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Biomedical subjects

S L Cooper

Publications and source records attributed to S L Cooper.

At least 55 records · Page 3Linked to original sources
PubMed1995

Use of adhesion-defective mutants of Staphylococcus aureus to define the role of specific plasma proteins in promoting bacterial adhesion to canine arteriovenous shunts.

We used an ex vivo canine arteriovenous shunt model, previously developed to study plasma protein adsorption and thrombogenesis on polymeric biomaterials, to define the role of host proteins in promoting adhesion of Staphylococcus aureus. Either polyethylene or polyvinyl chloride tubings were exposed to canine blood for 5, 15, or 60 min at a flow rate of 300 ml/min and then were flushed in phosphate-buffered saline (PBS), cut into 1.5-cm segments, and stored at -70 degrees C. After thawing, each segment was preincubated in 0.5% albumin in PBS to prevent nonspecific staphylococcal attachment to surfaces that were not exposed to blood. Each segment was then incubated with 4 x 10(6) CFU of [3H]thymidine-labelled S. aureus per ml for 60 min at 37 degrees C in an in vitro adhesion assay. Two site-specific mutants of S. aureus were tested: one specifically defective in adhesion to surface-bound fibronectin (FnAd-def) and the other defective in adhesion to fibrinogen (FgAD-def) [corrected]. Compared with their respective parental strains, the FgAd-def, but not the FnAd-def, mutant of S. aureus showed a strong (> 80%) decrease in attachment to ex vivo tubings. The adhesion of each strain of S. aureus onto polyethylene was consistently more than twofold higher than the adhesion onto polyvinyl chloride segments exposed to flowing blood for 5 or 15 min, but adhesion became similar to that on polyvinyl chloride after 60 min of exposure. In conclusion, the specific adhesion-defective mutants of S. aureus suggested that fibrinogen was the most active adhesion-promoting protein in a short-term blood-material interaction. The experimental approach described in this study should prove useful for screening materials thought to be resistant to protein-mediated staphylococcal adhesion and colonization.

Animals↗
PubMed1995

Quantitative comparison of clumping factor- and coagulase-mediated Staphylococcus aureus adhesion to surface-bound fibrinogen under flow.

The contributions of clumping factor and coagulase in mediating Staphylococcus aureus adhesion to surface-adsorbed fibrinogen have been quantified by using a new methodology and analysis. The attachment or detachment kinetics of bacteria were directly observed in a radial flow chamber with a well-defined laminar flow field and a spatially varying shear rate and were quantified by recursively scanning the chamber surface and counting cells via automated video microscopy and image analysis with a motorized stage and focus control. Intrinsic rate constants for attachment or detachment were estimated as functions of shear rate for the wild-type Newman strain of S. aureus and for mutants lacking clumping factor, coagulase, or both proteins on surfaces coated with plasma, fibrinogen, or albumin. Clumping factor, but not coagulase, increased the probability of attachment and decreased the probability of detachment of S. aureus on plasma-coated surfaces; however, both clumping factor and, to a lesser extent, coagulase increased the probability of attachment on the purified-fibrinogen-coated surface. All mutants were resistant to detachment on the purified-fibrinogen-coated surface, suggesting the possibility of an additional adhesion mechanism which was independent of coagulase or clumping factor and effective only for fully attached cells. Together, these results suggest that the presence of clumping factor plays the primary role in enhancing adhesion to surfaces with adsorbed fibrinogen, not only by enhancing the probability of cell attachment but also by increasing the strength of the resulting adhesion.

Bacterial Adhesion↗
PubMed1994

Synthesis, surface, and cell-adhesion properties of polyurethanes containing covalently grafted RGD-peptides.

In an attempt to improve endothelial cell adhesion and growth on a polyurethane copolymer, cell adhesive RGD-containing peptides were grafted to the polymer backbone. Two peptide grafting reaction schemes, including one-step and two-step approaches, were developed. FTIR and amino acid analysis confirmed that coupling of the peptide to the polyurethane backbone was achieved by both the one-step and two-step methods. However, the two-step approach showed a higher peptide coupling efficiency and resulted in better control of the orientation of the grafted peptide. The two-step reaction scheme was used to prepare Gly-Arg-Gly-Asp-Ser-Tyr (GRGDSY), Gly-Arg-Gly-Asp-Val-Tyr (GRGDVY), and Gly-Arg-Gly-Glu-Ser-Tyr (GRGESY) peptide-grafted polyurethanes with two different peptide densities (100 and 250 mumol/g polymer). Dynamic contact angle measurements indicated that the surfaces of the peptide-grafted polyurethanes were more hydrophilic than the starting and carboxylated versions of the precursor polyurethane. In addition, the surface hydrophilicity of the peptide-grafted polymers increased with increasing bulk peptide density. Electron spectroscopy for chemical analysis suggested that the grafted peptide was present at the polymer-air interface, in vacuo, for the peptide-grafted polyurethanes. The surface peptide density appeared to correlate with the incorporated peptide density in the bulk. In vitro endothelial cell adhesion experiments showed that, without the presence of serum in culture medium, the GRGDSY- and GRGDVY-grafted polyurethanes dramatically enhanced cell attachment and spreading compared with the starting, carboxylated, and GRGESY-grafted polymers. Increasing the peptide density from 100 to 250 mumol/g polymer for the GRGDSY- and GRGDVY-grafted polyurethanes resulted in an increase in cell attachment. With approximately the same peptide density (100 or 250 mumol/g polymer), the GRGDVY-grafted polymers supported more adherent cells than did the GRGDSY-grafted polymers. Similar trends were observed in the in vitro endothelial cell growth studies using culture medium containing serum and endothelial cell growth supplement. The GRGDSY- and GRGDVY-grafted polyurethanes promoted more cell growth than did the starting polyurethane. However, the presence of adhesive serum proteins and growth factor diminished the differences between the cell-adhesive peptide grafted polymers and the GRGESY-grafted polymers.

Amino Acid Sequence↗
PubMed1994

Effect of polyol molecular weight on the physical properties and haemocompatibility of polyurethanes containing polyethylene oxide macroglycols.

The physical properties and haemocompatibility of polyurethanes containing polyethylene oxide (PEO) of varying molecular weights but constant weight fraction of hard segment are investigated. The PEO molecular weights studied were 600, 1450 and 8000. Analysis of polyurethane phase separation and crystallinity using dynamic-mechanical analysis and differential scanning calorimetry show that the degree of phase separation and crystallinity increase with polyol molecular weight, but level off at the highest molecular weights. The degree of water absorption increases substantially with increasing PEO molecular weight, levelling off at the highest molecular weight. Tensile data show a maximum in extensibility at a polyethylene glycol (PEG) molecular weight of 1450, while ultimate strength increases with increasing segment length. When the materials are hydrated, there is a significant drop in the modulus, ultimate stress and ultimate elongation. Dynamic contact angle measurements show that surface hydrophobicity decreases as the soft segment molecular weight increases. Using electron spectroscopy for chemical analysis (ESCA) to determine the surface composition of these polyurethanes, it was found that the hard segment content at the surface increases as the polyol block length decreases. The haemocompatibility of these polyurethanes was investigated in an ex vivo canine blood-contacting model. Only for the shortest block length studied, PEG-600, are differences in blood compatibility observed. This material was found to be the most thrombogenic. The PEG-1450 sample shows comparable blood compatibility to PEG-8000.

Animals↗
PubMed1994

Blood-contacting properties of polydimethylsiloxane polyurea-urethanes.

A series of polyurethanes was synthesized from amino-terminated polydimethylsiloxane oligomers of two molecular weights. The oligomers had been extended with hexane diisocyanate to give internal urea linkages in the soft segment. These polymers have been shown to have higher tensile properties over similar polymers without the internal urea linkages due to the greater phase mixing and interfacial bonding between the hard and soft segment microdomains. The surface properties of these materials were evaluated by dynamic contact angle measurements and the blood compatibility by a canine ex vivo series shunt. The silicone-urea polyurethanes had favourable blood-contacting properties compared to a polyetherurethane. The polymers composed of the higher molecular weight silicone oligomers had the least platelet and fibrinogen deposition.

Animals↗
PubMed1994

Synthesis, characterization and ex vivo evaluation of polydimethylsiloxane polyurea-urethanes.

A series of segmented polydimethylsiloxane (PDMS) polyurea-urethanes was synthesized based on hexane diisocyanate modified polyether-PDMS soft segments. The hard segments consisted of 4,4'-methylene diphenylene diisocyanate, which was chain extended with 1,4-butanediol. The effect of chemical composition of the polyether-PDMS soft segments on the extent of phase separation, physical properties and surface properties was studied using a variety of techniques including dynamic mechanical analysis, tensile testing, X-ray photoelectron spectroscopy (XPS) and contact angle analysis. The polymers were also evaluated for their blood-contacting properties in a canine ex vivo model. The PDMS polyurea-urethanes containing polyether-PDMS soft segments showed three distinct phases: a PDMS-rich phase, a polyol soft segment-rich phase and a hard segment-rich phase. The tensile strength and modulus of these materials were not significantly lower compared to a polymer without PDMS in the soft segment. XPS revealed the surface enrichment of the hydrophobic PDMS component at the air-solid interface. Dynamic contact angle measurements indicated that the PDMS-based polyurea-urethanes possessed a hydrophobic surface in water. The PDMS polyurea-urethanes showed lower adherent platelet and fibrinogen deposition compared to a polymer without PDMS in the soft segment. Varying the amount of PDMS in the soft segment of these polymers did not reveal significant differences in their blood-contacting properties.

Animals↗
PubMed1993

Integrin receptors and platelet adhesion to synthetic surfaces.

The activation-independent and -dependent integrin receptors--glycoproteins GPIc-IIa (alpha 5-beta 1) and GPIIb-IIIa (alpha IIb-beta 3)--are involved in platelet adhesion and thrombus growth on damaged subendothelium through interactions with fibrinogen, fibronectin, von Willebrand factor, and other adhesive proteins. Because these receptors are used in normal in vivo hemostatic adhesion, they may also have a role for adhesion onto synthetic surfaces in the vasculature. Platelet adhesion in vitro was examined onto Formvar, glass, and four polyurethaneureas with various soft segment chemistries and surface properties. Platelets were pretreated with RGD peptides before and after adhesion. RGD peptide pretreatment inhibited spreading and close contact formation compared to treatment with saline or control RGE peptides, with no observable effect on the number of adherent platelets per area. High-voltage electron microscopy showed abnormally sparse and short microfilament structures with RGD peptide treatment, suggesting an indirect inhibition of actin filament formation. Video-enhanced light microscopy showed a cessation of spreading and a partial reversal of close contacts following RGD peptide application to adherent platelets. Because minimal amounts of plasma proteins are present in column-washed platelet suspensions, and as platelet secretion appeared to be minimal in these experiments, these observations suggest that RGD binding integrin receptors may function in platelet spreading even in the absence of exogenous ligand. As RGD peptides did not affect the numbers of adherent platelets, while producing substantial decreases in the extent of spreading, we suggest that platelet integrins, possibly GPIIb-IIIa, are involved in spreading on synthetic surfaces but not for initial adhesion.

Blood Platelets↗
PubMed1993

Effect of polyol type on the surface structure of sulfonate-containing polyurethanes.

Polyurethanes based upon polytetramethylene oxide (PTMO) as the polyol and derivatized with propyl sulfonate functionality pendant from the urethane nitrogen have previously been shown to possess good blood-contacting properties. Other investigators have shown that sulfonated polyurethanes containing polyethylene oxide (PEO) as the soft segment are much more thrombogenic than those containing PTMO as the soft segment. In this article, the surface properties of sulfonated polyurethanes based upon either PTMO or PEO are compared. Dynamic contact angle measurements show a significant decrease in the receding angles of the sulfonated PTMO-containing polyurethane as compared to its nonsulfonated precursor polymer. No significant difference is seen between the receding contact angles of either the sulfonated PEO-based polyurethane or its nonsulfonated analog. Variable-angle electron spectroscopy for chemical analysis (ESCA) studies of sulfonated PTMO-based polyurethane performed at room temperature show that there is a significant decrease in sulfur content at the surface. In contrast, the sulfonated PEO-based polyurethane showed little change in sulfur content with take-off angle. Finally, ESCA studies of freeze-dried surfaces show a significant increase in sulfur near the surface of the sulfonated PTMO-based polymer as compared to vacuum-dried samples but show no such increase for the sulfonated PEO-based polyurethane. It is suggested that the ability of the sulfonate functionality to be expressed at the surface may explain the observed differences in blood compatibility between the sulfonated polyurethanes based upon polyols of varying hydrophilicity.

Absorption↗
PubMed1993

Effect of polyol type on the physical properties and thrombogenicity of sulfonate-containing polyurethanes.

Polyetherurethanes (PEUs) based on polytetramethylene oxide (PTMO) as the polyol, and derivatized with propyl sulfonate functionality, have previously been shown to possess antithrombotic properties. In this article, the bulk physical properties of sulfonated and nonsulfonated polyurethanes containing either polyethylene oxide (PEO) or PTMO as the soft segment are studied. The in vitro shape-change of platelets in contact with these surfaces, and their ex vivo blood-contacting response are also investigated. It was found that PEO-base was physically weaker than PTMO-base, which is attributed to a lower degree or phase separation in the former. In the dry state, sulfonation enhanced the physical properties for PTMO-containing polyurethane (PTMO-SO3-0.20), but weakened the PEO-containing polyurethane (PEO-SO3-0.15). In vitro platelet spreading studies showed the lowest degree of platelet spreading and also the lowest platelet density on PEO-base, while platelet spreading and density on the other three materials and polyethylene (PE) was greater. The thromboresistance of these materials was evaluated using a canine arteriovenous series shunt ex vivo. It was determined that PTMO-SO3-0.20 was the least thrombogenic, followed by both PEO-base and PEO-SO3-0.15, and that PTMO-base was the most thrombogenic.

Alkanesulfonic Acids↗
PubMed1993

Effect of protein adsorption on the blood-contacting response of sulphonated polyurethanes.

Polyurethanes which are grafted with propyl sulphonate functionality have excellent blood-contacting properties. In a canine ex vivo series shunt experiment, very low platelet deposition was observed on these materials and those platelets which were adherent remained unspread. In contrast to this, large amounts of fibrinogen, of the order of a monolayer or greater, were deposited on these surfaces in this ex vivo experiment. This led to the hypothesis that perhaps the deposited fibrinogen did not retain its platelet-adhesive activity. In this paper, we investigate the possibility that these materials exert their antithrombotic effects through the adsorbed protein layer. Protein adsorption kinetics and isotherms on these sulphonated polyurethanes are determined. Multilayer protein adsorption or absorption into the hydrogel-like materials is found for each of the proteins studied, and the greatest amounts of protein are seen on the most highly sulphonated polyurethanes. Further, the blood-contacting response of these materials is investigated after pre-conditioning with either fibrinogen, fibronectin or albumin. When these materials are pre-adsorbed with either fibrinogen or fibronectin, a very thrombogenic response was observed, which suggests that the platelet-adhesive activity of these proteins is not being reduced. Pre-adsorption of albumin did not improve the thromboresistance of these surfaces.

Adsorption↗
PubMed1993

Surface characterization and platelet adhesion studies of plasma-sulphonated polyethylene.

Canine platelet adhesion on sulphur dioxide and allyl phenyl sulphone plasma-treated low density polyethylene (LDPE) was studied. Both 5 W plasma excitation energy-treated surfaces showed the highest S:C atomic ratio by ESCA analysis. Surface hydrophilicity increased drastically after plasma treatment. However, surface hydrophilicity decreased with time. This might be due to the diffusion of the hydrophilic functional groups into the bulk of the material and/or the migration of low molecular weight hydrocarbon species into the surface region. The allyl phenyl sulphone plasma-treated LDPE was less platelet-activating in terms of platelet adhesion and spreading and was independent of the different plasma excitation energy levels used. Sulphur dioxide plasma-treated LDPE showed a higher level platelet activation than the untreated LDPE. Among the sulphur dioxide plasma-treated LDPE samples, the sample prepared using the 5 W excitation energy was less platelet-activating than the samples treated by higher plasma excitation energies.

Allyl Compounds↗
PubMed1993

Effect of hand segment chemistry and strain on the stability of polyurethanes: in vivo biostability.

We investigated four polyurethanes that were synthesized with different hard segments and four commercial polyurethanes for in vivo biostability. The four polyurethanes with the varying hard segments were based on a 3:2:1 mole ratio of methylene diphenylene diisocyanate (MDI) or methylene dicyclohexane diisocyanate (H12MDI), butanediol (BD) or ethylene diamine (ED) and polytetramethylene oxide (PTMO) (MW = 1000). Four commercial polyurethanes were also used: Biomer, Pellethane, Medtronic experimental C-19 (C-19) and Medtronic experimental C-36 (C-36). Films of the polymers were implanted subcutaneously in rats for up to 12 wk to assess their biostability. Polymer films were implanted either with a 100% strain applied or in the unstrained state. Measurement of tensile properties, molecular weight and surface properties before and after implantation assessed the stability of each of the polymers. Surface cracking was observed with scanning electron microscopy and the extent and depth of cracking were determined. Pellethane, C-19 and C-36 showed the least evidence of degradation, although all underwent strain-induced phenomena that decreased their tensile elongation when an external force was applied. After implantation, the BD chain-extended polymers retained their tensile properties better than ED chain-extended polymers. H12MDI-based polyurethanes were more susceptible to surface cracking and molecular weight changes than MDI-based polyurethanes, possibly due to the lack of a crystallizable hard segment.

Animals↗
PubMed1993

Effects of oligoethylene oxide monoalkyl(aryl) alcohol ether grafting on the surface properties and blood compatibility of a polyurethane.

A series of oligoethylene oxide monoalkyl(aryl) alcohol ethers was grafted on to the backbone of a polytetramethylene oxide (PTMO)-based polyurethane, in an attempt to improve its biocompatibility. Each polyurethane contained a different pendant chain grafted to the urethane nitrogen atoms. The grafted chains consisted of various short lengths of hydrophillic oligomeric poly(ethylene oxide) (PEO) spacer segments and alkyl/aryl hydrophobic terminal groups. By using the 1H-NMR (nuclear magnetic resonance) technique, the extent of grafting was found to range from 7 to 12 mol% substitution of the urethane hydrogen groups. The surface properties of these materials were evaluated using high-vacuum, air-equilibrated and water-equilibrated methods. X-ray photoelectron spectroscopy (XPS) and static and dynamic contact angle experiments were performed. XPS showed that all of the grafted polyurethane surfaces contained higher ratios of C1s to O1s than the base polyurethane. These C:O contents correlate with the C:O ratios of the grafted chains. Dynamic contact angle analysis showed larger contact angle hysteresis for the grafted polyurethanes. The grafted polyurethanes generally exhibit lower complement activation, measured by an in vitro assay for C3a. A canine ex vivo arteriovenous series shunt was used to monitor platelet and fibrinogen deposition on these polymers. The incorporation of short ethylene oxide spacer segments with terminal C18 linear alkyl chains resulted in an improved short-term (up to 15 min) blood compatibility compared to the underivatized polyurethane. At longer blood contact times, all the grafted polyurethanes were more thrombogenic than the base polyurethane. In addition, there was no observable correlation between the material surface properties and the blood contact response.

Absorption↗
PubMed1993

Fibronectin adsorpton kinetics on phase segregated polyurethaneureas.

The kinetics of fibronectin (FN) adsorption upon three polyurethaneureas (PUU) were measured by Fourier transform infrared spectroscopy. The three polymers had soft blocks composed of polydimethylsiloxane (PDMS), polytetramethyleneoxide (PTMO), and polyethyleneoxide (PEO). On each polymer, the amount of adsorbate increased proportional to the square root of time, but the rates were less than that predicted for purely diffusion controlled adsorption. Adsorption rate constants and sticking coefficients (the fraction of encounters with the surface which result in adsorption) were calculated from the data. The adsorption rate constants are 4.8 x 10(-4), 1.3 x 10(-4), and 2.5 x 10(-5) cm/s on PDMS-PUU, PTMO-PUU and PEO-PUU respectively. The rate constants and sticking coefficients fall within the range of previously reported values for other protein/polymer systems. The sticking coefficients correlate in general with the amount of FN adsorbed at 120 min, and with the extent of conformational change of the adsorbed protein.

Adsorption↗
PubMed1993

Surface properties of RGD-peptide grafted polyurethane block copolymers: variable take-off angle and cold-stage ESCA studies.

Variable take-off angle and cold-stage ESCA measurements were utilized to analyze the surface composition of five polyurethane block copolymers. The polymers studied included a PTMO-polyurethane control, a carboxylated version of the control polyurethane, and three different peptide grafted (GRGESY, GRGDSY, and GRGDVY) polyurethanes. On dry samples the nitrogen signal detected using ESCA decreased with increasing take-off angle (i.e. as the specimen was probed closer to the surface) for all five polymers. This was believed to be due to the depletion of nitrogen-containing urethane hard segments at the surface. For all five polymers, the surface nitrogen concentration, associated with the hard segment, increased upon hydration. A greater increase of nitrogen concentration was observed for the peptide grafted polymers which suggests that grafting of the hydrophilic peptides to the polyurethane augments the hard segment enrichment at the surface upon hydration. Upon dehydration, the nitrogen concentration decreased for all five polymers suggesting migration of the more hydrophobic PTMO soft segment to the surface. In vitro endothelial cell adhesion showed an increase of cell attachment on prehydrated RGD-containing peptide grafted polyurethanes, but not on the other polymers. This result suggests an enhancement of peptide density at the aqueous interface, in good agreement with the ESCA studies.

Amino Acid Sequence↗
PubMed1992

The ex vivo effect of preadsorbed vitronectin on platelet activation.

The activation of ex vivo canine platelets by preadsorbed vitronectin (VN) was sensitive not only to the polymer substrate utilized but also to the adsorption conditions employed. Lower levels of maximal platelet deposition were obtained for VN-coated silicone rubber (SR) than for other VN-coated substrates with comparable levels of adsorbed VN, but this effect was diminished with increased residence time of VN on the SR surface. Submonolayer and monolayer surface concentrations of VN elicited similar maximal levels of platelet deposition at both short (less than 3 h) and long (greater than 12 h) residence times, but thrombi were larger and more dense for the submonolayer surface concentrations. VN was also more effective in forming thrombi when adsorbed sequentially before albumin instead of after albumin. To further examine these differences in the nature of adsorbed VN between substrates and adsorption conditions, sodium dodecyl sulfate (SDS) elutability measurements and Fourier transform infrared spectroscopy with attenuated total reflectance optics (FTIR-ATR) evaluations of the adsorbed protein were performed. An SDS solution was able to remove a greater percentage of the VN which was adsorbed to a submonolayer than a monolayer surface concentration when SDS displacement was initiated immediately after adsorption was terminated. However, if the adsorbed protein was allowed to reside on the surface for a length of time before the introduction of the SDS displacing media, a greater percentage of the monolayer surface concentration was removed. The submonolayer surface concentration may be better able to increase its strength of contact with the surface during the added residence time than the monolayer surface concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗
PubMed1992

Thrombus deposition on polyurethanes designed for biomedical applications.

Thrombogenicity was assessed by measuring the amount of 111In-platelets and 125I-fibrinogen deposited on the inner luminal surface of six polyurethanes for up to 60 min of blood contact in a canine ex-vivo shunt model. Commercial and laboratory synthesized polymers were examined. Two of the commercially synthesized polyurethanes (Biostable PURs) do not contain ether linkages in the polymer backbone and have previously shown resistance to oxidative and hydrolytic degradation. Static contact angle measurements, dynamic contact angle measurements, and ESCA were used to characterize the surfaces of these polyurethanes. The effectiveness of an acetone extraction used to remove extrusion waxes from Pellethane 2363-80A was similarly studied. Both Pellethane 2363-80A and the ether-free materials had relatively nonthrombogenic surfaces, as indicated by low platelet and fibrinogen deposition, making them potentially good candidates for biomedical applications.

Animals↗