The main limitations of currently available artificial spinal discs are geometric unfit and unnatural motion. Multi-material additive manufacturing (AM) offers a potential solution for the fabrication of personalized free-form implants with a better fit and variable material distribution to achieve a set of target physiological stiffnesses. The structure of the artificial spinal disc proposed in this paper is inspired from a natural disc and includes both a matrix and a crisscross fiber-like structure, where the design variables are their material properties. After carrying out design variable reduction using linking strategies, a finite element-based optimization is then conducted to calculate the optimized material distribution to achieve physiological stiffness under five loading cases. The results show a good match in stiffness of the multi-material disc compared with the natural disc and that the multi-material artificial disc outperforms a current known solution, the ball-and-socket disc. Moreover, the potential of achieving an improved match in stiffness with a larger range of available 3D printable materials is demonstrated. Although the direct surgical implantation of the design is hindered currently by the biocompatibility of the 3D printed materials, a potential improvement of the design proposed is shown.

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