Physicochemical and biochemical aspects of fibrinogen adsorption from plasma and binary protein solutions onto polyethylene and glass

Fibrinogen adsorption to biomaterials

Fibrinogen (Fg) adsorption is an important mechanism underlying cell adhesion to biomaterials and was the major focus of the author's research career. This article summarizes our work on Fg adsorption, with citations of related work as appropriate. The molecular properties of Fg that promote adsorption and cell adhesion will be described. In addition, the adsorption behavior of Fg from buffer, binary solutions with other proteins, and blood plasma will be discussed, including the Vroman effect. Studies of platelet adhesion to surfaces preadsorbed with blood plasmas selectively deficient in Fg, vitronectin (Vn), fibronectin (Fn), or von Willebrand's factor (vWf) will be reviewed. These studies clearly showed a major role for Fg in platelet adhesion under static conditions and both Fg and vWf for adhesion from flowing suspensions, but no significant role for Vn or Fn. However, it was also shown that platelet adhesion was poorly correlated with the total amount of adsorbed Fg, but very well correlated with the binding of antibodies specific to the cell binding domains of Fg. A brief overview of nonfouling surfaces for prevention of Fg adsorption will be given. A more extensive discussion of structural changes in Fg after its adsorption is included, including changes detected with both physicochemical and biological methods. A short discussion of the state of the art of structural determination of adsorbed proteins with computational methods is also given. A final section identifies Fg adsorption as the single most important event determining the biocompatibility of implants in soft tissue and in blood. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2777-2788, 2018.

Biofluid spectroscopic disease diagnostics: A review on the processes and spectral impact of drying

The complex patterns observed from evaporated liquid drops have been examined extensively over the last 20 years. Complete understanding of drop deposition is vital in many medical processes, and one which is essential to the translation of biofluid spectroscopic disease diagnostics. The promising use of spectroscopy in disease diagnosis has been hindered by the complicated patterns left by dried biological fluids which may inhibit the clinical translation of this technology. Coffee-ring formation, cracking and gelation patterns have all been observed in biofluid drops, and with surface homogeneity being a key element to many spectroscopic techniques, experimental issues have been found to arise. A better understanding of the fundamental processes involved in a drying droplet could allow efficient progression in this research field, and ultimately benefit the population with the development of a reliable cancer diagnostic.

Inorganic nanoparticle biomolecular corona: formation, evolution and biological impact

Physicochemical changes to inorganic nanoparticles (NPs) in biological environments determine their impact. Blood, lymph, mucus, complete cell culture media and other biological fluids contain a large amount and variety of different molecules. NPs dispersed in these fluids are sensitive to such environments. One of the most significant alterations is the formation of the NP–protein corona (PC) as a result of the adsorption of proteins onto the inorganic surface. This process is currently gaining attention in the field of inorganic NPs since this spontaneous coating gives a biological identity to the composite NP–PC and determines the interactions between the NP and the host in living systems. Therefore, knowledge of NP–PC formation is crucial for understanding the evolution, biodistribution and reactivity of NPs inside organisms and, therefore, for the safe design of engineered NPs.

Topography-induced cell adhesion to Acr-sP(EO-stat-PO) hydrogels: the role of protein adsorption

Topographic surface patterning of intrinsically non-adhesive P(EO-stat-PO)-based hydrogels can lead to the adhesion and spreading of fibroblasts. Explanations for this unexpected behavior are discussed, particularly with regard to non-specific protein adsorption from the serum-supplemented culture medium. The presence of serum proteins is shown to be essential for adhesion. Adsorption of plasma and ECM proteins (Fibronectin (FN) and Vitronectin (VN)) to the hydrogels is possible. The effect of VN on initial cell adhesion is analyzed in detail. It appears that VN is the main serum component that is crucial for initial cell adhesion to PEG and that surface topography is essential for further, durable adhesion establishment, and spreading.

Fibrinogen and von Willebrand factor mediated platelet adhesion to polystyrene under flow conditions

The roles of adsorbed fibrinogen (Fg) and von Willebrand factor (VWF) in mediating platelet adhesion to synthetic surfaces under flow were investigated using polystyrene (PS) as a model hydrophobic surface. We measured platelet adhesion to PS pre-adsorbed with Fg, VWF, normal plasma, afibrinogenemic plasma, VWF-deficient plasma and deficient plasmas with various concentrations of added Fg or VWF. Platelets in a red blood cell suspension were passed through a flow chamber at either low (50 or 100 s(-1)) or high (500 or 1000 s(-1)) shear. Adhesion to PS pre-adsorbed with afibrinogenemic plasma was very low under both low and high shear conditions, but was restored in a dose-dependent manner with addition of Fg. Less than 20 ng/cm(2)of adsorbed Fg was sufficient to support full-scale platelet adhesion under flow. At high shear rate, platelet adhesion on PS pre-adsorbed with VWF-deficient plasma was much less than on PS pre-adsorbed with normal plasma, but adhesion to PS pre-adsorbed with VWF-deficient plasma with added VWF was very similar to adhesion to PS pre-adsorbed with normal plasma. At low shear, adhesion to PS pre-adsorbed with VWF-deficient plasma was the same as on PS pre-adsorbed with normal plasma. As little as 1 ng/cm(2) of VWF adsorbed from plasma made platelet adhesion higher under high shear than under low shear. The effects of adsorbed Fg and VWF on the morphologies of platelets that adhered from suspensions flowing at high shear rates were also investigated. The lack of either Fg or VWF resulted in marked decreases in the extent of platelet spreading. Real-time observation of platelet adhesion under an epifluorescent microscope showed that platelets adhered to the surface in a linear pattern aligned in the direction of flow under high shear conditions.

Sol-gel-derived TiO(2)-SiO (2) implant coatings for direct tissue attachment. Part I: design, preparation and characterization

A series of sol-gel derived TiO(2)-SiO(2) mixed oxide coatings were prepared by carefully controlling the process parameters to obtain silica-releasing coatings consisting of nanoparticles. These features are of paramount importance for enhanced cell adhesion and activation. To achieve both these goals the Ti-alkoxide and Si-alkoxide were first separately hydrolysed and the titania-silica mixed sol was further reacted before the dipping process to obtain the desired particle sizes resulting to the biologically favourable topographical features. Silica release was observed from all the prepared coatings and it was dependent on SiO(2) amount added to the sols, i.e., the higher the added amount the higher the release. In addition, calcium phosphate was able to nucleate on the coatings. From the obtained SiO(2) dissolution data, together with the detailed XPS peak analysis, the mixed oxide coatings are concluded to be chemically heterogeneous, consisting of TiO(2) and SiO(2) species most likely linked together by Ti-O-Si bonds. TiO(2) is chemically stable making long-term implant coating possible and the desired nanoscale dimensions were well preserved although the composition was changed as a consequence of SiO(2) dissolution under in vitro conditions.

Mediation of biomaterial-cell interactions by adsorbed proteins: a review

An appropriate cellular response to implanted surfaces is essential for tissue regeneration and integration. It is well described that implanted materials are immediately coated with proteins from blood and interstitial fluids, and it is through this adsorbed layer that cells sense foreign surfaces. Hence, it is the adsorbed proteins, rather than the surface itself, to which cells initially respond. Diverse studies using a range of materials have demonstrated the pivotal role of extracellular adhesion proteins--fibronectin and vitronectin in particular--in cell adhesion, morphology, and migration. These events underlie the subsequent responses required for tissue repair, with the nature of cell surface interactions contributing to survival, growth, and differentiation. The pattern in which adhesion proteins and other bioactive molecules adsorb thus elicits cellular reactions specific to the underlying physicochemical properties of the material. Accordingly, in vitro studies generally demonstrate favorable cell responses to charged, hydrophilic surfaces, corresponding to superior adsorption and bioactivity of adhesion proteins. This review illustrates the mediation of cell responses to biomaterials by adsorbed proteins, in the context of osteoblasts and selected materials used in orthopedic implants and bone tissue engineering. It is recognized, however, that the periimplant environment in vivo will differ substantially from the cell-biomaterial interface in vitro. Hence, one of the key issues yet to be resolved is that of the interface composition actually encountered by osteoblasts within the sequence of inflammation and bone regeneration.

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.

Use of sol-gel-derived titania coating for direct soft tissue attachment

A firm bond between an implant and the surrounding soft tissue is important for the performance of many medical devices (e.g., stents, canyls, and dental implants). In this study, the performance of nonresorbable and reactive sol-gel-derived nano-porous titania (TiO(2)) coatings in a soft tissue environment was investigated. A direct attachment between the soft tissue and the sol-gel-derived titania coatings was found in vivo after 2 days of implantation, whereas the titanium control implants showed no evidence of soft tissue attachment. The coated implants were in immediate contact with the connective tissue, whereas the titanium controls formed a gap and a fibrous capsule on the implant-tissue interface. The good soft tissue attachment of titania coatings may result from their ability to initiate calcium phosphate nucleation and growth on their surfaces (although the formation of poorly crystalline bonelike apatite does not occur). Thus, the formation of a bonelike CaP layer is not crucial for their integration in soft tissue. The formation of bonelike apatite was hindered by the adsorption of proteins onto the initially formed amorphous calcium phosphate growth centers, thus preventing the dissolution/reprecipitation processes required for the formation of poorly crystalline bonelike apatite. These findings might open novel application areas for sol-gel-derived titania-based coatings.

Effects of fibrinogen residence time and shear rate on the morphology and procoagulant activity of human platelets adherent to polymeric biomaterials

Fibrinogen readily adsorbs to the surface of biomaterials and, because of its demonstrated ability to support platelet adhesion and aggregation, plays a role in thrombotic events associated with the implantation of synthetic materials in the human body. Thus, understanding the factors influencing the interactions of fibrinogen with biomaterials, and how platelet responses are affected, is crucial for the development of synthetic materials exhibiting improved blood compatibility. In this study, the effects of fibrinogen residence time and shear rate on the procoagulant activity of adherent platelets, along with their morphologic status, as deduced from scanning electron microscopy, were investigated. To examine whether adherent platelets promoted the generation of thrombin, polymeric materials (polytetrafluoroethylene, polyethylene, and silicone rubber) preadsorbed with fibrinogen were exposed to platelet suspensions at different wall shear rates and then incubated with clotting factors for 5 minutes under static conditions. The amount of thrombin generated per platelet was calculated from the optical density of the color developed by adding substrate S-2238. Scanning electron microscopy images of the platelets revealed that the platelets exhibited different morphologies, depending on the shear rate and residence time of the adsorbed fibrinogen. Platelets ranged from their normal discoid shape observed primarily under static conditions, to that of fully spread platelets. Results from this study show that platelets, in the presence of shear forces, undergo activation on exposure to surfaces on which adsorbed fibrinogen has resided for short residence times rather than long residence times. Interestingly, studies examining the procoagulant responses of such adherent platelets demonstrated that the platelets attached to the fibrinogen coated materials did not promote significant thrombin generation. Such low prothrombinase activity of adherent platelets suggests that adsorbed fibrinogen, while capable of supporting platelet adhesion and spreading on biomaterials, does not necessarily enhance the procoagulant activity of adherent platelets.

On-line deproteinization by adsorption of proteins on a polyethylene powder pre-column for the determination of Na, K, Mg and Ca in human serum by high-performance liquid chromatography

Deproteinization of human serum was carried out on-line using a polyethylene powder cartridge as pre-column. The serum sample, after dilution, was injected into the chromatograph, and when passing through the cartridge the proteins were adsorbed by the polyethylene. A protein-free eluate was carried to the analytical column while the pre-column was washed with methanol and water to elute the adsorbed proteins by changing the pump channels. After washing, the pre-column was conditioned with the eluent to receive the next sample. Deproteinization was evaluated off- and on-line using pooled serum, and testing the protein residue after passing through a polyethylene cartridge with the Comassie Brilliant Blue reaction. Parameters such as serum volume, eluent and washing solution were investigated. Sodium, potassium, magnesium and calcium determinations were performed by high-performance liquid chromatography with conductimetric detection. The proposed method is suitable for the determination of these cations in serum samples without further treatments. The total analysis time was about 20 min and a linear range from 0.3 to 1.2 mg/l for sodium, potassium, magnesium and calcium was observed. The method was characterized by a precision of about 95% and recoveries from spiked samples were between 96 and 102%. The results for serum samples analysed by the proposed method were compared with photometry and atomic absorption spectrometry.

Initial events at the bioactive glass surface in contact with protein-containing solutions

Upon implantation, bioactive glass undergoes a series of reactions that leads to the formation of a calcium phosphate-rich layer. Most in vitro studies of the changes that occur on the surface of bioactive glass have employed the use of buffer solutions with compositions reflecting the ionic composition of interstitial fluid. Although these studies have documented the physical and chemical changes associated with bioactive glass immersed in aqueous media, they do not reveal the effect of serum proteins and cells that are present at the implantation site. In the present study, we document, using atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS), significant differences in the reaction layer composition, thickness, morphology, and kinetics of formation arising from the presence of serum proteins. The data reveal that the uniform and rapid adsorption of serum proteins on the surface may serve to protect the surface from further direct interaction with the aqueous media, slowing down the transformation reactions. This finding is in agreement with previous studies that have shown that the presence of serum proteins significantly delays the formation of hydroxyapatite at the surface of bioactive glass. These data also support the hypothesis that initial reaction layers in vivo interact with cells in order to produce the tissue-bioactive glass interface typically observed on ex vivo specimens.

Human plasma fibrinogen adsorption and platelet adhesion to polystyrene

The purpose of this study was to further investigate the role of fibrinogen adsorbed from plasma in mediating platelet adhesion to polymeric biomaterials. Polystyrene was used as a model hydrophobic polymer; i.e., we expected that the role of fibrinogen in platelet adhesion to polystyrene would be representative of other hydrophobic polymers. Platelet adhesion was compared to both the amount and conformation of adsorbed fibrinogen. The strategy was to compare platelet adhesion to surfaces preadsorbed with normal, afibrinogenemic, and fibrinogen-replenished afibrinogenemic plasmas. Platelet adhesion was determined by the lactate dehydrogenase (LDH) method, which was found to be closely correlated with adhesion of 111In-labeled platelets. Fibrinogen adsorption from afibrinogenemic plasma to polystyrene (Immulon I(R)) was low and <10 ng/cm2. Platelet adhesion was absent on surfaces preadsorbed with afibrinogenemic plasma when the residual fibrinogen was low enough (<60 microg/mL). Platelet adhesion was restored on polystyrene preadsorbed with fibrinogen-replenished afibrinogenemic plasma. Addition of even small, subnormal concentrations of fibrinogen to afibrinogenemic plasma greatly increased platelet adhesion. In addition, surface-bound fibrinogen's ability to mediate platelet adhesion was different, depending on the plasma concentration from which fibrinogen was adsorbed. These differences correlated with changes in the binding of a monoclonal antibody that binds to the Aalpha chain RGDS (572-575), suggesting alteration in the conformation or orientation of the adsorbed fibrinogen. Platelet adhesion to polystyrene preadsorbed with blood plasma thus appears to be a strongly bivariate function of adsorbed fibrinogen, responsive to both low amounts and altered states of the adsorbed molecule.

Rapid postadsorptive changes in fibrinogen adsorbed from plasma to segmented polyurethanes

Fibrinogen adsorbed to biomaterials plays a key role in mediating platelet interactions that can lead to blood clotting so its behavior on surfaces is of fundamental interest. In previous work showing that fibrinogen adsorbed to surfaces quickly becomes non-displaceable upon exposure to blood plasma, the fibrinogen was adsorbed from buffer, so we performed new studies in which the displaceability of fibrinogen adsorbed from plasma was characterized. Fibrinogen was adsorbed from 1% plasma to seven different surfaces for 1-64 min and then transferred to 100% plasma lacking radiolabeled fibrinogen and the amount adsorbed before and after transfer measured. The surfaces were glass, Silicone rubber, and five different polyurethanes. As adsorption time increased, the fibrinogen became increasingly resistant to displacement during the 100% plasma step, but the rate of increase in resistance varied greatly with surface type. Fibrinogen adsorbed from 1% plasma evidently undergoes rapid, surface dependent transitions. This work shows that the transitions that occur when the fibrinogen is adsorbed from blood plasma are similar to what we have previously observed for fibrinogen adsorbed from buffer.

Kinetics of the homogeneous exchange of alpha-lactalbumin adsorbed on titanium oxide surface

The homogeneous exchange process whereby alpha-lactalbumine molecules adsorbed on hydrophilic titanium oxide particles are replaced by alpha-lactalbumine molecules in solution has been investigated by means of a 125I radio-labeling technique, alpha-lactalbumine is a compact and highly negatively charged protein, making this study complementary to previous work devoted to the general understanding of the exchange mechanisms of adsorbed proteins on solid surfaces. The isotherm of alpha-lactalbumine exhibits bimodal adsorption shape, and the exchange process whereby adsorbed proteins are replaced by new incoming ones from the bulk solution has been studied at both the upper and the lower plateau of the isotherm. In the upper plateau the exchange process was found to be of first order with respect to the bulk molecules, and the release rate constant was equal to 0.914 L. mol-1.s-1. This behavior is identical to what has been observed with other proteinic systems. In the lower plateau domain, in contrast, the protein release process is independent of the concentration of proteins in the bulk, but the release rates are higher than the pure desorption rates. This constitutes, to our knowledge, a behavior that never before has been observed and that remains to be explained.

Detection of specific plasma proteins on surfaces by immunospecific adhesion of dyed polystyrene beads

This paper describes and evaluates a method for quantifying the amounts of specific plasma proteins adsorbed to biomaterial surfaces. In particular, it demonstrates that macroscopic images ('stains'), that assess the spatial distribution of albumin, IgG, fibrinogen, and HMK (high molecular weight kininogen), can be obtained over areas of at least 12 cm2 using immunospecific adhesion of dyed polystyrene beads. Stain intensities, measured with a scanner and an image analysis system, were found to quantify the amount of specific protein in the solution used to coat the surfaces. Results obtained with the proposed method produced single protein isotherms for albumin, immunoglobulin G (IgG) and fibrinogen that followed Langmuir-like adsorption behavior and were similar to previously published isotherms. The HMK isotherm also exhibited Langmuir-like adsorption behavior. The proposed method also detected the presence of an expected maximum in the adsorption of fibrinogen onto glass as a function of plasma dilution. Adsorption of fibrinogen out of 6.4% plasma onto glass from a separated flow produced results indicating the quantity as well as the location of fibrinogen at the boundary of the separated region. This result confirmed the utility of the proposed method for detecting spatial distributions of specific proteins adsorbed from plasma in practical devices.

Initial hemocompatibility studies of titanium and zirconium alloys: prekallikrein activation, fibrinogen adsorption, and their correlation with surface electrochemical properties

Two novel metal alloys, Ti-13Nb-13Zr and Zr-2.5Nb, have been engineered for applications in orthopedic implants because of their favorable mechanical properties, corrosion resistance, and compatibility with bone and tissue. These alloys also have the ability to form a hard, abrasion-resistant, ceramic surface layer upon oxidative heat treatment (diffusion hardening, DH). Previous studies have indicated that these and other ceramics cause limited hemolysis and exhibit remarkable structural integrity after extended exposure to physiological environments. Such observations suggest that DH Ti-13Nb-13Zr and ZrO2/Zr-2.5Nb could be used successfully as components in blood-contacting devices. Materials intended for such applications must possess properties that do not elicit adverse physiological responses, such as the initiation of the coagulation cascade or thrombus formation. In the present study measurements of prekallikrein activation, fibrinogen adsorption from diluted human plasma, and the strength of fibrinogen attachment as judged by residence-time experiments were performed to evaluate the potential hemocompatibility of these materials. The results of the prekallikrein activation and fibrinogen-retention studies correlated well with two electrochemical properties of the alloys, the open circuit potential and reciprocal polarization resistance. The results indicate that both the original and treated Ti and Zr alloys activate prekallikrein and adsorb as well as retain fibrinogen in amounts similar to other materials used as components of blood-contacting devices. On the basis of these studies, these alloys appear to be promising candidates for cardiovascular applications and merit further investigation.

Protein adsorption studies on 'standard' polymeric materials

Adsorption of fibrinogen from buffer as a single protein and from plasma to four materials has been studied. The two NIH-NHLBI primary reference standards, filler free polydimethylsiloxane and low density polyethylene, were used along with polyvinylcholoride and cellulose materials supplied by the IUPAC Working Party. The materials were examined in both film and tubing form, except for polydimethylsiloxane which was studied only in tubing form. Adsorption was measured at room temperature using 125I-labelled fibrinogen. The order of adsorbed amounts in the single protein experiments was found to be: cellulose < PVC < PE = PDMS. Apparent adsorption affinities are in the same order. In plasma, all surfaces except cellulose showed maxima in adsorption as a function of plasma concentration after 5 min contact. This is indicative of initial adsorption followed by displacement of fibrinogen (the Vroman effect). Cellulose showed very low adsorption of fibrinogen from plasma. The Vroman maxima were more pronounced on the tubing samples than on the films, and, as for the single protein experiments, adsorption was found to be less on tubing than on film samples. A tentative interpretation of the Vroman effect data suggests that the order of procoagulant activity of the materials may be: PDMS = PE < PVC < cellulose.

Changes in fibrinogen adsorbed to segmented polyurethanes and hydroxyethylmethacrylate-ethylmethacrylate copolymers

Fibrinogen adsorption from blood to biomaterials may regulate platelet adhesion and thrombus formation because of fibrinogen's central role in the coagulation cascade and its ability to bind specifically to the platelet membrane glycoprotein (GP) IIb-IIIa. Adsorption of fibrinogen from blood plasma to many materials exhibits a maximum with respect to plasma dilution and exposure time (the Vroman effect). In this study fibrinogen adsorption to several polymers was examined to ascertain the influence of controlled changes in surface chemistry on the Vroman effect. The materials included hydroxyethylmethacrylate-ethylmethacrylate (HEMA/EMA) copolymers, Biomer, and a series of segmented polyurethanes (PEUs), two of which contained fluorinated chain extenders. Each material exhibited maximal adsorption of fibrinogen at intermediate plasma concentrations. Little effect of soft-segment type or molecular weight was observed and no significant differences in fibrinogen adsorption to the fluorinated PEUs were seen. Changes in the strength of fibrinogen attachment to these materials with time after adsorption were also assessed. Fibrinogen adsorbed for 1 min was displaced more readily by blood plasma than that adsorbed for 1 h, regardless of the material. The more hydrophobic polymers exhibited greater retention of adsorbed fibrinogen. In addition, the fraction of fibrinogen retained by polyethylene depended on the amount of fibrinogen adsorbed to the surface, being greatest when the surface loading was the least. These studies indicate that spreading or transition of adsorbed fibrinogen molecules from a weakly to tightly bound state is a general consequence of protein adsorption to solid surfaces.

Polyurethanes bearing pendant amino acids: fibrinogen adsorption and coagulant properties

Segmented polyurethanes based on 4,4'-diphenylmethane diisocyanate and polypropylene oxide and chain extended with a sulfonated diamine were derivatized by reaction of sulfonate groups in the polymer with amino acids. The chemical composition of the derivatized polymers was determined by elemental analysis. Tensile stress-strain measurements indicated a slight increase in modulus and elongation with incorporation of amino acids. Water uptake at room temperature showed little change following derivatization, but at 70 degrees C increased significantly. Water contact angles were not influenced by the presence of amino acids, but electron spectroscopy for chemical analysis data showed an increase in hard segment content in the near-surface layers so that bulk and surface compositions were more nearly the same in the amino-acid-containing materials. Fibrinogen adsorption from plasma, shown previously to be high on the sulfonated polyurethanes, was reduced by derivatization, due probably to the decrease in free sulfonate content. Thrombin times of plasma in contact with these materials were essentially the same for the derivatized and underivatized materials.

Delivery of passivating proteins to sutures during passage through the vessel wall reduces subsequent platelet deposition by blocking fibrinogen adsorption

Intraluminal vascular suture material, which attracts fewer than the expected number of platelets compared with the same biomaterial exposed to blood in vitro, differs from the untreated biomaterial in that it has been passed once through the vessel wall. The mechanism by which this apparently trivial maneuver reduces platelet deposition was investigated. Polypropylene suture (7-0 Prolene) was passed through human arteries (fetal and adult), and platelet deposition to the suture was measured in a standardized perfusion chamber. Single vessel passage of the sutures reduced platelet deposition by 68 +/- 23%, which contrasts sharply with the power of prostaglandin E1 (1 microM PGE1 is sufficient to abolish platelet shape change and aggregation), which inhibited only 11% of platelet deposition to the sutures. Aspirin treatment of the vessel (to prevent PGI2 formation) or endothelial stripping (to remove the ability to produce nitric oxide) had no effect on the degree of inhibition. Passage of the suture through a vessel analogue (expanded polytetrafluoroethylene) did not inhibit platelet deposition. 125I-fibrinogen adsorption to the suture after vessel passage was reduced to a degree similar to that of platelet deposition. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins eluted from vessel-passed sutures revealed bands at 66, 47, and 16 kd. Western blotting indicated the presence of large amounts of albumin and hemoglobin, a moderate amount of haptoglobin, and only trace amounts of fibrinogen. When sutures were exposed to each of these proteins in vitro before perfusion, albumin and hemoglobin were found to reproduce the effect of vessel passage alone on platelet deposition. We conclude that albumin and hemoglobin adsorb to sutures during their passage through the vessel subendothelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Postadsorptive transitions in fibrinogen adsorbed to polyurethanes: changes in antibody binding and sodium dodecyl sulfate elutability

Residence time-dependent changes in fibrinogen after adsorption to six different polyurethanes were examined by measuring polyclonal antifibrinogen binding to the adsorbed protein. The amount of adsorbed fibrinogen that could be eluted by sodium dodecyl sulfate (SDS) was also measured. Baboon fibrinogen was first adsorbed from dilute plasma to the polymers, which were then stored in either buffer or buffered albumin solution prior to testing. Subsequently, the amount of antifibrinogen bound by the adsorbed fibrinogen was measured using a direct enzyme linked immunosorbent assay (ELISA). Alternatively, the surface with the adsorbed fibrinogen was soaked in a 3% SDS solution, and the amount of retained 125I-radiolabeled fibrinogen was measured. With increasing residence time, decreases in both antibody binding and the SDS elutability of the adsorbed fibrinogen occurred, but the rate of change was dependent on the polyurethane to which the fibrinogen was adsorbed. In addition, the antibody binding per unit of adsorbed fibrinogen, when measured immediately after the adsorption step, varied by approximately a factor of 3 among the various polyurethanes. When the protein-coated surfaces were stored in buffered albumin solution rather than buffer, the decrease in the reactivity of fibrinogen with residence time did not occur on some of the surfaces. This study shows that the chemical properties of the adsorbing surface influence the rate at which adsorbed fibrinogen undergoes change. The significance of the polymer-dependent changes in adsorbed fibrinogen with respect to blood reactions with polymers is discussed.

Measurement of fibrinogen adsorption from blood plasma using 125I-fibrinogen and a direct ELISA technique

A direct enzyme-linked immunosorbent assay (ELISA), using a polyclonal anti-fibrinogen conjugated to horseradish peroxidase, was used to detect fibrinogen adsorption from blood plasma to ten different materials. Adsorption was also measured with [125I]-fibrinogen. The materials studied included glass, Biomer, Immulon I, and a series of hydroxyethylmethacrylate (HEMA) and ethylmethacrylate (EMA) co-polymers. For all the materials studied, the results from the ELISA technique closely paralleled those obtained using [125I]-fibrinogen. The cross-reactivity of the antibody with proteins other than fibrinogen was generally small. Both experimental methods detected the presence of a maximum in fibrinogen adsorption (as a function of the plasma dilution) to the more hydrophobic materials. For all but two HEMA/EMA co-polymers, a linear correlation between the ELISA and [125I]-fibronogen measurements was indicated by inspection of cross plots as well as by a statistical test.

Effect of sulfonation of segmented polyurethanes on the transient adsorption of fibrinogen from plasma: possible correlation with anticoagulant behavior

The influence of polyurethane sulfonation on fibrinogen adsorption from plasma and on plasma coagulation has been investigated. Sulfonated polyurethanes were synthesized using a two-step solution polymerization in which a diamino disulfonic acid was used as chain extender, thus incorporating sulfonate groups into the hard segments. Polymer molecular weights were determined by size exclusion chromatography and weight average values were in the range of 50,000 to 200,000. Equilibrium water uptake of solid polymer specimens was substantial and was found to increase with increasing sulfonate content. Titration of sulfonate groups allowed an estimate of the retention of free sulfonate in the polymers which ranged from 50 to 85%. Loss of free sulfonate is attributed to reaction of isocyanate with sulfonate groups during chain extension. Both surface chemistry and hydrophilicity were assessed using a combination of ESCA and water contact angle measurements. The ESCA data indicate enrichment of soft segment in the surface. Contact angles show increasing hydrophilicity with increasing sulfur content. Fibrinogen adsorption from plasma to the sulfonated polyurethane surfaces was studied using radioiodine labeling. Fibrinogen surface concentration was found to increase strongly as sulfonate content increased. Fibrinogen adsorption behavior is quite different from that of conventional unsulfonated polyurethanes in the sense that the adsorption levels are much higher and there is little displacement of initially adsorbed fibrinogen (Vroman effect). The data are interpreted in terms of two mechanisms: fibrinogen uptake (i.e., absorption) into a polymer-plasma "gel" hypothesized to exist at the surface of these materials, and adsorption in the usual sense. Thrombin times of human plasma in which polymer particles were suspended were prolonged and were found to increase with increasing sulfonate content of the polymers, suggesting that sulfonate groups confer a measure of anticoagulant activity on these materials.

Influence of a preadsorbed terpolymer on human platelet accumulation, fibrinogen adsorption, and ex vivo blood activation in hemodialysis hollow fibers

Results are presented on kinetics of platelet accumulation in charged polyacrylonitrile (AN69) hollow fibers by continuous data recording under flow conditions (wall shear rate 108-1050 s-1), using suspensions of washed 111In-labeled human platelets in Tyrode's-albumin buffer, containing washed red blood cells (0-40%). Preadsorption of a terpolymer of acrylonitrile, poly(ethyleneoxide) methacrylate and trimethylaminoethyl chloride methacrylate leads to very efficient passivation with respect to platelet accumulation and fibrinogen adsorption. In human ex vivo tests, evaluation of complement peptide C3a, platelet beta-thromboglobulin, leucocyte-polymorphonuclear neutrophile elastase and fibrinopeptide A shows no detectable activation. Furthermore, preadsorption appears to result in simultaneous improvement in hemocompatibility of the blood lines leading to and from the dialysis module. This single pretreatment of dialysis membranes should allow injection of lower doses of anticoagulant to patients submitted to hemodialysis.

Is the Vroman effect of importance in the interaction of blood with artificial materials?

The successive displacement of plasma proteins adsorbed to artificial surfaces (biomaterials) is well documented, mostly by specially designed experiments that stretch out the effect in time and space. Analysis of displacement has been focused principally on molecular events on the adsorbing surface. In this paper attention is directed rather to the antecedent transport phenomena necessary to deliver successive proteins to a surface. The different limitations on protein arrival fixed by the total quantity present and by the rates of transport of super-sufficient quantities are distinguished. The transport perspective is then used to ask, and partly answer, the question: Can protein displacement be responsible for patterns of thrombus formation and cellular adhesion that are seen on the blood-wetted surfaces of devices found in medical practice: artificial organs and vascular prostheses? Calculations and a small amount of preliminary data suggest that such patterns may form when blood is introduced into these devices, particularly in the neighborhood of boundary shapes that cause separated flows.

A comparison of the adsorption of three adhesive proteins to biomaterial surfaces

The adsorption of three cell adhesive proteins with known thrombogenic activity [fibrinogen (FGN), fibronectin (FN), and vitronectin (VN)] was quantified from mono-component protein solutions, from a quaternary-component protein solution, and from plasma and diluted plasma in order to compare their potential for adsorption to polymeric substrates from solutions of varying complexity. The surfaces studied included polyethylene (PE), silicone rubber (SR), Teflon-FEP (FEP), and two polyetherurethanes: one with a poly(tetramethylene oxide) soft segment (PTMO-PU) and one with a poly(ethylene oxide) soft segment (PEO-PU). The adsorption of these proteins from single-component solutions followed the Freundlich isotherm and the adhesive proteins showed similar trends in Freundlich parameters for surfaces of similar surface wettability. Adsorption from a quaternary-component solution composed of physiological molar ratios of the three proteins and human serum albumin (HSA) revealed a significant enrichment of adsorbed vitronectin as determined from ratios of the adsorbed surface fraction of each protein to its respective bulk fraction. The other proteins' adsorption was enriched to a lesser extent in the decreasing order of FGN greater than FN greater than HSA for all surfaces. The relative enrichment of VN from plasma was also high as compared with its bulk concentration, whereas the enrichment of FGN, FN, and HSA was much lower and of approximately the same magnitude. Compared with the three other proteins, VN showed a resistance to displacement from the polymer substrates as either the plasma concentration was increased or the length of contact with plasma and diluted plasma was increased.

Adsorption of baboon fibrinogen and the adhesion of platelets to a thin film polymer deposited by radio-frequency glow discharge of allylamine

Platelet adhesion under static and flow conditions from a washed platelet suspension containing albumin to a polymer deposited by radio-frequency glow discharge of allylamine vapour on a poly(ethylene terephthalate) substrate was measured. Electron spectroscopy for chemical analysis was used to characterize the surface. Fibrinogen adsorption from a series of dilute plasma solutions to radio-frequency glow discharge/allylamine, measured using 125I radiolabelled baboon fibrinogen, increased with decreasing plasma dilution to a level much higher than that previously observed on polyurethanes. Elutability by sodium dodecyl sulphate of fibrinogen adsorbed from dilute plasma also increased with increasing plasma concentration, but fibrinogen preadsorbed from plasma became non-elutable when surfaces were stored in buffer for 5 d before contact with sodium dodecyl sulphate. Platelet adhesion to substrates which had been pre-adsorbed with dilute plasma was measured using baboon platelets radiolabelled with 111In. Adhesion greatly decreased as the plasma concentration used for preadsorption increased, suggesting that non-specific platelet binding to the bare surface occurs when protein coverage is incomplete. Non-specific platelet binding was inhibited to varying degrees by preadsorption of different proteins to the surface. Platelet adhesion to surfaces preadsorbed with dilute (1.0%) baboon and human plasmas lacking fibrinogen (i.e. serum, heat-defibrinogenated plasma and congenitally afibrinogenemic plasma) was diminished compared with normal plasma. Addition of exogenous fibrinogen to the deficient plasma partially restored platelet adhesion to normal levels. Adhesion to surfaces preadsorbed with human plasma deficient in von Willebrand factor was comparable to that observed with normal plasma. The plasma preadsorption studies with fibrinogen deficient media suggested that adsorbed fibrinogen is necessary for platelet adhesion to the radio-frequency glow discharge/allylamine substrate at high protein coverage. However, since adhesion was greatly reduced when the plasma preadsorbed substrate was stored in buffer before platelet contact, the conformation of adsorbed fibrinogen is also important in mediating platelet adhesion to radio-frequency glow discharge.

Fibrinogen adsorption on Pyrex glass tubes: a continuous kinetic study

We present an experimental system to record continuously the adsorption kinetics of radiolabeled proteins, following an earlier study (Voegel et al., Colloids Surfaces 10 (1984) 9). We found results in accordance with the Lévêque equation at a wall shear rate of 50 s-1, for adsorption from fibrinogen solutions in Tyrode's buffer on Pyrex glass tubes. Dependence on concentration in the range 4 to 200 micrograms/mL and on distance to the tube entrance were examined. At the highest concentrations, a second slower regime appeared when coverage exceeded about 0.14 micrograms/cm2.

'Lens-on-surface': a versatile method for the investigation of plasma protein exchange reactions on solid surfaces

The exchange sequence of plasma proteins in narrow spaces on solid surfaces was studied by means of a modified 'lens-on-surface' method as originally described by Vroman and Adams. In our studies, lateral scanning ellipsometry was used as the detection method. With the use of antibodies it was demonstrated and confirmed that immunologically detectable plasma protein antigens appear and disappear in a time- and concentration-dependent sequence [IgG followed by fibrinogen followed by high-molecular weight kininogen (HMWK)] on silica surfaces. Plasma protein exchange reactions were also studied on hydrophilic titanium (Ti), vanadium (V), and silver (Ag) surfaces. Atypical exchange patterns were found on V and Ag surfaces as compared with hydrophilic silica (adsorbed fibrinogen was not removed).

Postadsorptive transitions in fibrinogen adsorbed to biomer: changes in baboon platelet adhesion, antibody binding, and sodium dodecyl sulfate elutability

Residence-time-dependent changes in fibrinogen after its adsorption to Biomer were examined by measuring platelet adhesion and antibody binding to the adsorbed protein, and the amount of adsorbed fibrinogen which could be eluted by sodium dodecyl sulfate (SDS). Baboon fibrinogen was first adsorbed (from either pure solution or dilute plasma) to Biomer, which was then stored in either buffer or buffered albumin solution prior to testing. Subsequently, the adherent protein layer was either probed for fibrinogen capable of mediating platelet adhesion using 111In radiolabeled, washed platelet suspensions under both static and shearing conditions, or for fibrinogen capable of binding antibody using a direct enzyme linked immunosorbent assay (ELISA). Alternatively, the surface with the adsorbed protein layer was soaked in a 3% SDS solution, and the amount of 125I radiolabeled fibrinogen retained was measured. Decreases in platelet and antibody binding, and in the SDS elutability of the adsorbed fibrinogen after it was stored in buffer were detected, although different rates of decrease were observed for each method. When the protein-coated surfaces were stored in buffered albumin solution rather than buffer, the decrease in the reactivity of fibrinogen was prevented. While each of the three assays measures a different property of adsorbed fibrinogen, this study suggests that the adherent protein undergoes time dependent conformational changes which render it less reactive toward platelets and antibodies, and more resistant to elution by SDS.

The effects of temperature and buffer on fibrinogen adsorption from blood plasma to glass

[125I]-Fibrinogen was used to measure the adsorption of fibrinogen from baboon plasma to two types of glass (Pyrex and a borosilicate glass) at 25 and 37 degrees C using two different buffers to dilute the plasma, the first being citrate-phosphate buffered saline (CPBSz) and the second isotonic Tris-saline (TRIS), both pH 7.4. In addition, the effects of hydration conditions, rinsing techniques, and glass-cleaning treatments on fibrinogen adsorption were evaluated. The data reveal that lower temperatures and the use of TRIS to dilute the plasma significantly enhance fibrinogen adsorption to both types of glass. As has been observed in the past, fibrinogen adsorption peaked at intermediate plasma concentrations on both Pyrex and borosilicate glass (the so-called Vroman effect), but almost twice as much fibrinogen adsorbed to glass when TRIS was used to dilute the plasma instead of CPBSz. Moreover, up to five times as much fibrinogen adsorbed to both types of glass at 25 degrees C compared with 37 degrees C. No effects of the rinsing technique or glass-cleaning treatment were observed.

The Vroman effect in tube geometry: the influence of flow on protein adsorption measurements

The transient adsorption of fibrinogen from plasma (a manifestation of the Vroman effect), due in large part to displacement by trace proteins such as high-molecular-weight kininogen (HK), factor XII, and plasminogen, has traditionally been studied in nonflowing systems in this laboratory. This paper reports new data on adsorption in tubing geometry under laminar flow. Fibrinogen adsorption from human blood plasma and whole blood diluted to varying exents was measured on glass and polyethylene tubing. The presence of flow did not change the nature of the Vroman effect, except that the processes of adsorption and displacement, which are typically diffusion-limited in static systems, were augmented by convective transport. At the highest applied shear rates of 408 and 510 s-1, the initial adsorption rate of fibrinogen was estimated to be 5.0 X 10(-5) cm/s on both surfaces. The intrinsic rate of displacement of fibrinogen (due to the Vroman effect) at high shear rates was about ten times faster from glass than from polyethylene based on data taken 5 min after the experiment started. The rates of fibrinogen adsorption and displacement were not observed to be significantly augmented by the cellular elements of whole blood at dilutions exceeding 20:1. The consistently observed axial dependence of adsorption in static and flow experiments in tubing geometry was investigated. It was concluded that the effect results, under most conditions, from the creation of a concentration boundary layer during the displacement of the equilibrating buffer by the injected protein solution. The possibility of local depletion due to rapid adsorption during injection or the final displacement of the protein solution was concluded to make lesser contributions to axial variations in measured adsorption.

Detection of surface-adsorbed (lipo)proteins by means of a two-step enzyme-immunoassay: a study on the Vroman effect

In view of reports on the involvement of high-molecular-weight (HMW) kininogen and high-density lipoprotein (HDL) in the Vroman effect, we studied the adsorption of fibrinogen, HMW kininogen, HDL and several other proteins from pooled human plasma and congenitally HMW kininogen-deficient plasma onto glass and low-density polyethylene, both as a function of the plasma concentration and the contact time. Mixtures of purified (lipo)proteins were also included in the study. Protein adsorption was determined by means of a two-step enzyme-immunoassay. Our results support the hypothesis that HMW kininogen is involved in the displacement of fibrinogen, which is almost instantly adsorbed from normal plasma onto glass. On hydrophobic polymers like polyethylene, the low amounts of adsorbed fibrinogen and HMW kininogen from plasma and concentrated plasma solutions may be due to a preferential adsorption of HDL.

Morphological characterization of surface-induced platelet activation

Morphological changes of platelets activated on glass and dimethyldichlorosilane-treated glass were investigated using video microscopy. The platelet morphological changes were quantified by measuring the area and circularity of spreading platelets. In addition, re-organization of cytoskeletal structures of spread platelets was examined. The effects of precoated albumin and fibrinogen on the platelet spreading kinetics were examined as a function of surface protein concentrations. Results showed that platelet shape changes were very sensitive to the surface concentration of precoated proteins. In general, platelets on fibrinogen-precoated surfaces spread fully to a circular shape and developed an extensive inner filamentous zone. In the presence of albumin on the surface, however, platelets could not spread fully and the development of the inner filamentous zone was very poor. For both albumin and fibrinogen, the maximum effects of precoated proteins on platelet shape changes were observed when the surface protein concentration reached the monolayer concentration.