Fig. 4: The development of silk strucutre and property is correlated with extensional strain accumulation.

The flow field calculated (a) for the sample before drawdown in Fig. 2 is shown along with the accumulation of extensional strain (c) versus the distance of sample extensional flow. The same calculation of an extruded sample is shown in b and d. The colour gradient from blue to red represents a low to high flowing rate. Note the simulation is built using an axial symmetry approximation and is not the accurate value due to limitations of the calculation. The samples showing slippery fibril bundle (SFB) structure and non-slippery fibril bundle (NFB) are marked in plots c and d. The development of a nanofibrillar structure with respect to the strain accumulation is shown in longitudinal SEM images (e–h) with the extensional flow direction marked by white arrows. The average sample mechanical strength of each stage is shown in plot (i). A representative stress-strain curve of each stage sample is shown in plot (j). The error bar represents the standard deviation for the tensile strength of each stage, which is ±21.3, ±44 and ±74.7 MPa, respectively, n = 5 for the gelation stage and n = 6 for the other two stages.