Revalorization of sheep-wool keratin for the preparation of fully biobased printable inks

Sheep wool waste has become a problem affecting the environment, as today the wool of most species has no commercial application and is considered a waste product. Sheep’s wool is mainly composed of keratin which, due to its protein nature and multiple functional groups, has attracted great interest in applications such as support materials in tissue engineering, bioactive materials, and targeted drug delivery. Support materials can be fabricated by 3D printing by syringe extrusion. However, keratin is not suitable for this technique as it does not present proper rheological characteristics. Alginate, a biopolymer derived from brown seaweed, offers a wide range of viscosities at room temperature and offers good performance in 3D printing. Thus, keratin and alginate-based mixtures, due to their properties and ecoefficiency, are interesting candidates to prepare 3D-printed scaffolds. The aim of this work was to develop fully biobased printable inks containing keratin, alginate, salvia extracts, and cellulose nanofibers. In a first stage, keratose, an oxidized form of keratin, was obtained from sheep wool by a clean extraction methodology, and the miscibility and viscosity of keratose-alginate mixtures were assessed. In a second stage, biobased inks were prepared parting from miscible keratose-alginate mixtures. Flow analysis, spectromechanical analysis, and recovery tests were carried out to analyze the effect of the ink formulation over rheological parameters and printability. Mesh and cylinder geometries were 3D printed and their mechanical properties, as well as shape fidelity and self-standing ability, were assessed.