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Biomedical subjects

V Schmitt

Publications and source records attributed to V Schmitt.

9 recordsLinked to original sources
PubMed2005

Particle-stabilized emulsions comprised of solid droplets.

We kinetically stabilize oil-in-water emulsions comprising paraffin crystals by adsorbing solid particles (silica) of colloidal size at the oil/water interface. We obtain a set of emulsions that are quiescently stable for a long period of time (months), while the same emulsions are destabilized after only a few hours in the presence of surfactant molecules alone. The emulsions are submitted to a shear stress in order to probe their stability under flow conditions. Partial coalescence and gelation occur when the shear is applied for a sufficiently long period of time. The experiments reveal the existence of a critical droplet mass fraction, phi*, that defines a sharp transition between slow and fast gelation. The process of gelation is rather slow for phi < phi*, occurring at the scale of hours, and becomes almost instantaneous above phi*.

Journal Article↗
PubMed2004

Coarsening of alkane-in-water emulsions stabilized by nonionic poly(oxyethylene) surfactants: the role of molecular permeation and coalescence.

We produce different alkane-in-water concentrated emulsions stabilized by the same nonionic surfactant, and we follow their kinetic evolution by granulometry. The size distribution becomes remarkably narrow during the first stages of coarsening and progressively turns to a wide function as time passes. We get evidence that the size evolution occurs under the effect of molecular permeation and coalescence. A second hydrophobic species of large molecular size is dissolved in the dispersed phase. This latter is expected to inhibit the permeation mechanism, and coalescence should act alone. Surprisingly, coalescence is also suppressed, even at a very low concentration of the second component (approximately 1% w/w). We vary the chemical nature and concentration of the second species, and we propose a simple mechanism to explain the stabilizing effect with respect to coalescence.

Alkanes↗
PubMed2003

Some general features of limited coalescence in solid-stabilized emulsions.

We produce direct and inverse emulsions stabilized by solid mineral particles. If the total amount of particles is initially insufficient to fully cover the oil-water interfaces, the emulsion droplets coalesce such that the total interfacial area between oil and water is progressively reduced. Since it is likely that the particles are irreversibly adsorbed, the degree of surface coverage by them increases until coalescence is halted. We follow the rate of droplet coalescence from the initial fragmented state to the saturated situation. Unlike surfactant-stabilized emulsions, the coalescence frequency depends on time and particle concentration. Both the transient and final droplet size distributions are relatively narrow and we obtain a linear relation between the inverse average droplet diameter and the total amount of solid particles, with a slope that depends on the mixing intensity. The phenomenology is independent of the mixing type and of the droplet volume fraction allowing the fabrication of both direct and inverse emulsion with average droplet sizes ranging from micron to millimetre.

Adsorption↗
PubMed2001

Epidemiology of severe brain injuries: a prospective population-based study.

BACKGROUND: The aim of this prospective study was to estimate annual incidences of hospitalization for severe traumatic brain injury (TBI) (maximum Abbreviated Injury Score in the head region [HAIS] 4 or 5) in a defined population of 2.8 million. METHODS: Severe TBI patients were included in the emergency departments in the 19 hospitals of the region. A prospective data form was completed with initial neurologic state, computed tomographic scan lesions, associated injuries, length of unconsciousness, and length of stay in acute care centers. Outcome at the time the patient left acute hospitalization was retrospectively assessed from medical notes. RESULTS: During the 1-year period (1996), 497 residents fulfilled the inclusion criteria, leading to an annual incidence rate of 17.3 per 100,000 population; 58.1% were HAIS5. Mortality rate was 5.2 per 100,000. Men accounted for 71.4% of cases. Median age was 44 years, with a quarter of patients more than 70 years old. Traffic accidents were the most frequent causes (48.3%), but falls accounted for 41.8% of all patients. Age and severity were different according to the major categories of external causes. In HAIS5 patients, 86.5% were considered as comatose (coma lasting more than 24 hours or leading to immediate death) but only 60.9% had an initial Glasgow Coma Scale score < 9. In the HAIS4 group, 7.2% had an initial Glasgow Coma Scale score < 9. Fatality rates were 30.0% in the whole study group, 7.7% in HAIS4, 12.8% in HAIS5 without coma, and 51.2% in HAIS5 with coma. CONCLUSION: This study shows a decrease in severe TBI incidence when results are compared with another study conducted 10 years earlier in the same region. This is because of a decrease in traffic accidents. However, this results in an increase in the proportion of falls in elderly patients and an increase in the median age in our patients. This increased age influences the mortality rate.

Abbreviated Injury Scale↗
PubMed1999

Rheological Behavior of Fluorinated Highly Concentrated Reverse Emulsions with Temperature.

Reverse highly concentrated fluorinated emulsions exist in a large temperature domain (between 10 and 50 degrees C). The study of the phase behavior reveals that the continuous medium composition varied with the temperature. Highly concentrated emulsions behave as elastic solids. Monitoring the evolution of their elasticity with time as a function of temperature by rheology is an original way to characterize their aging. This method was used to get more insight into the modification of the behavior of polydisperse emulsions with temperature and time. The elastic modulus decreased exponentially with time in the range of temperatures studied. This was interpreted as a result of coalescence due to a single film rupture frequency which was independent of its thickness. This coalescence mechanism is thermally activated with an activation energy of 50 k(B)T. Copyright 1999 Academic Press.

Journal Article↗
PubMed1998

Characterization of echoviruses that bind decay accelerating factor (CD55): evidence that some haemagglutinating strains use more than one cellular receptor.

Several echoviruses (EVs) have previously been shown to use decay accelerating factor (DAF) as a cellular receptor. Since DAF is expressed on erythrocytes, EVs that use this receptor cause haemagglutination. Here we show that all EVs that haemagglutinate do so via attachment to DAF and that this interaction can be inhibited by a monoclonal antibody (MAb) specific for DAF domain SCR3. Although the viruses haemagglutinate via DAF some can bind to rhabdomyosarcoma cells from which DAF has been removed and infect in the presence of a MAb against DAF. This suggests that some EVs have the capacity to interact with more than one cellular receptor.

Animals↗
PubMed1990

Fluid phase generation of terminal complement complex as a novel index of bioincompatibility.

Blood membrane interactions in hemodialysis have been shown to trigger complement (C) activation. As indicators of C-activation the anaphylatoxins (C3a and C5a) are problematical because of methodological difficulties and their kinetic properties. We developed a sensitive and specific micro-ELISA using a monoclonal antibody against neoantigens on the terminal complement complex (TCC); highly purified human TCC served as standard. Concentrations of TCC were measured in single-path perfusion systems (in vitro) and in the blood lines (arterial inlet; venous outlet) of patients on hemodialysis using steam-sterilized or ETO-sterilized dialyzers with the following membranes: cuprophan (CU), hemophan (HE) and polysulfone F6 (PS), respectively. All dialyzers with identical geometry were run under identical conditions. All membranes tested caused continuously ongoing net generation of TCC. In vitro, contact of serum with CU minidialyzers resulted in fivefold higher net release of TCC compared with HE and PS. In vivo TCC concentration-time profiles differed significantly between membranes in the rank order CU much much greater than HE greater than PS (mean basal concentration 58 x 10(-11) M; peak increase over baseline with CU 40-fold, HE fourfold, PS threefold). In addition, more TCC was generated from the same dialyzers with ETO than steam sterilization. TCC differed from C3a and C5a in the following respects: (i) lower detection limit (4 x 10(-11) vs. less than 5 x 10(-9) M for both C-anaphylatoxins); (ii) higher relative increment (inlet) during CU dialysis (25-fold vs. eightfold and twofold, respectively); (iii) C-anaphylatoxins yielded the same ranking (CU much greater than HE greater than PS), but TCC concentrations were not a linear function of C3a or C5a concentrations, respectively. Kinetic analysis (Bateman function) showed significant differences of invasion constants between membranes, that is, CU 0.088 min-1, HE 0.09, PS 0.168. The net amount of TCC released from the dialyzer was calculated under certain assumptions. It was 75.5 mg/4 hr for CU, 7.3 for HE and 5.0 for PS. The elimination constant was also dependent on the type of membrane. Using flow cytofluorometry and immunohistochemical methods (APAAP), TCC was demonstrated on membranes of granulocytes obtained during dialysis; this is compatible with potential in vivo cell activation. Generation of PGE2 and TNF alpha by adherent monocytes induced by cuprophan was C8 dependent: levels were significantly increased by addition of C8 to C8 deficient human serum concomitantly with generation of TCC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗