Amphiphilic azobenzenes: Antibacterial activities and biophysical investigation of their interaction with bacterial membrane lipids.

With the emergence of multi-drug resistant bacteria and hospital-acquired infections, there is an urgent need to develop new antibiotics. Here, we report the synthesis, physico-chemical characterizations, and antimicrobial activity assays of four Azo compounds that differ in their alkyl chain length. The molecular mechanism of their antibacterial activity was investigated by complementary in vitro and in silico biophysical studies. The compounds with alkyl chain lengths of four or six carbons showed a low MIC50 against Escherichia coli and Bacillus subtilis. Our investigations into the mechanism of their action revealed that phosphatidylethanolamine in the bacterial plasma membrane plays an important role in their antibacterial activity.

Soft tissue adhesion of polished versus glazed lithium disilicate ceramic for dental applications.

OBJECTIVE: Ceramics are widely used materials for prosthesis, especially in dental fields. Despite multiple biomedical applications, little is known about ceramic surface modifications and the resulting cell behavior at its contact. The aim of this study is to evaluate the biological response of polished versus glazed surface treatments on lithium disilicate dental ceramic. METHODS: We studied a lithium disilicate ceramic (IPS e.max(®) Press, Ivoclar Vivadent) with 3 different surface treatments: raw surface treatment, hand polished surface treatment, and glazed surface treatment (control samples are Thermanox(®), Nunc). In order to evaluate the possible modulation of cell response at the surface of ceramic, we compared polished versus glazed ceramics using an organotypic culture model of chicken epithelium. RESULTS: Our results show that the surface roughness is not modified as demonstrated by equivalent Ra measurements. On the contrary, the contact angle θ in water is very different between polished (84°) and glazed (33°) samples. The culture of epithelial tissues allowed a very precise assessment of histocompatibility of these interfaces and showed that polished samples increased cell adhesion and proliferation as compared to glazed samples. SIGNIFICANCE: Lithium disilicate polished ceramic provided better adhesion and proliferation than lithium disilicate glazed ceramic. Taken together, our results demonstrate for the first time, how it is possible to use simple surface modifications to finely modulate the adhesion of tissues. Our results will help dental surgeons to choose the most appropriate surface treatment for a specific clinical application, in particular for the ceramic implant collar.

Triblock siloxane copolymer surfactant: template for spherical mesoporous silica with a hexagonal pore ordering.

Ordered mesoporous silica materials with a spherical morphology have been prepared for the first time through the cooperative templating mechanism (CTM) by using a silicone triblock copolymer as template. The behavior of the pure siloxane copolymer amphiphile in water was first investigated. A direct micellar phase (L(1)) and a hexagonal (H(1)) liquid crystal were found. The determination of the structural parameters by SAXS measurements leads us to conclude that in the hexagonal liquid crystal phase a part of the ethylene oxide group is not hydrated as observed for the micelles. Mesoporous materials were then synthesized from the cooperative templating mechanism. The recovered materials were characterized by SAXS measurements, nitrogen adsorption-desorption analysis, and transmission and scanning electron microscopy. The results clearly evidence that one can control the morphology and the nanostructuring of the resulting material by modifying the synthesis parameters. Actually, highly ordered mesoporous materials with a spherical morphology have been obtained with a siloxane copolymer/tetramethoxysilane molar ratio of 0.10 after hydrothermal treatment at 100 °C. Our study also supports the fact that the interactions between micelles and the hydrolyzed precursor are one of the key parameters governing the formation of ordered mesostructures through the cooperative templating mechanism. Indeed, we have demonstrated that when the interactions between micelles are important, only wormhole-like structures are recovered.

Modelization of the release from a tetradecane/water/hexadecane multiple emulsion: evidence of significant micellar diffusion.

The release of tetradecane from a multiple emulsion of the type tetradecane/water/hexadecane was studied experimentally using the differential scanning calorimetry technique. The kinetics of the tetradecane release was measured for three formulations containing different concentrations of hydrophilic surfactant (2%, 4%, and 7%). A new mass transfer model derived from the shrinking core model was developed. The values of the model parameters deduced from the least-squares fittings led to the determination of the tetradecane diffusivity. Thus, the preponderant mechanism of mass transfer was proved to be micellar diffusion and not molecular diffusion. This conclusion was confirmed by considering the effect of the change in the hydrophilic surfactant concentration.

Morphology characterization of emulsions by differential scanning calorimetry.

This article is a review of some results obtained by Differential Scanning Calorimetry (DSC) for characterizing the morphology of emulsions. In a classical DSC experiment, an emulsion sample is submitted to a regular cooling and heating cycle between temperatures that include freezing and melting of the dispersed droplets. By using the thermograms found in the literature for various emulsions, how to get information about the solidification and melting, the presence of solute, the emulsion type, the transfer of matter, the stability and the droplet size is shown.

Adhesion of a Pseudomonas putida strain isolated from a paper machine to cellulose fibres.

The adhesion to cellulose fibres of a strain of Pseudomonas putida isolated from a paper machine was studied under different environmental conditions. The physicochemical properties of both P. putida cells and cellulose fibres were also determined to better understand the adhesion phenomenon. Adhesion was rapid (1 min) and increased with time, cell concentration and temperature (from 25 to 40 degrees C), indicating that bacterial adhesion to cellulose fibres is essentially governed by a physicochemical process. The P. putida cell surface was negatively charged, as shown by electrophoretic mobility measurements, and was hydrophilic due to a strong electron-donor character, as shown by the microbial adhesion to solvents method. Cellulose fibres were shown to be hydrophilic by contact angle measurements using the capillary rise method. These results suggest the importance of Lewis acid-base interactions in the adhesion process. In various ionic solutions (NaCl, KCl, CaCl(2) and MgCl(2)), adhesion increased with increasing ionic strength up to 10-100 mM, indicating that, at low ionic strength, electrostatic interactions were involved in the adhesion process. An increase in the C/N ratio of the growth medium (from 5 to 90) decreased adhesion but this could not be related to changes in physicochemical properties, suggesting that other factors may be involved. In practice, temperature, ionic strength and nitrogen concentration must be taken into consideration to reduce bacterial contamination in the paper industry.

Time-dependent loss of radioactivity counts associated with paracellular markers in the presence of cyclodextrin.

This communication reports an unexpected phenomenon observed during the counting of radiolabeled paracellular marker solutions in the presence of 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD). The results revealed time-dependent loss of 14C-mannitol and 14C-polyethlene glycol 4000 radioactivity counts with increased percentages of HPbetaCD. However, 14C-diazepam, a transcellular marker, displayed a stable count. A hypothesis behind this phenomenon is being proposed, involving water transfer from aqueous droplets to the surfactant rich scintillation fluid. The remaining droplets, becoming more and more concentrated in cyclodextrin, entrap the hydrophilic markers and consequently exhibit an increasing quenching effect. This effect shows that careful monitoring of radiolabeled markers used in transport experiments is necessary, even with high quench resistant scintillation fluids, to prevent erroneous interpretation of the transport data.

Enhanced pulmonary delivery of insulin by lung lavage fluid and phospholipids.

Pulmonary delivery appears to be the most promising non-parenteral route of insulin administration. In this work, we investigated the enhancement of insulin absorption in the presence of phospholipids and lung lavage fluid in vivo and in vitro. In-vitro experiments of insulin uptake by type II cells showed a significantly enhanced absorption in presence of lavage fluid, compared to various buffer preparations. The same trend was obtained with in-vivo studies of tracheal instillation of insulin. The incorporation of phospholipids as absorption enhancers in 1,2-dipalmitoyl phosphatidylcholine (DPPC) dispersion was compared to blank liposomes. A significantly higher blood glucose decrease was observed with a DPPC-insulin physical mixture compared to liposome, suggesting a possible effect of the phospholipid chain physical state on the insulin in-vivo absorption.

Lipid emulsions as vehicles for enhanced nasal delivery of insulin.

The objective of this work is to explore lipid emulsion based formulations of insulin as an enhancer of nasal absorption. Insulin was incorporated into the aqueous phases of water-in-oil (w/o) and oil-in-water (o/w) emulsions. The formulations were perfused through the nasal cavity of rats in situ. Enhancement of insulin absorption was observed when insulin was incorporated into the continuous aqueous phase of an o/w emulsion. The presence of a small fraction of oil droplets along with insulin in the aqueous phase appeared to favor insulin absorption. When the oil phase constitutes the external phase, as in w/o emulsion, no insulin absorption was noted. Inhibition of insulin absorption might arise from a rate limiting barrier effect of the membrane completely covered by a stagnant oil layer. The in situ model was validated by in vivo experiments, which also revealed an increase in insulin absorption with o/w emulsions. However at lower insulin doses there was no statistically significant enhancing effect. In situ perfusion experiments across rat nasal pathway appear to be an appropriate model to study the enhancement effect of nasal formulations.