Previous studies have shown that nanostructured coatings produced by plasma spraying can stimulate cellular activity and promote bone healing. Since then, a number of studies have been conducted to better understand how coating nanotopography can be controlled and how it influences bioactivity and healing. This paper reviews some of the key findings in three areas: the effects of nanotopography on bone cell adhesion, the effects of nanotopography on bone-like apatite formation in simulated body fluid, and how to refine the nanotopography of plasma-sprayed coatings.

SiO 2 -TiO 2 coatings were prepared by atmospheric plasma spraying followed by hydrothermal treatment in a solution of hydrogen fluoride. The as-sprayed coatings mainly consisted of rutile and quartz phases, which remained relatively unchanged during etching. All treated coatings have the typical characteristics of plasma-sprayed deposits, exhibiting rough surfaces with many splats. Differences in surface structure can be observed, however, at the nanoscale, depending on treatment conditions. Treatments of 60 min at 100 °C appear to be most beneficial, resulting in nanoporous coatings that are shown to promote cell proliferation and, in past studies, have been found to improve osteoblast adhesion.

In this study, acoustic emission sensing is used to monitor interfacial cracking in thermal barrier coatings during uniaxial tensile adhesion testing. The TBCs consist of a ZrO 2 topcoat and a NiCrAl bond coat, both of which are applied by atmospheric plasma spraying. Tensile testing was performed to failure and the resulting fracture surfaces were examined by SEM and XRD analysis. Experimental results show that cracks usually initiate in the ceramic layer then propagate toward the metallic-ceramic interface where failure occurs. Finite element simulations were also conducted, confirming the experimental findings.

In this paper, nanostructure Lanthanum zirconate thermal barrier coatings (MCrAlY+ La 2 Zr 2 O 7 ) were prepared by atmospheric plasma sprayed (APS). The microstructures and thermal stability properties were systematically studied by Scanning Electric Microscopy (SEM), transmission electron microscope (TEM) and X-Ray diffraction(XRD). The results showed that the nanostructured lanthanum zirconate coatings were typical lamellar structure which was composed of columnar grains about 90nm in diameter. A large quantity of micro-cracks and homogeneous distributed fine pores formed in the nanostructured zirconia coating. After ablation at 1300 °C for 24 h, no apparent phase transformation was observed in lanthanum zirconate coating. The growth mechanism of the grains was subsequently discussed.

In this work, the plasma sprayed titania coatings were treated by H 2 SO 4 for 24h at room temperature to improve the biological properties. The bioactivity was measured by simulated body fluid soaking test, and the biocompatibility was evaluated by quantifying the grafted collagen amount and in vitro cell culture test. The results showed that titania coatings treated by 0.1M and 1M H 2 SO 4 can induce bone-like apatite formation after immersion in SBF for 28 days, while the titania coating treated by 0.01M H 2 SO 4 can not. H 2 SO 4 treatment can promote the grafting of collagen on titania coatings. The in vitro cell culture test confirmed that collagen improved the cellular adhesion and proliferation on titania surface. In conclusion, a certain concentration of H 2 SO 4 treatment is beneficial in improving the bioactivity and biocompatibility of plasma sprayed titania coatings.

In this paper, nano-structured TiO 2 coatings have been successfully deposited onto titanium alloy substrates by atmospheric plasma spraying technology using optimized plasma parameters. A chemical treatment method was employed to induce bioactivity on the TiO 2 surface. The bioactivity of as-sprayed and chemical treated TiO 2 coatings were evaluated by investigating the formation of apatite on their surface after they were soaked in simulated body fluids (SBF) for a period of time. Microstructure and the phase composition of the as-sprayed coating and apatite were analyzed by Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS). The results obtained indicate that as-sprayed TiO 2 coating consists of rutile, anatase and suboxide such as Ti 3 O 5 . The surface of nano-TiO 2 coating is covered by nano particles of about 50nm in size. The bonding strength of TiO 2 coating with Ti alloy substrate is as high as 40 MPa. The corrosion resistance performance of nano-coating in SBF is better than that of Ti-6Al-4V alloy. The surface of as-sprayed TiO 2 coating can not induce bone-like apatite formation. Chemical treatment, such as acid and alkali, can improve bioactivity of TiO 2 coating surface.