Chemical modification of arginyl residues in silk fibroin: 1. Reaction of 1,2-cyclohexanedione in borate buffer

Functional modification of silk fibroin from silkworms and its application to medical biomaterials: A review

Silk fibroin (SF) from the silkworm Bombyx mori is a fibrous protein identified as a widely suitable biomaterial due to its biocompatibility, tunable degradation, and mechanical strength. Various modifications of SF protein can give SF fibers new properties and functions, broadening their applications in textile and biomedical industries. A diverse array of functional modifications on various forms of SF has been reported. In order to provide researchers with a more systematic understanding of the types of functional modifications of SF protein, as well as the corresponding applications, we comprehensively review the different types of functional modifications, including transgenic modification, modifications with chemical groups or biologically active substance, cross-linking and copolymerization without chemical reactions, their specific modification methods and applications. Furthermore, recent applications of SF in various medical biomaterials are briefly discussed.

Natural Fibrous Protein for Advanced Tissue Engineering Applications: Focusing on Silk Fibroin and Keratin

As one of the important branches of natural biopolymer, natural fibrous protein has a lot of advantages including good mechanical properties, excellent biocompatibility, controllable biodegradability, renewability, abundant sources, and so on. Moreover, natural fibrous protein is also a protein that could only be used for structure supporting without any bioactivities, which attracts a lot of attentions in the field of tissue engineering scaffold. This chapter is taking silk fibroin and keratin as model materials of natural fibrous protein, focusing on their protein structure, chemical compositions, processing and extraction methods, chemical modification methods, and their applications in tissue engineering through advanced manufacturing.

Silk-based stabilization of biomacromolecules

Silk fibroin is a high molecular weight amphiphilic protein that self-assembles into robust biomaterials with remarkable properties including stabilization of biologicals and tunable release kinetics correlated to processing conditions. Cells, antibiotics,monoclonal antibodies and peptides, among other biologics, have been encapsulated in silk using various processing approaches and material formats. The mechanistic basis for the entrapment and stabilization features, along with insights into the modulation of release of the entrained compounds from silks will be reviewed with a focus on stabilization of bioactive molecules.

Biomedical applications of chemically-modified silk fibroin

Silk proteins belong to a class of unique, high molecular weight, block copolymer-like proteins that have found widespread use in biomaterials and regenerative medicine. The useful features of these proteins, including self-assembly, robust mechanical properties, biocompatibility and biodegradability can be enhanced through a variety of chemical modifications. These modifications provide chemical handles for the attachment of growth factors, cell binding domains and other polymers to silk, expanding the range of cell and tissue engineering applications attainable. This review focuses on the chemical reactions that have been used to modify the amino acids in silk proteins, and describes their utility in biomedical applications.

Chemical modification of the arginyl residue in silk fibroin: 2. Reaction of 1,2-cyclohexanedione in aqueous alkaline medium

The arginyl residue of solubilized silk fibroin was chemically modified with 1,2-cyclohexanedione in aqueous alkaline medium to form a stable imidazolidinone ring, and its positive charge was masked. CD spectra of the modified silk fibroin in aqueous solution showed an increase in the fraction of random coil conformation. The increase may be caused by the exposure to alkaline medium in the modification reaction. FT-IR and CD spectra of the silk fibroin films before and after the modification indicated that the conformational change in the modified silk fibroin in the solid state did not occur by the modification of its arginyl residue with 1,2-cyclohexanedione. The chemical stability of the modified silk fibroin film was investigated in vitro with phosphate-buffered saline solution. The modified arginyl residue in the film was stable in the phosphate-buffered solution.

Chemical modification of silk fibroin with N-acetyl-chito-oligosaccharides

N-Acetyl-chito-oligosaccharides (NACOS)-silk fibroin (SF) conjugates (NACOS-CY-SF) were prepared by the reaction of solubilized SF and cyanuric chloride (CY)-activated NACOS modifier (NACOS-CY). N-Acetyl-D-glucosamine (NAG), as a model compound, was reacted with CY to clarify the chemical structure of the modifier. The 1H- and 13C-NMR spectra of the reactant suggest that the anomeric hydroxyl group of NACOS reacted with the chlorine atom of CY. The content of NACOS in the NACOS-CY-SF conjugates was calculated by comparing the integral values of the signals in the 1H-NMR spectra of the conjugates and the mixture of NACOS and SF. As the 1H-NMR spectrum of the conjugates showed a downfield shift of the aromatic protons of the tyrosine residue, the tyrosine residue in SF reacted with another chlorine atom of the triazine ring of the modifier. The result of the amino acid analysis of the conjugates suggests that lysine residues also reacted with the modifier.