This study developed a non-equiatomic Ti_28.33Zr_28.33Hf_28.33Nb_6.74Ta_6.74Mo_1.55 super-solid solutionized BioHEA using laser powder bed fusion (LPBF) to reach the full potential as BioHEA. We succeeded in significant suppression of elemental segregation, thus, resulting in a single crystalline-like texture by activating layer-to-layer epitaxial growth. Relatively low Young’s modulus was achieved in the single crystalline-like BioHEA. Moreover, LPBF-fabricated BioHEA exhibited significantly higher yield stress (1355–1426 MPa) due to the effective solid solution hardening compared to as-cast counterpart with marked segregation (949 MPa), and good biocompatibility. This is first report achieving BioHEA with low modulus, excellent strength-ductility balance, and good biocompatibility via LPBF. GRAPHICAL ABSTRACT IMPACT STATEMENT This study achieved super-solid-solutionized and single crystalline-like TiZrHfNbTaMo bio-high entropy alloy using laser powder bed fusion, resulting in low Young’s modulus along oriented direction, excellent strength-ductility balance, and good cytocompatibility.

Metal additive manufacturing is a powerful tool for providing the desired functional performance through a three-dimensional (3D) structural design. Among the material functions, anisotropic mechanical properties are indispensable for enabling the capabilities of structural materials for living tissues. For biomedical materials to replace bone function, it is necessary to provide an anisotropic mechanical property that mimics that of bones. For desired control of the mechanical performance of the materials, we propose a novel 3D puzzle structure with cube-shaped parts comprising 27 (3 × 3 × 3) unit compartments. We designed and fabricated a Co–Cr–Mo composite structure through spatial control of the positional arrangement of powder/solid parts using the laser powder bed fusion (L-PBF) method. The mechanical function of the fabricated structure can be predicted using the rule of mixtures based on the arrangement pattern of each part. The solid parts in the cubic structure were obtained by melting and solidifying the metal powder with a laser, while the powder parts were obtained through the remaining nonmelted powders inside the structure. This is the first report to achieve an innovative material design that can provide an anisotropic Young’s modulus by arranging the powder and solid parts using additive manufacturing technology.

Therapeutic devices for spinal disorders, such as spinal fusion cages, must be able to facilitate the maintenance and rapid recovery of spinal function. Therefore, it would be advantageous that future spinal fusion cages facilitate rapid recovery of spinal function without secondary surgery to harvest autologous bone. This study investigated a novel spinal cage configuration that achieves in vivo mechanical integrity as a devise/bone complex by inducing bone that mimicked the sound trabecular bone, hierarchically and anisotropically structured trabeculae strengthened with a preferentially oriented extracellular matrix. In vivo animal study. A cage possessing an anisotropic through-pore with a grooved substrate, that we termed "honeycomb tree structure," was designed for guiding bone matrix orientation; it was manufactured using a laser beam powder bed fusion method through an additive manufacturing processes. The newly designed cages were implanted into sheep vertebral bodies for 8 and 16 weeks. An autologous bone was not installed in the newly designed cage. A pull-out test was performed to evaluate the mechanical integrity of the cage/bone interface. Additionally, the preferential orientation of bone matrix consisting of collagen and apatite was determined. The cage/host bone interface strength assessed by the maximum pull-out load for the novel cage without an autologous bone graft (3360±411 N) was significantly higher than that for the conventional cage using autologous bone (903±188 N) after only 8 weeks post-implantation. These results highlight the potential of this novel cage to achieve functional fusion between the cage and host bone. Our study provides insight into the design of highly functional spinal devices based on the anisotropic nature of bone. The sheep spine is similar to the human spine in its stress condition and trabecular bone architecture and is widely recognized as a useful model for the human spine. The present design may be useful as a new spinal device for humans.