Nanoscopic hair-like polymer structures are being developed by US researchers and could help explain the way similar biological appendages, known as cilia, function inside the body.
Cilia are cell appendages that perform many different jobs in the human body - from picking up sounds inside the ear to performing a sensory function in the kidney.
Inside the lungs, cilia wiggle back and forth pushing mucus, and potentially harmful airborne particles, through the respiratory system. In this way they play a crucial role in protecting it from disease. But the mechanics of the process are not well understood.
So Richard Superfine and colleagues at the University of North Carolina at Chapel Hill, US, are developing synthetic cilia in an effort to understand precisely how their biological counterparts work in the lungs. They hope the work could help other researchers develop better treatments for diseases that affect the respiratory system, like cystic fibrosis.
Superfine's team created arrays of flexible polymer nanorods the same size as biological cilia (about 10 microns long and 0.2 microns wide), with similar physical properties. The nanorods were made by pouring liquid polydimethlsiloxane, containing iron oxide nanoparticles, into a mould. The mould itself is then chemically etched away, leaving hundreds of the nanorods protruding from a substrate.
Since the nanorods contain iron oxide particles they can then be manipulated magnetically. An electromagnet below the array was used to bend and move them while a microscope positioned above monitored the movement.
The researchers used computer simulations to work out how to stimulate the nanorods magnetically so that they move in a similar way to the lung's cilia - staying straight when moving one way and curling as they move the other.
"What we view as the most profound contribution is to our understanding of biology," Superfine told New Scientist. "There's very little understanding currently of how an individual cilium, or fields of cilia, move fluids."
The next step is to test the artificial cilia using viscous liquids that mimic the behaviour of mucus inside the lung. "It's a different fluid dynamics problem," Superfine says.
Superfine says the work might also help explain how cilia work in other biological contexts, such as inside the brain and in developing embryos.
Chang Liu, at the University of Illinois, US, who is developing similar artificial hair-like structures, but for sensing purposes rather than manipulation, is impressed by the work. However, Liu suspects it will be a while before the artificial cilia can accurately mimic the performance of the real thing. "It's definitely pretty interesting," he told New Scientist."But it will take a long time to become a fully-functional device - it always does."
Journal reference: Nano Letters (DOI: 10.1021/nl1070190c)
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