Deposition and roughness tailoring of calcium phosphate coatings on polyetheretherketone for orthopedic and dental implant applications

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The rapid, single-step coating of complexly shaped, 3D-printable polymer implant surfaces with robust, biomimetic inorganic layers that support osseointegration remains challenging for orthopedic and dental applications. Here, we demonstrate the deposition of ceramic, biomimetic calcium phosphate (CaP) layers onto polyetheretherketone (PEEK), an inert, 3D-printable high-performance polymer widely used as an implant biomaterial, in a single process step. For an initial parameter screening, planar PEEK foils were immersed in a simulated body fluid (SBF) and coated at 37°C for 3 to 24 h. The influence of surface pretreatment using air plasma and/or sulfonation on the topography and chemical composition of the CaP layers was examined. Closed CaP layers formed after 6 h independent of the applied pretreatment. Longer coating times resulted in thicker and rougher CaP layers prone to cracking. CaP layers reached thicknesses of up to 733 nm after 6 h and up to 1.2 μm after 24 h of deposition. Modification of the PEEK surfaces by sulfonation resulted in very rough CaP coatings, but subsequent plasma treatment allowed for tailored roughness adjustment. The CaP coatings significantly reduced the apparent water contact angles of the PEEK foils from 90° to below 20°. Qualitative adhesion testing confirmed that surface pretreatment significantly improves CaP coating adhesion on PEEK. The technique was also successfully adapted for 3D-printed PEEK rods, maintaining coatings with consistent nano-roughnesses between 30 and 100 nm and increased wettability irrespective of filler loading. These findings may help broaden the potential application range for calcium phosphate layers on PEEK, e.g. as a polymeric dental or orthopedic implant biomaterial.