Intelligent membranes with memory create the next generation of smart filters

April 19, 2023

(Nanowerk News) Researchers from the National Graphene Institute (NGI) have created ‘intelligent’ membranes whose ‘memory’ can be used in areas such as intelligent separation technology, wound management, drug delivery, sensors and memory devices.

“The history of membrane development spans more than 100 years and has led to a revolution in industrial separation processes,” said Professor Rahul Raveendran Nair, Carlsberg/Royal Academy of Engineering Research Chair and lead of the study team. “In recent years, there have been several attempts to create membranes that mimic biological structures, particularly their ‘intelligent’ characteristics.”

Now, in research published in Natural (“pH-dependent switching of water permeability and its memory in MoS2 membrane”), scientists explain how they have developed a smart membrane that can change its properties depending on the environment and given how permeable it was before. This means the membrane can adapt to different conditions in its environment and, more importantly, given its status, a feature that can be exploited in a wide variety of applications. Artist’s view of a smart membrane with a memory effect. (Image: R. Nair)

The phenomenon known as hysteresis is the most common expression of memory or intelligence in matter. It refers to situations where the current system properties depend on and are related to previous states. Hysteresis is commonly observed in magnetic materials. For example, a magnet may have more than one possible magnetic moment in each magnetic field depending on past magnetic fields. However, hysteresis is rarely seen in molecular transport across artificial membranes.

“Delivering simple and effective clean water solutions is one of our biggest global challenges. This study shows that insights at the level of basic molecules and nanoscale materials offer great potential for the development of ‘smart’ membranes for water purification and other applications,” said Professor Angelos Michaelides from Cambridge University.

In this work, the Manchester team in collaboration with scientists from Cambridge University, Xiamen University, Dalian University of Technology, University of York, and National University of Singapore have developed a smart membrane based on MoS.2 (a two-dimensional material called molybdenum disulphide) that can remember how permeable they were before. Researchers have shown that the way ions and water infiltrate the membrane can be regulated by controlling the external pH.

The membranes mimic the function of biological cell membranes and display hysteretic ion and water transport behavior in response to pH, meaning they remember the pH to which they were previously exposed. “The memory effect we saw is unique to this membrane and has not been observed before in any inorganic membrane,” said co-author Dr Amritroop Achari from the University of Manchester.

The researchers demonstrated that the biomimetic effect could be used to enhance autonomic wound infection sensing. To do this, they placed membranes in artificial wound exudate, which simulated the fluids produced by the wound, and subjected them to changes in pH. The membrane only allows permeation of wound exudate at pH levels relevant to the infected wound, allowing it to be used as a sensor for infection detection. The researchers say the new membrane could also be used in a number of other pH-dependent applications, from nanofiltration to mimicking nerve cell function.

Co-author Professor Kostya Novoselov, Langworthy Professor in the School of Physics and Astronomy at the University of Manchester and a professor at the Center for Advanced 2D Materials, National University of Singapore said, “A unique feature in this membrane is its hysteretic pH response. can be seen as a function of memory, which opens up many interesting avenues for the fabrication of smart membranes and other structures. Research in this direction can play an important role in the design of intelligent technologies for the future.”

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