Trillium coating of cardiopulmonary bypass circuits improves biocompatibility.

Coating of cardiopulmonary bypass circuits may be a solution to prevent adverse effects induced by contact of blood elements with foreign surfaces. Using an animal model, we investigated the Trillium TM coating of cardiopulmonary bypass circuits (a new process involving polyethylene oxide, sulphonate groups and heparin) at low systemic heparinization, focusing on haemolysis and clot formation. Cardiopulmonary bypass was initiated through jugulo-carotid access with ACT maintained around 180 sec. Treated circuits (Trillium group) were evaluated in 3 calves (mean weight of 66.0+/-8.7 kg), vs. untreated circuits in 3 control calves (mean weight of 60.7+/-7.5 kg). Blood samples were drawn at regular intervals for biochemical, hematological and blood gas analyses. After 6 consecutive hours, the animals were weaned from CPB and were awakened. The circuits were analyzed for clot deposits. After 7 days the animals were sacrificed and an autopsy was carried out. Red cell and white cell counts did not change over the 6 hours. Platelet counts dropped to 75.9+/-7.3% of the baseline value in the Trillium group after 6 hours whereas counts dropped to 57.2+/-26.0 in the control group (p<0.05). Plasma free Hb remained constant in the Trillium group but increased significantly to 280+/-65% of baseline value in the control group (p<0.05). The amount of clots were significantly higher in the control group, in the connectors, the reservoir, the heat exchanger, and the oxygenator. No renal emboli were seen in the Trillium group whereas the mean number of emboli was 3.0+/-2.4 in the control group. We conclude that Trillium coating significantly improves the biocompatibility of artificial surfaces exposed to blood.     

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.     

Hemocompatibility of heparin-coated surfaces and the role of selective plasma protein adsorption.

Although several studies have shown that heparin-coated surfaces reduce the activation of both the complement system and the coagulation system, there is still inadequate understanding of the factors initiating and controlling blood activation at these surfaces. We investigated the adsorption profile of 12 common plasma proteins (and the platelet receptor CD41) to a heparin coating (Carmeda BioActive surface (CBAS)) compared to uncoated controls (PVC) by using an in vitro whole blood Chandler-Loop model. Surface bound proteins were studied kinetically by a direct ELISA technique. Western blots were performed on the SDS eluates in order to detect adsorbed cleavage products and denatured proteins. Changes in plasma levels of neutrophil activation markers, platelet activation, coagulation activation, complement activation and the inflammatory response were measured by conventional ELISAs. This study showed significant differences in adsorption patterns among the heparin-coated and the uncoated surfaces, notably for fibronectin, fibrinogen, C3 and high molecular weight kininogen (HMWK). The kinetic studies confirmed the results obtained from Western blots and indicated specific adsorption profiles of plasma proteins. We assume that at least some of the improved blood compatibility of the heparin-coated surfaces may be ascribed to the selective uptake and cleavage of plasma proteins.     

Intra-aortic balloon: evaluation of heparin-coating under various experimental conditions.

In a calf model, heparin coated intra-aortic balloon (IAB) was compared with standard balloon. In group 1, 9 of each IAB type were set to the automatic mode for 15 min, 45 min and 6 hours respectively, while in group 2, 3 of each IAB type were left deflated during 20 minutes to simulate balloon dysfunction. At the end of the procedures, 3 samples of each IAB were analyzed with scanning electron microscopy (SEM) for surface deposits. Macroscopically, the 12/12 heparin coated IAB of both groups and the 9/9 standard IAB of group 1 were free of deposits, whereas the 3/3 standard IAB of group 2 exhibited clot deposits. SEM revealed deposit-free surfaces in the 36/36 heparin coated samples of both groups, while 14/27 standard samples of group 1 (p<0.01 when compared with heparin coated samples) and 8/9 standard samples of group 2 (p = 0.02, same comparison) disclosed blood cells and fibrin deposits. Morphometrically, the proportion of standard sample surfaces covered with deposits, estimated according to a score system (0% = 0; 0.1-25% = 1; 25.1-50% = 2; 50.1-75% = 3; 75. 1-100% = 4), was 0.69+/-0.82 in group 1 (p<0.01 when compared with heparin coated samples) and 1.22+/-0.83 in group 2 (p<0.01, same comparison). Thus heparin coated IAB presents no deposits either after 6 hours of intravascular ballooning or after 20 minutes of stagnation. It seems to be a promising strategy for patients with absolute or relative contraindications to systemic heparinization.     

Interactions of antithrombin and proteins in the plasma contact activation system with immobilized functional heparin

The interactions of antithrombin (AT) and the contact phase clotting factors with two commercially available heparinized surfaces are reported. The Carmeda (CBAS) and Corline surfaces along with controls (a sulfonated polyethylene surface and a CBAS analog in which the heparin used was devoid of specific AT-binding sequences) were exposed to human plasma. Adsorbed proteins were eluted and examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The CBAS and Corline surfaces adsorbed large amounts of AT, whereas adsorption on the controls was negligible. Immunoblots for the four contact phase clotting factors indicated less contact activation on the CBAS and Corline surfaces than on the controls. Determination of adsorbed functional AT using a FXa inhibition assay showed that the CBAS surface adsorbed about 4 times as much AT as the Corline surface. Adsorption of AT to the control surfaces was minimal. Assays for adsorbed FXII and FXIIa based on kallikrein generation showed that all four surfaces adsorbed similar amounts of FXII. However, on the controls, most of the FXII was in activated form, whereas on the CBAS and Corline surfaces very little activation occurred.     

Short term performance evaluation of a perfluorocopolymer coated gas exchanger for arteriovenous CO2 removal

A new perfluorocopolymer coating for micropore hollow fiber gas exchangers was developed to improve gas exchange, reduce plasma leakage, and reduce blood-surface interactions. The present authors evaluated gas exchanger performance using this new coating in a prospective, randomized, controlled, unblinded, large animal model of CO2 retention. Adult sheep (30-40 kg), under general anesthesia, underwent cannulation of the carotid artery (12 F) and jugular vein (14 F). The perfluorocopolymer coated (n = 5) and uncoated (n = 5) gas exchangers were attached to an arteriovenous CO2 removal (AVCO2R) circuit. Blood gases, CO2 removal, and hemodynamics were monitored throughout the 6 hour study. Average CO2 removal was 107.6 +/- 15.6 ml/min (coated) vs. 93.0 +/- 13.9 ml/min (uncoated; p < 0.01). PaCO2 and CO2 removal for both coated and uncoated did not deteriorate significantly over the study. Average AVCO2R blood flow was 1,130 +/- 25 ml/min (coated) versus 1,101 +/- 79 ml/min (uncoated; p = not significant). Likewise, cardiac output and AVCO2R blood flow did not change over the duration of the study. No significant differences in the pressure gradient or resistance between devices (coated, 6.89 +/- 1.14 mm Hg/L/min; uncoated, 6.42 +/- 0.23 mm Hg/L/min) was noted. The authors concluded that the new perfluorocopolymer coated gas exchanger improved CO2 removal without compromising hemodynamics in an acute performance evaluation.     

Improved biocompatibility of heparin surface-coated ventricular assist devices.

Heparin surface coated ventricular assist devices (VADs) and cannulas were evaluated in comparison to uncoated VADs in 10 bovine experiments (body weight 77 +/- 6 kg). All systems were primed with cristalloid solution. No systemic heparin was given. Left ventricular assist was started with a blood flow of 4.2 +/- 0.4 l/min and maintained over 6 hours. Besides hemodynamic monitoring, blood samples were taken at regular intervals for blood gas, hematological, biochemical and coagulation studies. All animals in the study group (coated) were assisted for the scheduled 6 hours without device failure. In the control group, however, total occlusion occurred in 1 VAD after 1 hour of left ventricular assist whereas the other 4 VADs remained functional throughout the protocol. Mixed venous oxygens saturation was preassist 56 +/- 12% for coated versus 63 +/- 11% for uncoated and the final value at 60 minutes after weaning was 58 +/- 16% versus 59 +/- 5% (NS). Mean hematocrit dropped from a baseline value of 33 +/- 4% for coated versus 29 +/- 8% for uncoated to 29 +/- 7% versus 30 +/- 5% (NS) after 6 hours of assist. There was no significant difference between the baseline values (5.7 +/- 3.0 mumol/l for coated versus 4.6 +/- 3.1 mumol/l for uncoated) and the 6-hour values (3.8 +/- 3.7 mumol/l versus 7.6 +/- 6.4 mumol/l) for mean plasma hemoglobine. The normalized platelet levels dropped after 10 minutes of assist to 91 +/- 21% for coated versus 94 +/- 49% for uncoated (NS) and 89 +/- 29% versus 65 +/- 44 at 6 hours (NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Albumin and heparin multilayer coatings for blood-contacting medical devices

Three types of covalently crosslinked assemblies consisting of multiple (1) molecular layers of human serum albumin (HSA); (2) alternating layers of HSA and unfractionated heparin; and (3) alternating layers of HSA and partly depolymerized heparin fixed with one end to HSA were prepared on various surfaces. Adsorption of fibrinogen, IgG, and antithrombin (ATIII) from human citrated plasma on coated surfaces was evaluated by ELISA. Fibrinogen adsorption on coated ELISA plates was lower than that on bare polystyrene. There was no IgG adsorption on the HSA coating alone, but considerably high IgG adsorption was detected on the heparin-containing surface. The adsorption of ATIII increased with increasing heparin on the surface. The effect of multilayer coatings on platelets was tested by incubation of modified vascular prostheses with citrated blood. The most favorable interaction with platelets was observed on the HSA assembly. The interaction of platelets with the surface bearing unfractionated heparin was higher than that of the surface covered with partly depolymerized heparin. The long-term durability of the HSA-heparin coating was proven by a 21-day implantation of coated polyurethane plates in goat heart.     

Presence of plasticizer di-2(ethylhexyl)phthalate in primed extracorporeal circulation circuits

Many centers advocate the use of a standby wet-primed extracorporeal membrane oxygenation (ECMO) circuit for rapid deployment during cardiopulmonary resuscitation. However, concerns with regard to the potential health hazards associated with the release of the plasticizer di-2(ethylhexyl)phthalate (DEHP) from the polyvinyl chloride (PVC) tubing exist. The purpose of this study was to determine the time course of DEHP release from a preprimed ECMO circuit and to evaluate the effect of PVC tubing coatings on DEHP release. Seven circuits including three uncoated (Medtronic, Medtronic with albumin, and Medtronic Super Tygon) and four attenuated surfaces (Carmeda, COBE Smart, Medtronic Trillium, and Terumo x-coated) were primed with Plasmalyte A. Samples of the circuit prime were collected over a period of 2 weeks and were analyzed for DEHP, using gas chromatography. Results were compared by using a two-tailed t test. One coated (Carmeda) and all three uncoated circuits leached DEHP. The greatest amount of leaching occurred in the uncoated Medtronic tubing with albumin. The COBE Smart, Medtronic Trillium, and Terumo x-coated circuits had undetectable amounts of DEHP (p = 0.006 vs Medtronic uncoated). Prepriming an ECMO circuit composed of uncoated PVC tubing is associated with DEHP release. Using coated PVC tubing appears to eliminate DEHP release over a 2-week period.     

A nonelutable low-molecular weight heparin stent coating for improved thromboresistance

Low-molecular weight heparin (LMWH) has been widely used as a systemic anticoagulant during percutaneous coronary intervention. In this study, LMWH was covalently immobilized to the surface of a cobalt chromium reservoir-based sirolimus-eluting stent to create a nonelutable nanoscale coating for enhanced thromboresistance. Toludine-blue stained stents revealed uniform heparin coverage on all surfaces of the stent. Scanning electron microscopy of stent strut cross-sections showed identical coating thickness on all sides; while the thickness was determined to be 320 nm by a focus-ion beam system. Secondary ion mass spectrometry showed constant concentrations of O, N, and S atoms throughout the depth of the surface, confirming the uniformity of the heparin coating. The nonelutable nature of the coating was confirmed in a modified Factor Xa inhibition assay which showed the stent had an equivalent of 3-5 heparin units/cm(2), while no elutable heparin was detected in wash solutions. The antithrombin binding capacity of the immobilized heparin was determined to be 60-80 pmol/cm(2) in an antithrombin uptake assay. The enhanced thromboresistance of the heparin coating was demonstrated in an in-vitro bovine blood flow loop which showed minimal visual thrombus accumulation and 95% reduction in platelet deposition compared to uncoated control stents. Drug-eluting stents with such nonelutable LMWH coating would represent a significant advance in the treatment of patients with complex lesions who are at increased risk of developing stent thrombosis.     

Analysis of cellular morphology, adhesion, and proliferation on uncoated and differently coated PVC tubes used in extracorporeal circulation (ECC)

The biggest challenge to improve extracorporeal circulation (ECC) circuits lays on avoiding platelet adhesion to their surfaces, because this contributes to thrombus formation, resulting in the activation of blood coagulation. One approach to minimize this effect is to improve the biocompatibility of ECC circuits by modifying their surfaces. This can be achieved by coating them with heparin or phospholipids. The present study investigated the adhesion and morphology characteristics of fibroblastic and blood cells cultured on uncoated poly (vinyl) chloride PVC tubes as well as on heparin, phosphatidylcholine (DMPC), and phosphatidylethanolamine (DMPE) -coated tubing. The results showed the importance of uniform coating regardless of the substance used, because the coatings cover the grooves on PVC surfaces, which favor cell adhesion. The comparison among the three different coatings showed the best biocompatibility results for the PVC tubes coated with heparin, followed by the coating with DMPE and with DMPC. For all coated tubes, cells did not spread on the PVC surfaces and, consequently, did not adhere to their surfaces, increasing the overall biocompatibility of PVC tubes. However, possible DMPE's alkylation, caused by sterilization, resulted in increased material hydrophobicity, which explains the decrease in fibroblastic adhesion. Furthermore, sterilization of DMPC-PVC improves its hydrophilic character, also decreasing adhesion. Based on these results, coating PVC with the phospholipids DMPC and DMPE seems to be a promising technique to improve the biocompatibility of PVC tubes, and is worthy of further investigation.     

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.     

Prevention of surface encrustation of urological implants by coating with inhibitors

The encrustation of materials used for urological implants is as yet an unresolved problem. The crystallisation-inhibiting effect of the glycosaminoglycan heparin was used to reduce encrustation. Heparin was covalently bound to the surface of slotted-tube stents of tantalum and stainless steel using a spacer molecule. To verify the inhibition of crystallisation processes, reproducible in vitro tests and in vivo tests using the rat as animal model were carried out. The in vitro and in vivo experiments showed that the heparin coating has a significant influence on the encrustation of the surface. After 7 days in vitro and 120 days in vivo, heparin coated stents were free of encrustation, whereas the uncoated reference stents were extensively covered.     

Improved neo-endothelialization of small diameter ePTFE grafts with titanium coating

BACKGROUND: Patency of small synthetic bypass grafts is inferior compared to autologous grafts for revascularization procedures. Titanium coating of foreign surfaces has shown to decrease thrombogenicity, enhance biocompatibility and promote adhesion of endothelial cells. The aim of this study was to test the effect of titanium coating of small diameter ePTFE grafts on short term patency, neo-endothelialization and neointimal proliferation. METHODS: Bilateral carotid graft interposition was performed in 5 pigs with uncoated (n=5) and titanium-coated (n=5) ePTFE grafts (internal diameter=4 mm, length=5 cm), thus each pig served as its own control. At the end of the study (30 +/- 3 days), patency and stenosis severity was assessed by carotid angiography. Animals were sacrificed and grafts were excised for histology and scanning electron microscopy. Morphometry of histologic sections was carried out to determine neointimal proliferation and percentage of neo-endothelial coverage. RESULTS: Patency rate was 80% for uncoated and titanium-coated grafts. Quantitative angiography did not show any significant difference in lumen size between two groups. Morphometry revealed a significantly higher cellular coverage with CD31 positive endothelial cells for titanium-coated (84 +/- 19%) than uncoated grafts (48 +/- 26%, p<0.001). There was a non significant trend (p=0.112) towards increased neointimal proliferation in titanium-coated (94 +/- 61 micron2/micron) compared to uncoated grafts (60 +/- 57 micron2/micron). CONCLUSIONS: Patency rate in uncoated and titanium-coated ePTFE grafts is similar at one month. However, titanium coated grafts show a significant improvement in neo-endothelialization compared to uncoated grafts.     

Heparin coating of the extracorporeal circuit combined with leukocyte filtration reduces coagulation activity, blood loss and blood product substitution

BACKGROUND: Cardiopulmonary bypass is associated with activation of the coagulation cascade. Occasionally, this results in postoperative hemorrhage and consequently the need for blood products associated with increasing costs and risk of infection. Contact activation of the intrinsic coagulation pathway, and damage to cellular blood components with the release of proteolytic substances from neutrophil granulocytes have been linked to these coagulation disorders. METHODS: Eighteen routine CABG-patients were randomly assigned to totally heparin coated circuits (Bioline coating) combined with leukocyte filtration in a double blind protocol (group I), 34 patients served as controls (group II). Leukocyte filters were activated before release of the aortic crossclamp. Coagulation activity, postoperative blood loss, and substitution with blood products were assessed. RESULTS: Blood loss in the first 24h after surgery was significantly lower with combined application of heparin coating and leukocyte filters (group I) vs. controls (group II) (526+/-78 ml vs. 786+/-88 ml; p<0.05). Thrombin formation represented by prothrombin fragments 1+2 was significantly lower in group I vs. group II after declamping of the aorta (2.1+/-0. 3 nmol/L vs. 4.0+/-0.3 nmol/L; p<0. 05). Group I showed higher AT II plasma than group II (48.8+/-3.2% vs. 41.5+/-1.77%; p<0.05). CONCLUSIONS: Leukocyte filtration during reperfusion in heparin coated cardiopulmonary bypass circuits is associated with lower coagulation activation, decreased blood loss and reduced transfusion of packed red cells in elective CABG patients.     

Antithrombogenicity of Hydromer's polymeric formula F202 immobilized on polyurethane and electropolished stainless steel

Hydromer's heparin-polymer complex (F202) was applied to polyurethane film and electropolished medical grade stainless steel. The presence of heparin on the surface was confirmed by FT-IR and immunofluorescent histochemistry. The F202 polymer was nonthrombogenic and the development of thrombi on these surfaces after exposure to recalcified human whole blood was minimal or absent. Platelet adhesion to these F202-coated surfaces, compared to control (uncoated) surfaces, was low or absent after exposure to platelet-rich plasma as determined by fluorescent staining and by immunohistochemistry. Our F202 polymer was not hemolytic after exposure to human erythrocytes and was not cytotoxic in a standard cytotoxic protocol. The F202 polymer could prove useful as an antithrombogenic coating for preventing thrombus formation on medical implants and catheters.     

Effect of hydroxyapatite coating and polymethylmethacrylate on stainless steel implant-site infection with Staphylococcus epidermidis in a sheep model

We aimed to study the influence of hydroxyapatite (HA) coating and polymethylmethacrylate (PMMA) cement on the risk of development of stainless steel implant-site infection with Staphylococcus epidermidis in a sheep model. Uncoated, HA-coated, and PMMA-cemented stainless steel implants were inserted in the left femur of 30 sheep. For each type of implant, sheep were inoculated with S. epidermidis in the intramedullary canal and one non-inoculated group was used as control. After 6 weeks, infection was evaluated using clinical, radiological, bacteriological, and histological criteria. Radiological and clinical results were normal. Cultures were negative in the control sheep. In the inoculated sheep, interposition tissue and bone cultures were positive in 2 of 6 uncoated, 6 of 6 HA, and 6 of 6 PMMA implants with a mean bacteria count of 5.2 +/- 1.17, 3.5 +/- 0.7, and 3.9 +/- 0.9 log10 cfu/g, respectively (NS), for interposition tissue, and 4 +/- 0.01, 2.9 +/- 0.6, and 2.5 +/- 1.3 log10 cfu/g, respectively (NS) for bone. The polymorphonuclear leukocyte (PMN) score (mean number of PMN per 10 different microscopic high-power fields >or=5) in interposition tissue was >or=3 in 6 of 6 HA, significantly different from uncoated (3 of 6) and PMMA (2 of 6) groups (p = 0.04). The HA and PMMA inoculated groups had a higher infection rate than the uncoated inoculated group (p = 0.06). In this experimental sheep model of S. epidermidis infection at the bone-biomaterial interface, HA seems to be at higher risk of infection compared with uncoated or PMMA-cemented stainless steel, when inoculation is intramedullary and contemporary with implantation.     

Carbon coated polyethylene: effect of surface energetics and topography on human platelet adhesion

The influence of surface energy and structural properties of carbon coated polyethylene (PE) on the human platelet adhesion was studied. Three types of amorphous carbon coating were obtained by plasma pulse discharge, with the number of pulses grading as 10, 50, 100. Human serum albumin adsorption experiments have been carried out with all samples in vitro. Platelet adhesion analysis by SEM included determination of total quantity of adherent platelets, and respective quantities of platelets at different stages of activation (single, spread, aggregates). Surface topographies ranged from bare PE and such (10 pulses), to globular 0.5 microm in size (50 pulses), and complex fibrillar 3-4 microm structures (100 pulses). Surface free energy varies from 31.7 +/- 0.6 to 40.4 +/- 0.6 mN/m for uncoated PE and 10 pulse coatings, respectively, as determined by contact angle techniques. All studied coatings demonstrate weaker platelet activation properties in comparison with untreated PE. Among all studied coatings, the 50 pulse coated surface seems to be the least suitable for contact with platelets, mainly due to its structural rather than to its energy properties. These data are related to a sharp decrease in the adsorbed protein level for the samples with 50 pulse coatings. The applied analysis of platelet activation enables more accurate characterization of platelet-biomaterial interaction.     

Optimal heparin surface concentration and antithrombin binding capacity as evaluated with human non-anticoagulated blood in vitro

Contact between blood and a biomaterial surface takes place in many applications and is known to activate the coagulation and complement systems. Heparin surface coatings have been shown to reduce blood activation upon contact with artificial surfaces. To establish the optimal heparin surface concentration, blood was incubated in a tubing loop model at 37 degrees C. The tubing was coated with different surface concentrations of heparin and rotated at three different velocities. We demonstrate that the blood compatibility of a surface with regard to coagulation, complement, and platelet activation can be improved by increasing the heparin surface concentration in the 6-12 pmol antithrombin/cm2 concentration interval. The binding of factor H is not influenced by the increased heparin surface concentration, suggesting that this factor is not the primary regulator of complement on heparin surfaces. In addition, the heparin coating has no effect on the complement activation that occurs on gas surfaces in extracorporeal circuits.     

Preparation and characterization of polymeric coatings with combined nitric oxide release and immobilized active heparin

A new dual acting polymeric coating is described that combines nitric oxide (NO) release with surface-bound active heparin, with the aim of mimicking the nonthrombogenic properties of the endothelial cell (EC) layer that lines the inner wall of healthy blood vessels. A trilayer membrane configuration is employed to create the proposed blood compatible coating. A given polymeric substrate (e.g., the outer surface of a catheter sleeve, etc.) is first coated with a dense polymer layer, followed by a plasticized poly(vinyl chloride) (PVC) or polyurethane (PU) layer doped with a lipophilic N-diazeniumdiolate as the NO donor species. Finally, an outer aminated polymer layer is applied. Porcine heparin is then covalently linked to the outer layer via formation of amide bonds. The surface-bound heparin is shown to possess anti-coagulant activity in the range of 4.80-6.39 mIU/cm2 as determined by a chromogenic anti-Factor Xa assay. Further, the surface NO flux from the underlying polymer layer containing the diazeniumdiolate species can be controlled and maintained at various levels (from 0.5 to 60 x 10(-10) mol cm(-2)min(-1)) for at least 24 h and up to 1 week (depending on the flux level desired) by changing the chemical/polymer composition of the NO release layer. The proposed polymeric coatings are capable of functioning by two complementary anti-thrombotic mechanisms, one based on the potent anti-platelet activity of NO, and the other the result of the ability of immobilized heparin to inhibit Factor Xa and thrombin (Factor IIa). Thus, the proposed polymeric coatings are expected to exhibit greatly enhanced thromboresistivity compared to polymers that utilize either immobilized heparin or NO release alone.