Figure 2. Images of additively manufactured specimens used for mode I fracture testing.

The dimensions of specimens are 64.75 mm × 58.5 mm with a thickness of 3.125 mm. The volume fraction of the soft phase is approximately 13.5 ± 0.1% for all samples. (a) Brick-and-mortar sample, representing a simplified nacre structure; (b,c) “hourglass” and “smooth honeycomb” samples: the respective motifs of the surface tessellations of these samples correspond to the two opposite faces of an osteomorphic block, as seen in Fig. 1d. Further details of the samples are given in Methods. Note that the sample consisting of interlayered interlocked osteomorphic blocks, which was also tested, is not shown, as it appears identical to the samples in (b,c) depending on which side is viewed.