Crosslinking, salt-induced aging, and secondary structure formation in Peptide-containing coacervates inspired by spider silk

Spider silks are exceptional biomaterials: biocompatible, biodegradable, and with remarkable mechanical properties. Unfortunately, attempts to replicate them tend to fail due to the difficulty of synthesizing the proteins that constitute them, and to an incomplete understanding of their processing conditions. Here, we report a synthetic system inspired by spider silk, consisting of a synthetic polyelectrolyte with grafted oligoalanine chains. We have used this peptide-polyelectrolyte conjugate to produce complex coacervates in an analogous process to the liquid-liquid phase separation (LLPS) observed during the natural processing of spider silk. We have characterized these coacervates using rheology, tack test, and solid-state NMR spectroscopy, observing α-helixes and β-sheets. These secondary structures crosslink the material, improving its mechanical properties and its processability, for example, for 3D printing. Furthermore, the peptide-based crosslinks cause distinctive behaviours - such as salt-induced aging. Our approach contributes to the fundamental understanding of the role that LLPS and peptide crosslinks play in spider silk, and to the development of new soft materials crosslinked by peptide aggregation.