Comparing the osteogenic effects of sputtered titanium- and strontium titanate (STO)-modified polyetheretherketone

Polyetheretherketone (PEEK) is widely used as an interbody cage due to its elastic modulus closely resembles that of human bone. However, its biological inertness is considered a major weakness, as it cannot directly bond with bone (lack of osseointegration capacity). Surface modification can impart bioactivity to PEEK while maintaining its mechanical properties. In this study, the surface of PEEK was modified with titanium or strontium titanate thin films formed by magnetron sputtering deposition. We evaluated the bone formation activity of strontium titanate-modified PEEK (PEEK-STO) by comparing three groups: unmodified PEEK (PEEK), titanium-modified PEEK (PEEK-Ti), and strontium titanate-modified PEEK (PEEK-STO). Osteogenic differentiation of cells, assessed by ALP activity, bone-related gene expression, and mineralization ability, demonstrated that PEEK-STO has the highest osteogenic activity. Furthermore, the evaluation of mineral deposition by non-cellular mechanisms using simulated body fluid showed that PEEK-Ti and PEEK-STO have higher calcium phosphate deposition capacity than PEEK. In vivo implantation of the materials into the rat femur demonstrated that bone-to-implant contact ratio (BIC%) and bone area ratio (BA%) in the proximity zone from the implant were significantly larger in PEEK-STO compared to PEEK-Ti and PEEK at 4 weeks post-surgery. This study demonstrates that surface modification of PEEK with strontium titanate through magnetron sputtering is an attractive option for solving the problems of PEEK’s biological inertness while making the most of the advantages of PEEK as a spinal fusion device.