Other comparisons are problematic, especially with bilayers made
only ofwood, since the experiments are rarely carried out in immersion
and also because the layers considered are always thicker (around
5mm[18] and 1.2mm[19]),which leads to stiffer actuators. In addition,
wood bilayers are naturally composed of swelling tracheid fibres bound
together by pectin cements. The overall fibre content within the tissue is
thus several times higher than in the biocomposite studied here, which
gives the wood bilayers a natural advantage. Fig. 7b shows the typical
curvature behaviour of the printed hygromorph biocomposite as a function
of sorption and desorption time. Such an actuation mechanism can
be characterized by its speed (dK
dt), the maximal amplitude Kmax with its
corresponding time tmax and the residual curvature after desorption Kr