Spiders’ dragline silk exhibits a specific strength five times higher than steel and the highest toughness of any material identified or invented by science, yet is composed solely of high molecular weight proteins and processed under mild conditions. The biomaterials and recombinant fields have made considerable progress over the last few decades at developing methods for producing the extremely large silk proteins that make up dragline silk fibers, and only recently confirmed long-standing hypotheses about the structure of the silk proteins pre-spinning. However, those studies revealed little about the transformations that occur during the spinning process itself and were limited to diluted silk proteins; additional studies using microfluidic approaches have begun to probe the silk processing space, but not with the full complexity of the natural system. Here, black widow spiders’ dragline silk glands are sectioned and imaged using high pressure freezing and freeze substitution ultrastructure techniques. Sectioning and imaging was guided by synchrotron mapping of the silk ducts and used to identify critical positions in the silk production process. Particular attention is paid to identifying and ruling out artifacts unique to fixing the silk proteins, which lack the lipids and amino acid residues commonly used to chemically fix structures. Combined with the high concentration of the silk proteins prior to spinning, this required the use of modified freeze substitution protocols with longer infiltration times to ensure structural preservation. This research, beyond guiding the development of biomimetic spinning devices for recombinant silk proteins, also has implications for improved spinning of high molecular weight synthetic polymers.

Characterization of the silk spinning process in black widow spiders

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ACS Fall 2022

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