Electrophoretic deposition of polyetheretherketone (PEEK) and PEEK/Bioglass® coatings on NiTi shape memory alloy wires

Polyetheretherketone (PEEK) and PEEK/Bioglass (R) coatings were produced on shape memory alloy (NiTi, Nitinol (R)) wires using electrophoretic deposition (EPD). Best results were achieved with suspensions of PEEK powders in ethanol in the range (1-6 wt%), using a deposition time of 5 minutes and applied voltage of 20 Volts. EPD using these parameters led to high quality PEEK coatings with a homogeneous microstructure along the wire length and a uniform thickness of up to 15 mu m without development of cracks or the presence of large voids. Suspensions of PEEK powders in ethanol with addition of Bioglass (R) particles (0.5-2 wt%) (size < 5 mu m) were used to produce PEEK/Bioglass (R) coatings. Sintering was carried out as a post EPD process in order to densify the coatings and to improve the adhesion of the coatings to the substrate. The sintering temperature was 340 degrees C, sintering time 20 min and heating rate 300 degrees C/h. Sintering led to uniform and dense PEEK and PEEK/Bioglass (R) coatings without any cracks. The bioactive behaviour of PEEK/Bioglass (R) composite coatings was investigated by immersion in acellular simulated body fluid (SBF) for up to two weeks. As expected, hydroxyapatite crystals formed on the surface of the coated wires after 1 week in SBF, confirming the bioactive character of the coatings. The results have demonstrated for the first time that EPD is a very convenient method to obtain homogeneous and uniform bioactive PEEK and PEEK/Bioglass (R) coatings on Nitinol (R) wires for biomedical applications.