Biocompatible antimicrobial coatings may enhance the function of many orthopedic implants by combating infection. Hydroxyapatite is a choice mineral for such a coating as it is native to bone and silver would be a possible antimicrobial agent as it is also commonly used in biomedical applications. The aim of the research is to develop a silver-containing calcium phosphate (Ag/Ca-P) coating via electrochemical deposition on titanium substrates as this allows for controlled coating buildup on complex shapes and porous surfaces. Two different deposition approaches are explored: one-step Ag/Ca-P(1) deposition coatings, containing silver ions as microsized silver phosphate particles embedded in the Ca-P matrix; and via a two-step method (Ag/Ca-P(2)) where silver is deposited as metallic silver nanoparticle on the Ca-P coating. The Ag/Ca-P(1) coating displays a bacterial reduction of 76.1 ± 8.3% via Ag-ion leaching. The Ag/Ca-P(2) coating displays a bacterial reduction of 83.7 ± 4.5% via contact killing. Interestingly, by preincubation in phosphate-buffered saline solution, bacterial reduction improves to 97.6 ± 2.7 and 99.7 ± 0.4% for Ag/Ca-P(1) and Ag/Ca-P(2) coatings, respectively, due to leaching of formed AgCl x (x–1)– species. The biocompatibility evaluation indicates that the Ag/Ca-P(1) coating is cytotoxic towards osteoblasts while the Ag/Ca-P(2) coating shows excellent compatibility. The electrochemical deposition of highly bactericidal coatings with excellent biocompatibility will enable us to coat future bone implants even with complex or porous structures.

Nanocarbons come in many forms and among their applications is the engineering of biocompatible and antibacterial materials. Studies have shown that diamond nanoparticles might have the interesting combination of both properties: they are highly biocompatible, while surprisingly reducing bacterial viability or growth at the same time. In this article, we consider for the first time the interaction of milled HPHT nanodiamonds with bacteria. These nanoparticles are capable of hosting nitrogen-vacancy (NV) centers, which provide stable fluorescence with potential use in sensing applications. An initial study was performed to assess the interaction of partially oxidized monocrystalline nanodiamonds with Gram positive S. aureus ATCC 12600 and Gram negative E. coli ATCC 8739. It was shown that for S. aureus ATCC 12600, the presence of these nanodiamonds leads to a sharp reduction of colony forming ability under optimal conditions. A different effect was observed on Gram negative E. coli ATCC 8739, where no significant adverse effects of ND presence was observed. The mode of interaction was further studied by electron microscopy and confocal microscopy. The effects of NDs on S. aureus viability were found to depend on many factors, including the concentration and size of nanoparticles, the suspension medium and incubation time.

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