capsule controllable even in fast-flowing blood, enabling it to reach regions deep in the brain’s vascular network. Once at its destination, a high-frequency magnetic field heats the nanoparticles, causing the gel shell to dissolve and release the drug precisely where it is needed.
To navigate complex vessel architectures, the team developed a three-strategy magnetic steering system. One mode uses a rotating magnetic field to roll the capsule along vessel walls, another applies a magnetic-gradient pull that lets the microrobot move even against blood flow, and a third method steers it through branch points by directing the field against the vessel wall. In head artery conditions, the robot can travel at speeds up to 4 millimetres per second — a notable achievement given the strong currents and confined spaces.
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The researchers further included tantalum nanoparticles to make the microrobot visible under X-ray imaging, which enables real-time tracking during its journey. This feature helps clinicians monitor and confirm where the drug payload is delivered, boosting both the safety and effectiveness of the therapy.
In animal trials, the microrobots have been successfully deployed through realistic vessel models as well as in large-animal testing: ETH Zurich confirmed they worked reliably in pigs’ vessels and even within the cerebrospinal fluid of sheep. These tests showed that the system could reliably steer, release medication and dissolve without causing damage.
The innovation has particular implications for stroke treatment. Traditional therapies often require high systemic doses of clot-dissolving drugs, which carry risk of side effects like internal bleeding. By delivering medication only to the clot site, the microrobots promise to reduce side effects significantly while maintaining efficacy.
