4D printing, at the time it was firstly brought to life by Skylar Tibbits, was defined as 3D printing with the addition of time, meaning featuring transformation by time in the object manufactured \cite{hirsch2014} . The last researches on the field have emphasized the importance of materials in the process, hence a more accurate formulation could be: "additive manufacturing of stimulus-responsive materials".
. Smart materials have been promoted as promising emergent technology and are already widely employed such as in biomedical \citep{Castro_2017}, electronic \citep{Liu_2016} devices and aerospace application \cite{engineering}.