However, by applying bio-inspiration fromseed dispersal (for example,
pinecones), the hygroscopic properties could be turned into an advantage
in the design of new kinds of passive hygromorph products.
Indeed, by printing a bilayer microstructure mimicking a pinecone, we
could generate a programmable moisture-actuated functionality for
biocomposites, by following the 4D printing concept. Such a concept
was first defined in 2014 [13], but there is still a lack of information on
the relationship between the layer-by-layer printing process (FDM)
and the actuation properties induced by natural-fibre composites. The
comparison of printed samples with compressed counterparts demonstrates
that the FDM process provides materials with characteristics
that are suitable for a range of moisture-induced actuation functionalities
in biocomposites, and with better mechanical properties. Indeed,
FDM allows us to improve the maximal curvature and actuation speed
of wood biocomposites.