Keratin, a fibrous structural protein, is the major component of hair (approximately 95 wt% in wool [1]), feathers (approximately 90 wt% [2]), and the outer layer of skin, nails, horns and beaks. According to its structure and function, keratin is categorized into two groups with-i) low sulfur content (soft keratin) and ii) high sulfur content (hard keratin) [3-5]. The former is the crucial structural component of epithelial tissues [6], whereas the latter is found in nails and beaks. Different from other fibrous proteins, keratin contains high amounts of cysteine (7-20% of total amino acid residues) [7, 8], mostly localized at the terminal regions of the protein [9, 10]. Similar to other biopolymers, the intrinsic biocompatibility [11-13], biodegradability [14, 15], and natural abundance of keratin make it a valuable candidate for biomedical and tissue engineering applications [16, 17]. The presence of the primary amino acid sequence of cellular-binding motifs, i.e. RGD (Arg-Gly-Asp), in