Deposition of the hydroxyapatite particles on the polyether ether ketone surface for orthopaedic applications

Abstract

Polyether-ether-ketone (PEEK) has a similar elastic modulus close to bone and as a result it can be a suitable alternative material to metallic implants which generally have higher moduli. However, the bio-inertness of PEEK prevents it from integrating well with the surrounding tissues. Many efforts have been made to overcome this problem including the deposition of hydroxyapatite (HA) on PEEK via plasma spraying. Current issues which have arisen with this method are low bonding strength between the substrate and the coating layer, as well as producing a non-uniform density of the coating. In this study, chemical deposition method was used to deposit HA crystalline particles on a treated PEEK substrate without any subsequent sintering process. The surface of PEEK was first sulphonated to create –SO3H functional group. It was then immersed in suspension of HA in water where the HA particles were chemically connected to the –SO3H functional group. The treated layer has a 3D porous property but exhibits very low mechanical properties. A compress force was applied on the coated layer for improving its mechanical properties. EDX and XRD results confirmed the existence of crystalline HA on the treated layer. FT-IR analysis was used to confirm the chemical bonding between HA and the substrate. The bioactivity of the HA treated layer was evaluated in terms of wettability. The water contact angle test showed 50% increase in wettability of the treated samples as compared to PEEK. The scratch and nano-indentation tests were carried out on the treated layer to assess its adhesion strength to the substrate and its mechanical strength respectively. The results showed that the compression caused 142% and 36.9% increment of the elasticity modulus and scratch hardness of the treated layer respectively. However, it caused 59% increase in the water contact angle. These findings indicate that the proposed new method is easy to process and does not require special equipment as compared to the Plasma Spray technique. The proposed method can be an alternative technique to change the bio-inertness of PEEK to become more bioactive PEEK which is good for polymeric implant material.