Feasibility study of bioactivity enhancement of polyetheretherketone (PEEK) using plasma implantation technology

Abstract

Polyetheretherketone (PEEK) recently attracts many applications in orthopaedics such as intervertebral spacer, spinal cage and prosthesis. However, literatures suggest this material is bio-inert in nature. Its inferior bioactivity may lead to poor bone-implant interaction. Some researchers incorporated hydroxyapatite or tri-calcium phosphate in PEEK to enhance its bioactivity. Mechanical properties such as elasticity and fatigue may, however, alter as material micro-structure has been changed. To avoid it, surface modification is therefore an alternative. This pilot study aims to investigate the feasibility of bioactivity enhancement of PEEK using an advance surface technique named plasma immersion ion implantation (PIII). PEEK discs were polished and undertaken PIII treatment with plasma sources such as water, ammonia and strontium at 15kV at 50Hz for 2 hours. Afterwards, surface morphology, roughness, elemental chemical profile, chemical bonding and hydrophilicity were examined by SEM, AFM, XPS, FT-IR, and contact angle measurement respectively. Bioactivity was evaluated by simulated body fluid immersion test at day 21 and cytotoxicity was assessed by MC3T3E1 cell culturing at day 2 and 5. The surface roughness slightly decreases after water and ammonium PIII, whereas it increases after strontium PIII. The surface contact angle of the treated samples reduces, but surface energy increases. Literatures suggested these changes favour cell attachment and proliferation. In our cell culture experiment, cells have attached more on the treated surfaces. All these results preliminarily demonstrate the feasibility of PIII treatment to enhance bioactivity of PEEK. Further study will focus on in vivo testing.