PURPOSE: To investigate the biomechanical and immunological reactions to coated and non-coated blasted PEEK implants in vivo after 12 weeks and review the associated literature.

METHODS: Two osteotomy sites were performed in each proximal tibia of 10 lop-eared rabbits (n= 4 per rabbit). Each rabbit received a randomly placed (1) blasted zirconium phosphate nano-coated PEEK- (nano-ZrP), (2) blasted PEEK- (PEEK) and (3) titanium implant (Ti) and an empty sham site. At 12 weeks, removal torque of all implants and biological investigation with qPCR was performed. The implant surfaces were analyzed prior to insertion with interferometry, SEM and XPS.

RESULTS: The interferometry analysis showed that there was no difference in roughness for the uncoated PEEK compared to the ZrP coated PEEK implants. The titanium implants were considerably smoother (Sa= 0.23 µm) than the uncoated Sa= 1.11 µm) and ZrP coated PEEK implants (Sa= 1.12 µm). SEM analysis on the PEEK implants corroborated the interferometry results; no difference in structure between the uncoated vs. the ZrP coated PEEK was visible on the micrometer level. At higher magnifications, the ZrP coating was visible in the SEM as a thin, porous network. All tested implants displayed osseointegration with the highest RTQ for nano-ZrP (18.4 Ncm) followed by PEEK (14.5 Ncm) and Ti (11.5 Ncm). All implants activated the immune system, with elevated macrophage and M2 macrophage qPCR markers at 12 weeks compared to the sham site.

CLINICAL SIGNIFICANCE: Nano-ZrP coating improves osseointegration of blasted PEEK implants at 12 weeks of follow-up. Osseointegration of titanium, PEEK and nano-ZrP PEEK is not a normal bone healing process, but rather a shield-off mechanism that appears to be regulated by the innate immune system.