Human plasma fibrinogen adsorption and platelet adhesion to polystyrene

Modulating cell adhesion and spreading by control of FnIII7–10 orientation on charged self-assembled monolayers (SAMs) of alkanethiolates

In this work, we demonstrate that surface charge can be used to modulate cell adhesion/spreading through the control of the orientation of adsorbed FnIII(7-10), which is a cell-adhesive protein containing RGD residues. Carboxylic acid (COOH) and amine (NH(2))-terminated self-assembled monolayers (SAMs) of alkanethiolates were used as model negatively and positively charged surfaces, respectively. The adsorbed amount of FnIII(7-10) is controlled to be equivalent on both SAMs as confirmed by the adsorption isotherms determined using I(125)-radiolabeled FnIII(7-10.) The binding of a monoclonal antibody specific for the cell-binding domain of FnIII(7-10) was measured by surface plasmon resonance (SPR) to evaluate FnIII(7-10) orientations on different SAMs. Results indicate that adsorbed FnIII(7-10) on NH(2)-SAM has an orientation with more cell-binding domains accessible than on COOH-SAM, confirming our predictions from Monte Carlo simulations. Both phase contrast images and Vybrant MTT cell proliferation assays show that the adhesion/spreading of bovine aortic endothelial cells (BAECs) on the NH(2)-SAM is significantly better than that on the COOH-SAM coated with an equivalent amount of FnIII(7-10). These results indicate that surface charge can be used to specifically orient cell adhesive proteins such as FnIII(7-10), thus providing a promising strategy to increase the activity of materials incorporating biological moieties.

Hemocompatibility of low-friction boron–carbon–nitrogen containing coatings

Mechanical heart valves are exposed to extreme mechanical demands, which require a surface showing not only nonhaemostatic properties, but also wear resistance and low friction. As alternative to different forms of amorphous carbon (a-C), so-called diamond-like carbon (DLC), the suitability of boron carbonitride (BCN) coatings is tested here for hemocompatible coatings. They have similar mechanical properties like a-C surfaces, but superior chemical stability at ferrous substrates or counterparts. BCN films with different nitrogen content were compared with hydrogenated a-C films regarding their mechanical properties, surface energy, adsorption of albumin and fibrinogen, blood platelet adherence, and activation of the contact system of the clotting cascade and kinin system. Similar mechanical properties and biological response have been found in the BCN films with respect to a-C, indicating the potential of these coatings for biomedical applications. The increase in the crystallinity and tribological properties of the BCN samples with a higher incorporation of N was also followed by a lower protein adsorption and low activation of the contact system, but an increased adherence of thrombocytes.

Conformational Changes of Fibrinogen after Adsorption

The adsorption behavior of fibrinogen to two biomedical polyurethanes and a perfluorinated polymer has been investigated. Changes in the secondary structure of adsorbed fibrinogen were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and sum frequency generation vibrational spectroscopy (SFG). SFG measurements were performed in the amide I range as well as in the C-H/N-H stretching range. Amide I signals from SFG demonstrate that fibrinogen has post-adsorption conformational changes that are dependent upon the polymer surface properties. For example, strong attenuation of the amide I and N-H stretching signals with increasing residence time was observed for fibrinogen adsorbed to poly(ether urethane) but not for the other two polymers. This change is not readily observed by ATR-FTIR. Differences in the observed spectral changes for fibrinogen adsorbed to each polymer are explained by different initial binding mechanisms and post-adsorption conformational changes.

A Model System to Assess Key Vascular Responses to Biomaterials

PURPOSE

To establish a reproducible laboratory test to evaluate prospective vascular biomaterials with respect to their thromboinflammatory properties by examining fibrinogen, platelet, and monocyte binding. Endothelial migration onto these surfaces was used as an index of vascular healing.

METHODS

To evaluate biomaterials for potential thrombogenicity and inflammation, binding assays of radiolabeled human fibrinogen, platelets, and monocytes were performed on standard pieces of vascular biomaterials, including metals and polymeric and ceramic-coated materials. Using an established in vitro endothelial cell migration model, the relative migration rate of cultured human aortic endothelial cells onto these vascular biomaterials was measured and compared. The fibrinogen, platelet, and monocyte binding results were combined along with the migration results to create an overall score of biocompatibility.

RESULTS

A significant direct relation of platelet and monocyte binding to the amount of adsorbed fibrinogen was observed. In contrast, migration rates of cultured human aortic endothelial cells onto the same biomaterial surfaces were found to be inversely related the amount of bound fibrinogen. Among the materials tested, stainless steel received the highest score of biocompatibility, while turbostratic carbon scored the lowest.

CONCLUSIONS

Fibrinogen, platelet, and monocyte binding levels, as well as endothelial migration rates onto vascular material surfaces, provide a basis for evaluating thrombogenicity, inflammatory potential, and endothelialization in the laboratory prior to in vivo testing.

Heparin-loaded zein microsphere film and hemocompatibility

Zein was studied as a drug-eluting coating film composed of zein microspheres for cardiovascular devices (e.g. stent). In vitro 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) analysis showed that both zein film and its degraded product had better biocompatibility compared with Corning culture plate on the growth of human umbilical veins endothelial cells (HUVECs, p<0.05, n=6), and the effect of zein degraded product on HUVECs was dose-dependent. The best result was obtained at 0.3 mg/ml of the addition. The encapsulation efficiency of heparin and heparin loading varied with the amount of both zein and heparin, and the highest encapsulation efficiency (heparin 1.33 mg/ml and zein 16 mg/ml) was 22.77+/-1.33% (n=3). Scanning electron microscope (SEM) observation indicated that the zein film was made of microspheres in diameter from nano- to micrometer, which could be controlled. Sizes of heparin-loaded zein microspheres changed before and after release of heparin because of conglutination among zein microspheres. Release rate of heparin from microsphere film reached to 33.5+/-1.2% within 12 h, and began to get into subsequent "slow release" phase; about 55% of the entrapped heparin was released after 20 days. Both zein film and heparin-loaded zein microsphere film were effective in suppressing platelet adhesion, and the heparin-loaded film showed a better anticoagulation as determined with thrombin time (TT) assay. These results suggest that zein film could be used directly as a new type of coating material for its better biocompatibility with HUVECs. Moreover, the heparin-loaded zein microsphere film can significantly improve the hemocompatibility.

Direct correlation between adsorption-induced changes in protein structure and platelet adhesion

It is widely recognized that adsorbed proteins on biomaterial surfaces tend to initiate thrombus formation, although the specific mechanisms involved are still not well understood. In attempts to decrease the conformational change of adsorbed proteins, surface treatments that reduce surface hydrophobicity have been considered, such as the sulfonation of low-density polyethylene and isotactic polypropylene. The objectives of this present research were to study how changes in surface chemistry influence the degree of conformational change of adsorbing proteins and to investigate the correlation between the change in adsorbed protein structure and platelet response. Adsorbed porcine serum albumin and porcine fibrinogen were used as the model proteins for determining the effects of sulfonation on protein conformational change. Circular dichroism spectroscopy studies showed that the proteins were less altered structurally on the sulfonated surfaces. Platelet adhesion studies were used to correlate the number of adhered platelets with the amount of conformational change in adsorbed proteins on the polymer surface. The results of these studies show a linear correlation between platelet adhesion and the degree of adsorption-induced protein conformational change. These findings suggest that the degree of protein conformational change after adsorption is a dominant mechanism governing platelet interactions with biomaterial surfaces.

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.

Hemodialysis Membranes Based on Functionalized High-density Polyethylene

Grafting vinyl acetate (VAc) and maleic anhydride (MAn) comonomer onto high-density polyethylene (HDPE) was performed by means of gamma rays. Conditions for the minimum homopolymer formation, maximum grafting yield and alternate copolymer grafts were carried out. Further chemical treatment with sodium hydroxide, hydrochloric acid, ammonium hydroxide, sulfamic acid and amino pyridine were made on the grafted membranes to increase functionality. The swelling, mechanical, solute permeability and biocompatibility properties of these copolymers were evaluated for possible application as dialysis membranes. The introduction of functional groups on HDPE membranes enhanced their hydration and transport flux. The treated grafting membranes showed improved permeability towards urea, creatinine and uric acid over the ungrafted HDPE. The permeability rate of the solutes through the membranes depended on the molecular weight and the size of the solutes. The presence of hydrophilic groups on the membranes reduced protein adsorption and enhanced membrane transport. The swelling, solute dialysis permeability and protein low affinity properties of HDPE-g-(VAc-alt-MAn) treated with sulfamic acid or 2-aminopyridine indicate potential use as hemodialysis membranes.

Plasma-immersion ion-implanted nitinol surface with depressed nickel concentration for implants in blood

Ion implantation into nitinol had been shown previously to decrease the surface nickel concentration of this alloy and produce a titanium oxide layer. Nothing is known yet about the blood compatibility of this surface and the suitability for implants in the blood vessels, like vascular stents. Nickel depletion of superelastic nitinol was obtained by oxygen or helium plasma-immersion ion implantation. The latter leads to the formation of a nickel-poor titanium-oxide surface with a nanoporous structure, which was used for comparison. Fibrinogen adsorption and conformation changes, blood platelet adhesion, and contact activation of the blood clotting cascade have been checked as in vitro parameters of blood compatibility; metabolic activity and release of cytokines IL-6 and IL-8 from cultured endothelial cells on these surfaces give information about the reaction of the blood vessel wall. The oxygen-ion-implanted nitinol surface adsorbed less fibrinogen on its surface and activated the contact system less than the untreated nitinol surface, but conformation changes of fibrinogen were higher on the oxygen-implanted nitinol. No difference between initial and oxygen-implanted nitinol was found for the platelet adherence, endothelial cell activity, or cytokine release. The nanoporous, helium-implanted nitinol behaved worse than the initial one in most aspects. Oxygen-ion implantation is seen as a useful method to decrease the nickel concentration in the surface of nitinol for cardiovascular applications.

Fibrinogen and von Willebrand's factor adsorption are both required for platelet adhesion from sheared suspensions to polyethylene preadsorbed with blood plasma

Previous studies showed that platelet adhesion to biomaterials from static suspensions was greatly increased by the adsorption of even very small amounts (<5 ng/cm2) of fibrinogen (Fg). In this study, the sensitivity of platelet adhesion to Fg was reexamined by measuring platelet adhesion under flow conditions. The role of adsorbed von Willebrand's factor (vWf) was also studied. Polyethylene (PE) tubing was preadsorbed with Fg, vWf, vWf-deficient plasma, and Fg-deficient plasma or serum with added Fg, and Fg adsorption measured with 125I Fg. Platelets in a red blood cell suspension were passed through the tubes at either low (50 s(-1)) or high (500 or 1000 s(-1)) shear rates and adhesion measured with an improved LDH assay. Adhesion from flowing suspensions measured after preadsorption with afibrinogenemic plasma or serum was very low, but increased greatly with addition of Fg. Less than 10 ng/cm2 of adsorbed Fg was enough to greatly enhance platelet adhesion. Adhesion at high shear was also strongly affected by vWf, as platelet adhesion at 500 s(-1) to PE preadsorbed with vWf-deficient plasma decreased by more than tenfold compared to adhesion at 50 s(-1), but platelet adhesion to PE preadsorbed with normal plasma increased about eightfold when shear rate was increased. The results show that very low amounts of adsorbed Fg are able to support platelet adhesion under shear flow. However, adsorbed vWf also appears to play an important cofactor role in platelet adhesion to biomaterials, as its presence greatly augments platelet adhesion under high shear.

Variations in the ability of adsorbed fibrinogen to mediate platelet adhesion to polystyrene-based materials: a multivariate statistical analysis of antibody binding to the platelet binding sites of fibrinogen

Platelet adhesion to the surfaces of biomaterials preadsorbed with plasma previously has been shown to be mediated exclusively by surface-bound fibrinogen and does not seem to involve the other adhesion proteins in plasma (Tsai et al., J Biomed Mater Res 2002;60:348-359). In this study, the influence of surface-bound fibrinogen on platelet adhesion to five different types of polystyrene-based microtiter plates preadsorbed with plasma was analyzed relative to the amount of adsorbed fibrinogen and monoclonal antibody binding to the adsorbed fibrinogen. There was no significant correlation between platelet adhesion and the absolute amount of adsorbed fibrinogen. However, platelet adhesion was positively correlated to the ability of the adsorbed fibrinogen to bind three types of monoclonal antibodies. The antibodies used bound to the sites on fibrinogen thought to be involved in platelet binding (the two gamma chain C-terminal dodecapeptides and the RGDF and RGDS sequences in each of the Aalpha chains). A partial least-squares calibration model was used to analyze the relative importance of these binding sites in fibrinogen to platelet adhesion. The gamma chain C-terminal dodecapeptide was shown to be the most important site in adsorbed fibrinogen in mediating platelet adhesion.

Silicone elastomers for reduced protein adsorption

Monofunctional poly(ethylene oxide) polymers of molecular weight (MW) 350, 750, and 2000, respectively, were modified with Si(OEt)3 groups. These polymers underwent classic condensation cure with hydroxy-terminated silicone polymers and Si(OEt)4 to give composites with poly(ethylene oxide) (PEO) rich surfaces under aqueous conditions, as shown by contact angle and XPS data. The hydrophobicity of the surfaces was considerably higher in air. The greatest PEO concentration was observed with relatively short chain polymers of MW 350. Silicone polymers bearing short chain PEO chains were also observed to be the most protein rejecting from either buffer (fibrinogen) (90%) or plasma (85%). The silicone/TES-MPEO formulation offers the advantage of a one step/one shot polymerization process that gives materials with a high protein rejection ability than can be cast as films, or molded into complex shapes. Covalently linked PEO films of a variety of chain lengths and total surface coverage can be readily accommodated.

Effects of adsorbed proteins and surface chemistry on foreign body giant cell formation, tumor necrosis factor alpha release and procoagulant activity of monocytes

The adhesion and activation of monocytes and macrophages are thought to affect the foreign body response to implanted medical devices. However, these cells interact with devices indirectly, because of the prior adsorption of proteins. Therefore, we preadsorbed several "model" biomaterial surfaces with proteins and then measured foreign body giant cell (FBGC) formation, tumor necrosis factor alpha (TNFalpha) release, and procoagulant activity. The model surfaces were tissue culture polystyrene (TCPS), untreated polystyrene (PS), and Primaria, whereas the proteins used were albumin, fibronectin, fibrinogen, and immunoglobulin. FBGC formation, TNFalpha release, and procoagulant activity of monocytes were the highest for surfaces preadsorbed with IgG. FBGC formation was lower on surfaces with adsorbed fibrinogen and fibronectin than on uncoated surfaces. TNFalpha release and procoagulant activity of monocytes were similar on surface adsorbed with fibrinogen, fibronectin, or albumin. Monocyte activation was also affected by the surface chemistry of the substrates, because FBGC formation was the highest on PS and the lowest on TCPS. Monocyte procoagulant activity was the highest on Primaria. Adsorbed proteins and surface chemistry were found to have strong effects on FBGC formation, monocyte TNFalpha release, and procoagulant activity in vitro, providing support for the idea that these same variables could affect macrophage-mediated foreign body response to biomaterials in vivo.

Material-dependent levels of heat-shock protein 70 (hsp70) in human plasma following contact of blood with artificial surfaces

Recently, it has been shown that heat-shock protein 70 (hsp70) functions in a dual role as a chaperone and a cytokine. However, no information is available on the occurrence of hsp70 in the extracellular milieu or on its ability to modulate cellular immune response. This study shows a material-dependent increase of hsp70 levels in plasma following contact of fresh heparinized whole human blood with three different biomaterials (PVC, heparin-coated PVC, Silicone). We report a previously unknown behavior of hsp70 to act as a plasma-adsorption protein. Further, high binding capacities for hsp70 to artificial surfaces (measured by Western blotting) and elevated hsp70 levels in plasma (measured by EIA) following contact with blood correspond with a reduced hemocompatibility. The degree of surface-induced activation of blood was determined by analysis of markers for coagulation, inflammation and complement activation. These findings indicate that the selective adsorption of hsp70 on artificial surfaces and the increased hsp70 levels in plasma may be important in directing host inflammatory and immune responses. We suggest that the levels of hsp70 in human plasma may represent a new prognostic factor or a diagnostic biomarker in hemostasis research.

Fibrinogen Conformation and Platelet Reactivity in Relation to Material−Blood Interaction: Effect of Stress Hormones

The performance of many biomaterials in hemocompatibility tests is altered when blood is drawn from stressed subjects. A salient physiological response during stress is one in which hormones are released into plasma by the hypothalamo-pituitary-adrenal axis. We investigated the influence of basal and stress levels of epinephrine and beta-endorphin on the conformation of fibrinogen (Fbg), both in saline solution (under physiological conditions) and after its adsorption to polyethylene (PE), by FT-IR spectroscopy. Moreover, as Fbg is one of the major mediators of platelet adhesion, the behavior of platelets in contact with PE was also evaluated as a function of the two different hormone concentrations. Epinephrine was found to affect Fbg conformation and to increase platelet adhesion to PE at stress level. Basal and stress levels of beta-endorphin did not significantly affect the Fbg conformation and only induced adhesion of isolated platelets to the PE surface. A direct relationship was therefore found between Fbg conformation and platelet behavior. The response of platelets was affected by the stress status of donors through the influence of epinephrine on Fbg conformation.

Blood compatible aspects of DNA-modified polysulfone membrane-protein adsorption and platelet adhesion

DNA was used as a biomaterial to modify the polysulfone (PSf) membrane by blending it with PSf. The blood compatibility of the membranes was then investigated. The water contact angle decreased, and the hydrophilicity increased when a single strand DNA was blended with PSf. Because of the hydrophilic surface, the DNA-blended PSf membranes had a lower protein adsorption than the PSf membrane, but it was not significantly decreased due to the interaction between the DNA and proteins. Circular dichroism (CD) spectroscopy was used to examine the changes in the secondary structure of the proteins after adsorption onto the polymer surface and desorption from the polymer surface into the SDS solution. The conformation of the proteins adsorbed onto the PSf membrane and desorbed from the PSf membrane significantly changed, but that of the proteins for the DNA-blended PSf membranes differed only slightly from the native one. The number of platelets that adhered on the surface of the DNA-blended PSf membranes was reduced compared to that on the PSf membrane. This suggested that DNA can be regarded as a biopolymer to modify PSf, and contributes to the hydrophilic and hemocompatible wipers on the surface of the hydrophobic PSf membranes.

PEO-like plasma polymerized tetraglyme surface interactions with leukocytes and proteins: in vitro and in vivo studies

Polyethylene oxide (PEO) surfaces reduce non-specific protein and cell interactions with implanted biomaterials and may improve their biocompatibility. PEO-like polymerized tetraglyme surfaces were made by glow discharge plasma deposition onto fluorinated ethylene propylene copolymer (FEP) substrates and were shown to adsorb less than 10 ng/cm2 of fibrinogen in vitro. The ability of the polymerized tetraglyme surfaces to resist leukocyte adhesion was studied in vitro and in vivo. Polymerized tetraglyme and FEP were implanted subcutaneously in mice and removed after 1 day or 4 weeks. Histological analysis showed a similar degree of fibrous encapsulation around all of the 4-week implants. Darkly stained wells were present in the fibrous tissues at the tissue-material interface of both FEP and tetraglyme. Scanning electron micrographs showed that in vivo macrophage adhesion to polymerized tetraglyme was much higher than to FEP. After 2-hour contact with heparinized whole blood, polymorphonuclear leukocyte (PMN) adhesion to polymerized tetraglyme was much higher than to FEP, while platelet adhesion to polymerized tetraglyme was lower than to FEP. When PMNs isolated from blood were suspended in 10% autologous plasma, cell adhesion to polymerized tetraglyme was higher than to FEP; however when the cells were suspended in heat inactivated serum, cell adhesion to FEP was higher than to polymerized tetraglyme. The surface chemistry of polymerized tetraglyme did not change after 2-hour blood contact, but displayed nitrogen functional groups after 1-day implantation and became slightly degraded after 4-week implantation. The surface chemistry of FEP did not change significantly after blood contact or implantation. Loosely bound proteins such as fibrinogen on polymerized tetraglyme may contribute to the adhesion of PMNs and macrophages and ultimately to fibrous encapsulation (the foreign body response) around the implants.

The effect of fluid shear and co-adsorbed proteins on the stability of immobilized fibrinogen and subsequent platelet interactions

The conformation adopted by the plasma protein fibrinogen upon its adsorption onto synthetic surfaces has been implicated to play an important role in determining the blood compatibility of biomaterials. It has recently been shown that adsorbed fibrinogen undergoes biologically significant conformational changes with increasing residence time on the surface of selected biomaterials. The purpose of this study was to examine the effects of co-adsorbed proteins and shear forces on such time-dependent functional changes in fibrinogen adsorbed onto polyethylene (PE), polytetrafluoroethylene (PTFE), and silicone rubber (SR). Fibrinogen was adsorbed onto these materials for 1 min and then allowed to 'reside' on these surfaces for up to 2 h prior to assessing its biological activity. Changes in fibrinogen reactivity were determined by measuring the adhesion of 51Cr-labeled platelets and the ability of blood plasma to displace previously adsorbed fibrinogen. The magnitude of platelet adhesion to substrates adsorbed with pure fibrinogen increased in the presence of shear, compared with static conditions; at the lowest shear rate of 200 s(-1), samples exhibited a 20-fold increase in adhered platelet levels. In contrast, at a higher shear rate of 1000 s(-1), the three polymers supported minimal levels of platelet attachment. Surfaces pre-adsorbed with 10% plasma did not promote a significant increase in the number of adherent platelets with increasing shear when compared with the pure fibrinogen-coated substrates. The presence of shear also significantly altered the materials' ability to retain fibrinogen. Under static conditions, the amount of fibrinogen retained following incubation in blood plasma increased on all materials with increasing fibrinogen residence time. However, the materials varied distinctly in their ability to retain adsorbed fibrinogen with increasing fibrinogen residence time, shear rate, and nature of the co-adsorbed proteins. Thus, the results from this study indicate that fluid shear, residence time of the adsorbed protein, nature of the co-adsorbed proteins, and surface chemistry of the material all play important roles in influencing platelet-surface interactions and that they act in a complex manner to influence the biocompatibility of a material.

Effects of base material, plasma proteins and FGF2 on endothelial cell adhesion and growth

Blood-contacting materials rapidly acquire a coating of plasma proteins which can lead to local platelet activation and thrombus formation. This phenomenon seriously limits the usefulness of small diameter synthetic vascular grafts. One solution to this problem is to pre-seed or encourage in situ colonisation of the material with endothelial cells to maintain a non-thrombogenic surface. We have investigated the effect of contact with plasma and serum on the subsequent ability of human endothelial cells to adhere to model hydrophobic and hydrophylic plastic surfaces, and the effect of surface bound fibroblast growth factor 2 (FGF2) on endothelial cell proliferation. Cell adhesion was mainly dependent on adsorbed fibrinogen or vitronectin, depending on the polymer surface, and correlated with antibody binding to these molecules rather than quantitative surface concentrations. Cell proliferation was directly correlated with surface bound FGF2. Surface binding of the latter was controlled both by the chemical nature of the polymer surface and by the presence of FGF-binding molecules adsorbed on the surface. FGF2 bound specifically to surface-adsorbed fibrinogen, fibronectin and vitronectin as well as to pre-coated heparan sulphate proteoglycan, perlecan. Binding was significantly inhibited by plasma and serum which contained high levels of FGF2 binding proteins. To be effective in supporting endothelialisation of vascular grafts in vivo, surface-bound FGF2 would need to be protected from surface dissociation into the circulating blood.

Fibrinogen adsorption and platelet interactions on polymer membranes

The hemocompatibility of four different wettable polymer membranes, namely Cuprophan (CE), polyether-polycarbonate (PC-PE), polysulfone (PSU), and polyetherimide (PEI), was investigated with respect to fibrinogen (Fng) adsorption and platelet adhesion/activation. In order to estimate the polar and dispersion components of the surface free energy, contact angles using water/vapor and water/n-hexadecane systems were measured. Adsorption of fibrinogen was studied using fluorescence-labeled protein. The adsorption isotherms showed that the amount and the affinity of adsorbed Fng increased with decreasing surface wettability of the membranes, which correlates with the dispersion and polar components of the surface free energy. The conformational changes of adsorbed Fng were detected by measuring the difference between monoclonal antibody binding to the conformation-sensitive epitope in the D-domain and the binding of polyclonal anti-Fng antibody. The anticipated conformational/orientational changes were greater for PEI and PSU membranes (the least wettable membranes) and negligible for the more wettable PC-PE and CE membranes. In addition, a possible relationship with the degree of platelet activation was found, showing negligible platelet adhesion on PC-PE and CE, but high platelet adhesion on PEI and PSU. Furthermore, platelets were spread to a large extent on PEI, while the formation of aggregates was observed on PSU. This may correspond to the anticipated differences in the conformational state of Fng on both membranes.

Characterizing multicomponent adsorbed protein films using electron spectroscopy for chemical analysis, time-of-flight secondary ion mass spectrometry, and radiolabeling: capabilities and limitations

Characterization of complex adsorbed protein films is a critical aspect of biomaterials science, particularly in understanding the in vivo response to biomaterials. The surface analysis techniques electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are particularly suited to the analysis of complex adsorbed protein films due to their wide applicability to a variety of materials. We have investigated the applicability of ESCA for studying the structure of adsorbed serum and plasma protein layers. ESCA was able to monitor the thickness of the adsorbed protein film. Due to its chemical specificity, ToF-SIMS was used to estimate the composition of the plasma and serum protein layers by comparison of their spectra with the spectra of single protein films. The limit of detection of ToF-SIMS for the plasma protein fibrinogen was determined by comparison with independent radiolabeled fibrinogen adsorption measurements. While ToF-SIMS was able to determine some qualitative trends in the composition of the plasma protein films as a function of adsorption time, the detection limit of the minor components in multicomponent adsorbed protein films ultimately limits the ability of ToF-SIMS to quantify the composition of these films. However, both ESCA and ToF-SIMS can provide useful information on adsorbed plasma protein films without further sample treatment. This study outlines the strengths and weaknesses of ESCA and ToF-SIMS for studying multicomponent adsorbed plasma protein films.

Ultrasensitive probing of the protein resistance of PEG surfaces by secondary ion mass spectrometry

The highly sensitive surface analytical techniques X-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-SIMS) were used to test the resistance of poly(ethylene glycol) (PEG) coatings towards adsorption of lysozyme (LYS) and fibronectin (FN). PEG coatings were prepared by grafting methoxy-terminated aldehyde-PEG (MW 5000 Da) onto two amino-functionalised surfaces with different amine group densities, generated by radio frequency glow discharge polymerisation of n-heptylamine and allylamine. Grafting was performed at the lower critical solution temperature to maximise the graft density of the PEG chains. XPS showed that the grafted density of PEG chains was slightly higher on the allylamine surface. XPS detected no adsorption of either protein on either PEG coating. ToF-SIMS analysis, on the other hand, found, in the positive ion spectra, minute but statistically significant signals assignable to amino acid fragment ions from both proteins adsorbed to the lower density PEG coating and from LYS but not FN on the higher density PEG coating. Negative ion spectra contained relatively more intense protein fragment ion signals for the lower density PEG coating but no changes assignable to adsorbed proteins on the higher density PEG coating. These results demonstrate the importance of utilising highly sensitive techniques to study protein adsorption on surfaces intended to be protein resistant, and that both positive and negative ion ToF-SIMS spectra should be acquired to probe for possible very low levels of protein adsorption.

Inhibition of monocyte adhesion and fibrinogen adsorption on glow discharge plasma deposited tetraethylene glycol dimethyl ether

Monocytes and macrophages play important roles in host responses to implanted biomedical devices. Monocyte and macrophage interactions with biomaterial surfaces are thought to be mediated by adsorbed adhesive proteins such as fibrinogen and fibronectin. Non-fouling surfaces that minimize protein adsorption may therefore minimize monocyte adhesion, activation, and the foreign body response. Radio-frequency glow discharge plasma deposition (RF-GDPD) of tetraethylene glycol dimethyl ether (tetraglyme) was used to produce polyethylene oxide (PEO)-like coatings on a fluorinated ethylene-propylene (FEP) surface. Electron spectroscopy for chemical analysis (ESCA) and static time of flight secondary ion mass spectrometry (ToF-SIMS) were used to characterize the surface chemistry of tetraglyme coating. Fibrinogen adsorption to the tetraglyme surface was measured with 125I-labeled fibrinogen and ToF-SIMS. Adsorption of fibrinogen to plasma deposited tetraglyme was less than 10 ng cm(-2), a 20-fold decrease compared to untreated FEP or tissue culture polystyrene (TCPS). Monocyte adhesion to plasma deposited tetraglyme was significantly lower than adhesion to FEP or TCPS. In addition, when the surfaces were preadsorbed with fibrinogen, fibronectin, or blood plasma, monocyte adhesion to plasma deposited tetraglyme after 2 h or 1 day was much lower than adhesion to FEP. RF-GDPD tetraglyme coating provides a promising approach to make non-fouling biomaterials that can inhibit non-specific material-host interactions and reduce the foreign body response.

Platelet adhesion to polystyrene-based surfaces preadsorbed with plasmas selectively depleted in fibrinogen, fibronectin, vitronectin, or von Willebrand's factor

Four plasma proteins have been shown to be able to mediate platelet adhesion to synthetic materials when they are adsorbed as purified proteins: fibrinogen (Fg), fibronectin (Fn), vitronectin (Vn), and von Willebrand factor (vWF). Among them, Fg is thought to play a leading role in mediating platelet adhesion to plasma-preadsorbed biomaterials, but this has been established for only three types of materials so far in our laboratory. Furthermore, the role of Fn, Vn, and vWF in mediating platelet adhesion to plasma-preadsorbed surfaces is still unclear. The aim of the current study was to assess the importance of Fg, Fn, Vn, and vWF in mediating platelet adhesion to a series of polystyrene-based surfaces. The strategy applied in the present investigation was to compare platelet adhesion to surfaces preadsorbed with normal plasma, plasma selectively depleted in Fn or Vn or both Fn and Vn, plasma from donors who were genetically deficient in vWF, and serum. Few platelets adhered to the surfaces preadsorbed with serum, whereas depletion of Fn, Vn, or vWF from plasma did not decrease platelet adhesion significantly. Replenishment of exogenous Fg to serum before protein adsorption restored platelet adhesion to the surfaces, suggesting that Fg was the major plasma protein that mediated platelet adhesion. Also, we found that a surface density of adsorbed Fg far below the amount that usually adsorbs to synthetic surfaces was sufficient to support full-scale platelet adhesion.

PEO-grafting on PU/PS IPNs for enhanced blood compatibility--effect of pendant length and grafting density

Polyurethane (PU) homopolymers and PU/polystyrene (PS) interpenetrating polymer networks (IPNs) were successfully synthesized changing the length of the pendant poly(ethylene oxide) (PEO) chains and the grafting density of PEO chains. All the PU/PS IPNs had the microphase-separated structures in which the PS-rich phase domains were dispersed in the matrix of the PU-rich phase. The domain size decreased a little, as the degree of grafting with PEO chains was increased. The water swelling ratio increased, and the interfacial energy decreased, as the length of the pendant PEO chains, and the grafting density of PEO chains of the PEO-grafted PU/PS IPNs were increased, since the mobile hydrophilic pendant PEO chains effectively induced and absorbed the water, when they were contacted with water. The hydrophilic and highly concentrated pendant PEO chains could easily prohibit the adhesion of the fibrinogens and the platelets on the surface, and the blood compatibility of IPNs was enhanced by increasing of grafting with PEO chains. The adsorption of the fibrinogens and the platelets was suppressed, as the length of pendant PEO chains, and the grafting density were increased.

GpIIb/IIIa is the main receptor for initial platelet adhesion to glass and titanium surfaces in contact with whole blood

Platelets are the first cells to adhere to a surface in contact with blood and are capable of mediating several different responses after contact with different protein-coated surfaces. They are the main source of growth factors such as platelet-derived growth factor and are therefore important in the healing process. In this study, initial platelet adhesion to and spread on hydrophilic and hydrophobic (methylized) glass and titanium with similar wettability were investigated. Whole coagulating blood was used to simulate the in vivo situation shortly after implantation, in which bleeding precedes inflammation and wound healing. Several different antibodies directed against platelet integrins and receptors (CD9, FcgammaRII, GPIIb/IIIa, vitronectin receptor, GPIb/V/IX) were used in an attempt to block platelet adhesion to the surfaces. Immunofluorescence results show that initial platelet adhesion to all the surfaces we investigated can be almost completely inhibited (approximately 95%) by clone M148, an antibody against the GPIIb/IIIa complex (integrin alpha(IIb)beta(3); CD41/CD61), but not with other antibodies to the separate parts of the integrin. Antibodies known to inhibit fibrinogen binding to GPIIb/IIIa after adenosine diphosphate- and collagen- induced aggregation had very little effect on initial platelet adhesion. None of the other integrins were found to have such an effect on initial platelet adhesion. Antibody clone M148 was furthermore found to inhibit platelet spreading. This study shows that regardless of wettability and the biomaterial used, initial adhesion of platelets appears to be mediated by GPIIb/IIIa binding to surface adsorbed fibrinogen.

Poly2-methoxyethylacrylate (PMEA) coated oxygenator: an ex vivo study

PMEA is a hydrophilic polymer coating with a unique design that minimizes the adsorption and denaturation of proteins and blood cells. This study compares thrombus resistance, blood path resistance, thrombocyte profile, and blood trauma of the PMEA coated Capiox membrane oxygenator (Terumo, Japan) vs. an uncoated version.

METHOD

Six calves (mean bodyweight: 75.3 +/- 4.5kg) were placed on cardiopulmonary bypass for 6 hours and randomly assigned to the coated or uncoated oxygenator, with a low heparinisation protocol (ACT > 180s).

RESULTS

Macroscopically, red staining was observed in all uncoated oxygenators, and in none of the coated ones. Inlet pressure was significantly higher in the uncoated group (at 1 h: 279 +/- 25 vs. 175 +/- 11mmHg, p < 0.01 and at 6h: 217 +/- 10 vs. 171(8mmHg, p < 0.01). Thrombocyte count values (corrected for hematocrit and normalized by prebypass values) were significantly higher in the coated group (at 1 h: 76 +/- 6 vs. 53 +/- 13%, p < 0.01 and at 6 h: 70 +/- 6 vs. 44 +/- 26%, p < 0.01). Plasma hemoglobin was below 100mg/L in both groups throughout the experiments.

CONCLUSIONS

When compared with uncoated oxygenator, PMEA coated oxygenator exhibited increased thrombus resistance with lower inlet pressure and lower thrombocyte consumption. In both groups, trauma to red cells was minimal, emphasizing the efficient design of this type of oxygenator.

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.

Co-adsorbed fibrinogen and von Willebrand factor augment platelet procoagulant activity and spreading

Previously we observed that platelets adherent to surfaces preadsorbed with blood plasma exhibited 1.3 to 2.4 times greater procoagulant activity than platelets on surfaces adsorbed with fibrinogen (Fg) only. These observations suggested that the adhesion proteins adsorbed from plasma may activate platelets in a cooperative, or synergistic manner. In the present study, polystyrene surfaces adsorbed with both Fg and vWF induced up to three times greater procoagulant activity than surfaces adsorbed with Fg or vWF only. The amounts of Fg and vWF adsorbed from binary mixtures that resulted in increased procoagulant activity were found to be similar to the amounts that adsorbed to PS from 100% plasma. The effect of adsorbed adhesion proteins on platelet spreading was also investigated. The proportion of fully spread platelets increased, depending on the adhesion protein preadsorbed to the surface, in the following order: vWF < Fg < Fn < (vWF + Fg) < Vn < plasma.

Hemocompatibility of heparin-coated surfaces and the role of selective plasma protein adsorption

Although several studies have shown that heparin-coated surfaces reduce the activation of both the complement system and the coagulation system, there is still inadequate understanding of the factors initiating and controlling blood activation at these surfaces. We investigated the adsorption profile of 12 common plasma proteins (and the platelet receptor CD41) to a heparin coating (Carmeda BioActive surface (CBAS)) compared to uncoated controls (PVC) by using an in vitro whole blood Chandler-Loop model. Surface bound proteins were studied kinetically by a direct ELISA technique. Western blots were performed on the SDS eluates in order to detect adsorbed cleavage products and denatured proteins. Changes in plasma levels of neutrophil activation markers, platelet activation, coagulation activation, complement activation and the inflammatory response were measured by conventional ELISAs. This study showed significant differences in adsorption patterns among the heparin-coated and the uncoated surfaces, notably for fibronectin, fibrinogen, C3 and high molecular weight kininogen (HMWK). The kinetic studies confirmed the results obtained from Western blots and indicated specific adsorption profiles of plasma proteins. We assume that at least some of the improved blood compatibility of the heparin-coated surfaces may be ascribed to the selective uptake and cleavage of plasma proteins.

The effects of surface chemistry and adsorbed proteins on monocyte/macrophage adhesion to chemically modified polystyrene surfaces

Monocytes and macrophages play critical roles in inflammatory responses to implanted biomaterials. Monocyte adhesion may lead to macrophage activation and the foreign body response. We report that surface chemistry, preadsorbed proteins, and adhesion time all play important roles during monocyte adhesion in vitro. The surface chemistry of tissue culture polystyrene (TCPS), polystyrene, Primaria, and ultra low attachment (ULA) used for adhesion studies was characterized by electron spectroscopy for chemical analysis. Fibrinogen adsorption measured by (125)I-labeled fibrinogen was the lowest on ULA, higher on TCPS, and the highest on polystyrene or Primaria. Monocyte adhesion on protein preadsorbed surfaces for 2 h or 1 day was measured with a lactate-dehydrogenase method. Monocyte adhesion decreased over time. The ability of preadsorbed proteins to modulate monocyte adhesion was surface dependent. Adhesion was the lowest on ULA, higher and similar on TCPS or polystyrene, and the highest on Primaria. Monocyte adhesion on plasma or fibrinogen adsorbed surfaces correlated positively and linearly to the amount of adsorbed fibrinogen. Preadsorbed fibronectin, immunoglobulin G, plasma, or serum also promoted adhesion compared with albumin preadsorbed or uncoated surfaces. Overall, biomaterial surface chemistry, the type and amount of adsorbed proteins, and adhesion time all affected monocyte adhesion in vitro.

Blood compatibility--a perspective

This perspective on blood- materials interactions is intended to introduce the set of papers stemming from the symposium, "Devices and Diagnostics in Contact with Blood: Issues in Blood Compatibility at the Close of the 20th Century," organized on August 4-6, 1999 at the University of Washington by the University of Washington Engineered Biomaterials (UWEB) Engineering Research Center. This article outlines some of the history of blood contacting materials, overviews the work that has originated at the University of Washington over the past 28 years, speculates on the origins of the controversies on blood compatibility and considers the issues that should be addressed in future studies.

Molecular basis of biomaterial-mediated foreign body reactions

Despite being inert and nontoxic, implanted biomaterials often trigger adverse foreign body reactions such as inflammation, fibrosis, infection, and thrombosis. With regard to the inflammatory responses to biomaterial implants, it was previously found that a crucial precedent event was the spontaneous adsorption and denaturation of fibrinogen on implant surfaces. It was further found that interactions between the phagocyte integrin Mac-1 (CD11b/CD18) and one short sequence within the fibrinogen D domain (gamma 190-202; P1) at least partially explained phagocyte accumulation on implant surfaces. However, the reason that adsorbed fibrinogen is proinflammatory--while soluble fibrinogen clearly is not--remained obscure. In this study, therefore, the question of how fibrinogen is converted to a proinflammatory state when adsorbed to biomaterial surfaces is investigated. In soluble fibrinogen, the 13 amino acid P1 sequence was found to be hidden. However, the adsorption and denaturation of fibrinogen on the surfaces of commonly used biomaterials lead to the exposure of P1 and a second neo-epitope, gamma 377-395 (P2), which also interacts with Mac-1 and is similarly occult in the soluble protein. The extent of biomaterial-mediated P1 and P2 exposure appears directly related to the severity of inflammatory responses to a test panel of biomaterials. Finally, thrombin-mediated conversion of fibrinogen to fibrin also exposes both P1 and P2 epitopes. These observations may help explain both the inflammation caused by many types of implanted biomaterials and that which occurs naturally following thrombotic events. (Blood. 2001;98:1231-1238)

The effect of adsorbed fibrinogen, fibronectin, von Willebrand factor and vitronectin on the procoagulant state of adherent platelets

Procoagulant (activated) platelets provide a site for assembly of the prothrombinase complex which can rapidly convert prothrombin into thrombin (a potent inducer of clot formation). Previously, we reported that adhesion of platelets to surfaces preadsorbed with blood plasma caused them to become procoagulant. In the present study we investigated the effect of adsorbed adhesion proteins (fibrinogen (Fg), fibronectin (Fn), von Willebrand factor (vWF) and vitronectin (Vn)) on the procoagulant activity of adherent platelets. Adsorbed Fn, vWF and Fg promoted platelet adhesion in the following order: Fn < vWF = Fg. However, these proteins promoted platelet activation (thrombin generation per adherent platelet) in the following order: Fg < Fn < vWF. Adsorption with a series of dilutions of normal plasma, serum, and plasmas deficient in or depleted of von Willebrand factor (de-vWF), fibronectin (de-Fn), vitronectin (de-Vn), or both vitronectin and fibronectin (de-VnFn) resulted in varied platelet adhesion, but little difference in platelet activation. However, preadsorption with dilute de-vWF plasma induced lower procoagulant activity than normal plasma. Preadsorption with normal plasma resulted in higher levels of platelet activation than preadsorption with Fg, suggesting that adsorption of plasma proteins other than Fg caused the high levels of activation observed for plasma preadsorbed surfaces.

Platelet adhesion and procoagulant activity induced by contact with radiofrequency glow discharge polymers: roles of adsorbed fibrinogen and vWF

The potential hemocompatibility of radiofrequency glow discharge (RFGD) polymers made by copolymerization of mixtures of hexafluoropropene and ethylene (C(3)F(6)/C(2)H(4)) or acrylic acid and 1,7-octadiene was investigated using in vitro assays for platelet adhesion and platelet catalyzed thrombin generation. Thrombin generation rate normalized to platelet number was used as a measurement of platelet activation (procoagulant activity). RFGD polymers produced by copolymerization of acrylic acid and 1, 7-octadiene contained varying amounts of carboxylic acid species as determined by electron spectroscopy for chemical analysis (ESCA). These polymers induced little variation in platelet adhesion, thrombin generation, or platelet activation. RFGD polymerization of C(3)F(6) and C(2)H(4) resulted in polymers with varying proportions of fluorinated species, as determined by ESCA. Fibrinogen adsorption from plasma was maximal on a polymer made with 25% C(3)F(6) (75% C(2)H(4)) in the feed. However von Willebrand factor (vWF) adsorption was greater on polymers made with increased %C(3)F(6) in the feed. Platelet adhesion decreased with increasing %C(3)F(6) in the feed. Thrombin generation was lowest for platelets adherent to polymers made from both C(3)F(6) and C(2)H(4). Therefore, procoagulant activity of platelets increased for polymers made with increased %C(3)F(6) in the feed, similar to the trend in vWF adsorption. These findings suggest that increased incorporation of fluorinated species into RFGD polymers leads to decreased platelet adhesion and increased platelet activation (which is possibly due to increased vWF adsorption).

Blood compatible aspects of poly(2-methoxyethylacrylate) (PMEA)--relationship between protein adsorption and platelet adhesion on PMEA surface

Platelet adhesion and spreading is suppressed when a poly(2-methoxyethylacrylate) (PMEA) surface is used, compared with other polymer surfaces. To clarify the reason for this suppression, the relationship among the amount of the plasma protein adsorbed onto PMEA, its secondary structure and platelet adhesion was investigated. Poly(2-hydroxyethylmethacrylate) (PHEMA) and polyacrylate analogous were used as references. The amount of protein adsorbed onto PMEA was very low and similar to that absorbed onto PHEMA. Circular dichroism (CD) spectroscopy was applied to examine changes in the secondary structure of the proteins after adsorption onto the polymer surface. The conformation of the proteins adsorbed onto PHEMA changed considerably, but that of proteins adsorbed onto PMEA differed only a little from the native one. These results suggest that low platelet adhesion and spreading are closely related to the low degree of the denaturation of the protein adsorbed onto PMEA. PMEA could be developed as a promising material to produce a useful blood-contacting surface for medical devices.

The in vitro blood compatibility of poly(ethylene oxide)-grafted polyurethane/polystyrene interpenetrating polymer networks

Poly(ethylene oxide) (PEO)-grafted polyurethane (PU)/polystyrene (PS) interpenetrating polymer networks (IPNs) were synthesized. The effects of the mobile pendant PEO chains with their microphase separated structure on blood-compatibility were investigated. The morphology of both the fracture surface as well as the top surface indicate that the size of the dispersed domains of the PS-rich phase decreased as the grafting with the PEO was increased. The swelling ratio also decreased as the grafting with the PEO was increased. However, the dynamic contact angle and the interfacial energy between IPN surface and water decreased, due to the structural reorganization of the pendant PEO chains. PU/PS IPNs have an excellent mechanical property as compared with PU homopolymers. The adsorption of bovine plasma fibrinogen (BPF) onto the PU/PS IPNs and PU homopolymers was effectively suppressed by the PEO-grafting. In the platelet adhesion test, the amount of platelets adsorbed, activated, and/or coagulated upon the PEO-grafted PU/PS IPNs were reduced when compared to the ungrafted PU homopolymers.