**10.11. Layers and biocoatings**

The nanostructured coatings are expected to enhance the mechanical properties and im‐ prove the strength of bonding between coating and implant. These materials can also promote the deposition of calcium-containing minerals on their surface (bioactivity). Some typical examples of the research carried out in recent years, in the field of fabrication of nanostruc‐ tured glass-ceramic coatings, utilize various techniques such as conventional enameling, sputtering, sol-gel processing, ion beam deposition, plasma spraying, electrophoretic deposi‐ tion and pulsed laser deposition [164].

As was mentioned earlier, among the bioactive ceramics, the apatite/wollastonite (A/W) glassceramics, containing apatite and wollastonite crystals in the glassy matrix, has been largely studied because of good bioactivity and was used in some fields of medicine, especially in orthopedics and dentistry. However, medical applications of bioceramics are limited to nonload-bearing applications because of their poor mechanical properties. The solution of this problem can be the preparation of layers on the titanium alloy base material. Thermally sprayed layers by APS (atmospheric plasma spraying) on Ti-6Al-4V substrates combine good bioactivity of the bioceramics and good mechanical strength. The microstructure and the resulting properties were evaluated depending on the processing parameters and postpro‐ cessing thermal treatments. Thermal treatments decreased the bioactivity of the coatings, and after specific treatments, some bioactive materials were transformed into inert materials [67].

The biological performance of a porous apatite-mullite glass-ceramics, manufactured via the selective laser sintering (SLS) method, was investigated by GOODRIDGE et al [165]. Laser-sintered A-M has shown similar cytotoxicity, in vitro bioactivity and in vivo results to cast A-M, indicating that the laser-sintering processing route does not alter the behavior of the materi‐ al. The porous structure produced by SLS was seen by in vivo testing to be excellent for bone in-growth. However, the inability of the material to form apatite in vitro raised the concerns over the material's ability to prove bioactive in vivo, and further assessment is required to confirm whether this material is not bioactive or whether it is just not particularly suited for the characterization through SBF testing [165].
