We show a novel, bioengineered, moldable platform for bone regeneration composed of porous bionanocomposite scaffolds made of components that are normally found in bone tissue (calcium, collagen, carbonate, sodium, and phosphorous). To accommodate high- or low-stress environments, the hardness and modulus (stiffness) of these scaffolds can be tuned in a wide range in Megapascal (MPa) to Gigapascal (GPa) regions, while maintaining the required viscoelasticity. Our approach to control the mechanical properties is based on a new formulation of mineralized bioscaffolds by incorporation of calcium carbonate in which, calcium and phosphorous are in the form of calcite, calcium polyphosphate (CPP) and hydroxyapatite (HAP). The variation in the calcium carbonate concentration allows tuning of calcite/CPP contents in the bioscaffold to tailor the degree of mineralization and mechanical and viscoelastic properties that closely match those of natural bone. Our results demonstrate an ideal framework for new bone scaffold designs for advanced bone substitute applications.