Figure 5|. 2D and 3D nanofibril fabrication.

a | Optically anisotropic silk nanofibrils can be generated by fabricating specific periodic shapes, for example, through confinement by polydimethylsiloxane-moulded rings. In these rings, mechanical tension can be introduced by either contraction in ethanol and water or through direct deformation. Finite element simulations illustrate the stress (σ) distribution in fibres, anchored through the rings, which are spaced by 250, 1,125 and 3,125 μm, respectively. The fibres undergo a 33% contraction in size. The scanning electron microscopy images show the birefringence and corresponding internal nanofibrillar morphology of a ring-anchored fibre. Mechanical stress causes an increase in birefringence and a change in the orientation of the silk nanofibrils. b | 3D printing techniques can be applied to regulate the site-specific 3D alignment of biopolymer nanofibrils. The photograph shows a 3D-printed block composed of parallel lines of cellulose in eight layers; the cross-polarized optical microscopy image shows the top view of the block. Complex orchid-inspired flower morphologies can be generated by 3D printing. The dynamics of the printed flower result from the cellulose nanofibril orientation, as illustrated in the micrograph. Part a is reproduced from REF. 87, Macmillan Publishers Limited. Part b is reproduced with permission from REF. 90,92, Macmillan Publishers Limited and John Wiley and Sons, respectively.