Mechanically enhanced cellular SS316L for patient specific implant fabricated by selective laser melting

The emergence of lattice structures with biomimetic geometries has transformed orthopedic implant designs. This study uses the laser powder bed fusion process to fabricate and characterize Triply Periodic Minimal Surface (TPMS) gyroid structures from stainless steel 316L, which has excellent resistance to corrosion, better biocompatibility, and improved mechanical properties. Despite advancements in orthopaedic biomaterials, stress shielding is a primary issue. Lattice structures can reduce Young's modulus and enhance bone ingrowth while improving the implant durability. The gyroid structures designed with varying porosity levels (50%, 60%, and 70%) with and without internal stiffeners were mechanically evaluated. The study found that a 50% porous gyroid with stiffener achieved the highest Young’s modulus (30.2 GPa). The material had uniform pore distribution and minimal structural defects, essential for bone ingrowth. The surface roughness achieved for printed samples ranged from 12.6 to 15.11 µm. After sandblasting, the roughness Ra values for the TPMS gyroid without stiffener were 3.56 µm, 3.09 µm, and 4.02 µm for G50, G60, and G70, respectively, whereas the gyroid samples with stiffener exhibited values of 3.61 µm, 5.85 µm, and 2.95 µm for GS50, GS60, and GS70, respectively. The friction values of the samples were below 0.4 and within the acceptable limit for medical implants. The GS50 sample achieved a corrosion-resistant Ecorr value of -340 mV and Icorr value of 1.175 × 10 -5 mA/cm², outperforming other printed gyroid structures. This work successfully achieved the Young’s modulus of cellular structure that matches the tibia bone for load-bearing applications.