Paul A. Charpentier

The Yin and Yang actions of North American ginseng root in modulating the immune function of macrophages

BackgroundImmuno-modulatory effects of ginseng, including both immuno-stimulatory and immuno-suppressive effects, have been widely reported. This study aims to determine whether the paradoxical immuno-modulatory effect is related to unique phytochemical profiles of different North American (NA) ginseng, namely aqueous (AQ) and alcoholic (ALC) extracts.MethodsAQ and ALC extracts were prepared and their immuno-bioactivity were studied in vitro in murine macrophages (Raw 264.7) through measuring the direct stimulatory production of pro-inflammatory mediator and cytokines as well as the suppression of lipopolysaccharide (LPS)-stimulatory response by the two extracts. Gel permeation chromatography was used to fractionate and isolate phytochemicals for characterization of ginseng extracts.ResultsAQ extract up-regulated the production of nitric oxide (NO), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) while ALC extract did not. ALC extract but not AQ extract suppressed LPS-induced macrophage NO and TNF-α production. These immuno-stimulatory and suppressive effects were exhibited at similar extract concentrations. Moreover, the macrophage-stimulating activity of the AQ extract was inhibited in the presence of ALC extract. Fractionation of AQ extract revealed the presence of two major peaks at 230 nm with average molecular weights of 73,000 and 37,000 Da. The first fraction had similar elution volume as the crude polysaccharide (PS) fraction isolated from the AQ extract, and it was the only bioactive species. Parallel fractionation study of ALC extract yielded similar elution profiles; however, both sub-fractions were devoid of PS. Fraction I of the ALC extract suppressed LPS-induced NO production dose-dependently.ConclusionALC extract of NA ginseng, which was devoid of PS, was immuno-inhibitory whereas the AQ extract, which contained PS, was immuno-stimulatory. These extract-related anti-inflammatory and pro-inflammatory effects may be considered as the Yin and Yang actions of ginseng.

Reinforcement of resin based cement with titania nanotubes

OBJECTIVE One of the limitations of resin cements and flowable dental composites is their poor mechanical properties such as low flexural strength and fracture resistance under body conditions. The present study was performed to enhance the mechanical properties of commercial acrylic cement (CMW1) by introducing novel nanostructured titania tubes (n-TiO(2) tubes) into the cement matrix, with the tubes acting as a reinforcing phase. The long term objective is to add these fillers as reinforcement to dental resin cements and flowable composites in combination with existing fillers. METHODS The surface of the n-TiO(2) tubes was modified using a bi-functional monomer, methacrylic acid. The n-TiO(2) tube content of the cement was varied from 0 to 2 wt.%. The following cement properties were investigated: maximum polymerization temperature (T(max)), dough time (t(dough)), setting time (t(set)), complex viscosity-versus-time, radiopacity, fracture toughness (K(IC)), flexural strength (FS), flexural modulus (FM) and in vitro biocompatibility. RESULTS Based on the determined mechanical properties, the optimized composition was found at 1 wt.% n-TiO(2) tubes, which provided a significant increase in K(IC) (73%), FS (42%) and FM (56%). However the rheology, radiopacity and biocompatibility were not different from the control (CMW1). SIGNIFICANCE Enhanced interaction and strong adhesion between the functionalized n-TiO(2) tubes and polymer matrix allows external mechanical stress to be more effectively transferred through the filler-matrix interface. This novel filler in conjunction with the existing ones can be used to reinforce orthopedic and dental cements as well as flowable dental composites without altering the rheology, radiopacity and biocompatibility.

One-pot procedure to synthesize high surface area alumina nanofibers using supercritical carbon dioxide.

For the first time, high surface area nanofibers were synthesized using aluminum isopropoxide monomer with acetic acid as the polycondensation agent in the green solvent, supercritical carbon dioxide (scCO(2)). It was found that the synthesis temperature, pressure, concentration, and acid/alkoxide ratio had a large effect on fiber formation. By optimizing the experimental conditions at 80 degrees C and 6000 psi of scCO(2) using aluminum isopropoxide at a concentration of 0.3 mmol/mL and acid/alkoxide ratio of 10, alumina nanofibers were formed ranging from 11 to 22 nm in diameter and 500 to 1000 nm in length, and with surface areas up to 580 m(2)/g. Lower temperatures gave irregular shaped nanoparticles, while a lower acid/alkoxide ratio (5:1) resulted in the formation of low surface area alumina bars. Increasing pressure led to better separation of the nanofibers and higher surface areas. In addition to the synthesis conditions, the influence of calcination temperature on the structural, textural, and morphological properties of the materials was examined using various physicochemical techniques including electron microscopy, TGA/DTA, powder XRD, FTIR, XPS, and nitrogen adsorption/desorption analysis. The long fibers with high aspect ratios were found to be thermally stable even after calcining at up to 1050 degrees C. The mechanism of fiber formation in scCO(2) is proposed based on a [Al(OH)(CH(3)CO(2))(2)](n) polycondensate backbone.

Long chain branching in ethylene polymerization using constrained geometry metallocene catalyst

We report an experimental investigation on long chain branching (LCB) in ethylene polymerization with the Dow Chemicals constrained geometry catalyst system, CGC-Ti/TPFPB/MMAO, using a continuous stirred-tank reactor (CSTR) at 140°C, 3.45 × 10 3 kPa, and a mean residence time (τ) of 4 min. The effects of the catalyst (CGC-Ti) and co-catalyst (TPFPB and MMAO) concentrations on the catalyst activity, polymer molecular weight, and shear thinning were systematically examined. The boron cocatalyst had a great influence on the CGC activity. Increasing the ratio TPFPB/CGC-Ti from 0.66 to 5 gave ethylene propagation rates from 1.65 × 10 3 to 1.36 × 10 4 L mol -1 . s -1 . The addition of MMAO appeared to be essential, most likely acting as an impurity scavenger. The LCB polyethylenes showed enhanced shear thinning properties. The melt flow index ratios I 10 /I 2 were in the range of 6.96 to 23.4, with the I 2 of 0.172 to 0.681 g/10 min. The weight-average molecular weight M w was correlated to I 2 using a power equation within narrow I 10 /I 2 ranges. The exponential factors were in the range of 4.24 to 6.31. The experimental and calculated M w s were in a good agreement.

Physical and Mechanical Properties of PMMA Bone Cement Reinforced with Nano-sized Titania Fibers:

X-ray contrast medium (BaSO4 or ZrO2) used in commercially available PMMA bone cements imparts a detrimental effect on mechanical properties, particularly on flexural strength and fracture toughness. These lower properties facilitate the chance of implant loosening resulting from cement mantle failure. The present study was performed to examine the mechanical properties of a commercially available cement (CMW®1) by introducing novel nanostructured titania fibers (n-TiO2 fibers) into the cement matrix, with the fibers acting as a reinforcing phase. The hydrophilic nature of the n-TiO2 fibers was modified by using a bifunctional monomer, methacrylic acid. The n-TiO2 fiber content of the cement was varied from 0 to 2 wt%. Along with the mechanical properties (fracture toughness (K IC), flexural strength (FS), and flexural modulus (FM)) of the reinforced cements the following properties were investigated: complex viscosity-versus-time, maximum polymerization temperature (T max), dough time (t dough), setting time (t set), radiopacity, and in vitro biocompatibility. On the basis of the determined mechanical properties, the optimized composition was found at 1 wt% n-TiO2 fibers, which provided a significant increase in K IC (63%), FS (20%), and FM (22%), while retaining the handling properties and in vitro biocompatibility compared to that exhibited by the control cement (CMW®1). Moreover, compared to the control cement, there was no significant change in the radiopacity of any of the reinforced cements at p = 0.05. This study demonstrated a novel pathway to augment the mechanical properties of PMMA-based cement by providing an enhanced interfacial interaction and strong adhesion between the functionalized n-TiO 2 fibers and PMMA matrix, which enhanced the effective load transfer within the cement.

Growing TiO2 nanowires on the surface of graphene sheets in supercritical CO2: characterization and photoefficiency

Tremendous interest exists towards synthesizing nanoassemblies for dye-sensitized solar cells (DSSCs) using earth-abundant and -friendly materials with green synthetic approaches. In this work, high surface area TiO(2) nanowire arrays were grown on the surface of functionalized graphene sheets (FGSs) containing -COOH functionalities acting as a template by using a sol-gel method in the green solvent, supercritical carbon dioxide (scCO(2)). The effect of scCO(2) pressure (1500, 3000 and 5000 psi), temperature (40, 60 and 80 °C), acetic acid/titanium isopropoxide monomer ratios (HAc/TIP = 2, 4 and 6), functionalized graphene sheets (FGSs)/TIP weight ratios (1:20, 1:40 and 1:60 w/w) and solvents (EtOH, hexane) were investigated. Increasing the HAc/TIPweight ratio from 4 to 6 in scCO(2) resulted in increasing the TiO(2) nanowire diameter from 10 to 40 nm. Raman and high resolution XPS showed the interaction of TiO(2) with the -COOH groups on the surface of the graphene sheets, indicating that graphene acted as a template for polycondensation growth. UV-vis diffuse reflectance and photoluminescence spectroscopy showed a reduction in titanias bandgap and also a significant reduction in electron-hole recombination compared to bare TiO(2) nanowires. Photocurrent measurements showed that the TiO(2)nanowire/graphene composites prepared in scCO(2) gave a 5× enhancement in photoefficiency compared to bare TiO(2) nanowires.

CdS and CdTeS quantum dot decorated TiO2 nanowires. Synthesis and photoefficiency

An easy process was developed to synthesize TiO(2) nanowires sensitized with CdS and CdTeS quantum dots (QDs) requiring no pretreatment of the TiO(2) nanowires prior to nanoparticle generation. CdS and CdTeS nanoparticles were firstly grown by an in situ colloidal method directly onto the TiO(2) surface, hence not requiring subsequent functionalization of the QDs. The resulting nanostructure assembly and composition was confirmed by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Successful decoration of the TiO(2) nanowires by the QDs was observed by TEM, while XPS spectra provided clear evidence for the coexistence of CdS and CdTeS QDs and TiO(2) nanowires. The electronic structure of the TiO(2) nanowires was preserved as indicated by Raman spectroscopy. Preliminary photocurrent measurements showed that inclusion of Te in CdS QDs improved the photocurrent efficiency. Compared to bare TiO(2) nanowires, CdS/TiO(2) nanoassemblies showed an enhancement in photocurrent efficiency of 300% while CdTeS/TiO(2) presented an improvement of 350%. This study indicates that the generation of strongly anchored CdS and CdTeS QDs on a TiO(2) nanowire surface is achievable without introduction of a linker molecule, whose presence is known to decrease the electron injection efficiency.

A novel approach to the synthesis of SiO2–PVAc nanocomposites using a one-pot synthesis in supercritical CO2

Inorganic–polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. A novel one-step synthesis route has been developed for making the polymer nanocomposites silica–poly(vinyl acetate) (SiO2–PVAc) in supercritical CO2 (scCO2), wherein all raw chemicals, tetraethoxysilane (TEOS)/tetramethoxysilane (TMOS), vinyltrimethoxysilane (VTMO), vinyl acetate, initiator, and hydrolysis agent were introduced into one autoclave. In-situ ATR-FT-IR was applied to monitor the process in scCO2, and the parallel reactions of free radical polymerization, hydrolysis/condensation, and linkage to the polymer matrix, were found to take place. The nanocomposites were also studied by transmission electron microscopy (TEM) and EDX element Si-mapping. Well-dispersed nanoparticles of 10–50 nm were formed. This process provides a significant improvement by providing a one-step synthesis route where the potentially recyclable scCO2 works as a solvent, a modification agent, and a drying agent. This green process has potentially many advantages in producing new and unique materials, along with waste-reduction and energy-saving properties. Production of metal-oxide–polymer nanocomposites from non-inhalable liquid precursors also has significant potential for non-toxicity in biomedical and other fields.

Hydroxyapatite−TiO 2 ‑based Nanocomposites Synthesized in Supercritical CO 2 for Bone Tissue Engineering: Physical and Mechanical Properties

Calcium phosphate-based nanocomposites offer a unique solution toward producing scaffolds for orthopedic and dental implants. However, despite attractive bioactivity and biocompatibility, hydroxyapatite (HAp) has been limited in heavy load-bearing applications due to its intrinsically low mechanical strength. In this work, to improve the mechanical properties of HAp, we grew HAp nanoplates from the surface of one-dimensional titania nanorod structures by combining a coprecipitation and sol-gel methodology using supercritical fluid processing with carbon dioxide (scCO2). The effects of metal alkoxide concentration (1.1-1.5 mol/L), reaction temperature (60-80 °C), and pressure (6000-8000 psi) on the morphology, crystallinity, and surface area of the resulting nanostructured composites were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), and Brunauer-Emmet-Teller (BET) method. Chemical composition of the products was characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure (XANES) analyses. HAp nanoplates and HAp-TiO2 nanocomposites were homogeneously mixed within poly(ε-caprolactone) (PCL) to develop scaffolds with enhanced physical and mechanical properties for bone regeneration. Mechanical behavior analysis demonstrated that the Youngs and flexural moduli of the PCL/HAp-TiO2 composites were substantially higher than the PCL/HAp composites. Therefore, this new synthesis methodology in scCO2 holds promise for bone tissue engineering with improved mechanical properties.

Fe doped TiO2?graphene nanostructures: synthesis, DFT modeling and photocatalysis

In this work, Fe-doped TiO(2) nanoparticles ranging from a 0.2 to 1 weight % were grown from the surface of graphene sheet templates containing -COOH functionalities using sol-gel chemistry in a green solvent, a mixture of water/ethanol. The assemblies were characterized by a variety of analytical techniques, with the coordination mechanism examined theoretically using the density functional theory (DFT). Scanning electron microscopy and transmission electron microscopy images showed excellent decoration of the Fe-doped TiO(2) nanoparticles on the surface of the graphene sheets >5 nm in diameter. The surface area and optical properties of the Fe-doped photocatalysts were measured by BET, UV and PL spectrometry and compared to non-graphene and pure TiO(2) analogs, showing a plateau at 0.6% Fe. Interactions between graphene and Fe-doped anatase TiO(2) were also studied theoretically using the Vienna ab initio Simulation Package based on DFT. Our first-principles theoretical investigations validated the experimental findings, showing the strength in the physical and chemical adsorption between the graphene and Fe-doped TiO(2). The resulting assemblies were tested for photodegradation under visible light using 17β-estradiol (E2) as a model compound, with all investigated catalysts showing significant enhancements in photocatalytic activity in the degradation of E2.