The role of stearic acid for silver nanoparticle formation on graphene and its composite with poly(lactic acid)

Graphene-based polymer nanocomposites have received much attention in the field of new hybrid materials, and in the enhancement of properties and diversification of applications. In this work, reduced graphene (rGO) and silver nanoparticles (AgNPs) were cooperated with poly(lactic acid) (PLA) (a semi-crystalline and brittle polymer) to improve mechanical strength and conductivity of the composites. The effect of various concentrations of stearic acid (SA-a precursor) on the formation of silver nanoparticles on graphene and its composite with PLA was studied for the first time. The rGO and AgNPs were first prepared using SA to enhance the AgNPs formation and improve surface wetting of rGO/AgNPs in PLA. The XPS atomic concentration of AgNPs in rGO-Ag-SA1 composite (1:1 mass ratio of SA: graphene oxide) was 5.77%, while, 2.55% in the rGO-Ag composite without SA. This enhancement is due to substitution of AgNPs onto the epoxy and hydroxyl groups on the graphene sheet. In addition, tensile strength of PLA-rGO-AgNPs-SA was higher than neat PLA when AgNPs and SA were added into the composites, especially the composite of PLA-rGO-Ag-SA1 which showed the highest strength increase of 47%. The volume resistivity of PLA-rGO-Ag-SA1 film was also two times lower than PLA-rGO-Ag; thus, this graphene-based composite of PLA-rGO-Ag showed a significant advantage for applications where antistatic properties are required along with an improvement of PLA\u27s tensile strength

Green fabrication route of robust, biodegradable silk sericin and poly(vinyl alcohol) nanofibrous scaffolds

Silk sericin (SS) has been extensively used to fabricate scaffolds for tissue engineering. However, due to its inferior mechanical properties, it has been found to be a poor choice of material when being electrospun into nanofibrous scaffolds. Here, SS has been combined with poly(vinyl alcohol) (PVA) and electrospun to create scaffolds with enhanced physical properties. Crucially, these SS/PVA nanofibrous scaffolds were created using only distilled water as a solvent with no added crosslinker in an environmentally friendly process. Temperature has been shown to have a marked effect on the formation of the SS sol–gel transition and thus influence the final formation of fibers. Heating the spinning solutions to 70 °C delivered nanofibers with enhanced morphology, water stability and mechanical properties. This is due to the transition of SS from β-sheets into random coils that enables enhanced molecular interactions between SS and PVA. The most applicable SS/PVA weight ratios for the formation of nanofibers with the desired properties were found to be 7.5/1.5 and 10.0/1.5. The fibers had diameters ranging from 60 to 500 nm, where higher PVA and SS concentrations promoted larger diameters. The crystallinity within the fibers could be controlled by manipulation of the balance between PVA and SS loadings. In vitro degradation (in phosphate buffer solution, pH 7.4 at 37 °C) was 30–50% within 42 days and fibers were shown to be nontoxic to skin fibroblast cells. This work demonstrates a new green route for incorporating SS into nanofibrous fabrics, with potential use in biomedical applications

Hydroquinine Inhibits the Growth of Multidrug-Resistant <i>Pseudomonas aeruginosa</i> via the Suppression of the Arginine Deiminase Pathway Genes

Hydroquinine has antimicrobial potential with demonstrated activity against several bacteria, including multidrug-resistant (MDR) P. aeruginosa reference strains. Despite this, there is limited evidence confirming the antibacterial activity of hydroquinine against clinical isolates and the underlying mechanism of action. Here, we aimed to investigate the antibacterial effect of hydroquinine in clinical P. aeruginosa strains using phenotypic antimicrobial susceptibility testing and synergistic testing. In addition, we examined the potential inhibitory mechanisms against MDR P. aeruginosa isolates using informatic-driven molecular docking analysis in combination with RT-qPCR. We uncovered that hydroquinine inhibits and kills clinical P. aeruginosa at 2.50 mg/mL (MIC) and 5.00 mg/mL (MBC), respectively. Hydroquinine also showed partial synergistic effects with ceftazidime against clinical MDR P. aeruginosa strains. Using SwissDock, we identified potential interactions between arginine deiminase (ADI)-pathway-related proteins and hydroquinine. Furthermore, using RT-qPCR, we found that hydroquinine directly affects the mRNA expression of arc operon. We demonstrated that the ADI-related genes, including the arginine/ornithine antiporter (arcD) and the three enzymes (arginine deiminase (arcA), ornithine transcarbamylase (arcB), and carbamate kinase (arcC)), were significantly downregulated at a half MIC of hydroquinine. This study is the first report that the ADI-related proteins are potential molecular targets for the inhibitory effect of hydroquinine against clinically isolated MDR P. aeruginosa strains

High-Throughput Transcriptomic Profiling Reveals the Inhibitory Effect of Hydroquinine on Virulence Factors in <i>Pseudomonas aeruginosa</i>

Hydroquinine is an organic alkaloid compound that exhibits antimicrobial activity against several bacterial strains including strains of both drug-sensitive and multidrug-resistant P. aeruginosa. Despite this, the effects of hydroquinine on virulence factors in P. aeruginosa have not yet been characterized. We therefore aimed to uncover the mechanism of P. aeruginosa hydroquinine-sensitivity using high-throughput transcriptomic analysis. We further confirmed whether hydroquinine inhibits specific virulence factors using RT-qPCR and phenotypic analysis. At half the minimum inhibitory concentration (MIC) of hydroquinine (1.250 mg/mL), 254 genes were differentially expressed (97 downregulated and 157 upregulated). We found that flagellar-related genes were downregulated by between −2.93 and −2.18 Log2-fold change. These genes were consistent with the analysis of gene ontology and KEGG pathway. Further validation by RT-qPCR showed that hydroquinine significantly suppressed expression of the flagellar-related genes. By analyzing cellular phenotypes, P. aeruginosa treated with ½MIC of hydroquinine exhibited inhibition of motility (30–54% reduction) and pyocyanin production (~25–27% reduction) and impaired biofilm formation (~57–87% reduction). These findings suggest that hydroquinine possesses anti-virulence factors, through diminishing flagellar, pyocyanin and biofilm formation