Interfacial engineering of HA-coated PEEK through microstructure control and sulfonate functionalization for improved cytocompatibility and antibacterial activity

Background The development of multifunctional biomaterial surfaces that simultaneously support bone-cell responses and reduce bacterial infection is important for orthopedic implants. However, polymer-based polyetheretherketone (PEEK) material exhibits limited surface bioactivity and insufficient antibacterial performance because of its chemical inertness and hydrophobicity. Methods A combined surface-engineering strategy was developed by integrating pH-regulated hydroxyapatite (HA) microstructures with sulfonate functionalization on PEEK substrates. Hydrothermal treatment under acidic, neutral, and alkaline conditions produced plate-like, cauliflower-like, and sea urchin-like Ca-based layers, respectively. Sodium p-styrenesulfonate (NaSS)-derived sulfonate functionalization was subsequently introduced through UV-assisted surface modification, followed by hydrothermal post-treatment to reduce loosely associated NaSS species. Significant findings The cauliflower-like HA layer prepared under neutral conditions exhibited the most favorable cytocompatibility after NaSS functionalization and hydrothermal post-treatment. Suitable modification of PEEK surface enhanced cell proliferation and spreading, reduced cytotoxicity, maintained bacterial growth inhibition for up to 72 h, and substantially decreased the accumulation of E. coli and S. aureus . These results demonstrate that the HA microstructure and the retained sulfonate groups jointly regulate the biological performance of HA-coated PEEK samples.