Silk‐Based Biomaterials

Abstract

IntroductionSilk is a hierarchically structured fibrous protein that has been used for thousands of years for different applications such as textile production and wound dressings [1]. Although silk proteins are produced by a large number of arthropod species such as wasps, bees, and crickets, during the past few decades, the scientific community has focused its attention in the silk produced by the mulberry silkworm Bombyx mori and by different spider species. Farming of the silkworm B. mori started around 5000 years ago in China, and since then, the cocoon case produced by this animal has been used as a source of silk for the textile industry. More recently, B. mori silk has been used commercially in the development of sutures for medical applications [1,2]. In contrast to B. mori silk, spider silk has not been commercialized for biomedical proposes mainly because of the territorial cannibalistic behavior of spiders, which makes them difficult to farm, along with the low levels of silk production. However, in the past, spider webs have been used as bandages for wound dressing, because of its antimicrobial properties, and in other human activities such as fishing and hunting [3]. The results from recent studies demonstrating the biocompatibility of silk and the exquisite mechanical properties of silk fibers, especially in the case of spider silk, are the main reasons why B. mori and spider silk proteins have been the target of intense research efforts, when compared with the silk produced by other arthropods, aimed at developing new silk-based biomaterials with superior mechanical and biological properties.On the basis of the background given above and since B. mori and spider silk are the most extensively characterized silk, this chapter focuses on the silk proteins produced by these animals and on the perspectives of using these proteins for future biomedical applications.The silk produced by B. mori is the most widely used, since this silkworm is easy to farm, allowing for steady and large-scale production [1]. The B. mori silk fiber is formed by two microfilaments embedded in a gluelike glycoprotein named sericin, which works as a coating and is used by the animal for cocoon assembly. Each microfilament results from the assembly of a hydrophobic ∼370 kDa heavy-chain fibroin protein, with a relatively hydrophilic ∼25 kDa light-chain fibroin and a 30 kDa P25 protein [4]. The heavy-chain fibroin is a large insoluble macromolecule formed by ∼5263 amino acids and is rich in glycine (G, 45.9%), alanine (A, 30.3%), serine (S, 12.2%), tyrosine (Y, 5.3%), and valine (V, 1.8%) residues [1,5]. This heavy-chain fibroin is formed by a highly repetitive crystalline fraction of 2377 repeats of GX. The X position is occupied by the A residue in 64% of the repeats, by S in 22%, by Y in 10%, by V in 3%, and by threonine (T) in 1.3% of the repeats [5,6]. These repetitive cores form 12 domains that alternate with 11 nonrepetitive amorphous domains formed by 25 amino acids residues, which connect the crystalline domains. These a...

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