Micro- and nanorobotics were once thought of as something reserved for science fiction movies. The realms of possibility have rapidly shifted in recent years, and nanoengineers and scientists are edging closer to realising the real-life benefits of micro- and nanorobotics in the prevention, diagnosis and treatment of disease.

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On 22 September 2022, nanoengineers at the University of California San Diego published in Nature Materials Journal about their bioinspired microscopic robots, called ‘microrobots'.

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Microrobots are very small at 6 micrometres. For context, the average human hair is around 75 micrometres wide so 12 microrobots can fit across the diameter of a strand of hair.

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In mice, the researchers found the microrobots safely eliminated life-threatening bacterial pneumonia in the lungs. The infections fully resolved after one week and all mice survived the entire duration of the 14 day study. By comparison, untreated mice all died within three days.

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The researchers used the microrobots to treat mice with a potentially life-threatening form of pneumonia caused by the Pseudomonas aeruginosa – a bacterial pneumonia. This acute form of pneumonia is known to be antibiotics resistant and patients in hospital settings, especially those on ventilators (breathing machines) in intensive care units, are most at risk.

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The microrobots move at fast speed (>110µm/s) around the lungs delivering medication to the precise location it’s required. The drug does not need to diffuse through the entire body before it reaches the part of the body it's required.

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Treatment via an IV injection of antibiotics required a dose 3000 times greater than the microrobots (500 nanograms versus 1.644 milligrams per mouse). Usually only a very small amount of the antibiotics reaches the lungs via IV injection, but with the help of the microrobots, the antibiotics treatment reached the lungs of the mice in highly concentrated quantities. Hence effectively killing the bacterial pathogens and saving the lives of all of the mice.

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But how do the microrobots work? The microrobots are made of microalgae cells which are loaded with antibiotic-filled polymeric nanoparticles on its surface. The algae moves the microbots, enabling them to 'swim' and deliver antibiotics directly to the bacteria in the lungs. The nanoparticles carrying the antibiotics are made of biocompatible polymeric spheres (polylactic co-glycolic acid). These are covered with the cell membranes of a type of white blood cell (called neutrophils). These membrane-coated nanoparticles absorb and neutralise inflammatory molecules produced by bacteria and the body's immune system. This allows the microrobots to reduce inflammation and improved treatment effectiveness in the mice.

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The researchers found the toxicity of the microrobots was negligible as the body’s immune cells efficiently digest the algae and any other nanoparticles.

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The University of California San Diago team next plan to study the interaction between the microrobots and the body’s immune system. The researchers also plan to further validate the efficiency of the microrobot treatment and to scale up before testing in larger animals. From there, they plan to progress to clinical trials in humans.

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This research is showing promising results to date. At this point, the work is still at the proof-of-concept stage.

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For further information, please refer to: Nanoparticle-modified microrobots for in vivo antibiotic delivery to treat acute bacterial pneumonia | Nature Materials