Humans have been trying to untangle the secrets of silk for at least a hundred years now. And why wouldn’t they? The material is legendary, after all. Silk’s unique and versatile properties have countless possibilities for sustainable future technologies. These are extraordinarily strong in relation to both fiber dimension and the perception of its delicate nature and weight, for weight is actually stronger than steel.
Today, the modern quest to tame the wonders of silk continues to take place in laboratories across the world. Scientists and start-ups race to create synthetic materials that mimic its properties. The pressure from consumers and animal welfare groups like PETA have led many retailer stores like ASOS, H&M, Zara, and GAP to ban animal fibers, including mohair and silk. New technologies are therefore helping create new and better alternatives to silk. One such example is Bolt Threads launching its first commercial spider silk. But the company does not use spiders in the process. In fact, the thread is made from yeast, water, and sugar. The raw silk is produced through fermentation, much like brewing beer, except instead of the yeast turning the sugar into alcohol, they turn it into the raw materials of spider silk. This innovative material is both strong and flexible and could be used in everything from bulletproof vests and biodegradable water bottles to shoes and flexible bridge suspension ropes. The brand even announced a partnership with British ethical designer Stella McCartney and outdoor wear brand Patagonia.
Surprisingly, silk is not just known as a luxury textile product. Although a larger part of the growing biomaterials industry produces synthetic silk in the hope to find a sustainable replacement for petroleum-based materials across a range of businesses, it recently has gained immense popularity in biomedicine and environmental science as well. Silk has come to the forefront of sustainability research.
Silk reinvention at the laboratory scale focuses on a variety of applications – in the form of drug delivery devices, biocompatible optics, as a biodegradable substrate, and more. Currently, silk’s use has also been investigated in relation to the food supply chain both as a crop booster and a food protective coating. The use of these silk coatings has immense potential to reduce food waste, which is a significant component of the global carbon footprint. As concerns of food wastage keep rising, researchers from the Tufts University in Massachusetts recently hailed silk fibroin-based edible coatings as a potential solution. The latest paper in Applied Physics Reviews outlines how silk’s “versatile” properties present possibilities for the food supply chain both as a crop booster and a food protective coating.
Silk fibroin is an ‘ideal candidate’ to preserve crop freshness, minimise food loss, and ensure food safety, said lead researcher and author, Giulia Guidetti. Once applied as a coating, it is edible, tasteless, odourless, transparent, biodegradable, and possesses ‘outstanding mechanical properties’ as well as low permeability to oxygen and water vapours. “We are continuing to improve the integration between different disciplines,” she continued. “For example, we can use silk as a biomedical device for drug delivery but also include an optical response in that same device. This same process could be used someday in the food supply chain. Imagine having a coating which preserves the food but also tells you when the food is spoiled.”
Tufts’ study of 2016 showcased the use of silk fibroin as an edible coating on strawberries and bananas by dipping the fruits in a silk fibroin suspension. These coatings were able to extend the shelf life of both kinds of fruit. They also decreased the respiration rate, weight loss, water vapor, and oxygen diffusion, thereby preserving its firmness and colour. Additionally, it delayed ripening of bananas compared to uncoated control during 14 and 9 days of storage for strawberries and bananas, respectively. Silk’s use is now being investigated as a crop booster. Speaking in this regard, silk fibroin was also previously used in combination with sugar additive trehalose to develop a seed coating that boosted seed germination and mitigated abiotic stressors by encapsulating, preserving, and releasing biofertilizers in the soil. Today, a few challenges remain unsolved and partially hinder silk’s use as a ubiquitous material both at the laboratory scale and at the industrial level, cautioned the researchers.
Silk is versatile and often superior to more traditional materials, solely because it can be easily modified chemically as well as physically and tuned for certain properties or assembled into a specific form depending on its final use. However, the real challenge lies in controlling and optimising these aspects depending on understanding the material’s origin. The bottom-up assembly of silk by silkworms has been studied for a long time, but a full picture of its construction is somewhat still lacking. The team at Tuft emphasised the importance of understanding these processes because it could allow them to fabricate the material more effectively and with more control over the final function.
“One big challenge is that nature is very good at doing things, like making silk, but it covers an enormous dimensional parameter space”, said another lead researcher, Fiorenzo Omenetto. “For technology, we want to make something with repeatability, which requires being able to control a process that has inherent variability and has been perfected over thousands of years.” As with all-natural materials, silk fibroins are dependent on environmental factors. This will require the development of “dedicated, monitored, and automated large-scale production approaches to mitigate batch to batch variability, external contaminants, and environmental influence,” explained Guidetti. Genetic engineering techniques can help achieve higher protein yields, she added, ultimately leading to silk proteins with new capabilities and, in the future, more economically competitive products. “Genome editing, indeed, could enable the advancement of silk-based devices with finely tuned physicochemical properties along with advanced functionalities,” wrote Guidetti, “while broadening the manufacturing capacity because of a robust control on genomic sequence, protein size, and homogeneity, as well as degradation rate, thereby generating responsive materials.
Moving forward, scientists are seeking to make more materials and devices using silk as an integral component in food technology and environmental sciences. Not only can such technology extend the shelf life of whole produce, but it can also have a dramatic effect on cut produce, meats, fish, and processed foods. A company called Cambridge Crops is leveraging its breadth of application to address the broader needs of the food industry through strategic partnerships. They are using specific properties of synthetics and textiles to harbour a new generation of advanced materials that can be interfaced with bio-based materials. Cambridge Crops remains optimistic about silk’s potential to mitigate many of the challenges facing complex food networks. The company iterates that their technology is one that can enable the elimination of plastic food packaging.
The increased food wastage around the world represents a significant global economic and environmental burden that negatively impacts society in several ways. Nutritious food is often sent to landfills. Plastic food packaging is also sent to landfills or finds its way into the ocean. The storage, transport, and disposal of discarded food are all costly processes, which requires huge funding. Innovative new strategies, like these, tend to address the core challenges regarding agricultural and biomaterial industries. These are essential as the world becomes increasingly aware of the need to reduce the use of “single-use” plastics, eliminate packaging troubles, and find new ways to keep producing fresh food longer, but in a sustainable and environmentally friendly way.