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In the present paper, the nanoindentation theory proposed in Ref. 1 is extended to nanoscratching, considering different sizes and shapes of a nanosized indenter/scratcher penetrating into a plastic material. The finding can explain the observed scaling of the mean pressure or specific energy for scratching; such a quantity is seen as 'lateral hardness', allowing one to unify nanoindentation and nanoscratching as different aspects of the same nanotribology. The scratching resistance and hardness are then discussed as a function of the penetration velocity. Finally, new experiments of nanoindentation, using an atomic forcemicroscope coupled technique for indentation and imaging, of a complex and anisotropic metallic-organic framework pulverised material are reported and discussed, quantifying the role of the nanohardness, Young's modulus, pile-up and nanoscratching resistance. [ABSTRACT FROM AUTHOR]

The growing global production of zinc oxide nanoparticles (ZnONPs) suggests a realistic increase in the environmental exposure to such a nanomaterial, making the knowledge of its biological reactivity and its safe-by-design synthesis mandatory. In this study, the embryotoxicity of ZnONPs (1-100 mg/L) specifically synthesized for industrial purposes with different sizes, shapes (round, rod) and surface coatings (PEG, PVP) was tested using the frog embryo teratogenesis assay-Xenopus (FETAX) to identify potential target tissues and the most sensitive developmental stages. The ZnONPs did not cause embryolethality, but induced a high incidence of malformations, in particular misfolded gut and abdominal edema. Smaller, round NPs were more effective than the bigger, rod ones, and PEGylation determined a reduction in embryotoxicity. Ingestion appeared to be the most relevant exposure route. Only the embryos exposed from the stomodeum opening showed anatomical and histological lesions to the intestine, mainly referable to a swelling of paracellular spaces among enterocytes. In conclusion, ZnONPs differing in shape and surface coating displayed similar toxicity in X. laevis embryos and shared the same target organ. Nevertheless, we cannot exclude that the physico-chemical characteristics may influence the severity of such effects. Further research efforts are mandatory to ensure the synthesis of safer nano-ZnO-containing products.