**4. Conclusions**

Thin films of FastOs®BG alkali-free bioactive films co-doped with copper and gallium were successfully synthesised by radio-frequency magnetron sputtering.

The introduction of Cu and Ga induced a slight polymerization of the silica glass network of the films with respect to the undoped ones, having as effect a slight increase of the hardness (from ~5.8 to ~6.1 GPa) and critical load of scratch delamination (from ~4.3 to ~4.9 N), and a decrease of the elastic modulus (from ~136 to 127 GPa), with the bonding strength being conserved (~54 MPa).

*Coatings* **2020**, *10*, 1119

Furthermore, the Cu&Ga-FastOs ®BG-derived coating showed a significantly improved wear behaviour with respect to bare titanium and to the FastOs ®BG coating.

While the contact angle with water is kept within the optimal 60–80◦ range for cell adhesion, and the cytocompatibility of the Cu & Ga silica-rich films remained unaltered, they manifested a marked antibacterial e ffect against the *S. aureus* strain, reducing its development by ~4 orders of magnitude after 24 h.

Overall, these preliminarily mechanical and in vitro biological performances of Cu & Ga co-substituted silica-based bioactive glass films are testifying for their certain promise, which demands further exploration, on route to bio-functionalisation solutions capable to protect metallic endo-osseous implants against post-surgical microbial infection.

**Author Contributions:** Conceptualization, G.E.S., A.-C.P., C.B., T.T., and J.M.F.F.; Powder synthesis: H.R.F. and J.M.F.F.; Film fabrication: G.E.S., T.T., I.M.C., and A.C.S.; AFM, FTIR spectroscopy analyses: T.T., I.M.C., C.B., A.C.S., and G.E.S.; XPS investigations: C.C.N.; Surface energy investigations: I.Z.; EDXS measurements: G.P.-P.; Mechanical tests: D.C.; Biological assays: A.-C.P., L.E.I., and M.N.; writing—original draft preparation: G.E.S. and T.T.; writing—review and editing: T.T., G.E.S., A.-C.P., and J.M.F.F.; funding acquisition: G.E.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Romanian National Authority for Scientific Research and Innovation (CNCS-UEFISCDI) in the framework of project PN-III-P1-1.1-TE-2016-1501. J.M.F.F. is thankful for the financial support from CICECO—Aveiro Institute of Materials and FCT Ref. UID/CTM/50011/2019 grant, financed through the FCT/MCTES.

**Acknowledgments:** The authors thank for the financial support of the Romanian National Authority for Scientific Research and Innovation (CNCS-UEFISCDI) in the framework of project PN-III-P1-1.1-TE-2016-1501, and to the institutional Core Program 21N. This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. NIMP authors acknowledge with thanks the acquisition of the Leica DM6 B fluorescence microscope in the framework of the Operational Programme Competitiveness project NANOBIOSURF-SMIS 103528 (2014−2020). D.C. acknowledges the structural funds project PRO-DD (POS-CCE, O.2.2.1., ID123, SMIS 2637, ctr. no 11/2009) for providing the CSM Instruments infrastructure used in this work.

**Conflicts of Interest:** The authors declare no conflict of interest.
