Effect of hydrophilic and hydrophobic microdomains on mode of interaction between block polymer and blood platelets

Phase studies of a urethane model compound and polyether macroglycols by infrared spectroscopy and the relationship between eutectic composition of soft segment and blood compatibility

The binary mixtures of a urethane model compound, diethyl 4,4'-methylenebis(N-phenylcarbamate) (MDU), and various polyether macroglycols have been investigated mainly by infrared (IR) spectroscopy. The mixtures of macroglycol and MDU showed two C=O bands (free C=O at higher wave number, hydrogen bonded C=O at lower wave number), and the intensity of free C=O increased while that of hydrogen bonded C=O decreased linearly with increasing molar ratio of macroglycol/MDU. The slope of the increase or decrease suddenly changed at the specific molar ratio around the eutectic composition. The eutectic molar composition for PTMO1000/MDU was determined as 1.15 or 1.1 by differential scanning calorimetry (DSC) or infrared (IR) studies while that for PTMO3000/MDU as 0.345 or 0.55 by DSC or IR, respectively. The eutectic compositions for other sets were determined by IR studies as follows: PEO1000/MDU, 0.4; PEO3000/MDU, 0.16; PPO1000/MDU, 1.4; PPO3000/MDU, 0.45. The number of ethylene oxide, tetramethylene oxide, and propylene oxide units to form a eutectic with MDU calculated from these values were 15-20, 10-11, and 23-24, respectively. The similar DSC or IR changes were observed in the various kinds of polyurethanes such as MDI/BD, MDI/PTMO/BD, and MDI/PTMO polymers. The relationship between the eutectic compositions of soft segments (MDI/macroglycol) and the ideal Mn of the macroglycols in blood compatibility of segmented polyurethanes are discussed.

Cell adhesion onto block copolymer Langmuir-Blodgett films

The attachment of cells onto the surfaces of various block copolymers fabricated either as well-defined, ordered Langmuir-Blodgett (LB) films, or solvent cast microphase-separated structures was studied. In general, more platelets adhered onto the multilayered LB surface than onto microphase-separated cast surfaces. Scanning electron micrographs of adhered platelets showed extensive morphological changes associated with the LB surface as compared to cast film surfaces. The morphology of adhered hepatocytes was similar for both LB films and cast surfaces. It may be assumed that the surface of a block copolymer LB film does not orient into microdomains, as in the solvent cast surfaces, and only one polymer domain interacts at the interface.

Nonspecific adsorption and covalent coupling of heparin on polyacrylate based microbeads

Polyacrylate based microbeads were prepared by copolymerization of four different acrylate monomers, namely 2-hydroxyethylmethacrylate (HEMA), ethyleneglycoldimethacrylate (EGDMA), methylmethacrylate (MMA) and dimethylaminoethylmethacrylate (DMEAMA). These beads were further activated with CNBr at alkaline pH. The extend of nonspecific adsorption and covalent coupling of heparin on these beads were investigated in a batch reactors at different temperatures. The effects of initial concentrations of activation agent and heparin were also studied. Nonspecific heparin adsorption on the microbeads containing DMAEMA was significantly higher than the others. Nonspecific adsorption decreased with increasing temperature. Heparin was covalently coupled on CNBr activated microbeads. The amount of coupled heparin increased by increasing concentration of CNBr.

Surface characterization of 2-hydroxyethyl methacrylate/styrene copolymers by angle-dependent X-ray photoelectron spectroscopy and static secondary ion mass spectrometry

The surface composition and structure of three structurally distinct amphiphilic copolymers of 2-hydroxyethyl methacrylate (HEMA) and styrene have been examined with angle-dependent X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS). The phase-separated block copolymer made by anionic living polymerization, HSH-A50, showed significant surface enrichment of styrene. The outermost 2-3 A appeared to be approximately 100% styrene, with the styrene concentration decreasing to its bulk value at a depth of approximately 50 A from the surface. However, HEMA was detected in the outer 20 A of this copolymer. The presence of HEMA in the surface region implies this copolymer may undergo significant restructuring when hydrated in a hydrophilic environment (as opposed to the hydrophobic environment in which the sample was prepared and analyzed). The phase-separated block copolymer made by telechelic coupling of free radical polymerized functionalized oligomers, HSH-B60, showed only slight styrene enrichment at the surface. Both HEMA and styrene were detected at all sampling depths, including the outermost surface layer, consistent with the presence of discrete HEMA and styrene domains at the copolymer surface. Since both components are already present at the surface under hydrophobic conditions, the degree of restructuring this copolymer may undergo upon hydration should be minor. The random HEMA--styrene copolymer made by conventional free radical initiation techniques, HS-RAN50, had a surface composition that was similar to the bulk composition and independent of depth, as expected for a homogeneously mixed copolymer film.

Study of blood compatible polymers. II. poly(N,N-disubstituted) acrylamides

Poly(N,N-disubstituted) acrylamides with both hydrophilic and hydrophobic groups as substituents were synthesized. Different degrees of hydrophilicity were achieved by varying the bulk of the hydrophobic substituent. N-alkyl, N-(2-hydroxyethyl) acrylamides with alkyl substituents propyl (PROPAAm), octyl (OCTAAm) and benzyl (BENAAm) were synthesized. The swelling capacity of the polymers decreased with increase in bulk of the hydrophobic substituent. In vitro studies showed that the surfaces of these polymers did not induce platelet aggregation. Cell compatibility of these polymers was assessed by following the growth of human umbilical cord fibroblast cells. Pronounced cell growth and spreading was observed on the surfaces of polyOCTAAm and polyBENAAm. The relatively low cell growth on polyPROPAAm was ascribed to its high water content.

Biologically modified PHEMA beads for hemoperfusion: preliminary studies

Polyhydroxyethylmethacrylate (PHEMA) beads were prepared by phase separation polymerization. Hydroxyl groups on PHEMA beads were activated with CNBr at alkaline pH. Adsorption of heparin, blood proteins (i.e. albumin, fibrinogen and gamma-globulin), protein A, HIgG and DNA on these beads were studied. Preparation and activation procedures are given here. The preliminary results of these studies are also reported.

Materials for enhancing cell adhesion by immobilization of cell-adhesive peptide

Materials to enhance cell adhesion were synthesized by surface integration of peptide, Arg-Gly-Asp-Ser(RGDS), which is an active-site sequence of cell-adhesive proteins. Polystyrene film was glow-discharged and graft-copolymerized with acrylic acid. Then the peptide was immobilized to the poly(acrylic acid) grafts by using water-soluble carbodiimide. The cell-adhesive activity of the RGDS-immobilized film increased with increasing amount of immobilized peptide, and approached the activity of fibronectin(FN)-immobilized film. The RGDS-immobilized film was more stable against heat treatment and pH variation than the FN-immobilized film. In addition, the RGDS-immobilized film enhanced cell growth more strongly than the FN-immobilized film.

Electrically controlled proliferation of human carcinoma cells cultured on the surface of an electrode

Human carcinoma cells, MKN45, were cultured on the surface of a metal-coated plastic plate electrode the potential of which was controlled. The proliferation rate and cell morphology were altered depending on the applied potential. Cell proliferation was halted in the potential range above 0.4 V vs. Ag/AgCl, although cells started to proliferate again when the applied potential was shifted from 0.4 V to 0.1 V vs. Ag/AgCl. Fluorescence probe studies indicated that the fluidity of plasma membrane decreased in association with halting of cell proliferation. These results suggest that electrical stimulation causes cells to temporarily halt proliferation, and that cell proliferation was reversibly controlled by electrode potential. The mechanism is interpreted in relation to the change of plasma membrane structure represented by membrane fluidity.

Blood compatibility of PEO grafted polyurethane and HEMA/styrene block copolymer surfaces

HEMA/styrene (HEMA/STY) block copolymers and poly(ethylene oxide) 4,000 M.W. (PEO4K) grafted Biomer (B-PEO4K) surfaces have been synthesized, characterized, and evaluated as blood-contacting materials. These surfaces have demonstrated improved blood compatibility, compared to Biomer, in in vitro and ex vivo experiments. Biomer vascular grafts (6 mm I.D. 7 cm in length) were fabricated by a dip coating process. The luminal surface was modified either with PEO grafting, HEMA/STY coating, or Biomer coating (control). These surface-modified grafts were implanted in the abdominal aortas of dogs and evaluated for graft patency and protein adsorption. Surface protein layer thickness was measured by transmission electron microscopy (TEM). B-PEO4K and Biomer showed thick multilayers of adsorbed proteins (1000-2000 A) after 3 weeks to 1 month implantation. In contrast, HEMA/STY only showed a monolayer protein thickness (less than 200 A), even after 3 months. Visualization of adsorbed plasma proteins (albumin, IgG, and fibrinogen) was performed with scanning electron microscopy (SEM)/TEM using an immunogold double antibody technique. The pattern of protein distribution showed high concentrations of fibrinogen and IgG, and less albumin adsorbed onto Biomer and B-PEO4K. In contrast, HEMA/STY showed a patchy protein distribution pattern with high concentrations of albumin and IgG, and relatively less fibrinogen. Adsorbed monolayer patterns showed improved compatibility over multilayered proteins. The Biomer and B-PEO4K grafts occluded within 1 month, while HEMA/STY grafts were patent for over 3 months. The thin and stable adsorbed protein layer on HEMA/STY surfaces may be associated with the microdomain structures of the surface, and will play an important role in long-term in vivo blood compatibility. This manuscript will evaluate the long-term in vivo performance of these polymers, analyze the extent of protein adsorption onto the surfaces, and correlate protein layer thickness to the thrombogenicity of the polymer surfaces.

Reduced thrombogenicity of polymers having phospholipid polar groups

The thrombogenicity of polymers having a phospholipid polar group, poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate (BMA)), was evaluated by a microsphere-column method with attention to the activation and adhesion of platelets on the polymer surface. When citrated platelet-rich plasma (PRP) contacted with the polymers, a large number of platelets adhered and aggregated on poly(BMA). The number of adherent platelets decreased and deformation and aggregation were suppressed with increasing MPC composition. The same tendency was noted when Ca2(+)-re-added PRP came in contact with the polymers. In the case of poly(MPC-co-BMA) with 0.320 mole fraction of MPC, activation of platelets and formation of fibrin were completely suppressed. Therefore, MPC moieties in the polymer play an important role in the reduction of thrombogenicity of the polymer.

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. III: Surface and bulk compositional differences

Previously observed bioactivity of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin (PDMS-PEO-Hep) triblock copolymers has prompted studies of the surface and bulk character of this copolymer using angular-dependent electron spectroscopy for chemical analysis (ADESCA), static secondary mass spectroscopy (SIMS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Because the low-energy PDMS phase dominates surfaces of this copolymer when solvent cast under air or vacuum conditions, attempts were made to explain surface restructuring and rearrangements induced in hydrated or aqueous environments that permit surface accessibility and bioactivity of heparin moieties. Based on comparisons with PDMS, PEO, and heparin homopolymers, PEO/heparin blends, and an unheparinized PDMS-PEO diblock copolymer, PDMS-PEO-heparin demonstrates both phase-mixed and phase-separated regions in DSC analysis. During annealing cycles above the Tg values of the copolymer constituents, phase-mixed regions become increasingly phase separated and PEO enriched. TGA analysis confirmed the presence block copolymer constituents and presented evidence of intermolecular segmental interactions, hence phase-mixing in the copolymers. ADESCA analysis indicates that the outer 5 A of both the PDMS-PEO and PDMS-PEO-Hep copolymers is essentially pure PDMS. However, significant amounts of PEO are detected 5 to 20 A below the surface. Static SIMS also detects the presence of PDMS at the surfaces of the PDMS-PEO and PDMS-PEO-Hep copolymers. Compositional models based on ADESCA, SIMS, and DSC data are presented for desiccated and hydrated copolymer surfaces.

Adsorption of plasma proteins and adhesion of platelets onto novel polyetherurethaneureas--relationship between denaturation of adsorbed proteins and platelet adhesion

Novel polyetherurethaneureas which have been synthesized by the present authors were chosen for the substrate polymers, on which adhesion of platelets was investigated. The number of adhered platelets and the amount of serotonin released from platelets adhered on the polymers and the protein-coated polymers were determined by radioisotope method. Both of them were enhanced with increasing content of urea linkages in the polyetherurethaneureas. The platelet adhesion was discussed in terms of the denaturation of plasma proteins upon adsorption, which was determined by Fourier-transform infrared spectroscopy. With increasing degree of protein denaturation, the platelet adhesion and the serotonin release were enhanced. This relationship was particularly evident in the case of albumin adsorption. It was shown that the surface properties of substrate polymers affect the protein adsorption, which in turn influences the adhesion of platelets.

In vitro and ex vivo platelet interactions with hydrophilic-hydrophobic poly(ethylene oxide)-polystyrene multiblock copolymers

Hydrophilic-hydrophobic multiblock copolymers synthesized from telechelic oligomers of poly(ethylene oxide) (PEO) and polystyrene (PS) have been used to study the influence of hydrophilic and hydrophobic balance on interfacial interactions of these surfaces with blood components. In vitro coagulation assays show no inherent ability of these amphiphilic surfaces to affect contact activation or coagulation factors. In vitro platelet adhesion and release reactions from rabbit platelet-rich plasma were shown to be greatest on Biomer and PS homopolymer surfaces and least on cross-linked PEO surfaces, with the PEO-PS block copolymers demonstrating intermediate responses. These same substrates were tested in a new low-flow, low-shear arterio-artery shunt system in rabbits. Whole blood occlusion times were not a direct function of hydrophilic content as both PEO and PS homopolymers and Biomer showed short occlusion times, while PEO-PS block copolymers prolonged occlusion times considerably, depending on composition. Overall, results suggest that PEO-PS block copolymers promote unique whole blood responses in contrast to homopolymer and Biomer controls which are more complex than direct correlations to bulk hydrophilic and hydrophobic contents.

Preparation and surface characterization of PEO-grafted and heparin-immobilized polyurethanes

Surfaces of commercial polyurethanes (PUs) were modified by poly(ethylene oxide) (PEO) grafting and/or heparin immobilization for long-term biomedical applications. PU surfaces were treated with diisocyanate and then reacted with PEO or heparin. The heparin immobilized by various methods on the PU surface was very stable, with concentrations of 1.45-1.84 micrograms/cm2. Surface structure and characteristics of each modified PU were examined by performing the following surface analyses: attenuated total reflection infrared (ATR-IR), electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), and dynamic contact angle measurements. The reaction scheme and surface chemical structure of modified PUs were confirmed by ATR-IR and ESCA, respectively. SEM results showed that the PU-PEO surface was very smooth and that the smoothness of the heparinized PU surfaces varied, depending upon the solvent and coupling agent used in the process. The hydrophilicity of the surface was significantly increased after PEO grafting or heparin immobilization. Increase in the chain length of the grafted PEO resulted in significant increases in hydrophilicity and surface mobility.

The spatial resolution of protein adsorption on surfaces of heterogeneous metallic biomaterials

This study was designed to examine the heterogeneity of the adsorption of proteins onto metallic materials. The materials studied included pure Ag, Au, and Ti and sintered Ag 10% Ti and Ag 10% Ta. The distribution of the protein adsorption was studied using I-125 labeled albumin detected by microautoradiography. The surface morphology of the specimens was examined in the scanning electron microscope prior to exposure to the protein solution. A heterogeneous distribution in albumin adsorption was observed over the Ag surface. Similar regions were observed over parts of the mixed metal specimens, but superimposed on this pattern were distinct regions of very low protein adsorption which appeared to correlate closely with the regions of Ti or Ta observed in the scanning electron microscope. A uniform distribution of adsorbed albumin was observed on the Au and Ti, with Au giving a much denser microautoradiograph than Ti. This work demonstrates that variations in the protein adsorption to heterogeneous materials can be observed on a microscopic scale.

The interaction of cultured cells with membranes composed of random and block copolypeptides

Random copolypeptides and block copolypeptides were synthesized, and an interaction between these polypeptide membranes and the cells was studied by a cell culture method (cell line, Ca. 9.22). In random copolypeptides composed of gamma-methyl L-glutamate and gamma-benzyl L-glutamate, cell attachment and cell growth depended on the monomer composition, and showed a maximum at around 70 mole % of benzyl glutamate. Block copolypeptide composed of L-methionine and oxyethylene exhibited low cell attachment and cell growth even at 10 mole % of oxyethylene content, compared to L-methionine homopolymer. ESCA study of the membrane suggested this result to be due to concentration of the poly(oxyethylene) block chain of the polymer on the surface of the membrane. Block copolypeptide composed of N5-(3-hydroxypropyl) L-glutamine and L-leucine exhibited low cell attachment and cell growth, while the corresponding random copolypeptide exhibited high cell attachment and cell growth. This difference is attributable to the microheterophase structure with the hydrophilic domains embedded in the hydrophobic matrix in the block copolypeptide membrane.

Platelet adhesion onto protein-coated and uncoated polyetherurethaneurea having tertiary amino groups in the substituents and its derivatives

Interactions of platelet with novel polyetherurethaneurea and its heparinized derivative were investigated. Platelet adhesion onto the material and release of serotonin or adenosine phosphate from platelet-rich plasma (PRP) were suppressed by an introduction of amino groups to polyetherurethaneurea, by quaternization of the polymer, and further by heparinization of the polymer. When the material was precoated with one of major plasma proteins and the protein-coated materials were taken to contact with washed platelet suspension (WP), the dependence of platelet adhesion and activation on the properties of polymers was different from that observed for PRP interaction. Platelet adhesion and activation were promoted according to the nature of coating proteins in the order albumin less than gamma-globulin less than fibrinogen and with increasing degree of denaturation of coating proteins. When the polymer materials were coated with proteins by immersing in aqueous solution containing two kinds of plasma proteins, adhesion behaviors of platelet were similar to those observed for PRP-uncoated material interaction. These experimental facts indicate that the selectivity of platelet for protein-coated material cannot be assessed by the interaction of WP with materials coated with a single kind of protein. It was concluded that material surface to which albumin is selectively adsorbed without denaturation does not stimulate adhering platelets for release reactions.

Effects of alkyl grafting on surface properties and blood compatibility of polyurethane block copolymers

In order to probe the factors which affect the interaction between the surface of a multiphase polyurethane material and blood, a series of butanediol-chain-extended polyetherurethanes was synthesized. These polyurethanes contained different levels of phase separation, produced by systematically varying the hard segment chemical structure by grafting ethyl and octadecyl groups to the urethane nitrogen atom. Surface characterization using high vacuum, air-equilibrated, and water-equilibrated methods was performed. A canine ex vivo arteriovenous series shunt was used to monitor initial platelet and fibrinogen deposition on these polymers. The ex vivo response to these materials, along with contact angle and ESCA surface chemistry, was found to vary with the degree of alkyl derivatization. This study demonstrated that an increase in the degree of phase separation and also the incorporation of long chain (C18) alkyl groups can affect surface properties and improve the short-term blood compatibility of the underivatized polyurethane.

Surface properties and blood compatibility of polyurethaneureas

A series of polyurethaneureas of varying soft segment type and hard/soft segment ratio were synthesized, and their bulk and surface properties evaluated. A canine ex vivo arteriovenous series shunt was used to monitor initial thrombus deposition. Significant levels of surface hard segment components are apparent in these materials. Polymers with poly(tetramethylene oxide) and poly(propylene oxide) soft segments showed blood compatibility variations with changes in hard/soft segment ratios: the more well-phase-separated materials showing lower platelet and fibrinogen deposition levels. Those trends apparent in polymers synthesized with poly(dimethylsiloxane) or poly(ethylene oxide) soft segments, but poly(dimethylsiloxane)-based materials showed higher levels of thrombus deposition than the poly(ethylene oxide)-based polymers.

Adhesion behavior of rat lymphocytes to poly(ether)-poly(amino acid) block and graft copolymers

Block and graft copolymers consisting of poly(ether) and poly(amino acid) were synthesized, and adhesion behavior of rat lymphocytes to the surface of the film made from these copolymers was analyzed by the microsphere column method. Poly(ethylene glycol) (PEG) and poly(benzyl L-glutamate) (PBLG) were used as poly(ether) and poly(amino acid), respectively. Adhesion behavior of lymphocytes was found to depend on the content and chain length of the components in these copolymers.

Suppression of platelet activity on microdomain surfaces of 2-hydroxyethyl methacrylate-polyether block copolymers

Block copolymers constructed from chains of poly(2-hydroxyethyl methacrylate) (PHEMA) and either poly-ethyleneoxide (PEO) or poly-propyleneoxide (PPO) were synthesized. These block copolymers exhibited microdomain structure. Platelet adhesion on their surfaces was investigated by a column elution method to examine the effect of microdomain structure. The number of platelets adhered from whole blood was smaller for the block copolymer systems than for the homopolymers. Minimum points of platelet adhesion appeared at approximately 0.38 mol fraction of HEMA in the HEMA-PO system. Both block copolymer surfaces showed microdomains of alternate lamellar structure. Furthermore, the percent of platelets released from the column after incubation was investigated using PRP. In the case of homopolymers, released platelet percentages decreased with an increase of incubation time. Released platelet percentages from the block copolymers, however, were nearly constant with changing incubation time. These results show that HEMA-EO and HEMA-PO block copolymers had the ability to suppress both reversible and irreversible adhesion of platelets to their respective microdomain surfaces.

Hydrophilic-hydrophobic microdomain surfaces having an ability to suppress platelet aggregation and their in vitro antithrombogenicity

Block copolymers were synthesized by a coupling reaction of hydrophilic chains of poly(2-hydroxyethyl methacrylate) (PHEMA) with hydrophobic chains of polystyrene (PSt), or poly(dimethyl siloxane) (PDMS). Microstructures of films of the block copolymers exhibited a hydrophilic-hydrophobic microphase separated structure. For evaluation of in vivo antithrombogenicity, small diameter tubes (1.5 mm I.D. and 20 cm length) coated by the copolymers on their internal surfaces were implanted in rabbits as arteriovenous shunts. Occlusion times of the tubes, measured by formation of thrombus, were three days for PHEMA, two days for PSt, and three days for PDMS. The block copolymers showed excellent antithrombogenic properties: occlusion times were 20 days for HEMA-St block copolymer and 12 days for HEMA-DMS block copolymers. In vitro examination of polymer-platelet interaction in terms of platelet adhesion and aggregation, which are important initial processes of blood coagulation, demonstrated suppressed adhesion and aggregation on microdomain surfaces constructed of hydrophilic and hydrophobic block copolymers. From both in vivo and in vitro examination, it was concluded that HEMA-St and HEMA-DMS block copolymers showed promising antithrombogenic activities by suppressing activation and aggregation of platelets.

Adhesion behavior of rat lymphocyte subpopulations (B cell and T cell) on the surface of polystyrene/polypeptide graft copolymer

Polyvinyl/polypeptide graft copolymers having microdomain structure on their surfaces were newly synthesized for the development of a specific cell separator, and the adhesion behavior of rat lymphnode lymphocytes with these materials was examined by column method. Morphologic change of lymphocytes adherent to the graft copolymers was found to be less than that of cells adherent to corresponding homopolymers, i.e., polystyrene and poly (gamma-benzyl L-glutamate). Separation of lymphocyte subpopulations (B cell and T cell) was examined in the absence of serum proteins. The adhesion selectivity for B cell was found to depend on the microdomain structure, since the highest value, 2,2, was observed for the graft copolymer with the polypeptide content of 50 wt%. Synthetic polypeptide derivatives may be promising materials which substitute for a conventional system with nylon fiber and fetal calf serum.

Reversibility of granulocyte adhesion using polyamine-grafted nylon-6 as a new column substrate for granulocyte separation

Reversibility of leucocytes adhered onto the surface of polyamine-grafted nylon-6 was investigated to estimate its feasibility as a new column substrate for granulocyte separation from whole blood. Polyamine-grafted nylon-6 was synthesized by a radical polymerization of 2-diethylaminoethyl methacrylate monomer onto nylon-6. The surfaces of these graft copolymers were found to show a microphase-separated structure composed of island-like phases of cationic polyamine and continuous phases of nonionic nylon-6. Interaction between leucocytes and these copolymer surfaces was studied by passing rabbit heparinized blood through a column packed with glass beads precoated with these copolymers. Columns of these copolymers showed a selective adhesion of granulocytes among leucocyte populations. Also, the adhering granulocytes were able to be recovered from the column by a gentle elution procedure. From these results, it was concluded that polyamine-grafted nylon-6 having a microphase-separated structure is suitable for use as a column substrate in granulocyte separation from whole blood.

Heparinized polyurethanes: in vitro and in vivo studies

Heparin immobilization chemistry using alkyl spacer arms was adapted to optimize yield on polyurethane (PU) surfaces. The resultant biological activity of immobilized heparin (HI) was examined in vitro and in vivo, and compared with a heparin releasing (HR) system. Immobilized heparin retained its ability to bind and inactivate thrombin and Factor Xa; nonspecific coagulation factor binding was insignificant. Such activity cannot be attributed to the leakage of improperly bound heparin. Immobilized heparin-polyurethane catheters implanted in canine femoral and jugular veins for 1 h periods exhibited significant reduction in thrombus formation compared with untreated PU contralateral controls. Polyurethane catheters coated with a 9% heparin dispersion in PU (HR) system provided even greater improvement in antithrombogenicity.

Physical theory of some interface phenomena in hemorheology

The following four subjects are discussed theoretically from a physical standpoint: (1) the effect of the wall of a capillary viscometer on the apparent viscosity of blood; (2) the effect of electric charge on capillary flow; (3) the electric aspect of platelet adhesion and aggregation; and (4) multiphase polymeric materials as antithrombogenic materials. Copley and Scott Blair found a remarkable decrease in the apparent viscosities of blood, plasma, and serum in a fibrin-coated glass tube as compared with those in a glass tube without fibrin-coating. It is shown that the phenomenon cannot be explained by the existence of an electric double layer unless the zeta potential is positive. It is suggested that a reduction of the apparent viscosity of blood may be explained by a slight increase in the thickness of a plasma layer. It is shown that the existence of a slight gap between red cells and the capillary wall due to an electrostatic repulsion will remarkably lower the capillary flow resistance. An electric aspect of endothelial injury is discussed in relation to the adhesion of platelets to the injured endothelium. Platelet aggregation is discussed in accordance with the theory of Verwey and Overbeek , and a possible mechanism of thrombus formation due to a turbulent motion of blood is suggested. The significance of a multiphase polymeric material for an antithrombogenic surface is emphasized. It is suggested that sufficiently large conformational change of macromolecules will be favorable to antithrombogenicity of a polymeric material.

Effect of microphase separated structure of polystyrene/polyamine graft copolymer on adhering rat platelets in vitro

Rat platelet adhesion on microphase separated surface of polystyrene/polyamine graft copolymers (SA copolymers) was investigated. Shapes of adhering platelet were very much changeable in response to the mode of microphase separation of SA copolymer surfaces. We assume that the microphase separated structure of SA copolyer may regulate the shape change of platelet through its effect on a redistribution of proteins and/or lipids present at the plasma membrane of platelets.

Polyphosphazenes: effect of molecular motions on thrombogenesis

The effect and interrelationship between primary (segmental backbone) and secondary (side chain) molecular motions on thrombogenesis, independent of morphological order/disorder, crystallinity, and/or associated water is elucidated using an amorphous hydrophobic polymer of poly-[(trifluoroethoxy) (fluoroalkoxy)phosphazene] PNF. The results indicate that thrombogenesis for an amorphous hydrophobic polymer is sensitive and dependent on the degrees and types of primary and secondary molecular motions at the polymer interface.