Towards new strut-based auxetic meta-biomaterials for trabecular bone scaffolds

The work proposes new highly porous, bone-mimicking auxetic meta-biomaterials as trabecular scaffolds for additively manufactured titanium orthopedic implants. The elementary cell of the lattice architecture proposed here consists of strut-based prismatic trabecular units connected by chiral ligaments at their corners. Through an analytical model and Finite Element simulations, we evaluate the quasi-static effective mechanical properties of the investigated bio-designs, revealing that these meta-biomaterials exhibit a wide range of porosities, Young’s moduli, and yield stresses similar to those of human bones, and particularly, vertebral cancellous bone tissues. The developed analytical and computational models consider both the Euler-Bernoulli and Timoshenko beam theories to estimate the meta-biomaterial properties. We also show that these lattice models possess a transverse isotropic property for a specific geometric configuration of the elementary units, and a wide range of negative Poisson’s ratios. In addition, analytical expressions for the elastic properties of such lattices as a function of their unit cell topology are derived and presented. A physical prototype of the proposed lattice architecture is then fabricated using additive manufacturing, in polymeric material, and experimentally tested to assess its auxetic potential, thus validating our analytical and computational predictions. Overall, our results demonstrate that these novel meta-biomaterials exhibit a combination of relatively low elastic moduli and high porosity values that potentially reduce the stress-shielding phenomena while promoting the bone ingrowth within them. The preliminary findings of this work provide new insights into the development of lightweight auxetic lattices for additively manufactured metallic vertebral implants and devices in the spinal oncology.