Assessment of material-induced procoagulant activity by a modified Russell viper venom coagulation time test

2-methoxyethylacrylate modified polyurethane membrane and its blood compatibility

Hydrophilic material 2-methoxyethylacrylate (MEA) was grafted onto polyurethane (PU) membrane via Michael addition reaction. Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS) characterizations of the modified membrane proved that MEA was successfully grafted onto PU membrane surface. The water contact angle of the modified PU membrane decreased from 86° to 48° compared with unmodified PU membrane, which means that the hydrophilicity of the modified membrane was greatly improved. A series of blood compatibility tests including bovine serum protein adsorption, platelet adhesion, hemolysis assay, plasma recalacification time, prothrombin time (PT), partial thromboplastin time (APTT) and thrombin time (TT) were carried out on PU membrane and the modified PU membrane with highest grafted density of MEA. The combined results indicate that MEA plays an important role in improving the blood compatibility of PU membrane.

2-methoxyethylacrylate modified polysulfone membrane and its blood compatibility

Hydrophilic material 2-methoxyethylacrylate (MEA) was grafted onto polysulfone (PSF) membrane via Michael addition reaction. The ¹H nuclear magnetic resonance (¹H NMR), Attenuated total reflectance-Fourier transform infrared spectroscope (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) characterization of the modified membrane proved that MEA had been successfully grafted onto PSF membrane surface. The water contact angle of the membrane surface was tested. The results showed that the water contact angle changed from 76° to 59.5°, which means that the hydrophilicity of the modified membrane was improved. A series of blood compatibility tests including bovine serum protein adsorption, platelet adhesion, prothrombin time (PT), partial thromboplastin time (APTT) and thrombin time (TT) were carried out on PSF membrane and the modified PSF membrane with highest grafted density of MEA. All of the results indicate that MEA plays an important role in improving the blood compatibility of PSF membrane.

Blood activation and compatibility on single-molecular-layer biointerfaces

Research on the interactions between living systems and materials is fuelled by diverse biomedical needs, for example, drug encapsulation and stimulated release, stem cell proliferation and differentiation, cell and tissue cultures, as well as artificial organs.

Hemocompatibility of Inorganic Physical Vapor Deposition (PVD) Coatings on Thermoplastic Polyurethane Polymers

Biocompatibility improvements for blood contacting materials are of increasing interest for implanted devices and interventional tools. The current study focuses on inorganic (titanium, titanium nitride, titanium oxide) as well as diamond-like carbon (DLC) coating materials on polymer surfaces (thermoplastic polyurethane), deposited by magnetron sputtering und pulsed laser deposition at room temperature. DLC was used pure (a-C:H) as well as doped with silicon, titanium, and nitrogen + titanium (a-C:H:Si, a-C:H:Ti, a-C:H:N:Ti). In-vitro testing of the hemocompatibility requires mandatory dynamic test conditions to simulate in-vivo conditions, e.g., realized by a cone-and-plate analyzer. In such tests, titanium- and nitrogen-doped DLC and titanium nitride were found to be optimally anti-thrombotic and better than state-of-the-art polyurethane polymers. This is mainly due to the low tendency to platelet microparticle formation, a high content of remaining platelets in the whole blood after testing and low concentration of platelet activation and aggregation markers. Comparing this result to shear-flow induced cell motility tests with e.g., Dictostelium discoideum cell model organism reveals similar tendencies for the investigated materials.

Biomaterial-associated thrombosis: roles of coagulation factors, complement, platelets and leukocytes

Our failure to produce truly non-thrombogenic materials may reflect a failure to fully understand the mechanisms of biomaterial-associated thrombosis. The community has focused on minimizing coagulation or minimizing platelet adhesion and activation. We have infrequently considered the interactions between the two although we are generally familiar with these interactions. However, we have rarely considered in the context of biomaterial-associated thrombosis the other major players in blood: complement and leukocytes. Biomaterials are known agonists of complement and leukocyte activation, but this is frequently studied only in the context of inflammation. For us, thrombosis is a special case of inflammation. Here we summarize current perspectives on all four of these components in thrombosis and with biomaterials and cardiovascular devices. We also briefly highlight a few features of biomaterial-associated thrombosis that are not often considered in the biomaterials literature: The importance of tissue factor and the extrinsic coagulation system. Complement activation as a prelude to platelet activation and its role in thrombosis. The role of leukocytes in thrombin formation. The differing time scales of these contributions.

A new activated factor X-based clotting method with improved specificity for procoagulant phospholipid

An improved activated factor X-based clotting method was used to investigate activity of procoagulant phospholipid (PPL) in blood samples collected into various anticoagulants and in plasmas with a range of abnormalities. The dilute activated factor X-activated clotting time (XACT) was carried out on a mixture of specimen with phospholipid-free porcine plasma. PPL from the test sample is then rate-limiting, controlling the clotting time so that the XACT is shortened from a maximum of approximately 120 s with citrated platelet-free plasma to approximately 30 s with freeze-thawed platelet-rich plasma. XACT results were only shortened slightly by fresh normal platelet-rich plasma, but were shortened significantly by platelets that had been activated by freeze-thawing. This improved method for PPL was not prolonged by deficiencies of known clotting factors and therapeutic levels of heparin, and it was surprisingly resistant to most lupus anticoagulants. However, it was extremely sensitive to PPL, detecting down to 50 ng/ml synthetic phospholipid added to phospholipid-free plasma. Excellent correlation was achieved between XACT shortening and microparticle count assessed by annexin V-binding and flow cytometry in normal plasma spiked with platelet microparticles. In citrated blood specimens, XACT shortened with time in a temperature-dependent manner. XACT results on blood samples anticoagulated with ethylenediamine tetra-acetate were more stable, and these would be preferable for assessing PPL expression ex vivo. XACT was significantly shorter in whole blood samples than in normal platelet-rich or platelet-poor plasmas, suggesting that PPL was normally expressed more by cells or aggregates larger than platelets or microparticles.

Proinflammatory phenotype of endothelial cells after coculture with biomaterial-treated blood cells

An understanding of the endothelial cell/blood/biomaterial interactions is central to advancing the success of cardiovascular devices that continue to fail because of the lack of nonthrombogenic biomaterials. A simplified endothelial cell/blood cell/biomaterial static model was used to assess these interactions. Human whole blood or isolated blood cells (mononuclear cells, neutrophils, platelets) were pretreated with biomaterial beads with different surface chemistries: polystyrene (PS), PS beads grafted with 3-kDa polyethylene glycol (PEG) with either hydroxyl (PS-PEG-OH) or amine (PS-PEG-NH2) terminal groups at bead concentrations of 5.4 or 54 x 10(4) beads/mL. Leukocyte and platelet activation and microparticle formation was assessed using flow cytometry. Biomaterial-activated whole blood or isolated cells or mononuclear cell fractions were applied to human umbilical cord endothelial cells (HUVEC) for static coculture, and the resultant proinflammatory HUVEC phenotype was characterized. ICAM-1 and E-selectin expression on HUVEC was increased after 4-h static coculture with biomaterial-treated human whole blood or mononuclear cells but not neutrophils or platelets. VCAM-1 expression on HUVEC was similarly increased after 24-h static coculture but not after 4 h of coculture. Increased concentrations of cytokines, IL-6, IL-8, and MCP-1, were detected in the supernatant of cocultures of HUVEC with biomaterial-treated whole blood or mononuclear cells but not neutrophils or platelets, compared with the media control. After 24 h, cytokine release was significantly increased for both IL-8 and MCP-1 but not IL-6 above concentrations after 4 h of coculture. Neither the cell adhesion molecule (CAM) expression nor cytokine release induced by coculture with biomaterial-treated whole blood or isolated cells was dependent on either material surface chemistry or material surface area. The changes in HUVEC CAM expression and cytokine release induced by biomaterial-treated mononuclear cells can be attributed predominantly to adherent cells on beads and nonadherent bulk cells with moderate regulation by the soluble supernatant; however, mononuclear cell-derived microparticles induced no significant changes in CAM expression or cytokine release after static coculture with HUVEC.

Influence of abciximab on the adhesion of platelets on a shielded plasma gradient prepared on polyethylene

INTRODUCTION

Thrombotic effects of biomaterial implants are mediated merely through activation of the platelet glycoprotein IIb-IIIa (GpIIb-IIIa) receptor. Consequently, platelet GpIIb-IIIa receptor inhibitors are successfully used during stent implantation procedures to prevent thrombosis. However, currently a new generation of stents contains surface coating, which changes the surface to more hydrophobic or hydrophilic. This change markedly affects the interaction of platelets and may influence the efficiency of GpIIb-IIIa inhibitors.

MATERIALS AND METHODS

To study the influence of the wettability of biomaterials on the effectiveness of abciximab, 5-cm polyethylene gradients with contact angles of 100 degrees to 40 degrees were made by means of glow discharge. Fresh whole blood with or without abciximab was recirculated over this gradient.

RESULTS

Inhibition of platelet adhesion by abciximab was maximal, but not complete, on the hydrophobic and moderate hydrophobic part of the gradient, with contact angles of 55 degrees to 90 degrees. Percentage inhibition by abciximab was maximal around 60 degrees.

CONCLUSIONS

Intermediate hydrophobicity of currently applied stent materials, such as stainless steel, seems optimal in combination with abciximab. However, on hydrophobic and particularly on hydrophilic materials, abciximab is less effective.

Activation of platelets by in vitro whole blood contact with materials: increases in microparticle, procoagulant activity, and soluble P-selectin blood levels

Non-adherent platelets and plasma were analyzed for evidence of platelet activation after whole blood contact with materials under conditions of low shear for one hour at 37 degrees C. The contact involved adding heparinized whole blood to small diameter tubes that were connected to two arms extending from a rocking platform. For all surfaces (polyethylene, polypropylene, Silastic, PVA hydrogel) tested there was strong evidence of platelet activation in the bulk blood: platelet-derived microparticles, procoagulant platelet membranes and soluble P-selectin levels. Flow cytometric quantification of microparticles (MPs) was highly sensitive and entailed the direct determination of microparticle concentrations as opposed to the traditional quantification of microparticle percentages (relative to total number of MPs and platelets). Whole blood contact with polypropylene surfaces led to the greatest drops in bulk platelet counts and also to the lowest increases in microparticle concentrations. Flow cytometry was also used to assess procoagulant levels (annexin V binding) within a light scatter region known to contain platelets and some large microparticles. All surfaces were noted to generate a significant procoagulant population that was, based on forward light scatter, mostly very small platelets or large microparticles. In contrast, most of the P-selectin positive platelets were averaged sized. Lastly. all surfaces generated soluble P-selectin levels that were approximately double the level (25 ng ml(-1)) noted in the resting whole blood samples. In addition to our previous reports, these findings support the observation that there is strong evidence of platelet activation in the bulk that we anticipate will ultimately lead to more relevant in vitro testing of the compatibility of platelets towards materials.

Platelet adhesion and activation on a shielded plasma gradient prepared on polyethylene

Contact of blood with foreign materials evokes thrombogenic effects to an extent determined partly by the wettability of the biomaterials surface. Tools to study blood response towards a variation in materials wettability with minimal variation in chemistry are "gradient surfaces". However, most gradients have been prepared by diffusion or density immersion techniques, which results in a limited gradient range. Through glow discharge with partial shielding, gradients on polymers were prepared over a length of 5 cm, which facilitated studies to platelet adhesion on separate gradient sections. On polyethylene, advancing water contact angles varied from 90 degrees to 40 degrees, with a hysteresis of 30 degrees. ESCA indicated an increasing incorporation of oxygen towards the hydrophilic end. To examine the role of materials wettability on the activation of adhering platelets, sections of shielded plasma gradients were incubated in anticoagulated whole human blood. Fewer platelets adhered to the hydrophobic end, but those platelets were more activated than those on the hydrophilic end, as judged from their morphology and exposure of GpIIb-IIIa complex. However, partly related to the increased binding of platelets, the clotting activation after platelet deposition was highest on the hydrophilic end. Concluding, this new technique results in a large gradient range, which facilitates studies of formed blood elements in relation to the wettability. Platelets are more activated on hydrophobic polyethylene, while on moderate hydrophilic polyethylene more platelet adhesion and activation of the clotting system occurs.

What really is blood compatibility?

The criteria for nonthrombogenicity are classically defined as long clotting times and minimal platelet deposition. The inability to point to unequivocal progress in the development of truly nonthrombogenic materials, highlights the inadequacy if not actually invalidity of these criteria. Our approach is to define nonthrombogenicity in terms of: (1) a thrombin production rate constant, kp < 10(-4) cm s(-1); (2) low platelet consumption and low degree of platelet activation (e.g., microparticle formation); (3) perhaps some platelet spreading; and (4) low complement and leukocyte activation. Only when the target becomes clear, will it be possible to identify clear strategies for producing the materials we need.

Flow cytometric evaluation of material-induced platelet and complement activation

Flow cytometry is used to characterize the activation state of platelets and leukocytes within whole blood after contact for 4 h at 37 degrees C with various materials under conditions of low shear. The contact involved adding heparinized whole blood to small diameter tubes that were connected to two arms extending from a rocking platform. For all surfaces (polyethylene, polypropylene, Silastic, PVA hydrogel) tested there was strong evidence of platelet activation in the bulk blood: platelet-derived microparticles. P-selectin expression and platelet-leukocyte aggregates. Only contact with PVA hydrogel surfaces led to dramatic increases in CD11b up-regulation on monocytes and neutrophils that was inhibited by complement inhibition (sCRI). Flow cytometry was also used to evaluate the effectiveness of various agents to inhibit material-induced complement activation. The assay involved incubating 10 microm polystyrene beads for 1 h with serum at 37 degrees C before isolating the beads so as to label them with a monoclonal antibody against a neoantigen on SC5b-9. The beads were then identified by flow cytometry and the fluorescence associated with their SC5b-9 level recorded. The ability of C1-INH, pentamidine and benzamidine to moderately inhibit SC5b-9 levels suggests a role for classical complement activation in material-induced complement activation.