Are Titania Photocatalysts and Titanium Implants Safe? Review on the Toxicity of Titanium Compounds

Abstract

Titanium and its compounds are broadly used in both industrial and domestic products, including jet engines, missiles, prostheses, implants, pigments, cosmetics, food, and photocatalysts for environmental purification and solar energy conversion. Although titanium/titania-containing materials are usually safe for human, animals and environment, increasing concerns on their negative impacts have been postulated. Accordingly, this review covers current knowledge on the toxicity of titania and titanium, in which the behaviour, bioavailability, mechanisms of action, and environmental impacts have been discussed in detail, considering both light and dark conditions. Consequently, the following conclusions have been drawn: (i) titania photocatalysts rarely cause health and environmental problems; (ii) despite the lack of proof, the possible carcinogenicity of titania powders to humans is considered by some authorities; (iii) titanium alloys, commonly applied as implant materials, possess a relatively low health risk; (iv) titania microparticles are less toxic than nanoparticles, independent of the means of exposure; (v) excessive accumulation of titanium in the environment cannot be ignored; (vi) titanium/titania-containing products should be clearly marked with health warning labels, especially for pregnant women and young children; (vi) a key knowledge gap is the lack of comprehensive data about the environmental content and the influence of titania/titanium on biodiversity and the ecological functioning of terrestrial and aquatic ecosystems.

Nanostructured Surfaces to Promote Osteoblast Proliferation and Minimize Bacterial Adhesion on Titanium

“…Although titanium has already been used for several purposes [ 27 ], the toxicity of this metal has not been addressed in detail, considering the direct and indirect consequences and acute and chronic toxicity [ 28 ]. In the present study, no cell cytotoxicity was found after 24 h in nanotube titanium sheets (100 nm and 150 nm) showing potential biocompatibility, which is a favorable property for osseintegration.…”

Novel Coatings to Minimize Corrosion of Titanium in Oral Biofilm

“…Bacteria corrosion on implants is due to biofilm formation, under which the interfacial electrochemical processes start and are followed by microbially-influenced corrosion on substratum metals and alloys [ 19 , 20 ]. Corrosion is a complex process mediated by interaction occurring between anaerobic and aerobic bacteria [ 7 , 21 ].…”

“…The lack of aeration in these areas helps create an anode where corrosion can occur by releasing metal ions into the saliva. Moreover, by combining the released metal ions with the saliva’s chloride ions or the bacteria’s end-products, more reactive species will be generated, and the metal will be corroded further [ 20 , 23 ].…”

Custom-Made Zirconium Dioxide Implants for Craniofacial Bone Reconstruction

“…Titanium alloys are currently the standard in craniomaxillofacial surgery. Alloys grade 5 or 23 are mainly used, but they are not ideal implantation materials for humans [ 20 ]. Titanium alloy is implanted into the bone; after some time, it passes into the surrounding soft tissues and reaches high concentrations there.…”