Wool keratin: extraction, processing and applications in the biomedical sector

Keratins are proteins characterised by a high sulphur amount and by the presence of strong disulphide bonds which make keratins water insoluble and resistant to different chemical agents. Wool keratin can be extracted by the cleavage of the cystine bonds by treatment with reducing agents or by sulphitolysis or using oxidising agents. From these extractions intact proteins with molecular weight ranging from less than 10 and 60 kDa are obtained. The hydrolysis of keratins can be obtained by the cleavage of peptide bond using strong acids or strong bases. Recently, green processes such treatments with superheated water and treatment by steam-explosion have been proposed with the aim of avoiding the use of harmful agents. In these cases, due to the cleavage of peptide bonds, protein material with lower molecular weight is obtained. Keratin biomaterials possess many distinct advantages over conventional biomolecules, including a unique chemistry afforded by their high sulfur content, remarkable biocompatibility, biodegradability, hygroscopicity, propensity for self-assembly, and intrinsic cellular recognition. Proteins extracted from wool can be processed as pure keratin, or in blend with other polymers, with cross-linking agents, or in presence of additives (e.g. plasticisers). Films, sponges, nanofibres, microcapsules, hydrogels, powders and solutions can be obtained by the extraction or hydrolysis of wool keratin and by the following processing.