Wool keratin fibrils sponges for bone tissue engineering

Among the natural polymers proposed for biomedical applications, seeking for biocompatibility, biodegradability and, enhanced cellular adhesion, keratin-based materials have emerged as promisingly candidates. Keratin, found in hair, wool, horn, hooves and nails, shows the highest amount of the amino acid cystine in comparison with other proteins. Wool shows a complex histological structure: the external envelop (cuticle) is made of overlapping cuticle cells arranged like roof tiles which wrap the cortex and the cell membrane complex. The cortex is the bulk made of elongated spindle shaped "cortical cells" (fibrils), while the cell membrane complex, sticks the cortical and cuticle cells together. Keratin fibrils sponges have been produced by disruption of the histological structure of the wool fibres through mild alkali treatment, followed by ultrasonication, casting and saltleaching. The sponges showed highly interconnected porosity (93 %) and a microscopic structure which mimicks the Extracellular Bone Matrix (ECM). The alcali treatment converts intermolecular disulphide cystine bonds into shorter monosulphide lanthionine bonds resulting in an improvement of the thermal and water stability. The sponges show a volume swelling in water up to 38 %, however, sponges were stable in water without structural changes and showed excellent resilience to repeated compression stresses. The sponges showed cell adhesion and proliferation for the SAOS-2 cell line, according to in vitro biocompatibility-cell viability assays, due to the excellent biocompatibility of wool keratin and the unique structure of the cortical cells network, with controlled-size macroporosity for cell guesting, in addition to structural interconnected micro-porosity suitable for nutrient feeding.