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“The field of microrobotics has really matured over the past two to three decades. Suddenly, we have these sci-fi technologies. They’re here. It’s exciting.”
– Fabian Landers, PhD, Multi-Scale Robotics Lab, ETH Zurich
Researchers at ETH Zurich, a Swiss university, have designed a new method of targeted drug delivery using microrobotics. Call it a magic bullet. The microbot itself is elegantly simple: a spherical capsule, roughly the size of a grain of sand. It’s made of a dissolvable gel and iron oxide nanoparticles, and can carry a pharmaceutical drug dose.
After being injected into the bloodstream (or cerebrospinal fluid) via an insertion catheter, the robot is guided by magnets—thanks to that iron oxide—to its destination within the body. A high-frequency magnetic field then dissolves the gel and the microrobot, delivering the drug precisely where it’s needed.
The method may be elegant, but the conditions it operates in are complex: the neurovascular system is an intricate three-dimensional maze with many forked pathways; blood can flow at different speeds in different places; and this very small microbot needs to be guided with total accuracy, sometimes against the flow of current.
For visibility, the microrobot includes nanoparticles of tantalum (named after a thieving Greek deity whose name and fate form the root of the word tantalize), which are radiopaque and thus trackable via X-ray as it moves through the vessels.
The researchers have developed three modes of navigating the microrobot to its target, and these modes can be switched between depending on the context. Wall-rolling literally rolls the capsule along the blood vessel wall using a rotating magnetic field. Magnetic field-gradient pulling uses a spatial magnetic gradient to pull the capsule, allowing it to travel against the flow of blood. And at bifurcations where steering is difficult—the vessel branching in different directions—in-flow navigation angles the gradient towards the vessel wall, using the natural current of blood flow to maneuver the capsule down the desired path.
By integrating these three navigation strategies, the researchers have gained effective control over the microrobots across various flow conditions and anatomical scenarios. So far, it’s been used in highly detailed silicone models, several pigs, and the brain of a sheep. In more than 95 percent of cases, the capsule has successfully delivered the drug to the correct location. The microbot’s precision in drug delivery could drastically reduce the side effects of traditional treatments, improve efficacy, and enable treatment of patients with previously incurable diseases.
Meet the Expert: Fabian Landers, PhD
Dr. Fabian Landers is a postdoctoral researcher at the Multi-Scale Robotics Lab (MSRL) at ETH Zurich. His work focuses on the design, fabrication, and control of small-scale robotic platforms capable of navigating complex physiological environments—such as the bloodstream—to deliver therapeutics with high precision and minimal systemic side effects
Dr. Landers earned both his BSc and MSc in mechanical engineering at ETH Zurich. For his master’s thesis, he joined the Harvard Microrobotics Laboratory, where he developed electroadhesive devices that allowed small-scale robots to walk and climb on inclined and vertical surfaces. At ETH Zurich, his contributions have been central to recent breakthroughs in microrobot-mediated drug delivery, demonstrating controlled navigation and targeted release in realistic vascular models and large-animal tests.
The Origins of the Magic Bullet
“The idea of targeted drug delivery is probably 25 to 30 years old, and even more if you look back to Paul Ehrlich, who pioneered the concept of a magic bullet,” Dr. Landers says.
In the early 1900s, Paul Ehrlich, a Nobel-winning German physician and scientist, proposed the idea of a Zauberkugel, or magic bullet, a therapeutic agent that selectively destroyed disease-causing cells while leaving healthy tissue unharmed. While Ehrlich thought in molecular terms—and it helped launch the modern fields of chemotherapy and immunology—microrobotics has provided a new kind of magic bullet.
“I would say in the early 2000s, the idea of doing targeted drug delivery with robots inside your body was born,” Dr. Landers says. “Not counting Fantastic Voyage from the 1980s, where they had a tiny submarine going into someone’s blood vessels.”
Building on work by colleagues in the lab and the community, Dr. Landers’ project began in 2020, with funding from Horizon Europe, the EU’s research and innovation funding program.
“Just the capsule itself took us about six years to figure out,” Dr. Landers says. “There were a lot of design choices that seemed obvious in retrospect but required deep understanding at the time: how to overcome a certain flow, or how exactly to move your magnetic field in order to get propulsion.”
Dr. Landers and his colleagues have very tight control over how large the microbot can be. The perfect size depends on what it’s being used for: pigs have a slightly larger vessel diameter than humans, so a slightly larger capsule is needed; for humans, going into the distal vasculature, smaller capsules are better. But the capsule can’t be smaller than one that researchers (and clinicians) can see.
“The limit has more to do with imaging than fabrication,” Dr. Landers says. “Around 0.3mm to 0.5mm, you can’t go much smaller—not because it can’t be made or steered, but because it couldn’t be seen as easily.”
An Interdisciplinary Concert
Rather than a Newtonian apple falling on anyone’s head, Dr. Landers attributes the success of the project to a confluence of innovation across several different domains. His own career has taken him to Taiwan, Harvard, and now Switzerland—through specializations (and fascinations) with small-scale systems, robotics, and medicine. Advances across multiple research areas have unlocked innovation that can translate into clinical settings.
“It’s so interdisciplinary,” Dr. Landers says. “You have medicine, material science, robotics, mechanical, and electrical engineering. Only if you get all these aspects together are you really able to make a project like this happen.”
Dr. Landers and his team studied up on anatomy, learning about flow speeds and arterial architecture, and received feedback from doctors—many ‘just across the street’ at the University Hospital in Zurich—who support the microbot project.
“Every now and then, we get the opportunity to join for operations and interventions,” Dr. Landers says. “It’s very good for us, because we get to see the workflows, we get to see how they do things. There’s a huge difference between theory and practice.”
The microrobots were first tested on silicone models that accurately replicate the vessels of humans and animals. Worthy of an art gallery, they look like blocks of clear ice, with squiggling arterial chambers drilled into them (they’re actually 3D-printed). They are the team’s own design: nothing like them existed on the market previously. Based on CT and MRI scans—real human data—they enabled the researchers to test the microbot in a realistic setting.
“It’s very impressive what the body can do,” Dr. Landers says. “In order to navigate these types of environments, we needed to replicate the process in vitro—outside of an animal or human body—to study the flow kinetics,” Dr. Landers says.
In fact, they’re so realistic that they’re now being used in medical training, supplied through Swiss Vascular, an ETH Zurich spin-off.
“We never actually planned on selling them until we were approached by doctors who asked if they could buy them,” Dr. Landers says. “We gave one out for free, and when more requests came in, we incorporated a small company to market these models.”
After numerous successes on silicone models, the team moved on to animals. First, they demonstrated on pigs that all three navigation methods work, with the microrobot remaining visible throughout the procedure. Next, they navigated through the cerebral fluid of a sheep. Now they’re eyeing human trials.
“What really drives us now is we want to see this technology in the hospital,” Dr. Landers says. “We want to help patients. That’s the biggest goal we have.”
A Positive Feedback Loop of Development
From a technological standpoint, optimizations are still needed—but that’s what Dr. Landers and his team are best at. In going to human trials, the top challenge is regulatory (and, relatedly, financial). This microbot delivery system is an entirely new process, a new way of treating disease, and regulators will have lots of specific questions about how it will be used. So far, researchers have loaded the microcapsule with three common drugs: a thrombus-dissolving agent (for stroke patients), an antibiotic, and a tumor medication.
“We’re analyzing where we can have the biggest impact, and then we can find a regulatory pathway,” Dr. Landers says. “We also need a good business case, because without one, this will not make it into a hospital.”
Dr. Landers and his team are looking to spin off a company this year, then engage with regulatory bodies to understand what’s necessary to bring a product to market. Realistically, it’ll take years, but the team is very committed.
“There’s been a lot of investment in these technologies,” Dr. Landers says. “This is 20 years of research that has been mostly publicly funded. It’s really important to make sure this benefits the society that paid for it. We don’t want this to just end up in a box somewhere.”
Looking towards the horizon, there are many more opportunities for microbots beyond this particular bloodstream capsule. It makes sense to miniaturize the medical approach, to treat from within—and this is only the start. For most of medical history, applications like this one have not been possible, but more will soon become a reality.
“As we look to the future, we’ll have more precedents of these types of systems coming to market,” Dr. Landers says. “I think that will kick off even more development.”
For students interested in microrobotics, the future is bright. But it’s also interdisciplinary: one’s domain of expertise, within the natural sciences, is less important than one’s commitment to curiosity and collaboration. Scientists, physicists, engineers, computer scientists, medical doctors, toxicologists, and even business specialists are needed to help bring about the next breakthroughs.
“The people who make a difference are the people who are ready to push,” Dr. Landers says. “And you’re only ready to push if you really like what you’re doing. I know this sounds like your parents, but it makes sense to follow your passion. It will keep you motivated. You’ll be ready for night shifts. You’ll be excited when you go to work—because it won’t feel like work. It’s a positive feedback loop: you just get better and better.”
The Not-So-Tiny Future of Medical Microrobotics
The immediate future remains on the drug delivery side: its elegant, singular functionality makes it easier to integrate into the medical world. But looking further ahead, microrobotics will become a much larger part of medical practice: already assisting in certain surgeries, it may soon include swarms of small robots swimming through the body, constantly patrolling, looking for cancerous cells. Everything is being rethought.
As robotics, AI, and automation are increasingly integrated into doctors’ workflows, magnetic navigation has a host of applications. Magnetic fields can penetrate the human body and manipulate from within, without the need for an entry wound. Another ETH Zurich spin-off, Nanoflex Robotics, makes guide wires that can be manipulated magnetically.
In thrombectomies (where a patient has had a stroke and needs the blood clot—the thrombus—removed), a speedy and accurate intervention is key. These magnetic guidewires can be navigated more easily and more effectively than the traditional method. Hooked up to telerobotics, they can be performed without the physician and patient being in the same place
“There’s so much cool stuff coming,” Dr. Landers says. “The field of microrobotics has really matured over the past two to three decades. Suddenly, we have these sci-fi technologies. They’re here. It’s exciting.”
