A Novel Model for Computing D-Shore Hardness of PLA: Numerical and Experimental Investigation

Biomaterials such as polylactic acid (PLA) are utilized in tissue engineering to produce bone scaffolds by 3D printing; to resemble and integrate with natural bone, the scaffolds need a precise pore structure. However, PLA scaffold surfaces show indenting behavior when loads are applied, indicating that they are hard. Based on this behavior, the D-Shore index is a direct dimensionless measure of surface hardness, compared with the Brinell test, which uses the ratio of applied load to the area of the spherical indentation. In addition, the D-Shore method lacks analytical tools, has measurement variance due to PLA rebound and creep during measurement, and is affected by printed lines in the surface layers; it also lacks a mathematical model. Therefore, the current study focuses on developing an empirical model for D-Shore hardness based on experimental data from the Brinell and D-Shore methods. At the same time, explicit finite element analysis (EFEA), as a preliminary step, can predict a feasible scaffold design that provides the best resistance to indentation on the printed surface. Design-wise, the efficient levels used for the scaffold samples were 100, 150, and 200 μm for pore size, and 0°/90° and −45°/45° for layer orientation, to predict and validate the Brinell number and experimentally determine the D-Shore. Accordingly, the analysis of variance reveals that the layer orientation is a dominant parameter, and the feasible level was 100 × 100 μm2, with −45°/45° for pore sizes and layer orientation, respectively; the best correlation factor was R2 = 0.995. Ultimately, this practical approach shows that the empirical model for D-Shore is a robust tool for computing the hardness based only on Brinell outputs and can estimate the hardness of biomaterials fabricated from PLA without extensive testing, helping identify the optimal path for bone scaffold design.