Melanin is a ubiquitous compound in nature and is produced by many organisms. However, its potential as a biomass source for the production of chemicals and value-added materials remains relatively unexplored. In a recent study, researchers from Japan investigated the chemical breakdown of melanin derived from squid ink and demonstrated its application in the synthesis of biopolymer films and particles. Their efforts will hopefully pave the way for the adoption of melanin upcycling.
Every year the negative effects of human activities on the environment become more and more apparent. From climate change and microplastics to the endangerment and extinction of countless species, it’s clear we need to find new ways to achieve sustainability. Fortunately, many research groups in leading fields such as chemistry and materials science are working tirelessly to develop solutions to bring us closer to circular and sustainable economies.
One area that has attracted a lot of attention in this regard is biomass upcycling. It refers to the transformation of naturally available organic materials into valuable products, such as biofuels and bioplastics. Although many scientific studies have focused on plant biomass, such as cellulose fibers, the potential of melanin as a biomass source remains underexplored. One of the main reasons for this is that the degradation of melanin – a complex but ubiquitous biopolymer – needs to be further investigated.
From a recent study published in ACS Sustainable Chemistry & Engineering, a research team led by Associate Professor Michinari Kohri from the Graduate School of Engineering at Chiba University, Japan, set out to address this knowledge gap. Using both artificial and natural melanin, they performed a detailed analysis of melanin breakdown and demonstrated its upcycling potential. Their article, which was made available online on April 19, 2024 and published in Volume 12, Issue 18 of the journal on May 6, 2024, was co-authored by Mr. Takumi Morita and Prof. Keiki Kishikawa of the Graduate School of Engineering at Chiba University, Prof. Toshihiko Matsuura from the Laboratory of Biotechnology and Bioengineering at Hokkaido University of Education, and Prof. Hironori Izawa from the Faculty of Engineering, Miyazaki University.
First, the researchers synthesized artificial melanin from polydopamine, yielding a polymer that is structurally very similar to natural melanin. Using powdered samples as a model substance, they performed a series of decomposition tests under different conditions, followed by a series of analytical experiments on the resulting decomposition products.
They then repeated many of these tests with natural melanin, which they extracted from the ink sacs of squids. “From a resource perspective, the melanin concentrated in the ink sacs of squid and squid is easily extracted natural melanin. The catch of squid and octopus has been increasing annually and has hovered around three million tons in recent years,” explains Dr. Kohri out. . Interestingly, the researchers found that both artificial and natural melanin broke down into pyrrole derivatives containing carboxylic acids. This result suggests that melanin derived from other renewable and easily accessible sources, such as insect exoskeletons, animal hair, or melanin-producing microorganisms, could be equally useful as a chemical precursor.
Finally, using the degradation products obtained from artificial and natural melanin as raw materials, the researchers fabricated various polymer films and particles. These experiments serve as a demonstration of the untapped potential of melanin in biomass upcycling. “Since melanin is naturally abundant in biomass and is ultimately degraded by microorganisms, polymeric materials produced using the breakdown products of melanin are also likely to be biodegradable,” points out Dr. Kohri. “Biodegradable polymers can be disposed of without harming the environment, and so the proposed approach for making polymers from melanin breakdown products could lead to the development of sustainable materials.”
Overall, the findings of this study could pave the way for the widespread adoption of melanin upcycling, which could ultimately help us protect the environment. “Just as cellulosic biomass research has advanced because cellulose can be extracted from a variety of underutilized plants, we hope that our efforts will enhance the use of melanin as a biomass source,” concludes Dr. Kohri, with an eye on the future.
