Adsorption of plasma proteins to the derivatives of polyaminoetherurethaneurea: the effect of hydrogen-bonding property of the material surface

A new biodegradable and biocompatible hydrogel with polyaminoacid structure

The preparation and physicochemical and biological characterization of a novel polyaminoacid hydrogel have been reported. The alpha,beta-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) has been used as a starting polymer for a derivatization reaction with methacrylic anhydride (MA) to give rise to the methacrylate derivative named PHM. Photocrosslinking of PHM has been performed in aqueous solution at 313 nm and in the absence of toxic initiators. PHM-based hydrogel has been characterized by scanning electron microscopy, X-ray diffractometry, swelling measurements in aqueous media; the degradation of PHM-based hydrogel has been evaluated as a function of time in the absence or in the presence of esterase. Besides, the biocompatibility of this hydrogel and of its degradation products has been evaluated by performing in vitro assays on human chronic myelogenous leukaemia cells (K-562), chosen as a model cell line. Finally, ATR-FTIR measurements have showed that interaction between PHM-based hydrogel and each of four plasma proteins (albumin, gamma-globulin, transferrin and fibrinogen) does not cause change in protein conformation thus supporting its potential use as a material to prepare parenteral drug delivery systems.

Blood compatible aspects of poly(2-methoxyethylacrylate) (PMEA)--relationship between protein adsorption and platelet adhesion on PMEA surface

Platelet adhesion and spreading is suppressed when a poly(2-methoxyethylacrylate) (PMEA) surface is used, compared with other polymer surfaces. To clarify the reason for this suppression, the relationship among the amount of the plasma protein adsorbed onto PMEA, its secondary structure and platelet adhesion was investigated. Poly(2-hydroxyethylmethacrylate) (PHEMA) and polyacrylate analogous were used as references. The amount of protein adsorbed onto PMEA was very low and similar to that absorbed onto PHEMA. Circular dichroism (CD) spectroscopy was applied to examine changes in the secondary structure of the proteins after adsorption onto the polymer surface. The conformation of the proteins adsorbed onto PHEMA changed considerably, but that of proteins adsorbed onto PMEA differed only a little from the native one. These results suggest that low platelet adhesion and spreading are closely related to the low degree of the denaturation of the protein adsorbed onto PMEA. PMEA could be developed as a promising material to produce a useful blood-contacting surface for medical devices.

Protein adsorption, lymphocyte adhesion and platelet adhesion/activation on polyurethane ureas is related to hard segment content and composition

Segmented polyurethane ureas with different hard segment content and composition were synthesized using 4,4'-diphenylmethane diisocyanate and polytetramethylene glycols. Using polyols with different molecular weights, it was possible to synthesize polyurethane ureas with either: (i) a constant ratio of urethane to urea bonds; (ii) a constant urethane content; or (iii) a constant urea content. Bulk properties were assessed by dynamic mechanical analysis. Surface properties were estimated by contact angle measurements and streaming potential measurements. Haemocompatibility was evaluated in vitro by measuring the adsorption of human serum albumin (HSA) and fibrinogen (Fg), the adhesion of human peripheral blood lymphocytes (PBL), and the presence of activated platelets on the biomaterial surfaces. Enzyme immuno assays (EIA) have been specially developed for this purpose for the detection of antibody-recognizable plasma proteins and platelet surface membrane proteins. No simple correlation between chemical structure of the polymers and surface properties was found. Parameters of haemocompatibility correlated more closely with hard segment content and chemical composition than with the surface characteristics of the polymers. Adsorption of plasma proteins, adhesion of lymphocytes and the adhesion/activation of platelets were found to increase with increasing hard segment content of the polyurethane ureas. However, the monoclonal-antibody recognisable fibrinogen and the platelet activation were nearly constant with increasing hard segment content, if the urea content was kept constant.

Synthesis and nonthrombogenicity of fluoroalkyl polyetherurethanes

New polyetherurethanes carrying fluoroalkyl substituents in the side chains were synthesized from N,N-di(hydroxyethyl)heptadecafluorooctyl-sulfonamide (a chain extender), 4,4'-disocyanatodiphenylmethane, and poly(tetramethylene glycol). Various kinds of polyetherurethanes having different tensile properties were prepared by changing the content of fluoroalkyl chain extender or the molecular weight of poly(tetramethylene glycol). The surface of a film made from the fluoroalkyl polyetherurethane was strongly water-repulsive. The in vitro thrombus formation on the fluoroalkyl polyetherurethanes was reduced by increasing the content of chain extender for the same molecular weight of poly(tetramethylene glycol). Protein adsorption, platelet adhesion, and platelet activation on the fluoroalkyl polyetherurethanes were also investigated.

Activity of horseradish peroxide adsorbed on radio frequency glow discharge-treated polymers

Horseradish peroxidase (HRP) has been used as a model enzyme in this study of its physical adsorption and residual enzyme activity on radio frequency glow discharge (RFGD)-treated polymers. The specific enzymatic activity of HRP adsorbed on different surfaces was assumed to be an indication of the extent of its conformational alterations on the surfaces. The surfaces studied were poly (ethylene terephthalate) (PET), polytetrafluoroethylene (PTFE), and tetrachloroethylene and tetrafluoroethylene glow discharge-treated PET, abbreviated as TCE/PET and TFE/PET. All surfaces were characterized by electron spectroscopy for chemical analysis (ESCA) and liquid contact angles in air. HRP adsorbs more strongly onto the two discharge-treated surfaces than onto the untreated polymers, as evidenced by the lower amount of HRP eluted by sodium dodecyl sulfate (SDS) from the treated polymers. For example, seventy percent of the HRP adsorbed on TCE/PET or TFE/PET remains on the surface after overnight elution with a 1% solution of SDS. In contrast, untreated PET and PTFE each retains only c. 20% of the absorbed enzyme. The enzymatic activity of HRP adsorbed on the different surfaces was studied using hydrogen peroxide (H2O2) as the substrate. HRP adsorbed on the higher energy surfaces, PET and TCE/PET, retains significantly more activity than the HRP adsorbed on the lower energy surfaces, PTFE and TFE/PET which appear to destroy rapidly almost all of the activity of HRP after it adsorbs. HRP adsorbed on TCE/PET is relatively more stable over time than HRP adsorbed on PET or free HRP in solution. (For example, only 45% of the specific enzymatic activity of HRP adsorbed on TCE/PET was lost after 3 h of storage in phosphate buffer at 37 degrees C, while 70% of that adsorbed on PET was lost.) In summary, when HRP is adsorbed on TCE/PET, it is very tightly bound, and yet it maintains a significant fraction of its initial specific activity and also retains this activity for 3 h in phosphate buffer at 37 degrees C. Thus, tenacious physical adsorption of proteins such as enzymes on TCE glow discharge-treated surfaces may have potential as a new method of immobilization of such molecules, for uses in biosensors, diagnostics, bioseparations, cell culture and bioreactors.

Non-thrombogenicity by novel surface modification methods

Three novel methods, recently developed by us, for the synthesis of non-thrombogenetic materials were reviewed. The first was the utilization of poly(vinyl sulfonate) as a heparinoid and a newly synthesized polymerizable-thrombin-inhibitor. The chemicals were grafted onto the surfaces of materials. The second was the use of thrombin-substrate-analog peptide. The immobilized peptide was decomposed by blood coagulation factors and inhibited thrombus formation on the surface. The third method was the enhancement of endothelialization by immobilization of bio-signal molecules. The immobilized biosignals remarkably accelerated the growth of endothelial cells.

Synthesis and antithrombogenicity of heparinized polyurethanes with intervening spacer chains of various kinds

Heparin was immobilized to polyetherurethaneurea membrane by covalent or ionic bondings with intervening spacer chains having different lengths and different terminal functional groups. The amount of immobilization of heparin and the release rate of immobilized heparin were controlled by the nature and the mode of bonding of spacer chains. The heparinized polyetherurethaneurea membranes became more in vitro antithrombogenic and suppressed more strongly the adhesion and activation of platelets, as the amount of immobilization increased. It was also shown that the membrane to which the low-molecular-weight fraction of heparin was immobilized was less stimulating to platelets.

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.

Synthesis and non-thrombogenicity of polyurethanes with poly(oxyethylene) side chains in soft segment regions

Epoxidized polybutadiene-urethanes were synthesized and grafted with poly(oxyethylene)s. The non-thrombogenicity of the graft polyurethanes was investigated in relation to the content of poly(oxyethylene). The grafting of poly(oxyethylene) to polyurethane suppressed adsorption and denaturation of plasma proteins and platelet adhesion. It was also found that there exists an optimum content of poly(oxyethylene) for the graft polyurethane to attain the highest non-thrombogenicity.

Adsorption of plasma proteins and platelet adhesion on to polydimethylsiloxane/poly(gamma-benzyl L-glutamate) block copolymer films

A-B-A-type block copolymers of four different compositions were synthesized, in which A and B represent poly(gamma-benzyl L-glutamate) and polydimethylsiloxane segments, respectively. Among the block copolymers and their surface-modified derivatives, those containing 40-70 mol% polydimethylsiloxane and having water contact angles ranging from 50 degrees to 85 degrees were found not to induce conformational change of plasma proteins upon adsorption. It was also observed that the number of adhered platelets and the rate of serotonin release from adhered platelets increased when plasma proteins underwent conformational change upon adsorption. These experimental observations indicate that hydrophobic-hydrophilic block copolymers having a certain composition do not induce conformational change of plasma proteins upon adsorption and do not adhere to and activate platelets, thus leading to a suppression of thrombus formation.

Albumin adsorption on alkyl chain derivatized polyurethanes. II. The effect of alkyl chain length

Linear alkyl chains containing 2, 10 and 18 carbon atoms were grafted to 10% of the urethane nitrogens in a polyether-polyurethane. The polyurethane was synthesized from methylene bis(p-phenyl isocyanate), 1,4-butanediol, and polytetramethylene oxide of 1000 molecular weight in a molar ratio of 3/2/1. Fourier transform infrared spectroscopy and attenuated total reflectance optics were used to study the adsorption of 5.0 mg/ml human serum albumin (HSA) at 37 degrees C to the derivatized and non-derivatized polymers. Both delipidized HSA and HSA containing 6.5 mol stearic acid per mol of albumin were used to study the effect of chain length upon the initial adsorption rate, the total amount adsorbed in 1 h, and the desorption rate. The initial adsorption rates revealed that non-specific adsorption was similar upon all four polymers. An increase in initial adsorption rate upon the C-18 derivatized polymer was attributed to a specific binding interaction between the HSA and the grafted alkyl chains. The conformational stability of the HSA also affected the adsorption rate. The total amount adsorbed after 1 h decreased as the alkyl chain length increased from 2 to 18 methylene groups. The desorption rate decreased in magnitude as the alkyl chain length increased from C-2 to C-18. These results support a hypothesis that alkyl chain length influences the interaction between albumin and an alkylated polymer system.

Attachment and proliferation of fibroblast cells on polyetherurethane urea derivatives

Interactions of novel polyetherurethane urea derivatives with fibroblast cells as well as with plasma proteins were investigated. Fibronectin, which is a cell adhesion protein, was found to be very active in attaching fibroblast cells onto a heparinized polyetherurethane urea: its activity was found to be strongly dependent on the surface properties of the material. Fibronectin was easily adsorbed by the heparinized polyetherurethane urea, but the degree of its adsorption to the material in competition with other proteins was so low that cell attachment to polyetherurethane ureas was decreased by heparinization. Different degrees of cell attachment onto different materials due to different adsorptivities of plasma proteins were considered. Proliferation of fibroblast cells was suppressed on cationic polyetherurethane urea but unaffected on other derivatives of polyetherurethane urea. Since specific suppression of cell proliferation was not observed on the heparinized polyetherurethane urea, the latter material was expected to be useful as a long-term antithrombogenic material in vivo.

Antithrombogenic heparin-bound polyurethanes

Many kinds of heparin-bound polyurethanes have been developed. Polyurethanes are a family of elastomers displaying better blood-compatibility than other polymeric materials. It is useful to modify this material by heparinization. Several approaches to heparinization have been devised: 1) a general method of heparinization, applicable to all polymeric materials, 2) a heparinization method specific to polyurethanes, and 3) the design of heparinizable polyurethane derivatives. These three approaches are first explained in detail. Then, the antithrombogenic mechanism of the heparinized polymers is discussed. Finally, the interactions of the heparinized polymers with blood coagulation factors, plasma proteins, and platelets are discussed.

Adsorption of plasma proteins to the derivatives of polyetherurethaneurea carrying tertiary amino groups in the side chains

Polyetherurethaneureas carrying tertiary amino groups in the side chains were synthesized, quaternized, and heparinized. The adsorption of plasma proteins to the polyurethane derivatives was investigated using Fourier-transform infrared, surface fluorescence, ultraviolet, and circular dichroism spectroscopy. Bovine gamma-globulin and bovine plasma fibrinogen were easily adsorbed to hydrophobic polyurethanes and denatured. It was found that the beta structure was generated during the irreversible conformational change of the proteins on adsorption to hydrophobic polyurethane materials. On the other hand, bovine serum albumin was easily adsorbed to hydrophilic quaternized and heparinized polyurethanes without a serious conformational change. The conclusion was drawn that a polymer material that selectively adsorbs bovine serum albumin in a native state could be antithrombogenic.

Synthesis and antithrombogenicity of anionic polyurethanes and heparin-bound polyurethanes

Two kinds of novel antithrombogenic polyurethane materials were synthesized. One of them is a polyetherurethane with anionic charges on the film surface, and the other is a polyetherurethaneurea to which heparin was covalently bound. The mechanism of their antithrombogenicity was investigated. The anionic polyetherurethane selectively adsorbed albumin, did not cause a conformational change of plasma proteins adsorbed, and suppressed the adherence and deformation of platelets but did not deactivate the blood-clotting system, thus leading to a moderate antithrombogenicity. The heparin-bound polyetherurethaneurea was not favorable for the selective adsorption of albumin, caused the denaturation of plasma proteins adsorbed, and induced the adherence and deformation of platelets but deactivated the blood-clotting system, leading to excellent antithrombogenicity. For the investigation of blood-material interaction, the importance of a multiparameter estimation of the activation of platelets and the blood-clotting system was indicated.

Interaction of polystyrene/poly(gamma-benzyl L-glutamate) and poly(methyl methacrylate)/poly(gamma-benzyl L-glutamate) block copolymers with plasma proteins and platelets

A-B-type block copolymers, consisting of polystyrene (PST) or poly(methyl methacrylate) (PMMA) forming segment (A) and poly(gamma-benzyl L-glutamate) (P[Glu(OBzl)]) segment (B), were synthesized and the thrombus formation on these block copolymer films was investigated in relation to the adsorption of plasma proteins and the activation of platelets. The relative amount of thrombus formation was higher on homopolymers than on block copolymers. The amount of thrombus formation became less, with decreasing content of P[Glu(OBzl)] in the PST block copolymers and with increasing content of P[Glu(OBzl)] in the PMMA block copolymers. Adsorption of bovine serum albumin(BSA), bovine gamma-globulin (B gamma G) and bovine plasma fibrinogen(BPF) onto polymer films was also investigated. More proteins were adsorbed and denatured when adsorbed onto PST and PMMA than onto block copolymers. With increasing content of P[Glu(OBzl)] in the PST block copolymers, the degree of denaturation of adsorbed proteins increased, while the amount of protein adsorption was unaffected. Conversely, with increasing content of P[Glu(OBzl)] in the PMMA block copolymers, the degree of denaturation of adsorbed proteins decreased, while similarly the amount of protein adsorption was unaffected. Adhesion of platelets from platelet suspension (WP) to polymer films coated with one of the plasma proteins showed that the activation of adhered platelets was suppressed when there was a lower degree of denaturation of coated proteins. In the same experiments using platelet-rich plasma(PRP), neither the number of platelets adhered nor the degree of activation of the adhered platelets was correlated with the composition of the polymer films.(ABSTRACT TRUNCATED AT 250 WORDS)