Surface properties and hemocompatibility of alkyl-siloxane monolayers supported on silicone rubber: effect of alkyl chain length and ionic functionality.

Self-assembled monolayers of alkylsiloxanes supported on poly(dimethylsiloxane) (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface composition. The inner lumen of PDMS tubes were first treated with an oxygen plasma. The resultant oxidized surfaces were post-derivatized by reaction with alkyltrichlorosilanes to form the monolayer films. The alkyl chain lengths used were slightly longer than in a previous study, and this may alter the phase-state of the monolayer from liquid-like to crystalline. The chemical properties of the monolayer were controlled by varying the chemical composition of the alkyltrichlorosilanes used. Terminal functionalities included -CH3, -CF3, -COOH, -SO3H and -(CH2CH2O)4OH. Surface derivatization was verified with static contact angle measurements and X-ray photoelectron spectroscopy. Blood compatibility was evaluated using a canine ex vivo arterio-venous series shunt model. Surfaces grafted with hydrophobic head groups such as -CH3 and -CF3 were significantly less thrombogenic than the surfaces composed of ionic head groups such as -COOH and -SO3H. Surfaces enriched in -(CH2CH2O)4OH had an intermediate thrombogenicity. Silastic pump grade tubing and polyethylene tubing, used as controls, were found to be the least thrombogenic of all the surfaces tested.

Histopathologic evaluation of an expanded polytetrafluoroethylene-nitinol stent endoprosthesis in canine iliofemoral arteries.

PURPOSE: The authors assess a new ePTFE-nitinol stent for its long-term patency, healing, and properties of endothelialization. MATERIALS AND METHODS: Adult greyhounds (n = 18) underwent bilateral iliofemoral placement of an endoprosthesis (Hemobahn) consisting of a nitinol stent lined with an ultrathin expanded polytetrafluoroethylene (ePTFE) material. Histologic and quantitative morphometric analyses were performed on devices explanted at 2 weeks and 1, 3, 6, and 12 months. The source of endothelialization was examined in four additional devices modified by sealing either the proximal and distal ends or the entire graft with poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), a nonporous laminate to prevent potential transgraft endothelial cell migration. RESULTS: Device patency assessed with both intravascular ultrasound and histologic study showed minimal arterial stenosis, irrespective of implant duration. The neointima at less than 3 months consisted of fibrin and inflammatory infiltrate; at later time points, it was composed of mostly smooth muscle cells. Flow surfaces were more than 75% endothelialized by 3 months, which was nearly complete by 6 months. Modified endoprostheses entirely enveloped with FEP resulted in endothelialization of only the proximal and distal ends; the middle regions showed nonocclusive thrombi. Conversely, devices wrapped proximally and distally showed nearly complete endothelialization. CONCLUSIONS: This ePTFE-nitinol endoprosthesis demonstrated long-term patency at up to 1 year after implantation and showed early and nearly complete endothelialization by 6 months. The design promoted rapid endothelialization of flow surfaces, particularly in the midregion of the device possibly by transgraft migration.

Surface and blood-contacting properties of alkylsiloxane monolayers supported on silicone rubber.

Self-assembled monolayers of alkylsiloxanes supported on polydimethyl siloxane (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface chemistry. The inner lumen of PDMS tubes was first treated with an oxygen plasma. The resultant oxidized surfaces were postderivatized by reacting them with alkyltrichlorosilanes to form the monolayer films. The chemical properties of the monolayers were controlled by varying the head-group chemical compositions. Surface derivatization was verified using variable-angle X-ray photoelectron spectroscopy (XPS or ESCA). Blood compatibility was evaluated using a canine ex vivo arteriovenous series shunt model. Surfaces grafted with hydrophobic head-groups as -CH3 and -CF3 had significantly lower platelet and fibrinogen deposition than the surfaces composed of hydrophilic groups such as -CO2CH3, -(CH2CH2O)3COCH3, and -(OCH2CH2)3OH.

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.

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.

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.

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.

Anticoagulant effects of sulphonated polyurethanes.

Sulphonated polyurethanes have been shown to have excellent blood contacting properties. In this paper, similar polyurethanes which are water soluble have been investigated to determine their influence on thrombus formation. These polymers were shown to delay clotting times in the following ways: by direct complex formation between the polymer and thrombin; by interference with fibrin polymerization; and by complex interactions between polymer, thrombin, plasma antiproteases and fibrinogen in plasma.

Cataracts and cigarette smoking. The City Eye Study.

The City Eye Study is a nine year longitudinal prospective epidemiological study. During the first three year phase the study recruited 1029 volunteers, aged between 54 and 65 years, primarily from companies and organisations working in or around the City of London. The analysis of the first cohort data shows a significant association between nuclear lens opacities and moderate to heavy cigarette smoking. The Relative Risk for nuclear lens opacity and cigarette smoking ranges from 1.0 for past light-smokers through 2.6 for past heavy-smokers, to 2.9 for present heavy smokers.

Visual disability and home lighting.

13 men and 43 women (average age 76) attending a low-vision clinic with visual acuity of 6/18 (Snellen) or less had acuity measurements made under standard (measured) hospital conditions, under normal home conditions, and under home conditions with augmented lighting. Median levels of ambient lighting in the home were 1/10 of those in hospital, while levels for reading were 1/7. Augmented lighting at home (a 60 watt bulb in a small adjustable lamp) improved visual acuity in 82% of subjects, restoring all but 11% to the levels achieved in hospital or above. Improvement was unrelated to disease. General levels of lighting are often so poor in the homes of elderly people that the number of people functioning as "blind" is twice what it need be. Simple improvements to lighting would reduce the prevalence of "visual disability" (less than 6/18 Snellen) from 520/100,000 home-based adults to about 300.

Visual acuity at home and in eye clinics.

Most elderly visually disabled people have lower levels of visual acuity for both reading and getting about in their homes than would be inferred from clinic measurements. Even with optimum optical correction, performance can be much improved by simple modifications to existing facilities, individual advice, and in most cases the addition of a simple adjustable reading lamp.