Looking inside an intact fibre
Silk is extremely dense, which makes its internal organisation difficult to inspect without altering it. The researchers prepared sections no thicker than about 100 nanometres using cryo-focused ion beam milling, then reconstructed their structure with cryo-electron tomography.
The work compared force-drawn silk from the spider Araneus ventricosus, silkworm silk, and an artificial fibre made from regenerated silk protein. It therefore describes those sampled materials rather than every silk type produced by every spider.
Different packing, not just different ingredients
Spider silk showed densely packed nanofibrils with their long axes closely aligned along the fibre and with minimal visible gaps. Silkworm silk also contained aligned nanofibrils, but its internal gaps varied more from region to region. The artificial silk lacked the ordered packing seen in the natural fibres.
The authors argue that this hierarchy—from protein building blocks to nanofibrils and then to a full fibre—helps explain why reproducing natural silk requires more than manufacturing the correct proteins.
What remains unresolved
The researchers note limits in resolution and possible effects from sample preparation. Complementary methods and comparisons among silk from different spider glands and species will be needed before the molecular details are settled.