Francois Malherbe

Differences in colonisation of five marine bacteria on two types of glass surfaces

The retention patterns of five taxonomically different marine bacteria after attachment on two types of glass surfaces, as-received and chemically etched, have been investigated. Contact angle measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectrometry (XPS) were employed to investigate the impact of nanometer scale surface roughness on bacterial attachment. Chemical modification of glass surfaces resulted in a ∼1 nm decrease in the average surface roughness (R a) and the root-mean-squared roughness (Rq ) and in a ∼8 nm decrease in the surface height and the peak-to-peak (R max) and the 10-point average roughness (Rz ). The study revealed amplified bacterial attachment on the chemically etched, nano-smoother glass surfaces. This was a consistent response, notwithstanding the taxonomic affiliation of the selected bacteria. Enhanced bacterial attachment was accompanied by elevated levels of secreted extracellular polymeric substances (EPS). An expected correlation between cell surface wettability and the density of the bacterial attachment on both types of glass surfaces was also reported, while no correlation could be established between cell surface charge and the bacterial retention pattern.

Physicochemical characterization of solid lipid nanoparticles (SLNs) prepared by a novel microemulsion technique

HYPOTHESIS Solid lipid nanoparticles (SLNs) produced by conventional microemulsion techniques using thermal heat have specific limitations (e.g. high polydispersity, instability and low encapsulation). Replacing thermal heat with microwave heat may produce SLNs which overcome some of these limitations. EXPERIMENTS Stearic acid-based SLNs prepared with Tween® 20 as the emulsifier were chosen as the optimum formulation to encapsulate and potentially deliver the antibacterial drug tetracycline. All formulations were characterized for their particle size, zeta potential, encapsulation efficiency, loading capacity, thermal and X-ray diffraction analyses. Short-term stability and in vitro drug studies were also performed. FINDINGS Microwave heating helps to overcome several disadvantages associated with thermal heating (nonuniform, inefficient and slow) and results in improved particle characteristics. There is thus the potential for new opportunities in the development of colloidal carriers. The particle sizes of microwave-produced SLNs were in the desired nanometer range (200-250 nm) with both lower size and lower polydispersity than the conventional SLNs. We take this as an indication of improved stability; however zeta potential measurements were not different, indicating similar stability. True stability testing (visual observation with time) did show that the microwave-induced SLNs were found to be more stable, particularly when refrigerated. The microwave-produced SLNs also demonstrated improved encapsulation efficiency and loading capacity. Thermal and diffraction analysis confirmed a lowered crystallinity of stearic acid with successful incorporation of tetracycline into the SLNs. In vitro release studies indicated that, after an initial burst release, SLNs could provide prolonged release of tetracycline. The presence of tetracycline and non-toxicity of carriers towards microbes was confirmed by antimicrobial susceptibility tests.

Identification of Traditional Medicinal Plant Extracts with Novel Anti-Influenza Activity

The emergence of drug resistant variants of the influenza virus has led to a need to identify novel and effective antiviral agents. As an alternative to synthetic drugs, the consolidation of empirical knowledge with ethnopharmacological evidence of medicinal plants offers a novel platform for the development of antiviral drugs. The aim of this study was to identify plant extracts with proven activity against the influenza virus. Extracts of fifty medicinal plants, originating from the tropical rainforests of Borneo used as herbal medicines by traditional healers to treat flu-like symptoms, were tested against the H1N1 and H3N1 subtypes of the virus. In the initial phase, in vitro micro-inhibition assays along with cytotoxicity screening were performed on MDCK cells. Most plant extracts were found to be minimally cytotoxic, indicating that the compounds linked to an ethnomedical framework were relatively innocuous, and eleven crude extracts exhibited viral inhibition against both the strains. All extracts inhibited the enzymatic activity of viral neuraminidase and four extracts were also shown to act through the hemagglutination inhibition (HI) pathway. Moreover, the samples that acted through both HI and neuraminidase inhibition (NI) evidenced more than 90% reduction in virus adsorption and penetration, thereby indicating potent action in the early stages of viral replication. Concurrent studies involving Receptor Destroying Enzyme treatments of HI extracts indicated the presence of sialic acid-like component(s) that could be responsible for hemagglutination inhibition. The manifestation of both modes of viral inhibition in a single extract suggests that there may be a synergistic effect implicating more than one active component. Overall, our results provide substantive support for the use of Borneo traditional plants as promising sources of novel anti-influenza drug candidates. Furthermore, the pathways involving inhibition of hemagglutination could be a solution to the global occurrence of viral strains resistant to neuraminidase drugs.

Marinobacter salarius sp. nov. and Marinobacter similis sp. nov., isolated from sea water.

Two non-pigmented, motile, Gram-negative marine bacteria designated R9SW1T and A3d10T were isolated from sea water samples collected from Chazhma Bay, Gulf of Peter the Great, Sea of Japan, Pacific Ocean, Russia and St. Kilda Beach, Port Phillip Bay, the Tasman Sea, Pacific Ocean, respectively. Both organisms were found to grow between 4°C and 40°C, between pH 6 to 9, and are moderately halophilic, tolerating up to 20% (w/v) NaCl. Both strains were found to be able to degrade Tween 40 and 80, but only strain R9SW1T was found to be able to degrade starch. The major fatty acids were characteristic for the genus Marinobacter including C16:0, C16:1 ω7c, C18:1 ω9c and C18:1 ω7c. The G+C content of the DNA for strains R9SW1T and A3d10T were determined to be 57.1 mol% and 57.6 mol%, respectively. The two new strains share 97.6% of their 16S rRNA gene sequences, with 82.3% similarity in the average nucleotide identity (ANI), 19.8% similarity in the in silico genome-to-genome distance (GGD), 68.1% similarity in the average amino acid identity (AAI) of all conserved protein-coding genes, and 31 of the Karlins genomic signature dissimilarity. A phylogenetic analysis showed that R9SW1T clusters with M. algicola DG893T sharing 99.40%, and A3d10T clusters with M. sediminum R65T sharing 99.53% of 16S rRNA gene sequence similarities. The results of the genomic and polyphasic taxonomic study, including genomic, genetic, phenotypic, chemotaxonomic and phylogenetic analyses based on the 16S rRNA, gyrB and rpoD gene sequence similarities, the analysis of the protein profiles generated using MALDI-TOF mass spectrometry, and DNA-DNA relatedness data, indicated that strains R9SW1T and A3d10T represent two novel species of the genus Marinobacter. The names Marinobacter salarius sp. nov., with the type strain R9SW1T ( =  LMG 27497T  =  JCM 19399T  =  CIP 110588T  =  KMM 7502T) and Marinobacter similis sp. nov., with the type strain A3d10T ( =  JCM 19398T  =  CIP 110589T  =  KMM 7501T), are proposed.

Collagen type I together with fibronectin provide a better support for endothelialization

Endothelialization of vascular implants is limited by the inability of cells to retain adhesion when exposed to flow. Extracellular matrix proteins, including fibronectin and collagen, enhance cell adherence on materials. This study investigated the behaviour of Human Umbilical Vein Endothelial Cells (HUVEC) on extracellular matrix coated polystyrene. Collagen and fibronectin were coated as single and double layers to analyse differences in cell proliferation, morphology, and cell-protein interactions. Significantly higher endothelial cell proliferation and migration rates were observed on the collagen and collagen+fibronectin coating compared to the uncoated or fibronectin-coated sample. Immmunofluorescent microscopy showed evidence of extracellular matrix remodelling in the double, collagen+fibronectin coating. These results strongly suggest that a double coating of collagen+fibronectin provides a better support structure for endothelial cell growth and contributes to improve the ability of vascular implants to become and remain endothelialized.

Carbon nanotube and graphene oxide directed electrochemical synthesis of silver dendrites

We report a simple one-step electro-deposition method for the synthesis of silver dendritic structures with the aid of graphene oxide (GO) modified multi-walled carbon nanotubes (MWCNTs) which are dispersed in an AgNO3 solution. Scanning electron microscopy indicated that the formed silver material had a well-defined dendritic structure and XRD confirmed that the silver was in a cubic phase. UV-vis spectroscopy indicated the presence of GO in the silver dendrites which was electrochemically reduced during the silver electro-deposition process. It was found that the presence of MWCNT is crucial for the formation of the dendrite structure of the deposited Ag. The concentration of AgNO3 and the electrochemical deposition cycles also had significant effects on the shape of the formed nanostructures. A possible growth mechanism for the Ag dendrites was proposed based on the experimental results. In addition, the electro-catalytic properties of the as-prepared silver dendrites towards the reduction of hydrogen peroxide were investigated by cyclic voltammetry. The results showed that Ag dendrites prepared in the presence of MWCNT and GO had a higher electro-catalytic activity than silver materials prepared with only either MWCNT or GO.

Properties and in vitro evaluation of high modulus biodegradable polyurethanes for applications in cardiovascular stents

This study examined the suitability of a family of biodegradable polyurethanes (PUs) NovoSorb developed for the vascular stent application. These segmented PUs are formulated to be biodegradable using degradable polyester and PU blocks. A series of PUs comprising different hard segment weight percentage ranging from 60 to 100 were investigated. The mechanical properties of the PUs were evaluated before and after gamma sterilization to assess their suitability for vascular implants. The real-time (PBS/37°C/pH 7.4) hydrolytic degradation studies were carried out under sterile conditions and PU glass transition temperature, molecular weight, and mass loss at 3, 6, and 9 months were determined. The viability and growth of Human Umbilical Vein Endothelial Cells (HUVEC) on PU surfaces were determined to assess the effect of PU degradation. The effect of coating of extracellular matrix (ECM) components on cell viability was also investigated. The study showed that the PUs possess excellent mechanical properties exhibiting high tensile strength (41-56 MPa) and tensile modulus (897-1496 MPa). The PU films maintained mechanical strength during the early phase of the degradation but lost strength at latter stages. The unmodified polymer surface of each PU promotes endothelial cell growth and proliferation, with a HUVEC retention rate of >70%.

Highly selective synthesis of 2-butoxy ethanol over Mg/Al/V mixed oxides catalysts derived from hydrotalcites

The catalytic activity of a series of mixed oxides obtained by the thermal decomposition of hydrotalcite‐like precursors was assessed for the alkoxylation of n-butanol with ethylene oxide. The calcination products of a decavanadate intercalated magnesium–aluminium layered double hydroxide were shown to possess extremely high activity for the alkoxylation reaction achieving up to 100% conversion in batch reaction. In all cases, the catalysts exhibit a much higher selectivity towards the monoglycol adduct than that obtained with the industrial catalyst.

Defects regulating of graphene ink for electrochemical determination of ascorbic acid, dopamine and uric acid

A simple water immersing treatment has been established for regulating the electrocatalytic activity of commercial graphene ink. This process enables to remove additives in graphene ink and consequently expose the surface defects. A graphene ink coated glass has been fabricated as an example platform for simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Cyclic voltammetry studied indicated electrocatalytic reaction can be initiated after the additives leaching during the water immersing treatment. Under optimal conditions, the linear calibration curves were achieved in the range of 50-1000, 3-140, and 0.5-150μM, with detection limits of 17.8, 1.44 and 0.29μM for AA, DA, and UA, respectively. This work demonstrated that the removal of additives of the graphene ink after film coating could be applied as a simple and cost-effective electrochemical platform for sensing application.

Advanced Catalytic and Electrocatalytic Performances of Polydopamine-Functionalized Reduced Graphene Oxide-Palladium Nanocomposites

A polydopamine‐functionalized reduced graphene oxide (PDA‐RGO)/Pd nanocomposite was synthesized by a simple wet chemical approach at room temperature. Graphene oxide (GO) was first modified with PDA by the self‐polymerization of dopamine (DA) followed by the deposition of Pd nanoparticles. UV/Vis and FTIR spectroscopies confirmed the reduction of GO to RGO during the self‐polymerization of DA. SEM images revealed that Pd nanoclusters were formed on both sides of the PDA‐RGO sheets. The as‐prepared PDA‐RGO/Pd nanocomposites exhibited excellent catalytic activity in the chemical degradation of methylene blue with a reaction rate constant of 0.6028 min−1, which was 2.5‐fold faster than that of the PDA/Pd catalyst without RGO. Moreover, the PDA‐RGO/Pd nanocomposite also showed an outstanding electrocatalytic activity towards the electro‐oxidation of paracetamol. The current response had a linear relationship to the concentration of paracetamol in the range of 0.28–100 μm with a low detection limit of 0.087 μm (S/N=3). In addition, the sensor also exhibited good selectivity for the detection of paracetamol.