Segmented Polyurethane Surface Research Articles

Graft-type antithrombogenic MPC polymers as the surface modifier on the small-diameter vascular prostheses of segmented polyurethane

Event Abstract Back to Event Graft-type antithrombogenic MPC polymers as the surface modifier on the small-diameter vascular prostheses of segmented polyurethane Yihua Liu1*, Yuuki Inoue2, Atsushi Mahara3, Sachiro Kakinoki3, Tetsuji Yamaoka3 and Kazuhiko Ishihara1, 2 1 School of Engineering, The University of Tokyo, Department of Bioengineering, Japan 2 School of Engineering, The University of Tokyo, Department of Materials Engineering, Japan 3 National Cerebral and Cardiovascular Center Research Institute, Japan Introduction: The foreign surfaces of cardiovascular biomedical devices always cause blood coagulation. The adherent endothelial cells protect the surfaces of synthetic vascular prostheses with diameter over 6 mm from blood coagulation. However, the applications of these vascular prostheses as small arteries (diameter: less than 2 mm) were failure due to limited thrombogenicity.The objective of this study is to develop an antithrombogenic surface modifier of the segmented polyurethane (SPU) by the graft-type 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers. The SPU is widely used as biomedical materials because of its excellent mechanical properties. To achieve molecular interaction between MPC polymer and SPU even under the blood flow condition, the graft-type poly(MPC-co-2-ethylhexyl methacrylate (EHMA)) (graft-PMEH) was synthesized and hybridized with the SPU [1]. The affinity between poly(EHMA) segments and soft segments of SPU is a key intermiscibility in the SPU/graft-PMEH. Initial blood interactions were observed by passing through the SPU/graft-PMEH tubing [2]. Materials and methods: The graft-PMEH was synthesized by two different living radical polymerizations. The SPU/graft-PMEH membrane was prepared by a double-solution casting procedure. The surface elements of membranes were confirmed by X-ray photoelectron spectroscopy (XPS). Biocompatibility was evaluated by protein adsorption test from human plasma with gold-colloid labeled immunoassay, and human umbilical vein endothelial cells (HUVEC) adhesion assay. The SPU/graft-PMEH tubings (Φ2 mm, length 35 mm) were prepared with the similar procedure of membranes on a revolving stick. The tubing was directly connected to the living porcine blood vessel for 2 min. The samples were observed by scanning electron microscopy (SEM). Results: The phosphorus peak and nitrogen peak attributed to phosphorylcholine group of MPC unit were observed on the XPS in SPU/graft-PMEH membranes. Plasma proteins adsorbed in a dispersed pattern on the SPU surface. In contrast, the SPU/graft-PMEH membrane dramatically suppressed 90% amount of protein adsorption. Also, a little HUVEC could be adhered and no proliferation was observed. On the luminal surface of SPU/graft-PMEH tubing, blood cell adhesion was inhibited even after whole blood was passed through without anticoagulation (Fig.1). Discussion: The graft-PMEH shows a high stability on the SPU surface because that poly(EHMA) segments side chains promote intermiscibility with the soft segment domain of SPU. The graft-PMEH could prevent thrombus formation even after blood contacting without any anticoagulant. This is due to the nature of the MPC polymers, that is, high resistance to adsorption of proteins and adhesion of cells to obtain antithrombogenicity. Conclusion: The SPU/graft-PMEH combined with excellent blood compatibility, mechanical properties and non-endothelialization is a potential biomaterial for small diameter vascular prostheses. We would like to thank Dr Tomohiro Konno and Dr Kyoko Fukazawa from the University of Tokyo for their valuable and constructive discussions.; This work was financially supported by a Health and Labour Sciences Research Grant (Grant H24-018) from the Ministry of Health, Labour, and Welfare of Japan.

Biofunctional Surface Layer and its Bonding Strength in Low Modulus β-Type Titanium Alloy for Biomedical Applications

Recently, low-modulus β-type titanium alloys have been the focus of considerable attention because of their high biocompatibility and their low moduli that make them effective for inhibiting bone atrophy and for enhancing bone remodeling. However, the biofunctinalities of titanium alloys, such as bone conductivity, blood compatibility, and soft tissue compatibility, are poor. Therefore, surface modification techniques such as bioactive ceramic surface modification and blood-and soft-tissue-compatible polymer surface modification are applied to titanium alloys. Hydroxyapatite (HAp) surface modification via metal organic chemical vapor deposition (MOCVD) and segmented polyurethane (SPU) surface modification via silane coupling treatment are effective techniques to add biofunctionalites to titanium alloys. HAp surface modification via MOCVD and SPU surface modification using three kinds of silane coupling agents on a low modulus beta-type titanium alloy, namely, TNTZ, are discussed. Moreover, the bonding strengths of HAp and SPU on the surface of TNTZ, which are important parameters, are also discussed.

Effects of molecular architecture of phospholipid polymers on surface modification of segmented polyurethanes

To modify the surface properties of segmented polyurethane (SPU), effects of the molecular architecture of the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers on the performance of the SPU/MPC polymer membrane were investigated. We combined the random-type, block-type, and graft-type of the MPC polymers with a typical SPU, Tecoflex® using double solution casting procedure. The graft-type MPC polymers composed of a poly(MPC) main chain and poly(2-ethylhexyl methacrylate (EHMA)) side chains were synthesized through the combination of two different living radical polymerization techniques to regulate the density and chain length of the side chains. The SPU membranes modified with the MPC polymers were characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results revealed that the MPC units were located on the SPU surface. Although the breaking strength of the SPU membranes modified with block-type poly(MPC-block-EHMA) and graft-type poly(MPC-graft-EHMA) was lower than that of SPU membranes modified with random-type poly(MPC-random-EHMA), their breaking strengths were adequate for manufacturing medical devices. On the other hand, better stability was observed in the MPC polymer layer on the SPU membrane after immersion in an aqueous medium, wherein the SPU membrane had been modified with the poly(MPC-graft-EHMA). This was because of the intermixing of the hydrophobic poly(EHMA) segments in the domain of the hard segments in the SPU membrane. After this modification, each SPU/MPC polymer membrane showed hydrophilic nature based on the MPC polymers and a dramatic suppression of protein adsorption. From these results, we concluded that the SPU membrane modified with the poly(MPC-graft-EHMA) was one of the promising polymeric biomaterials for making blood-contacting medical devices.

Segmented polyurethane modified by photopolymerization and cross-linking with 2-methacryloyloxyethyl phosphorylcholine polymer for blood-contacting surfaces of ventricular assist devices

To improve the biocompatibility of pulsatile ventricular assist devices (VADs), the blood-contacting surface of the segmented polyurethane (SPU) diaphragm employed in an electromechanical VAD was modified by introducing 2-methacryloyloxyethyl phosphorylcholine (MPC) units into its surface and forming an interpenetrating polymer network (IPN) structure, which contained independently cross-linked MPC polymer and SPU. The SPU diaphragm modified with an IPN structure was then assembled into a target test pump and underwent continuous pump operation at 37°C for 2 weeks in a simulated systemic circulation using a mock circulatory loop. The surface characteristics of the pump diaphragm after 2 weeks of pump operation were then analyzed with an X-ray photoelectron spectroscope (XPS) and gold-colloid-labeled immunoassay. The XPS surface analysis of the IPN-modified SPU indicated the firm anchoring of MPC units even after 2 weeks of pump operation (the phosphor : carbon ratio was reduced by only 0.09%). The IPN-modified diaphragm prevented protein adsorption as well as cell adhesion in comparison to the unmodified SPU surface. This result thus validated that (1) the IPN structure could firmly secure MPC units to the SPU surface even in a high-mechanical-stress and high-shear environment, (2) the antithrombogenic power of MPC units remained unchanged after 2 weeks of continuous exposure to a high-shear environment, and (3) the IPN modified SPU cross-linked with MPC could be a powerful antithrombogenic surface for blood pumps used for chronic circulatory support of cardiac patients.

Chitosan/poly(vinyl alcohol) blending hydrogel coating improves the surface characteristics of segmented polyurethane urethral catheters

Segmented polyurethane (SPU) is commonly used to manufacture urethral catheters. Surface modifications for SPU catheters are needed to reduce friction and protein adsorption, in order to minimize catheter-related complications, including urethral trauma, encrustation, catheter obstruction, bacterial colonization, and infection. In this study, a four-step surface modification method was developed to create a thin lubricious layer of chitosan/poly(vinyl alcohol) (PVA) hydrogel on the SPU catheter. Modification steps included oxidation of the SPU surface, functionalities modification, carbodiimide reaction and coupling, and hydrogel crosslinking. The success of each modification step was confirmed by Fourier transform infrared spectroscopy. Measurement of the water contact angle revealed that hydrogel coating created a highly hydrophilic surface and atomic force microscope analyses demonstrated that the surface was slippery. Protein absorption of the SPU catheter was significantly reduced by coating hydrogel. Chitosan in the hydrogel could provide antimicrobial activity, and the hydrogel coating SPU samples showed significant antibacterial effects in this study. In summary, the four-step modification method developed in this study provided a simple and effective way to coat the surface of SPU catheters with a chitosan/PVA blending hydrogel that could help to minimize the risk of complications related to the use of urethral catheters.

Segmented polyurethane modified by photopolymerization and cross-linking with 2-methacryloyloxyethyl phosphorylcholine polymer for blood-contacting surfaces of ventricular assist devices

To improve the biocompatibility of pulsatile ventricular assist devices (VADs), the blood-contacting surface of the segmented polyurethane (SPU) diaphragm employed in an electromechanical VAD was modified by introducing 2-methacryloyloxyethyl phosphorylcholine (MPC) units into its surface and forming an interpenetrating polymer network (IPN) structure, which contained independently cross-linked MPC polymer and SPU. The SPU diaphragm modified with an IPN structure was then assembled into a target test pump and underwent continuous pump operation at 37 degrees C for 2 weeks in a simulated systemic circulation using a mock circulatory loop. The surface characteristics of the pump diaphragm after 2 weeks of pump operation were then analyzed with an X-ray photoelectron spectroscope (XPS) and gold-colloid-labeled immunoassay. The XPS surface analysis of the IPN-modified SPU indicated the firm anchoring of MPC units even after 2 weeks of pump operation (the phosphor : carbon ratio was reduced by only 0.09%). The IPN-modified diaphragm prevented protein adsorption as well as cell adhesion in comparison to the unmodified SPU surface. This result thus validated that (1) the IPN structure could firmly secure MPC units to the SPU surface even in a high-mechanical-stress and high-shear environment, (2) the antithrombogenic power of MPC units remained unchanged after 2 weeks of continuous exposure to a high-shear environment, and (3) the IPN modified SPU cross-linked with MPC could be a powerful antithrombogenic surface for blood pumps used for chronic circulatory support of cardiac patients.

Platelet adhesion onto segmented polyurethane surfaces modified by carboxybetaine

Polyurethanes are widely used as blood-contacting biomaterials due to their good biocompatibility and mechanical properties. Nevertheless, their blood compatibility is still not adequate for more demanding applications. Surface modification is an effective way to improve the hemocompatibility for biomaterials. The purpose of present study was to synthesize a novel nonthrombogenic biomaterial by modifying the surface of polyurethane with Zwitterions of carboxybetaine monomer. The films of polyurethane were grafted with two kinds of carboxybetaine by a three-step procedure. In the first step, the film surfaces were treated with hexamethylene diisocyanate (HDI) in toluene at 50°C in the presence of di-n-butyl tin dilaurate (DBTDL) as a catalyst. The extent of the reaction was measured by ATR-FT-IR spectra; a maximum number of free NCO group was obtained after a reaction time of 90 min. In the second step, the hydroxyl group of N,N-dimethylethylethanolamine (DMEA) or 4-dimethylamino-1-butanol (DMBA) was allowed to react in toluene with isocyanate groups bound on surface. In the third step, carboxybetaines were formed in the surface through the ring-opening reaction between tertiary amine of DMEA or DMBA and β-propiolactone (PL). It was characterized by ATR-FT-IR and XPS that the grafted surfaces were composed of carboxybetaine. The results of the contact angle measurements showed that they were strongly hydrophilic. Platelet adhesion tests showed that films grafted carboxybetaine have good blood compatibility, as featured by the low platelet adhesion.

Effects of thermal annealing of segmented-polyurethane on surface properties, structure and antithrombogenicity.

Analyses of the surface structure and properties of thermally heat-treated and non-treated segmented-polyurethane (SPU) surfaces showed that a crystalline structure, the domain size of which was larger than that of the micro-phase separation structure, appeared when the SPU surface was annealed in the temperature range of 60-140 degrees C. The appearance of the crystalline structure resulted in a decrease in surface free energy, that is, an increase in the hydrophobicity of the surface. Whole blood or platelet-rich plasma (PRP), when in contact with a SPU surface, which had previously been in contact with a glass surface during casting, coagulation of the whole blood occurred within approximately 30 min and, in case of PRP, in approximately 60 min. When the SPU surface was modified by thermal annealing, the coagulation time for PRP was delayed, whereas that of whole blood remained essentially unchanged. Relationships between the surface properties and the structure of annealed SPU and antithrombogenicity are discussed. The data collected herein suggest that the heat treatment of SPU might be useful for improving antithrombogenicity.

Visible-light-induced surface graft polymerization via camphorquinone impregnation technique.

A surface modification method that is particularly applicable to complexly shaped fabricated devices has long been awaited. In this article, we describe the visible-light-induced surface photograft polymerization technique by which an inner surface of the device is modified by visible-light irradiation through the external surface. Comphorquione, as a photoradical initiator, was impregnated on a segmented polyurethane surface by solvent soaking, followed by visible-light irradiation in the presence of monomers such as acrylamide and poly(ethylene glycol) methacrylate. The resultant surfaces were highly wettable with water, and surface chemical compositional analysis by X-ray photoelectron spectroscopy revealed that the surface was graft-polymerized with these monomers. The simple and widespread applicability of this surface modification technique to biomedical devices is discussed.

Immobilization of a nonsteroidal antiinflammatory drug onto commercial segmented polyurethane surface to improve haemocompatibility properties

A method has been developed in which a layer of p-aminosalicylic acid (4-amino-2-hydroxybenzoic acid) (PAS), a water soluble pharmaceutical compound of the nonsteroidal anti-inflammatory drug (NSAID) class with antiaggregant platelet activity, is covalently immobilized onto a segmented polyurethane, Biospan TM (SPU) surface. Thus, SPU surfaces were modified by grafting of hexamethylenediisocyanate, and the free isocyanate remaining on the SPU surface were then coupled through a condensation reaction to amine groups of p-aminosalicylic acid. The bonding of PAS from aqueous solution onto SPU surface was studied by ATR–FTIR, UV and fluorescence spectroscopy. Plateau levels of coupled PAS were reached within 1.2 μg/cm 2 using PAS solution concentrations of 1 mg/ml. The surface wettability of the polymeric films measured by contact angle indicate that the introduction of the PAS turns the surface more hydrophilic ( θ water=43.1°±2.1°) relatively to the original SPU films ( θ water=70.3°±1.9°). The in vitro albumin (BSA) adsorption shows that the PAS–SPU films adsorb more BSA (250/μg mm 2) than the original SPU (112 μg/mm 2). Thrombogenicity was assessed by measuring the thrombus formation and platelet adhesion of the SPU containing PAS relatively to nonmodified SPU surfaces. The polymeric surfaces with immobilized PAS had better nonthrombogenic characteristics as indicated by the low platelet adhesion, high adsorption of albumin relatively to fibrinogen and low thrombus formation, making them potentially good candidates for biomedical applications.

Proliferation of endothelial cells on the plasma-treated segmented-polyurethane surface: attempt of construction of a small caliber hybrid vascular graft and antithrombogenicity

To prepare a porous segmented-polyurethane (SPU) tube, a solution of SPU containing different concentrations of NaCl was coated on a glass rod and the coated SPU was immediately immersed in water. When the surface of the porous SPU, where bovine aortic endothelial cells are not normally capable of adhering and proliferating, was modified by plasma treatment, the proliferation of endothelial cells could be drastically improved. The cells proliferated confluently on the porous SPU surface prepared at low concentrations of NaCl below 10 g per 100 ml, but poorly on the porous surface prepared at high concentrations of NaCl. The construction of a hybrid vascular graft consisting of a porous SPU tube (2 mm in inner diameter, 5 cm in length) and endothelial cells was attempted. The cells cultured on the inner surface of the tube proliferated to confluency everywhere. From an in vitro antithrombogenic evaluation test, which involved the use of human blood, the present hybrid graft can be considered to provide an inert surface against thrombus formation and blood coagulation. Negligible changes in shape of human leukocytes in contact with bovine aortic endothelial cell surface occurred, suggesting that the bovine aortic endothelial cells used are immunologically less active against human blood.

Grafting 2-(Methacrylorloxy)ethyl-2-(trimethylammonium)ethyl Phosphate onto Segmented Polyurethane Surfaces To Improve Hemocompatibilities

We reported herein that 2-(methacrylorloxy)ethyl-2-(trimethylammonium)ethyl phosphate (MTP) was successfully grafted onto a segmented polyurethane (SPU) cast film surface. We found MTP orientated onto a film surface had excellent hemocompatibility, and the addition of the cross-linking agent N,N‘-methylenebisacrylamide (MBAA) further increased MTP orientation on the surface and lead to better hemocompatibility. 1,4-Butanediol (BD) as a chain extender was used to synthesize the SPU which was based on diphenylmethane diisocyanate (MDI), vinyl group-containing poly(butadiene) diol (PBD), and hydrogenated poly(butadiene) diol (HPBD). To obtain an alcohol-orientated surface of SPU, glycidyl methacrylate (GMA) was copolymerized with the SPU using α,α‘-azobis(isobutyronitrile) (AIBN) as a radical initiator, and diethanolamine (DEA) was used to open the epoxy group leading to hydroxylated SPU. Furthermore, MTP and the cross-linking agent MBAA were grafted onto the cast film surface of hydroxylated SPU by using di...

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.

Endothelial cells on plasma-treated segmented-polyurethane: adhesion strength, antithrombogenicity and cultivation in tubes.

When the surface of segmented-polyurethane (SPU), where endothelial cells are not capable of proliferating, is modified by plasma treatment, the adhesion and proliferation of bovine aortic endothelial cells (BAECs) can be drastically improved. The cells were capable of proliferating on the inner surface of a plasma-treated SPU-coated tube (length: 50 mm; inner diameter: 1.5 mm). When a steady flow shear stress of 9 Pa was applied to the cells proliferated on the modified SPU surface for 90 min, most cells did not detach from the surface. From an in vitro evaluation test of antithrombogenicity, the cell surface can be considered to provide an inert surface against thrombus formation and blood coagulation. From analyses of the plasma-treated SPU surface, it was suggested that the improvements in BAEC proliferation and adhesion after plasma treatment were due to the change in wettability of the surface. Data suggest that the plasma treatment would be useful for developing a small-calibre hybrid vascular graft.

Promotion and control of selective adhesion and proliferation of endothelial cells on polymer surface by carbon deposition.

The adhesion and proliferation of endothelial cells can be drastically improved when cultivated on a carbon-deposited polymer surface. When the surface of segmented polyurethane, in which endothelial cells are not capable of proliferating, is modified by carbon deposition, cell adhesion and proliferation occurred selectively on the carbon-deposited region. Carbon deposition to a tissue culture-treated polystyrene surface on which cells are capable of proliferating further promoted cell spreading and proliferation. Cell patterning on carbon-deposited segmented polyurethane was also attempted by controlling the direction or region of cell proliferation. Carbon deposition onto the polymer surface brought about a decrease in the water contact angle of the surface. Precoating fibronectin or laminin on the carbon-deposited polymer surface brought about cell adhesion and proliferation in the carbon-deposited region, but not in the non-carbon-deposited region. Our data suggest that promotion of cell proliferation on a carbon-deposited surface is probably due to selective adhesion of adhesive proteins to the surface.

Promotion and control of selective adhesion and proliferation of endothelial cells on polymer surface by carbon deposition

The adhesion and proliferation of endothelial cells can be drastically improved when cultivated on a carbon-deposited polymer surface. When the surface of segmented polyurethane, in which endothelial cells are not capable of proliferating, is modified by carbon deposition, cell adhesion and proliferation occurred selectively on the carbon-deposited region. Carbon deposition to a tissue culture-treated polystyrene surface on which cells are capable of proliferating further promoted cell spreading and proliferation. Cell patterning on carbon-deposited segmented polyurethane was also attempted by controlling the direction or region of cell proliferation. Carbon deposition onto the polymer surface brought about a decrease in the water contact angle of the surface. Precoating fibronectin or laminin on the carbon-deposited polymer surface brought about cell adhesion and proliferation in the carbon-deposited region, but not in the noncarbon-deposited region. Our data suggest that promotion of cell proliferation on a carbon-deposited surface is probably due to selective adhesion of adhesive proteins to the surface. © 1996 John Wiley & Sons, Inc.

Cultured Cell Patterning For Bio-Electronics

Abstract Adhesion and proliferation of cells on ion-implanted segmented Polyurethane (SPU) surfaces was investigated. Cell adhesion and proliferation on non-implanted SPU surfaces was not observed. However, complete cell adhesion and proliferation was observed on ion-implanted SPU surfaces. Also, selective cell adhesion on the patterned organic substrates was controlled by ion implantation. A specific interaction between cells and micro-periodic structures produced by ion implantation is demostrated. It was concluded that the improvement of cell adhesion and proliferation was due to carbonized SPU surface. The obtained pattern of cultured cells may be useful for formation of neural networks and bio-electronics.

Selective adhesion and proliferation of cells on ion-implanted polymer domains

We have found that the adhesion and proliferation of endothelial cells can be drastically improved when cultivated on an ion-implanted polymer surface. When the surface of segmented polyurethane, where endothelial cells are not capable of proliferating, is modified by Ne + or Na + ion implantation with a fluence of 1 × 10 15 ions/cm 2 at an energy of 150 keV, cell adhesion and proliferation occurred selectively on the ion-implanted region irrespective of the ion species. The cells did not proliferate at ion fluences below 1 × 10 14 ions/cm 2. Most cells migrated into the ion-implanted domain within 1–2 h, but some of the cells attached outside of the region and then slowly migrated into the region. Ion implantation of polystyrene, on which cells are capable of proliferating, further promoted cell spreading and proliferation, and increased resistance to detachment when the cells were exposed to trypsin.

Influences of ventricular assist device pumping on blood coagulation.

A left ventricular assist device (VAD) with a smooth surface of segmented polyurethane was implanted in five goats for 10-55 days, and plasma levels of fibrinogen (Fg), prekallikrein (PK), fibrinogen, fibrin degradation products (FDP), antithrombin III (AT III), prothrombin time (PT), partial thromboplastin time (PTT), platelet (Pl) count, and platelet aggregation (PlAg) induced by adenosine diphosphate were measured during the experiment. Heparin was administered during surgery and no systemic antithrombotic therapy was given thereafter. Before the third postoperative day (POD), plasma levels of Fg and PK were at their lowest, and increased afterward. Between the second and fifth POD PT and PTT increased to 130-160%, and returned to normal gradually. Plasma FDP appeared on the second POD and reached peak values of 10-40 micrograms/ml on the sixth POD. Platelet and AT III levels showed no uniform tendency, but the rate of PlAg decreased to levels of 6-77% before the fifth POD and remained low at approximately 80%, influenced by the pumping even after the 25th POD. In summary, VADs themselves activated coagulation and induced consumption coagulopathy to some degree. However, most of the parameters returned to normal within 2 weeks.

Interactions between segmented polyurethane surfaces and the plasma protein fibrinogen.

Surfaces of a segmented polyurethane were varied by casting on poly(ethylene terephthalate) (PET) and glass substrates, and were characterized through infrared-attenuated total-reflection spectroscopy (ATR). Surfaces cast on glass substrates showed a higher content of polyether segments, whereas those cast on PET contained a higher relative concentration of aromatic segments. Adsorption, and possible conformational changes of fibrinogen, were found to be more substantial on polymer surfaces having a higher content of polyether segments. It is concluded that the relatively good blood compatibility of segmented polyurethanes is partly due to the presence of peptide-like bonds on aromatic segments.