Fig. 1: Synthesis, structure, and processability of peptide-containing coacervates inspired by spider silk.

a Schematic representation of some of the key elements in spider silk production: the liquid-liquid phase separation of spidroins inside of the major ampullate gland leads to a liquid, highly-concentrated spinning dope. This spinning dope contains only spidroins, proteins with a repeating structure that alternates oligoalanines with hydrophilic sequences. In the final material, the hydrophilic sequences form a soft matrix, while the oligoalanines form β-sheet crystals that crosslink the material. b Bioinspired design of peptide-containing complex coacervates. The polymers synthesized in this work combine a polyelectrolyte backbone with grafted oligoalanine chains. The polyelectrolyte backbone allows for complex coacervation, a type of LLPS analogous to the phase separation observed in spider silk. The oligoalanines lead to β-sheet formation and crosslinking of the material. c Scheme of the reactions leading to the synthesis of the final material. d 3D printed structures of coacervates with and without grafted peptides, 15 min after printing. As it can be observed, only the peptide-containing coacervates were able to retain any structural definition, while the coacervates without peptides relaxed quickly into droplets.