Preparation, characterization and antimicrobial activity of a range of surface coated copper nanoparticles for bone cement

Use of metals such as Fe, Cu, Ag, Au, Ni, Ga, Hg, Te, Cd, Co, Zn, and their oxides in medical field has grown up during the last decade due to their antimicrobial properties conjugated with their high biocompatibility. In particular, the use of metal nanoparticles is nowadays exploited as a replacement for antibiotics therefore new methods of synthesis and novel applications have been developed with the aim of creating nanoparticles through less expensive and more tenable techniques. In this work copper nanoparticles were prepared through reduction and stabilization of copper salts with different well-known stabilizing agents, in order to be used as microbicidal agents embedded into bone cement. Nature and amount of stabilizers significantly affected the physical and biological properties of the nanoparticles, as demonstrated by size and zeta potential measurements, Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD), Fourier Transform Infra-Red spectroscopy (FTIR), ), X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA), Ultra-Violet Visible spectroscopy (UV-vis), Minimum Inhibitory Concentration (MIC) analysis and cytotoxicity tests (MTT and LDH assays). All the nanoparticles prepared have shown a good antimicrobial activity against Gram-positive bacteria (MRSA, S.aureus, S.epipidermidis) while a weaker effect against Gram-negative ones (A.baumannii, E. coli, P.aeruginosa) with Minimum Inhibitory Concentrations dependent on the nature of stabilizing agents, on their concentration and on the kind of surface coating created on the nanoparticles. The most effective stabilizing agent was found to be 1-undecanethiol, since it appears to promote the interaction between bacteria and nanoparticles enhancing their cellular intake and, hence, their toxic effect, but still preserving viability in eukaryotic cells. Nevertheless, these nanoparticles have not shown any remarkable microbicidal effect after their embedding within the bone cement so deeper and more accurate investigations of this phenomenon should be carried on.