Porous biomaterials with the proper three-dimensional (3D) surface network can enhance biological functionalities especially in tissue engineering, but it has been difficult to accomplish this on an important biopolymer, polyetheretherketone (PEEK), due to its inherent chemical inertness. In this study, a 3D porous and nanostructured network with bio-functional groups is produced on PEEK by sulfonation and subsequent water immersion. Two kinds of sulfonation-treated PEEK (SPEEK) samples, SPEEK-W (water immersion and rinsing after sulfonation) and SPEEK-WA (SPEEK-W with further acetone rinsing) are prepared. The surface characteristics, in vitro cellular behavior, in vivo osseointegration, and apatite-forming ability are systematically investigated by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, cell adhesion and cell proliferation assay, real-time RT-PCR analysis, micro-CT evaluation, push-out tests, and immersion tests. SPEEK-WA induces pre-osteoblast functions including initial cell adhesion, proliferation, and osteogenic differentiation in vitro as well as substantially enhanced osseointegration and bone-implant bonding strength in vivo and apatite-forming ability. Although SPEEK-W has a similar surface morphology and chemical composition as SPEEK-WA, its cytocompatibility is inferior due to residual sulfuric acid. Our results reveal that the pre-osteoblast functions, bone growth, and apatite formation on the SPEEK surfaces are affected by many factors, including positive effects introduced by the 3D porous structure and SO3H groups as well as negative ones due to the low pH environment. Surface functionalization broadens the use of PEEK in orthopedic implants.
Keywords: Bioactivity; Biocompatibility; Interface; Osseointegration; Polyetheretherketone; Surface modification.
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