Durability of APC2/polyurethane adhesive joints for biomedical applications

Thermoplastic polyurethane elastomer was thermally bonded to carbon fibre-reinforced polyetheretherketone (APC2) in the development of a biomedical device. Argon plasma treatment of the APC2 substrate was investigated as a means of enhancing bonding. Contact angle measurements were used to optimise the surface treatment and, it was observed that the wettability decreased on ageing. Kinetic analysis gave an activation energy of 25 kJ/mol, which was consistent with a bond rotation mechanism. Optimally treated substrates were bonded to polyurethane and bond stability at 37°C was evaluated. While the bond was stable in air for over 1 year, storage in aqueous media lead to rapid deterioration of bond strength. This phenomenon was observed both in distilled water and in Ringer's solution. Measured diffusion rates for both environments were very similar and it is suggested that the observed faster rate of loss of bond strength in Ringer's solution is by the interaction of buffered components from the Ringers or solubilisation of low molecular weight material by the Ringers.