Characteristics and in vitro response of thin hydroxyapatite-titania films produced by plasma electrolytic oxidation of Ti alloys in electrolytes with particle additions

The enhancement of the biological properties of Ti by surface doping with hydroxyapatite (HA) is of great significance, especially for orthodontic applications. This study addressed the effects of HA particle size in the electrolyte suspension on the characteristics and biological properties of thin titania-based coatings produced on Ti–6Al–4V alloy by plasma electrolytic oxidation (PEO). Detailed morphological investigation of the coatings formed by a single-stage PEO process with two-step control of the electrical parameters was performed using the Minkowski functionals approach. The surface chemistry was studied by glow discharge optical emission spectroscopy and Fourier transform infrared spectroscopy, whereas mechanical properties were evaluated using scratch tests. The biological assessment included in vitro evaluation of the coating bioactivity in simulated body fluid (SBF) as well as studies of spreading, proliferation and osteoblastic differentiation of MC3T3-E1 cells. The results demonstrated that both HA micro- and nanoparticles were successfully incorporated in the coatings but had different effects on their surface morphology and elemental distributions. The micro-particles formed an irregular surface morphology featuring interpenetrated networks of fine pores and coating material, whereas the nanoparticles penetrated deeper into the coating matrix which retained major morphological features of the porous TiO2 coating. All coatings suffered cohesive failure in scratch tests, but no adhesive failure was observed; moreover doping with HA increased the coating scratch resistance. In vitro tests in SBF revealed enhanced bioactivity of both HA-doped PEO coatings; furthermore, the cell proliferation/morphometric tests showed their good biocompatibility. Fluorescence microscopy revealed a well-organised actin cytoskeleton and focal adhesions in MC3T3-E1 cells cultivated on these substrates. The cell alkaline phosphatase activity in the presence of ascorbic acid and β-glycerophosphate was significantly increased, especially in HA nanoparticle-doped coatings

Comparative investigation of Al- and Cr-doped TiSiCN coatings

The aim of this work was a comparative investigation of the structure and properties of Al- and Cr-doped TiSiCN coatings deposited by magnetron sputtering of composite TiAlSiCN and TiCrSiCN targets produced by self-propagating high-temperature synthesis method. Based on X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy data, the Al- and Cr-doped TiSiCN coatings possessed nanocomposite structures (Ti,Al)(C,N)/a-(Si,C) and (Ti,Cr)(C,N)/a-SiCxNy/a-C with cubic crystallites embedded in an amorphous matrix. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum at 1000, 1100, 1200, and 1300°C or in air at 1000°C for 1h. The results obtained show that the hardness of the Al-doped TiSiCN coatings increased from 41 to 46GPa, reaching maximum at 1000°C, and then slightly decreased to 38GPa at 1300°C. The Cr-doped TiSiCN coatings demonstrated high thermal stability up to 1100°C with hardness above 34GPa. Although both Al- and Cr-doped TiSiCN coatings possessed improved oxidation resistance up to 1000°C, the TiAlSiCN coatings were more oxidation resistant than their TiCrSiCN counterparts. The TiCrSiCN coatings showed better tribological characteristics both at 25 and 700°C and superior cutting performance compared with the TiAlSiCN coatings. © 2011 Elsevier B.V.The work was fulfilled due to financial support from the Ministry of Education and Science of the Russian Federation (Contracts 02.740.11.0859 and П1248). The authors thank A.V. Levanov (Moscow State University) for Raman spectroscopy investigations and T.B. Sagalova (MISIS) for help with XRD measurements.Peer Reviewe