Interaction of graphene-related materials with human intestinal cells: an in vitro approach

Graphene-related materials (GRM) inherit unique combinations of physicochemical properties which offer a high potential for technological as well as biomedical applications. It is not clear which physicochemical properties are the most relevant factors influencing the behavior of GRM in complex biological environments. In this study we have focused on the interaction of GRM, especially graphene oxide (GO),and Caco-2 cells in vitro. We mimiked stomach transition by acid-treatment of two representative GRM followed by analysis of their physicochemical properties. No significant changes in the material properties or cell viability of exposed Caco-2 cells in respect to untreated GRM could be detected. Furthermore, we explored the interaction of four different GO and Caco-2 cells to identify relevant physicochemical properties for the establishment of a material property–biological response relationship. Despite close interaction with the cell surface and the formation of reactive oxygen species (ROS), no acute toxicity was found for any of the applied GO (concentration range 0–80 μg ml−1) after 24 h and 48 h exposure. Graphene nanoplatelet aggregates led to low acute toxicity at high concentrations, indicating that aggregation, the number of layers or the C/O ratio have a more pronounced effect on the cell viability than the lateral size alone

The nature of the silicaphilic fluorescence of PDMPO

PDMPO (2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole), has unique silica specific fluorescence and is used in biology to understand biosilicification. This ‘silicaphilic’ fluorescence is not well understood nor is the response to local environmental variables like solvent and pH. We investigated PDMPO in a range of environments: using UV-vis and fluorescence spectroscopy supported by computational data, (SPARC, molecular dynamics simulations, density functional theory calculations), dynamic light scattering and zeta potential measurements to understand the PDMPO–silica interaction. From absorption data, PDMPO exhibited a pKa of 4.20 for PDMPOH22+ to PDMPOH+ . Fluorescence emission measurements revealed large shifts in excited state pKa* values with different behaviour when bound to silica (pKa* of 10.4). PDMPO bound to silica particles is located in the Stern layer with the dye exhibiting pH dependent depolarising motion. In aqueous solution, PDMPO showed strong chromaticity with correlation between the maximum emission wavelength for PDMPOH+* and dielectric constant (4.8–80). Additional chromatic effects were attributed to changes in solvent accessible surface area. Chromatic effects were also observed for silica bound dye which allow its use as a direct probe of bulk pH over a range far in excess of what is possible for the dye alone (3–5.2). The unique combination of chromaticity and excited state dynamics allows PDMPO to monitor pH from 3 to 13 while also reporting on surface environment opening a new frontier in the quantitative understanding of (bio)silicification

Interference of silica nanoparticles with the traditional Limulus amebocyte lysate gel clot assay

Endotoxin contaminations of engineered nanomaterials can be responsible for observed biological responses, especially for misleading results in in vitro test systems, as well as in vivo studies. Therefore, endotoxin testing of nanomaterials is necessary to benchmark their influence on cells. Here, we tested the traditional Limulus amebocyte lysate gel clot assay for the detection of endotoxins in nanoparticle suspensions with a focus on possible interference of the particles with the test system. We systematically investigated the effects of nanomaterials made of, or covered by, the same material. Different types of bare or PEGylated silica nanoparticles, as well as iron oxide-silica core shell nanoparticles, were tested. Detailed inhibition/enhancement controls revealed enhanced activity in the Limulus coagulation cascade for all particles with bare silica surface. In comparison, PEGylation led to a lower degree of enhancement. These results indicate that the protein-particle interactions are the basis for the observed inhibition and enhancement effects. The enhancement activity of a particle type was positively related to the calculated particle surface area. For most silica particles tested, a dilution of the sample within the maximum valid dilution was sufficient to overcome non-valid enhancement, enabling semi-quantification of the endotoxin contamination

Single exposure to aerosolized graphene oxide and graphene nanoplatelets did not initiate an acute biological response in a 3D human lung model

The increased mass production of graphene related materials (GRM), intended for a broad spectrum of applications, demands a thorough assessment of their potential hazard to humans and the environment. Particularly, the paramount concern has been expressed in regard to their interaction with the respiratory system in occupational exposure settings. It has been shown that GRM are easily respirable and can interact with lung cells resulting in the induction of oxidative stress or pulmonary inflammation. However, a comprehensive assessment of potential biological effects induced by GRM is currently hardly feasible to accomplish due to the lack of well-defined GRM materials and realistic exposure data. Herein, a 3D human lung model was combined with a commercial aerosolization system to study potential side effects of GRM. Two representative types of GRM were aerosolized onto the lung epithelial tissue surface. After 24 h post exposure, selected biological endpoints were evaluated, such as cell viability, morphology, barrier integrity, induction of (pro-)inflammation and oxidative stress reactions and compared with the reference material carbon black. Single exposure to all tested GRM at the two different exposure concentrations (∼300 and 1000 ng/cm2) did not initiate an observable adverse effect to the 3D lung model under acute exposure scenarios

Biological Photonic Crystals: Diatoms

Deutschen Forschungsgemeinschaft (DFG), Universität Kassel „Stipendiums zur Förderung von Frauen in Technik und Naturwissenschaften“ und Universität Kassel „Promotionsabschlussstipendiums für Promovierende mit Kind

The intracellular localization of inorganic engineered versus biogenic materials: a comparison

The uptake of engineered nanoobjects into cells is assumed to significantly account for their potential toxicity. By internalisation, nanoparticles are at least temporarily trapped in the confined volume of a single cell and come into close contact with cellular components, like organelles, structural proteins, enzymes or signalling molecules. As cells are highly structured entities, exhibiting various types of chemically and biologically distinct compartments, first of all the uptake mechanism determines which types of molecules are encountered. In this review, an introduction into the compartmentalisation of cells as well as some uptake processes is given. The localisation of engineered materials within cells of human and animal origin is exemplified. On the other hand, many living organisms are known for their ability to intracellularly precipitate inorganic structures. Some of these biogenic materials are chemically and structurally similar to artificially generated nanostructures. Therefore, the localisation of some biogenic structures within cells is also illustrated. Finally, the relevance of the specific cellular localisation for toxicity is discussed

Diatoms as living photonic crystals

We present an analysis of the optical structure of a representative diatom, Coscinodiscus granii. The silica cell wall can be regarded as a photonic crystal slab waveguide with moderate refractive-index contrast. In a cell, at least two different patterns are found: a hexagonal array of pores with a large lattice constant in the valve, and a square array of holes with a small lattice constant in the girdle. It is demonstrated that light can be coupled into the waveguide and that there are some photonic resonances in the visible spectral range, which have been determined by band-structure calculations