Nanotechnology has transformed medicine through nanoparticles and liposomes, but the next frontier lies in microrobots – tiny devices that can navigate the body’s most intricate spaces. Professor Alain Astier examines how innovations in design and materials are unlocking their potential to deliver precise, side effect-reducing therapies, while traversing ongoing ethical and regulatory challenges around this novel drug delivery method.
The field of medicine continually pursues innovations in drug delivery that enhance precision while minimising side effects. Traditional systemic drug administration can suffer from poor specificity, leading to significant off-target effects. Similarly, conventional surgical techniques can be invasive, risky and resource intensive.
For decades, researchers have utilised nanotechnologies in medicine, particularly by developing nanovectors such as nanoparticles and liposomes, which now play a pivotal role in numerous therapeutic areas.
Recent advances in microfabrication, material science and robotics have converged to create microrobots that can navigate complex biological environments and perform therapeutic tasks with great accuracy.1,2
Microrobots, operating at scales comparable to cells and microorganisms – typically 1-100 µm – are poised to revolutionise medicine. Their integration into targeted therapeutics holds promise for the future, offering minimally invasive treatment options that combine diagnosis, therapy and monitoring in a single platform.
Principles of microrobot design
Microrobot design requires a careful balance of size, biocompatibility, propulsion and control.
A microrobot typically comprises a specialised payload compartment for therapeutic agents, a propulsion system and a fuel source. Stimuli-responsive mechanisms of propulsion allow controlled navigation and local, precise drug release.
Magnetic actuation remains the most widely used method of propulsion, exploiting external magnetic fields to enable wireless control; magnetic microrobots can be precisely navigated through blood vessels, cerebrospinal fluid and other tissues.3,4
Acoustic propulsion is a method particularly suitable for deep tissue penetration.5 It employs ultrasound-driven microstreaming to drive the microrobots. Optical actuation offers high precision through light-controlled microrobots; however, its limited tissue penetration depth constrains its use.
More recently, biohybrid propulsion, harnessing living microorganisms such as bacteria or sperm cells as carriers, has emerged. This approach combines the cells’ natural motility with engineered drug payloads.6
Material selection is equally critical. Biodegradable polymers, hydrogels and biocompatible metals reduce toxicity and allow microrobots to degrade safely after completing their task. Some designs incorporate stimuli-responsive materials that release drugs in response to pH, temperature or enzyme activity.7
Applications and uses of microrobots
The most direct application of microrobots is in drug delivery. By actively navigating toward disease sites, they address the limitations of passive nanoparticle diffusion.
Microrobots can be engineered to release drugs in response to external triggers such as magnetic fields or light, or local conditions such as low pH in tumours. This reduces premature release and increases efficacy. Multifunctional microrobots can deliver drug combinations paired with immunomodulators or imaging agents for theranostic applications.8
Preclinical studies have demonstrated that microrobots can achieve higher local drug concentrations while reducing systemic toxicity compared to conventional administration.9
A diverse range of therapeutic applications
Microrobots hold promise across a broad spectrum of therapeutic fields. In cardiovascular medicine, they could be used to clear vascular occlusions or deliver clot-dissolving agents, potentially transforming the management of stroke and myocardial infarction.
In infectious diseases, microrobots may mechanically or chemically disrupt biofilm-associated infections.10 Their ability to cross the blood-brain barrier offers new opportunities in neurology, enabling precise delivery of neuroprotective therapies.11 In the gastrointestinal tract, micromotors have already shown potential in treating Helicobacter pylori infection.12
However, cancer remains the leading therapeutic target for microrobot research due to the complexity of tumour microenvironments and the limitations of conventional treatment methods.9 Microrobots offer several distinct advantages in oncology.13
Microrobots and cancer care
Microrobots can be engineered to carry chemotherapeutics directly to tumour sites, guided by magnetic or acoustic fields.14 This approach increases drug accumulation in tumours while minimising exposure to healthy tissues. Preclinical studies have demonstrated improved tumour regression with fewer adverse effects compared with systemic delivery.15
For example, bacteria-driven microrobots carrying doxorubicin successfully targeted colorectal tumours in mice, with up to 55% of the magnetotactic bacterial cells penetrating hypoxic regions of HCT116 colorectal xenografts.16 Similarly, magnetically guided microrobots have been tested for intravesical drug delivery in bladder cancer models.17
Solid tumours often present unique barriers such as abnormal vasculature, hypoxic regions and high interstitial pressure. Microrobots are capable of penetrating these barriers actively, unlike passive nanoparticles that rely on diffusion.18
Certain microrobots are functionalised with nanoparticles (e.g. gold nanorods, carbon-based nanostructures) that convert near-infrared light into heat, selectively ablating tumour cells.19 Others combine drug delivery with photodynamic therapy, where photosensitisers generate reactive oxygen species upon light activation, thereby enhancing tumour cell death.20
Microrobots have been explored as vectors for gene-editing systems such as small interfering RNA, known as siRNA and CRISPR-Cas9.21 Furthermore, immunotherapeutic strategies are being investigated, such as delivering immune checkpoint inhibitors or cytokines directly to the tumour microenvironment, thereby enhancing adoptive cell transfers.22
By incorporating imaging agents such as fluorescent dyes, MRI contrast agents, or radionuclides, microrobots could enable real-time monitoring of their navigation and therapeutic action.23
Ensuring patient safety
The transition from laboratory prototypes to clinical practice faces significant challenges. Indeed, the development of microrobots for therapeutic use introduces complex ethical, safety and regulatory challenges that must be addressed before clinical translation.
These issues are critical not only to ensure patient safety but also to build public trust and meet international biomedical standards.
Microrobots must be fabricated from biocompatible and biodegradable materials to avoid toxicity and immune rejection. Materials such as biodegradable polymers, hydrogels and magnesium alloys are being investigated for their ability to degrade in vivo safely.24
However, long-term safety studies are still limited, and potential accumulation in organs remains a concern.25 Biosafety evaluations should include not only acute toxicity but also chronic exposure and genotoxicity testing.
Microrobots can trigger immune responses, leading to clearance from circulation or unintended inflammatory reactions. For biohybrid microrobots such as bacteria-driven systems, there is an added risk of pathogenicity and horizontal gene transfer.26 Engineering attenuated or genetically modified organisms reduces risk but raises further regulatory and ethical considerations.
The effective navigation and retrieval of microrobots is essential to avoid uncontrolled migration or retention in healthy tissues. Strategies include external magnetic guidance, biodegradability after completing the task and the development of so-called ‘kill-switches’ for biohybrid systems.27 Without robust fail-safe mechanisms, regulatory approval is unlikely.
Consent, regulation and transparency
The use of microrobots raises questions about patient autonomy and informed consent, particularly when they involve autonomous decision-making or real-time data collection inside the body. Clear communication about potential risks, benefits and uncertainties is necessary. There are also concerns about the privacy of physiological data transmitted by diagnostic microrobots.28
Currently, there are no established regulatory frameworks specifically tailored for microrobots. The FDA and EMA are expected to classify them within existing categories of medical devices or combination products as drug–device hybrids. This classification will affect requirements for clinical trials, manufacturing quality control and post-marketing surveillance. Microrobots may face stricter standards compared with conventional nanomedicines, given their mobility and potential for autonomous behaviour.
As with any emerging technology, societal acceptance is key. Ethical concerns include potential misuse, such as for surveillance or military applications, and equity of access, as microrobot-based therapies may initially be expensive and limited to wealthy healthcare systems. Broad public engagement and transparent policymaking will be crucial to avoiding mistrust and ensuring fair access.28
Future perspectives on microrobotics
The future of microrobotics lies in intelligent, autonomous systems. Advances in artificial intelligence, machine learning and nanomaterials will likely enable microrobots capable of sensing their environment, making decisions and adapting in real-time. Hybrid devices that integrate diagnosis and therapy could enable personalised medicine.
Microrobots represent a paradigm shift in targeted therapeutics. By combining precise navigation, controlled drug release and multifunctional capabilities, they hold the promise of addressing many of the limitations of conventional therapies. Although challenges remain, they are poised to become an integral component of next-generation medicine.
Author
Alain Astier PharmD PhD
Honorary head of the Department of Pharmacy, Henri Mondor University Hospital, and French Academy of Pharmacy, Paris, France
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