Every year, millions of lives are tragically cut short or forever altered by strokes. But what if we could deliver life-saving medication directly to the source of the problem, minimizing harm and maximizing impact? This is the groundbreaking promise of magnetic microrobots, a revolutionary advancement in medical technology. Currently, the standard treatment for strokes involves administering drugs to dissolve blood clots, or thrombi, that block blood vessels. However, these drugs circulate throughout the entire body, necessitating high doses to reach the affected area. This approach can lead to serious side effects, such as internal bleeding. The quest for a more precise method has driven medical researchers to explore the potential of microrobots to deliver pharmaceuticals directly to the site of the stroke. And now, a team of researchers at ETH Zurich has achieved major breakthroughs, publishing their findings in the journal Science.
The key to this innovation lies in precision. The researchers' microrobot is a spherical capsule made from a soluble gel shell, controlled by magnets and guided through the body to its destination. This capsule contains iron oxide nanoparticles, which provide the magnetic properties necessary for navigation. But here's where it gets technically challenging: the vessels in the human brain are incredibly small, limiting the size of the capsule. Ensuring that such a tiny capsule possesses sufficient magnetic properties is a significant hurdle. As study lead author and postdoctoral researcher Fabian Landers explains, "Because the vessels in the human brain are so small, there is a limit to how big the capsule can be. The technical challenge is to ensure that a capsule this small also has sufficient magnetic properties."
To track the microrobots' journey, doctors need a contrast agent, and the researchers focused on tantalum nanoparticles. While commonly used in medicine, these are more challenging to control due to their density and weight. Professor Bradley Nelson, who has been researching microrobots for decades, emphasizes the complexity, stating that "Combining magnetic functionality, imaging visibility and precise control in a single microrobot required perfect synergy between materials science and robotics engineering, which has taken us many years to successfully achieve." Professor Salvador Pané and his team developed precision iron oxide nanoparticles to overcome this challenge.
The microrobots are designed to carry the active ingredient, such as a thrombus-dissolving agent, an antibiotic, or a tumour medication. These drugs are released via a high-frequency magnetic field that heats the magnetic nanoparticles, dissolving the gel shell. The researchers employ a two-step strategy: First, the microrobot is injected into the bloodstream or cerebrospinal fluid via a catheter. Then, an electromagnetic navigation system guides it to the target location. The catheter design is based on a commercially available model, with a flexible polymer gripper to release the microrobot.
Navigating the complex maze of blood vessels presents another significant challenge. The speed of blood flow varies greatly depending on the location, making navigation incredibly complex. The researchers developed a modular electromagnetic navigation system suitable for operating theatres. They combined three different magnetic navigation strategies to navigate all regions of the head's arteries. One method involves rolling the capsule along the vessel wall using a rotating magnetic field, enabling precise guidance at a speed of 4 millimeters per second. In another approach, a magnetic field gradient pulls the microrobot towards the stronger field, even allowing it to go against the current, at a flow velocity of over 20 centimetres per second. As Landers points out, "It's remarkable how much blood flows through our vessels and at such high speed. Our navigation system must be able to withstand all of that."
To handle vessel junctions, the researchers use in-flow navigation, directing the magnetic gradient against the vessel wall to guide the capsule into the correct vessel. By integrating these three strategies, the researchers achieved effective control over the microrobots across various flow conditions. In over 95% of the tested cases, the drug was successfully delivered to the correct location. Nelson explains that magnetic fields and gradients are ideal for minimally invasive procedures because they penetrate deep into the body and have no detrimental effect.
The innovation extends beyond the robotics themselves. To test the microrobots in a realistic environment, the researchers developed silicone models that accurately replicate patient and animal vessels. These models are now used in medical training and are marketed by the ETH spin-off Swiss Vascular. Pané notes that these models are crucial for optimizing the strategy and its components. The team successfully targeted and dissolved a blood clot in the model. After successful trials in the model, the team demonstrated the microrobot's capabilities under real clinical conditions in pigs and sheep. Landers is particularly excited about the microrobot's ability to navigate the cerebral fluid of a sheep, opening up possibilities for further therapeutic interventions.
The applications of these microrobots extend beyond stroke treatment. They could also be used for localized infections or tumours. The research team's goal is to ensure that their creations are ready for operating theatres as soon as possible, with human clinical trials planned for the near future. Landers sums up the team's motivation: "Doctors are already doing an incredible job in hospitals. What drives us is the knowledge that we have a technology that enables us to help patients faster and more effectively and to give them new hope through innovative therapies."
What are your thoughts on this groundbreaking technology? Do you believe that this approach represents a significant step forward in medical treatment? Share your opinions and questions in the comments below!
Source:
Journal reference:
Landers, F. C., et al. (2025). Clinically ready magnetic microrobots for targeted therapies. Science.DOI:10.1126/science.adx1708.https://www.science.org/doi/10.1126/science.adx1708.
