To investigate how the CNCs influence the mechanical properties of the APCNs, uniaxial tensile tests were carried out in both dry and water-swollen conditions. Stress-strain curves are reported in Figure , and the results of the mechanical tests are summarized as maximum stress-at-break, maximum strain-at-break, Young´s modulus, and toughness in Figure (see also the SI). For the dry samples, there was a three-fold increase in maximum stress from 2.8 ± 0.4 at 0 wt% CNCs to 6.6 ± 3.0 MPa at 22 wt% CNCs. The maximum strain-at-break peaked at 214 ± 33 % with 6 wt% CNCs and decreased to 37 ± 9 % at 22 wt% CNCs, lower than the strain-at-break of the control peptide APCN. Young´s modulus increased continuously from 2.7 ± 0.1 MPa at 0 wt% CNCs to 14.8 ± 6 for 22 wt% CNC. The toughness of CNC-reinforced APCNs with CNC contents between 1 wt% and 16 wt% was approximately twice as high as that of APCNs without CNCs. At a higher CNC content, the toughness was reduced to values similar to those of the APCNs without CNCs.