Silver ions are antimicrobial agents with powerful action
against
bacteria. Applications in surface treatments, as Ag+-functionalized
sol–gel coatings, are expected in the biomedical field to prevent
contaminations and infections. The potential cytotoxicity of Ag+ cations toward human cells is well known though. However,
few studies consider both the bactericidal activity and the biocompatibility
of the Ag+-functionalized sol–gels. Here, we demonstrate
that the cytotoxicity of Ag+ cations is circumvented, thanks
to the ability of Ag+ cations to kill Escherichia
coli (E. coli) much
faster than normal human dermal fibroblasts (NHDFs). This phenomenon
was investigated in the case of two silver nitrate-loaded sol–gel
coatings: one with 0.5 w/w% Ag+ cations and the second
with 2.5 w/w%. The maximal amount of released Ag+ ions
over time (0.25 mg/L) was ten times lower than the minimal inhibition
(MIC) and minimal bactericidal (MBC) concentrations (respectively,
2.5 and 16 mg/L) for E. coli and twice
lower to the minimal cytotoxic concentration (0.5 mg/L) observed in
NHDFs. E. coli were killed 8–18
times, respectively, faster than NHDFs by silver-loaded sol–gel
coatings. This original approach, based on the kinetic control of
the biological activity of Ag+ cations instead of a concentration
effect, ensures the bactericidal protection while maintaining the
biocompatibility of the Ag+ cation-functionalized sol–gels.
This opens promising applications of silver-loaded sol–gel
coatings for biomedical tools in short-term or indirect contacts with
the skin.