Printability, Performance and Adaptive Moisture Response: Advanced Hygromorphic materials using synergistic properties of keratin and lignin

Abstract

Developing materials that respond and adapt to external stimuli are of increasing interest in additive manufacturing as their potential to react to triggers can be used as a response required of a user. As biopolymers, keratin and lignin exhibit macromolecular behaviours influenced by moisture and these properties have been evaluated as four dimensional (4D) responsive hygromorphic materials. Through three dimensional (3D) paste keratin-lignin hydrogel deposition, the integrity, mechanical properties and 4D moisture sorption responses of these materials was found to be enhanced by additives including carrageenan, guar gum and calcium chloride. As an example, inclusion of carrageenan and calcium led to greater dynamic vapour moisture sorption behaviours compared to guar gum. While carrageenan acted to improve mechanical properties, combination with calcium led to lower mechanical performance and plasticization of hydrogels. In contrast, the cross-linking provided by calcium ions reduced liquid water sorption and was found to extend sample mechanical performance on water immersion. Inclusion of guar gum improved keratin-lignin hydrogel deposition, but provided minimal enhancements of material properties or moisture responses. Overall, study findings suggest selective combinations of carrageenan and calcium can produce 4D moisture responsive keratin-lignin hydrogels where these resulting adaptative swell or softening behaviours may be used in hygromorphic material applications.