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

Recent advances in the design and immobilization of heparin for biomedical application: A review

Heparin, a member of the glycosaminoglycan family, is renowned as the most negatively charged biomolecule discovered within the realm of human biology. This polysaccharide serves a vital role as a regulator for various proteins, cells, and tissues within the human body, positioning itself as a pivotal macromolecule of significance. The domain of biology has witnessed substantial interest in the intricate design of heparin and its derivatives, particularly focusing on heparin-based polymers and hydrogels. This intrigue spans a wide spectrum of applications, encompassing diverse areas such as protein adsorption, anticoagulant properties, controlled drug release, development of implants, stent innovation, enhancement of blood compatibility, acceleration of wound healing, and pioneering strides in tissue engineering. This comprehensive overview delves into a multitude of developed heparin conjugates, employing various methods, and explores their functions in both the biomedicine and electronics fields. The efficacy of materials derived from heparin is also thoroughly investigated, encompassing considerations such as thrombogenicity, drug release kinetics, affinity for growth factors (GFs), biocompatibility, and electrochemical analyses. We firmly believe that by redirecting focus towards research and advancements in heparin-related polymers/hydrogels, this study will ignite further research and accelerate potential breakthroughs in this promising and evolving field of discovery.

Combination of two antithrombogenic methodologies for preventing thrombus formation on a poly(ether ether ketone) substrate

To enhance the total antithrombogenicity of poly(ether ether ketone) (PEEK), we examined a combination of two methodologies for the suppression of activation in both the platelet and coagulation systems. A random copolymer (PMT) composed of a zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) unit and a cationic 2-methacryloyloxyethyl trimethylammonium chloride (TMAEMA) unit was grafted onto the PEEK surface by photoinduced self-initiated graft polymerization of the PEEK substrate (PMTx-g-PEEK). Then, negatively charged heparin was immobilized by ionic binding with TMAEMA units (Hep/PMTx-g-PEEK). The TMAEMA unit composition on grafted PMT altered the surface ζ-potentials of the PEEK substrates. Amounts of immobilized heparin depended on the ζ-potential. The concentration of heparin became constant on the sample surface where the TMAEMA unit composition was 30% or more, and was approximately 2.0 μg/cm2. The Hep/PMTx-g-PEEK with a TMAEMA unit composition of 50% showed not only decreased platelet adhesion, but also a 4-fold extension of the blood coagulation time of the poly(MPC)-g-PEEK substrate. The poly(MPC) layer could inhibit platelet adhesion and activation, resulting in surface antithrombogenic properties. Additionally, heparin released from the Hep/PMTx-g-PEEK prevented activation of the coagulation system in whole blood. Therefore, the combination of these antithrombogenic methodologies was promising for prolonging the blood coagulation period of the materials.

Fluorescence labeling to study platelet and leucocyte deposition onto vascular grafts in vitro

Platelets and leucocytes are important participants in the response of the body to small diameter vascular grafts implanted into the arterial circulation. A sensitive and quick method for measuring platelet and leucocyte deposition contributes to material evaluation. With a newly developed fluorescence labeling method we examined the deposition of platelets and leucocytes onto vascular grafts in vitro. Human platelets and leucocytes were isolated and labeled with the fluorescence label Europium trichloride (EuCl3). After reconstitution of the labeled cells in plasma their functionality appeared intact and competitive with unlabeled cells. Eu-labeled platelets or leucocytes were then incubated with expanded polytetrafluoroethylene (ePTFE), Dacron and polyurethane (PU) vascular grafts in autologous plasma. Beta-thromboglobin and thromboxane release from platelets and beta-glucuronidase release from leucocytes during the incubation experiments were measured. Platelets and leucocytes deposited significantly less onto ePTFE compared to Dacron and polyurethane (P < 0.01). Our results are in accordance with results of in vivo studies using radio-active labeling to study platelet and leucocyte deposition. However, a new finding was that this reduced cell deposition may in part be due to possible toxic effects of ePTFE, shown by increased haemolysis and beta-thromboglobin release.

Studies on segmented polyetherurethane for biomedical application: effects of composition and hard-segment content on biocompatibility

Segmented polyetherurethane (SPEU) materials based on polytetramethylene oxide (PTMO, Mw 1000 and 2000) with various hard-segment contents were synthesized and their biocompatibilities studied via different tests. The static contact angle data reveal that the higher hard-segment-content SPEU material possesses a lower contact angle, implying that the surface of the higher hard-segment-content SPEU is more hydrophilic than its low hard-segment-content SPEU counterpart. The catalyst- and additive-free PTMO-based SPEU materials in this study possess neither a hemolytic nor a cytotoxic response that could be considered non toxic for biomedical applications. By using L-929 cell lines, a cell-seeding test indicated that the higher hard-segment-content SPEU material possesses quicker cell attachment and proliferation behaviors. In vitro platelet adhesion tests indicated that the lower hard-segment-content SPEU possesses less platelet adhesion than the high hard-segment-content SPEU material. Both ex vivo canine artery-artery (A-A) and arterio-venous (A-V) shunting tests revealed that the extent of platelet adhesion reaction is less for lower hard-segment content SPEU. In addition, the blood compatibility of SPEU material synthesized from PTMO 1000 excels over PTMO 2000 SPEU material by near the same levels as the hard-segment-content SPEU.

New polyurethane compositions able to bond high amounts of both albumin and heparin. Part I

In order to prepare polymers provided with better haemocompatibility with respect both to the coagulative cascade and to platelet aggregation and activation, we have synthesized new polyurethanes containing in the chain-extender [di(2-hydroxyethyl)hexadecylamine] both a long chain alkyl group (able to bond albumin) and a tertiary ammonium group able, after suitable quaternization reaction, to bind ionically significant amounts of heparin. The amounts of heparin and albumin bonded to the polymer films were determined spectrophotometrically. A biological in vitro evaluation of the heparinized and albuminized films was also carried out with respect to blood coagulation factors (by activated partial thromboplastin time measurements) and to platelet adhesion and activation (by platelet count and scanning electron microscopy examination). It was seen that the type of adsorption sequence for albumin and heparin, respectively, onto the various homo- and copolymer films, plays an important role on their biological properties; the possible mechanisms involved are also discussed on the basis of X-ray photoelectron spectroscopy and attenuated transmission reflectance evaluation of the polymer surfaces.

Heparin-coated cardiopulmonary bypass circuits

The indications for heparin-coated extracorporeal circuits cannot be defined or limited at present. Clinical investigation remains at an early stage of development. In situations where the risk of systemic anticoagulation is high, this technology would seem to hold great promise. Examples include extracorporeal lung assist and resuscitation from accidental hypothermia. Some have also suggested the use of heparin-coated circuits for percutaneous bypass in cardiopulmonary resuscitation. A significant advantage might also accrue in noncardiac surgical procedures requiring cardiopulmonary bypass, such as complex cerebral aneurysm or arteriovenous malformation resections, resections of the tracheal carina, or bilateral lung transplantations. Its role in routine cardiac surgical procedures remains uncertain, but the work of von Segesser et al suggests a need for continued investigation in that setting using reduced levels of systemic anticoagulation. That endeavor will be greatly assisted by the recent development of heparin-coated cardiotomy reservoirs. Although heparin-coated circuits have been safely used for extracorporeal lung assist with little or no systemic anticoagulation, prospective studies are clearly needed to determine if this approach is advantageous, and it would seem appropriate to develop heparin coating for silicone-based membrane oxygenators.

Synthesis and nonthrombogenicity of polymer membrane with surface-graft polymers carrying thrombin inhibitor

An acrylamide derivative of a thrombin inhibitor was synthesized and graft polymerized to the surfaces of polymer membranes. The thrombin-inhibitor activity was unaffected by the introduction of an acryloyl group. The surface-graft membrane deactivated thrombin markedly and suppressed adhesion of platelets, resulting in a high nonthrombogenicity. Immersion of polymer membranes blended with the thrombin inhibitor in phosphate-buffered saline for 10 d resulted in the loss of nonthrombogenicity, while the polymer membranes grafted with the thrombin inhibitor derivative maintained the nonthrombogenicity over a long period.

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 physicochemical characterization of a hydrophilic polyurethane able to bind heparin

The synthesis of a new segmented polyurethane containing quaternary ammonium groups in the side-chain is reported. The quaternization was carried out both on the polymer dissolved in an organic solvent and on polymer films. Polymeric films quaternized by both techniques were heparinized. The amount of bonded heparin, determined by spectrophotometry, was remarkably higher than previously described. Polymer quaternized in solution bonded more heparin than that heparinized directly on film. In vitro evaluations of antithrombogenicity by activated partial thromboplastin time (APTT) carried out on the films confirmed these data. The polymers were also characterized by chemical, i.r., n.m.r., differential scanning calorimetry and viscometric techniques.

Synthesis and nonthrombogenicity of polyetherurethaneurea film grafted with poly(sodium vinyl sulfonate)

Synthesis of nonthrombogenic materials without using biologically active substances was explored. Poly(sodium vinyl sulfonate) is a water-soluble synthetic polymer and activates antithrombin III to exert nonthrombogenicity that was dependent on the molecular weight. Polyetherurethaneurea film was plasma-treated and graft-polymerized with sodium vinyl sulfonate. The graft film showed excellent in vitro and ex vivo nonthrombogenicity by suppressing interactions with plasma proteins and platelets as well as by inactivating blood-clotting factors.

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.

In vitro non-thrombogenicity of a thrombin-substrate-immobilized polymer surface by the inhibition of thrombin activity

Derivatives of thrombin substrate were synthesized and immobilized on a poly(acrylic acid)-grafted polyurethane film. The carboxyl terminal of the thrombin substrate peptide should be blocked for a higher inhibitory effect of the thrombin activity. Immobilization of the thrombin substrate peptide enhanced adsorption and inactivation of thrombin on the polymer film to prolong the time for fibrin network formation, and suppressed adhesion and deformation of platelets on the film. Consequently, in vitro thrombus formation on the polymer film was strongly suppressed.

Compositional analysis of Biomer

Biomer, a segmented polyether polyurethane, has been analyzed via hydrolysis/gas chromatography to determine its composition. In addition to the previously reported 4,4'-methylene bis(phenyl isocyanate) (MDI), polytetramethylene glycol (PTMO), and ethylenediamine, we now report the presence of diethylamine, 1,3-diaminocyclohexane and poly(diisopropylaminoethyl methacrylate-co-decyl methacrylate), Biomer's cloudy insoluble phase. In addition, a method is presented to characterize the methacrylate additive by molecular weight based on GPC. Also found by chromatography were the antioxidants Santowhite Powder and BHT. XPS shows no Si (silicone) on the Biomer surface, and a total chloride analysis reports no chloride (less than 0.03%). Time-of-flight SIMS data suggest evidence for the methacrylate additive at the surface, and mass spectroscopy can be interpreted as evidence for a diaminocyclohexane.

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.

Platelet adhesion on to polyamide microcapsules coated with lipid bilayer membrane

Polyamide microcapsules with diameters of 3-4 microns were coated with lipid bilayer membrane and their interaction with canine platelets was investigated. Platelet adhesion on to the microcapsules was significantly suppressed by the lipid-coating. Coating with dimyristoylphosphatidylcholine (liquid-crystalline state) reduced platelet adhesion on to the microcapsules to a greater extent than that with dipalmitoylphosphatidylcholine (gel state) at 37 degrees C. The surface properties of the microcapsule in adsorption of plasma proteins were also changed by lipid coating. The amount of gamma-globulin and fibrinogen adsorbed on to the microcapsule was slightly decreased by lipid coating, while the amount of adsorbed albumin was increased. Platelet adhesion on to the lipid-coated microcapsules was suppressed most strongly in the presence of gamma-globulin. Apparently platelet adhesion on to the polyamide microcapsules is controlled by the nature of lipid membrane and gamma-globulin adsorbed on to the microcapsules.

Attachment and growth of fibroblast cells on polypeptide derivatives

Attachment and growth of mouse fibroblast cells on polypeptide derivatives with different wettabilities were studied in the presence or absence of serum proteins. In the presence of serum, a peak level of cell attachment was observed for substrates with a contact angle of around 70 degrees. However, no relationship was found between cell attachment and water contact angle of the substrate in the absence of serum. Ca2+ -dependent cell attachment was observed on hydrophobic polypeptides in the absence of serum proteins. This suggests that Ca2+ -dependent membrane proteins function as mediators for cell attachment to hydrophobic polypeptides. In the presence of serum proteins, it was found that cell attachment is affected by the metabolism, Ca2+, and the cytoskeleton of the cell. Cell growth rate on hydrophilic polypeptide substrates was higher than that on intermediate or hydrophobic polypeptide substrates. This demonstrates that the strong interaction between cells and substrates will be unfavorable for a dewebbing process during mitosis.

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.

In vitro platelet adhesion and in vivo antithrombogenicity of heparinized polyetherurethaneureas

We investigated in-vitro platelet adhesion to polyetherurethaneureas, to which heparin was bound covalently or by ionic bonding. When heparin was bound to polymers, platelet adhesion and platelet activation upon adhesion were suppressed with the increasing content of bound heparin in the polymer. Platelets were activated upon adsorption to different degrees according to the method of heparinization. The platelet adhesion and the platelet activation upon adhesion appeared to be regulated by the electrostatic repulsion between platelet and anionic surface of covalently or ionically heparinized polymer, rather than by the physiological action of bound heparin. The effect of the method of heparinization seemed to be related to the molecular heterogeneity of heparin. Heparinized polyurethanes which interacted very weakly with platelets in vitro were tested for in-vivo antithrombogenicity. The test was carried out by the implantation of a suture of the heparinized polyurethane into canine veins. Ionically heparinized polyurethane did not form a thrombus and maintained a smooth surface over a long period. On the other hand, covalently heparinized polyurethane formed a small amount of thrombus and grew endothelial cells from the insertion point.