**The Beneficial Mechanical and Biological Outcomes of Thin Copper-Gallium Doped Silica-Rich Bio-Active Glass Implant-Type Coatings**

**George E. Stan 1,\*, Teddy Tite 1, Adrian-Claudiu Popa 1, Iuliana Maria Chirica 1, Catalin C. Negrila 1, Cristina Besleaga 1, Irina Zgura 1, Any Cristina Sergentu 1, Gianina Popescu-Pelin 2, Daniel Cristea 3, Lucia E. Ionescu 4, Marius Necsulescu 4, Hugo R. Fernandes 5 and José M. F. Ferreira 5**


Received: 12 October 2020; Accepted: 18 November 2020; Published: 20 November 2020

**Abstract:** Silica-based bioactive glasses (SBG) hold grea<sup>t</sup> promise as bio-functional coatings of metallic endo-osseous implants, due to their osteoproductive potential, and, in the case of designed formulations, suitable mechanical properties and antibacterial e fficacy. In the framework of this study, the FastOs ®BG alkali-free SBG system (mol%: SiO2—38.49, CaO—36.07, P2O5—5.61, MgO—19.24, CaF2—0.59), with CuO (2 mol%) and Ga2O3 (3 mol%) antimicrobial agents, partially substituting in the parent system CaO and MgO, respectively, was used as source material for the fabrication of intentionally silica-enriched implant-type thin coatings (~600 nm) onto titanium (Ti) substrates by radio-frequency magnetron sputtering. The physico-chemical and mechanical characteristics, as well as the in vitro preliminary cytocompatibility and antibacterial performance of an alkali-free silica-rich bio-active glass coating designs was further explored. The films were smooth (RRMS < 1 nm) and hydrophilic (water contact angle of ~65◦). The SBG coatings deposited from alkali-free copper-gallium co-doped FastOs ®BG-derived exhibited improved wear performance, with the coatings eliciting a bonding strength value of ~53 MPa, Lc3 critical load value of ~4.9 N, hardness of ~6.1 GPa and an elastic modulus of ~127 GPa. The Cu and Ga co-doped SBG layers had excellent cytocompatibility, while reducing after 24 h the *Staphylococcus aureus* bacterial development with 4 orders of magnitude with respect to the control situations (i.e., nutritive broth and Ti substrate). Thereby, such SBG constructs could pave the road towards high-performance bio-functional coatings with excellent mechanical properties and enhanced biological features (e.g., by coupling cytocompatibility with antimicrobial properties), which are in grea<sup>t</sup> demand nowadays.

**Keywords:** implant coating; bioactive glass; copper doping; gallium doping; mechanical; cytocompatibility; antibacterial

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