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Search Results: 1 - 10 of 5965 matches for " Oscar Komla Awitor "
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Photokilling of Escherichia coli Using Hybrid Titania Nanoparticles Suspended in an Aqueous Liquid  [PDF]
Christophe Massard, Muriel Bonnet, Philippe Veisseire, Yves Sibaud, Eric Caudron, Komla Oscar Awitor
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2013, DOI: 10.4236/jbnb.2013.42019

In this work, the photokilling of Escherichia coli using a “one-pot” synthesized suspension of anatase crystallized nanoparticles is evaluated. Preliminary to the biological tests concerning the antibacterial efficiency, the fabricated suspension, using a derived solgel process in soft chemistry condition, is characterized. Structural properties of the nanoparticles are investigated using Electronic Transmission Microscopy (TEM) equipped with Selected Area Electron Diffraction (SAED) probe and X-ray diffraction. The inorganic solid content was evaluated by Thermogravimetric Analysis (TGA). Photodegradation of Acid Orange 7 in aqueous solution was used a probe to assess the photocatalytic activity of the elaborated suspension under UV irradiation. The photokilling of Escherichia coli in presence of hybrid TiO2 nanoparticles suspended in aqueous liquid under UV irradiation is evaluated. Such TiO2 nanoparticles suspension shows a strong bactericidal activity with the total destruction of bacteria after only one hour.

Environmental Toxicity and Antimicrobial Efficiency of Titanium Dioxide Nanoparticles in Suspension  [PDF]
Muriel Bonnet, Christophe Massard, Philippe Veisseire, Olivier Camares, Komla Oscar Awitor
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2015, DOI: 10.4236/jbnb.2015.63020
Abstract: The aim of this work was to evaluate the photokilling efficiency of synthesized titanium dioxide nanoparticles in suspension. Two strains of Escherichia coli, Lactobacillus casei rhamnosus and Staphylococcus aureus were used as probes to test the photokilling activities of the nanoparticles. The toxicity effects of TiO2 nanoparticles on the environment were determined by a standard test using gram-negative bioluminescent bacteria Vibrio fischeri. The antimicrobial activity of these nanoparticles (NPs) was then investigated versus NPs concentration, UV irradiation time and micro- organism strains. We evaluated the LC50 values of the nanoparticles suspension by counting the Colony-Forming Units. Results highlighted the differences in bacteria sensitivity facing photokilling treatment induced by the irradiation of anatase TiO2 nanoparticles suspension. At the concentration of 1 g·L-1 TiO2, tested bacteria were killed after 30 minutes of photo-treatment. Using different TiO2 concentrations, the Staphylococcus aureus gram-positive/catalase-positive bacteria were more resistant than gram-negative/catalase-positive ones or gram-positive/catalase-negative bacteria. An effect of UV irradiation was evaluated by the quantification of hydrogen peroxide generated by the photolysis of water molecules in presence of the nanoparticles with or without the most resistant bacterium (S. aureus). After 30 minutes with UV irradiation in these two conditions, the concentration of hydrogen peroxide was 35 μM in presence of 1.2 g·L-1 TiO2 suspension. This result suggested that the resistance mechanism of S. aureus was not due to an extracelullar H2O2 enzymatic degradation.
Impact of Annealing Treatment on the Behaviour of Titanium Dioxide Nanotube Layers  [PDF]
Marie Siampiringue, Christophe Massard, Eric Caudron, Yves Sibaud, Mohammed Sarakha, Komla Oscar Awitor
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2016, DOI: 10.4236/jbnb.2016.73015
Abstract: In this work, we study the influence of the annealing treatment on the behaviour of titanium dioxide nanotube layers. The heat treatment protocol is actually the key parameter to induce stable oxide layers and needs to be better understood. Nanotube layers were prepared by electrochemical anodization of Ti foil in 0.4 wt% hydrofluoric acid solution during 20 minutes and then annealed in air atmosphere. In-situ X-ray diffraction analysis, coupled with thermogravimetry, gives us an inside on the oxidation behaviour of titanium dioxide nanotube layers compared to bulk reference samples. Structural studies were performed at 700°C for 12 h in order to follow the time consequences on the oxidation of the material, in sufficient stability conditions. In-situ XRD brought to light that the amorphous oxide layer induced by anodization is responsible for the simultaneous growths of anatase and rutile phase during the first 30 minutes of annealing while the bulk sample oxidation leads to the nucleation of a small amount of anatase TiO2. The initial amorphous oxide layer created by anodization is also responsible for the delay in crystallization compared to the bulk sample. Thermogravimetric analysis exhibits parabolic shape of the mass gain for both anodized and bulk sample; this kinetics is caused by the formation of a rutile external protective layer, as depicted by the associated in-situ XRD diffractograms. We recorded that titanium dioxide nanotube layers exhibit a lower mean mass gain than the bulk, because of the presence of an initial amorphous oxide layer on anodized samples. In-situ XRD results also provide accurate information concerning the sub-layers behavior during the annealing treatment for the bulk and nanostructured layer. Anatase crystallites are mainly localized at the interface oxide layer-metal and the rutile is at the external interface. Sample surface topography was characterized using scanning electron microscopy (SEM).
Boosted Photoactivity of Titania Nanotube Layers Doped with a Suspension of Gold Nanoparticles  [PDF]
Christophe Massard, Sébastien Pairis, Yves Sibaud, Christelle Blavignac, Oscar Komla Awitor
Advances in Nanoparticles (ANP) , 2017, DOI: 10.4236/anp.2017.63010
Abstract: In the present work, we report on the behavior of synthesized gold nano-particles suspension, incorporated in titanium dioxide nanotube layers (TiO2- NT) and fabricated by electrochemical anodization in 0.4 wt% hydrofluoric acid solution and we study its photocatalytic response. Gold nanoparticles were characterized using Transmission electron microscopy and X-ray diffraction. Scanning electron microscopy was used to study the morphology of TiO2 nanotube layers doped by gold nanoparticles. Boosted photocatalytic performances on the degradation of an azo dye were obtained by using TiO2 nanotube layers doped by gold nanoparticles (Au/TiO2-NT), compared to undoped TiO2 nanotube layer (TiO2-NT) catalysts. Under UV irradiation, this new nanomaterial, with noble metal-semi conductor heterojunction (Au/ TiO2-NT) exhibits a synergetic effect in accelerating the electron transfert, resulting in an enhanced photoactivity recorded in the kinetics of degradation of Acid Orange 7 (AO7). Chronoamperometry was used to highlight higher photocurrent produced by gold-titania interface submited to UV irradiation.
Feasibility of a Chronic Foreign Body Infection Model Studying the Influence of TiO2 Nanotube Layers on Bacterial Contamination  [PDF]
Charles Vorilhon, Christophe Massard, Vincent Raspal, Yves Sibaud, Christiane Forestier, Nicolas Charbonnel, Stéphane Descamps, Komla Oscar Awitor
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2016, DOI: 10.4236/jbnb.2016.71006

Bacterial infections on the surface of medical devices are a significant problem in therapeutic approach, especially when implants are used in the living. In cardiology, pacemaker generator pocket surfaces, made in titanium alloy can be colonized by pathogen microorganism. This contamination represents a major risk of sepsis, endocarditis and localized infections for patients. A way to limit this bacterial contamination is to modify the surface topography using nano-structuration process of the titanium alloy surface of the implanted devices. The aim of this study is to evaluate the influence of TiO2 nanotube layers on bacterial infection in the living, considering the feasibility of an animal model of chronic foreign body infection. TiO2 nanotube layers prepared by electrochemical anodization of Ti foil in 0.4 wt% hydrofluoric acid solution were implanted subcutaneously in Wistar rats. Three weeks after implantation, TiO2 implants were contaminated by a Staphylococcus epidermilis strain using two different concentrations at 106 and 108 colony forming unit (CFU) in order to induce a sufficient infection level and to avoid unwanted over infection consequences on rats health during the experiments. After 28 days in the living, 75% of nanotube layers initially submitted to the 108 CFU inoculum were contaminated while only 25% nanotube layers initially submitted to the 106 CFU inoculum remained infected. This significant result underlines the influence of TiO2 nanotube layers in decreasing the infection level. Our in vitro experiments showed that the synthesized TiO2 nanotubes indeed decreased the Staphylococcus epidermilis adhesion compared to unanodized Ti foil.

Cytotoxicity Study of Gold Nanoparticles on the Basal-Like Triple-Negative HCC-1937 Breast Cancer Cell Line  [PDF]
Christophe Massard, Clémence Dubois, Vincent Raspal, Pierre Daumar, Yves Sibaud, Emmanuelle Mounetou, Mahchid Bamdad, Oscar Komla Awitor
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2018, DOI: 10.4236/jbnb.2018.91002
Abstract: The Triple Negative “Basal-like” breast cancer (TNBL) tumours have a high proliferative capacity and develop a resistance phenotype associated with metastases. However, the management of TNBL carcinomas is still not standardized. Among the promising trails, gold nanoparticles could be a relevant tool for the development of a targeted treatment for this breast cancer subtype in monotherapy, associated and/or conjugated with other drugs. In this work, we report the cytotoxicity impact of gold nanoparticles wrapped in Poly-Ethylene Glycol (PEG) on the TNBL HCC-1937 breast cancer cell line. PEG-coated gold nanoparticles (PEG-Au NPs) were synthesized by a two-step method using a reduction process followed by a post-functionalization called PEGylation. PEG-Au NPs were characterized using transmission electron microscopy and X-ray diffraction. The gold content of the samples was determined using atomic absorption spectrometer. The cytotoxicity tests were performed using Sulforhodamine B survival test and resazurin viability test. PEG-Au NPs impact analysis on HCC1937 TNBL cell line showed a clear toxic action of type dose dependent and at long term. These PEGylated gold nanoparticles present a promising tool for the development of tumor-specific radiosensitizing vectors, with or without the association of other treatment strategies.
One-pot Synthesis of TiO2 Nanoparticles in Suspensions for Quantification of Titanium Debris Release in Biological Liquids  [PDF]
Christophe Massard, Daniel Bourdeaux, Vincent Raspal, Emmanuelle Feschet-Chassot, Yves Sibaud, Eric Caudron, Thierry Devers, Kolma Oscar Awitor
Advances in Nanoparticles (ANP) , 2012, DOI: 10.4236/anp.2012.13012
Abstract: In this work we have developed an analytical method to measure potential titanium debris released from TiO2 nanotube layers devices immersed in biological fluids. This quantitative study is highly required to ensure both the security and non toxicity of the nanostructured surfaces used as future implantable medical devices in the living. A one-pot synthesis process is developed to produce high quality standard solutions of titanium dioxide nanoparticles in aqueous medium. The elaborated dispersion is then used to fabricate standard solutions in both aqueous and human blood plasma media. The synthesized nanoparticles dispersion was characterized by granulometry. The nanoparticles structure and morphology were then observed using Transmission Electron Microscopy (TEM). Thermogravimetric Analysis (TGA) was used to evaluate the concentration of TiO2 in the suspension. A quantitative routine by the use of Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) is developed. The quantification threshold of titanium species is found to be in the 30 - 40 ppb range. None interference is detected between the particles and the human blood plasma. Using the established quantitative routine, the titanium species release from titania nanotube layers in human blood plasma is evaluated.
Overview of Concentrated Photovoltaic (CPV) Cells  [PDF]
Chukwubuikem Chukwuka, Komla Agbenyo Folly
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.211001

Previous studies have shown that renewable energy is one of the effective ways to fight global climate change and emissions not to mention the increasing price of fossil fuels. Among the various renewable energy sources which include wind, solar, biofuel, geothermal and tidal waves, solar power has attracted much attention especially here in Africa because of the abundance of solar radiation. A lot of studies have been done on various photovoltaic (PV) cells ranging from silicon to thin film and most recently multi-junction solar cells. In this paper, we focused on concentrated photovoltaic cells (CPV) which are promising ways of converting solar energy to electricity. It is expected that if the most cost effective ways of converting solar energy to electricity is used, both the cost of installation and the running cost of concentrated photovoltaic cells will equate the utility grid electricity cost in a few years to come.

Making Social Science Matter?: Case Studies from Community Development and Empowerment Education Research in Rural Ghana and Aboriginal Australia
Komla Tsey
Asian Social Science , 2009, DOI: 10.5539/ass.v6n1p3
Abstract: Despite potential opportunities offered by exceptional advances in science and technology, we are increasingly polarised from each other. Social inequalities, poverty and deprivation are only a few of the challenges facing most societies. By combining the theoretical perspective of Bent Flyvberg’s Making Social Science Matter (2001) and related Perestroika discourse with insights from community development and empowerment research in rural Ghana and Aboriginal Australia, this paper demonstrates a strengths-based approach to social science that builds social capital through enhancing the capacity of individuals and communities to routinely consider ethical questions; where they are going; what can be done to make things better. Focus is on Flyvbjerg’s challenge to social scientists to undertake research relevant to challenges and opportunities facing contemporary society. Highlighted is a need for researchers to reflect more explicitly about ways they seek to make their work relevant to people with whom they work. Strengths-based approaches, grounded in relevant ethical values, norms and local histories and traditions, offer one avenue for making social research relevant.
Assessment of Organochlorine Pesticide Residues in Vegetable Samples from Some Agricultural Areas in Togo  [PDF]
Lankondjoa Kolani, Gbénonchi Mawussi, Komla Sanda
American Journal of Analytical Chemistry (AJAC) , 2016, DOI: 10.4236/ajac.2016.74031
Abstract: The study was conducted to monitor the concentration of pesticide residues in three staple vegetables (tomato, cabbage, lettuce) collected from 12 prefectures belonging to 4 agro-ecological regions of Togo. A total of 150 samples of ripe tomato, cabbage and lettuce were collected from the study areas and analyzed for 20 OCPs (organochlorine pesticides) residues, which can be grouped into DDTs, Drins, Heptachlors, Chlordanes and HCHs. The data revealed that 100% of the analyzed vegetable samples were contaminated by one or more pesticide residues; 83.32% and 100% were below the maximum residue limits (MRLs) set par European Union and FAO/WHO respectively whereas 16.68% were above the EU (MRLs) adopted values. Overall, cabbage contained the highest number of samples with pesticide residues above the MRLs followed by tomato, whilst none of lettuce samples contained pesticide residues above the MRLs. It is therefore proposed to perform continuous monitoring studies of pesticide residues in vegetables cultivated in Togo.
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