Blood compatibility of surfaces with immobilized albumin-heparin conjugate and effect of endothelial cell seeding on platelet adhesion

Adhesion and growth of human umbilical vein endothelial cells on collagen-treated PU/PEGDA IPNs

For ideal non-thrombogenicity under normal physiologic conditions, we propose endothelialization. Endothelialization means that synthetic biomaterials are seeded by endothelial cells to mimic natural blood vessels. In our study, we synthesized amphiphilic polyurethane (PU)/poly(ethyleneglycol)diacrylate (PEGDA) interpenetrating polymer networks (IPNs) with different levels of surface energy to investigate the effect of adhesion and the growth of human umbilical vein endothelial cells (HUVECs). Collagen with cell-binding molecules was adsorbed on the surface of PU/PEGDA IPNs to enhance the adhesion of HUVECs. The morphology of collagens adsorbed on the IPN surfaces depends highly on the surface energy of the IPNs. As the surface becomes hydrophilic, there is greater aggregation of the adsorbed collagens on the IPN surface. The HUVECs successfully adhere to the collagen-immobilized IPN surface. The morphology of the endothelial cells (ECs) that adhere to IPN 2k-C and IPN 2k after 1 day and after 3 days incubation shows that ECs were successfully spread. The adhesion and the proliferation of ECs increase on non-treated IPN surfaces as the hydrophobicity of the IPNs increases. The surface energy of IPN 2k-C is suitable for the adhesion and proliferation of ECs. Therefore, platelet adhesion is significantly reduced on the EC-hybridized surface of IPNs.

Novel thrombo-resistant coating based on iron-polysaccharide complex multilayers

The biocompatibility of iron-polysaccharide complexes has been well-documented. Herein, a stable thrombo-resistant coating was fabricated by consecutive adsorption of Fe (III) and polysaccharides including heparin (Hep) and dextran sulfate (DS) onto various surface by layer-by-layer self-assembly technique via both electrostatic interaction and chemical complexation process. The absorbance at 350 nm increased linearly with the number of Fe3+/Hep multilayer, indicating the formation of multilayer structure and the uniform coating. Compared with (Fe3+/Hep)10, the (Fe3+/DS/Fe3+/Hep)5 coating was more hydrophilic and stable due to the incorporation of DS. The activated partial thromboplastin time (APTT) and platelet adhesion assays showed that both (Fe3+/Hep)10 and (Fe3+/DS/Fe3+/Hep)5 coated surfaces were anticoagulant. The complexing with ferric ions did not compromise the catalytic capacity of heparin to promote antithrombin(III)-mediated thrombin inactivation. Chromogenic assays for heparin activity proved definitively that the inhibition of locally produced thrombin was contributed to the thromboresistance of the surface-bound heparin. The surface with Hep or DS as the outmost layer showed stronger anticoagulant activity than Fe3+, indicating that the outermost layer of the coating played a key role in anticoagulant activity. The utilization of dextran sulfate/heparin surfaces was more advantageous than merely the heparin surface for improving blood-contacting medical devices for long-term usage.

Doubly stochastic Poisson distribution of platelet adhesion on material surfaces and its implication on fluorescence image analysis

An image based assay has been developed to quantify platelet adhesion on material surfaces. Briefly, citrated platelet rich plasma (PRP) is incubated with materials for 2 h to allow platelet adhesion on the surface, followed by fluorescence labeling of platelets with Celltracker Green. Multiple images are acquired by an automatic fluorescence microscope, IN Cell Analyzer 1000. Platelets are identified and counted by an automatic image analysis algorithm. We have observed that the variance of the counts is considerably greater than expected from simple distribution laws. Statistical analysis of that difference shows that these measurements will often follow a doubly stochastic Poisson process in which the variance is inherently very large. To overcome this, multiple images (n > or = 8 images/well, about 3% of total area) are necessary to achieve accurate counting. This method has been compared to the commonly used enzyme based platelet adhesion assay, lactate dehydrogenase (LDH) assay. It is concluded that the present method is only effective in quantifying adherent platelets when a large number of samples are used. However, this method does provide additional information on platelet morphology and spatial distribution, which is lacking in the LDH assay.

The influence of biomaterials on endothelial cell thrombogenicity

Driven by tissue engineering and regenerative medicine, endothelial cells are being used in combination with biomaterials in a number of applications for the purpose of improving blood compatibility and host integration. Endothelialized vascular grafts are beginning to be used clinically with some success in some centers, while endothelial seeding is being explored as a means of creating a vasculature within engineered tissues. The underlying assumption of this strategy is that when cultured on artificial biomaterials, a confluent layer of endothelial cells maintain their non-thrombogenic phenotype. In this review the existing knowledge base of endothelial cell thrombogenicity cultured on a number of different biomaterials is summarized. The importance of selecting appropriate endpoint measures that are most reflective of overall surface thrombogenicity is the focus of this review. Endothelial cells inhibit thrombosis through three interconnected regulatory systems (1) the coagulation cascade, (2) the cellular components of the blood such as leukocytes and platelets and (3) the complement cascade, and also through effects on fibrinolysis and vascular tone, the latter which influences blood flow. Thus, in order to demonstrate the thrombogenic benefit of seeding a biomaterial with EC, the conditions under which EC surfaces are more likely to exhibit lower thrombogenicity than unseeded biomaterial surfaces need to be consistent with the experimental context. The endpoints selected should be appropriate for the dominant thrombotic process that occurs under the given experimental conditions.

In vitro hemocompatibility of albumin-heparin multilayer coatings on polyethersulfone prepared by the layer-by-layer technique

Polyethersulfone foils (PES)--a unique material for blood purification membranes--were coated with a multilayer assembly of heparin (unfractionated or high anticoagulant activity fraction heparin) and albumin (albumin-heparin coatings), or with a multilayer of albumin (albumin coating), using the layer-by-layer technique. The coatings combine advantages of albumin (reduction of nonspecific interactions) and heparin (specific interactions with blood coagulation proteins). The differences between the two heparins, while significant for their biological activity, had only a minor effect on the multilayer assembly with albumin monitored in situ by reflection infrared spectroscopy (FTIR MIRS). Uncoated as well as modified PES surfaces were evaluated using an in vitro assay with freshly drawn, slightly heparinized (1.5 IU heparin/mL) human whole blood. The blood was circulated with a roller pump over the sample surfaces in shear flow across rectangular slit channels ( app. 6 mL/min and 120 s(-1)) for 1.5 h at 37 degrees C. All coatings effectively reduced platelet adhesion and activation according to the PF4 release. The activation of coagulation evaluated as TAT generation was significantly lowered for the coating composed of albumin and high activity heparin. A further beneficial effect of the heparin containing coatings was reduced complement activation as determined by different complement fragments.

Adhesion and growth of endothelial cell on amphiphilic PU/PS IPN surface: effect of amphiphilic balance and immobilized collagen

Since natural blood vessels are lined with an endothelial cell (EC) monolayer, it is proposed that synthetic biomaterial surfaces be covered or seeded with endothelial cells for ideal nonthrombogenicity under normal conditions. The effects of the surface energy of hydrophilic-hydrophobic IPN on EC adhesion and growth were investigated. The human umbilical vein endothelial cells (HUVECs) were cultured on polyurethane (PU)/polystyrene (PS) IPN prepared by changing only the amphiphilic balance and controlling the microphase separated surface structure. The collagens were immobilized on the IPN surfaces for enhanced adhesion of HUVECs, and the morphology of the collagens immobilized highly depended on the surface energy of the IPNs. The stranded rope structure of the collagen molecules in the solution state was maintained only on the surface of the IPN with intermediate hydrophilicity. The adhesion and the proliferation of ECs on the nontreated IPN surfaces increased by increasing the hydrophobicity of the IPNs, and they were optimized on the collagen-treated IPN surface having an intermediate hydrophilicity. Finally, platelet adhesion was significantly reduced on the EC-hybridized surface of the IPNs.

Studies of a novel human thrombomodulin immobilized substrate: surface characterization and anticoagulation activity evaluation

Immobilization of the anticoagulative or antithrombogenic biomolecule has been considered as one of the important methods to improve the blood compatibility of artificial biomaterials. In this study, a novel immobilization reaction scheme was utilized to incorporate the human thrombomodulin, an endothelial cell associated glycoprotein, onto the cover glass surface with an aim to develop an anticoagulative substrate. Trichlorotriazine and amino-terminated silane were employed as the coupling agents, while the polyethylene glycol with a molecular weight of 1500 was used as the spacer in this reaction scheme. Protein C activation assay indicated the immobilized human thrombomodulin still has this coenzymatic activity but is lower, possibly due to the conformation variation by the coupling agents. In vitro platelet adhesion assay has demonstrated the surface with immobilized human thrombomodulin is much less platelet-activating than others. Therefore, the novel reaction scheme proposed here is very promising for future development of an anticoagulative silicon or cover glass substrate (e.g. implantable sensor or biochip) by the immobilization of antithrombogenic protein, such as the human thrombomodulin in this study.

Pharmaceutical strategies utilizing recombinant human serum albumin

Gene manipulation techniques open up the possibility of making recombinant human serum albumin (rHSA) or mutants with desirable therapeutic properties and for protein fusion products. rHSA can serve as a carrier in synthetic heme protein, thus reversibly carrying oxygen. Myristoylation of insulin results in a prolonged half-life because of self aggregation and increased albumin binding. Preferential albumin uptake by tumor cells serves as the basis for albumin-anticancer drug conjugate formulation. Furthermore, drug targeting can be achieved by incorporating drugs into albumin microspheres whereas liver targeting can be achieved by conjugating drug with galactosylated or mannosylated albumin. Microspheres and nanoparticles of different sizes can, with or without drugs and/or radioisotopes, be used for drug delivery or diagnostic purposes. In vivo implantation of albumin fusion protein expressing cells encapsulated in HSA-alginate coated beads showed promising results compared to organoids in rats. Chimeric peptide strategy with cationized albumin as the transport can deliver drugs via receptor mediated transcytosis through the blood brain barrier. Gene bearing, albumin microbubbles containing ultrasound contrast agents can non-invasively deliver gene after destruction by ultrasound. Various site-directed mutants of HSA can be tailor made depending on the application required.

Effect of biologically active coating on biocompatibility of Nitinol devices designed for the closure of intra-atrial communications

Anti-thrombogenicity and rapid endothelialisation are prerequisites for the use of closure devices of intra-atrial communications in order to reduce the risk of cerebral embolism. The purpose of this study was therefore to assess the effect of bioactive coatings on biocompatibility of Nitinol coils designed for the closure of intra-atrial communications. Nitinol coils (n = 10, each) and flat Nitinol bands (n = 3, each) were treated by basic coating with poly(amino-p-xylylene-co-p-xylylene) and then coated with either heparin, r-hirudin or fibronectin. Anti-thrombogenicity was studied in vitro in a dynamic model with whole blood by partial thromboplastin time (PTT), platelet binding and thrombin generation, respectively, and cytotoxicity by hemolysis. Endothelialisation was studied on Nitinol bands with human umbilical venous endothelial cells (HUVEC) by 3-(4,5-dimethylthiazole-2yl)-2,5-triphenyl tetrazolium (MTT) assay and immnuofluorescence analysis of Ki67, vinculin, fibronectin and von Willebrand Factor. Uncoated or coated devices did not influence hemolysis and PTT. r-Hirudin (but not heparin) and fibronectin coating showed lower platelet binding than uncoated Nitinol (p < 0.005, respectively). Heparin and r-hirudin coating reduced thrombin formation (p < 0.05 versus Nitinol, respectively). HUVEC adhesion, proliferation, and matrix formation decreased in the order: fibronectin coating > uncoated Nitinol > r-hirudin coating > heparin coating > basic coating. MTT assay corroborated these findings. In conclusion, r-hirudin and fibronectin coating, by causing no acute cytotoxicity, decreasing thrombogenicity and increasing endothelialisation improve in vitro biocompatibility of Nitinol devices designed for the closure of intra-atrial communications.

Synthesis of blood compatible polyamide block copolymers

Blood compatibility of polyamides has been improved by introducing amido-amine groups in polymer backbone. Polyamide block-copolymer are synthesized by reacting amine end-capped polyamides with N,N'-methylene-bisacrylamide. Polyamide block-copolymers, thus produced found to have the ability of absorbing heparin. Heparinized polyamide block-copolymers have shown significant improvement in blood compatibility as evident from thrombus formation and hemolysis studies.

Improved haemocompatibility of cysteine-modified polymers via endogenous nitric oxide

A novel method for improving the haemocompatibility of biomedical materials through endogenous nitric oxide (NO) is presented. L-cysteine was covalently immobilized onto two biomedical polymers: polyurethane (PU) and polyethylene terephthalate (PET). The L-cysteine content on the polymers was approximately 5-8 nmol/cm2 as quantified via a chemiluminescence-based assay. The haemocompatibility of the modified polymers was evaluated in terms of the number of adhered platelets when exposed to a platelet suspension labeled with Cr51. Platelet adherence on the L-cysteine-modified polymers was reduced more than 50% as compared to the control (glycine-modified polymers) when the platelet suspension contained plasma constituents. No difference in platelet adhesion was observed in the absence of plasma constituents. Further experiments demonstrated that NO was easily transferred to the L-cysteine-modified polymers from S-nitroso-albumin in PBS buffer. The NO was then released from the polymer. NO transfer or release was not observed for the control. The results suggest that L-cysteine-modified polymers are effective in reducing platelet adhesion via the transfer of NO from endogenous S-nitrosoproteins in plasma to the polymer followed by the subsequent release of NO. Thus, exploiting endogenous NO is a viable option for improving the haemocompatibility of biomaterials.