gms | German Medical Science

Objectives: The inhibition of the initial bacterial implant colonization by supportive antimicrobial agents such as silver is a strategy to reduce implant-related infections. A rapid and time-limited oxidative Ag ion (Ag⁺) release can be achieved by silver nanoparticles (AgNP) due to their high specific surface area. A further promising approach to enhance Ag⁺ release based on the sacrificial anode principle is the combination of Ag with an electrochemically more noble metal, such as platinum (Pt). Previously we demonstrated the efficiency of such a sacrificial anode system [1].

Here, we compare the potency of a physical mixture of AgNP and PtNP to pure AgNP by analysis of NP dissolution, antimicrobial activity towards S.aureus and E.coli and the biological effects on human mesenchymal stem cells (hMSC).

Methods: PVP-coated spherical AgNP and PtNP (diameter 5-10 nm) were synthesized by reducing AgNO₃ and H₂PtCl₆ with NaBH4 or citrate/tannin. NP were characterized using AAS, DCS and TEM/EDX. The antimicrobial activity of the NP was analyzed by determination of the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The viability of hMSC exposed to NP was accessed by calcein-AM staining and real-time cell tracking, while osteogenic differentiation was analyzed using Alizarin Red and the AttoPhos assay. The Ag⁺ release was analyzed by dissolution experiments and electrochemistry.

Results and conclusion: A physical mixture of 50-wt% AgNP and 50-wt% PtNP showed significantly enhanced antimicrobial effects against S.aureus and E.coli as well as enhanced toxicity towards hMSC compared to pure AgNP at same total Ag concentration. The toxic effects of the physical mixture occurred within minutes of incubation and were therefore substantially faster than for pure AgNP. Since pure PtNP induced no toxic effects at the used concentrations, an electrochemically induced enhancement of Ag⁺ release from AgNP in the presence of PtNP was assumed and confirmed by dissolution experiments and cyclic voltammetry. Significantly, for the first time to our knowledge we additionally identified an osteo-promotive effect of pure PtNP on hMSC.

In conclusion, these findings might be useful for the development of multifunctional biomaterial coatings using AgNP and PtNP. Such coatings would have the advantages of an antimicrobial activity at low total silver amount concomitantly with a supporting effect on bone regeneration.