4D printed hydromorph biocomposites with shape change and force generation properties: progress towards structural actuation

The study focuses on hydromorph biocomposites that change shape when exposed to water, while still being able to generate force. It draws inspiration from plant tissues and hydroexpansion behavior in wood, aiming to better understand structural actuation potential. The researchers use spruce wood as a reference to characterize hydroexpansion and quantify structural actuation via energy density. They then 4D print hydromorph biocomposites made from continuous unidirectional flax yarn reinforced polylactic acid (PLA) with rectilinear shape-changing architecture. They examine how free versus constrained hydroexpansion relates to the actuation performance, and show that key properties—hydroexpansion, blocked force, and energy density—can be tuned by adjusting layer height, print angle orientation, and interfilament distance. Reported energy densities reach 37.1 ± 3.3 J.g-1.cm-3 and are compared as being within the range of different wood species during water immersion.