New insight into the biocompatibility/toxicity of graphene oxides and their reduced forms on Chlamydomonas reinhardtii.

Graphene oxides (GOs) and their reduced forms are often discussed both positively and negatively due to the lack of information about their chemistry and structure. This study utilized GOs with two sheet sizes that were further reduced by two reducing agents (sodium borohydride and hydrazine) to obtain two different degrees of reduction. The synthesized nanomaterials were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy (RA) to understand their chemistry and structure. The second focus of our investigation included in vitro testing of the biocompatibility/toxicity of these materials on a model organism, the freshwater microalga Chlamydomonas reinhardtii. The effects were studied on the basis of biological endpoints complemented by biomass investigation (FTIR spectroscopy, EA, and atomic absorption spectrometry (AAS)). The results showed that the biocompatibility/toxicity of GOs is dependent on their chemistry and structure and that it is impossible to generalize the toxicity of graphene-based nanomaterials.

Modifications of Parylene by Microstructures and Selenium Nanoparticles: Evaluation of Bacterial and Mesenchymal Stem Cell Viability.

Parylene-based implants or coatings introduce surfaces suffering from bacteria colonization. Here, we synthesized polyvinylpyrrolidone-stabilized selenium nanoparticles (SeNPs) as the antibacterial agent, and various approaches are studied for their reproducible adsorption, and thus the modification of parylene-C-coated glass substrate. The nanoparticle deposition process is optimized in the nanoparticle concentration to obtain evenly distributed NPs on the flat parylene-C surface. Moreover, the array of parylene-C micropillars is fabricated by the plasma etching of parylene-C on a silicon wafer, and the surface is modified with SeNPs. All designed surfaces are tested against two bacterial pathogens, Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). The results show no antibacterial effect toward S. aureus, while some bacteriostatic effect is observed for E. coli on the flat and microstructured parylene. However, SeNPs did not enhance the antibacterial effect against both bacteria. Additionally, all designed surfaces show cytotoxic effects toward mesenchymal stem cells at high SeNP deposition. These results provide valuable information about the potential antibacterial treatment of widely used parylene-C in biomedicine.