Antithrombogenic heparin-bound polyurethanes

Recent advances in heparinization of polymeric membranes for enhanced continuous blood purification

Continuous blood purification technology such as hemodiafiltration has been used worldwide for saving patients suffering from severe diseases or organ function failure, especially in the intensive care unit and emergency setting. The filters as core devices are commonly made of polymer materials as hollow fiber membranes. However, the membrane is often inductively blocked by blood clot formation due to its interactions with blood components. Heparin is the anticoagulant often used in clinical practice for anti-coagulation. Recently, heparin is also employed to modify the hollow fiber membranes either chemically or physically to improve the filtration performance. This review summarizes recent advances in methodology for surface heparinization of such hollow fiber membranes, and their filtration performance improvement. The review also provides expert opinions for further research in this rapidly expanding field.

Antithrombogenic Poly(vinyl chloride) with Heparin- and/or Prostaglandin I2-Immobilized in Hydrogels

Poly(vinyl chloride) (PVC) with heparin- and/or prostaglandin I2 (PGI2)- immobilized on crosslinked polyacrylamide hydrogels were prepared by the ad dition of the dry hydrogels to a PVC tetrahydrofuran solution. Immobilized heparin was found to be continuously released from the PVC matrix at 37 ° C in a physiological saline. Antithrombogenic activity of PVCs with heparin and/or PGI2 was evaluated by activated partial thromboplastin time (aPTT), whole blood clotting time, and inhibition of platelet aggregation. The heparin- immobilized PVC's exhibited excellent anticoagulant activity and the PGI2 immobilized PVC's completely inhibit platelet aggregation of human blood after sitting for 46 h in a physiological saline.

Synthesis and Evaluation of Heparinized Biocompatible Materials Using Heparin/Surface-Active Compound Complexes

Heparin, an antithrombogenic mucopolysaccharide, forms com plexes with lecithin and other surface-active compounds (SAC). The complexes are soluble in organic solvents. The heparin/SAC complexes have antithrombo genic activity similar to heparin. Heparinized materials, in which the heparin/SAC complexes were used, showed an excellent in vitro nonthrombo genicity. The heparinized materials do not influence in vitro cell growth and showed an excellent biocompatibility.

Dual-functional anticoagulant and antibacterial blend coatings based on gemini quaternary ammonium salt waterborne polyurethane and heparin

A simple design of the dual-functional anticoagulant and antibacterial blend coatings with controlled release of heparin.

Micropattern-immobilization of heparin to regulate cell growth with fibroblast growth factor

Heparin was immobilized on a polystyrene plate in a specificpattern by photolithography. Heparin was coupled with azidoaniline. Thederivatized heparin was cast on the polystyrene plate from aqueoussolution. After drying, the plate was photo-irradiated in the presence of aphotomask. The micropatterning was confirmed by staining with a dye,ethydium bromide. Since heparin has negative charges, the cationic dyewas adsorbed on the regions where heparin was immobilized. In thepresence fibroblast growth factor (FGF), the growth of mouse fibroblastSTO cells was enhanced only on the heparin-immobilized regions. Thisresult indicated that micropattern-immobilized heparin activated FGF forcell growth activity.

In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 degrees C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.

Interaction of blood components with heparin-immobilized polyurethanes prepared by plasma glow discharge

The blood compatibility of poly(ethylene oxide) (PEO)-grafted and heparin (Hep) immobilized polyurethanes was investigated using in vitro plasma recalcification time (PRT), activated partial thromboplastin time (APTT), platelet adhesion and activation, and peripheral blood mononuclear cell (PBMC) adhesion and activation. In the experiment with plasma proteins, the PRT of the polyurethane (PU) surface was prolonged by PEO grafting and further prolonged by heparin immobilization. The APTT was prolonged on PU-Hep, suggesting the binding of immobilized heparin to antithrombin III. The percentage of platelet adhesion on PU was not much different from that on acrylic acid- and PEO-grafted PUs (PU-C, PU-6, PU-33), yet was substantially decreased by heparin immobilization (PU-6-Hep, PU-33-Hep). The release of serotonin from adhering platelets was slightly suppressed on PEO-grafted PUs yet significantly suppressed on heparin-immobilized PUs. In the PBMC experiments, the adhesion and activation of the cells were significantly suppressed on heparin-immobilized PUs, and the amount of interleukin-6 (IL-6) released from PBMCs stimulated with surface-modified PUs decreased with a decrease in PBMC adhesion.

Gradient micropattern immobilization of heparin and its interaction with cells

Heparin was immobilized on a polystyrene plate in a graded micropattern by photolithography. The micropattern was confirmed by staining with brilliant green. In the presence of basic fibroblast growth factor (bFGF), the growth of NIH3T3 cells was enhanced only in the heparin-immobilized regions. This result indicated that gradient-micropattern-immobilized heparin activated bFGF for cell growth. In addition, the growth of cells was found to be affected by the surface density of immobilized heparin. The surface density was regulated by a gap length of 2 microm-width stripes immobilized with heparin. Although a high density (a region having short gap length) of immobilized heparin suppressed the cell growth in the absence of bFGF, it enhanced cell growth in the presence of bFGF. The dependence of cell function on the density of immobilized heparin was visualized by gradient-micropattern-immobilization.

In vitro study of blood-contacting properties and effect on bacterial adhesion of a polymeric surface with immobilized heparin and sulphated hyaluronic acid

The blood-contacting properties and the effect on bacterial adhesion of a material based on polyurethane and poly(amido-amine) (PUPA), both in its native form and with the anticoagulant molecules heparin or sulphated hyaluronic acid (HyalS3.5) electrostatically bonded to its surface, were evaluated and compared in vitro. The presence of the biological molecules on the surface was revealed by a dye test and ATR/FTIR analysis. Bound heparin was found to maintain its physiological action, in terms of thrombin inactivation, as well as did free heparin. Moreover, it reduced the degree of platelet adhesion. On the contrary, bound HyalS3.5 lost its anticoagulant activity, though it reduced platelet adhesion. The number of platelets on both modified surfaces was low. Their shape distribution, as determined by SEM, did not differ significantly on the two modified surfaces or with respect to the bare PUPA surface. HyalS3.5 and heparin also inhibited adhesion of Staphylococcus epidermidis to the material. A possible relationship between the platelet and bacterial adhesion is ascribed to the mediating role of plasma proteins.

Micropattern immobilization of polysaccharide

Two types of polysaccharides, sulfated hyaluronic acid and heparin, were pattern-immobilized on a poly(ethylene terephthalate) and polystyrene film, respectively, in a specific pattern by photolithography. Sulfated hyaluronic acid was prepared from hylaronic acid by the treatment of sulfur trioxide/pyridine complex. Heparin was purchased and used without further treatment. The polysaccharides were coupled with azidoaniline. The derivatized polysaccharides were cast on a film from aqueous solution. After drying, the film was photo-irradiated in the presence or absence of a photomask. The micropatterning was confirmed by staining with a cationic dye. Platelet adhesion was reduced on the sulfated hyaluronic acid-immobilized areas. The immobilized sulfated hyaluronic acid significantly reduced thrombus formation. On the other hand, cells were cultured on the heparin-immobilized film. In the presence of fibroblast growth factor (FGF), the growth of mouse fibroblast STO cells was enhanced only on the heparin-immobilized regions. This result indicated that micropattern-immobilized heparin activated FGF for cell growth activity.

Heparin-coated bypass circuits (Carmeda) suppress the release of tissue plasminogen activator during normothermic coronary artery bypass graft surgery

OBJECTIVES

To study fibrinolysis in a homogeneous first-time coronary artery bypass surgery (CABG) population in whom heparin-coated circuits were used.

DESIGN

A prospective, blinded, randomized, placebo-controlled study.

SETTING

A university hospital, tertiary care, intraoperative and postoperative intensive care unit.

PARTICIPANTS

Twenty-one adult elective primary CABG patients.

INTERVENTIONS

Randomized circuit-type centrifugal pump, membrane oxygenator, rigid cardiotomy reservoir, either placebo (n = 10) or heparin-coated (n = 11) (Carmeda; Medtronic Inc., Anaheim, CA).

MEASUREMENTS AND MAIN RESULTS

Blood samples were analyzed for tissue plasminogen activator (TPA) activity, TPA antigen, plasminogen activator inhibitor-1 (PAI-1) activity, prothrombin complex F1.2, and antithrombin III (AT-III) at the following times: before cardiopulmonary bypass (CPB), during CPB (30 and 60 minutes), post-CPB, and day 1 postsurgery. TPA activity and antigen increased fivefold in the placebo group during CPB, whereas it did not even double in the heparin-coated group. PAI-1, F1.2, and AT-III were not different between groups.

CONCLUSIONS

Heparin-coated CPB circuits reduced TPA release in this homogeneous CABG population with routine heparin/protamine management.

In vitro blood compatibility of functional group-grafted and heparin-immobilized polyurethanes prepared by plasma glow discharge

Blood compatibilities of functional group-grafted and heparin-immobilized polyurethanes (PUs) were investigated using in vitro thrombus formation, plasma recalcification time (PRT), activated partial thromboplastin time (APTT), platelet adhesion and activation, and peripheral blood mononuclear cell (PBMC) activation. In the experiment with plasma proteins, PRT was shortened on amine group-grafted PU (PU-NH2) but prolonged on heparin-immobilized polyurethane (PU-Hep) when compared to PU control. APTT was significantly prolonged on PU-Hep, suggesting the binding of immobilized heparin to antithrombin III. The percentage of platelet adhesion was slightly increased by the introduction of functional groups such as carboxylic acid and primary amine on PU surfaces, but significantly decreased by the immobilization of heparin on the same substrate. The percentage of serotonin released from platelets adhered on surface-modified PUs was increased with increase of platelet adhesion. In the PBMC experiment, cells adhered less on heparin-immobilized PUs than on functional group-grafted PUs, and the production levels of tumour necrosis factor mRNAs from the cells stimulated by heparin-immobilized PU (PU-N-Hep) were smaller than those by the other substrates.

Interaction of heparin with amphiphile assemblies and biocompatibility of the heparin complexes

Addition of heparin to preformed vesicles of a cationic surface-active compound, dioctadecyldimethylammonium bromide (DODAB), resulted in fast precipitation of the heparin/DODAB complex. On the other hand, heparin stabilized the vesicle composed of dipalmitoyl L-alpha-phosphatidylcholine (DPPC) which is a neutral lipid. However, DPPC precipitated with heparin by the addition of a small amount of stearylamine (SA), which is a cationic substance. Differential scanning calorimetry of the heparin/amphiphile mixtures showed that the heparin/DODAB complex possess a structure different from that of the original DODAB vesicle. The structure of the DPPC vesicle was unaffected by the addition of heparin, while the structure of the heparin/DPPC-SA complex was found to be different from that of the DPPC-SA vesicle. The interaction of heparin with vesicles depended on the nature of amphiphiles. Heparin was solubilized in organic solvent when complexed with DODAB or DPPC-SA vesicles. Polyurethaneurea membranes blended with heparin/DODAB or heparin/DPPC-SA complexes were highly nonthrombogenic, but somewhat cytotoxic.

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.

Synthesis and nonthrombogenicity of fluoroalkyl polyetherurethanes

New polyetherurethanes carrying fluoroalkyl substituents in the side chains were synthesized from N,N-di(hydroxyethyl)heptadecafluorooctyl-sulfonamide (a chain extender), 4,4'-disocyanatodiphenylmethane, and poly(tetramethylene glycol). Various kinds of polyetherurethanes having different tensile properties were prepared by changing the content of fluoroalkyl chain extender or the molecular weight of poly(tetramethylene glycol). The surface of a film made from the fluoroalkyl polyetherurethane was strongly water-repulsive. The in vitro thrombus formation on the fluoroalkyl polyetherurethanes was reduced by increasing the content of chain extender for the same molecular weight of poly(tetramethylene glycol). Protein adsorption, platelet adhesion, and platelet activation on the fluoroalkyl polyetherurethanes were also investigated.

Synthesis and interactions with blood of polyetherurethaneurea/polypeptide block copolymers

Polyurethane/polypeptide block copolymers were synthesized. Infrared spectroscopy and differential scanning calorimetry revealed that in the block copolymers both segments undergo phase-mixing, while in polyurethane/polypeptide blend both components undergo phase-separation. Contact angle measurement showed that in the block copolymers polyurethane segments tended to appear on the membrane surface, whereas in polyurethane/polypeptide blend polypeptide components appeared on the membrane surface. In vitro nonthrombogenicity of the block copolymers was similar to that of homopolymers or polymer blends, though adhesion and deformation of platelets were suppressed on the block copolymer membranes.

Synthesis and nonthrombogenicity of polymer membrane with surface-graft polymers carrying thrombin inhibitor

An acrylamide derivative of a thrombin inhibitor was synthesized and graft polymerized to the surfaces of polymer membranes. The thrombin-inhibitor activity was unaffected by the introduction of an acryloyl group. The surface-graft membrane deactivated thrombin markedly and suppressed adhesion of platelets, resulting in a high nonthrombogenicity. Immersion of polymer membranes blended with the thrombin inhibitor in phosphate-buffered saline for 10 d resulted in the loss of nonthrombogenicity, while the polymer membranes grafted with the thrombin inhibitor derivative maintained the nonthrombogenicity over a long period.

Non-thrombogenicity by novel surface modification methods

Three novel methods, recently developed by us, for the synthesis of non-thrombogenetic materials were reviewed. The first was the utilization of poly(vinyl sulfonate) as a heparinoid and a newly synthesized polymerizable-thrombin-inhibitor. The chemicals were grafted onto the surfaces of materials. The second was the use of thrombin-substrate-analog peptide. The immobilized peptide was decomposed by blood coagulation factors and inhibited thrombus formation on the surface. The third method was the enhancement of endothelialization by immobilization of bio-signal molecules. The immobilized biosignals remarkably accelerated the growth of endothelial cells.

Synthesis of photoreactive poly(ethylene glycol) and its application to the prevention of surface-induced platelet activation

Photoreactive poly(ethylene glycol) (PEG) was synthesized by reacting 4-fluoro-3-nitrophenyl azide (FNPA) with sodium salt of PEG. The synthesized 4-azido-2-nitrophenyl PEG (ANP-PEG) was characterized by 1H-NMR, IR, and UV spectroscopy. ANP-PEG was grafted to dimethyldichlorosilane-coated glass (DDS-glass) by photolysis without any premodification of the surface. The effects of various grafting factors, such as the polymer adsorption time, concentration of ANP-PEG, and UV irradiation time, on the PEG grafting efficiency were examined. The PEG-grafted DDS-glass was characterized by measuring surface free energies, surface-induced platelet activation, and the relative amount of PEG grafted on the surface using electron spectroscopy for chemical analysis (ESCA). Platelet adhesion and activation was analyzed by measuring the number and spread area of adherent platelets. The results showed that ANP-PEG had to be adsorbed onto DDS-glass for at least 12 h before photolysis for the maximum grafting efficiency. No platelets could adhere to the PEG-grafted DDS-glass, if the bulk concentration of ANP-PEG in the adsorption solution was between 1 mg/mL and 10 mg/mL. Above 10 mg/mL, platelet activation gradually increased and reached the maximum at 30 mg/mL. Our data indicate that the grafting of ANP-PEG requires careful control of the grafting conditions and that the grafted PEG can prevent surface-induced platelet activation.

Chemical methods for improving the haemocompatibility of synthetic polymers

Synthetic high polymers differ widely in their interactions with blood, and unfortunately polymers offering promising combinations of mechanical properties for prosthetic applications are rarely those with the highest haemocompatibility. This paper is concerned with methods available for reducing the thrombogenicity of polymer surfaces but does not include discussion of other important issues such as complement activation. A brief review of the processes occurring in blood coagulation is followed by a statement of the chief methods for improving haemocompatibility: (1) coupling anti-platelet agents (e.g. prostaglandins or analogues) or anti-coagulants such as heparin to the surface: (2) 'passivation', for example by increasing the hydrophilicity of the surface: (3) coupling an inert biomaterial (e.g. albumin) or biomimetic (e.g. phosphatidyl choline) to the surface. Chemical techniques for effecting these processes are described, together with some results obtained. An account is also included of solution studies, carried out for mechanistic purposes, of bioactivities of appropriate polymer-drug adducts.

Synthesis and nonthrombogenicity of polyetherurethaneurea film grafted with poly(sodium vinyl sulfonate)

Synthesis of nonthrombogenic materials without using biologically active substances was explored. Poly(sodium vinyl sulfonate) is a water-soluble synthetic polymer and activates antithrombin III to exert nonthrombogenicity that was dependent on the molecular weight. Polyetherurethaneurea film was plasma-treated and graft-polymerized with sodium vinyl sulfonate. The graft film showed excellent in vitro and ex vivo nonthrombogenicity by suppressing interactions with plasma proteins and platelets as well as by inactivating blood-clotting factors.

Coating of commercially available materials with a new heparinizable material

Different commercial materials, such as polyurethane (PU), plasticized PVC (PVC), glass, Gore-tex, and Dacron, were coated with a well-characterized biomaterial (PUPA) based on polyurethane and poly(amido-amine) components. Two different classes of coating were obtained due to the different characteristics of the substrates. In the case of PVC and polyurethane which are soluble in the solvent of the PUPA-coating solution, there was penetration and blending of the coating and underlying materials. In the case of glass, Gore-tex, and Dacron, which are insoluble in the solvent of the coating solution, only a superficial layer of PUPA could be obtained. The coating stability was investigated and the interaction between coating and underlying material studied by FT-IR. All the stable coatings showed the ability to bind as much heparin as PUPA material by itself.

Synthesis and antithrombogenicity of heparinized polyurethanes with intervening spacer chains of various kinds

Heparin was immobilized to polyetherurethaneurea membrane by covalent or ionic bondings with intervening spacer chains having different lengths and different terminal functional groups. The amount of immobilization of heparin and the release rate of immobilized heparin were controlled by the nature and the mode of bonding of spacer chains. The heparinized polyetherurethaneurea membranes became more in vitro antithrombogenic and suppressed more strongly the adhesion and activation of platelets, as the amount of immobilization increased. It was also shown that the membrane to which the low-molecular-weight fraction of heparin was immobilized was less stimulating to platelets.

In vitro non-thrombogenicity of a thrombin-substrate-immobilized polymer surface by the inhibition of thrombin activity

Derivatives of thrombin substrate were synthesized and immobilized on a poly(acrylic acid)-grafted polyurethane film. The carboxyl terminal of the thrombin substrate peptide should be blocked for a higher inhibitory effect of the thrombin activity. Immobilization of the thrombin substrate peptide enhanced adsorption and inactivation of thrombin on the polymer film to prolong the time for fibrin network formation, and suppressed adhesion and deformation of platelets on the film. Consequently, in vitro thrombus formation on the polymer film was strongly suppressed.

Platelet adhesion onto protein-coated and uncoated polyetherurethaneurea having tertiary amino groups in the substituents and its derivatives

Interactions of platelet with novel polyetherurethaneurea and its heparinized derivative were investigated. Platelet adhesion onto the material and release of serotonin or adenosine phosphate from platelet-rich plasma (PRP) were suppressed by an introduction of amino groups to polyetherurethaneurea, by quaternization of the polymer, and further by heparinization of the polymer. When the material was precoated with one of major plasma proteins and the protein-coated materials were taken to contact with washed platelet suspension (WP), the dependence of platelet adhesion and activation on the properties of polymers was different from that observed for PRP interaction. Platelet adhesion and activation were promoted according to the nature of coating proteins in the order albumin less than gamma-globulin less than fibrinogen and with increasing degree of denaturation of coating proteins. When the polymer materials were coated with proteins by immersing in aqueous solution containing two kinds of plasma proteins, adhesion behaviors of platelet were similar to those observed for PRP-uncoated material interaction. These experimental facts indicate that the selectivity of platelet for protein-coated material cannot be assessed by the interaction of WP with materials coated with a single kind of protein. It was concluded that material surface to which albumin is selectively adsorbed without denaturation does not stimulate adhering platelets for release reactions.

Synthesis and non-thrombogenicity of polyurethanes with poly(oxyethylene) side chains in soft segment regions

Epoxidized polybutadiene-urethanes were synthesized and grafted with poly(oxyethylene)s. The non-thrombogenicity of the graft polyurethanes was investigated in relation to the content of poly(oxyethylene). The grafting of poly(oxyethylene) to polyurethane suppressed adsorption and denaturation of plasma proteins and platelet adhesion. It was also found that there exists an optimum content of poly(oxyethylene) for the graft polyurethane to attain the highest non-thrombogenicity.