Advancements in Artificial Cilia: Mimicking Nature's Microfluidic Wonders
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One tiny flick of a microscopic cellular hair, known as a cilium, can’t do much on its own. But together, these structures routinely pull off biological marvels within the body. Cilia remove inhaled pathogens from the respiratory tract, carry cerebrospinal fluid across brain cavities, transport eggs from the ovary to the uterus, and drain mucus from the middle ear to the nasal cavity. These tiny, extracellular organelles exert precise microfluidic control over life-sustaining liquids in the body. To better understand how these crucial wonders of nature work, scientists have been trying for years to mimic them. Now researchers [from Cornell University] have come close to doing so, creating a chip covered with artificial cilia that can precisely control the minuscule flow patterns of fluids… Researchers had previously tried to make artificial cilia that worked by means of pressure, light, electricity and even magnets. But a major hurdle remained: designing extremely tiny actuators—the motion-triggering parts of a machine—that can be controlled individually or in small clusters rather than all at once.
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The Cornell researchers vaulted that hurdle by taking inspiration from some things they learned in their earlier work. In August 2020 Guinness World Records recognized Itai Cohen, a Cornell University physicist and senior author of [this] new Nature study, and his team for designing the world’s smallest walking robot, a machine that was just a fraction of a millimeter wide and could walk on four bendable legs. Much like those legs, the new artificial cilia are made of bendable, nanometer-thin film that can respond to electrical control. Each cilium is one-twentieth of a millimeter long and 10 nanometers thick, with a strip of platinum on one side and a coating of titanium film on the other.
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The key to electrically controlling these artificial cilia comes from their metal makeup. Running a low positive voltage through a cilium triggers a chemical reaction: as a droplet of test fluid flows past, the electrified platinum breaks apart the water molecules within the droplet. This frees up oxygen atoms, which are absorbed into the platinum’s surface. The added oxygen stretches the strip, making it bend in one direction. Once the voltage is reversed, the oxygen is driven out of the platinum—and the cilium returns to its original shape. “So by oscillating the voltage back and forth, you can bend and unbend the strip, which will generate waves to drive the movement,” Cohen says. Meanwhile the electrically inert titanium film stabilizes the structure…
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[With] the new technology [imitating] biological structures, […] researchers envision a cilia-covered chip as the basis of a diagnostic device that could test any sample of water, blood or urine to find contaminants or markers of disease. A user would place a drop of blood or urine on the chip, and the artificial cilia would carry the sample—along with any chemicals or pathogens within it—from one spot to another, allowing it to mix and react with various testing agents as it moves. Biosensors built into the chip would measure the products of these chemical reactions and then direct the cilia to further manipulate the liquid’s flow, allowing the chip to perform additional tests to confirm the results…
