Increasing the biocompatibility of PEEK through O2/H2 low-pressure plasma treatment in vitro

The osseointegration of the implant material PEEK (polyether ether ketone) regularly represents a challenge due to its inert properties. This in vitro study evaluates the effect of hydrogen/oxygen low-pressure plasma treatment on the soft and hard tissue integration of PEEK. For this, 255 PEEK discs (diameter: 16 mm; thickness: 3 mm) were divided into 7 groups according to different low-pressure plasma treatment durations: 0 min, 1/6 min, 1/2 min, 1 min, 4 min, 10 min and 15 min. Afterwards, water contact angle (WCA) was measured to determine the hydrophilicity. Surface roughness and microhardness were measured to characterize the topography and mechanical behavior of the surfaces. X-ray photoelectron spectroscopy was used to determine the effect of plasma treatment on the chemical bonds on the PEEK surfaces. Cell culture tests with immortalized human gingival fibroblasts (iHGFs) were conducted to test the effect of PEEK plasma treatment on the cell adhesion, proliferation, and morphology, while human osteosarcoma cell line (Saos-2) was used to investigate the osteoconductivity. After plasma treatment, the hydrophilicity of PEEK was significantly improved: the WCA of untreated PEEK was 75.72° ± 1.31°, while after 10 s of plasma treatment, the WCA decreased to 28° ± 2.29°. XPS results showed that plasma treatment introduced hydrophilic groups onto the PEEK surfaces. Cell culture tests confirmed that cell adhesion, proliferation and osteoconductivity were also significantly improved due to low-pressure H/O plasma treatment. Taken together, the study suggests that hydrogen/oxygen low-pressure plasma can effectively improve the biocompatibility for both soft and hard tissue. Scheme 1. Schematic diagram of the effect of plasma surface technology on the PEEK surface