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If you want to work in Mark MacLachlan’s lab, it helps to have a taste for seafood. The chemist, who works at the University of British Columbia in Vancouver, is working on turning the discarded shells of shrimp, crabs, and lobsters into advanced materials that could be used in batteries, plastics, or even for growing new organs. And it is up to his students to provide a steady supply of carcasses.
“One of my students buys lobsters and crabs, eats them, and then brings the shells to work,” MacLachlan says. Another has managed to secure a free supply of shells from a seafood restaurant.
MacLachlan is after one particular component of the material that makes up the shells—chitin, a tough substance that is structurally similar to the cellulose in plant cell walls. The chitin is made of rod-shaped nanocrystals that are organized in a helix. Their orientation reflects light in a way that makes the shells iridescent.
From this starting point, MacLachlan has figured out how to transform chitin into a number of useful materials, such as an iridescent film that changes color when pressure is applied, and a litmus paper-like film that detects different chemicals in water.
But one of the most promising materials begins when the chitin is cooked at 900 °C in a nitrogen atmosphere. This transforms it into a nitrogen-doped carbon that can be used to make electrodes for batteries. “Chitin-based films are very porous, so they have a large surface area,” says MacLachlan. This gives them a high capacity for storing charge.
Battery companies are always looking for newer and better electrode materials, but MacLachlan says that, for now, chitin-based electrodes remain prohibitively expensive. Though waste crustacean shells are very cheap, the equipment needed is too costly to be economical. “I think this would be too expensive to sell to Tesla,” he jokes.
But other options, such as chitin-based bioplastics, have great potential. “You can make really tough, biodegradable plastics from chitin nanocrystals,” MacLachlan says. The plastic could be used to make food wrap and food containers, perhaps even bandages. The process for making these bioplastics is as simple as making conventional plastics: the chitin is dissolved in a solvent, which is allowed to evaporate, leaving a film of the bioplastic. Not only are the bioplastics environmentally friendly (because they biodegrade), but they can help repurpose waste from the shellfish industry.
João Borges, a materials scientist from the New University of Lisbon, says he expects development of chitin-based bioplastics to advance quickly over the next few years. Eventually, he thinks chitin bioplastics, alongside cellulose-based bioplastics, will become frequent substitutes for synthetic plastics in many common applications.
Borges, though, thinks the more exciting possibility for chitin-based materials is in tissue engineering. Biomaterials based on chitin or cellulose could form scaffolds to help support the growth of new tissues in the body, then dissolve once they are no longer needed. He says these kinds of products are probably 20 years away, though, because it is difficult to get consistent chemical and mechanical properties from materials based on natural products. “In the medical field we must have complete control over the properties of the material,” he says.
MacLachlan’s students will keep munching their way through shrimp cocktails for science, but, it’s likely that you will have a crab-based sandwich bag long before a crab battery or crab-assisted heart valve.