Nature reports on a water filter based on computer pioneer Alan Turing’s only biology paper that appears to clean salt out of water three times better than conventional filters:
The filter is the most finely constructed example of the mathematician’s ‘Turing structures’ yet, and their first practical application, say researchers. “These 3D structures are quite extraordinary,” says Patrick Müller, a systems biologist at the Friedrich Miescher Laboratory in Tübingen, Germany. The filter’s tubular strands, just tens of nanometres in diameter, would be impossible to produce by other methods, such as 3D printing, he says. The work is published on 3 May in Science.
[In 1952, Alan Turing] proposed a mathematical model for a process by which the cells of an embryo might begin to form structures — limbs, bones and organs. In this process, two substances continuously react with each other, but diffuse through their container at very different rates. The quicker-diffusing reactant — called the inhibitor — pushes back against the slower one, called the activator, effectively corralling the resulting product into a pattern of spots or stripes. (The terminology was coined by biologists Hans Meinhardt and Alfred Gierer, who independently formulated an equivalent theory in 1972.)
A team led by material scientist Lin Zhang of Zhejiang University in Hangzhou, China, set out to create a 3D Turing structure out of a polyamid, a material similar to nylon, formed by a reaction between the chemicals piperazine and trimesoyl chloride. In a conventional process, trimesoyl chloride diffuses faster than piperazine, but the difference is not big enough to produce a Turing structure. Zhang’s trick was to add polyvinyl alcohol to the piperazine, further lowering its diffusion rate and allowing it to act as the activator to the trimesoyl chloride’s inhibitor.
The result is a rough, porous mesh with a nanostructure resembling a Turing pattern that can be seen under an electron microscope. The team was able to produce variants showing both dots and tubes — the two types of self-organizing structure predicted by Turing’s model.
The researchers were elated to produce the Turing structures, says Zhang. But they were more surprised when they found that their membranes functioned as efficient water filters — surpassing conventional nylon-like filters in some respects.
The filter’s tubular structure gives it a larger surface area compared to conventional filters, which increases the flow of water through the membrane, says Ho Bum Park, a membrane scientist at Hanyang University in Seoul. It’s an improvement on conventional membrane structures, which resemble a series of ridges and valleys, he says. “It’s a really smart approach.”