In vitro osteogenesis of rat bone marrow mesenchymal cells on PEEK disks with heat-fixed apatite by CO2 laser bonding.

Polyether-ether-ketone (PEEK) is increasingly being used for spinal applications. However, because of its biologically inactive nature, there are risks of false joint loosening and sinking. PEEK materials are coated with apatite to enhance the osteoconductive properties. In this study, we aimed to evaluate whether strontium apatite stimulate osteogenesis on the surface of PEEK by using the CO2 laser technique. We prepared non-coated disks, laser-exposed disks without apatite, and four types of apatite-coated by laser PEEK disks (hydroxyapatite (HAP), strontium hydroxyapatite (SrHAP), silicate-substituted strontium apatite (SrSiP), and silicate-zinc-substituted strontium apatite (SrZnSiP)). A part of the study objective was testing various types of apatite coatings. Bone marrow mesenchymal cells (BMSCs) of rats were seeded at a density of 2 × 104/cm2 onto each apatite-coated, non-coated, and laser-irradiated PEEK disks. The disks were then placed in osteogenic medium, and alkaline phosphatase (ALP) staining and Alizarin red staining of BMSCs grown on PEEK disks were performed after 14 days of culture. The concentrations of osteocalcin (OC) and calcium in the culture medium were measured on days 8 and 14 of cell culture. Furthermore, mRNA expression of osteocalcin, ALP, runt-related transcription factor 2 (Runx2), collagen type 1a1 (Col1a1), and collagen type 4a1 (Col4a1) was evaluated by qPCR. The staining for ALP and Alizarin red S was more strongly positive on the apatite-coated PEEK disks compared to that on non-coated or laser-exposed without coating PEEK disks. The concentration of osteocalcin secreted into the medium was also significantly higher in case of the SrHAP, SrSiP, and SrZnSiP disks than that in the case of the non-coated on day14. The calcium concentration in the PEEK disk was significantly lower in all apatite-coated disks than that in the pure PEEK disks on day 14. In qPCR, OC and ALP mRNA expression was significantly higher in the SrZnSiP disks than that in the pure PEEK disks. Our findings demonstrate that laser bonding of apatite-along with trace elements-on the PEEK disk surfaces might provide the material with surface property that enable better osteogenesis.