Fibroin is a type of protein created by Bombyx mori (silkworms) in the production of silk. Silk emitted by the silkworm consists of two main proteins, sericin and fibroin, fibroin being the structural center of the silk, and sericin being the sticky material surrounding it.
The fibroin protein consists of layers of antiparallel beta sheets. Its primary structure mainly consists of the recurrent amino acid sequence (Gly-Ser-Gly-Ala-Gly-Ala)n. The high glycine (and, to a lesser extent, alanine) content allows for tight packing of the sheets, which contributes to silk's rigid structure that can't be stretched (tensile strength). A combination of stiffness and toughness make it a material with applications in several areas, including biomedicine and textile manufacture.
Fibroin is known to arrange itself in three structures, called silk I, II, and III. Silk I is the natural form of fibroin, as emitted from the Bombyx mori silk glands. Silk II refers to the arrangement of fibroin molecules in spun silk, which has greater strength and is often used in various commercial applications. Silk III is a newly discovered structure of fibroin.[1] Silk III is formed principally in solutions of fibroin at an interface (i.e. air-water interface, water-oil interface, etc.).
According to a Scientific American, AOL News, Huffington Post Healthy Living online news story article posted on Sunday, January 1, 2012, by Sophie Bushwick,: "Engineers from Tufts University have created ... micro-needles- made from the major protein in silk, fibroin. The work is in the journal "Advanced Functional Materials".[[[Konstantinos Tsioris]] et al., "Fabrication of Silk Micro-Needles for Controlled Release Drug Delivery"] The researchers created molds for arrays of needles just 500 microns tall and 10 microns wide. That's a tenth the width of the average human hair. They then poured a solution of fibroin mixed with a drug into the molds. The resulting micro-needles are dried and undergo further processing. In tests, a patch containing numerous micro-needles successfully released the drug, which maintained its biological activity. The tiny needles are too short to reach the nerves under the skin, so they can deliver drugs without the pain of a traditional shot. Even better, they can gradually release medication over time. While skin patches and slow-release pills are currently used for this purpose, they only work with certain kinds of medication. ..."[2]