Cilia Are Minuscule Wonders, and Scientists Are Finally Figuring Out How to Mimic Them

The cilium can only do a small amount on its own. These structures pull off biological wonders in the body. Eggs are transported from the ovary to the uterus, mucus is removed from the middle ear, and Cilia carry fluids from the respiratory Tract to the Brain. Microprocessors exert precise control over fluids in the body. Scientists have been trying to mimic the wonders of nature for a long time.

Researchers have come close to making a chip that can control the flow of fluids. The developers hope that this technology will lead to portable diagnostic devices. Diagnostic lab tests are time consuming and require close human support. A chip covered in cilia could allow field testing that would be easier, cheaper and more efficient than lab-based tests, as well as using smaller samples of blood, urine or other testing material.

Humans have achieved spectacular large-scale engineering feats, but "we are still kind of stuck when it comes to engineering smaller machines," says Itai Cohen, a Cornell University physicist and senior author of a new Nature study. Artificial cilia that worked by means of pressure, light, electricity and even magnets were once tried by researchers. The biggest hurdle was the design of extremely tiny actuators that can be controlled individually or in small clusters.

The Cornell researchers took inspiration from what they learned in their previous work. Cohen and his team were recognized as the world's smallest walking robot in August 2020 by Guinness World Records. The artificial cilia are made of a thin film that can respond to electrical control. The 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.

Metal makeup is the key to controlling artificial cilia. A chemical reaction can be triggered by running a low positive voltage through a cilium. The oxygen atoms are freed up by this. The oxygen stretches the strip and makes it bend. The oxygen is driven out of the platinum when the voltage is reversed. Cohen says that by alternating the voltages back and forth, you can bend and unbind the strip, which will generate waves to drive the movement. The titanium film is stable.

The researchers had to figure out how to pattern a surface. By bending and unbending the strips, they can drive a small amount of fluid. To direct a droplet to flow in a more complex pattern, the researchers had to divide their chip's surface into a few dozenciliary units. The Cornell team collaborated with the University of Cambridge to create a three-dimensional simulation of how a droplet would move.

After using computer simulations to check out the theoretical aspects of what they were doing, the researchers created a physical device. Each of the 16 ciliary units of 64 cilia is composed of about a thousand tiny Platinum-titanium strips. Each unit is connected to a computer control system and can be programmed to move the test fluid in different directions. Near-endless combinations of flow patterns could be created by working together.

The researchers would like the device to be more efficient, but it is not. Next- generation chips with more than onehinge are being planned. This will allow them to have more efficient flow of the fluid.

Zuankai Wang is a researcher at the City University of Hong Kong who was not involved in the new study. It is hoped that the mass production of low cost diagnostic devices will be possible in the future.

It makes sense to use the technology in medical applications. The researchers envision a chip covered in cilia that could be used to test water, blood or urine for disease markers. A user would place a drop of blood or urine on the chip and the artificial cilia would carry the sample from one spot to another, allowing it to mix and react with various testing agents. Cohen says that the chemistry experiments can be done in a chip instead of in a lab. The chip can be made to work on its own, as it can use little solar panels fitted on the chip itself. It would be great for use in the field.

A materials scientist who was not involved in the new study says it is fantastic how they have combined microelectronics with fluid mechanics. The researchers have solved an important problem, but it will take more work to bring the product to fruition. He says that when designing a reactor system to analyze a drop of blood there have to be local stations. It would be interesting to see how they integrate all of this in a reactor.