Rapid growth in nanotechnology is increasing the likelihood of engineered nanomaterials coming into contact with humans and the environment. Nanoparticles interacting with proteins, membranes, cells, DNA and organelles establish a series of nanoparticle/biological interfaces that depend on colloidal forces as well as dynamic biophysicochemical interactions. These interactions lead to the formation of protein coronas, particle wrapping, intracellular uptake and biocatalytic processes that could have biocompatible or bioadverse outcomes. For their part, the biomolecules may induce phase transformations, free energy releases, restructuring and dissolution at the nanomaterial surface. Probing these various interfaces allows the development of predictive relationships between structure and activity that are determined by nanomaterial properties such as size, shape, surface chemistry, roughness and surface coatings. This knowledge is important from the perspective of safe use of nanomaterials.

Understanding biophysicochemical interactions at the nano–bio interface

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Functional Nanomaterials for Phototherapies of Cancer

Owing to their unique physical and chemical properties, graphene and its derivatives such as graphene oxide (GO), reduced graphene oxide (RGO) and GO-nanocomposites have attracted tremendous interest in many different fields including biomedicine in recent years. With every atom exposed on its surface, single-layered graphene shows ultra-high surface area available for efficient molecular loading and bioconjugation, and has been widely explored as novel nano-carriers for drug and gene delivery. Utilizing the intrinsic near-infrared (NIR) optical absorbance, in vivo graphene-based photothermal therapy has been realized, achieving excellent anti-tumor therapeutic efficacy in animal experiments. A variety of inorganic nanoparticles can be grown on the surface of nano-graphene, obtaining functional graphene-based nanocomposites with interesting optical and magnetic properties useful for multi-modal imaging and imaging-guided cancer therapy. Moreover, significant efforts have also been devoted to study the behaviors and toxicology of functionalized nano-graphene in animals. It has been uncovered that both surface chemistry and sizes play key roles in controlling the biodistribution, excretion, and toxicity of nano-graphene. Biocompatibly coated nano-graphene with ultra-small sizes can be cleared out from body after systemic administration, without rendering noticeable toxicity to the treated mice. In this review article, we will summarize the latest progress in this rapidly growing field, and discuss future prospects and challenges of using graphene-based materials for theranostic applications.

Nano-graphene in biomedicine: theranostic applications

Carbon nanotubes: a review of their properties in relation to pulmonary toxicology and workplace safety.

Rats exposed to high airborne mass concentrations of low solubility low toxicity particles (LSLTP) have been reported to develop lung disease such as fibrosis and lung cancer. These particles are regulated on a mass basis in occupational settings, but mass might not be the appropriate metric as animal studies have shown that nanoparticles (ultrafine particles) produce a stronger adverse effect than fine particles when delivered on an equal mass basis. 
The present study investigated whether the surface area of LSLTP is a better descriptor than mass of their ability to stimulate pro-inflammatory responses in vitro. In a human alveolar epithelial Type II-like cell line, A549, we measured interleukin-8 (IL-8) mRNA, IL-8 protein release and glutathione (GSH) depletion as markers of pro-inflammatory effects and oxidative stress after treatment with a range of LSLTP (fine and nanoparticles) and DQ12 quartz, a particle with a highly reactive surface.
In all the assays, nanoparticle preparations of titanium dioxide [TiO2-np] and of Carbon Black [CB-np] produced much stronger pro-inflammatory responses than the same mass dose of fine TiO2 and CB. The results of the GSH assay confirmed that oxidative stress was involved in the response to all the particles, and two ultrafine metal dusts (cobalt and nickel) produced GSH depletion similar to TiO2-np, for similar surface-area dose. As expected, DQ12 quartz was more strongly inflammatory than the low toxicity dusts, on both a mass and surface area basis.
Dose response relationships observed in the in vitro assays appeared to be directly comparable to dose response relationships in vivo when the doses were similarly standardised. Both sets of data suggested a threshold in dose measured as surface area of particles relative to the surface area of the exposed cells, at around 1 to 10 cm 2 /cm 2 . 
These findings are consistent with the hypothesis that surface area is a more appropriate dose metric than mass for the pro-inflammatory effects of LSLTP in vitro and in vivo and consequently that the high surface area of nanoparticles is a key factor in their inflammogenicity.

/pdf/the-pro-inflammatory-effects-of-low-toxicity-low-solubility-498vfk9d49.pdf

The Pro-Inflammatory Effects Of Low toxicity low solubility Particles, Nanoparticles and Fine Particles, on Epithelial Cells In Vitro: the Role of Surface Area.

Graphene is a new nanomaterial with unusual and useful physical and chemical properties. However, in the form of nanoplatelets this new, emerging material could pose unusual risks to the respiratory system after inhalation exposure. The graphene-based nanoplatelets used in this study are commercially available and consist of several sheets of graphene (few-layer graphene). We first derived the respirability of graphene nanoplatelets (GP) from the basic principles of the aerodynamic behavior of plate-shaped particles which allowed us to calculate their aerodynamic diameter. This showed that the nanoplatelets, which were up to 25 μm in diameter, were respirable and so would deposit beyond the ciliated airways following inhalation. We therefore utilized models of pharyngeal aspiration and direct intrapleural installation of GP, as well as an in vitro model, to assess their inflammatory potential. These large but respirable GP were inflammogenic in both the lung and the pleural space. MIP-1α, MCP-1, MIP-2, IL-8, and IL-1β expression in the BAL, the pleural lavage, and cell culture supernatant from THP-1 macrophages were increased with GP exposure compared to controls but not with nanoparticulate carbon black (CB). In vitro, macrophages exposed to GP showed expression of IL-1β. This study highlights the importance of nanoplatelet form as a driver for in vivo and in vitro inflammogenicity by virtue of their respirable aerodynamic diameter, despite a considerable 2-dimensional size which leads to frustrated phagocytosis when they deposit in the distal lungs and macrophages attempt to phagocytose them. Our data suggest that nanoplatelets pose a novel nanohazard and structure-toxicity relationship in nanoparticle toxicology.

Graphene-based nanoplatelets: a new risk to the respiratory system as a consequence of their unusual aerodynamic properties

Two types of experiments were carried out to examine the effects of deposition and clearance on the accumulation in the lungs of rats of inhaled fibres of UICC amosite. In the first experiment the mass lung burdens of the dust in question were measured as a function of the time at which animals were killed after the cessation of the six week exposure period, and in the second the masses were measured for rats removed from exposure and killed at intervals during the exposure period itself. The experimental conditions were chosen to complement those of earlier work. Taken together with the results of that earlier work, the new results provide the basis for a simple mathematical model of the kinetics of deposition and clearance which appears to account for the major observed trends. Most significantly, there is strong evidence for an overload of clearance at high lung burdens (exceeding about 1500 micrograms/rat), in which a breakdown occurs of the intermediate rate clearance mechanisms (time constants of the order of 12 days). This hypothesis is supported for inhaled asbestos dust, quartz dust, and diesel fume by results obtained elsewhere. Biological explanations for the clearance overload hypothesis are at present speculative, involving discussion of the role of the macrophage in pulmonary clearance. It is believed that the clearance overload hypothesis could have possible consequences for people occupationally exposed to airborne dusts.

https://oem.bmj.com/content/oemed/40/3/264.full.pdf

An overload hypothesis for pulmonary clearance of UICC amosite fibres inhaled by rats.

The study objectives were to assess the ability of intratracheal injection methods to discriminate between nine fibre types in respect of pulmonary biopersistence, and to provide approximate estimates of relative biopersistence and durability for a study of general relationships with biological and toxicological responses. The test fibres included six samples of size-selected fibre types specially prepared for research purposes, two commercially available fibres, and amosite. A 1 mg dose of each fibre type was administered to rats by intratracheal injection. The relative biopersistence of fibres in diAerent size categories was assessed from the changes in mean lung burden, as determined by electron microscopy, at 3 days and 1, 6 and 12 months after injection. The ability of the test materials to resist dissolution was measured in a parallel series of simple in vitro acellular experiments at two pHs and in a continuous flow dissolution test. The observed diAerences in the persistence of fibres of diAering length recovered from rat lungs were consistent with the current hypothesis that short fibres are cleared by cellular processes and long fibres by dissolution and disintegration. DiAerences in persistence of long (>20 mm) fibres were correlated with measured rates of dissolution in vitro. DiAerences in persistence among those fibre types also studied by others workers were consistent with their findings after inhalation and intratracheal injection. Overall, the diAerences in the biopersistences of the test fibres following intratracheal injection were suAcient to enable an examination of the relationship of biopersistence with other biological and toxicological responses. Biopersistence was influenced by both fibre dimensions and solubility. # 1999 Published by Elsevier Science Ltd on behalf of BOHS. All rights reserved.

Biopersistence and durability of nine mineral fibre types in rat lungs over 12 months.

New inhalation studies have been carried out with rats exposed to UICC (Union International Contre le Cancer) amosite asbestos, with the main aim of further elucidating the factors the influence the accumulation of dust in the lung during prolonged chronic exposure. The results show that, for exposure times beyond a few weeks, the lung burden rises linearly and does not level off as predicted by simple models based on ideas taken from the 1966 report of the Task Group on Lung Dynamics. Furthermore, the lung burden is found to scale directly in proportion to the exposure concentration in a way that seems to contradict the overload hypothesis stated earlier. Nevertheless, the general pattern exhibited by our results for asbestos is markedly similar to that found elsewhere for rats inhaling diesel fume, leading to the suggestion that it is general (and not specific to fibrous dust); and the hypothesis that, whereas overload of clearance can take place at high lung burdens after exposure has ceased, it is cancelled by the sustained stimulus to clearance mechanisms provided by the continuous challenge of chronic exposure. The linearity of the increase in lung burden is explained in terms of a kinetic model involving sequestration of some inhaled material to parts of the lung where it is difficult to clear. The particular sequestration model favoured is one where, the longer a particle remains in the lung without being cleared, the more likely it will be sequestrated (and therefore less likely cleared). It is believed that such ideas may eventually be useful in forming exposure-dose relations for epidemiology.

https://oem.bmj.com/content/oemed/42/10/707.full.pdf

A D Jones

Papers

The Pro-Inflammatory Effects Of Low toxicity low solubility Particles, Nanoparticles and Fine Particles, on Epithelial Cells In Vitro: the Role of Surface Area.

Graphene-based nanoplatelets: a new risk to the respiratory system as a consequence of their unusual aerodynamic properties

An overload hypothesis for pulmonary clearance of UICC amosite fibres inhaled by rats.

Biopersistence and durability of nine mineral fibre types in rat lungs over 12 months.

Kinetics of deposition and clearance of inhaled mineral dusts during chronic exposure.