Biomechanical and osteointegration study of 3D-printed porous PEEK hydroxyapatite-coated scaffolds

The objective of this study as to evaluate the biomechanical and osteointegration properties of 3D printed porous polyetheretherketone (PEEK) with hydroxyapatite (HA) coating by simulated body fluid (SBF) method. Cylindrical scaffolds were designed and fabricated by using PEEK material through fused deposition molding (FDM). The scaffolds were divided into solid group, porous group and porous-HA group (decorated by hydroxyapatite). The mechanical properties of each group of scaffolds were tested. Then, a total of 12 New Zealand rabbits were implemented for implantation of scaffolds at femoral condyle. Finally, the osteointegration ability of scaffolds were evaluated by Micro computed tomography (Micro-CT), histology and fluorescence staining. The HA was successfully decorated on the surface of the PEEK scaffold. The modulus of solid, porous and porous-HA group was 1289.43 ± 71.44 MPa, 196.36 ± 9.89 MPa and 183.29 ± 7.71 MPa, and the compressive strength was 107.24 ± 5.15 MPa, 33.12 ± 3.86 MPa and 29.99 ± 4.16 MPa, respectively. The micro-CT results showed that the bone volume/total volume ratio (BV/TV) in the porous-HA group was significantly greater than that in solid and porous group. Compared with porous group, the trabecular number (Tb. N) and trabecular thickness (Tb. Th) of porous-HA group was higher, and the trabecular spacing (Tb. Sp) was lower. The histology and fluorescence staining showed that more new bone tissue was formed in the porous-HA at different periods compared with the porous and solid groups. In addition, according to the results of the biomechanical test and osteointegration assessment, the biomechanical properties of 3D-printed porous PEEK scaffolds are close to human trabecular bone tissue, and the hydroxyapatite coating does not degrade its biomechanical performance. The porous structure can facilitate the integration of bone tissue, and the HA coating can markedly improve this process.