<p>In the pursuit of replicating the remarkable mechanical properties of natural biological composites like bone and seashell, developing artificial bulk materials that seamlessly integrate rigid inorganic components with ductile organic constituents has been a longstanding challenge. A key hurdle has been the establishment of robust and reliable linkages between these disparate building blocks. Mechanical metamaterials achieved by well-designed chemical structures, however, offer a promising solution to address this challenge. In this study, we demonstrate that the calcium phosphate-based inorganic-organic hybrid metamaterials trapping inorganic nanoparticles within long-chain polymeric networks and anchoring inorganic blocks to these networks via short-chain organic crosslinkers exhibit switchable and tunable high stiffness and elasticity. Additionally, these metamaterials not only exhibit peculiar mechanical characteristics, but also present excellent biocompatibility, as demonstrated by the in vivo tests using male rats and the in vitro tests. These results suggest a wide range of potential clinical applications.</p>