Geometric design and mechanical performance of isotropic bone scaffolds

• A mechanical metamaterial design strategy for isotropic bone scaffolds is proposed. • The isotropy is achieved without nesting and complex adjustments. • Ti4Al6V scaffolds were studied by calculation, simulation and experiment. • High strength and permeability of ST structure are achieved. • The scaffolds have a large surface area for osteogenic differentiation. Bone tissue engineering scaffolds with reduced elastic anisotropy, enhanced mechanical performance, and high ratio of surface to volume are continuous pursuits. In this work, a mechanical metamaterial design strategy for isotropic bone scaffolds is proposed. The design of isotropic bone scaffolds is realized by interactive clipping of the lattice structure without nesting and complex adjustments. Employing homogenization, elastic stiffness tensors were estimated to evaluate the anisotropic measure, according to Zener ratio and elastic modulus. The designed scaffolds have a Zener ratio of nearly 1.0 and an increase of 20 % in stiffness over the pristine lattice. Quasi-static compression experiments were performed to investigate the Ti4Al6V scaffolds fabricated by selective laser melting, and the results showed that the isotropic scaffolds had compressive strengths of 100.59–198.53 MPa and stiffnesses of 1.86–4.88 GPa, which met the requirements for bone implants. Finite element simulations further revealed the structure’s mechanical response mechanism. Computational fluid dynamics results demonstrated that the structure’s permeability of 8.56 × 10 −9 -1.29 × 10 −8 m 2 , matches well with the requirements of human trabecular bone. Its large surface area facilitates osteogenic differentiation and enhances osseointegration. This study has important contribution in overcoming the constraints in the clinical applications of bone tissue engineering scaffolds.