Utilization of the platelet release reaction in the blood compatibility assessment of polymers

In vitro Blood Compatibility Evaluation of Hollow Fibre Membrane Using a Controlled Flow System: A Comparative Study

A procedure has been established for the in vitro assessment of hollow fibre haemodialysis membranes. A 30 ml syringe containing 20 ml of fresh non-anticoagulated blood was mounted onto a non-pulsatile syringe pump and blood was perfused through minimodules constructed from 80 fibres retrieved from Cuprophan (Baxter ST15), cellulose acetate (M57-12, JMS Co Ltd, Hiroshima, Japan), and AN69HF (Filtral 20, Hospal, France) dialysers. Samples were collected before perfusion, 3, 6, 9 and 12 minutes. The modules were clamped vertically to minimise the effect of red cell pooling and the dialysate compartment was filled with 0.9% saline to minimise ultrafiltration. After sample processing, complement C3a, thrombin-antithrombin III complexes, prothrombin F1 + 2, and factor XII-like activity were evaluated. The results indicated that the system could discriminate between the membranes evaluated and therefore was a relevant procedure for the assessment of hollow fibre haemodialysis membranes.

Activation of coagulation and platelets by candidate membranes of implantable devices in a whole blood model without soluble anticoagulant

Implantable devices are challenged with thrombus formation at their biomaterial interface. Thus the importance of identifying compatible biomaterials that will help to improve the performance of these devices are becoming increasingly paramount. The aim of this study was to evaluate the activation of coagulation and platelets by candidate membranes considered for use in implantable devices on the basis of an adapted whole blood model without soluble anticoagulants. Evaluated materials were incubated with whole blood without soluble anticoagulant in wells coated with heparin. Prothrombin fragment 1+2 (PTF 1+2), thrombin-antithrombin complex (TAT), and β-thromboglobulin (BTG) were analyzed in plasma samples using enzyme immunoassays. The C5 inhibitor eculizumab was used to evaluate the role of complement. Incubation of two of the polyamide membranes PAR and PATF led to an increase in concentration of PTF 1+2 and TAT (p < 0.01 for PAR, ns for PATF). The BTG concentration was significantly increased for five materials [PAR, PATF, polycarbonate (PC), and two polyarylethersulphone membranes PAES-1 and PAES-2]. Complement inhibition had no effect on coagulation or platelet activation induced by PAR and PATF. In conclusion, PAR and PATF were not compatible with blood and should be avoided for use in implantable devices.

Biocompatibility and performance in vitro of a hemostatic gelatin sponge

The biocompatibility of a hemostatic gelatin sponge (Cutanplast Standard) was evaluated in vitro. Cytotoxicity was assessed by neutral red uptake and amido black staining tests; genotoxicity was assayed using the Ames test, Sister Chromatides Exchanges (SCE) and chromosomal aberrations. The ability of the hemostatic gelatin sponge to induce platelet adhesion and release reaction was also determined. The undiluted extract of the test material was found to be cytotoxic, but cell viability was not affected by 1:2 and 1:10 diluted extract. The same extract was found to be non-genotoxic using the three assays for genotoxicity. A significant decrease of platelet number, as well as a significant release of platelet factor 4 was found to be caused by the solid material. In conclusion, Cutanplast Standard is neither cytotoxic nor genotoxic, while inducing platelet adhesion and release reaction when challenged with blood.

Influence of Sulfation on Platelet Aggregation and Activation with Differentially Sulfated Hyaluronic Acids

A number of sulfated hyaluronic acid derivatives (HyalS(2.5), HyalS(3), and HyalS(4)) were prepared by sulfation of the -OH groups present on hyaluronic acid and were generically termed HyalS(x). The anticoagulant properties of this series of compounds has previously been shown to be good in terms of their whole blood clotting inhibition and factor Xa and thrombin inactivation. The purpose of the present study was to investigate whether the use of these compounds would be beneficial to patients who would normally be given heparin, and to perform some preliminary investigations into their effects on platelets. The three compounds were thus studied by investigating their ability to inhibit von Willebrand factor-dependent platelet agglutination in comparison with unfractionated heparin. Agglutination was determined turbidometrically after the addition of ristocetin to stirred formaldehyde-fixed platelets and was demonstrated to be dependent on the presence of sulfate groups on the polysaccharide chain and correlated with the degree of HyalS(x) sulfation. Interactions possibly important in low shear environments were investigated by measuring the pharmacological action of the HyalS(x) on spontaneous platelet activation and aggregate formation by flow cytometry. The data indicate that platelet activation is not correlated with the number of sulfate or hydroxyl groups on HyalS(x), suggesting that activation occurs not via electrostatic interactions or H bonding, but via some other mechanism. A differentiation between low and high glycosaminoglycan sulfation densities is observed with respect to platelet aggregation, which is correlated with the number of sulfated groups per disaccharide unit. The ability of HyalS(x) to inhibit platelet aggregation induced by ADP and thrombin was measured by aggregometry. HyalS(4) resisted thrombin stimulation to a similar extent as heparin. All Hyal derivatives, however, were better at inhibiting ADP-induced aggregation than was heparin. We conclude, therefore, that clinical use of HyalS(x) in place of heparin may be beneficial because ristocetin-dependent agglutination, and therefore resistance to platelet aggregation in high shear environments, in addition to resistance to stimulation by ADP, has been shown to be superior to heparin. Spontaneous platelet activation and aggregation are induced at an overall low level, even at high HyalS(x) concentrations, and are comparable with that of heparin.

CD62, thromboxane B2, and beta-thromboglobulin: a comparison between different markers of platelet activation after contact with biomaterials

The authors examined the modifications of some markers of platelet activation after contact with biomaterials. Glycoprotein GMP-140 (CD62) was evaluated by flow cytometry; beta-thromboglobulin (beta-TG) and thromboxane B2 (TXB2) were determined by radioimmunoassay. Polyethylene terephthalate (PET) induced a remarkable platelet adhesion and a significant increase in beta-TG and TXB2, with no increase in CD62 on the nonadherent platelets. Pyrolytic carbon-coated PET (PC) did not induce platelet adhesion after 15 min of contact, but a significant increase in CD62 was detected. After 30 min a significant increase in platelet adhesion as well as the release of beta-TG and TXB2 were noted. The increase was lower than that observed for uncoated PET, and after 30 min of contact with PC the increase no longer was observed.

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.

Biomaterials for blood-contacting applications

Consideration of biomaterials for blood-contacting applications should take into account blood-biomaterial interactions, factors influencing the blood response and evaluation procedures. Examination of blood-biomaterial interactions indicates that relevant features are protein adsorption, platelet reactions, intrinsic coagulation, fibrinolytic activity, erythrocytes, leucocytes and complement activation. Factors influencing the blood response to a biomaterial in clinical application are the biomaterial structure, the presence of an antithrombotic agent, the patient status as determined by the disease and drug therapy, and the nature of the application. Evaluation options for biomaterials are clinical, in vivo, ex vivo and in vitro, with ex vivo and in vitro procedures relevant for biomaterial development.

Blood interactions with novel polyurethaneurea hydrogels

The influence on blood of polyurethaneurea hydrogels in vitro was investigated based on poly(ethylene oxide). A hydrogel was compared with the regenerated cellulose membrane Cuprophan in terms of complement activation, as determined by measurement of C3a concentration. The hydrogel induced less complement activation and the presence of poly(ethylene oxide) is likely to be beneficial to platelet reactivity. The ability to vary the polymer composition and the solubility of the polymers in organic solvents makes the polyurethaneurea hydrogels strong candidates for composite biomaterials.

Serotonin and beta-thromboglobulin release reaction from platelet as triggered by interaction with polypeptide derivatives

The effect of wettability of 14 polypeptide derivatives upon adhesion and activation of platelets was investigated with reference to release reactions from adhered platelets, using radioisotope labeling and radioimmunoassay method. The serotonin release was more significant from platelets adhered to polymer materials to which a large number of platelets are adhered. However, no clear relationship was found between adhesion of platelets and beta-thromboglobulin release from adhered platelets. Therefore, stimuli inducing serotonin release and beta-thromboglobulin release were considered to be from different origins. The trend in beta-thromboglobulin release was well correlated with the extent of morphological change of adhered platelets as observed by scanning electron microscope. It was suggested that the determination of released beta-thromboglobulin in association with the measurement of platelet adhesion could be useful for evaluation of blood compatibility of materials.

Platelet adhesion onto polyether-urethane urea derivatives: effect of cytoskeleton proteins of the platelet

Adhesion and activation of platelets upon adhesion onto synthetic polymers were investigated with reference to participation of the cytoskeleton proteins. Platelets were treated with cytoskeleton breakers, and then the adhesion of platelets onto polyetherurethane urea derivatives and serotonin release from adhered platelets were investigated. In the adhesion onto glass, platelets were strongly stimulated and accompanied rearrangement of the cytoskeleton system, and also serotonin release involved the action of the cytoskeleton system. On the other hand, platelets were not strongly stimulated upon adhering onto polyetherurethane urea derivatives. The platelet adhesion onto cationic polymers exceptionally accompanied the rearrangement of the cytoskeleton system. The participation of the cytoskeleton in platelet adhesion onto polyetherurethane urea derivatives was influenced by the presence of plasma proteins. It was found that protein layers deposited on the material surface play an important role in platelet adhesion.

Measurement of platelet loss in the blood compatibility assessment of biomaterials

In the assessment of the in vitro blood compatibility of biomaterials, platelet loss is often attributed solely to platelet adhesion and consideration is not given to platelets lost in platelet aggregate formation. In order to distinguish between those platelets lost to adhesion and those lost to aggregate formation, the Wu and Hoak method for the quantification of circulating platelet aggregates in patients has been modified to establish a new test procedure. This procedure, which measures both platelet adhesion (PA) in the absence of platelets lost to aggregate formation and also the tendency of a material to induce aggregate formation, has been used to evaluate the influence of a range of polyamides and a hydrogel. The evaluation demonstrated the ability of polymers to induce readily platelet aggregates during in vitro blood-material contact. The sensitivity of the aggregate measurement was exemplified by the polyamides, where PA was similar for materials of different porosity but platelet aggregate formation increased significantly with porosity. The importance of considering platelets lost to aggregate formation was emphasized with the hydrogel, where PA was low.

An in vitro study of the adhesion of blood platelets onto vascular catheters. Part I

The adhesion of human blood platelets onto vascular catheters was studied using a specially designed perfusion chamber. Polyurethane catheters were exposed to citrated human blood for different periods (up to 20 min) and at different wall shear rates (190, 260, 330 sec-1). The rate of platelet adhesion was determined using 111In-labeled platelets, while the morphology of adhering platelets was investigated using scanning electron microscopy. A linear increase in platelet adhesion was found within the first 10 min of perfusion, after which a plateau value was reached. The number of adhering platelets did not vary significantly with the shear rates applied, which may indicate that within the range of shear rates studied, the adhesion of platelets onto the catheter surface is mainly determined by the rate of the reaction between the platelets and the material surface. Catheters coated with a conjugate of heparin and albumin showed a four- to five-fold reduction in platelet adhesion as compared to uncoated catheters. This reduction in platelet adhesion was not only due to the presence of albumin moieties at the surface but also to the presence of heparin residues in the adsorbed albumin-heparin conjugate.