Effect of surface treatment using non-thermal atmospheric pressure plasma jet on dissimilar material direct joining using Polyetheretherketone

• Plasma treatment significantly enhanced PEEK-titanium bond strength. • Treatment introduced oxidation-induced functional groups (O=C–O) on PEEK. • Plasma removed "weak bonding layers" on the PEEK surface. • Bond strength correlated linearly with etching depth from the surface. • Plasma-treated PEEK showed enhanced MC3T3-E1 cell adhesion/proliferation. Polyetheretherketone (PEEK) is widely used as a biomaterial due to its excellent mechanical strength and biocompatibility. However, its bioinert surface and poor adhesion to metallic materials, such as titanium, often limit its performance in implant applications. To address these issues, this study investigated the influence of atmospheric-pressure radio-frequency (RF) plasma treatment on the surface of PEEK, aiming to improve both its interfacial bonding with pure titanium TP340 (JIS H4600 TP340, ASTM B265 Grade 2) and biological response. The plasma treatment effectively introduced oxidation-induced functional groups—such as O=C–O—onto the PEEK surface and successfully eliminated cracks and voids, commonly referred to as "weak bonding layers," which typically form during the molding process of PEEK materials. These surface modifications resulted in a marked enhancement in tensile shear strength when PEEK was directly bonded to TP340. Comprehensive surface characterizations employing XPS, AFM, and SEM verified the presence of both chemical and topographical alterations that contributed to improved interfacial bonding. Notably, the elimination of weak bonding layers on the PEEK surface played a pivotal role in augmenting bond strength. Furthermore, in vitro biological evaluations using MC3T3-E1 osteoblast-like cells revealed significantly enhanced cell adhesion and proliferation on plasma-treated PEEK surfaces in comparison to untreated PEEK.