Functional Graded PEEK Cellular Lattice as a Bone Implant

Poly-Ether-Ether-Ketone (PEEK) emerges as a reliable thermoplastic used in various orthopedic applications, notably for its mechanical properties and mitigating stress shielding properties. Its thermoplastic nature enables 3D printing, allowing the use of established techniques for fabricating Triply Periodic Minimal Surface (TPMS) architectures like Gyroid, Diamond, and Primitive. This study proposes four strategies to explore the Young’s modulus E and ultimate strength σₛ design space: uniform latticing and three functional grading configurations based on relative density, unit cell size, or their hybrid combination. PEEK-based lattices are fabricated, and deviations between printed samples (as-built) and designed models are evaluated. The apparent mechanical properties: ultimate and yield strength (σₛ, σ_Y), toughness U, and Young’s modulus E, are estimated. The 3D-printed samples demonstrated high fabrication fidelity, with sheet thickness deviations of ~ 9.5% for uniform and ~ 7–17% for graded lattices. In situ tracking of spatial variations within unit cells reveals how grading influences Poisson’s ratio and auxetic behavior. Overall, PEEK scaffolds achieve E values within ~ 7% of trabecular bone and exceed its strength by over > 11.8 times. To objectively assess property matching, we introduce a Bone Matching Index using radar plots to quantify deviations in σₛ, σ_Y, E, and U. Among TPMS architectures, Gyroid matches trabecular bone most closely in E, while the hybrid Primitive configuration shows the most balanced mechanical response and highest index.