Making living materials move: Janus microgel robots improve antibiotic degradation and recovery

Antibiotic contamination in water is not only an environmental problem; it can also accelerate the spread of antimicrobial resistance. Microalgae offer a greener route for pollutant remediation because they are living, photosynthetic systems capable of metabolizing organic compounds. Yet free-floating algal cells work passively, degrade pollutants slowly, and are difficult to collect after treatment. A new study published in Research by researchers from Hangzhou Normal University, Zhejiang University, and collaborating institutions addresses these limitations by developing Janus microgel robots that combine living photocatalytic activity with magnetic mobility and recovery.

The design places two functions into separate hemispheres of a single microgel particle. One side contains TiO₂-mineralized Chlorella pyrenoidosa, which performs biological degradation and photocatalytic reactions under light. The other side contains Fe₃O₄ nanoparticles, enabling magnetic actuation and rapid recovery. This spatial separation is essential because the magnetic particles are needed for motion, but high concentrations can harm microalgal growth. By using gas-shearing microfluidics, the researchers produced a well-defined Janus architecture and then added a hydrogel shell to prevent cell leakage while allowing small molecules to pass through.

The performance gain comes from both biochemical synergy and active motion. TiO₂ generates photogenerated electrons and holes under illumination. These charge carriers contribute to reactive oxygen species formation for photocatalytic degradation, while some electrons can enter the photosynthetic electron transport chain of the microalgae. This interaction boosts the metabolic capacity of the living component. Photocurrent measurements, radical detection, ATP and NADPH analysis, and degradation product identification support a coupled photocatalytic–photosynthetic degradation mechanism.

Using levofloxacin as a model antibiotic, the Janus microgel robots degraded about 77% of the pollutant within 10 hours under simulated sunlight, compared with only 7.6% for free C. pyrenoidosa. Control experiments showed that the gel matrix and magnetic particles contributed little to degradation, while the TiO₂–microalgae hybrid outperformed either component alone. When a rotating magnetic field was applied, the robots’ motion improved local mixing and mass transfer, increasing degradation efficiency by an additional 10.6%.

Recovery and reuse are central to the platform. Because the Fe₃O₄ phase is built into the microrobots, the particles can be collected with an external magnet after use. The same batch retained more than 95% of its initial activity over three consecutive degradation cycles, and further testing suggested sustained performance over additional reuse. The encapsulation layer also limited algal escape and reduced titanium leaching, providing an initial biosafety basis for using such living materials in environmental remediation.

The study does not claim that these microrobots are ready for wastewater treatment plants. Their performance was demonstrated under controlled laboratory conditions with a model antibiotic and simulated sunlight. Future work will need to test complex real-water matrices, mixed pollutants, long-term ecological safety, scalable production, and cost. Still, the work provides a useful prototype for active, recyclable living materials and points toward a new generation of photocatalytic–biological hybrid systems for sustainable water treatment.

Sources: https://spj.science.org/doi/10.34133/research.1167