Adhesion of calcium phosphate ceramic on polyethylene (PE) and polytetrafluoroethylene (PTFE)

Calcium phosphate (CaP) ceramic coatings are often used on biomedical implants for its osteoinductive properties. In this work, the adhesion of r.f. magnetron sputter deposited CaP ceramic on PE and PTFE was studied by tensile and interface elongation tests. Both untreated and oxygen plasma pretreated substrates were used. The adhesion of CaP to PE was found to be good. In tensile tests, the coated material was glued to the pull rods using an epoxy adhesive. Usually, the epoxy failed instead of the CaP–PE interface. Moreover, the interfacial plane of the CaP coated PE could be extended to twice its normal size without the delamination of the coating. No significant difference was found between the untreated and plasma pretreated material. Additional experiments were performed to clarify what mechanism is responsible for the good adhesion of CaP to PE. Good adhesion is the result of a bombardment by energetic oxygen ions that originate from the sputtering target. The absence of this bombardment causes a lower number of chemical bonds between the polymer and the coating, and therefore the delamination of the coating. The PTFE showed a different behavior. The locus of failure in the tensile tests was within the PTFE. No significant difference was found whether or not a plasma pre-treatment was given. UV light induced damage of the PTFE is the most likely reason for the cohesive failure. The UV light is emitted from the plasma and is transmitted by the CaP coating.