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Biomedical subjects

M Michel

Publications and source records attributed to M Michel.

At least 19 recordsLinked to original sources
PubMed2006

Composite interfacial layers containing micro-size and nano-size particles.

Surface layers of micro- and nanoparticles at fluid/liquid interfaces in absence and presence of surfactants are of large importance in the process of re-discovering Pickering systems, i.e. emulsions and foams stabilized by particles. The surface pressure/area isotherms of such layers can provide information about the properties of the used particles (dimensions, interfacial contact angles), the structure of interfacial layers, the interactions between the particles as well as about relaxation processes within the layers. For a correct description of Pi-A isotherms of composite surface layers containing particles the significant difference in size of these particles to that of solvent and surfactant molecules should be taken into account. Corresponding equations can be derived on the basis of the two-dimensional solution theory. The gained equations provide satisfactory agreement with experimental data and predict realistic values for the area of particles at the interface. Also equations of state and of the dilational elasticity for composite surface layers containing particles can be obtained in the framework of the presented methodology.

Adsorption↗
PubMed2006

Vasculitis restricted to the lower limbs: a clinical and histopathological study.

BACKGROUND: Rare cases of vasculitis restricted to the lower limbs have been reported, but the characteristics, outcome and response to treatment of this entity are not well known. OBJECTIVE: To describe the clinical, complementary examinations and response to treatment of this rare entity in the first retrospective series, and to compare data with historical pooled cases. METHODS: Retrospective analysis of all biopsy-proven cases observed over a 10-year period in four French tertiary medical units. Diagnosis of vasculitis restricted to the lower limb required the absence of any clinical symptom and complementary test finding, suggesting major extramuscular visceral involvement. RESULTS: 11 patients were included. Vasculitis restricted to the lower limb was associated with disabling muscle pain of the calves. Fever was present in 50% of cases; ankle arthralgia in 50% and skin involvement in 40%. MRI was the cornerstone of the diagnosis, showing hyperintense signal in T2 weight and in T1 weight after gadolinium injection. MRI findings correlated well with clinical outcome and were useful in guiding biopsy. Muscle biopsy was consistent with a polyarteritis nodosa-type vasculitis in only 40% cases, whereas a leucocytoclastic vasculitis was seen for all other cases. Treatment with corticosteroids was effective in all cases, but there were relapses requiring immunosuppressive agents in 54% of cases. CONCLUSION: Vasculitis of the calf muscles must be considered for patients with calf pain and with a biological inflammatory syndrome.

Adult↗
PubMed2006

Reversibility and irreversibility of adsorption of surfactants and proteins at liquid interfaces.

It is shown experimentally that the desorption of sodium decyl sulphate from the liquid/air interface is purely diffusion controlled, while the desorption of higher surface active surfactants such as the non-ionic surfactants Triton X-100 and tridecyl dimethyl phosphine oxide obeys a mixed mechanism. The desorption kinetics of beta-lactoglobulin (BLG) and beta-casein is, however, determined by a barrier mechanism. From the analysis of the BLG and beta-casein desorption kinetics at different temperatures the activation energy of desorption is calculated. The values obtained are rather close to the free energy of adsorption. The theoretical model of desorption kinetics predicts that these two energetic parameters are similar if the adsorption activation energy is low. This explains why substances with a higher adsorption activity have a lower desorption rate. Adsorption kinetics studies for beta-casein with and without forced convection show the same equilibrium surface tension values. This leads to the conclusion that the protein adsorption at liquid interfaces is thermodynamically reversible, although the slow desorption kinetics would allow to assume it to be an irreversible process.

Adsorption↗
PubMed2006

Imaging of oral cavity cancer.

Despite many advances in surgical techniques, technology, radiation therapy, and chemotherapy, survival rates for head and neck cancer (HNCa) have not improved significantly in decades, with many patients being diagnosed at advanced disease stages. Adequate assessment of oral cavity malignancies is critical for appropriate planning of surgical, radiation, and chemotherapy treatment. Imaging modalities used to evaluate the oral cavity include plain radiography (panoramic radiography and intraoral radiography), nuclear medicine scintigraphy, ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET). This review describes these imaging techniques and their utility, primarily CT and MRI.

Humans↗
PubMed2006

Surface-pressure isotherms of monolayers formed by microsize and nanosize particles.

The thermodynamic model of a 2D solution developed earlier for protein monolayers at liquid interfaces is generalized for monolayers composed of micro- and nanoparticles. Surface pressure isotherms of particle monolayers published in the literature for a wide range of particles sizes (between 75 microm and 7.5 nm) are described by the theoretical model with one modification. The calculations of surface pressure pi on area A provide satisfactory agreement with the experimental data. The theory also yields reasonable cross-sectional area values of the solvent molecule water in the range between 0.12 and 0.18 nm2, which is almost independent of particle size. Also, the area per particle in a closely packed monolayer obtained from the theory is quite realistic.

Membranes, Artificial↗
PubMed2006

[The association of cardiac involvement and ischemic stroke in Churg Strauss syndrome].

In Churg and Strauss syndrome (CSS), three patterns of neurological involvement can be found, including mono or polyneuropathy, encephalopathy and stroke. We report two cases of stroke associated with major hypereosinophilia and cardiac involvement, leading to a diagnosis of CSS. Neurological and general outcome were good under treatment with steroids in combination with cyclophosphamide in one case. Churg and Strauss syndrome must be considered when a stroke is associated with a cardiac involvement and hypereosinophilia.

Adrenal Cortex Hormones↗
PubMed2006

Crystallography of dispersed liquid crystalline phases studied by cryo-transmission electron microscopy.

Low molecular weight surfactants, for example monoglycerides and phospholipids, form a multitude of self-assembled structures, such as inverted cubic or hexagonal mesophases, if brought into contact with water/oil. These mesophases can be dispersed in water using adequate surface-active materials such as low molecular weight surfactants or surface active polymers. In order to use such mesophase particles for incorporating drugs and aromas, it is essential to determine their internal crystallographic structure and to understand their mechanism of stabilization. Cryo-transmission electron microscopy was used to investigate the internal structure of different dispersed particles at various temperatures and oil contents. It is shown here that cryo-transmission electron microscopy, in combination with fast Fourier transform and tilting experiments, is effective in obtaining information on crystallographic structure, space group and morphology of particles with reversed bicontinuous cubic and hexagonal structures. In particular, using the presence or the absence of the {111} reflections and viewing the same particle under different axes of observation allows one to discriminate between the Im3m and Pn3m space groups. A major advantage of cryo-transmission electron microscopy is the ability to analyse single particles. This allows the identification of particles present at very low concentrations and the coexistence of particles with different internal self-assembly structures. With this technique we have obtained strong evidence for the presence of two cubic internal self-assembly structures with different space groups within the same dispersion. In addition, we found that cryo-transmission electron microscopy combined with tilting experiments enables the analysis of internal particle morphology, allowing the discussion of mechanisms for hexosome stabilization.

Journal Article↗
PubMed2005

Layer by layer self-assembled polyelectrolyte multilayers with embedded phospholipid vesicles obtained by spraying: integrity of the vesicles.

In a previous paper (Michel, M.; Vautier, D.; Voegel, J.-C.; Schaaf, P.; Ball, V. Langmuir 2004, 20, 4835), we showed that phospholipid vesicles can be incorporated into poly(glutamic-acid)/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films built by the alternated dipping of a surface in polyanion and polycation solutions. AFM imaging, quartz crystal microbalance, and ellipsometry suggested that the vesicles remain intact when adhering on the surface. In the present paper, we show that such films can also be realized by spraying both the polyelectrolyte solutions and the vesicles onto the surface. Using such vesicles filled with ferrocyanide ions, we prove by cyclic voltammetry that the sprayed vesicles remain intact when embedded in the multilayers. We show that multilayers containing two distinct layers of intact vesicles separated by several polyanion/polycation bilayers can also be constructed. Polyelectrolyte multilayers containing layers of phospholipid vesicles could act as reservoirs for drug or other biologically active molecules in controlled release bioactive coatings.

Electrochemistry↗
PubMed2005

A multicentre randomized controlled trial of epidural corticosteroid injections for sciatica: the WEST study.

OBJECTIVE: To determine the effectiveness and predictors of response to lumbar epidural corticosteroid injections (ESI) in patients with sciatica. We performed a 12-month, multicentre, double-blind, randomized, placebo-controlled, parallel-group trial in four secondary pain-care clinics in the Wessex Region. METHODS: Two hundred and twenty-eight patients with a clinical diagnosis of unilateral sciatica of 1-18 months' duration were randomized to either three lumbar ESIs of triamcinolone acetonide or interligamentous saline injections at intervals of 3 weeks. The main outcome measure was the Oswestry low back pain disability questionnaire (ODQ). RESULTS: At 3 weeks, the ESI group demonstrated a transient benefit over the placebo group (patients achieving a 75% improvement in ODQ, 12.5 vs 3.7%; number needed to treat, 11.4). No benefit was demonstrated from 6 to 52 weeks. ESIs did not improve physical function, hasten return to work or reduce the need for surgery. There was no benefit of repeated ESIs over single injection. No clinical predictors of response were found. At the end of the study the majority of patients still had significant pain and disability regardless of intervention. CONCLUSIONS: In this pragmatic study, ESIs offered transient benefit in symptoms at 3 weeks in patients with sciatica, but no sustained benefits in terms of pain, function or need for surgery. Sciatica is a chronic condition requiring a multidisciplinary approach. To fully investigate the value of ESIs, they need to be evaluated as part of a multidisciplinary approach.

Adolescent↗
PubMed2005

Surface dilational rheology of mixed beta-lactoglobulin/surfactant layers at the air/water interface.

The general theoretical model by Garrett and Joos proposed in 1976 for the estimation of the dilational elasticity of mixed surfactant solutions, and also the theoretical model proposed by Joos for the limiting elasticity of such mixtures, demonstrate quite satisfactory agreement with experimental results obtained from the oscillating bubble shape method for mixtures of a nonionic surfactant and a protein, that is, beta-lactoglobuline and decyl dimethyl phosphine oxide, C10DMPO.

Air↗
PubMed2005

Kinetics of the desorption of surfactants and proteins from adsorption layers at the solution/air interface.

It is shown by experiments that the DeSNa desorption kinetics is governed by a pure diffusion mechanism, while the desorption of more surface active surfactants such as C13DMPO and Triton X-100 obeys a mixed mechanism. The BLG desorption kinetics, as shown by experiments, is determined by a barrier mechanism. From the analysis of the temperature dependence of the BLG desorption kinetics it is possible to calculate the activation energy of this process, which is quite close to the free energy of BLG adsorption. The theoretical model of desorption kinetics predicts that these two energetic parameters are approximately equal to each other if the adsorption activation energy is low. This can explain the fact that the higher the adsorption activity of a substance is, the lower is its desorption rate.

Adsorption↗
PubMed2004

Determination of protein adsorption by comparative drop and bubble profile analysis tensiometry.

Proteins adsorb at a liquid interface at very low bulk concentrations which is significantly decreased due to the adsorbed amount. Depending on the surface area A to solution bulk volume V ratio this loss in protein can be significant. Using experimental methods with large differences in the A/V ratio the adsorbed amount can be determined from the measured quantities, for example the surface tension. For beta-casein and bovine and human serum albumin data from literature obtained by the Wilhelmy technique and own data measured by drop profile analysis tensiometry are used. The adsorbed amounts measured directly from ellipsometry agree very well with those determined by the proposed method.

Adsorption↗
PubMed2004

Competitive adsorption from mixed nonionic surfactant/protein solutions.

A thermodynamic model is derived which is suitable to describe adsorption from a mixed protein/surfactant solution. The comparison with experimental data for HSA mixed with the nonionic surfactant decyl dimethyl phosphine oxide shows good agreement. Some model calculations are discussed in terms of the competitive character of the process of adsorption from mixed protein/surfactant solutions. The behavior of globular (HSA) and flexible (beta-casein) proteins appears to be quite different due to the possibility of changing the molar area of adsorbed protein molecules.

Adsorption↗
PubMed2004

Dynamic surface tension and adsorption kinetics of beta-casein at the solution/air interface.

A diffusion model is proposed to describe the adsorption kinetics of proteins at a liquid interface. The model is based on the simultaneous solution of the Ward-Tordai equation and a set of recently developed equations describing the equilibrium state of the adsorption layer: the adsorption isotherm, the surface layer equation of state, and the function of adsorption distribution over the states with different molar areas. The new kinetics model is compared with dynamic surface tensions of beta-casein solutions measured with the drop/bubble profile and maximum bubble pressure methods. The adsorption process for low concentrations is governed by the diffusion mechanism, while at large protein concentrations this is only the case in the initial stage. The effective diffusion coefficients agree fairly well with literature data. The adsorption values calculated from the dynamic surface tension data agree very well with the used equilibrium adsorption model.

Journal Article↗
PubMed2003

Optical detection of the Aharonov-Bohm effect on a charged particle in a nanoscale quantum ring.

We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.

Journal Article↗