Grafting sulfobetaine monomer onto the segmented poly(ether-urethane) surface to improve hemocompatibility

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 the present study was to synthesize a novel nonthrombogenic biomaterial by modifying the surface of polyurethane. Ozonization was used to introduce active peroxide groups onto the segmented poly(ether-urethane) (SPEU) film surface and graft polymerization of N,N′-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate (DMAPS), a sulfobetaine structure, onto the ozone-activated SPEU surface was conducted. The SPEU-g-PDMAPS film was characterized by ATR-FTIR, XPS, and contact angle measurements. ATR-FTIR and XPS confirmed the graft polymerization. The grafted film possessed a relatively hydrophilic surface, as revealed by contact angle measurement. The blood compatibility of the grafted films was evaluated by a platelet-rich plasma (PRP) adhesion study and scanning electron microscopy, using SPEU film as the reference. No platelet adhesion was observed for the grafted films incubated with PRP at 37°C for 60 and 180 min. This new sulfobetaine structure grafted biomaterial might have potential for biomedical applications.     

Grafting sulfobetaine monomer onto the segmented poly(ether-urethane) surface to improve hemocompatibility

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 the present study was to synthesize a novel nonthrombogenic biomaterial by modifying the surface of polyurethane. Ozonization was used to introduce active peroxide groups onto the segmented poly(ether-urethane) (SPEU) film surface and graft polymerization of N,N'-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate (DMAPS), a sulfobetaine structure, onto the ozone-activated SPEU surface was conducted. The SPEU-g-PDMAPS film was characterized by ATR-FTIR, XPS, and contact angle measurements. ATR-FTIR and XPS confirmed the graft polymerization. The grafted film possessed a relatively hydrophilic surface, as revealed by contact angle measurement. The blood compatibility of the grafted films was evaluated by a platelet-rich plasma (PRP) adhesion study and scanning electron microscopy, using SPEU film as the reference. No platelet adhesion was observed for the grafted films incubated with PRP at 37 degrees C for 60 and 180 min. This new sulfobetaine structure grafted biomaterial might have potential for biomedical applications.     

Synthesis, characterization and platelet adhesion of segmented polyurethanes grafted phospholipid analogous vinyl monomer on surface.

New segmented polyurethanes (SPUs) grafted phospholipid analogous vinyl monomer, 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) on surface were synthesized. The soft segment of these polyurethanes was hydroxylated poly(isoprene) diol and the hard segments were 4,4'-methylenediphenyl diisocyanate (MDI) and 1,4-butanediol (BD). SPUs were hydroxylated by potassium peroxodisulfate and MPC was grafted on the surface of hydroxylated SPUs using di-ammonium cerium (IV) nitrate (ceric ammonium nitrate, CAN) as a radical initiator. The bulk characterization of synthesized SPUs was investigated by infrared spectroscopy (IR) and gel-permeation chromatography (GPC). The existence of phospholipid analogous groups on the surface of these SPUs was revealed by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The surfaces of MPC-grafted SPUs showed decreased water contact angles compared to non-grafted SPU and the presence of phosphorylcholine groups. The blood compatibilities of the new polymers were evaluated by platelet rich plasma (PRP) contact studies and viewed by scanning electron microscopy (SEM) using BioSpan and non-grafted polyurethane as references. We found that fewer platelets adhered to the MPC-grafted surfaces and that they showed less shape variation than the references. These results suggest that these grafted polymers may have the possibility of the usage for biomaterials.     

Haemocompatibility of polymer having phospholipid polar groups evaluated by monoclonal antibody method.

The haemocompatibility of a polymer having the phospholipid polar group, poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate(BMA)), was evaluated by a monoclonal antibody SZ-21 (directing specifically against the membrane glycoprotein complex IIIa of human platelet) radioimmunoassay method. The study showed that poly(MPC-co-BMA) possessed better haemocompatibility than segmented polyurethane (SPEU). Radioactivity of platelets adhered (counts per min/cm) on a polyethylene (PE) tube coated with poly(MPC-co-BMA) was 19.51 +/- 5.58, with albumin; 20.05 +/- 7.29, with SPEU having sulphonated group; 76.10 +/- 18.9, with SPEU; 287.0 +/- 95.0, PE treated by plasma irradiation; 2091 +/- 261, and original PE was 1772 +/- 116. The results were further certified by scanning electron microscopic observations.     

Preparations and properties of a novel grafted segmented polyurethane-bearing glucose groups

Novel grafted polyurethane-bearing glucose groups were synthesized through a graft copolymerization of a prefabricated polyurethane containing poly(butadiene) glycol (PBD) and hydrogenated poly(butadiene) glycol (HPBD) soft segments, and 4,4'-methylenediphenyl diisocyanate (MDI) hard segment with a hydrophilic monomer glycosylethyl methacrylate (GEMA) in solution in the presence of 2,2'-azobis(isobutyronitrile) (AIBN) as an initiator. The bulk characteristics of the grafted polyurethanes were investigated by infra-red (IR) spectroscopy and gel permeation chromatography (GPC) measurements. The glucose groups were oriented on the surface of the cast film of grafted polyurethane with different graft-on percentages as revealed by electron spectroscopy for chemical analysis (ESCA), attenuated total reflectance infra-red spectroscopy (ATR-FTIR), and water contact angle. The grafted polyurethane surfaces which showed decreased water contact angles also indicate that hydrophilic glucose groups are present at the surface. The hemocompatibilities of these polymer surfaces were evaluated by platelet-rich plasma (PRP) contacting tests. It was found that the surface of grafted polyurethane with a graft-on percentage of 23.4% showed a good hemocompatibility in terms of platelet adhesion and shape variation. It indicates that glucose groups on the surface are effective for the improvement of hydrophilicity as well as hemocompatibility.     

Preparations and properties of a novel grafted segmented polyurethane-bearing glucose groups

Novel grafted polyurcthane-bearing glucose groups were synthesized through a graft copolymerization of a prefabricated polyurethane containing poly(butadiene) glycol (PBD) and hydrogenated poly(butadiene) glycol (HPBD) soft segments, and 4,4'-methylenediphenyl diisocyanate (MDI) hard segment with a hydrophilic monomer glycosylethyl methacrylate (GEMA) in solution in the presence of 2,2'-azobis(isobutyronitrile) (AIBN) as an initiator. The bulk characteristics of the grafted polyurethanes were investigated by infra-red (IR) spectroscopy and gel permeation chromatography (GPC) measurements. The glucose groups were oriented on the surface of the cast film of grafted polyurethane with different graft-on percentages as revealed by electron spectroscopy for chemical analysis (ESCA), attenuated total reflectance infra-red spectroscopy (ATR-FTIR), and water contact angle. The grafted polyurethane surfaces which showed decreased water contact angles also indicate that hydrophilic glucose groups are present at the surface. The hemocompatibilities of these polymer surfaces were evaluated by platelet-rich plasma (PRP) contacting tests. It was found that the surface of grafted polyurethane with a graft-on percentage of 23.4% showed a good hemocompatibility in terms of platelet adhesion and shape variation. It indicates that glucose groups on the surface are effective for the improvement of hydrophilicity as well as hemocompatibility.     

Platelet adhesive resistance of segmented polyurethane film surface-grafted with vinyl benzyl sulfo monomer of ammonium zwitterions

Platelet from human plasma adhered on the segmented poly(ether urethane) (SPEU) film grafted with N,N-dimethyl-N-(p-vinylbenyl)-N-(3-sulfopropyl) ammonium (DMVSA) was studied. SPEU films were hydroxylated by potassium peroxosulfate (KPS) and then grafted with DMVSA using ceric ammonium nitrate (CAN) as initiator. The mixing time of hydroxylated SPEU/CAN and the monomer concentration effect on graft polymerization yield were determined by ATR-FTIR. Surface analysis of the grafted films by ATR-FTIR and ESCA confirmed that DMVSA was successfully grafted onto the SPEU film surface. The grafted film possessed a relatively hydrophilic surface, as revealed by water contact angle measurement. The improved blood compatibility of the grafted films was preliminarily evaluated by a platelet-rich plasma adhesion study and scanning electron microscopy, using original SPEU and hydroxylated SPEU films as the controls. The results showed that platelet attachment was decreased greatly on the segmented polyurethane films grafted with DMVSA. This kind of new biomaterials grafted with sulfo ammonium zwitterionic monomers might have potential for biomedical applications.     

Effect of reduced protein adsorption on platelet adhesion at the phospholipid polymer surfaces

We prepared polymers having a phospholipid polar group, poly[ω-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate(BMA)], as new biomedical materials and evaluated their blood compatibility with attention to protein adsorption and platelet adhesion. The total amount of proteins adsorbed on the polymer surface from human plasma was determined, and the distribution of adsorbed proteins on the plasma-contacting surface was analyzed. The amount of proteins adsorbed on every poly(MAPC-co-BMA) was small compared with that observed on polymers without the phospholipid polar group. However, there was no significant difference in the amount of adsorbed proteins on the poly(MAPC-co-BMA) even when the methylene chain length between the phospholipid polar group and the backbone in the MAPC moiety was altered. Platelet adhesion on the polymer surface from a platelet suspension in a buffered solution was evaluated with and without plasma treatment on the surface. When a rabbit platelet suspension was brought into contact with the poly(BMA) surface after treatment with plasma, many platelets adhered and aggregated. However, a reduced amount of platelet adhered on the poly(BMA) was found in the case of direct contact with the platelet suspension. On the other hand, the poly(MAPC-co-BMA)s could inhibit platelet adhesion under both conditions. Based on these results, it can be concluded that the proteins adsorbed on the surface play an important role in determining the platelet adhesion and suppression of the protein adsorption on the surface, which is one of the most significant ways of inhibiting platelet adhesion.     

Synthetic studies on nonthrombogenic biomaterials 14: synthesis and characterization of poly(ether-urethane) bearing a Zwitterionic structure of phosphorylcholine on the surface

A new Zwitterionic compound of the phosphorylcholine analogue, 4-hydroxylbutyl phosphorylcholine (HBPC), was synthesized and characterized. HBPC was chemically tethered onto the surface of poly(ether-urethane) (PEU) films with hexamethylene diisocyanate (HDI) as a coupling agent. The existence of a phosphorylcholine structure on the PEU surface was demomstrated by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. The nonthrombogenicity of the modified films was evaluated by platelet-rich plasma (PRP) assay. The results showed that films grafted with HBPC have excellent platelet adhesion resistance.     

Covalently grafted phospholipid monolayer on silicone catheter surface for reduction in platelet adhesion

We report a novel method of surface grafting a polymeric phospholipid system containing an acryloyl end group (1stearoyl-2-[12-(acryloyloxy)-dodecanoyl]-sn-glycero-3-phosphocholine) onto medical grade silicone catheters. The surface of silicone catheters was functionalized in a sequence of steps: plasma polymerization of allyl alcohol on the catheter surface, grafting acryloyl moieties and in situ polymerization of the pre-assembled acryloyl terminated phospholipids on the acryloyl functionalized catheter surface. The surface morphological changes analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), a sharp decrease in water contact angle, and appearance of N1s peak in XPS analysis indicated a successful monolayer grafting of the phospholipid. In platelet adhesion tests performed using platelets isolated from rabbit plasma, the phospholipid grafted surface showed fewer adhered platelets, without emerging pseudopodes or aggregation. However, ungrafted catheter surface showed large number of platelets in extensively spread and aggregated states. Thus, this modified phospholipid system and its simple grafting technique was very effective with regard to suppressing in vitro platelet adhesion on the silicon catheter surface.     

Photoimmobilisation of poly(N-vinylpyrrolidinone) as a means to improve haemocompatibility of polyurethane biomaterials.

A novel method to improve the haemocompatibility of polymeric biomaterials (in particular: polyurethane elastomers) is reported. The new approach essentially rests upon photochemical immobilisation of the highly biocompatible polymer poly(N-vinylpyrrolidinone) (poly(NVP)) onto the biomaterial's surface. One of the key steps in the surface modification procedure is the preparation of a copolymer of NVP and the photoreactive building block 4-[4'-azidobenzoyl]-oxo-n-butylmethacrylate (1). This copolymer is first dissolved in a volatile solvent, then sprayed onto the biomaterial's surface, and subsequently immobilised via irradiation with ultraviolet light. The paper describes: (i) preparation of 1, (ii) preparation of the copolymer (NVP + 1), (iii) physico-chemical characterisation of the modified surfaces, and (iv) results of two in vitro haemocompatibility assays (i.e. thrombin generation and adhesion of blood platelets from recalcified human platelet-rich plasma). Furthermore, the surface modification was performed with a microporous polyurethane vascular graft (Chronoflex), which is already in clinical use. The in vitro experiments revealed that significant improvement of the haemocompatibility of polyurethanes can be achieved through this method.     

Preparation of a chemically anchored phospholipid monolayer on an acrylated polymer substrate

This paper describes a strategy for designing a chemically anchored phospholipid monolayer that could be used as coating materials for biomedical implants. To make a chemically anchored phospholipid monolayer on the polymer substrate, we prepared the mono-acrylated phospholipid (1-palmitoyl-2-[12-(acryloyloxy)-dodecanoyl]-sn-glycero-3-phosphocholine; acryloyl-PC) and the acrylated polymer (poly(octadecylacrylate-co-4-acryloyloxy butylacrylate)), which was synthesized by the acrylation of poly(octadecyl acrylate-co-hydroxybutyl acrylate, poly(OA-co-HA)) with acryloyl chloride. The chemically anchored phospholipid monolayer was prepared by using in situ photopolymerization of a pre-assembled phospholipid monolayer, produced by lipid vesicle fusion, onto the acrylated polymer coated silicon wafer. Optimal condition of vesicle fusion and irradiation time was determined from the degree of hydrophilicity rendered by the polymerized phospholipid surface. The physicochemical properties of polymerized phospholipid monolayer on the substrate were evaluated using water contact angle, field-emission scanning electron micrograph (FE-SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). These results confirmed that the polymerized phospholipid monolayer was chemically anchored on the acrylated polymer substrate. The chemically anchored phospholipid monolayer was stable in aqueous condition for 2 weeks, but the physically adsorbed phospholipid monolayer got removed within 1 day. Moreover, the polymerized phospholipid monolayer also suppressed albumin absorption and platelet adhesion, in vitro. This polymerized phospholipid monolayer provides a new biomimetic system for coating medical devises.     

Kinetic study of NTPDase immobilization and its effect of haemocompatibility on polyethylene terephthalate

Poor haemocompatibility of material surfaces is a serious limitation that can lead to failure of blood-contacting devices and implants. In this work, we have improved the haemocompatibility of polyethylene terephthalate (PET) surfaces by immobilizing apyrase/ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) on to the carboxylated PET. NTPDase immobilized PET surfaces scavenge the ADP released by activated platelets, which prevents further platelet activation and aggregation. The surface properties of the modified PET were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDAX), and contact angle measurement. The enzyme attachment and stability on the modified PET surfaces were evaluated. The kinetics of free enzyme and immobilized enzyme were studied and fitted using the Michaelis-Menten kinetic model. Both free and immobilized NTPDase followed Michaelis-Menten kinetics with similar Michaelis-Menten constants (K_m). This suggests that the activity of NTPDase was unchanged upon immobilization. Protein adsorption and %hemolysis was significantly reduced for carboxylated PET and NTPDase immobilized PET surfaces compared to unmodified PET. Lactate dehydrogenase assay showed that the number of adhered platelets reduced by more than an order of magnitude for the NTPDase immobilized PET surface compared to unmodified PET. These results clearly indicate that NTPDase immobilization significantly enhances the haemocompatibility of PET surfaces.     

Novel blood compatible polyurethanes containing long-chain alkyl groups and phosphatidylcholine analogues

A series of new amphiphilic polyurethanes containing long-chain alkyl groups as hydrophobic part and phosphatidylcholine analogues as hydrophilic part in the side chains was synthesized and characterized by their IR and ¹H NMR spectral data and elemental analyses. The detailed studies for polyurethane 7b show that no evidence of any blood platelet attachment was apparent from the platelet rich plasma (PRP) contact studies and by scanning electron microscopy (SEM) evaluation for the synthesized polyurethane. Moreover, it quickly forms a gel in chloroform, N,N-dimethylformamide, dimethyl sulfoxide and even to some extent in water. Preliminary studies suggest that these new polyurethanes are very interesting due to their excellent blood compatibilities and prospective importance for biomedical applications.     

Synthesis,surface properties and performance of thiosulphate-substituted plasticized poly(vinyl chloride)

Plasticized poly(vinyl chloride) (PVC) was surface modified by nucleophilic substitution of the chlorine atoms of PVC by thiosulphate in aqueous media in the presence of a phase-transfer catalyst. The properties of the modified surface were evaluated by contact angle measurements, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Migration of the plasticizer di-(2-ethylhexyl) phthalate from control as well as modified PVC was examined in hexane, in cottonseed oil and in poly(ethylene glycol)-400 (PEG-400). While the modified PVC was found to be highly migration resistant in hexane, cottonseed oil and PEG-400 extracted the plasticizer. The modified PVC was found to cause haemolysis and was cytotoxic. A possible explanation for the difference in performance of the modified material in different extraction media and its toxicity is presented from a mechanistic view of the substitution process.     

Effect of surface hydrophilicity on ex vivo blood compatibility of segmented polyurethanes

The relationship between surface, bulk and ex vivo blood-contacting properties of segmented polyurethanes with various polyol soft segment was investigated. The polyols used in this study were poly(ethylene oxide), poly(tetramethylene oxide), hydrogenated poly(butadiene), poly(butadiene) and poly(dimethylsiloxane). The hard segment of these segmented polyurethanes was composed of 4,4' diphenylmethane diisocyanate and 1,4 butanediol, present at 50 wt%. An experimental polyurethane, Biostable PUR, which has shown excellent biostability, was used in this study. The segmented polyurethanes based on the hydrophobic polyols such as poly(dimethylsiloxane) and hydrogenated poly(butadiene) showed distinct microphase separation between hard and soft segments. X-ray photoelectron spectroscopy revealed the surface enrichment of the hydrophobic component at the air-solid interface. Dynamic contact angle measurements indicated that the poly(dimethylsiloxane)-based segmented polyurethane possessed a hydrophobic surface in water. The poly(dimethylsiloxane)-based segmented polyurethane had the lowest platelet adhesion among the segmented polyurethanes investigated in this study, whilst the platelet deposition on the poly(ethylene oxide)-based polymer increased with time.     

The role of Fbg in platelet adhesion to polymeric materials in conditions of psychological stress.

The effect of psychological stress on platelet adhesion to five polymeric materials (polyurethane, polyurethane filled with BaSO4, polyethyleneterephthalate, silicone and low-density polyethylene) was studied. The platelets were obtained from non-stressed and stressed rabbits as platelet-rich plasma (PRP) and, once washed (Pw), were suspended in different media, i.e. in platelet poor plasma (Pw-PPP), in serum (Pw-S) and in Krebs-Ringer solution (Pw-KR). Scanning electron microscopy of platelet adhesion and morphology revealed differences in the platelet activating power of the various materials. The washing procedure and resuspension in PPP generally resulted in an increased number of adherent platelets, compared with the number of platelets adherent to the same material in PRP. However, platelets washed and suspended in Pw-KR or Pw-S showed the same shape distribution as in PRP. When platelets from stressed rabbits were used, there was very strong aggregation and activation of the platelets in both PRP and Pw-PPP, independent of the chemical nature and surface structure of the material. In contrast, in Pw-KR and Pw-S (in which Fbg is absent) a general picture of single, not very modified platelets was observed. Their number and shapes changed according to the nature of the different materials. On the whole, the present results confirm our original hypothesis of a key role of the psychological condition of the blood donor and strongly indicate Fbg as the determinant factor in the pattern of platelet adhesion.     

Polyethylene/phospholipid polymer alloy as an alternative to poly(vinylchloride)-based materials

To develop new biomaterials for making medical devices, polymer alloys composed of a phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and polyethylene (PE) were prepared. The PE/PMPC alloy membrane could be obtained by a combination of solution mixing and solvent evaporation methods using xylene and n-butanol mixture as a solvent. Moreover, thermal treatment was applied to improve the mechanical properties of the PE/PMPC alloy membrane. In the PE/PMPC alloy membrane, the PMPC domains were located not only inside the membrane but also at the surface. Surface analysis of the PE/PMPC alloy membrane with X-ray photoelectron spectroscopy, wettability evaluation, and dynamic contact angle measurements revealed that the phospholipid polar groups in the PMPC covered the surface even after thermal treatment. Blood compatibility tests with attention to platelet adhesion and change in morphology of adhered platelets showed that the PE/PMPC alloy membrane had excellent platelet adhesion resistance. We finally concluded that the PE/PMPC alloy could be used as biomaterials instead of poly(vinyl chloride)-based materials.     

Radiation-induced graft copolymerization of methacrylic acid on to poly(vinyl chloride) films and their thrombogenicity

Methacrylic acid (MAA) was radiation grafted on to poly(vinyl chloride) (PVC) films to improve the blood compatibility of PVC. The thromobogenicity of MAA grafted PVC was evaluated by thrombus formation, platelet adhesion and haemolytic activity in vitro. The hydrophilicity of grafted PVC films was investigated by contact angle measurement. Methacrylic acid grafted PVC film showed lower thrombogenicity than that of PVC. It was found that the weight of thrombus formed on grafted PVC was less than that of PVC and glass and decreased with the increase in the graft level. The adhesion of platelets on grafted PVC was retarded after grafting with MAA hydrogels.     

含氟聚醚聚氨酯与聚醚聚氨酯共混的表面结构及血液相容性的研究

为了获得一种高氟聚氨酯表面 ,进一步改善聚醚聚氨酯的生物相容性和生物稳定性 ,将侧链含氟聚氨酯与聚醚聚氨酯共混而实现这一目的。通过 XPS、AFM、接触角和血小板黏附对含氟聚醚聚氨酯和聚醚聚氨酯共混物表面结构和血液相容性进行研究发现 ,在聚醚聚氨酯共混入极少量的氟 (0 .342 wt% )就能具有与含氟聚醚聚氨酯相同的表面结构和良好的血液相容性 ,而且共混物表面的强疏水性和对血小板的黏附与体系中混入的含氟聚醚聚氨酯的量无关 ,与表面 CF3的含量有关