Fibroïne

Fibroïne is the principal structural protein of silk fibers produced by silk-producing insects, most notably the domesticated silkworm Bombyx mori. It is secreted by the middle silk gland and forms the core of the silk filament, which is surrounded by sericin, a glue-like protein that is removed during textile processing (degumming).

Biochemically, fibroïne consists of a heavy chain (~390 kDa) and a light chain (~25–27 kDa) linked by disulfide bonds; a noncovalent P25 protein accompanies the two chains. The heavy chain contains repetitive glycine- and alanine-rich motifs that assemble into beta-sheet-rich crystalline regions, providing high tensile strength and stiffness, while noncrystalline regions contribute elasticity.

In nature, fibroïne is secreted into the silk gland lumen and extruded as a filament that hardens into fiber. The resulting silk fiber is a composite of fibroïne and sericin, with properties influenced by processing conditions and the beta-sheet content.

Applications include textile production and, increasingly, biomedical materials. Silk fibroïne can be processed into films, fibers, sponges, and hydrogels and is valued for its biocompatibility, tunable degradation, and mechanical properties. Researchers also pursue recombinant fibroïne production to enable scalable, standardized materials.

Different species produce distinct fibroïne varieties; Bombyx mori silk fibroïne is the best characterized. Ongoing work seeks to tailor amino-acid composition, crystallinity, and processing to optimize performance for specific uses.