Albumin and fibrinogen adsorption on PU-PHEMA surfaces

Materials that adsorb specific proteins may find a variety of applications in the biomedical field. The aim of this study was the preparation of a hydrophilic surface, with low protein adsorption, to be used in the future as a support for the immobilisation of several species, e.g. Cibacron Blue F3G-A, which has been described to induce specific albumin adsorption. Poly(hydroxyethylmethacrylate) (PHEMA) and poly(hydroxyethylacrylate) (PHEA) were chosen as the hydrophilic surface because they can be easily polymerised and possess hydroxyl groups that can be used for the immobilisation of different compounds. Thin films of PHEMA and PHEA were successfully graft polymerised onto the surface of a commercial poly(etherurethane) (PU) using ceric ion as initiator. Grafting polymerisations were followed by mass gain and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Since stability tests demonstrated that only PU-PHEMA was stable in alkaline solutions, a necessary condition to future immobilisations, the investigation was focused on the coating of PU with PHEMA. PU-PHEMA films were characterised in detail using several techniques as mass gain, ATR-FTIR, contact angle measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Protein adsorption was evaluated using radiolabelled albumin and fibrinogen from pure solutions and from mixtures of both proteins. PU surfaces modified with PHEMA have demonstrated low protein adsorption, showing their potential use as substrates. This opens the possibly of exploring the advantages of selective adsorption by appropriate immobilisation of specific molecules.     

Antithrombogenicity of hydrophilic polyurethane-hydrophobic polystyrene IPNs. II. In vitro and ex vivo studies

To investigate the effect of hydrophilic and hydrophobic surfaces with phase separated structure on their blood responses, interpenetrating polymer networks (IPNs) composed of hydrophilic polyurethane (PU) and hydrophobic polystyrene (PS) were prepared by simultaneous polymerization. In vitro protein adsorption, in vitro platelet adhesion, and ex vivo A-A shunt test were carried out to evaluate the blood compatibility of the PU/PS IPNs. The results of protein adsorption on the PU/PS IPN surfaces indicated that albumin preferentially adsorbed on the hydrophilic surface (PU), while fibrinogen preferentially adsorbed on the hydrophobic surface (PS). The PU/PS IPNs exhibited suppressive properties for both platelet adhesion and activation. The occlusion time of U50S50 IPN containing 50 wt% of PS was twice as long as that of the PU control (50 min), indicating enhanced blood compatibility, presumably due to the selective adsorption of plasma proteins and the suppression of the adhesion and activation of platelets.     

Introduction of surface functional groups onto biomaterials by glow discharges

An attempt was made to graft the monomer HEMA to the polymer surface by "Glow discharge" technique. Experiments were carried out for different surfaces varying the exposure times of samples to HEMA and also as a function of glow discharge time. It was found that as the percentage of grafting increases the hydrophilicity also increases. Contact angle measurements were performed on these substrates, which confirmed the hydrophilic nature of the grafted samples compared to the controls. The role of protein adsorption and their effects to modulate the blood polymer interaction is briefly discussed. When a foreign material comes in contact with blood, the initial event is the adsorption of plasma proteins in parallel with the adhesion of platelets to the material. Albuminated surfaces discourage platelet adhesion while fibrinogen enhances the platelet attachment and thrombosis. Hence a decreased ratio of fibrinogen to albumin on a substrate can be correlated as an indication to its improved blood compatibility. Fibrinogen to albumin ratios of the grafted samples showed a reduction, indicating that albumin adsorption is high; which may make the modified surfaces non-thrombogenic.     

Hemocompatibilty of new ionic polyurethanes: influence of carboxylic group insertion modes

New segmented polyurethane (PU) anionomers based on hydroxytelechelic polybutadiene (HTPB) were synthesized via two environment-friendly chemical routes. The effects of carboxylic content and ion incorporation mode on the surface properties were investigated by mean of water absorption analysis and static contact angle measurements using water, diiodomethane, formamide and ethylene glycol. Blood compatibility of the PUs was evaluated by in vitro adhesion assay using 111In-radiolabeled platelet rich plasma and 125I-fibrinogen. The morphology of platelet adhesion was also observed by scanning electron microscopy (SEM). Results were compared with a biomedical-grade PU, Pellethane. Insertion of the carboxylic groups on the soft segments (S-alpha series), using thioglycolic acid (TGA), increases surface hydrophilicity, limits water uptake (5%, for an ion content of 3.6 wt%), and reduces platelet adhesion and fibrinogen adsorption on the PUs' surfaces. In contrast, the classical insertion onto the hard segment (H-alpha series), using dimethylolpropionate (DMPA) as chain extender, leads to high water uptake (18%, for an ion content of 3.6 wt%) and promotes platelet and fibrinogen adhesion. SEM analyses of the non-ionic PUs exhibited surfaces with adhered platelets which underwent morphological modification. Similarly, the H-alpha ionic PUs show adherent and activated platelets. On the contrary, no platelet morphology changes were observed on the S-alpha ionic surfaces. In conclusion, insertion of carboxyl groups on the soft segments of PUs reduces their thrombogenicity.     

Time-related contact angle measurements with human plasma on biomaterial surfaces

Axisymmetric drop shape analysis by profile (ADSA-P) was used to assess in time contact angle changes of human plasma drops placed on four different biomaterials. Results were related with conventional blood compatibility measurements: albumin adsorption, fibrinogen adsorption and platelet adhesion. While contact angle measurements with water are material-related but constant in time, contact angle measurements with plasma changed over time owing to protein adsorption on the solid-liquid interface. The contact medium plasma did not influence the initial contact angle. Contact angles on PDMS decreased most in time (41 degrees) and demonstrated highest levels of conventionally measured albumin and fibrinogen adsorption and platelet adhesion. PTFE, with the lowest contact angle decrease over a 500 minutes period (19 degrees), showed low fibrinogen and albumin adsorption as well as low platelet adhesion. PU and HDPE demonstrated almost similar initial contact angles with plasma and contact angle decreases (26 and 27 degrees), intermediate protein adsorption, and platelet adhesion. We conclude that biocompatibility properties of the tested materials may be more related to the behaviour of their contact angles in time, than to the initial hydrophobic or hydrophilic state.     

The role of plasma proteins in cell adhesion to PEG surface-density-gradient-modified titanium oxide

Surface-density gradients of poly(ethylene glycol) (PEG) were fabricated, in order to carry out a systematic study of the influence of PEG chain density on protein adsorption and cell-adhesion behavior, as well as the correlation between them. Gradients with a linear change in coverage of the polycationic polymer Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) were prepared on titanium dioxide surfaces by a controlled dipping process and characterized by variable-angle spectroscopic ellipsometry and fluorescence microscopy. The adsorption behavior of single proteins (fibrinogen and albumin) generally correlated with semiempirical geometric models, illustrating the effect of the PEG-chain surface distribution on the inhibition of protein adsorption. Distinct differences could be observed between individual adsorbing proteins, attributable to their mode of surface attachment. The single and competitive adsorption of protein solutions containing albumin and fibrinogen was then investigated by fluorescence microscopy, indicating a larger amount of fibrinogen adsorption compared with albumin adsorption (in minutes to hours) along the entire PLL-g-PEG gradient samples. To further elucidate the underlying mechanism of cell adhesion and spreading as a function of PEG coverage and the potential involvement of integrins, cell-adhesion assays were carried out with human foreskin fibroblasts (hFF). The use of surface-gradient samples demonstrated the importance for protein adsorption of PEG conformation, the amount of exposed titanium dioxide surface area (and its distribution), and the structure and chemistry of the proteins involved. Correspondingly the influence of these factors on cell adhesion could be directly observed, and insights gained into the roles of both nonspecific binding and specific integrin binding in cell adhesion.     

Protein adsorption on mixtures of hydroxyl- and methyl-terminated alkanethiols self-assembled monolayers

The effect of surface composition and wettability on the adsorption of human serum albumin (HSA) was studied. Self-assembled monolayers (SAMs) containing mixtures of longer chain methyl- and shorter chain hydroxyl-terminated alkanethiols on gold were used to produce a range of surfaces with different wettabilities and exposed functional groups. Different SAMs were characterized by X-ray photoelectron spectroscopy, water contact angles, and Fourier transform infrared reflection absorption spectroscopy (IRAS). HSA adsorption onto the different SAMs was evaluated by contact angle measurements (wetting tension determinations), radiolabeling of proteins, and IRAS. Concerning HSA adsorption, all the techniques demonstrated higher HSA adsorption on more hydrophobic surfaces. The wetting tension measurements and IRAS suggested a gradual decrease of the HSA adsorption with increases of surface hydrophilicity. Radiolabeled albumin measurements also demonstrated a significant decrease of HSA adsorption on the pure hydroxyl-terminated SAMs. However, no significant differences were detected between mixed and pure methyl-terminated SAMs. Studies of HSA exchangeability with human fibrinogen have suggested that an ideal percentage of hydroxyl groups on the surface may increase albumin affinity without fibrinogen adsorption.     

Non-fouling biomaterials based on blends of polyethylene oxide copolymers and polyurethane: simultaneous measurement of platelet adhesion and fibrinogen adsorption from flowing whole blood

Measurements of platelet adhesion and fibrinogen adsorption from flowing whole blood to a series of polyethylene oxide (PEO)-based materials were carried out. A unique experimental design was used in which both quantities were measured in the same experiment. The materials consisted of a polyurethane (PU) as a matrix into which various triblock copolymers of general structure PEO-PU-PEO were blended; the PU block was the same in all materials but the PEO blocks ranged in molecular weight from 550 to 5000. Platelets were isolated from fresh human blood and labeled with ⁵¹Cr; purified fibrinogen was labeled with ¹²⁵I. A whole blood preparation containing these labeled species was used for the adhesion/adsorption studies. The surfaces were exposed to the flowing blood in a cone and plate device at a wall shear rate of 300?s^?1. It was found that both platelet adhesion and fibrinogen adsorption decreased with increasing copolymer content in the blends and with decreasing PEO block size for a given copolymer content. The block size effect was due probably to higher PEO surface coverage for the lower molecular weight blocks. Fibrinogen adsorption and platelet adhesion were linearly and strongly correlated. The best performing materials showed very low fibrinogen adsorption of the order of 25?ng/cm², and correspondingly low platelet densities around 10,000 per cm², i.e. fractional platelet coverage in the vicinity of 0.2%.     

Protein adsorption to poly(ethylene oxide) surfaces.

Surfaces containing poly(ethylene oxide) (PEO) are interesting biomaterials because they exhibit low degrees of protein adsorption and cell adhesion. In this study different molecular weight PEO molecules were covalently attached to poly(ethylene terephthalate) (PET) films using cyanuric chloride chemistry. Prior to the PEO immobilization, amino groups were introduced onto the PET films by exposing them to an allylamine plasma glow discharge. The amino groups on the PET film were next activated with cyanuric chloride and then reacted with bis-amino PEO. The samples were characterized by scanning electron microscopy, water contact angle measurements, gravimetric analysis, and electron spectroscopy for chemical analysis (ESCA). The adsorption of 125I-labeled baboon fibrinogen and bovine serum albumin was studied from buffer solutions. Gravimetric analysis indicated that the films grafted with the low-molecular-weight PEO contained many more PEO molecules than the surfaces grafted with higher-molecular-weight PEO. The high-molecular-weight PEO surfaces, however, exhibited greater wettability (lower water contact angles) and less protein adsorption than the low-molecular-weight PEO surfaces. Adsorption of albumin and fibrinogen to the PEO surfaces decreased with increasing PEO molecular weight up to 3500. A further increase in molecular weight resulted in only slight decreases in protein adsorption. Protein adsorption studies as a function of buffer ionic strength suggest that there may be an ionic interaction between the protein and the allylamine surface. The trends in protein adsorption together with the water contact angle results and the gravimetric analysis suggest that a kind of "cooperative" water structuring around the larger PEO molecules may create an "excluded volume" of the hydrated polymer coils. This may be an important factor contributing to the observed low protein adsorption behavior.     

等离子体表面改性涤纶材料的血浆蛋白吸附与血小板黏附行为研究

采用等离子体表面接枝改性技术在涤纶 (聚对苯二甲酸乙二醇酯 ,PET)材料表面接枝不同分子量的聚乙二醇 (PEG) ,从表面能与界面自由能的角度分析了血浆蛋白 (纤维蛋白原和白蛋白 )在材料表面的竞争吸附关系 ,结果表明接枝了 PEG长链分子的 PET材料具有优先吸附白蛋白的性质 ,其中接枝 PEG6 0 0 0的 PET优先吸附倾向最明显。预接触白蛋白和纤维蛋白原的 PET材料表面的血小板黏附实验表明 :吸附白蛋白的表面能够显著抑制血小板的黏附和聚集 ,表现出好的血液相容性 ,而吸附了纤维蛋白原的材料表面具有降低血液相容性的性质。     

Albumin adsorption on to aluminium oxide and polyurethane surfaces

The changes in protein adsorption onto aluminium surfaces coated with different thicknesses of oxide layers were examined. The oxide layers on aluminium substrates were derived by the anodizing technique. Protein adsorption studies were conducted using 125I-labelled albumin and the amount of albumin adsorbed was estimated with the help of a gamma counter. An increase in albumin adsorption was observed on oxide layer coated aluminium surfaces. The effect of anti-Hageman factor on albumin and fibrinogen adsorption on to bare aluminium, oxide layer coated aluminium and bare polyether urethane urea surfaces was also investigated. It was observed that the presence of anti-Hageman factor increased the adsorption of albumin and fibrinogen on to all these substrates.     

Irreversible adsorption of human serum albumin to hydrogel contact lenses: a study using electron spin resonance spectroscopy.

Human serum albumin (HSA) was specifically spin labelled with 4-maleimido-tempo (MSL) at its cysteine 34 residue (HSA-MSL). The irreversible adsorption of HSA-MSL to hydrogel contact lenses (etafilcon A, tefilcon and vifilcon A) was investigated using electron spin resonance (ESR) spectroscopy. Changes in ESR spectral characteristics of adsorbed HSA-MSL as compared to HSA-MSL in solution displayed an additional immobilisation of the spin label due to the adsorption. This immobilisation of MSL corresponds to a large conformational alteration of the HSA-MSL near the modified Cys 34 residue. For both etafilcon A and tefilcon, the rate of irreversible adsorption was relatively slow compared with that of vifilcon A where the maximum state of immobilisation and hence conformational change occurred within the first hour of adsorption. Furthermore, tefilcon produced markedly different ESR spectra where a strong conformational change to a less mobile protein was apparent. This supported a model where the direct irreversible adsorption of HSA from solution dominated on tefilcon as opposed to conversion of the adsorbed protein from the reversible to the irreversible state on both etafilcon A and vifilcon A. HSA-MSL adsorption onto hydrophobic poly(methylmethacrylate) (PMMA) and hydrophilic poly(N-ter-butylacrylamide) (PTBAM) latex beads was also investigated. The spin label MSL was found to be less mobile when HSA was adsorbed onto PMMA compared with PTBAM beads. It was also found that the rate of irreversible adsorption of HSA is far higher onto PMMA surfaces than onto PTBAM surfaces.     

Human erythrocyte adhesion and spreading on protein-coated polymer surfaces

Protein adsorption is the first event which occurs when polymer surfaces are exposed to blood. The adsorption of proteins modifies the surface properties of the substrates and therefore influences subsequent cell-surface interactions. In an attempt to elucidate the fundamental mechanisms governing cell-proteinated-surface interactions, the extent of fresh human erythrocyte adhesion and spreading on protein-coated surfaces was examined. Five human serum proteins (albumin, fibrinogen, immunoglobulin G, fibronectin, and transferrin) were used at bulk concentrations ranging from 0.01 mg/mL to 50 mg/mL. Polymer substrates covering a wide range of wettability were employed. Protein adsorption significantly reduces erythrocyte adhesion and spreading on all test surfaces with minimum adhesion observed on fibrinogen: IgG greater than albumin greater than fibronectin greater than transferrin greater than fibrinogen. The extent of these effects is dependent on the nature of the adsorbed protein, the protein bulk concentration, and the surface properties of the underlying polymer substrates.     

MMA/MPEOMA/VSA copolymer as a novel blood-compatible material: effect of PEO and negatively charged side chains on protein adsorption and platelet adhesion

This study was designed to evaluate the effect of polyethylene oxide (PEO) and negatively charged side chains on blood compatibility. For this, novel copolymers (MMA/MPEOMA/VSA copolymers) with both PEO and negatively chargeable side chains were synthesized by random copolymerization of methyl methacrylate (MMA), methoxy PEO monomethacrylate (MPEOMA; PEO mol wt 1000), and vinyl sulfonic acid sodium salt (VSA) monomers of different compositions. MMA/MPEOMA copolymer (with PEO side chains) and MMA/VSA copolymer (with negatively chargeable side groups) also were synthesized for purposes of comparison. The synthesized copolymers were characterized by 1H-nuclear magnetic resonance spectroscopy and gel permeation chromatography. They were coated onto polyurethane (PU) or polymethyl methacrylate (PMMA) films by spin coating. The surface properties of MMA/MPEOMA/VSA copolymers were compared by water contact angle and zeta potential with those of MMA/MPEOMA and MMA/VSA copolymers of similar MPEOMA or VSA composition. Using electron spectroscopy for chemical analysis and scanning electron microscopy, respectively, the behaviors of the adsorption of blood proteins (albumin, gamma-globulin, fibrinogen, and plasma proteins) and the adhesion of platelets on the copolymer-coated surfaces also were compared. Among the copolymers, the MMA/MPEOMA/VSA copolymer with a monomer molar ratio 8:1:1 was observed to be particularly effective in preventing both protein adsorption and platelet adhesion on the surfaces, probably owing to the combined effects of highly mobile, hydrophilic PEO side chains and negatively charged side groups in aqueous solution.     

Biostability and biocompatibility of a surface-grafted phospholipid monolayer on a solid substrate

We have previously demonstrated phosphorylcholine monolayer chemically grafted onto a methacryloyl-terminated solid substrate by in situ polymerization. The in situ polymerization was carried out at the interface between a pre-assembled acrylated phospholipid monolayer produced by vesicle fusion and a methacryloyl-terminated substrate using a water-soluble initiator, 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPD). Herein, we examined the biostability and biocompatibility of a surface-grafted phospholipid monolayer (poly-PC) on a methacryloyl-terminated substrate using a "wash off' test, in vitro protein adsorption and in vivo cage implantation for time intervals of 4, 7, 14 and 21 days, respectively. In order to compare the biostability and biocompatibility of phospholipid surfaces on solid substrates, we used two types of phospholipid surfaces: a physically adsorbed phospholipid monolayer (PC) and a poly-PC. Atomic force microscopy and water contact angle measurements indicated that the poly-PC surface was more stable in PBS, Triton X-100 and to EO gas sterilization than the PC surface. The adsorption of proteins such as albumin, fibrinogen, IgG and human plasma proteins on the poly-PC surfaces were significantly reduced, in vitro. Moreover, the poly-PC surface greatly reduced macrophage adhesion and the formation of foreign body giant cells, in vivo.     

Bacterial adhesion to polyurethane surfaces in the presence of pre-adsorbed high molecular weight kininogen

The factors which affect the adherence of a bacteria cell to the surface of a biomaterial include the surface chemistry of the cell and material, as well as the composition of the adsorbed protein layer when the biomaterial is exposed to circulating blood. In an effort to better understand the mechanisms by which bacteria adhere to such surfaces, and specifically to determine the effects of high molecular weight kininogen on bacterial adhesion, experiments were performed in which the attachment of Staphylococcus aureus was directly observed on glass and on a series of functionalized polyurethanes. These surfaces had been pre-adsorbed with various concentrations of high molecular weight kininogen and fibrinogen. Attachment was observed using a radial flow chamber, in which shear stress varied inversely with radial distance. Protein adsorption studies were also performed using ¹²⁵I labeled fibrinogen to investigate the relationship between surface chemistry, protein adsorption, and bacterial attachment. Bacterial attachment was significantly decreased when the glass surface was pre-adsorbed with high molecular weight kininogen-either alone, or following adsorption of fibrinogen. High molecular weight kininogen thus exhibited anti-adhesive effects. On polyurethane surfaces pre-adsorbed with fibrinogen, kininogen, and albumin, the highest bacterial attachment was found on the base polyurethane, while significant decreases were seen on the hydrophilic polyurethanes. In addition, it was found that the surface with the least bacterial attachment and fibrinogen deposition was the polyurethane with pendant phosphonate groups.     

Polyurethane modified with an antithrombin-heparin complex via polyethylene oxide linker/spacers: Influence of PEO molecular weight and PEO-ATH bond on catalytic and direct anticoagulant functions

A segmented polyurethane (PU) was modified with polyethylene oxides (PEO) of varying molecular weight and end group. The PEO served as linker/spacers to immobilize an antithrombin-heparin (ATH) anticoagulant complex on the PU. Isocyanate groups were introduced into the PU to enable attachment of either "conventional" homo-bifunctional dihydroxy-PEO (PEO-OH surface) or a hetero-bifunctional amino-carboxy-PEO (PEO-COOH surface). The PEO surfaces were functionalized with N-hydroxysuccinimide (NHS) groups using appropriate chemistries, and ATH was attached to the distal NHS end of the PEO (PEO-OH-ATH and PEO-COOH-ATH surfaces). Water contact angle and fibrinogen adsorption measurements showed increased hydrophilicity and reduced fibrinogen adsorption from buffer on all PEO surfaces compared to unmodified PU. ATH uptake on NHS-functionalized PEO was quantified by radiolabeling. Despite the different PEO molecular weights and end groups, and NHS-functionalization chemistries, the surface densities of ATH were similar. The adsorption of fibrinogen and antithrombin (AT) from plasma was measured in a single experiment using dual radiolabeling. On PEO-ATH surfaces fibrinogen adsorption was minimal while AT adsorption was high showing the selectivity of the heparin moiety of ATH for AT. The PEO-COOH-ATH surfaces showed slightly greater AT adsorption than the PEO-OH-ATH surfaces. Thrombin adsorption on all of the PEO-ATH surfaces was greater than on the corresponding PEO surfaces without ATH, and was highest on the PEO-OH-ATH, suggesting potential anticoagulant properties for this surface via direct thrombin inhibition by the AT portion of ATH. ? 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A:2821-2828, 2012.     

Protein-resistant polyurethane by sequential grafting of poly(2-hydroxyethyl methacrylate) and poly(oligo(ethylene glycol) methacrylate) via surface-initiated ATRP

Protein-resistant polyurethane (PU) surfaces were prepared by sequentially grafting poly(2-hydroxyethyl methacrylate) (poly(HEMA)) and poly(oligo(ethylene glycol) methacrylate) (poly(OEGMA)) via surface-initiated atom transfer radical polymerization (s-ATRP). The chain lengths of poly(HEMA) and poly(OEGMA) were regulated via the ratio of monomer to sacrificial initiator in solution. The surfaces were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS). The protein resistant properties of the surfaces were assessed by single and binary adsorption experiments with fibrinogen (Fg), lysozyme (Lys), and lactalbumin (Lac). The adsorption of all three proteins on the sequentially grafted poly(HEMA)-poly(OEGMA) surfaces (PU/PH/PO) was greatly reduced compared with the unmodified PU. Adsorption decreased with increasing poly(OEGMA) chain length. On the PU/PH/PO surface with longest poly(OEGMA) chain length (～100), the decrease in Lys adsorption was in the range of 95-98% and the decrease in Fg and Lac adsorption was >99% compared with the unmodified PU. Adsorption from binary protein solutions showed that the PU/PH/PO surfaces resisted these proteins more or less equally, that is, independent of protein size.     

Adsorption behavior of fibrinogen to sulfonated polyethyleneoxide-grafted polyurethane surfaces

Fibrinogen adsorptions to surface modified polyurethanes (PU, PU-PEO, and PU-PEO-SO₃) were studied from plasma in vitro. PU and PU-PEO surfaces demonstrated that initial adsorption increases with increasing plasma concentration in kinetic profiles and adsorption time in adsorption profiles as a function of plasma concentration, but after the plateau is reached, its adsorption amount decreases as plasma concentration (0.2-2.0%) and adsorption time (1-120 min) increase, respectively. In contrast, PU-PEO-SO₃ showed that initial adsorption is almost same regardless of plasma concentration and adsorption time, which is due to the high affinity of surface sulfonate group to fibrinogen. All the surfaces indicated the Vroman effect at about 0.6% plasma concentration; however, the displacement was relatively low. Adsorbed amount of fibrinogen at steady state decreased in the order: PU > PU-PEO-SO₃ > PU-PEO, regardless of adsorption time and plasma concentration. The adsorption behavior of PU-PEO-SO₃ is attributed to both effect of low binding affinity of PEO chain and high affinity of pendant sulfonate group toward fibrinogen.     

In vitro interactions of biomedical polyurethanes with macrophages and bacterial cells

Three commercial medical-grade polyurethanes (PUs), a poly-ether-urethane (Pellethane), and two poly-carbonate-urethanes, the one aromatic (Bionate) and the other aliphatic (Chronoflex), were tested for macrophages and bacterial cells adhesion, in the presence or absence of adhesive plasma proteins. All the experiments were carried out on PUs films obtained by solvent casting. The wettability of these films was analysed by measuring static contact angles against water. The ability of the selected PUs to adsorb human fibronectin (Fn) and fibrinogen (Fbg) was checked by ELISA with biotin-labelled proteins. All PUs were able to adsorb Fn and Fbg (Fn > Fbg). Fn adsorption was in the order: Pellethane > Chronoflex > Bionate, the highest Fbg adsorption being detected onto Bionate (Bionate > Chronoflex > Pellethane). The human macrophagic line J111, and the two main bacterial strains responsible for infection in humans (Staphylococcus aureus Newman and Staphylococcus epidermidis 14852) were incubated in turn with the three PUs, uncoated or coated with plasma proteins. No macrophage or bacterial adhesion was observed onto uncoated PUs. PUs coated with plasma, Fn or Fbg promoted bacterial adhesion (S. aureus > S. epidermidis), whereas macrophage adhered more onto PUs coated with Fn or plasma. The coating with Fbg did not promote cell adhesion. Pellethane showed the highest macrophage activation (i.e. spreading), followed, in the order, by Bionate and Chronoflex.