Biodegradable Materials Based on Silk Fibroin and Keratin

Abstract

Wool and silk were dissolved and used for the preparation of blended films. Two systems are proposed: (1) blend films of silk fibroin and keratin aqueous solutions and (2) silk fibroin and keratin dissolved in formic acid. The FTIR spectra of pure films cast from aqueous solutions indicated that the keratin secondary structure mainly consists of alpha-helix and random coil conformations. The IR spectrum of pure SF is characteristic of films with prevalently amorphous structure (random coil conformation). Pure keratin film cast from formic acid shows an increase in the amount of beta-sheet and disordered keratin structures. The FTIR pattern of SF dissolved in formic acid is characteristic of films with prevalently beta-sheet conformations with beta-sheet crystallites embedded in an amorphous matrix. The thermal behavior of the blends confirmed the FTIR results. DSC curve of pure SF is typical of amorphous SF and the curve of pure keratin show the characteristic melting peak of alpha-helices for the aqueous system. These patterns are no longer observed in the films cast from formic acid due to the ability of formic acid to induce crystallization of SF and to increase the amount of beta-sheet structures on keratin. The nonlinear trend of the different parameters obtained from FTIR analysis and DSC curves of both SF/keratin systems indicate that when proteins are mixed they do not follow additives rules but are able to establish intermolecular interactions. Degradable polymeric biomaterials are preferred candidates for medical applications. It was investigated the degradation behavior of both SF/keratin systems by in vitro enzymatic incubation with trypsin. The SF/keratin films cast from water underwent a slower biological degradation than the films cast from formic acid. The weight loss obtained is a function of the amount of keratin in the blend. This study encourages the further investigation of the type of matrices presented here to be applied whether in scaffolds for tissue engineering or as controlled release drug delivery vehicles.

Alternative Methods of Preparation of Soluble Keratin from Chicken Feathers

“…30 % [17,18], and DTT ca. 80 % [18]. Thompson and O'Donnell [34] solubilized wool keratin with thioglycolic acid to a maximum value of 70 %.…”

“…Reduction of keratin by 2-mercaptoethanol, dithiothreitol (DTT) or dithioerythritol, thioglycolic acid, glutathione, sulphites, and bisulphite generates free cysteine residues, and the resulting cysteine-containing derivatives are called ''kerateines'' [7,[15][16][17][18]. They are less polar and more stable in acidic and alkaline solutions than the oxidized derivatives, and they contain amino acid residues capable of re-crosslinking.…”

“…Keratin-based materials are suitable for biomedical [18,23,24], cosmetical [25] and agricultural applications [26]. Due to biodegradability and high mechanical strength, keratin materials have a promising potential for biodegradable packaging production [27,28].…”

Poly(ε-caprolactone)/keratin-based composite nanofibers for biomedical applications

“…23 Keratin proteins give rise to several characteristic absorption bands known as amide A (3286 cm 21 ), amide B (3056-3075 cm 21 ), amide I (1600-1700 cm 21 ), amide II (1480-1580 cm 21 ), and amide III (1220-1300 cm 21 ). 10,24 PCL/keratin nanofibers showed the characteristic bands of keratin in addition to the characteristic peaks of PCL but the relative strengths of these peaks changed with increasing keratin concentration of the nanofibers. Amide I and amide II bands are two major characteristic bands of peptides which are sensitive to the secondary structure of the proteins.…”

Effect of freezing methods on the properties of lyophilized porous silk fibroin membranes

“…SF has been used for cell culture, wound dressing, drug delivery, enzyme immobilization, and as a scaffold for bone tissue engineering 1,2 . SF is composed primarily of glycine, alanine, and serine amino acids, and presents three kinds of secondary structure: in crystalline areas, α-helical and β-folded structures (silk I and silk II, respectively), and in amorphous areas, disordered conformation and random globules (random coil) 3,4 . Biomaterials made of proteins, such as SF, are prone to physical and chemical degradation during storage.…”