fibroin

Fibroin is a fibrous protein that forms the core of silk fibers produced by certain arthropods, most notably the domesticated silkworm Bombyx mori. It is secreted by the silkworm’s posterior silk gland as a concentrated solution and is combined with sericin, the gummy coating that binds the fibers together in raw silk.

In Bombyx mori silk, fibroin consists mainly of two protein components: a heavy chain (~390–400 kDa) and a light chain (~25–26 kDa) linked by disulfide bonds, together with a small glycoprotein called P25 that associates with the complex. The typical stoichiometry is heavy:light:P25 about 6:6:1. The heavy chain contains long repetitive regions rich in glycine, alanine, and serine, which form beta-sheet crystalline domains interspersed with amorphous sequences. This architecture underpins the fiber’s strength and toughness.

Silk fibroin is insoluble in water once the fiber is formed, but it can be dissolved in certain chaotropic solvents or regenerated for processing into fibers, films, foams, or hydrogels. Degumming removes the sericin coating to obtain pure fibroin fibers.

Applications of fibroin-derived materials span biomedicine and materials science. Because of its biocompatibility and biodegradability, silk fibroin is used in sutures, tissue-engineering scaffolds, drug delivery systems, and various regenerative medicine applications. Advances include recombinant production and chemical modification to tailor mechanical properties, degradation rates, and biofunctionality.

Although most well-known in silkworms, silk derived fibroin has inspired research into other silk sources and synthetic approaches, broadening its potential applications.