


Water filter inspired by Alan Turing passes first test  
Researchers in China have developed a filter that removes salt from
water up to three times as fast as conventional filters. The membrane
has a unique nanostructure of tubular strands, inspired by the
mathematicalbiology work of codebreaker Alan Turing.
British mathematician 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 quickerdiffusing 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. Whether such a process actually occurs at a cellular level has been hotly debated. But this reactiondiffusion behaviour has been invoked to explain patterns in nature and society, including zebra stripes, sand ripples and the movements of financial markets. So far, however, attempts to synthesize such structures in the lab have mostly been limited to 2D patterns. Researchers from 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. The team added 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 selforganising structure predicted by Turing?s model. They found that their membranes functioned as efficient water filters ? surpassing conventional nylonlike filters in some respects. 


