Bonding properties of carbon fiber reinforced (CFR)-PEEK and hydroxyapatite (HA)-PEEK joined by ultrasonic welding

Abstract

Acetabular cup is a component of hip prosthesis that replaces the acetabulum of pelvis bone in total hip arthroplasty. As shown in clinical studies, the stiffness mismatch between the implant and the bone leads to stress-shielding and bone resorption. The formation of wear debris due to contact between the acetabular cup and the femoral head can also cause adverse tissue reactions leading to massive bone loss around the implant and consequently implant loosening. This study attempted at solving the problem through the use of double-layer polymer composites. Carbon fiber reinforced polyetheretherketone (CFR-PEEK) was incorporated as the acetabular cup liner part to reduce wear rates whilst a second layer Hydroxyapatite-Polyetheretherketone (HA-PEEK) was used to create low modulus acetabular cup shell part. This new design was developed with the aim of reducing stress shielding, promote bone in-growth, and reducing wear debris from modular interfaces. The objective of this study was to prepare beam samples of the double-layer polymer composites via injection moulding process and ultrasonic welding. The strength of welding interface was evaluated by single cantilever beam (SCB) and lap shear tests. Response surface method (RSM) optimization process was used in the design of experiments in order to optimize the ultrasonic welding parameters. Coating of hydroxy-apatite on polymer composite substrate was investigated and the substrate was tested by CSM Micro scratch tester machine. SCB test showed stronger welding for partial energy director compared to those performed with whole energy director. The optimized maximum debonding force of the composite layers was achieved for 3.5 seconds welding time, 3 seconds holding time, and 8 bar pressure of ultrasonic welding parameters. Scratch test assessment showed plasma spraying as an appropriate method for coating of HA on PEEK substrate with a coefficient friction of 0.67.