Magnetically guided microrobots coated with bacteriophages penetrate and dismantle bacterial biofilms, achieving targeted removal of microbial contamination through coordinated mechanical disruption and species-specific viral infection.
(Nanowerk Spotlight) Biofilms are among the most persistent biological challenges in medicine and industry. They form when bacteria attach to a surface and secrete a dense mixture of sugars, proteins, and DNA that locks them in place. Once this structure develops, bacteria inside it can survive concentrations of antibiotics or disinfectants that would kill free-floating cells. The result is not mechanical failure but contamination and infection that are exceptionally difficult to eliminate. Biofilms on catheters, stents, or prosthetic joints can cause chronic infection. Those in water systems, pipelines, or food-production lines reduce efficiency and raise serious safety concerns.
Efforts to remove these bacterial layers have advanced slowly because of the complex architecture that protects them. The biofilm’s outer matrix slows diffusion, limits chemical access, and supports coordinated behavior among its cells. Chemical cleaning, surface coatings, and mechanical agitation can reduce contamination but rarely eliminate it entirely. Once a few layers remain, the community regrows. The problem is not simply killing bacteria but reaching them where they live.
That need for precision has led researchers to explore tools that combine biological selectivity with physical mobility. Bacteriophages, which are viruses that infect bacteria, offer species-level targeting and destroy only their specific hosts. Magnetic microrobots, in contrast, can move through liquid environments when directed by external magnetic fields and carry active agents directly to defined sites. Each technology addresses part of the challenge. Phages know their targets but cannot penetrate the matrix effectively. Microrobots can navigate complex structures but lack selectivity.
The study, published in Advanced Materials (“Virus Enhanced Microrobots for Biofilm Eradication”), brings these two technologies together. It describes magnetically guided microrobots whose surfaces are coated with bacteriophages designed to infect Staphylococcus aureus, one of the bacteria most commonly responsible for medical and industrial biofilms. Under a low magnetic field, the virus-conjugated microrobots (virus@microbots) move through the biofilm, physically disturbing its structure while delivering viruses directly to the bacteria within. The combined system outperforms either method alone and offers a new route to targeted, controllable biofilm removal.
Dual-action biofilm removal by Virus@microbots: Illustration of the synergistic biofilm eradication by virus@microbots. Viruses deliver precise targeting and bactericidal action, while microbots provide magnetic navigation and mechanical disruption. Combined, they effectively suppress bacterial proliferation and eliminate biofilms on diverse surfaces, including milk, leaves, and chicken or porcine skin. (Image: Reprinted from DOI:10.1002/adma.202508299, CC BY) (click on image to enlarge)
The microrobots are built from magnetite, a magnetic form of iron oxide (Fe₃O₄) that responds predictably to external fields. The particles were synthesized through a hydrothermal process that heats and pressurizes chemical solutions to form uniform, crystalline spheres. Microscopy revealed their smooth surfaces, and X-ray analyses confirmed that the structure was pure magnetite rather than mixed oxides. This ensured stable magnetic behavior and chemical compatibility with the biological coating.
To attach the viruses, the researchers relied on natural molecular forces rather than synthetic linkers. The outer protein shell of each phage carries a negative charge that interacts with hydroxyl groups on the magnetite surface through electrostatic attraction and hydrogen bonding. A thin layer of bovine serum albumin was added to prevent nonspecific binding and preserve viral activity.
Measurements of surface charge, particle size, and infrared absorption all confirmed that the viruses were successfully attached without altering the particles’ structure or magnetism.
The hybrid particles were then tested against S. aureus biofilms. Using a magnetic field of five millitesla, which is about one thousandth the strength of a refrigerator magnet, the researchers guided the microrobots across contaminated surfaces. In liquid, bare microrobots moved at roughly 221 micrometres per second. When coated with viruses and placed inside the biofilm, their speed fell to around 54 micrometres per second, indicating active interaction with the dense network rather than loss of motion control.
Four treatment conditions were compared: no treatment, bare microrobots, free bacteriophages, and virus-coated microrobots. After six hours, the combined treatment removed about two-thirds of the total biofilm biomass, far more than any other condition. Without magnetic guidance, the effect dropped sharply, confirming that directed movement and local delivery were essential. Increasing the virus concentration improved results up to a plateau at 10⁸ plaque-forming units per millilitre.
Microscopic imaging showed how the system operated. The microrobots mechanically disrupted the biofilm, creating channels that allowed the attached viruses to reach bacteria embedded deeper within the matrix. Fluorescence microscopy revealed a visible thinning of the film, and protein-specific stains showed that much of the structural material had been degraded. The two mechanisms, mechanical penetration and viral infection, worked together to dismantle the bacterial community.
A fluorescence-based viability assay further confirmed bacterial death. Green fluorescence marked intact cells, while red fluorescence indicated damaged or dead ones. Biofilms treated with virus-guided microrobots showed predominantly red signals, meaning extensive cell death. Treatments using only viruses or only microrobots had limited impact. When the same system was tested against Escherichia coli, which the chosen phages cannot infect, the biofilm remained largely intact, demonstrating the method’s high specificity.
To assess performance in more realistic conditions, the researchers applied the technique to several complex materials. In milk contaminated with S. aureus, viable bacterial counts dropped markedly after treatment. On porcine and chicken skin, microscopy and absorbance data showed that the treated surfaces were substantially cleaner than untreated ones. Even on plant leaves, the approach disrupted surface biofilms. These results suggest that the hybrid microrobots function across different environments and substrates, not just ideal laboratory conditions.
The advantages of this approach lie in combining targeted biological action with controlled physical movement. The attached viruses maintain a concentrated presence at the biofilm interface rather than dispersing through liquid. Magnetic steering allows precise positioning, while the microrobots’ motion mechanically exposes new bacterial layers to infection. The protein layer that anchors the phages may also protect them from enzymatic degradation and extend their activity.
Together, these effects produce a localized and selective antibacterial system that avoids the environmental and toxic limitations of chemical disinfectants.
The authors emphasize that the work remains at an early stage. Scaling production of virus-coated microrobots, testing their biocompatibility, and examining long-term stability will be essential before clinical or industrial use. They also highlight future possibilities such as adding sensing functions that could allow the microrobots to detect bacterial growth and respond automatically. Each of these steps will determine whether the technology can move beyond laboratory experiments to practical deployment.
This study demonstrates how combining magnetic motion with viral precision can overcome the physical and biological barriers that make biofilms so persistent. By integrating mechanical disruption with selective infection, virus-guided microrobots achieve controlled biofilm removal in a way that neither antibiotics nor traditional cleaning methods can match. The findings point toward a new generation of antibacterial strategies built on intelligent and localized control of microbial environments.
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