Jul 18, 2017 | By Benedict
Physicists from the Sapienza University of Rome have used free-swimming, light-driven E. coli bacteria to propel tiny 3D printed micromotors in a process that resembles how running water rotates a watermill.
Bacteria, unicellular microorganisms that are essential to global ecology (but which can also cause disease in living things), have traditionally had a bad rap with humans. And perhaps with good reason: after all, bacteria can lead to ill health and even death, with cholera, syphilis, anthrax, leprosy, and bubonic plague all helped along nicely by the pesky microorganisms.
But bacteria can also be a good thing. The human immune system combats most of the negative effects of bacteria, and the microorganisms also produce some positive effects: gut immunity, conversion of sugars to lactic acid, and improved digestion. These effects have become well-known amongst non-scientific communities in recent years, largely thanks to the marketing campaigns of probiotic yogurt companies.
Excitingly, bacteria could soon become useful even beyond breakfast, because physicists from the Sapienza University of Rome have used free-swimming, light-driven, genetically engineered E. coli bacteria to power tiny 3D printed machines. The machines could someday be used for medical tasks like delivering drugs into the body.
In a study that has been published in Nature Communications, the Sapienza researchers report how they were able to deposit a drop of fluid containing thousands of the E. coli onto an array of micromotors.
When some of these bacteria swim head-first into one of the 15 microchambers etched on the outer edge of each micromotor—and with their flagella (tails) protruding outside the microchambers—the movement of the bacteria causes the tiny 3D printed micromotors to rotate.
The physicists liken the bacteria-driven movement of these micromotors to a watermill, which rotates when running water passes through its blades.
“Our design combines a high rotational speed with an enormous reduction in fluctuation when compared to previous attempts based on wild-type bacteria and flat structures," said Roberto Di Leonardo, a professor of physics at both Sapienza and NANOTEC-CNR, both in Rome.
“We can produce large arrays of independently controlled rotors that use light as the ultimate energy source. These devices could serve one day as cheap and disposable actuators in microrobots for collecting and sorting individual cells inside miniaturized biomedical laboratories.”
To make the micromotors work properly, the researchers took steps to ensure that they would always rotate the right way when propelled by the bacteria. To do this, they 3D printed the microchambers of the micromotors at a 45° angle (maximizing the total torque), and used a radial ramp which created bacteria-directing barriers.
The fabrication system for the micromotors is described as a "custom-built, two-photon polymerization setup" based on a near-infrared femtosecond fiber laser.
During experiments on their bacteria-driven system, the Rome-based physicists found that, when lots of bacteria had been “captured” by a micromotor, rotational speeds of 20 revolutions per minute could be achieved. This speed was lower when fewer bacteria took up places in the microchambers.
The researchers also took steps to make their E. coli as efficient as possible. They achieved this by genetically modifying the E. coli strain to swim faster in response to light. By illuminating the 3D printed micromotors with different light intensities, the researchers could therefore control their speed.
Although the system uses living microorganisms as its driving force, the researchers surprisingly managed to keep the micromotors highly controllable—by using a feedback algorithm to uniformly illuminate the system every 10 seconds. With this lighting system in place, the physicists showed that the micromotors can be synchronized with minimal variation in speed.
Di Leonardo and his team believe that their 3D printed, bacteria-driven micromotors could be used in drug and cargo delivery within the field of medicine; they will continue their research to see if they can make this a reality.
The study, titled “Light controlled 3D micromotors powered by bacteria,” was authored by Di Leonardo, Gaszton Vizsnyiczai, Giacomo Frangipane, Claudio Maggi, Filippo Saglimbeni, and Silvio Bianchi.
Posted in 3D Printing Application
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