Wet-spinning of regenerated silk fiber from aqueous silk fibroin solutions: Influence of calcium ion addition in spinning dope on the performance of regenerated silk fiber

Ca(II) ions are added in the spinning dope to adjust the solidification rate of regenerated silk fibroin (RSF) solution during the wet-spinning process since Ca(II) ions are proved to be favorable to maintain the stable silk fibroin network in our previous work. The results show that when Ca(II)/RSF ratios are 1/50 and 1/20, the resulted RSF fibers exhibit good performance with the breaking energy more than 70 kJ/kg. However, higher Ca(II)/RSF ratio (for example, 1/10) hinders the solidification of spinning dope and results in poor RSF fibers. These observations together with earlier papers from this laboratory confirm that to produce tough silk fibers the spinning conditions must allow sufficient time for the adjustment of silk fibroin molecular chains.