Design and investigation of mechanical properties of porous spine implants produced by additive manufacturing

Objective: The aim of this study is to investigate the mechanical and biomechanical performance of lumbar interbody fusion cages with BCC, FCC, and diamond pore structures developed based on a biomimetic approach, and to evaluate the potential of parametric and genetic algorithm-supported polar lattice designs in spinal implant applications. Material and Methods: The cage structures were designed using parametric modeling and genetic algorithm optimization. In the first stage, the structures were produced by the melt filament fabrication method, and their mechanical performance was evaluated with compression tests. Then, the same structures were refabricated with hydroxyapatite (HAp) reinforced denture pink resin using a stereolithography-based Anycubic Photon Mono M7 Pro printer, and the results were compared. Mechanical behaviors were investigated with finite element analysis and experimental tests. In addition, FTIR and thermal analyses were performed on the produced material. Findings: Experimental results showed that porous structures regulate stress distribution, reduce stress protection, and increase biomechanical compatibility. FCC structures exhibited the most stable mechanical performance with low deformation and controlled stress distribution. The FCC-Core structure demonstrated the highest performance with an elastic modulus of 168.1 MPa, a plateau stress of 13.41 MPa, and an energy absorption of 14.96 MJ/m³. The FCC-Petal exhibited shockabsorbing behavior, while the FCC-Leaf offered an advantage for soft tissue transition zones due to its high ductility. Stereolithography fabrication provided a more precise geometry and more stable mechanical behavior compared to melt filament fabrication. Mechanical performance improved in samples with 0.5-1% HAp additive, while brittle behavior was observed at 3% HAp. Thermal analysis of the material shows that the degradation peak is wider in samples with 0.5% and 1% HAp additives, suggesting that thermal decomposition occurs in a more controlled manner. Conclusion: Parametric genetic algorithm-supported polar FCC lattice structures have been determined to have high potential for patient-specific spinal and orthopedic implant applications due to their lightness, high energy absorption, optimized stress distribution, and biomechanical compatibility. Keywords: Biomimetic design, Finite Element Analysis, FCC, Lumbar interbody fusion cage, Genetic algorithm optimization