Fig. 1: A variety of  porous region related mesoscale structures are observed in natural and artifical silk fibres.

Formation of mesoscale structures in a partially spun regenerated silk fibre, featuring a porous region in a raised central area and sub-micrometre scale voids (a). Void structures are identified by orange arrows. As an example of the generality of our observations, a magnified area of this sample (b) is compared with similar porous regions and nanofibrillar structures present in cryo-cross sections of native Antheraea mylitta (c) and the outer edge (d) and central region (e) of Antheraea pernyi silk. While indicative, it is worth noting the diversity, scale and distribution of these mesoscale structures are likely to be specific to each species and spinning conditions, much like fibre mechanical property variation on an intra and interspecific level.