Disruption of the Metal Ion Environment by EDTA for Silk Formation Affects the Mechanical Properties of Silkworm Silk

Abstract

Silk fiber has become a research focus because of its comprehensive mechanical properties. Metal ions can influence the conformational transition of silk fibroin. Current research is mainly focused on the role of a single ion, rather than the whole metal ion environment. Here, we report the effects of the overall metal ion environment on the secondary structure and mechanical properties of silk fibers after direct injection and feeding of silkworms with EDTA. The metal composition of the hemolymph, silk gland, and silk fiber changed significantly post EDTA treatment. Synchrotron FTIR analysis indicated that the secondary structure of silk fiber after EDTA treatment changed dramatically; particularly, the β-sheets decreased and the β-turns increased. Post EDTA treatment, the silk fiber had significantly decreased strength, Young’s modulus, and toughness as compared with the control groups, while the strain exhibited no obvious change. These changes can be attributed to the change in the metal ion environment in the silk fibroin and sericin in the silk gland. Our investigation provides a new theoretical basis for the natural silk spinning process, and our findings could help develop a method to modify the mechanical properties of silk fiber using metal ions.

Comparative Study of Silk-Based Magnetic Materials: Effect of Magnetic Particle Types on the Protein Structure and Biomaterial Properties

“…With the experimental evidence and analysis provided above, we can confirm that Fe 3 O 4 and BaM particles can slightly prevent the β-sheet crystal formation, suggesting that the Fe 3 O 4 -SF and BaM-SF composite films have more noncrystalline structures ( Figure 7 ). This is probably caused by the strong coordination bonding between Fe 3+ ions and carboxylate ions on silk fibroin chains [ 36 , 37 , 38 ] due to the dissolved Fe found from the magnetization studies. Most β-sheet crystals usually formed during the water annealing and wet pressing process.…”

In situ preparation of molybdenum-dioxide-incorporated carbonized silk fiber and its application in supercapacitors

“…Metal ions can coordinate with silk fibroin, promoting its conformational transition ( Xu and Zhang, 2008 ; Liu et al, 2019 ). We believe that a low concentration of molybdate can induce the formation of β -sheets and β -turns through coordination and chelation with SF, thereby helping to align and orient SF molecular chains.…”

Biological Materials Processing: Time-Tested Tricks for Sustainable Fiber Fabrication

“…172 Fibers spun by silk worms injected with calcium, 173 copper, 174 and ferric ions, 175 respectively, are stronger than the wild-type fiber, which could be explained by metal ion mediated cross-linking of the protein chains. 176 From this comparison, we can conclude that both silkworms and spiders are able to produce high performance fibers rich in β-sheet crystalline structures from highly concentrated liquid feedstocks that are stored at high concentrations in a gland lumen. The principal polymeric building blocks are similar in that they are Ala-and Gly-rich, large, and repetitive proteins capped by terminal nonrepetitive domains.…”

“…Rheological studies of the dope show that potassium and calcium ion concentrations during storage are important for controlling molecular alignment and protein aggregation, and in line with this, there is an increase in the concentration of calcium, magnesium, and zinc along the gland, which together with ferric ions have been shown to induce β-sheet formation of the fibroins in vitro . Fibers spun by silk worms injected with calcium, copper, and ferric ions, respectively, are stronger than the wild-type fiber, which could be explained by metal ion mediated cross-linking of the protein chains …”