Material extrusion 3D printing of polyether-ether-ketone scaffolds based on triply periodic minimal surface designs: A numerical and experimental investigation

Polyether-ether-ketone (PEEK) scaffolds have recently emerged as a promising alternative to traditional metallic orthopedic implants. However, reproducing the intricate microstructure of natural bone in PEEK scaffolds, while simultaneously matching their mechanical properties presents a significant challenge. This challenge is particularly pronounced in clinical settings where prioritizing safety, efficiency, and cost-effectiveness demands innovative manufacturing approaches. In this study, and for the first time we designed, and 3D printed density-graded triply periodic minimal surfaces (TPMS) PEEK scaffolds achieved through cost-effective material extrusion 3D printing. Notably the scaffolds integrate Gyroid, Diamond and Schwartz P unit cells. The structures feature a relative density transition from 22 % to 68 %, achieving graded porosity with a diverse pore size distribution that mirrors natural bone microstructure. Our experimental and numerical investigation examined the impact of unit cell and density variations on manufacturability, morphological and mechanical characteristics of PEEK scaffolds. Micro-CT imaging validated the reproducibility of all scaffolds, with minor deviations in pore morphology attributed to material shrinkage. Finite element analysis and compressive tests revealed horizontal stress concentration in all gradient structures, contrasting with lattice-dependent deformations in uniform structures. The gradient Gyroid scaffold exhibited superior mechanical properties, with an elastic modulus and strength of 200 MPa and 5.15 MPa, surpassing Diamond (178 MPa, 4.3 MPa) and Schwartz (147 MPa, 4.1 MPa). In summary, the Gyroid and Diamond configurations excel among gradient scaffolds, displaying mechanical properties like trabecular bone and facilitating optimal pore size for effective bone regeneration.