Fig. 4: Mechanical properties of hydrogels made of metal ion-clad picot fibres.

a Typical stress‒strain curves under tension for PAM, p-Pep and p-Pep/Cu²⁺ hydrogels. b Typical strain‒stress curves of p-Pep/Cu²⁺ hydrogels under tension at various peptide concentrations in the precursor of hydrogels (0%, 2%, 4%, 6% and 9% w/v). The inset corresponds to the summarised Young’s modulus and work of rupture (W_r) of the p-Pep/Cu²⁺ hydrogels. Values represent the mean and standard deviation (n = 3 independent samples). c Typical stretching-relaxation cycles of PAM, p-Pep and p-Pep/Cu²⁺ hydrogels at a strain of 4 mm mm⁻¹. d Stretching-relaxation cycles for p-Pep/Cu²⁺ hydrogels subjected to various strains (4, 8, 12, 16 and 20 mm mm⁻¹). The curves are offset for clarity, and the overlapping curves are shown in the inset image. e Stress‒strain curves for 100 consecutive stretching-relaxation cycles without any stops for p-Pep and p-Pep/Cu²⁺ hydrogels. The cycle numbers are 1, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100. f Extension of cracks per cycle as a function of the energy release rate for the PAM, p-Pep and p-Pep/Cu²⁺ hydrogels. The inset illustrates the stretching of notched samples. The R² values of the linear fitting to estimate fatigue thresholds for PAM, p-Pep and p-Pep/Cu²⁺ hydrogels were 0.99, 0.99 and 0.95, respectively. The data points represent the mean and standard deviation (n = 3 independent experiments). For a, c, d–f, the peptide concentration in the hydrogel precursors was 6% w/v.