In a recent direction of research, the study of these mechanical metamaterials now goes even beyond the single unit cell, similarly to the work done to understand crystal size influence on adsorption-induced flexibility (as detailed in subsection 2.5). In 2022, Xing et al. demonstrated that the design of MOFs with targeted metamechanical properties 21 could be improved by a concerted design involving both the supramolecular assembly and the mesoscopic structural design. They engineered hollow octahedron particles of the UiO-66 MOF, that demonstrated experimentally distinct mechanical properties from the UiO-66 single crystals due to this hierarchical design. On the same family of materials, Rogge et al. proposed in a computational approach to develop strain engineering of the rigid UiO-66 through the introduction of missing linker defects. While the parent defect-free material becomes amorphous under external pressure, the authors showed that introducing flexibility into the material in the form of shear instabilities lead to a more robust framework. Indeed, these instabilities act as "crumple zones", locally focussing the strain (see Figure ), and preserving the rest of the material's structural integrity and porosity.