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

Synthesis, Biological Evaluation and Reversal of Sulfonated Di- and Triblock Copolymers as Novel Parenteral Anticoagulants

Despite targeting different coagulation cascade sites, all Food and Drug Administration-approved anticoagulants present an elevated risk of bleeding, including potentially life-threatening intracranial hemorrhage. Existing studies have not thoroughly investigated the efficacy and safety of sulfonate polymers in animal models and fully elucidate the precise mechanisms by which these polymers act. The activity and safety of sulfonated di- and triblock copolymers containing poly(sodium styrenesulfonate) (PSSS), poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPS), poly(ethylene glycol) (PEG), poly(sodium methacrylate) (PMAAS), poly(acrylic acid) (PAA), and poly(sodium 11-acrylamidoundecanoate) (PAaU) blocks are synthesized and assessed. PSSS-based copolymers exhibit greater anticoagulant activity than PAMPS-based ones. Their activity is mainly affected by the total concentration of sulfonate groups and molecular weight. PEG-containing copolymers demonstrate a better safety profile than PAA-containing ones. The selected copolymer PEG47-PSSS32 exhibits potent anticoagulant activity in rodents after subcutaneous and intravenous administration. Heparin Binding Copolymer (HBC) completely reverses the anticoagulant activity of polymer in rat and human plasma. No interaction with platelets is observed. Selected copolymer targets mainly factor XII and fibrinogen, and to a lesser extent factors X, IX, VIII, and II, suggesting potential application in blood-contacting biomaterials for anticoagulation purposes. Further studies are needed to explore its therapeutic applications fully.

Electrical Conductivity, Thermo-Mechanical Properties, and Cytotoxicity of Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) (PEDOT:PSS)/Sulfonated Polyurethane Blends

Electrically conductive polymeric materials have recently garnered significant interest from researchers due to their potential applications in the biomedical field, including medical implants, tissue engineering, flexible electronic devices, and biosensors. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is considered the most successful conducting polymer due to its higher electrical conductivity and chemical stability, but it suffers from limited solubility in common organic solvents, poor mechanical properties, and low biocompatibility. An area of tremendous interest is in combining PEDOT:PSS with another polymer to form a blend or composite material in order to access the beneficial properties of both materials. However, the hydrophilic nature of PEDOT:PSS makes it difficult to produce composites with non-polar polymers. In order to overcome these problems, we have specifically designed and synthesized two new sulfonated polyurethanes (PUS) with high sulfonic acid functionality. The two polyurethanes, one water-soluble (PUS1) and one water-insoluble (PUS2), were used to make blends with two commercially available PEDOT:PSS formulations (CleviosTM FET and PH1000). Solvent cast films on glass substrates were made from water-soluble PEDOT:PSS/PUS1 blends while free-standing films of PEDOT:PSS/PUS2 blends were fabricated by compression-moulding. Ethylene glycol was used as conductivity enhancer, which showed an increase in the conductivity by several orders of magnitude in most of the compositions investigated. The highest conductivity of 438 S cm-1 was achieved for the blend with 80 wt% of PEDOT:PSS (PH1000) in PUS1.

Advancements in left ventricular assist devices to prevent pump thrombosis and blood coagulopathy

Mechanical circulatory support (MCS) devices, such as left ventricular assist devices (LVADs) are very useful in improving outcomes in patients with advanced-stage heart failure. Despite recent advances in LVAD development, pump thrombosis is one of the most severe adverse events caused by LVADs. The contact of blood with artificial materials of LVAD pumps and cannulas triggers the coagulation cascade. Heat spots, for example, produced by mechanical bearings are often subjected to thrombus build-up when low-flow situations impair washout and thus the necessary cooling does not happen. The formation of thrombus in an LVAD may compromise its function, causing a drop in flow and pumping power leading to failure of the LVAD, if left unattended. If a clot becomes dislodged and circulates in the bloodstream, it may disturb the flow or occlude the blood vessels in vital organs and cause internal damage that could be fatal, for example, ischemic stroke. That is why patients with LVADs are on anti-coagulant medication. However, the anti-coagulants can cause a set of issues for the patient-an example of gastrointestinal (GI) bleeding is given in illustration. On account of this, these devices are only used as a last resort in clinical practice. It is, therefore, necessary to develop devices with better mechanics of blood flow, performance and hemocompatibility. This paper discusses the development of LVADs through landmark clinical trials in detail and describes the evolution of device design to reduce the risk of pump thrombosis and achieve better hemocompatibility. Whilst driveline infection, right heart failure and arrhythmias have been recognised as LVAD-related complications, this paper focuses on complications related to pump thrombosis, especially blood coagulopathy in detail and potential strategies to mitigate this complication. Furthermore, it also discusses the LVAD implantation techniques and their anatomical challenges.

Sulfonate Groups and Saccharides as Essential Structural Elements in Heparin-Mimicking Polymers Used as Surface Modifiers: Optimization of Relative Contents for Antithrombogenic Properties

Blood compatibility is a long sought-after goal in biomaterials research, but remains an elusive one, and in spite of extensive work in this area, there is still no definitive information on the relationship between material properties and blood responses such as coagulation and thrombus formation. Materials modified with heparin-mimicking polymers have shown promise and indeed may be seen as comparable to materials modified with heparin itself. In this work, heparin was conceptualized as consisting of two major structural elements: saccharide- and sulfonate-containing units, and polymers based on this concept were developed. Copolymers of 2-methacrylamido glucopyranose, containing saccharide groups, and sodium 4-vinylbenzenesulfonate, containing sulfonate groups, were graft-polymerized on vinyl-functionalized polyurethane (PU) surfaces by free radical polymerization. This graft polymerization method is simple, and the saccharide and sulfonate contents are tunable by regulating the feed ratio of the monomers. Homopolymer-grafted materials, containing only sulfonate or saccharide groups, showed different effects on cell-surface interactions including platelet adhesion, adhesion and proliferation of vascular endothelial cells, and adhesion and proliferation of smooth muscle cells. The copolymer-grafted materials showed effects due to both sulfonate and saccharide elements with respect to blood responses, and the optimum composition was obtained at a 2:1 ratio of sulfonate to saccharide units (material designated as PU-PS1M1). In cell adhesion experiments, this material showed the lowest platelet and human umbilical vein smooth muscle cell density and the highest human umbilical vein endothelial cell density. Among the materials investigated, PU-PS1M1 also had the longest plasma clotting time. This material was thus shown to be multifunctional with a combination of properties, suggesting thromboresistant behavior in blood contact.

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.

Synthesis and anticoagulant activity of polyureas containing sulfated carbohydrates

Polyurea-based synthetic glycopolymers containing sulfated glucose, mannose, glucosamine, or lactose as pendant groups have been synthesized by step-growth polymerization of hexamethylene diisocyanate and corresponding secondary diamines. The obtained polymers were characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy. The nonsulfated polymers showed similar results to the commercially available biomaterial polyurethane TECOFLEX in a platelet adhesion assay. The average degree of sulfation after reaction with SO₃ was calculated from elemental analysis and found to be between three and four −OSO₃ groups per saccharide. The blood-compatibility of the synthetic polymers was measured using activated partial thromboplastin time, prothrombin time, thrombin time, anti-IIa, and anti-Xa assays. Activated partial thromboplastin time, prothrombin time, and thrombin time results indicated that the mannose and lactose based polymers had the highest anticoagulant activities among all the sulfated polymers. The mechanism of action of the polymers appears to be mediated via an anti-IIa pathway rather than an anti-Xa pathway.

In vitro thrombogenicity investigation of new water-dispersible polyurethane anionomers bearing carboxylate groups

New segmented polyurethane (PU) anionomers based on hydroxytelechelic polybutadiene were synthesized via an aqueous dispersion process. Incorporation of carboxylic groups was achieved using thioacids of different length. 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 assays using 111In-radiolabeled platelet-rich plasma and [125I]fibrinogen. Morphology of the adhered platelets was examined by scanning electron microscopy (SEM). Results were compared to two biomedical-grade PUs, namely Pellethane and Tecoflex. Insertion of carboxylic groups increased surface hydrophilicity and limited water uptake ( < 8% for an ion content of 5% by weight). Surface energy of all synthesized PUs was between 40 and 45 mJ/m2. Platelet adhesion and fibrinogen adsorption on the PU anionomer surfaces were affected as a function to the increase of graft length; thiopropionic was the most haemocompatible, followed by thiosuccinic and then thioglycolic acid. SEM analyses of all ionic PU samples exhibited low platelet adhesion to surfaces with no morphological modification. In conclusion, increased hydrophily, dynamic mobility and charge repulsion are synergistic key factors for enhanced haemocompatibility.

Tailored Synthesis of Nitric Oxide-Releasing Polyurethanes Using O-Protected Diazeniumdiolated Chain Extenders

Nitric oxide (NO) has been shown to exhibit significant anti-platelet activity and its release from polymer matrices has been already utilized to increase the biocompatibility of various blood-contacting devices. Herein, details of a new synthetic approach for preparing NO-releasing diazeniumdiolated polyurethanes (PU) are described. The method's utility is demonstrated by the incorporation of methoxymethyl- or sugar-protected pre-formed diazeniumdiolate moieties directly into chain extender diols which are then incorporated into the polyurethane backbone. This approach provides the ability to control the number of diazeniumdiolate groups incorporated into the polymer backbone, and hence the surface flux of NO that can ultimately be liberated from polymeric films prepared from the new PU materials. The method provides a means of covalently attaching diazeniumdiolate groups to polyurethanes in a form that resists dissociation of NO during processing but can be activated for spontaneous NO release via hydrolysis of the carbohydrate or methoxymethyl moieties under basic and acidic conditions, respectively.

Nitric Oxide Releasing Polyurethanes with Covalently Linked Diazeniumdiolated Secondary Amines

Two novel strategies for synthesizing stable polyurethanes (PUs) capable of generating bioactive nitric oxide (NO) are described. The methods rely on covalently attaching diazeniumdiolate (N(2)O(2)(-)) groups onto secondary amine nitrogens at various positions within the polymer chain such that, when in contact with water or physiological fluids, only the two molecules of NO available from each diazeniumdiolate moiety are released into the surrounding medium, with potential byproducts remaining covalently bound to the matrix. Extensive analysis of the NO(x)() products released from the polymers was employed to develop appropriate strategies to better stabilize the diazeniumdiolate-based polymer structures. In one approach, diazeniumdiolate groups are attached to secondary amino nitrogens of alkane diamines inserted within the diol chain extender of a PU material. Oxidative loss of NO was minimized by blending the polymer with a biocompatible, relatively nonnucleophilic salt before exposing solutions of the polymer to NO during the diazeniumdiolation step. Fluxes of molecular NO from such materials during immersion in physiological buffer reached levels as high as 19 pmol x cm(-2) x s(-1) with a total recovery of 21 nmol of NO/mg of PU. A second general synthetic strategy involved omega-haloalkylating the urethane nitrogens and then displacing the halide from the resulting polymer with a nucleophilic polyamine to form a PU with pendent amino groups suitable for diazeniumdiolation. Commercially available Pellethane 2363-80AE that was bromobutylated and then reacted with diethylenetriamine and further exposed to gaseous NO proved stable in solid form for several months, but released NO with a total recovery of 17 nmol/mg upon immersion in physiological buffer. This material showed an initial NO flux of 14 pmol x cm(-2) x s(-1) when immersed in pH 7.4 buffer at 37 degrees C, with gradually decreasing but still observable fluxes for up to 6 days.

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.

Chitosan based surfactant polymers designed to improve blood compatibility on biomaterials

We developed chitosan based surfactant polymers that could be used to modify the surface of existing biomaterials in order to improve their blood compatibility. These polymers consist of a chitosan backbone, PEG side chains to repel non-specific protein adsorption, and hexanal side chains to facilitate adsorption and proper orientation onto a hydrophobic substrate via hydrophobic interactions. Since chitosan is a polycationic polymer, and it is thrombogenic, the surface charge was altered to determine the role of this charge in the hemocompatibility of chitosan. Charge had a notable effect on platelet adhesion. The platelet adhesion was greatest on the positively charged surface, and decreased by almost 50% with the neutralization of this charge. A chitosan surface containing the negatively charged SO(3)(-) exhibited the fewest number of adherent platelets of all surfaces tested. Coagulation activation was not altered by the neutralization of the positive charge, but a marked increase of approximately 5-6 min in the plasma recalcification time (PRT) was displayed with the addition of the negatively charged species. Polyethylene (PE) surfaces were modified with the chitosan surfactant resulting in a significant improvement in blood compatibility, which correlated to the increasing PEG content within the polymer. Adsorption of the chitosan surfactants onto PE resulted in approximately an 85-96% decrease in the number of adherent platelets. The surfactant polymers also reduced surface induced coagulation activation, which was indicated by the PEG density dependent increase in PRTs. These results indicate that surface modification with our chitosan based surfactant polymers successfully improves blood compatibility. Moreover, the inclusion of either negatively charged SO(3)(-) groups or a high density of large water-soluble PEG side chains produces a surface that may be suitable for cardiovascular applications.

Electron microscopy as a quantitative method for investigating tau fibrillization

Fibrillization of tau protein is a hallmark lesion in Alzheimer's disease. To clarify the utility of electron microscopy as a quantitative assay for tau fibrillization in vitro, the interaction between synthetic tau filaments and carbon/formvar-coated grids was characterized in detail. Filament adsorption onto grids was hyperbolic when analyzed as a function of time or bulk protein concentration, with no evidence for competitive displacement or elution from other components in the reaction mixture. Filament length measurements were linear with filament concentration so long as the concentration of total tau protein in the sample was held constant, suggesting that measurement of filament lengths was accurate under these conditions. Furthermore, exponential filament length distributions were not significantly affected by adsorption time or filament concentration, suggesting that preferential binding among filaments of differing lengths was minimal. However, monomeric tau protein was found to be a strong competitor of filament adsorption, indicating that comparison of filament length measurements at different bulk tau concentrations should be interpreted with caution.

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.

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.

Study of the adsorption of fibrinogen on gold-coated silicon wafer by an impedance method

In 0.1 mol/l KH(2)PO(4)-Na(2)HPO(4) (pH 7.80) buffer solution, the potential of zero charge (PZC) and the open circuit potential of gold-coated silicon were determined to be about -0.6 and +0.10 V (vs SCE), respectively. The open circuit potential was higher than the PZC, which indicated that the surface of the gold-coated electrode had a positive charge. The ellipsometry experiment showed that the adsorption of fibrinogen onto the gold-coated silicon wafer surface arrived at a saturated state when the adsorption time exceeded 50 min. The percentage of surface without adsorbed protein, theta, was about 63%. This means that the proportion of surface actually occupied by fibrinogen was only about 37% after the adsorption arrived at saturation. The solution/protein capacitance value was determined in an impulse state around -0.59 V (vs SCE) and was stable (4.2x10(-5) F) at other potentials.

Enhanced blood compatibility of polymers grafted by sulfonated PEO via a negative cilia concept

In our laboratory sulfonated PEO (PEO-SO(3)) was designed as a "negative cilia model" to investigate a synergistic effect of PEO and negatively charged SO(3) groups. PEO-SO(3) itself exhibited a heparin-like anticoagulant activity of 14% of free heparin. Polyurethane grafted with PEO-SO(3) (PU-PEO-SO(3)) increased the albumin adsorption to a great extent but suppressed other proteins, while PU-PEO decreased the adsorption of all the proteins. The platelet adhesion was decreased on PU-PEO but least on PU-PEO-SO(3) to demonstrate an additional effect of SO(3) groups. The enhanced blood compatibility of PU-PEO-SO(3) in the ex vivo rabbit and in vivo canine implanting tests was confirmed. Furthermore, PU-PEO-SO(3) exhibited an improved biostability and suppressed calcification in addition to the enhanced antithrombogenicity. The in vivo antithrombogenicity and biostability were improved in the order of PU<PU-PEO<PU-PEO-SO(3). The calcium amounts deposited was decreased in the order of PU>PU-PEO>PU-PEO-SO(3) in spite of the possible attraction between negative SO(3) groups and positive calcium ions. The bioprosthetic tissue (BT) was grafted with H(2)N-PEO-SO(3) via glutaraldehyde (GA) residues after conventional GA fixation. BT-PEO-SO(3) also displayed the decreased calcification by in vivo animal models. The application of PEO-SO(3) was extended by designing amphiphilic copolymers containing PEO-SO(3) moiety and hydrophobic long alkyl groups as anchors. The superior effect of PEO-SO(3) groups on thromboresistance compared to PEO was confirmed also in the case of copolymers coated or blended with other polymers and the systems coupled by UV irradiation, photoreaction or gold/sulfur or silane coupling technology, and therefore it might be very useful for the medical devices.

Blood compatibility of titanium oxides with various crystal structure and element doping

BACKGROUND

Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade.

METHODS

Titanium oxide films were produced by metal plasma deposition and implantation in the form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the Fermi level of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples.

RESULTS

The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces.

CONCLUSION

Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

Novel dendrimer based polyurethanes for PEO incorporation

A series of segmented polyurethanes based on methylene diisocyanate/poly (tetramethylene oxide) and chain extended with either ethylene diamine or butane diol in combination with a generation 2 polypropylenimine octaamine dendrimer were synthesized. For polymer synthesis, the dendrimers were protected with either t-boc or Fmoc groups and were incorporated into the polyurethane microstructure to permit further functionalization with biologically active groups. Following deprotection, the dendrimers were reacted with succinimidyl propionate polyethylene oxide (SPA-PEO) to improve the protein resistance of the polymers and to examine the potential of this technique for polymer functionalization. Different synthesis techniques were examined to optimize the incorporation of the PEO into the polymer microstructure. Incorporation of the dendrimers and the PEO were confirmed by NMR and FTIR. Gel permeation chromatography was used to examine the molecular weights of the various polyurethanes. The dendrimer incorporated polymers had significantly lower molecular weights than the ED or BDO chain extended controls, likely due to lower reactivity of the dendrimers as a result of steric factors. Following PEO reaction, the molecular weights of the resultant polymers were consistent with the levels of PEO incorporation noted by comparison of peak intensities in the NMR spectra. Due to the highly hydrophilic nature of the PEO, some migration to the polymer surface was expected. Water contact angles and XPS, used to characterize the surfaces, suggest that there was some PEO enrichment at the surface of the polymers. Adsorption of radiolabeled fibrinogen to the polymer surfaces was decreased by a factor of approximately 40% in some of the PEO incorporated polymers. There were also differences in the patterns of plasma protein adsorption on the various surfaces as evaluated by SDS PAGE and immunoblotting. Therefore, the use of dendrimers in biomaterials for incorporation of a large number of functional groups seems to be promising.

Interaction of fibrinogen with surfaces of end-group-modified polyurethanes: a surface-specific sum-frequency-generation vibrational spectroscopy study

Fibrinogen adsorption on polyurethanes with different surface-modifying end groups (SMEs) has been studied with sum-frequency-generation vibrational spectroscopy (SFG). The results show very different protein adsorption properties for different SMEs on the same backbone polymer. Fibrinogen binds weakly on the hydrophilic backbone of a poly(dimethyl siloxane) (PDMS)-modified polyurethane surface but leaves the hydrophobic PDMS part untouched. On sulfonate end-group-modified (SO(3(-) )) polyurethane surfaces, fibrinogen adsorbs well. However, on poly(ethylene oxide) (PEO)-modified surfaces, it adsorbs poorly. The protein-resistant character of PEO is probably due to steric repulsion. This work demonstrates the utility of SFG in the study of protein adsorption on polymeric biomaterials at the molecular level and the ability of SMEs to mediate protein adsorption.

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.

Anticoagulant mechanism of sulfonated polyisoprenes

The influence of sulfonated polyisoprene (SPIP) on coagulation factors and human blood cells was investigated to elucidate and compare its anticoagulant mechanism with that of heparin. While the number of red cells was unaffected, the number of platelets decreased dramatically in the presence of SPIP due to aggregation. Using a synthetic peptide substrate to assay thrombin activity in the presence of its natural inhibitor, antithrombin (AT), we observed no stimulation by SPIP of AT-mediated inhibition. Nevertheless, thrombin cleavage of its natural substrate fibrinogen to fibrin peptide A was slightly inhibited. SPIP altered the electrophoretic mobility of fibrinogen and completely inhibited fibrinogen from clotting. We detected no significant influence of SPIP on factors II, VII, IX, and X, while factor XI and factors V and VIII were only slightly affected. Therefore, the main mechanism of SPIP's anticoagulant activity appears to be a strong interaction with fibrinogen and fibrin monomer, first, to prevent proteolytic conversion of the former to the latter and second, to inhibit polymerization of the fibrin monomer, once formed.

The influence of thrombus components in mediating bacterial adhesion to biomaterials

Thrombosis and infection represent the two largest limiting factors determining the long term success of implanted biomaterials. Infections associated with biomaterials are difficult to treat, and appear to evade the host defense systems. Mechanisms relating infection to thrombosis are described. Investigations into the role of receptors in mediating adhesion to thrombi are also discussed, in addition to strategies to reduce bacterial adhesion to biomaterial surfaces.

Cell adhesion peptide modification of gold-coated polyurethanes for vascular endothelial cell adhesion

Gold-coated polyurethanes were chemisorbed with three cell-adhesion peptides having an N-terminal cysteine: cys-arg-gly-asp (CRGD), cys-arg-glu-asp-val (CREDV), and the cyclic peptide cys-cys-arg-arg-gly-asp-try-leu-cys (CCRRGDWLC). The peptides were selected based on their presumed preferential interactions with the cell-surface integrins on vascular endothelial cells. The ability of the surfaces to support the preferential adhesion of human vascular endothelial cells was studied by comparing in vitro adhesion results for these cells with those from mouse 3T3 fibroblasts. Surface modification with the peptides was confirmed by water-contact angles and XPS. Surface morphology was determined by AFM and SEM. In vitro cell-culture studies in conjunction with plasma-protein adsorption and immunoblotting were performed on the various modified surfaces. The data suggest that peptide-modified surfaces have significant potential for supporting cell adhesion. Little or no cell adhesion was noted on gold- or cysteine-modified control surfaces. Human vascular endothelial cells showed the greatest adhesion to the CCRRGDWLC-modified surfaces, and the 3T3 fibroblasts adhered best to the CREDV-modified surfaces. Protein adsorption studies suggest that the preferential adsorption of the cell-adhesive proteins fibronectin and vitronectin is not likely mediating the differences noted. It is concluded that the cell-adhesive peptide-modified gold-coated polymers have significant potential for further development both as model substrates for fundamental studies and for use in biomaterials applications.

Synthesis, surface characterization, and platelet reactivity evaluation for the self-assembled monolayer of alkanethiol with sulfonic acid functionality

Owing to the capability of fabricating a well-defined chemical structure on the surface, self-assembled alkanethiols with a variety of terminal functionalities were prepared on the gold substrate for investigating the interactions between the biological environment and synthetic surface. In this study, we report the synthesis of the sulfonic acid terminated long-chain alkanethiol, 10-mercaptodecane-sulfonic acid, for direct preparation of a self-assembled monolayer (SAM) with -SO(3)H functionality. Nuclear magnetic resonance (NMR) and elemental analysis studies indicated that a high purity of sulfonic acid terminated alkanethiol was obtained. Surface characterization results showed that the -SO(3)H terminated SAM is hydrophilic and has a slightly higher hysteresis value, possibly because of the slower chain mobility of the bound sulfonic acid alkanethiol. Electron spectroscopy for chemical analysis (ESCA) analysis demonstrated that the -SO(3)H terminal group is situated in the outermost layer of the monolayer, as previous alkanethiol SAM structure models proposed. The platelet reactivity of the -SO(3)H SAM was higher than that of -OH SAM but less than the -CH(3) terminated one in vitro, whereas similar platelet reactivity was noticed between the -SO(3)H and -COOH SAMs. The higher platelet reactivity found on the -SO(3)H SAM could be caused by the higher surface functional group density inherent in the SAM structure and/or the composition and conformation state of the adsorbed protein layer.

Synthesis, characterization, and platelet adhesion studies of novel aliphatic polyurethaneurea anionomers based on polydimethylsiloxane-polytetramethylene oxide soft segments

Two novel aliphatic polyurethaneurea anionomers were synthesized based on polydimethylsiloxane (PDMS)-polytetramethylene oxide (PTMO) soft segments. The hard segments consisted of either 4,4'-methylene dicyclohexyl diisocyanate (H12MDI), sulfonic acid-containing diol and 1,4-butandiol (BD) or H12MDI, carboxylic acid-containing diol and BD. The nonionic counterpart chain extended with BD was prepared. In addition, the base nonionic polyurethaneurea containing a pure PDMS soft segment, which is denote H-D-BD, was also studied for comparison. The effects of soft segment type and ion incorporation on the physical properties, surface properties, and plateled adhesion are discussed. The ionic polyurethaneureas exhibited poor phase separation, a smaller fraction of PTMO present at the surface, and a smaller contact angle. On the other hand, it also showed a larger fraction of PDMS present at the surface and a higher water absorption value than its nonionic counterpart. H-D-BD had more phase-separated structure, a larger fraction of PDMS present at the surface, and larger contact angle but lower water absorption value than the PTMO-containing polyurethaneureas. The in vitro platelet adhesion experiments indicated that the ionic groups, especially for carboxylate, and surface enrichment PDMS soft segment could effectively inhibit platelet adhesion.

Synthesis, characterization and platelet adhesion studies of novel ion-containing aliphatic polyurethanes

Two novel ion-containing aliphatic polyurethanes based on 4,4'-methylene dicyclohexyl diisocyanate (H12MDI), polytetramethyl oxide (PTMO) were synthesized using either sulfonated or carboxylated chain extender. The nonionic polyurethane chain extended with 1,4-butanediol, which is denoted as H-M-BD, was synthesized. Pellethane, a biomedical-grade polyurethane, was also studied for comparison. The polymer's bulk, surface, and platelet-contacting properties were studied using Fourier transform infrared spectrophotometry, differential scanning calorimetry, water absorption analysis, electron spectroscopy for chemical analysis, static contact angle analysis, and in vitro platelet adhesion experiments. The effects of ion incorporation on the morphology, surface properties and blood compatibility are discussed. Unlike MDI-based Pellethane, all H12MDI-based polyurethanes are not composed of crystalline hard segment domain but are amorphous. The ionic polyurethanes exhibit a smaller fraction of hydrogen-bonded carbonyl groups, poorer phase separation, smaller fraction of PTMO residing at the surface, and smaller contact angle; however, significant higher water absorption value than H-M-BD and Pellethane. The in vitro platelet adhesion experiments indicated that ion incorporation, especially for carboxylate, significantly reduced the number and the degree of activation of the adherent platelets.

Peptide modified gold-coated polyurethanes as thrombin scavenging surfaces

Thin layers of gold were deposited on polyurethane film and chemisorbed with three peptides having an N-terminal cysteine: Cys-Pro-Arg, Cys-(L)Phe-Pro-Arg, and Cys-(D)Phe-Pro-Arg. The ability of these surfaces to act as thrombin scavengers was evaluated. The peptides are related to the known thrombin inhibitor Phe-Pro-Arg chloromethyl ketone and were shown to have significant thrombin inhibitory activity in solution. Attachment of the peptides to gold was confirmed by water contact angle and X-ray photoelectron spectroscopy measurements. Thrombin adsorption from a buffer and plasma was investigated, and chromogenic substrate assays were carried out for thrombin activity on the surfaces and in the supernatant following adsorption. The data suggest that the peptide-modified surfaces are able to adsorb thrombin with high affinity from a buffer and that thrombin is taken up selectively from plasma. The Cys-(D)Phe-Pro-Arg modified surfaces showed particularly high affinity for thrombin. It was also found that the activity of thrombin adsorbed on the peptide surfaces was inhibited, and inhibition was greatest on the Cys-(D)Phe-Pro-Arg surface. We concluded that the peptide surfaces may have potential as antithrombogenic materials via their ability to scavenge and inhibit thrombin generated as a result of blood-material contact.

Residence-time dependent changes in fibrinogen adsorbed to polymeric biomaterials

It has generally been accepted that biomaterials adsorbing the least amount of the plasma protein fibrinogen following exposure to blood will support less platelet adhesion and therefore exhibit less thrombogenicity. Several studies suggest, however, that the conformation or orientation of immobilized fibrinogen rather than the total amount adsorbed plays an important role in determining the blood compatibility of biomaterials. The purpose of this study was to investigate time-dependent functional changes in fibrinogen adsorbed to polytetrafluoroethylene (PTFE), polyethylene (PE), and silicone rubber (SR). Fibrinogen was adsorbed to these materials for 1 min and then allowed to 'reside" on the 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, the binding of a monoclonal antibody (mAb) directed against an important functional region of the fibrinogen molecule (the gamma-chain dodecapeptide sequence 400-411), and the ability of blood plasma to displace previously adsorbed fibrinogen. Platelet adhesion differed among the polymeric materials studied, and PTFE and PE samples exhibited a small decrease in adhesion with increasing fibrinogen residence time. Platelet adhesion to SR was the least among all materials studied and showed no variation with residence time. When using PTFE and SR as substrates, mAb recognition of adsorbed fibrinogen did not change with residence time whereas that on PE decreased slightly. The mAb binding was least to fibrinogen adsorbed to SR, which is in agreement with the platelet adhesion results. Finally, the ability of plasma to displace previously adsorbed fibrinogen decreased dramatically with increasing residence time on all materials. These in vitro studies support the hypothesis that fibrinogen undergoes biologically significant conformational changes upon adsorption to polymeric biomaterials, a phenomenon that may contribute to the hemocompatibility of the materials following implantation in the body.

Platelet adhesion onto segmented polyurethane surfaces modified by PEO- and sulfonated PEO-containing block copolymer additives

Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO- and sulfonated PEO-containing amphiphilic block copolymers as surface-modifying additives in a segmented polyurethane (PU). PEO-PPO-PEO triblock copolymers (Pluronics) with different PEO chain lengths (from 2 to 80) were used as additives. The prepared film surfaces were characterized by the measurement of dynamic water contact angles and electron spectroscopy for chemical analysis. It was observed that the PU films containing 10 wt% of PEO additives were surface-saturated with the additives regardless of their PEO chain length, but the PEO chains were more projected from the film surfaces containing the additives with longer PEO chains. The water absorption of the films increased largely with the increasing PEO chain length of the additives. The addition of PEO additives produced film surfaces that were in a gel-like state. The films demonstrated some extraction of the PEO additives. However, the additives with higher molecular weights were entrapped more stably into the PU matrix. The mechanical properties (tensile strength and elongation) of the films were changed by the addition of PEO additives, but the differences were not significant compared to the control PU. The platelet adhesion on the film surfaces decreased with increasing PEO chain length of the additives. The film surface containing additives with long PEO chains (chain length of 80) was particularly effective in preventing platelet adhesion. The effect of negatively charged sulfonate groups on the prevention of platelet adhesion appeared only on the film surfaces containing additives with short PEO chains. For longer PEO chains, the chain mobility effect was more dominant than the negative charge effect on the prevention of platelet adhesion.

Immobilization of functionalized alkyl-poly(ethylene oxide) surfactants on poly(ethylene) surfaces by means of an argon plasma treatment

Alkyl-poly(ethylene oxide) (PEO) surfactants containing a terminal hydroxyl, sulfate, or carboxylate group were grafted at the surface of poly(ethylene) (PE) samples to improve their blood compatibility. Grafting was achieved by immobilizing PEO surfactants on PE using an argon plasma treatment. The sulfate group containing PEO surfactant was synthesized by sulfating polyoxyethylene(20)stearylether (Brij78; B) with chlorosulfonic acid. A carboxylate-terminated surfactant was synthesized by a substitution reaction of the sodium alkoxide form of B with sodium iodoacetate. XPS analysis of the modified PE samples showed that at short plasma treatment times of up to 5 s the structure of the immobilized surfactants is largely retained. When plasma treatment times longer than 30 s were applied, the PEO chains of the surfactants were degraded. The wettability of the modified PE samples was improved compared to the unmodified PE samples. The wettability of the modified samples did not change when they were stored in air at room temperature for at least 12 weeks.

Protein depositions on one hydrocephalus shunt and on fifteen temporary ventricular catheters

Biomaterials are commonly used in modern medicine. Proteins are adsorbed to the surface of the biomaterial immediately after insertion. This report demonstrates the presence of adsorbed proteins in one infected cerebrospinal shunt from a child with hydrocephalus and on fifteen temporary ventricular catheters from adult patients with spontaneous or traumatic brain injuries. Depositions of vitronectin, fibrinogen and thrombospondin-fibronectin to some extent--on the shunt surface was imaged by field-emission scanning electron microscopy. Vitronectin, fibronectin, fibrinogen, and thrombospondin on the ventricular catheters were shown with radio-actively labelled antibodies. Furthermore, protein adsorption from human cerebrospinal fluid to heparinized and unheparinized polymers was studied under flowing conditions in vitro. On heparinized polymer, significantly reduced levels of vitronectin, fibronectin, and thrombospondin were exposed, as measured after 4 hours in vitro perfusion. After 24 hours perfusion, the differences in protein exposition between heparinized and unheparinized polymers were substantially reduced.

Blood compatible phospholipid-containing polyurethanes: synthesis characterization and blood compatibility evaluation

A new diol, bis[2-(2-hydroxyethyldimethylammonio)ethyl] butylenediphosphate, that contains two phosphatidylcholine analogous moieties in one diol molecule, was synthesized and characterized. The diol together with 1,4-butanediol as chain extender was further incorporated into the propolymer of poly(ethylene oxide) (Mn = 1000, 2000, 6000) and 4,4'-methylenediphenyl diisocyanate. The resulting phospholipid poly(ether urethane)s show viscosity behavior of common polyelectrolytes. The bulk and surface characteristics of the new phospholipid poly(ether urethane)s were investigated by IR, GPC, ATR-FTIR, ESCA and contact angle measurements. The new polymers possessed relatively hydrophilic surface revealed by contact angle measurements. The blood compatibilities of the polyurethanes were evaluated by platelet rich plasma contacting studies and scanning electron microscopy observation using medical grade PVC as the reference. No platelet adhesion was observed for all new phospholipid polyurethane casting films. This new type of phospholipid polyurethane is expected to have potential biomedical applications.

Photochemical grafting of alpha-propylsulphate-poly(ethylene oxide) on polyurethane surfaces and enhanced antithrombogenic potential

The aim of this study is the grafting of photoreactive alpha-propylsulphate-poly(ethylene oxide) (PEO-SO3), one end of which is capped with an azidophenyl group, on polyurethane (PU) surfaces via a photochemical technique. The anti-Factor Xa activity and the platelet adhesion characteristics of the modified PU surface were evaluated by a chromogenic assay method and by a flow-controlled chamber method, respectively. X-ray photoelectron spectroscopy analysis showed that PEO-SO3 was covalently grafted on the PU surface. The grafted surface showed anti-Factor Xa activity in the presence of antithrombin III, and significantly reduced platelet adhesion characteristics as compared with those of the unmodified PU surface. These results suggest that the grafting of PEO-SO3 improves the antithrombogenicity of PU surfaces.

The effect of hard segment size on the hydrolytic stability of polyether-urea-urethanes when exposed to cholesterol esterase

Previous studies have shown that both polyester and polyether-based polyurea-urethanes are susceptible to cleavage by hydrolytic enzymes. Furthermore, it has been hypothesized that the degree of hard segment micro-domain formation in polyurethane materials, as well as its structure, influences the ability of enzymes to degrade the polymers. The current study has investigated a series of segmented polyether-urea-urethanes synthesized with the same reagents but having different hard segment content. Using these materials, the relationship between the formation of hard segment domains and the hydrolysis of urea/urethane groups was specifically addressed. Both differential scanning calorimetry and X-ray photo-electron spectroscopy data indicated that the three materials differed significantly in the extent of hard segment domain formation and the nature of the chemical groups located in the top 10 nm of the surface. Biodegradation studies showed a strong dependence on hard segment domain formation and indicated that the polymer containing the highest number of hydrolytically labile urea and urethane bonds exhibited the least degradation. The ability of a polyurethane material to form hard segment micro-domains may contribute to the formation of a protective structure for the hydrolysable hard segment linkages located within the micro-domains.

Physicochemical properties and platelet interactions of segmented polyurethanes containing sulfonate groups in the hard segment

The adhesion of platelets to a series of segmented polyurethanes having sulfonate groups in the hard segment is reported. The polyurethanes were synthesized using sulfonated chain extenders of different structure. Analogous control materials without sulfonate groups also were studied. Adhesion was measured in vitro using washed human platelets in a carrier fluid consisting of Tyrode's buffer with apyrase, albumin, and red cells at normal concentration. The polymers were characterized by gel permeation chromatography and elemental analysis. Water absorption and thermal transitions also were determined. It was found that the sulfonated materials absorb significant amounts of water while the nonsulfonated analogs do not. The surfaces of polymer films were characterized by water contact angle and XPS. The contact angles of the sulfonated surfaces were relatively low. Platelet adhesion to the sulfonated polymers was found to be very high compared to the nonsulfonate analogs. The local environment of the sulfonate groups (different chain extenders) also appears to have an effect on platelet interactions. Albumin adsorption was high on all the materials and was not correlated with platelet adhesion. It appears from this work that platelets may have a binding site that is specific for sulfonate groups.

Biocompatibility of sulphonated polyurethane surfaces

Surfaces of medical devices made of polymeric materials may promote thrombosis and inflammation. Therefore, in an attempt to produce surfaces which might diminish biomaterial-mediated thrombosis and inflammation, surface derivatization with 2-acrylamido-2-methylpropanesulphonic acid (AMPS) was carried out. The derivatization procedure generates free radicals which initiate the copolymerization of AMPS monomers directly to a polyurethane surface. In an in vitro blood loop study using non-anticoagulated human blood, the resulting AMPS-derivatized material completely abrogates the generation of fibrinopeptide A, decreases the production of beta-thromboglobulin and C3a, and decreases the adherence of platelets. The derivatized material also attracts fewer adherent neutrophils when implanted in mice. However, AMPS derivatization unexpectedly increases the recruitment of macrophages to implanted material and promotes the formation of adherent sleeve thrombi on central venous catheters indwelling in non-anticoagulated canine femoral veins. Thus, AMPS derivatization has highly variable effects on inflammatory and thrombotic systems. Further investigation is clearly required to determine the mechanisms underlying both desired and adverse effects.