Biomedical subjects

S Lerouge

Publications and source records attributed to S Lerouge.

12 recordsLinked to original sources

PubMed2006

Local velocity measurements in heterogeneous and time-dependent flows of a micellar solution.

We present and discuss the results of pointwise velocity measurements performed on a viscoelastic micellar solution made of cetyltrimethylammonium bromide and sodium salicylate in water, respectively, at the concentrations of 50 and 100 mmol. The sample is contained in a Couette device and subjected to flow in the strain controlled mode. This particular solution shows shear banding and, in a narrow range of shear rates at the right end of the stress plateau, apparent shear thickening occurs. Time-dependent recordings of the shear stress in this range reveal that the flow has become unstable and that large sustained oscillations of the shear stress and of the first normal stresses difference emerge and grow in the flow. Local pointwise velocity measurements clearly reveal a velocity profile typical of shear banding when the imposed shear rate belongs to the plateau, but also important wall slip in the entire range of velocity gradients investigated. In the oscillations regime, the velocity is recorded as a function of time at a fixed point close to the rotor of the Couette device. The time-dependent velocity profile reveals random fluctuations but, from time to time, sharp decreases much larger than the standard deviation are observed. An attempt is made to correlate these strong variations with the stress oscillations and a correlation coefficient r is computed. However, the small value found for the coefficient r does not allow us to draw a final conclusion as concerns the correlation between stress oscillations and velocity fast decreases.

Journal Article↗

PubMed2006

Interface instability in shear-banding flow.

We report on the spatiotemporal dynamics of the interface in shear-banding flow of a wormlike micellar system (cetyltrimethylammonium bromide and sodium nitrate in water) during a start-up experiment. Using the scattering properties of the induced structures, we demonstrate the existence of an instability of the interface between bands along the vorticity direction. Different regimes of spatiotemporal dynamics of the interface are identified along the stress plateau. We build a model based on the flow symmetry which qualitatively describes the observed patterns.

Journal Article↗

PubMed2005

Temporal oscillations of the shear stress and scattered light in a shear-banding--shear-thickening micellar solution.

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.

Journal Article↗

PubMed2005

Rayleigh scattering and flow birefringence measurement in colloidal solutions.

A unique method for measuring the birefringence intensity of colloidal solutions which become anisotropic under the action of orienting flow is described. When a laser beam crosses a liquid-containing asymmetrical particle orientated by the flow, the scattered intensity in a direction perpendicular to the wave vector of the incident light shows nodes and antinodes. The distance between two antinodes is related to the phase difference between the eigenpolarizations of the medium and thus to the birefringence of the medium.

Journal Article↗

PubMed2002

Safety of plasma-based sterilization: surface modifications of polymeric medical devices induced by Sterrad and Plazlyte processes.

Plasma-based sterilization is a promising alternative to the use of pure ethylene oxide (EO), for low-temperature clinical sterilization of medical instruments and devices. However, few studies have been published that evaluate its safety in terms of possible damage to materials, particularly polymers. The objective of this work was to evaluate polymer surface modifications induced by commercial plasma-based sterilizers, in comparison with pure EO: Samples from 5 polymer-based devices were subjected to 1, 5, and 10 sterilization cycles by Sterrad-100, Plazlyte, and pure EO. Surface analysis was carried out by X-ray photoelectron spectroscopy (XPS), dynamic contact angle measurements (DCA), and scanning electron microscopy (SEM). Surface oxidation and wettability changes were observed on all samples sterilized by plasma-based techniques, the degree of modifications depending on the sterilizer (Sterrad, Plazlyte) and the type of polymer. Drastic changes of surface appearance were also observed by SEM on PVC samples sterilized by Plazlyte and by pure EO. Possible repercussions on safety are discussed.

Adsorption↗

PubMed2001

[Determination by flow cytometry of reference values of erythrocyte parameters in aged subjects].

OBJECTIVES: Normal values for hemoglobin and hematocrit have been established for healthy young adults, but it is unknown whether age-related decline in hematological values occurs in the elderly. We compared normal values of hematological parameters in healthy adults and healthy persons aged 65 years and over using flow cytometry. SUBJECTS AND METHODS: Erythrocyte and reticulocyte parameters were determined in 585 subjects (294 men and 206 women aged 26 to 64 years, and 37 men and 48 women aged 65 years and over), living independently and without medication, symptom and disease, using Technicon H1 (Bayer) and R2000 (Roche) analyzers. Serum erythropoietin levels, red cell folate and creatinine clearance were determined in subjects aged 65 years and over. RESULTS: Irrespective of subject age, hemoglobin (Hb), hematocrit (Hct), red blood cell count (RBC), mean cell volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) were higher in males than in females, but sex-related differences tended to decrease with aging. In males, there was a trend toward lower Hb and Hct with aging, due to an increase in RBC, MCV and MCH. In females, Hb and Hct (p < 0.05) increased with aging, due to a trend toward higher values of RBC, MCV and MCH. Red blood cell distribution width and hemoglobin distribution width were not modified by aging. Despite these age-related changes in erythrocyte parameters, values for anemia defined in adults appear appropriate for geriatric subjects (Hb < 130 g/l in males and Hb < 120 g/l in females). Reticulocyte count and creatinine clearance decreased in men and women aged 65 years and over (p < 0.05), whereas erythropoietin levels and red cell folate were not influenced by aging. CONCLUSION: Normal erythrocyte values defined in adults are appropriate for evaluating hematological test results in older individuals. The decrease in reticulocyte count observed in men and women aged 65 years and over does not appear to be linked to a decrease in erythropoietin production with aging.

Adult↗

PubMed2001

Insight in shear banding under transient flow.

The rheo-optical behavior of a viscoelastic solution of a surfactant subjected to transient shear flows is reported. A steplike shear rate is suddenly imposed and we record the transient physical characteristics of the liquid, i.e., the shear stress sigma, the transmitted intensity I(t), and the scattering pattern. At the inception of the flow the shear stress shows an important overshoot followed by damped oscillations which also appear in the intensity profile. Then a sigmoïdal relaxation process brings the liquid in its final steady state. During this first phase, the diffusion pattern due to enhanced concentration fluctuations can also be observed. A fine anisotropic layer appears near the moving wall shortly after the inception of the flow, but its width starts to increase significantly well after the end of the relaxation process. When the laser beam travels through this band a diffraction pattern can be observed indicating that it is formed by small subbands, the characteristic width of which is in the order of 100 micro m.

Journal Article↗

PubMed2000

Plasma-based sterilization: effect on surface and bulk properties and hydrolytic stability of reprocessed polyurethane electrophysiology catheters.

Plasma-based sterilization is a promising alternative to ethylene oxide (EO) for reprocessing of electrophysiology catheters. To assess its safety in terms of material damage, modifications of surface and bulk properties as well as hydrolytic stability of sterilized catheters were evaluated. Polyurethane (PU) single-use electrophysiology catheters were subjected to one, five, and ten sterilization cycles by Sterrad-100S and Plazlyte, as well as by pure EO for comparison. Surface analysis techniques (ATR-FTIR, XPS, DCA) showed oxidation limited to the near-surface layer induced by both plasma-based sterilizers, whereas EO induced slight but deeper alkylation. Using bulk analysis techniques (RP-HPLC, SEC), oligomer alteration was observed after all three sterilization techniques, without modification of molecular weights. Hydrolytic stability of catheters was slightly changed by plasma-based sterilization, with a small increase in released oligomers. Finally, although Plazlyte and Sterrad are both plasma-based techniques, they induced different impacts on catheters, such as the degradation of an additive with Sterrad, and a clear difference in coloration with Plazlyte.

Catheterization↗

PubMed2000

Effect of gas composition on spore mortality and etching during low-pressure plasma sterilization.

The aim of this work was to investigate possible mechanisms of sterilization by low-temperature gas plasma: spore destruction by plasma is compared with etching of synthetic polymers. Bacillus subtilis spores were inoculated at the bottom of glass vials and subjected to different plasma gas compositions (O(2), O(2)/Ar, O(2)/H(2), CO(2), and O(2)/CF(4)), all known to etch polymers. O(2)/CF(4) plasma exhibited much higher efficacy than all other gases or gas mixtures tested, with a more than 5 log decrease in 7.5 min, compared with a 2 log decrease with pure oxygen. Examination by scanning electron microscopy showed that spores were significantly etched after 30 min of plasma exposure, but not completely. We speculate about their etch resistance compared with that of synthetic polymers on the basis of their morphology and complex coating structure. In contrast to so-called in-house plasma, sterilization by Sterrad(R) tended to increase the observed spores' size; chemical modification (oxidation), rather than etching, is believed to be the sterilization mechanism of Sterrad(R).

Bacillus subtilis↗

PubMed2000

Ceramic/ceramic total hip arthroplasty.

Alumina-on-alumina total hip arthroplasty has been used for 30 years, mainly in Europe. The theoretical advantages of this combination are represented by its remarkable sliding characteristics, its very low wear debris generation, and its sufficient fracture toughness. These advantages are achieved if the material is properly controlled with high density, high purity, and small grains. The authors summarize the results obtained with ceramic/ceramic total hip arthroplasty. Information is provided about in vivo behavior regarding wear debris characterization and quantification, and histological tissue examinations for inflammatory reactions, which were not encountered except when alumina debris was mixed with metal or cement. Modification of socket fixation resulted in improved clinical outcomes. With a press-fit metal shell and an alumina liner utilized for 10 years, the results are excellent especially in a young and active population. Alumina-on-alumina seems at the moment to be one of the best choices when a total hip arthroplasty has to be performed in young and active patients.

Aluminum Oxide↗

PubMed1997

Ceramic-ceramic and metal-polyethylene total hip replacements: comparison of pseudomembranes after loosening.

We made a semiquantitative study of the comparative histology of pseudomembranes from 12 loose cemented ceramic-ceramic and 18 metal-polyethylene total hip replacements. We found no significant difference in cellular reaction between the two groups, but there was a major difference in the origin of the particulate debris. In the metal-polyethylene group, polyethylene of articular origin was predominant, while in the ceramic-ceramic group the cellular reaction appeared to be a response to zirconia ceramic particles used to opacify cement used for fixation. Isolation and characterisation of the debris showed that the zirconia particles formed the greatest proportion (76%) in ceramic-ceramic hips, while alumina debris of articular origin formed only 12%. Our study has indicated that aseptic loosening of ceramic cups is not due to a response to debris generated at the articular interface, but to mechanical factors which lead to fragmentation of the cement.

Bone Cements↗

PubMed1996

Characterization of in vivo wear debris from ceramic-ceramic total hip arthroplasties.

In contrast to the much-studied mechanism of aseptic loosening of the metal-polyethylene joint couple, the mechanism responsible for failure of ceramic-ceramic (CC) total hip arthroplasties (THAs) has not been evaluated. The aim of this study was to conduct a systematic characterization of the in vivo wear debris from 15 cases of CC THAs revised for aseptic loosening. Two methods were used to evaluate the wear debris; a semiquantitative histological analysis of H&E-stained periprosthetic pseudomembranes; and an evaluation of isolated debris particles using SEM, energy-dispersive X-ray analysis, and image analysis. The three main types of particulate debris identified were titanium alloy (TiAlV) and alumina ceramic (Al2O3) of prosthetic origin, and zirconium dioxide (ZrO2) from the contrast agent used in the cement for prosthetic fixation. Alumina debris was present in the smallest proportion (12%) and was consistent with the low wear rate of the CC joint couple. Zirconium dioxide debris was present in the greatest proportion (76%) and was an unexpected finding. The ZrO2 debris represented microstructural grains of the original ZrO2 particles added as contrast agent to the cement. The presence of a histiocytic foreign body reaction to ZrO2 debris on histologic sections leads us to believe that these particles play an important role in aseptic loosening of the CC THAs evaluated in this study.

Alloys↗