A new method for preparing nonthrombogenic plastic surfaces

Protein adsorption on polyurethane catheters modified with a novel antithrombin-heparin covalent complex

Highly anticoagulant covalent antithrombin-heparin complex (ATH) was covalently grafted onto polyurethane catheters to suppress adsorption/activation of procoagulant proteins and enhance adsorption/activation of anticoagulant proteins for blood compatibility. Consistency of catheter coating was demonstrated using immunohistochemical visualization of ATH. The ability of the resulting immobilized ATH heparin chains to bind antithrombin (AT) from plasma, as measured by binding of (125)I-radiolabeled AT, was greater than that for commercially-available heparin-coated catheters, and much greater than for uncoated catheters. Complementary measurements of antifactor Xa (FXa) activity and plasma protein binding were also performed. Both ATH-coated and heparin-coated catheters demonstrated functional binding of exogenous AT. However, the ATH-coated catheters gave a trend towards elevated anti- FXa activities/AT binding ratios, consistent with the higher active pentasaccharide content in starting ATH. Western blot analysis of proteins adsorbed to catheters after incubation with rabbit plasma established protein binding profiles that showed AT and albumin as major plasma proteins adsorbed to ATH-coated catheters, while AT and altered forms of fibrinogen were major plasma protein species adsorbed to heparinized catheters.

Whole blood coagulation on protein adsorption-resistant PEG and peptide functionalised PEG-coated titanium surfaces

The aim of this study was to investigate whole blood coagulation on low blood plasma protein adsorbing surfaces. For this purpose, the polycationic graft copolymer poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), PLL-g-PEG grafted with a cell adhesive peptide containing the amino acid sequence -Arg-Gly-Asp- (RGD), and PLL-g-PEG with a control peptide -Arg-Asp-Gly- (RDG) were adsorbed onto titanium (oxide), forming stable monomolecular adlayers through electrostatic attraction. Free oscillation rheometry and complementary techniques were used to measure the coagulation time (CT) and other interactions of the surfaces with native whole blood, recalcified platelet-rich plasma (PRP), and recalcified citrated platelet-free plasma (PFP). The results show that the uncoated titanium surfaces (reference) activated platelets and quickly triggered the coagulation cascade via the intrinsic pathway, whereas the PLL-g-PEG surfaces displayed a prolonged CT, approximately 2-3 times longer compared to uncoated titanium. We hypothesise that blood coagulates outside the vascular system independent of low protein adsorption to or activation by surfaces, due to the absence of an active down-regulation of procoagulative processes by the vascular endothelium.

Surface modification of the polymers present in a polysulfone hollow fiber hemodialyser by covalent binding of heparin or endothelial cell surface heparan sulfate: flow characteristics and platelet adhesion

The present study addresses the problem of simultaneous surface modification of various polymers, i.e. polysulfone (PSU), polycarbonate (PC), and polyurethane (PU), which constitute the Ultraflux AV 600 S hollow fibre hemodialyser. An investigation was first made into six different chemical routes aimed at introducing carboxyl groups onto the surface of PSU, PC, and PU model polymers to which heparin (HE) or endothelial cell surface heparan sulfate (ESHS) was covalently bound via the reaction of residual amino groups and a coupling reagent. Carboxyl groups were introduced using three specific reactions based on their nucleophilic or electrophilic introduction into aromatic repeating units of the polymers and three non-specific carboxylation reactions, i.e. UV, heat or redoxactivation via nitrene or radical species. Concentrations of 1-20 nmol COOH groups per cm(-2) led to HE or ESHS surface concentrations corresponding to one or several layers. Two nonspecific carboxylation reactions followed by HE- or ESHS-coupling provided the lowest change in membrane pore structure according to cut off, clearance (urea, phosphate, maltose), ultrafiltration, and diafiltration assessments. In some cases the introduction of excess negatively-charged carboxyl groups and HE improved the flux properties of the modified membranes. The various methods were applied to the dialysis module. Platelet adhesion was not observed in the case of the ESHS-coating of PSU membrane at shear rates of 1050 s(-1), whereas HE and subendothelial matrix showed 56 and 100% coverage, respectively, under similar conditions. The coating of PSU or of other high-flux membranes by ESHS appears a promising method for improving membrane properties and to generate biocompatibility characteristics similar to those of natural blood vessels, i.e. inertness to platelet adhesion and no level effects for complement and intrinsic coagulation cascade activation. The ESHS coating may be used without anticoagulants.

Heparin-coated cardiopulmonary bypass circuits

The indications for heparin-coated extracorporeal circuits cannot be defined or limited at present. Clinical investigation remains at an early stage of development. In situations where the risk of systemic anticoagulation is high, this technology would seem to hold great promise. Examples include extracorporeal lung assist and resuscitation from accidental hypothermia. Some have also suggested the use of heparin-coated circuits for percutaneous bypass in cardiopulmonary resuscitation. A significant advantage might also accrue in noncardiac surgical procedures requiring cardiopulmonary bypass, such as complex cerebral aneurysm or arteriovenous malformation resections, resections of the tracheal carina, or bilateral lung transplantations. Its role in routine cardiac surgical procedures remains uncertain, but the work of von Segesser et al suggests a need for continued investigation in that setting using reduced levels of systemic anticoagulation. That endeavor will be greatly assisted by the recent development of heparin-coated cardiotomy reservoirs. Although heparin-coated circuits have been safely used for extracorporeal lung assist with little or no systemic anticoagulation, prospective studies are clearly needed to determine if this approach is advantageous, and it would seem appropriate to develop heparin coating for silicone-based membrane oxygenators.

Surface modification of polymeric biomaterials with poly(ethylene oxide), albumin, and heparin for reduced thrombogenicity

Appropriate surface modification has significantly improved the blood compatibility of polymeric biomaterials. This article reviews methods of surface modification with water-soluble polymers, such as polyethylene oxide (PEO), albumin, and heparin. PEO is a synthetic, neutral, water-soluble polymer, while albumin and heparin are a natural globular protein and an anionic polysaccharide, respectively. When grafted onto the surface, all three macromolecules share a common feature to reduce thrombogenicity of biomaterials. The reduced thrombogenicity is due to the unique hydrodynamic properties of the grafted macromolecules. In aqueous medium, surface-bound water-soluble polymers are expected to be highly flexible and extend into the bulk solution. Biomaterials grafted with either PEO, albumin, or heparin are able to resist plasma protein adsorption and platelet adhesion predominantly by a steric repulsion mechanism.

Preparation and ESCA characterization of poly(vinyl chloride) surface-grafted with heparin-complexing poly(amido amine) chains

By a simple process poly(amido-amine) chains have been grafted on the surface of poly(vinyl chloride). Grafted poly(vinyl chloride) is able to adsorb heparin, thus providing potentially non-thrombogenic surfaces. The grafting of poly(amido-amine), and the heparin adsorption have been studied by ESCA. It has been found that the total amount of grafted poly(amido-amine) depends on the molecular weight of the poly(amido-amine) used in the grafting reaction, but the amount of heparin adsorbed on the grafted material is relatively independent of the length of the poly(amino-amine) grafted chains.

Complications of angiography in children and means of prevention

In 267 consecutive angiographic examinations in children 14 thromboembolic complications occurred: following surgical exposure 8 complications in 14 cases and 6 complications in 253 percutaneous angiographies. The origin of thrombus during angiography has recently been clarified. Technical advances such as thin walled catheters, systemic heparinization and lately heparinized catheters decreased the complication rate significantly, no complication occurred among the last 153 examinations.

Heparinized catheters for long-term intraarterial infusion of 5-fluorouracil in liver metastases

A heparinized catheter was used for the regional infusion of 5-fluorouracil in seven patients with liver metastases. The hepatic artery was catheterized from the left brachial artery. The period of treatment varied from one to 13 weeks. Pull-out angiograms, obtained after eight catheterizations, revealed complete occlusion of the brachial artery in five and partial occlusion in three, although no patient had ischemic symptoms in the hand. Thus, heparinization of the catheter did not prevent thrombosis during long-term infusion therapy.

Thromboresistance and stability of a heparinized polymer

Untreated shunts and shunts heparinized according to a modification of the method of Eriksson et coll. were inserted between the femoral artery and vein in mongrels. Scanning electron microscopy of pieces excised at different time periods of exposure to blood was performed. The heparinized surface had excellent thromboresistant properties with no thrombus formation after 4 hours, while the untreated shunts were covered with platelets already within 20 min. The leakage of heparin in vitro was less than 3 per cent of the total wall-bonded heparin during 90 min.