  Hierarchical biomaterials embody nature's intricate design principles,
offering advanced functionalities through the complex, multi-level organization
of their molecular and nanosized building blocks. However, the comprehensive
characterization of their 3D structure remains a challenge, particularly due to
radiation damage caused by conventional X-ray- and electron-based imaging
techniques, as well as due to the length scale limitations of scattering-based
investigation methods. Here, we present a study utilizing multi-directional
dark-field neutron imaging in tomographic mode to visualize the 3D
nanoarchitecture of nanocellulose solid foams, a class of sustainable materials
possessing complex and highly tunable hierarchical structures. By exploiting
the unique properties of neutrons as a probe, this non-destructive method
circumvents the inherent limitations of damage-inducing ionizing radiation,
preserving the structural and chemical integrity of the biomaterials, and
allowing for truly multiscale characterization of the spatial orientation and
distribution of cellulose nano fibrils within large-volume samples. In
particular, the study showcases the 3-dimensional anisotropic orientation and
degree of alignment of nanofibrils with different crystallinity, across various
length scales, from nanometers to centimeters. This approach offers a valuable
and generally applicable tool for multi-scale characterisation of biobased
materials where complex nanoscale arrangements inform macroscopic properties.
