Bioactive inks suitable for 3D printing based on waterborne polyurethane urea, cellulose nanocrystals and Salvia extract

This work explores the preparation of a bioactive ink suitable for direct ink writing (DIW) 3D printing by adding extract obtained from Salvia officinalis L. during the synthesis of a waterborne polyurethane urea (WBPUU). Additionally, to guarantee a successful printing performance, cellulose nanocrystals (CNC), a well-known rheology modulator, have been added after the synthesis process. In order to predict the behaviour of the inks in DIW, the rheological properties of the inks with and without the Salvia extract and the CNC have been studied. The results showed that the incorporation of Salvia extract into the WBPUU ink resulted in a decrease of the viscosity, yield point and storage modulus, obtaining an ink that cannot maintain the shape after being printed. On the contrary, the incorporation of the CNC into the WBPUU/Salvia ink increased the aforementioned rheological parameters leading to the obtaining of pieces presenting a good shape fidelity without compromising their printability. Finally, scaffolds were prepared from the printed pieces by freeze-drying technique and were tested against Gram negative Escherichia coli and Gram positive Staphylococcus aureus. The scaffolds containing CNC and Salvia showed bactericide behaviour against both bacteria, which was not seen in the WBPUU matrix, confirming the bioactive capacity of this ink.