Surface Modification of PEEK and Its Osteoconductivity and Anti-Inflammatory Properties

Polyetheretherketone (PEEK) is known as one of the “super-engineering plastics” and is used as an intervertebral disk spacer in the body. PEEK has a hydrophobic surface (water contact angle (WCA) > 80°) and high chemical resistance, and it is thus difficult to perform any surface treatment, such as hydrophilization. In this study, we aimed to form a hydrophilic surface on PEEK without coating layers by using hydroprocessing (aqueous solution processing), and we examined the osteoconductivity and anti-inflammatory properties of surface-treated PEEK in vivo compared with Ti implants. The WCA value of PEEK reached ~20° using a combination of immersion in a solution of >16.2 M H2SO4 and ultraviolet irradiation (172 nm). In in vivo testing, the hydrophilization of PEEK by surface modification without a coating layer improved the osteoconductivity and anti-inflammatory properties. The relationship between the bone-implant contact ratio and the WCA values of the surface-modified PEEK agreed well with that of the surface-treated Ti.