Implant-related infections pose a severe economical and societal burden, hence solutions capable of exerting suitable efficacy while not causing toxicity and/or development of resistant bacterial strains are needed. Thus, inorganic antibacterial coatings, and in particular silver coatings, have been extensively studied and used in the clinical practice. However, some drawbacks such as scarce adhesion to the substrate, delamination, or scarce control over silver release have been evidenced. Here, antibacterial nanostructured silver thin films have been developed by a novel plasma-assisted technique. The technique allows deposition on several substrates, including heat sensitive materials and objects of complex shape. Thanks to nanostructured surface, a tuned release can be achieved, preventing citoxicity. Composition (grazing incidence XRD, XPS) and morphology (SEM, AFM, ASTM) of the obtained coatings were characterized, then, their efficacy was validated in vitro against relevant bacterial strains (gram+ S. Aureus and gram– E. Coli). Live/dead kit and confocal microscopy were used to evaluate antibacterial efficacy. Super resolution imaging in the Structured Illumination Microscopy (SIM) setup was used to investigate damage to the bacterial wall. Results indicate that the coatings are composed of nanosized aggregates of metallic silver, indicating a perfect transfer of composition from the deposition target to the coating. Because of the sub-micrometric thickness, they do not alter the micro- and macro- morphology and surface finishing of the implants, developed by the manufacturers to ensure optimal integration in the host bone. Finally, remarkable efficacy was found against both gram+ and gram- bacteria, indicating that the developed coatings are promising for antibacterial applications.

Fabrication of biogenic coatings with suitable mechanical properties is a key goal in orthopedics, to overcome the limitations of currently available coatings and improve the clinical results of coated implants compared to uncoated ones. In this paper, biological-like apatite coatings were deposited from a natural bone-apatite source by a pulsed electron deposition technique (PED).

Bone apatite-like (BAL) films were deposited directly from bone targets, obtained by standard deproteinization of bovine tibial cortical shafts and compared to films deposited by sintered stoichiometric-hydroxyapatite targets (HA). Deposition was performed at room temperature by PED in the Ionized Jet Deposition (IJD) version. Half of the samples was annealed at 400°C for 1h (BAL_400 and HA_400). As-deposited and annealed coatings were characterized in terms of composition and crystallinity (XRD, FT-IR), microstructure and morphology (SEM-EDS, AFM) and mechanical properties (nanoindentation and micro-scratch). For the biological tests, human dental pulp stem cells (hDPSCs) were isolated from dental pulp from patients undergoing a routine tooth extraction, plated on the samples (2500 cells/cm2) and cultured for 3 weeks, when the expression of typical osteogenic markers Runx-2, osteopontin, Osx and Osteocalcin in hDPSCs was evaluated.

Results showed that deposition by PED allows for a close transfer of the targets” composition. As-deposited coatings exhibited low cristallinity, that was significantly increased by post-deposition annealing, up to resembling that of biogenic apatite target. As a result of annealing, mechanical properties increased up to values comparable to those of commercial plasma-sprayed HA-coatings.

In vitro biological tests indicated that BAL_400 promotes hDPSCs proliferation to a higher extent compared to non-annealed bone coating and HA-references. Furher, immunofluorescence and western blot analyses revealed that the typical osteogenic markers were expressed, indicating that BAL_400 alone can efficiently promote the osteogenic commitment of the cells, even in absence of an osteogenic medium.

In conclusion, bone-like apatite coatings were deposited by PED, which closely resembled composition and structure of natural-apatite. Upon annealing at 400°C, the coatings exhibited satisfactory mechanical properties and were capable of providing a suitable microenvironment for hDPSCs adherence and proliferation and for them to reach osteogenic commitment.

These results suggest that bone apatite-like thin films obtained by biogenic source may represent an innovative platform to boost bone regeneration in the orthopedic, maxillofacial and odontoiatric field.