  Additive manufacturing of shape memory polymers has gained tremendous
interest in recent years due to their versatile potential applications in
various industries, such as biomedicine and aerospace. However, the polymers'
mechanical properties, specifically stiffness and strength, often hinder their
use in mechanically demanding applications, e.g. as structural materials. In
this work we produced nacre-inspired composites with a covalent adaptable
network, which enables fast and mechanically lossless self-healing, reshaping,
and shape memory capabilities. We demonstrate a novel direct write 4D-printing
strategy to print smart, nacre-inspired, organic-ceramic composites based on
alumina platelets and vitrimers with up to 3.3 and 26.7 times higher tensile
strength and stiffness, respectively, in comparison to the pristine vitrimer.
To the best of our knowledge, we introduce for the first time a single step
4D-printing process for nacre-inspired composites, that exploits suspension
spreading to align micron sized alumina platelets along a common plane, and
which utilizes solvent evaporation to induce polycondensation of the monomers
resulting in a vinylogous urethane vitrimer after extrusion of the suspension.
This work presents a facile, direct write 4D-printing strategy at ambient
printing conditions, establishing a foundation for adaptive additive
manufacturing of smart organic-ceramic composites of interest to various
industries.
