Improving the biomechanical behavior of TPMS structures with radial gradient porosity for 3D-printed bone fixation devices: Numerical simulation and experimental validation

This study presents the design, modeling, and experimental validation of 3D-printed interference screws fabricated from polylactic acid (PLA) and structured with radially graded triply periodic minimal surfaces (TPMS). The radial cell architecture conforms to the cylindrical geometry of orthopedic implants, generating a porosity gradient that enhances integrity. Mechanical performance was evaluated through finite element simulations under compression, pull-out, and torsional loading, and validated experimentally with compression tests. Results showed that relative density primarily governs global stiffness, consistent with the Gibson–Ashby model, while the number of radial cells controls stress redistribution and displacement patterns. Compression and pull-out tests revealed that eight-cell configurations improved load homogenization and reduced displacements, whereas torsional insertion, the most critical loading scenario, was best managed by four-cell designs, which minimized peak stresses at the screw head and thread roots. The normalized compressive Young’s modulus ranged from 0.31 to 0.60 GPa, closely matching cancellous bone and supporting biomechanical compatibility. Beyond load-bearing capacity, the TPMS-based porous architecture provides interconnected channels for bone ingrowth, while the biodegradable PLA core allows gradual resorption and replacement by new tissue. These findings validate radially graded TPMS structures as strong candidates for next-generation bioresorbable fixation systems, offering an integrating stiffness, strength, and structural efficiency. ARTICLE HIGHLIGHTSRadially graded diamond triply periodic minimal surfaces (TPMS) polylactic acid(PLA) interference screws were digitally designed, 3D printed and targeted for tendon-to-bone fixation.Finite element models and tests under compression, pull-out, and torsional insertion quantified stress, stiffness, and critical regions.