Morphological and structural characterisation of osseointegrable Mn2+ and CO32- doped hydroxylapatite thin films

We report a morphological and structural study of osseointegrable hydroxylapatite thin films doped with divalent manganese and carbonate ions. The films were grown by pulsed laser deposition on medical grade Ti substrates at low oxygen pressure (13 Pa). Deposition targets were prepared from powders obtained by precipitation. During deposition, the substrates were kept at constant temperature within the temperature range 350-450 oC and the obtained films were subsequently annealed in hot water vapours at the deposition temperature. The films were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). Film specimens for cross-section TEM were prepared by focused ion beam (FIB) machining. The inferred Ca/P atomic ratio in films varied between 1.6 and 1.8, depending on experimental conditions. XPS confirmed the presence of chemically bonded Mn2+. Cross-section TEM micrographs showed uniform thickness of the coatings, which consisted of amorphous and crystalline domains. Examination of the SEM micrographs revealed an increased smoothness of the surface with increase in substrate deposition temperature. XRD patterns of samples processed at temperatures over 400 oC showed well-crystallized hydroxylapatite, suggesting that deposition and annealing have to be performed at higher substrate temperature if highly crystalline coatings are required