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Membrane structure; the top layer (pink) shows selective layer morphology containing packed micelles. The spaces between the micelles form membrane nanopores with size of 1-3 nanometer.Credit: Ilin Sadeghi, study co-author and Tufts University Ph.D. candidate

A new type of filter has been designed to allow manufacturers to separate organic compounds not only by their size, but also by their electrostatic charge.

A team of chemical and biological engineers from Tufts University has developed highly selective membrane filters that could enable manufacturers to separate and purify chemicals in ways that are currently impossible, allowing them to potentially use less energy and cut carbon emissions. The technology has initial applications in manufacturing pharmaceuticals such as antibiotics, amino acids and antioxidants.

Corresponding-author Ayse Asatekin, PhD, a chemical and biological engineering professor in the Tufts School of Engineering, said in an interview with R&D Magazine that the new filters would benefit manufacturers looking to save energy costs.

“Our goal of this project was to make filters that can separate chemicals that are similar in molecular size but different in chemical structure,” she said. “Most filters today are basically sieves, they separate the big from the small and filters are a good way of separating chemicals from each other because they are very energy efficient, especially when you compare it to something like distillation or extraction.”

The researchers used a simple, scalable process to create the membranes, in which a specialty polymer is dissolved in a solvent and coated onto a porous support. The polymer self-assembles to create approximately one nanometer-sized channels that mimic biological systems, such as ion channels, which control the passage of compounds through cell membranes with great effectiveness.

The newly designed membranes can allow neutral compounds to pass through 250 times faster than charged compounds of similar size. When charged and uncharged compounds are mixed, the membrane filters prevent the charged compound from passing through at all. The passage is averted because the neutral compound gets into the channels first and prevents the charge compound from entering.

They also provide the ability to separate charged and uncharged compounds in various filtration systems.

The charge-based separation is enhanced when the solution contains a mixture of solutes, indicating that the membrane’s structure successfully mimics how biological systems work. The researchers said the new approach could be used to address other separations and provide selectiveness above and beyond what can be attained using conventional membranes.

The researchers are looking to develop the next generation of membranes by designing them from the molecules up. The membranes rely on polymers that self-assemble, form nanostructures and expose chemical functionalities that enable them to perform tasks normally not expected from membranes.

Asatekin said that while the initial application would be for the pharmaceutical industry, they hope to expand into other industries.  

 “Our goal is to adapt this approach to other types of separations where you don’t rely on charge but other molecular characteristics,” she said. “Then you could expand the applications even more broadly.”

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