Cations influence the cross-linking of hydrogels made of recombinant, polyanionic spider silk proteins

• Characterized spider silk bioinks in the presence of Dulbecco's Modified Eagle Medium.
• Examined effects of cations on the behavior of spider silk-based bioinks.
• Determined possibility of ionic crosslinking in charged, spider silk-based bioinks.

Hydrogels made of polyanionic recombinant spider silk proteins (spidroins) were prepared either in the presence or the absence of Dulbecco's Modified Eagle Medium (DMEM). Mono- and divalent cations present in DMEM severely affected the self-assembly process of the spidroins. Although the addition of DMEM had no apparent effect on secondary structure formation, there was a significant effect on the kinetics as well as on the hydrogel network; in the presence of DMEM, gelation occurred more rapidly. Additionally, the hydrogels were stiffer; however, the hydrogels were still shear-thinning. In summary, it can be concluded that there is a significant impact of ionic cross-linking on recombinant spidroin-based hydrogels.