Designing Nanoparticles for Safety – the 4 Micron Rule
Research from the UK appears to present a lesson in smart product design, in this instance as to nanoparticles. Prior studies have shown that nanoparticles cause inflammation in the lung, and show signs of having the adverse health impacts of asbestos. So, the researchers experimented with fiber length to see if different fibers produced different impacts.
Sure enough, there were indeed differences. Particles at or above 4 microns are more inflammatory than are shorter fibers (and there are some further subtleties on length/width ratios). The research paper is online, and the abstract is pasted below. The results are consistent with prior research on less uniform asbestos fibers. Hat tip to RJ Lee Group for flagging the research.
"Suspicion has been raised that high aspect ratio nanoparticles or nanofibers might possess asbestos-like pathogenicity. The pleural space is a specific target for disease in individuals exposed to asbestos and by implication of nanofibers. Pleural effects of fibers depends on fiber length, but the key threshold length beyond which adverse effects occur has never been identified till now because all asbestos and vitreous fiber samples are heterogeneously distributed in their length. Nanotechnology advantageously allows for highly defined length distribution of synthetically engineered fibers that enable for in-depth investigation of this threshold length. We utilized the ability to prepare silver nanofibers of five defined length classes to demonstrate a threshold fiber length for acute pleural inflammation. Nickel nanofibers and carbon nanotubes were then used to strengthen the relationship between fiber length and pleural inflammation. A method of intrapleural injection of nanofibers in female C57Bl/6 strain mice was used to deliver the fiber dose, and we then assessed the acute pleural inflammatory response. Chest wall sections were examined by light and scanning electron microscopy to identify areas of lesion; furthermore, cell–nanowires interaction on the mesothelial surface of the parietal pleura in vivo was investigated. Our results showed a clear threshold effect, demonstrating that fibers beyond 4 µm in length are pathogenic to the pleura. The identification of the threshold length for nanofiber-induced pathogenicity in the pleura has important implications for understanding the structure–toxicity relationship for asbestos-induced mesothelioma and consequent risk assessment with the aim to contribute to the engineering of synthetic nanofibers by the adoption of a benign-by-design approach."