Say the word silk, and your mind conjures images of smooth and shiny textures, rich colours and glistening threads. Silk is synonymous with sophistication and elegance. It’s also loaded with historical and cultural significance. Unravelling the silkworm’s secrets is a tale of accidental revelation, fierce protectionism, fantastic wealth and scientific discovery.
Silk was a highly guarded state secret in ancient China. Successive rulers prohibited the export of live silkworms, and guards lined the famed “Silk Road,” executing anyone caught trying.
Silk enchanted royal courts, fashion icons and industry titans for centuries. More recently, previously unknown applications of silk proteins have been identified, fueling research into biomedical, cosmetic and industrial applications.
And – if the legend is true – the highly profitable industry was discovered by accident.
The Legend of Silk
Once upon a time (about 4,000 years ago), China’s Yellow Empress rested in the shade of a white mulberry tree sipping hot tea. Suddenly – plop! - a tiny cocoon landed in her cup. Before she could react, it unravelled into a soft, strong thread.
The Empress was transfixed. She vowed to locate the source of the cocoon, discovering the Bombyx Mori silkworm feeding on the mulberry leaves above. According to the legend, she invented the reel to join the strands into long threads. Next, the Empress designed looms to weave them into vibrant fabrics. The mystery and history of silk began.
The process of growing mulberries, cultivating silkworms and harvesting their cocoons to produce silk was refined over time. It marked the beginning of sericulture.
Silk was highly sought-after across the empires of the Western world. The famed “Silk Road" connected East Asia to India, Europe and Africa, bringing incredible riches to China. For nearly 3,000 years, silkworms remained China's exclusive domain, resulting in a monopoly on silk production and trade in silk fabric.
Silkworms are now cultivated on mulberry plantations around the world. Yet, they continue to reveal new secrets that will impact many aspects of our lives.
From Silkworm to Silk Protein: Silk’s Other Secret
In its final stage of larval development, the silkworm produces fibroin and sericin. Fibroin makes up 75% of the cocoon and is the main ingredient in silk fiber production. Sericin, the glue that holds the filaments together, was once considered a waste by-product and discarded.
But these two remarkable natural proteins have a multitude of uses. They are biocompatible, meaning our bodies do not reject or react to them. And the fact that they are biodegradable increases potential environmentally friendly applications.
Silk proteins have captured the attention of scientists developing modern biomedical treatments, cosmetic products, and industrial applications.
The Science of Natural Silk Proteins
Fibroin has unique properties. It is known for “good biocompatibility, slow biodegradability and excellent mechanical properties.” Fibroin can absorb water, tolerate temperature variations, and insulate. It is an ideal raw material for a range of biomedical applications.
Fibroin has been used for decades for medical sutures. Now, countless biomedical and industrial uses have been identified. From tissue engineering, ligament replacement and cardio-vascular grafts to antibacterial wound dressings, bio-membranes and UV protection, the list of fibroin applications continues to grow.
Researchers at Tufts University envisage a new era of fibroin coatings like “automotive windshields where rainwater just rolls off without using wipers, coatings on metals that help prevent rust, or on fabrics to make them easier to clean.”
Silk sericin is revealing an array of applications. “Silk sericin was considered an unutilized protein by-product from the textile industry, generating tons of residues every year. However, much effort has been dedicated to its recovery after being associated with numerous biological properties such as antioxidant, antibacterial, anti-coagulation and regenerative activities.”
Sericin is roughly 30% of the cocoon weight and contains 18 amino acids. It has proven effective in biomedical applications and cosmetics products. It is an ideal candidate for new industrial coatings and biodegradable membranes to reduce environmental waste.
Sericin is recognized for “easy cross-linking, copolymerization and blending with other natural or synthetic polymers.”
Researchers around the globe continue to expand our knowledge of silk proteins. Catholic University of Portugal researcher Anabela Veiga, currently on a Fulbright Scholarship to Tufts University, told me, “Silk proteins hold the answers to so many questions. As researchers, we are discovering, developing, honing and looking to commercialize several applications. And personally, one of the best aspects is silk proteins are sustainable, non-toxic and environmentally friendly.”
Extracting Silk Proteins at Scale
Developing large-scale extraction solutions becomes imperative as commercial applications using silk proteins multiply. A fundamental impediment to commercial-scale extraction is accessing a consistent pipeline of silk cocoons. Creating an ecosystem that secures raw material supply is critical.
Cooperatives are emerging to meet this demand. And because cocoons used for silk protein extraction do not require intact silk fibers, it helps silk farmers generate income from cocoons the traditional fiber market would typically discard.
Historically, inefficient and outdated processes limited silk protein production, resulting in inconsistent quality. Increased demand for silk proteins leads to better extraction methods and improved consistency.
A favoured method is high temperature, high pressure (HTHP) water degumming procedures to separate fibroin and sericin. It is the least toxic technique and activates the highest collagen production. It has been observed that “hot-water extraction is a simple and environmentally friendly method that preserves the main characteristics of silk sericin.
Silk’s Bright Future
The Bombyx mori silkworm is more than fabric. The exceptional qualities exhibited by silk proteins are opening a world of opportunity. Companies have started extracting fibroin and sericin at scale in response to increased demand from researchers and manufacturers. They are producing a variety of molecular weights, achieving uniformity and protein chain integrity.
Soon, we will see biomedical and industrial applications everywhere.
Here are a few examples of companies using silk proteins:
Mori “uses just salt and water to extract the protein from silk to create an all-natural and edible protective layer that keeps food fresher for longer.”
Evolved by Nature uses silk proteins to make medical therapeutics, skincare and textiles.
Silk Technologies is developing silk protein-based eye drops to combat Dry Eye Disease.
Orthox makes fibroin-based tissue scaffolds to repair damaged cartilage and orthopedic injuries.
Fibroheal uses silk proteins for wound healing and wound management.
Revoterial replaces toxic materials in manufacturing apparel and consumer products with its “organic, renewable, cost-effective, and non-toxic” patented Silxt alternative.
The list continues to grow as research moves from the lab to commercial products.
From an accidental discovery to modern medical, cosmetic and industrial applications, we continue unravelling the silkworm’s secrets.