Overview
Fibroin is the fibrous, insoluble protein that constitutes the core of many natural silks. It is produced in the silk glands of arthropods such as the silkworm (Bombyx mori) and various spiders and is covered in the native fibre by a glue-like protein called sericin. Chemically and mechanically distinct from the surrounding coating, fibroin gives silk its characteristic strength and luster. In descriptions of molecular biology it is often referred to simply as a protein.
Structure and chemistry
The polymeric chains of fibroin are high‑molecular‑weight polypeptides with repeating amino acid motifs rich in glycine, alanine and serine. These repeats pack into stacked beta-sheet crystalline regions interspersed with less-ordered, amorphous segments. The crystalline zones provide tensile strength and stiffness; the amorphous regions contribute extensibility and toughness. Native fibroin does not dissolve in water under normal conditions but can be processed into solutions by specialized solvents and salts for laboratory and industrial use.
History and production
Silk production by humans—sericulture—has ancient origins and historically focused on Bombyx mori fibres whose fibroin was harvested after degumming to remove sericin. Spiders also spin fibroin-based silk, but their silk glands and spinning behavior differ from silkworms; spider silk is more difficult to harvest in large quantities. Modern biotechnology has enabled recombinant expression of fibroin-like proteins and methods to regenerate fibroin from dissolved fibres.
Properties and processing
Fibroin’s combination of strength, flexibility and biocompatibility makes it a valuable material. Common processing steps include degumming, dissolution in chaotropic media, and reformation by spinning, casting or electrospinning to produce fibres, films, hydrogels and foams. Material properties can be tuned by controlling beta-sheet content, crystallinity and molecular alignment.
Uses and applications
- Traditional textiles and high-performance fabrics.
- Medical sutures, tissue scaffolds, wound dressings and drug-delivery matrices.
- Biodegradable films, optical devices and experimental sensors.
Distinctions and notable facts
Fibroin should be distinguished from sericin (the hydrophilic coating). Spider fibroins and silkworm fibroins differ in sequence and mechanical behavior; researchers often compare them when engineering new materials. For further general context on silk itself, see silk. Ongoing work explores recombinant production, composite materials and environmentally friendly processing to widen fibroin’s industrial and biomedical roles.