Titanium dioxide (TiO2) nanomaterials have considerable beneficial applications varying from additives in paint, paper, plastics and cosmetics to uses in photocatalysts, solar cells and medical materials and devices. It has been established for many years that pigment-grade TiO2 (200 nm sphere) is relatively inert when internalized into a biological model system (in vivo or in vitro).
For this reason, TiO2 nanomaterials are an attractive alternative in applications where biological exposures will occur. Unfortunately, metal oxides on the nanoscale (one dimension <100 nm) may or may not exhibit the same toxic potential as the original material. A further complicating issue is the effect of modifying or engineering of the nanomaterial to be structurally and geometrically different from the original material. TiO2 nanospheres, short (<5 µm) and long (>15 µm) nanobelts were synthesized, characterized and tested for biological activity using primary murine alveolar macrophages and in vivo in mice. This study demonstrates that alteration of anatase TiO2 nanomaterial into a fibre structure of greater than 15 µm creates a highly toxic particle and initiates an inflammatory response by alveolar macrophages.
These fibre-shaped nanomaterials induced inflammasome activation and release of inflammatory cytokines through a cathepsin B-mediated mechanism. Consequently, long TiO2 nanobelts interact with lung macrophages in a manner very similar to asbestos or silica.
These observations suggest that any modification of a nanomaterial, resulting in a wire, fibre, belt or tube, be tested for pathogenic potential.
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