Fig. 4.

Mechanical testing of syn-n4, syn-7, and syn-n11 samples. (A) Stress–strain curves show that toughness and extensibility of synthetic polypeptides increase as a function of protein molecular weight. (Inset) Fractured samples show brittle fracture for syn-n4, whereas syn-n7 and syn-n11 show ductile fracture (crazing lines marked with arrows). (B) DIC shows full-field strain measurement for all three samples at the locations marked with point labels (labels a–t) in the stress–strain graph. Syn-n4 sample shows homogeneous strain along the gauge length, whereas syn-n7 and syn-11 samples show local strain concentration during yielding. (C) FTIR analysis of pristine and drawn syn-n11 samples. α, α-helix, β, β-sheet; rc, random coil; sc, side chain; t, turn.