Biomedical subjects

P Descouts

Publications and source records attributed to P Descouts.

At least 19 recordsLinked to original sources

PubMed2003

Haemocompatibility evaluation of DLC- and SiC-coated surfaces.

Diamond-like carbon (DLC) and silicon carbide (SiC) coatings are attractive because of low friction coefficient, high hardness, chemical inertness and smooth finish, which they provide to biomedical devices. Silicon wafers (Si(waf)) and silicone rubber (Si(rub)) plates were coated using plasma-enhanced chemical vapour deposition (PE-CVD) techniques. This article describes: 1- the characterization of modified surfaces using attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FTIR) and contact angle measurements, 2- the results of three in-vitro haemocompatibility assays. Coated surfaces were compared to uncoated materials and various substrates such as polymethylmethacrylate (PMMA), polyethylene (LDPE), polydimethylsiloxane (PDMS) and medical steel (MS). Thrombin generation, blood platelet adhesion and complement convertase activity tests revealed the following classification, from the most to the least heamocompatible surface: Si(rub)/ DLC-Si(rub)/ DLC-Si(waf)/ LDPE/ PDMS/ SiC-Si(waf)/ Si(waf)/ PMMA/ MS. The DLC coating surfaces delayed the clotting time, tended to inhibit the platelet and complement convertase activation, whereas SiC-coated silicon wafer can be considered as thrombogenic. This study has taken into account three events of the blood activation: coagulation, platelet activation and inflammation. The response to those events is an indicator of the in vitro haemocompatibility of the different surfaces and it allows us to select biomaterials for further in vivo blood contacting investigations.

Biocompatible Materials↗

PubMed2003

Adhesion of Pseudomonas aeruginosa strains to untreated and oxygen-plasma treated poly(vinyl chloride) (PVC) from endotracheal intubation devices.

Pseudomonas aeruginosa pneumonia is a life threatening complication in mechanically ventilated patients that requires the ability of the bacteria to adhere to, and colonize the endotracheal intubation device. New strategies to prevent or reduce these nosocomial infections are greatly needed. We report here the study of a set of P. aeruginosa clinical isolates, together with specific mutants, regarding their adhesion on native and chemically modified poly(vinyl chloride) (PVC) surfaces from endotracheal intubation devices. The adhesion of the different strains to untreated PVC varied widely, correlating with several physico-chemical characteristics known to influence the attachment of bacteria to inert surfaces. The adhesion patterns were compared to the calculations obtained with the DLVO theory of colloidal stability. These results illustrate the importance of testing different clinical isolates when investigating bacterial adhesion. Oxygen plasma treatment of the PVC pieces yielded a hydrophilic surface and reduced the number of adhering bacteria by as much as 70%. This reduction is however unlikely to be sufficient to prevent P. aeruginosa colonization of endotracheal intubation devices.

Bacterial Adhesion↗

PubMed2001

Hydrogen desorption from sand-blasted and acid-etched titanium surfaces after glow-discharge treatment.

Hydrogen desorption from argon plasma-treated titanium implants with a high surface roughness was studied. Implants with a high surface roughness have shown an increase in mechanical stability in bone tissue and a different behavior of osteoblasts in vitro. High surface roughness was produced by grit blasting and acid etching, resulting in an increase of the sub-surface hydrogen concentration and the formation of a titanium hydride. After an argon plasma treatment the surface oxide, which always covers titanum surfaces exposed to an oxygen-containing environment, and some of the hydrogen were sputtered away, decreasing the hydrogen concentration in the sub-surface region. Nuclear reaction analysis was used to determine the hydrogen concentration as a function of depth. The total amount of sub-surface (down to a depth of < or = 2 microm) hydrogen remaining after plasma treatment decreased with increasing plasma intensity to below the levels observed in non-acid-etched samples (approximately 1-2%). Thermal desorption spectroscopy was used for desorption studies and investigation of H(2) desorption activation energies. With a surface oxide present, the onset of hydrogen desorption is at ca 400 degrees C, which is the oxide decomposition temperature in vacuum, with an activation energy of ca 2 eV/molecule of H(2). After plasma treatment, that is, without surface oxide present, the onset of desorption was observed at ca 300 degrees C and with an activation energy of ca 0.8 eV/molecule of H(2), indicating a bulk diffusion-limited desorption.

Acids↗

PubMed1998

Temperature-responsive size-exclusion chromatography using poly(N-isopropylacrylamide) grafted silica.

Silica-based packing materials induce non-specific interactions with proteins in aqueous media because of the nature of their surface, mainly silanol groups. Therefore, the silica surface has to be modified in order to be used as stationary phase for the High Performance Size-Exclusion Chromatography (HPSEC) of proteins. For this purpose, porous silica beads were coated with hydrophilic polymer gels (dextrans of different molecular weights) carrying a calculated amount of diethyl-aminoethyl groups (DEAE). Actually, as shown by HPSEC, these dextran modified supports minimize non-specific adsorption for proteins and pullulans in aqueous solution. Then, in order to change the pore size in response to temperature, temperature responsive polymer of poly(N-isopropylacrylamide) (PIPAAm) was introduced into the surface of dextran-DEAE on porous silica beads. The structure of these supports before and after modification was alternately studied by Scanning Electronic Microscopy (SEM) and Scanning Force Microscopy (SFM). An adsorption of radiolabelled albumin was performed to complete our study. Silica modifications by dextran-DEAE and PIPAAm improve the neutrality of the support and minimize the non-specific interactions between the solid support and proteins in solution. At low temperature, the support having PIPAAm exhibits a high resolution domain in HPSEC and finally permits a better resolution of proteins and pullulans. At higher temperature, hydrophobic properties of PIPAAm produce interactions with some proteins and trigger off a slight delay of their elution time.

Acrylic Resins↗

PubMed1997

Influence of surface treatments developed for oral implants on the physical and biological properties of titanium. (I) Surface characterization.

We present an investigation of the physico-chemical surface properties of commercially pure titanium coverslips which were submitted to various treatments designed to optimize their topography in view of application in oral implantology. The surface microroughness, chemical composition and water wettability were analyzed on titanium coverslips prepared by mechanical polishing, acid attack in HCl/H2SO4, after mechanical polishing or sandblasting, and titanium plasma-spray. The chemical composition has been measured by Auger electron spectroscopy. The treatments have no major influence on the surface chemical composition and all the samples display a composition approaching that of TiO2 with minor amounts of carbon, sulfur, silicon and calcium as impurities. The roughness has been measured by scanning force microscopy on an area of 20 microns x 20 microns on each sample. Polished titanium is smooth (peak-to-valley roughness 81 nm), whereas the acid-attacked surfaces exhibit a micro-roughness in the microns range (2100 nm for polished and acid attacked; 3600 nm for sandblasted and acid attacked) which is quite reproducible over large areas of the sample. The acid attacked samples present a subsurface layer which contains hydrogen below the native passivating oxide layer. Water wettability measurement shows that all surfaces are hydrophobic with a slightly higher contact angle for the acid attacked surfaces. The different treatments analyzed in this study essentially influence the surface roughness by preserving the chemical composition and the wettability properties of titanium native oxide surface layer.

Dental Polishing↗

PubMed1997

Influence of surface treatments developed for oral implants on the physical and biological properties of titanium. (II) Adsorption isotherms and biological activity of immobilized fibronectin.

The influence of titanium surface properties on in vitro adsorption isotherms of fibronectin, promotion of Staphylococcus aureus adhesion, and binding of a monoclonal antibody to the cell-binding domain of fibronectin was examined. Treatments producing different surface roughness were applied to a single side of commercially pure titanium coverslips, which was either mechanically polished (P), or polished and then acid attacked with H2SO4/HCl (PA), or sandblasted and then acid attacked (SLA), whereas the untreated side was blocked by an albumin coating layer. Incubation of the coverslips with concentrations of soluble 3H-labelled fibronectin increasing from 1 to 16 micrograms/ml led to the saturation of all surfaces with immobilized protein from 4 to 16 micrograms/ml. Promotion of S. aureus adhesion by fibronectin adsorbed on all surfaces and binding of the monoclonal antibody to its cell-binding domain was to some extent proportional to the amount of immobilized protein but also showed some minor differences between surfaces. More important material-related differences were observed when fibronectin adsorption isotherms were expressed as a function of the effective, roughness-corrected surface area, yielding amounts of immobilized fibronectin on the rough PA and SLA titanium surfaces which were 50% lower than those adsorbed on either smooth P or polymethylmethacrylate coverslips used as controls. In conclusion, surface treatments increasing the surface roughness of titanium do not increase, but may partly decrease in vitro adsorption of fibronectin. Despite adsorbing different amounts of fibronectin, both rough and smooth titanium surfaces promote normal expression of 2 major functional domains of this protein.

Adsorption↗

PubMed1996

Organic monolayers chemisorbed on gold observed by scanning probe microscopy.

Scanning force (SFM) and scanning tunneling (STM) microscopies are suitable techniques for the investigation of the structure of organic monolayers. Results are presented on thioalkane monolayers and thiolipid monolayers on gold. Both molecules attach covalently to the gold surface. STM images of the self assembled dodecanethiol layer display the molecular order of the film and reveal the presence of defects at the molecular scale. Moreover, domains and domain boundaries can be distinguished. Thiolipid layers on gold have been observed by SFM. The monolayer separates in solid-analogous star shaped domains and fluid-analogous domains. Imaging under water demonstrates the stability of the layer.

Journal Article↗

PubMed1996

Physical and biological effects of a surface coating procedure on polyurethane catheters.

Central venous catheters are widely used in clinical practice; however, complications such as venous thrombosis or infection are frequent. The physical and biological effects of a coating procedure designed to improve the blood-contacting properties of polyurethane central venous catheters (CVCs) were studied. The surface atomic composition of poly(vinyl pyrrolidone) (PVP)-coated or uncoated Pellethane single lumen CVCs was characterized by electron spectroscopy for chemical analysis (ESCA), which confirmed the presence of an oxygen-rich PVP layer on the former material. Topological analysis of both single and triple lumen CVCs by scanning force microscopy (SFM) revealed a very smooth surface in PVP-coated catheters compared to the more frequent surface irregularities found either in uncoated Pellethane or in four additional randomly selected, commercially available triple lumen polyurethane CVCs. The PVP-coated Pellethane showed a strong reduction in either fibrinogen or fibronectin adsorption compared to all other PVP-free polyurethane CVCs. This decreased protein adsorption led to a proportional reduction in protein-mediated adhesion of either Staphylococcus aureus or Staphylococcus epidermidis and in the binding of a monoclonal antibody directed against the cell-binding domain of fibronectin. Increased surface smoothness and hydrophilic properties of polyurethane CVCs might decrease the risk of bacterial colonization and infection.

Adsorption↗

PubMed1995

Bovine serum albumin conformation on methyl and amine functionalized surfaces compared by scanning force microscopy.

We investigated the adsorption of albumin on chemically modified gold surfaces by scanning force microscopy operating both in contact and noncontact mode. The surface modification was performed with thiol-based self-assembling molecules carrying amine or methyl groups. The albumin on the aminoethanethiol-coated gold formed a uniform layer and single molecules could be distinguished. On the dodecanethiol-coated surface the protein adsorbed in aggregates or single isolated molecules depending on the incubation time. The width of the albumin molecule on both surface was similar, but the height was much lower on the amine than on the methyl surface. This was interpreted as a difference in the conformation of albumin depending on the substrate, and could explain the promotion of cell adhesion on amine-treated polymers coated with albumin.

Adsorption↗

PubMed1995

Effect of toluene extraction on Biomer surface: II. An atomic force microscopy study.

The surface characterization of Biomer and extracted Biomer has been investigated using atomic force microscopy (AFM) in order to show the influence of extraction process on the morphology and local interactions which monitor surface properties at a molecular scale. The high viscoelasticity of these polymers provided by the soft segments makes AFM imaging in contact mode quite difficult, the scanning of the tip inducing artifacts on the surface. The rate, direction, and number of scans strongly influence this friction effect. The recording of force curves has shown that the extraction and conditions of drying can modify the interaction forces present at the polymer surface. Imaging of the extracted Biomer obtained with AFM in non-contact mode has revealed inclusion nodules embedded in an amorphous phase. This may be attributed to the migration at the surface of the non-eliminated poly(aminomethacrylate) additive.

Biocompatible Materials↗

PubMed1995

Effect of toluene extraction on Biomer surface: I. ESCA, ATR/FTIR, contact angle analysis and biological properties.

Biomer is a poly(ether-urethane-urea) block copolymer widely used as biomedical devices. Extraction process of this polymer has purified its surface of low molecular weight polyurethane chains and Santowhite Powder additive. ESCA and ATR/FTIR have suggested a homogenization of the polymer by enrichment of the first layers with poly(aminomethacrylate) additive after extraction. Therefore, the surface of the extracted Biomer exhibits a different wettability and biological response. The treatment causes a significant decrease in fibronectin adsorption and induces a reduction in Staphylococcus aureus adhesion.

Adsorption↗

PubMed1994

Influence of surface and protein modification on immunoglobulin G adsorption observed by scanning force microscopy.

Scanning force microscopy has been used successfully to produce images of individual protein molecules. However, one of the problems with this approach has been the high mobility of the proteins caused by the interaction between the sample and the scanning tip. To stabilize the proteins we have modified the adsorption properties of immunoglobulin G on graphite and mica surfaces. We have used two approaches: first, we applied glow discharge treatment to the surface to increase the hydrophilicity, favoring adhesion of hydrophilic protein molecules; second, we used the arginine modifying reagent phenylglyoxal to increase the protein hydrophobicity and thus enhance its adherence to hydrophobic surfaces. We used scanning force microscopy to show that the glow discharge treatment favors a more homogeneous distribution and stronger adherence of the protein molecules to the graphite surface. Chemical modification of the immunoglobulin caused increased aggregation of the proteins on the surface but did not improve the adherence to graphite. On mica, clusters of modified immunoglobulins were also observed and their adsorption was reduced. These results underline the importance of the surface hydrophobicity and charge in controlling the distribution of proteins on the surface.

Adsorption↗

PubMed1993

Preparation of isolated biomolecules for SFM observations: T4 bacteriophage as a test sample.

The T4 bacteriophage has been used to investigate protocols for the preparation of samples for scanning force microscopy in air, in order to obtaining reproducible images. The resolution of images and the distribution of bacteriophages on the substrate depends on the buffer type, its concentration, the surface treatment of substrate, and the method of deposition. The best imaging conditions for the phages require dilution in a volatile buffer at low ionic strength and adsorption onto hydrophilic surfaces. When imaging with the scanning force microscopy the quality of the images is influenced by the vertical and lateral forces applied on the sample and by the tip geometry.

Bacteriophage T4↗

PubMed1993

Solution structure and direct imaging of fibronectin adsorption to solid surfaces by scanning force microscopy and cryo-electron microscopy.

In this study, we present the scanning force and electron microscopic visualization of single molecules of fibronectin either frozen hydrated or adsorbed onto metallic and polymeric surfaces with different solid surface tensions. The surfaces were characterized by dynamic contact angle measurements, X-ray photo emission spectroscopy (XPS or ESCA) and scanning force microscopy. The proteins were prepared by fast protein liquid chromatography (FPLC) and characterized by gel electrophoresis. Protein films on surfaces were investigated by surface plasmon resonance spectroscopy and directly imaged by scanning force microscopy. The spreading of the adsorbed fibronectin revealed dependence on the chemical composition and the solid surface tension. Structure of fibronectin in solution as well as on solid interface appeared as an extended straight strand as obtained by imaging with electron and scanning probe microscopies. Imaging of DNA was performed by scanning force microscopy to test the accuracy and reproducibility of our measurements. The measured contour lengths were accurate and the larger widths were caused by convolution of the tip shape and sample. Frictional forces during the scan have been of significant contribution in the imaging mechanism. Moreover, this work demonstrated that scanning force microscopy can be used for mapping the orientation and organization of protein film adsorbed onto various surfaces at the nanoscale.

Adsorption↗

PubMed1992

[Regional coronary flow in ml/min measured with conventional coronarography].

We have developed a new method of measuring absolute coronary blood flow (CBF) in all major branches of the coronary circulation using computer analysis of conventional cineangiograms. A coronary cineangiogram is obtained in any biplane projections at 50 fps and digitized into a 512 x 512 x 8 matrix. The artery is reconstructed in 3D using the x-ray projection matrices calculated from a cube filmed in the same projections. All diameters along the artery are automatically determined. The arterial volume is calculated from the 3D reconstructed true arterial length and diameters. The absolute flow is obtained by dividing the arterial volume filled by contrast medium during the first cardiac cycle following the injection by the duration of that cycle. The method was validated in vivo by comparing LAD flow measured by angiography with great cardiac vein flow simultaneously measured by thermodilution. Ten patients were studied at baseline and during pacing-induced hyperemia at 100 and 120/min. Mean flow was 52.1 ml/min (range 28-93) by angiography and 51.5 ml/min (range 11-115; NS) by thermodilution. The two methods correlated well: r = 0.82, SE = 9.8 ml/min, n = 27, p less than 0.0001. Thus, absolute CBF can be measured by computer analysis of conventional biplane coronary cineangiograms.

Aged↗

PubMed1992

3D-reconstruction of coronary arteries in view of flow measurement.

An angiographic method for measurement of absolute coronary blood flow in patients was developed. It is based on 3D-reconstruction of the left or right coronary tree from digitized biplane coronary cineangiograms. The apparatus is presently composed of a 35 mm cinefilm projector with a video camera and a 512 x 512 x 8 bits image array processor controlled by a VAX-11/750 computer. First, the parameters of the two angiographic projections are determined in form of two 4 x 3 matrices from a pair of cineframes showing a 4 cm cube bearing markers. The cube is filmed after the coronary injection, with unchanged geometric configuration. The coronary arteries of interest are then 3D-reconstructed from a pair of cineframes showing them fully opacified. This allows to compute the intravascular volumes needed for flow determination. In vitro experiments showed that the obtained volume are reasonably accurate. For the measurement of coronary flow, the concentration of contrast medium along the involved arteries is computed (in arbitrary units) from two cineframes taken one (or two) cardiac cycle after onset of the injection. This yields a 'concentration-distance' curve per artery. The volume of fluid (contrast medium mixed with blood) which flows into the arteries during this (or these two) cardiac cycle is determined by applying a concentration threshold to the obtained concentration-distance curves. Measurements performed on a constant flow model were satisfying. Preliminary measurements in 12 patients showed that flow values obtained angiographically into the left anterior descending coronary artery correlate well with the values measured simultaneously by thermodilution in the great cardiac vein (Qangio = 0.83 x Qthermo + 16.1 ml, r = 0.87, n = 29).

Cineradiography↗

PubMed1992

Morphological difference between fibronectin sprayed on mica and on PMMA.

We have imaged with scanning force microscopy in air fibronectin (Fn) molecules sprayed on mica and on polymethylmetacrylate (PMMA), the latter being extensively used as biomaterial for implants. On mica we can observe small aggregates as well as individual molecules whose shape is influenced by the tip interaction during the scanning process, most of the isolated molecules showing a V-shape oriented in the scan direction. This indicates that the arms of the molecules are relatively free to move and the binding to the mica substrate is located near the disulfide bridge between the two subunits of the molecule. On the other side, when Fn molecules are sprayed on PMMA under the same conditions as for mica, we observe a thin network which we interpret as Fn molecules bound to each other. We relate our observation to the fact that mica is known to be strongly hydrophilic, which could reduce the Fn binding properties by interacting relatively strongly with molecules. On the other side, PMMA being hydrophobic, would interact less with molecules, leaving more binding sites for inter-molecular attachment.

Aluminum Silicates↗

PubMed1992

Scanning force microscopy and cryo-electron microscopy of tobacco mosaic virus as a test specimen.

In this study, tobacco mosaic virus (TMV) provides a resolution criterion for specimen preparation methods as well as for imaging parameters of the scanning force microscope (SFM). We present scanning force microscopic images of the virus embedded in 0.5% buffered phosphotungstic acid solution adsorbed on a freshly cleaved mica surface, and imaged under atmospheric conditions. Individual TMV particles were clearly identified with a characteristic shape of long rods of about 300 nm long and 60-70 nm in apparent width due to the geometric parameters of the tip. The structure of the virus was compared with cryo-electron microscopic data of vitrified suspensions observed to a resolution of 1.15 nm. Uncoated TMV particles were also deposited on evaporated titanium thin films and imaged by SFM.

Cryopreservation↗