Silk biomaterial

A silk biomaterial is a biomaterial made from the structural proteins of silk, primarily silk fibroin and, less often, the associated protein sericin. Most are obtained from the silk cocoons of the silkworm Bombyx mori, although spider silk and the silks of a few other insects are also used. The medical use of silk is far older than the term biomaterial. Silk thread served as a surgical suture for centuries before the protein was first dissolved and cast into films, gels, sponges, fibres and particles. Fibroin presents a unique combination of properties rarely found in one material. It is strong and tough, dissolves and reconstitutes in water rather than aggressive solvents, and breaks down in the body over a period that can be lengthened or shortened as required. Once the sericin is removed, it provokes only a mild immune response. A single quantity of purified protein can therefore be shaped into many different forms, each suited to a particular use. Until the late 1990s, reliable methods for dissolving silk fibres and forming the resulting solution were not available, and most of the work after that has been based on them. Silk biomaterials are used in tissue engineering, drug delivery, wound care and bioelectronics, and a small number have reached clinical use. The factors limiting them are specific: the raw material varies from batch to batch, silk is difficult to sterilise without damaging the protein, and production is hard to scale.