Bioactive hydroxyapatite coatings on polymer composites for orthopedic implants

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] coatings on polymer composite substrates were investigated for their bioactivity and their physicochemical and mechanical characteristics. HA holds key characteristics for use in orthopedic applications, such as for coating of the femoral stem in a hip replacement device. The plasma-spray technique was used to project HA onto a carbon fiber/polyamide 12 composite substrate. The resulting HA coatings exhibited mechanical adhesion as high as 23 MPa, depending on the surface treatment of the composite substrate. The purpose of this investigation was to evaluate the bioactivity of an HA-coated composite substrate. HA- coated samples have been immersed in simulated body fluid (SBF) and maintained within a shaker bath for periods of 1, 7, 14, 21, and 28 days at 37 degrees C. Scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were performed on the samples before and after immersion into SBF. SBF was analyzed using inductively coupled plasma atomic emission spectrometry for element concentration and evaluation of the solution's purity. SBF conditioning led to the deposition of crystalline HA onto the surface of the coatings. The calcium-to-phosphorous ratios of initial HA coating and of newly deposited HA were respectively 1.72 and 1.65, close to the HA theoretical calcium/phosphorous value of 1.67. Results demonstrated that bioactive HA coatings were produced by plasma spraying, because SBF conditioning induced newly formed HA with high crystallinity. Mechanical adhesion of the HA coatings was not significantly affected upon SBF conditioning.