As can be seen in Fig. , the R-curves of the test specimen initiate at K 0 = 0.91 ± 0.10 MPa m 0.5 which lies between the K IC of the supercrystalline material (1st HL) and the used epoxy resin. Upon crack extension, ∆a, the K R gradually increases up to 3.7 ± 0.1 MPa m 0.5 at ∆a max = 270 ± 40 µm which is a significant 4-fold increase of the fracture toughness. The materials' architectured design fosters extrinsic toughening mechanisms, like crack deflection on multiple length scales/hierarchical level (see crack path in the micrographs in Fig. ). This leads to a shallow R-curve which gives the 2 HL composite a significant damage tolerance. It is astonishing that the rising R-curves have an almost perfect linear slope of s R = 10.3 MPa m 0.5 mm -1 . Such linear behavior was shown for human cortical bone while nacre and nacre-inspired composites typically reach a plateau. The advantage of the increased damage tolerance can be demonstrated when comparing the ultimate flexural strength as a function of the specimen size (Fig. ). Crosslinked oleic acid functionalized Fe 3 O 4 NCs (i.e. the 1st HL) achieve a record high bending strength up to 600 MPa for µm-sized test specimens. Increasing the specimen dimensions, d, by preparing larger samples or via novel additive manufacturing techniques 29 dramatically decreased the strength, σ c , due to an increased size, a 0 , of preexisting flaws like voids or cracks in accordance with the Griffith criterion, K IC = σ c √ πa 0 (Fig. dashed, black line), and the supercrystals' fracture toughness, K IC = 0.3 MPa m 0.5 . Using polymeric ligands (hydroxyl terminated polybutadiene resin with a molecular weight of 2800 g mol -1 ) also did not allow to increase the robustness of larger test specimens but only led to an overall softer response due to an increased organic content highlighting that the addition of a polymer phase without a multi-hierarchical design doesn't improve the robustness of the material. For the 2 HL design, the composite's material property can be expressed as K R = K 0 +s R ∆a, for 0 ≤ ∆a ≤ ∆a max according to the measured R-curve. The strength, σ c , can be modeled assuming an infinite plate with a Griffith crack of length 2a. With ∆a = a -a 0 the corresponding stress intensity factor is K I (a) = σ π(a 0 + ∆a). With this R-curve it follows that for crack lengths smaller than a 0,min =