Biotechnology

Microfluidic device for collecting microplastics via

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Particles of plastic waste smaller than 5 mm, known as microplastics (MP), are a serious environmental problem. Formed from the decomposition of plastic waste due to wear and tear or produced by waste fibers in laundry wastewater and as microbeads in beauty products, they absorb and introduce harmful chemicals that pollute the environment. By 2050, lawmakers may outnumber the fish in the seas. In these circumstances, the collection and removal of MPs from the water becomes very important.

Particles of plastic waste smaller than 5 mm, known as microplastics (MP), are a serious environmental problem. Formed from the decomposition of plastic waste due to wear and tear or produced by waste fibers in laundry wastewater and as microbeads in beauty products, they absorb and introduce harmful chemicals that pollute the environment. By 2050, lawmakers may outnumber the fish in the seas. In these circumstances, the collection and removal of MPs from the water becomes very important.

Conventionally, MP is collected by filtering water through a mesh. Sand and biological debris were removed from the collected MP by density separation and chemical treatment respectively. After that, MPs were retrieved manually, which was laborious and time-consuming. In addition, meshes can easily become clogged and cannot collect particles smaller than their aperture. They also require frequent and expensive maintenance. Given this shortcoming, researchers have developed a microfluidic device—a system that controls small amounts of liquid using micrometer-sized channels—that uses acoustic focusing to collect MP.

Acoustic technology generates ultrasonic waves that transport MP to the center of the fluid flow and thereby enrich, that is, increase the amount of MP accumulated. However, the high MP enrichment using current microfluidic devices requires recirculation of the liquid through it. In this regard, a group of researchers, led by Professor Yoshitake Akiyama of the Department of Mechanical and Robotics Engineering at the Faculty of Textile Science and Technology at Shinshu University, have developed a high-enrichment device for 10–200 μm MP.

This device has been reported in a study co-authored by Professor Hiroshi Moriwaki of the Department of Applied Biology, Faculty of Textile Science and Technology, Shinshu University, which became available online on 26 March 2023 and will be published in Volume 315 of Separation and Purification Technology journal on June 15, 2023.

“Our proposed microfluidic device, designed on the basis of an electric-hydraulic analogy, has three 1.5 mm wide microchannels connected via four 0.7 mm wide trifurcation joints. The MP is aligned in the middle of the center microchannel using a bulk acoustic wave of resonant frequency of 500 kHz. As a result, a 3.2-fold MP enrichment should occur at each junction, resulting in an overall 105-fold enrichment in the device.” explained Prof. Akiyama, described the design of their device. While MP is collected from the middle branch of the trifurcation junction, the remaining MP free fluid is excreted from the other branch.

The researchers evaluated the device’s collection performance by measuring its total collection rate for microparticles of 5, 10, 15, 25, 50, and 200 μm in diameter. The collection rate exceeded 90% for all microparticles except 5 μm, which were too small to be acoustically controlled. Next, the researchers tested the device using two mixed water samples, one with small MP (25–200 μm) and one with very small MP (10–25 μm). Collection rates range from 70–90%, and actual MP enrichment varies from half a design grade of 105 to a design grade.

Although some MPs were found to slow down and clog the walls of the device’s microchannels by acoustic radiation forces, the researchers believe this minor limitation can be easily overcome through pre-filtration and by enhancing 2D focusing.

Prof. The optimistic Akiyama concluded, “This proposed microfluidic device based on acoustic focusing can efficiently, quickly and continuously collect 10–200 μm MP without recirculation after pre-filtration of larger MP through the mesh. It can be installed in washing machines, factories, and other sources of MP to efficiently enrich and remove MP of various sizes from laundry and industrial wastewater. This will make it possible to prevent the dumping of MPs into the environment.”

We hope for a cleaner environment free of microplastics, thanks to this useful discovery by Shinshu University researchers.

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About Shinshu University

Shinshu University is a national university founded in 1949 located beneath the Japanese Alps in Nagano which is known for its stunning natural scenery. Our motto, “Powered by Nature – strengthening our networks with society and applying nature to create innovative solutions for a better tomorrow” reflects our mission of nurturing promising creative professionals and deepening collaborative relationships with local communities, which results in our contribution to development regional. development with innovation in various fields. We strive to provide solutions for building a sustainable society through interdisciplinary research fields: materials science (carbon, fiber and composites), biomedical science (for incurable diseases and preventive medicine) and mountain science, and aim to enhance research and innovation capabilities through collaborative projects with leading researchers from the world. For more information, visit https://www.shinshu-u.ac.jp/english/ or follow us on Twitter @ShinshuUni for our latest news.




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