Environmental Toxicity and Antimicrobial Efficiency of Titanium Dioxide Nanoparticles in Suspension

The aim of this work was to evaluate the photokilling efficiency of synthesized titanium dioxide nanoparticles in suspension. Two strains of Escherichia coli, Lactobacillus casei rhamnosus and Staphylococcus aureus were used as probes to test the photokilling activities of the nanoparticles. The toxicity effects of TiO2 nanoparticles on the environment were determined by a standard test using gram-negative bioluminescent bacteria Vibrio fischeri. The antimicrobial activity of these nanoparticles (NPs) was then investigated versus NPs concentration, UV irradiation time and micro- organism strains. We evaluated the LC50 values of the nanoparticles suspension by counting the Colony-Forming Units. Results highlighted the differences in bacteria sensitivity facing photokilling treatment induced by the irradiation of anatase TiO2 nanoparticles suspension. At the concentration of 1 g·L-1 TiO2, tested bacteria were killed after 30 minutes of photo-treatment. Using different TiO2 concentrations, the Staphylococcus aureus gram-positive/catalase-positive bacteria were more resistant than gram-negative/catalase-positive ones or gram-positive/catalase-negative bacteria. An effect of UV irradiation was evaluated by the quantification of hydrogen peroxide generated by the photolysis of water molecules in presence of the nanoparticles with or without the most resistant bacterium (S. aureus). After 30 minutes with UV irradiation in these two conditions, the concentration of hydrogen peroxide was 35 μM in presence of 1.2 g·L-1 TiO2 suspension. This result suggested that the resistance mechanism of S. aureus was not due to an extracelullar H2O2 enzymatic degradation.

One-pot Synthesis of TiO2 Nanoparticles in Suspensions for Quantification of Titanium Debris Release in Biological Liquids

In this work we have developed an analytical method to measure potential titanium debris released from TiO2 nanotube layers devices immersed in biological fluids. This quantitative study is highly required to ensure both the security and non toxicity of the nanostructured surfaces used as future implantable medical devices in the living. A one-pot synthesis process is developed to produce high quality standard solutions of titanium dioxide nanoparticles in aqueous medium. The elaborated dispersion is then used to fabricate standard solutions in both aqueous and human blood plasma media. The synthesized nanoparticles dispersion was characterized by granulometry. The nanoparticles structure and morphology were then observed using Transmission Electron Microscopy (TEM). Thermogravimetric Analysis (TGA) was used to evaluate the concentration of TiO2 in the suspension. A quantitative routine by the use of Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) is developed. The quantification threshold of titanium species is found to be in the 30 - 40 ppb range. None interference is detected between the particles and the human blood plasma. Using the established quantitative routine, the titanium species release from titania nanotube layers in human blood plasma is evaluated.

Feasibility of a Chronic Foreign Body Infection Model Studying the Influence of TiO2 Nanotube Layers on Bacterial Contamination

Bacterial infections on the surface of medical devices are a significant problem in therapeutic approach, especially when implants are used in the living. In cardiology, pacemaker generator pocket surfaces, made in titanium alloy can be colonized by pathogen microorganism. This contamination represents a major risk of sepsis, endocarditis and localized infections for patients. A way to limit this bacterial contamination is to modify the surface topography using nano-structuration process of the titanium alloy surface of the implanted devices. The aim of this study is to evaluate the influence of TiO2 nanotube layers on bacterial infection in the living, considering the feasibility of an animal model of chronic foreign body infection. TiO2 nanotube layers prepared by electrochemical anodization of Ti foil in 0.4 wt% hydrofluoric acid solution were implanted subcutaneously in Wistar rats. Three weeks after implantation, TiO2 implants were contaminated by a Staphylococcus epidermilis strain using two different concentrations at 106 and 108 colony forming unit (CFU) in order to induce a sufficient infection level and to avoid unwanted over infection consequences on rats health during the experiments. After 28 days in the living, 75% of nanotube layers initially submitted to the 108 CFU inoculum were contaminated while only 25% nanotube layers initially submitted to the 106 CFU inoculum remained infected. This significant result underlines the influence of TiO2 nanotube layers in decreasing the infection level. Our in vitro experiments showed that the synthesized TiO2 nanotubes indeed decreased the Staphylococcus epidermilis adhesion compared to unanodized Ti foil.

Photokilling of Escherichia coli Using Hybrid Titania Nanoparticles Suspended in an Aqueous Liquid

In this work, the photokilling of Escherichia coli using a “one-pot” synthesized suspension of anatase crystallized nanoparticles is evaluated. Preliminary to the biological tests concerning the antibacterial efficiency, the fabricated suspension, using a derived solgel process in soft chemistry condition, is characterized. Structural properties of the nanoparticles are investigated using Electronic Transmission Microscopy (TEM) equipped with Selected Area Electron Diffraction (SAED) probe and X-ray diffraction. The inorganic solid content was evaluated by Thermogravimetric Analysis (TGA). Photodegradation of Acid Orange 7 in aqueous solution was used a probe to assess the photocatalytic activity of the elaborated suspension under UV irradiation. The photokilling of Escherichia coli in presence of hybrid TiO2 nanoparticles suspended in aqueous liquid under UV irradiation is evaluated. Such TiO2 nanoparticles suspension shows a strong bactericidal activity with the total destruction of bacteria after only one hour.