Effect of fluorine substitution on sintering behaviour, mechanical and bioactivity of hydroxyapatite.

Fluorine substituted hydroxyapatite (FAp) with different degree of fluorine (F) substitution, has been synthesized using hydrothermal synthesis method. In the present work, as synthesized powders were consolidated by sintering at 1200 °C in air for 1 h. The sintered specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) for phase analysis. Further, fluorine intake in the sintered specimens was evaluated using ion chromatography (IC). XRD peaks clearly showed biphasic nature of the sintered specimen. However, the sintered samples containing more than ∼60% fluorine substitution showed no ß-tricalcium phosphate (ß-TCP) phase formation. The IC results revealed that the degree of fluoridation decreased significantly in the sintered specimen compare to the respective as synthesized powders. The effect of actual fluorine content in the sintered specimens was further evaluated in terms of sinterability, surface energy, mechanical properties and in vitro cytocompatibility study. The surface energy of the sintered specimen decreased from 51.8 mN/m to 42.5 mN/m, in which degree of fluoridation varies from 0% to 110%. The in vitro cytocompatibility of the sintered specimen were carried out against mouse osteoblast cell line (MC3T3-E1). In vitro study showed that all the samples were nontoxic but cell proliferation for the samples containing more than 40% fluorine substitution became significantly low.

Nano- and micro-tribological behaviours of plasma nitrided Ti6Al4V alloys.

Plasma nitriding of the Ti-6Al-4V alloy (TA) sample was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as TAPN. The TA and TAPN samples were characterized by XRD, Optical microscopy, FESEM, TEM, EDX, AFM, nanoindentation, micro scratch, nanotribology, sliding wear resistance evaluation and in vitro cytotoxicity evaluation techniques. The experimental results confirmed that the nanohardness, Young's modulus, micro scratch wear resistance, nanowear resistance, sliding wear resistance of the TAPN samples were much better than those of the TA samples. Further, when the data are normalized with respect to those of the TA alloy, the TAPN sample showed cell viability about 11% higher than that of the TA alloy used in the present work. This happened due to the formation of a surface hardened embedded nitrided metallic alloy layer zone (ENMALZ) having a finer microstructure characterized by presence of hard ceramic Ti2N, TiN etc. phases in the TAPN samples, which could find enhanced application as a bioimplant material.

Nanotribological response of a plasma nitrided bio-steel.

AISI 316L is a well known biocompatible, austenitic stainless steel (SS). It is thus a bio-steel. Considering its importance as a bio-prosthesis material here we report the plasma nitriding of AISI 316L (SS) followed by its microstructural and nanotribological characterization. Plasma nitriding of the SS samples was carried out in a plasma reactor with a hot wall vacuum chamber. For ease of comparison these plasma nitrided samples were termed as SSPN. The experimental results confirmed the formations of an embedded nitrided metal layer zone (ENMLZ) and an interface zone (IZ) between the ENMLZ and the unnitrided bulk metallic layer zone (BMLZ) in the SSPN sample. These ENMLZ and IZ in the SSPN sample were richer in iron nitride (FeN) chromium nitride (CrN) along with the austenite phase. The results from nanoindentation, microscratch, nanoscratch and sliding wear studies confirmed that the static contact deformation resistance, the microwear, nanowear and sliding wear resistance of the SSPN samples were much better than those of the SS samples. These results were explained in terms of structure-property correlations.