Mg₂TiO₄-Mg₂SnO₄ spinels for microbial anti adhesion

Full text: The development of materials with surfaces which avoid the cellular adhesion and the consequent biofilm formation is an important issue for chemists and material engineers. In this work, the microbial anti-adhesion of spinel materials with stoichiometry Mg₂Ti_1-xSn_xO₄ (x = 0.0, 0.25, 0.50, 0.75, 1.0), obtained by the modified Pechini method, was evaluated. The materials were characterized by X-ray diffraction, UV-visible spectroscopy, Raman spectroscopy, infrared spectroscopy, surface area measurements and determination of the point of zero charge (PZC) by the salt addition method. Stainless steel was used as negative control to evaluate the microbial adhesion and the biofilm formation, because it is widely employed in hospital environment, as tables and surgical instruments. The XRD patterns confirmed the formation of single phase spinel with high long-range order, while IR spectra showed the formation of magnesium carbonate. Surface areas varied from 2 to 14 m²/g. Mg₂SnO₄ and Mg₂TiO₄ presented the highest PCZ values, 7.7 and 8.3 respectively, while the solid solutions presented PCZ values of 7.5, 6.9 and 7.5 for Mg₂Sn_0,75Ti_0,25O₄, Mg₂Sn_0,50Ti_0,50O₄ and Mg₂Sn_0,25Ti_0,7-5O₄, respectively. The obtained spinels were effective in inhibiting bacterial and fungal growth as indicated by fluorescence analysis for Gram positive bacteria (S. aureus and S. mutans), Gram negative bacteria (P. aeruginosa and E. coli) and fungus (Candida albicans) showing high potential for microbial anti-adhesion material. Tests with higher titanium content showed the best results except for E. coli. The different results are related to the inoculation, hydrophobicity and pH of the medium, which influence the adhesion process, favoring or not the electrostatic interaction between the solid surface and the microbial cells. (author)