Mechanical Optimization of 3D-Printed PEEK Spinal Fusion Cages: An Integrated Experimental–Computational Framework

Spinal fusion cages must withstand complex physiological loading while maintaining vertebral height and promoting successful fusion. This study aims to evaluate and optimize the mechanical performance of five iteratively developed spinal fusion cage designs polyetheretherketone (PEEK) fabricated via additive manufacturing. To identify the design with the best structural behavior and load-bearing capability, experimental axial compression and cyclic loading tests were conducted according to ASTM F2077-18 standards and compared with finite element analysis (FEA) simulations performed in Ansys. The study assessed stiffness, displacement response, stress distribution, and overall structural integrity to validate the effectiveness of the design modifications. Results demonstrated progressive improvements across design iterations, with Optimized Load-Bearing Cage exhibiting the greatest load-bearing capacity, reduced deformation, and more favorable stress distribution relative to earlier prototypes. Comparisons between experimental and numerical results showed general agreement in displacement trends, validating the simulation framework, although discrepancies emerged at higher loads, likely due to simplifications in material modeling and manufacturing-related defects. The Optimized Load-Bearing Cage (OLC) required approximately 3.7-fold higher load to reach equivalent displacement compared to DLC and 2.5-fold higher than SSC. Yield strength of OLC was significantly higher than all other designs (p < 0.001), with mean differences ranging from 40.9 to 50.1. The contact area increased from 8.16 mm² to 10.12 mm² (~24% increase), contributing to improved load distribution. Stiffness rankings from both experimental and FEA analyses consistently followed the trend: OLC > RDC > SSC > HPC > DLC, confirming improved structural rigidity with iterative design optimization. Cyclic loading tests further showed that OLC exhibited minimal cumulative deformation and only three failure cycles at 400 N and 10 mm s⁻¹, outperforming the earlier designs in fatigue resistance. The findings support the role of iterative design optimization combined with FEA and standardized experimental validation in improving spinal fusion implant performance. Future work should expand the mechanical testing matrix, include multi-axis loading and fatigue simulations, and refine manufacturing parameters to enhance reproducibility and long-term implant stability.