In yesterday's post we mentioned how some experts compare plastic in the oceans to an invasive species that impacts on biodiversity. So let's shift our attention today to an invasive species that is worrying many Mediterranean countries - the blue crab - to ponder a bit about bio-materials.
In 2019, tourists heading to the South of Italy, and in particular to the Puglia region, received warnings about the dangerous invasion of Atlantic blue crabs.
The blue crab's presence in the Mediterranean dates back to around 1898, following the opening of the Suez Canal. Gradually the crabs spread along Spain's Mediterranean coast and also reached Italy. Their proliferation was accelerated due to increased trans-oceanic marine traffic and rising temperatures caused by climate change. As a result, they started posing a serious threat to native wildlife, biodiversity, and fishing in the region.
Originally from the coasts of North and South America, the Atlantic blue crab is not problematic in its native habitat, but in the Mediterranean it is regarded as an invasive species that is currently causing significant damage to the ecosystem. The clam industry has indeed been severely affected as these crabs proliferate in several lagoon-like locations in Italy, preying on local shellfish and other aquatic organisms. Clam aquafarms, especially in the delta of the Po river valley, have suffered heavy losses, with the crabs devouring up to 90% of young clams, severely impacting future production.
Some have suggested eating the crabs: this has proved the main solution in other countries such as Tunisia where blue crabs quickly spread since 2014, destroying nets and causing trouble for fishermen and other aquatic life. Yet now the crabs have turned into one of the region's most sought-after seafood items and they are also frozen and exported to Asia (mainly to Korea).
But this may not be the final solution as experts state that at this point it is not possible to eradicate the population of blue crabs in Italy as they are multiplying at great speed and the numbers are out of control. Only a small portion of the caught crabs is indeed sold for human consumption due to limited demand, while the rest are discarded and there are plans to use them for animal feed.
Some propose exporting the crabs to other countries, where they may be in demand as a delicacy. Yet that may be tricky: the blue crab population in Maryland's Chesapeake Bay has declined so much that local authorities implement stricter limits on crab harvests. But shipping live crabs from Italy to the Chesapeake Bay shores could introduce diseases or other invasive species that might further harm the bay's delicate ecosystem. At the same time, directly importing to grocery stores, markets, or restaurants, could adversely affect Maryland's economy.
Invasive species that impact on native ecosystems are usually exterminated, but dealing with this aggressive species of crabs capable of eating plastic and metals as well (so you wonder if it is a good idea to eat them…) requires alternative approaches and creative solutions.
Maybe design and science can help us in this case and we can start from taking into consideration the structures and composition of crab carapaces (blue crabs have rather beautiful yet dangerous sharp claws and spiny shells) helped by the studies about this topic made by biomimetic designers and materials scientists.
The answer in dealing with the proliferation of crabs may indeed be in the structural, chemical and compositional makeup of crab carapaces. Let's look at some examples. In 2022, Liangbing Hu, Drector of the University of Maryland's Center for Materials Innovation, and a group of researchers published a paper in the journal Matter. They proposed using crab and lobster shells to create renewable batteries, presenting an eco-friendly alternative to conventional batteries that contain harmful and slow-to-degrade chemicals like lithium-ion, the most common batteries in mobile phones.
These batteries have impressive longevity and are capable of powering devices for many years. Typically, they utilize plastic-polymer-based electrolytes, which are less toxic compared to other options. However, these electrolytes can still take centuries or even millennia to decompose fully.
The exoskeletons of crustaceans, such as crabs, shrimps, and lobsters, are composed of cells containing chitin, a polysaccharide that gives their shells remarkable hardness and resistance. This valuable material, abundant in nature and found in fungi and insects as well, is often discarded as food waste by restaurants and the food industry. However, scientists have long explored its diverse applications, including biomedical engineering for wound dressings and anti-inflammatory treatments, and even in electrical engineering.
According to researchers, through enzymatic or chemical deacetylation, chitin can be converted to its most well-known derivative, chitosan, that can then be used as an electrolyte for batteries. An electrolyte facilitates the movement of charged molecules (ions) between the two ends of a battery, enabling it to store energy. By combining this chitosan electrolyte with zinc, a naturally occurring and cost-effective metal widely used in batteries for its safety, Hu's team successfully created a renewable battery.
The prototype battery demonstrated an impressive 99.7% energy efficiency even after 1,000 battery cycles, equivalent to approximately 400 hours of usage.
These innovative batteries are non-flammable, and the two-thirds of the battery composed of chitosan can break down in soil within five months, thanks to microbial degradation, leaving behind recyclable zinc.
Chitosan has actually been employed for other applications over the years: farmers have been using it since the 1980s to boost plant growth and protect crops from fungal infestations. Beyond agricultural fields, chitosan plays a crucial role in water purification, helping remove sediment and impurities from drinking water, while also serving as a clarifying agent in alcohol-making processes. Its utility extends to the medical field, where hemorrhage control bandages infused with chitosan help in wound healing and sealing.
Moreover, the biodegradable and non-toxic nature of chitosan makes it an ideal material for crafting medical devices that interact with the human body. The prospect of specialized 3D printers creating chitosan-based tissues and organs for transplants holds promise for the future of healthcare.
The researchers at the University of Maryland weren't actually the first to explore the potential of chitosan in batteries. Scientists worldwide have been experimenting with this crab-derived material, yet this study was considered innovative as it combined zinc ions with the chitosan structure, enhancing its physical strength and increasing the battery's overall efficiency.
In February this year, a new study published on ACS Omega revealed that crab shells could be used to create anode materials for sodium-ion batteries, a potential alternative to lithium-ion batteries. In this case researchers converted crab shells into "crab carbon," a material that can be combined with tin sulfide or iron sulfide to form viable sodium-ion battery anodes.
The porous and fibrous structure of the crab carbon enhances conductivity and ion transportation efficiency. In tests, both composites showed good capacities and could endure at least 200 cycles.
Yet crab shells could also be used to make other materials: in March this year, researchers from the Philippines came up with a method to transform crab shells into a bioplastic suitable for creating optical components called diffraction gratings.
In a study published in the Optica Publishing Group journal Applied Optics, the researchers showed how these lightweight, inexpensive gratings are biodegradable and could potentially be used in portable, disposable spectrometers. The chitosan-based bioplastic derived from dried and crushed crab shells showed promising optical properties and was molded using soft lithography, a replication process.
The resulting chitosan gratings demonstrated the expected rainbow pattern when illuminated with white light and produced correct diffraction patterns when tested with a laser beam. This breakthrough offers a sustainable, biodegradable and cost-effective alternative to conventional spectrometer components made from heavy materials like glass. The researchers are now focusing on improving the power efficiency of chitosan gratings for practical real-world applications, particularly in disposable spectrometers for environmental and industrial analysis.
But there are even more opportunities that chitosan may offer: in 2018, researchers at the Georgia Institute of Technology developed a material made from crab shells and tree fibers that could replace flexible plastic packaging used for food preservation.
The material consists in a film created by suspending cellulose and chitin nanofibers in water and spraying them onto a surface in alternating layers (the chitin nanofibers are positively charged, and the cellulose nanocrystals are negatively charged, so alternating layers allows to form an interface between them), creating a strong, transparent, and compostable film.
The new material showed a significant reduction in oxygen permeability compared to traditional polyethylene terephthalate (PET), potentially extending the shelf life of packaged foods. With an abundant supply of cellulose and chitin-rich byproducts from the shellfish industry, the material offers a renewable and sustainable alternative to petroleum-based plastics. However, further research is needed to optimize the manufacturing process and enhance water vapor resistance.
Further researchers could even help us developing an alternative material made with chitosan for plastic bags used in the fashion industry. Talking about clothes and accessories, chitosan could be used also for garments.
Tidal Vision, the only commercial scale US-based manufacturer of chitosan, developed Tidal-Tec®, a platform producing nontoxic flame retardant and antimicrobial textiles and a while back launched a partnership with Leigh Fibers, a large textile fiber processing and upcycling company in North America.
We regularly see in the news features about companies, designers and environmentalists looking for renewable alternatives to replace petroleum-based materials. The abundance of chitin-rich byproducts from the shellfish food industry offers a potential solution, but further research and manufacturing processes are obviously necessary. These advancements regarding chitin and chitosan present a significant market opportunity for batteries and packaging and let's hope we will see more of them.
In the meantime, for those intrigued by close-up studies, a visit to the beach to look for crab carcasses can be truly inspiring. Their shells, sharp thorns, carapace, joints, and ligaments provide fascinating subjects for examination. Indeed, remarkable research often begins with careful observations up close (Please note: no crabs were hurt to write this post – I only collect carcasses of crabs found on the beach for study purposes – you don't need to be a taxidermist to preserve them, but you can leave them to dry buried in a small pile of sand under the sun for a few weeks, then you can keep them in a box and create your own portable cabinet of curiosities).
If you fancy instead a fictitious narrative twist to this crab story, well, get more informed about crab divination in Kapsiki, North Cameroon. Looks like there is much we can learn from (and about) crabs, even when they are a nasty invasive species.
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