Controlled dual functionalization of lignin generates unique properties in gelatin-based hydrogels

Uncontrolled side reactions during lignin fractionation lead to the loss of its chemical functionalities and the uncontrolled formation of unwanted structures. Because of these structural issues, functionalization steps are usually performed on residual active sites of isolated lignin in order to improve reactivity and/or miscibility towards other materials. Even with these additional steps, potential applications—especially high-performance applications—are generally substantially curtailed. In this work, we use aldehyde assisted fractionation (AAF) on this process with two multifunctional aldehydes to introduce multiple functionalities (aldehydes and carboxylic acids) on the lignin in a controlled way and in a single step from lignocellulosic biomass. We show that the quantity of the various functionalities can be easily monitored and tuned in order to impart different properties to the lignin in terms of reactivity and solubility. These bi-functional lignins were then employed in the fabrication of novel cross-linked gelatin-based hydrogels for soft tissue engineering. The resulting hydrogels showed enhanced and controllable mechanical (rheology, compressive and tensile), adhesive, temperature-resistant and self-healing properties but only when a bi-functional lignin was used. This work demonstrates the importance and potential of controlled multi-functionalization of lignin, opening the way for its use in high performance materials.