Treatment for intervertebral disc degeneration involves the complete removal of the disc and the fusion of two adjacent vertebrae via a biocompatible implant. The implant must be capable of both supporting the mechanical forces experienced by the spine, as well as promoting bone growth. PEEK has been shown to perform well in spinal fusion surgeries, but can face challenges with osseointegration as it is highly hydrophobic. Post-processing techniques have been considered as a method to improve the osseointegration of PEEK spinal cages, with ultraviolet (UV) light assisted functionalization being one possible method. The addition of calcium phosphate to bone scaffolds has been shown to increase osseointegration due to similarities to hydroxyapatite, a major inorganic component of bone. We investigated the use of UV-assisted functionalization to add a calcium phosphate layer to PEEK samples in order to improve osseointegration.

PEEK samples with dimensions of 10x10x1 mm were obtained via fused filament fabrication/3D printing and submerged in simulated body fluid (SBF). Samples were exposed to a 2W/cm² UV light for six hours, and then placed in a water bath set to 37°C for a total of 72 hours, with SBF being changed after 48 hours. After functionalization, the PEEK samples were washed with DI water and dried. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was performed on the functionalized samples, control PEEK samples that were not treated, and control samples that were soaked in SBF for 72 hours but were not exposed to UV light. Images of the surface of the functionalized samples and controls were obtained using a scanning electron microscope (SEM) (Zeiss Supra 50VP) with EDS (Oxford) capabilities.

SEM/EDS analysis of UV functionalized PEEK samples showed morphological surface changes as well as calcium and phosphorous on the surface of the material. The functionalized PEEK samples were found to have a molar Ca:​P ratio of 1.69, while natural hydroxyapatite has a molar ratio of 1.67. EDS analysis of non-functionalized control samples found no calcium or phosphorus. FTIR results found that the nonfunctionalized PEEK samples and the PEEK samples that were soaked in SBF but were not treated by UV were nearly identical, with no calcium phosphate. For functionalized samples, notable peaks were observed at 560 and 600 cm⁻¹, and between 1000 and 1100 cm⁻¹, which has shown to be a phosphate group.

Analysis of functionalized PEEK revealed that UV-assisted functionalization successfully applied a layer of calcium phosphate material to the surface of the sample. While the goal was to obtain a layer of hydroxyapatite in order to promote osteoblast adhesion, the observed ratios of calcium to phosphate obtained via EDS are more likely to indicate an amorphous calcium phosphate layer. The addition of this layer to the PEEK surface is believed to enhance the osseointegration of newly developed biomedical implants.