Role of the chemical modification of titanium dioxide surface on the interaction with silver nanoparticles and the capability to enhance antimicrobial properties of poly(lactic acid) composites

In this work, the antimicrobial activity of neat and silanized titanium dioxide deposited with silver nanoparticles was evaluated when it was used as filler in a poly(lactic acid) matrix. The silanization and deposition processes were evaluated by scanning transmission electron microscopy and X-ray photoelectron spectroscopy confirming the chemical modification on the titanium dioxide surface by 3-aminopropyltriethoxy silane and the formation of silver nanoparticles. According to the elemental analysis conducted by energy-dispersive X-ray spectroscopy, more silver, 7.4% higher, was deposited on the oxide when this was previously silanized and when 30% w/w of silver nitrate was used as a precursor. The antimicrobial effect was confirmed for the nanoparticles through the disk diffusion method and for the composites by drop test, against Staphylococcus aureus and Escherichia coli bacteria; the results showed that the inhibition rate increased by 14.2% and 39.1% for nanoparticles and by 57.6% and 38.8% for composites against each bacteria, respectively, when deposition was performed on silanized titanium dioxide. Also, better mechanical properties were obtained in the composites filled with silanized oxide; the best results were obtained in the PLA/sTiO₂–Ag 20% system with an improvement of 45.7% in tensile stress and of 38.73% for Young’s modulus. Finally, the toxicity of the composites was evaluated by seeding peripheral blood mononuclear cells; results show evidence that composites filled with these nanoparticles are non-toxic since these do not migrate from the polymeric matrix, which helps to enhance the prolonged surface antibacterial effect and to open a broad perspective of the commercial use of these composites.