Nanosilver particles – Mechanisms of action and investigation of their possible interaction with tissues, cells and molecules. Definition of their relevant potential for intolerance
The objective of the project Nanosilver-Particles was to develop methods for the production of silver nanoparticles (AgNP) that can be safely introduced into a product whilst maintaining the intended. From different products consisting both of permanently embedded silver nanoparticles and of releasing, resorbable systems, detailed knowledge of the respective nanoparticles and nanomaterials was to be gained to exclude potential risks of application.
Different nanosilver-containing materials were developed to serve as model systems for three product types with silver nanoparticles:
- Organic base: Rapid short-term release of silver from e.g. collagen films
- Metallic base: Intermediate implants for osteosynthesis e.g. titanium screws or titanium plates
- Synthetic base: Permanent implants e.g. bone cement
Materials with different contents of silver nanoparticles were investigated to find the effective dose that enables a sufficient release and effectiveness of silver while having no toxic effect on the analysed cells. For that purpose, release profiles were analysed and the toxic effects on different cell types of the organism were determined. In addition to silver nanoparticles, conventional completely soluble silver salts were tested for comparison. Besides, the products’ antimicrobial efficiency was determined after simulated use to determine the possible duration of effect. Compatibility with the organism as well as a possible accumulation of the respective silver nanoparticles in organs were studied in limited animal experiments. No such accumulation was observed in the implants used.
The obtained results enable a better and more realistic assessment of the risk potential of silver nanoparticles and nanosilver-containing materials and allow safe assessment of the hazards when using these in medical products. According to the results, antimicrobially active nanosilver-containing medical products present a low risk to consumers while reducing the risk of implant-associated infections.
In the developed products, the silver nanoparticles show:
- a good bactericidal effect
- a good efficacy already at low dosages
- a good incorporation in the tested materials without reducing the materials’ performance
- no undesirable release during incorporation (this does not apply to resorbable products)
NanoPHARM – New photocatalytically active composite materials for elimination of pharmaceutical residues
The objective of the NanoPharm project was to develop and test novel technological approaches to the degradation of drug contaminants in different waters by use of photocatalysts (e.g. zinc or TiO2 nanoparticles) modified by means of different methods.
Biocomposite materials manufactured by use of S-layers as well as a granulate material consisting of zinc nanoparticles doped with silver ions proved to be particularly efficient. Besides, sufficiently stable aptamers for detection of selected agents and enrichment of these agents were selected and characterised.
Both the stability and activity of the novel photocatalysts were found to be significantly higher than the stability and activity of known materials and were tested in comprehensive degradation experiments. For the purpose of testing, individual agents and agent mixtures were demonstrably transformed in laboratory and test facilities. The respective tests were accompanied by an extensive chemical-analytical and toxicological evaluation of the transformation products.
For practical implementation of the findings, a water treatment concept combining the process of photocatalysis with that of photooxidation and enabling simultaneous processes in the same reaction space was developed. In that way, energy and oxidising-agent consumption can be reduced by approximately 20-30%.
NanoKON – Systematic evaluation of health effects of nanoscale contrast agents
The NanoKon project was dedicated to assessing the health effects of orally administered nanoscale contrast agents. For that specific purpose, nanoparticles were produced and tested together with commercially available reference particles in numerous in vitro, in vivo, and in silico assays.
Within work package 1, the respective nanomaterials were thoroughly characterised and their specific properties e.g., ion release of toxically relevant species (Ba, Gd) in artificial gastric juice analysed. The changing conditions (pH, high ionic strength) were tolerated only insufficiently by most of the (commercially available and self-synthesised) particle systems causing agglomeration for the majority of the tested nanoparticles. In the course of the project different modifications of the nanoparticles’ surface were investigated with the objective of obtaining as stable as possible suspensions that are functional with regards to reproducibility.
Work packages 2 and 3 were dedicated to in vitro analyses of the respective nanoparticles in relevant cell lines and barrier models. The objective was to investigate the contrast agents’ fate and uptake in systems coming into contact with them when administered orally. In addition, the adsorption of surrounding proteins on the surface of the contrast agent during formation of a protein corona was investigated. Concordantly, an uptake of the respective contrast agents (FexOy and FexOy@SiO2) and SiO2-NP (reference surface) was observed in intestinal epithelial cells, endothelial cells and macrophages. In the case of some examples, particle uptake was detected already after 15 to 30 minutes. The tested iron oxide nanoparticles were absorbed by endothelial cells and revealed no cytotoxicity in the relevant concentration range. However, under these conditions, cell-type specific biological effects such as a decrease in the impedance pointing towards a change in the barrier properties of the cells could be observed.
In addition to the above, a complex multicellular in vitro model of the intestinal barrier was established to analyse the effects of nanoparticles (see also work package 3). For this coculture model, the intestinal epithelial cell line Caco-2 was used together with the microvascular endothelial cells ISO-HAS-1. In that system, the used nanoparticles proved to be neither toxic nor inflammatory.
Besides, the studies proved that the formation of the nanoparticle protein corona is a decisive factor for (nano)-medical and (nano)-biotechnological applications. The time-resolved quantitative analysis of the protein corona shows that the protein envelope forms extremely rapidly, is highly complex, and affects the toxicity or intracellular uptake of the nanoparticles.
After uptake the particles used in the different cell types were localized in lysosomes, which indicates uptake via endocytosis or phagocytosis. After uptake, the nanoparticles were found to be located outside the cytosol. They cannot reach the latter before having penetrated the vesicular membrane. There was found to be no uptake of nanoparticles into the nucleus of intestinal epithelial cells.
Within work package 4, the biological effects of nanoscale contrast agents were analysed in vivo in the mouse model. There, none of the tested particle suspensions caused any significant organ toxicity. Besides, all tested serum parameters proved to be inconspicuous. The distribution of the particles after oral administration was analysed by means of magnetic resonance tomography (MRT) and computer tomography (CT). Additionally, element and electron-microscopic analyses were carried out on various organs. Whereas approximately 95 percent of the administered quantity of the respective nanoparticles suspensions was directly excreted, the major part of the remaining 5 percent was removed from the stomach, small intestine, and rectum by rinsing with a buffer solution. For the respective organism, this means that less than 0.5 percent of the applied nanoparticle dose remained in the body.
Work package 5 was dedicated to establishing and developing different image analysis elements to be applied to the results of the microscopy data. By applying tailor-made image analysis methods, the three-dimensional structures of the cell membrane and MT network were reconstructed. The simulation model developed within work package 5 considers different uptake mechanisms at the cell membrane and the dynamics of the nanoparticles in different cell compartments. The analysis of the MT structure suggests an influence of the nanoparticles on the persistence length of the MT network.
The analyses yielded the following basic results:
- Nanoscale contrast agents are taken up by the majority of the tested cell lines (intestinal epithelial cells, endothelial cells, and macrophages)
- As a rule, no organo-toxic, cytotoxic or inflammatory effects were observed for the tested systems neither in vitro nor in vivo. Exceptions to this rule are the activation and amplification of inflammatory signalling pathways in macrophages by silica reference particles as well as the slightly inflammatory potential of Gd-doped BaSO4 nanoparticles in Caco-2 monocultures
- As a function of the particle surface, the presence of protein-containing biological media creates a protein corona influencing the physicochemical and biological behaviour of the nanoparticles
- In vitro and in vivo, Gd-containing BaSO4 suspensions revealed good X-ray contrasting potential which was weaker for the MRT in the in vivo situation
- The correlation between the structure of the close-to-membrane actin network and the particle dynamics was determined.
- It was shown that the absorption of nanoparticles influences the persistence length of the MT filaments.