Effect of Additive Manufactured Gyroid Porous Structure of Hybrid Gradients on Mechanical and Failure Properties

In bone tissue engineering, good structural and forming qualities are prerequisites for the long-term implantation of scaffolds. To mitigate the stress-shielding effect between porous bone scaffolds and the human skeleton, this study proposes a method for designing non-linear gradient gyroid porous structures with radial-axial hybrid gradients that are precisely controlled by multivariate polynomial functions to simulate human bone characteristics. The influence of the volumetric energy density on the forming quality of the porous structures was evaluated by characterizing the internal strut morphology and measuring the strut width and porosity. Finite element analysis combined with experimental observations revealed that during compression, the thin struts at the top and bottom of the hybrid-gradient porous structure deformed first, and the compressive stress and shear stress were gradually transferred from the thin struts at the upper and lower ends of the structure to the thicker struts in the middle. Compared with the axial gradient, the edge struts of the hybrid-gradient porous structures can withstand higher shear and compressive stresses. Furthermore, owing to the variation in the radial gradient, compared to structures with 20 % axial porosity variation, the hybrid-gradient porous structure with 40 % radial porosity variation and 20 % axial porosity variation exhibited an 18.10 % increase in elastic modulus and a 4.29 % increase in yield strength. Additionally, its effective energy absorption was 20.39 % higher than that of the homogeneous structures. Compared to radial-gradient porous structures, the hybrid-gradient porous structure showed a lower sensitivity of the elastic modulus and yield strength to the volumetric energy density.