Uncoated Tubes Research Articles

Field study on superheater tubes in the loop seal of a wood fired CFB plant

AbstractTwo full scale superheaters were exposed in the loop seal of a 30 MW wood‐fired CFB plant in Nässjö, Sweden, for one firing season each. Some austenitic steel tubes from the first tube bundle were reinstalled in the second superheater. The superheater tubes were made from one ferritic steel, X10 (Fe8.8Cr) and three austenitic steels; Esshete 1250 (Fe15Cr9Ni6Mn), 347H (Fe17Cr11Ni) and AC66 (Fe27Cr32Ni). Commercial coatings mainly on iron, nickel and carbide base were deposited on some of the X10 and 347H tubes.The material wastage kinetics was non‐linear showing that pure corrosion and not erosion‐corrosion is the major degradation mechanism in the loop seal. It is however clear that the environment is not very aggressive and the corrosion attack on the uncoated tubes is very small. The largest oxide thickness was only about 150 μm recorded on the X10 alloy. The austenitic steels mainly suffered from internal corrosion and grain boundary corrosion, the extent and distribution of which strongly depended on the alloy composition. Generally, it was more pronounced in the regions with the thinnest deposit layers.Eight out of 17 coating qualities tested were unaffected by the exposure. Corrosion was only recorded on the lowest alloyed iron based coatings. The only coatings which could not resist the conditions in the loop seal were the carbide containing Metco 3006 and Metco 3007, where severe oxidation and delamination took place. Also the thermally sprayed Inconel 625 coating delaminated, but this was rather due to a mechanical failure resulting from thermal expansion.

Experimental and clinical experience of albumin coating of tympanostomy tubes

Objectives: Typical problems involved in the function of middle-ear ventilation tubes are otorrhea through the tube and tube occlusion. We will introduce albumin coating of the ventilation tubes to prevent occlusion of the tube lumen by protein, bacteria, and blood. We have reported marked binding inhibition of fibronectin, one of the most adhesive glycoproteins known, on albumin-coated tympanostomy tubes and the durability of the binding inhibition during an 8-month storage of the tubes. The purpose of the current study was to test bacterial adhesion on the coated and uncoated tube surface. Furthermore we wanted to show the effects of the albumin coating of tympanostomy tubes on the tympanostomy tube sequelae in vivo. Methods: Human serum albumin (HSA) was used to coat standard tympanostomy tubes. The binding of Staphylococcus aureus and Pseudomonas aeruginosa on the tubes was tested in vitro. In a clinical, double-blind, prospective trial, 170 patients were randomized to study the effects of HSA-coated tubes on the tympanostomy tube sequelae. Results: Depending on the bacterial concentration the binding of S aureus on HSA-coated tubes was inhibited from 82% to 95% and P aeruginosa from 29% to 37% when compared with uncoated tubes. The typical tube sequelae: acute otitis media and tube occlusion, especially with blood, were found less in the ears with a HAS-coated tube. Conclusions: HSA-coating of tympanostomy tubes reduced significantly the adhesion of S aureus and P aeruginosa on the tube surface. Clinical observations will be presented and discussed.

High-performance capillary electrophoresis separation of hyaluronan oligosaccharides produced by Streptomyces hyalurolyticus hyaluronate lyase

The action of Streptomyces hyalurolyticus hyaluronate lyase on hyaluronic acid (HA) determined by high-performance capillary electrophoresis (HPCE) (electrokinetic chromatography with sodium dodecyl sulphate) was examined and compared with the HPLC procedure. By using an uncoated fused-silica capillary tube, 50 μm ID, 65 cm long from the injection point to the detector, the separation of HA species from DP 4 to approx. DP 30 was obtained. The length of the capillary was found to be fundamental for the separation and resolution of the unsaturated HA oligosaccharides. Furthermore, the HPCE separation of HA Δ-tetrasaccharide and Δ-hexasaccharide species produced a greater detection sensitivity (about 20 times greater) than HPLC. Various HA samples were analyzed for the ratio of tetrasaccharide/hexasaccharide ( T/ H) after treatment with S. hyalurolyticus hyaluronidase. HA samples of extractive origin of different molecular masses showed a T/ H ratio between 1.28 and 1.48 determined by HPCE, with a good correspondence with the HPLC separation. On the contrary, a sample of cross-linked HA resulted in a great discrepancy between the two analytical techniques (greater than 40%). HA of fermentative origin had a T/ H ratio of approx. 1.92–2.00, close to that of HA (approx. 1.80) for the first time extracted and purified from the body of a species of mollusc bivalve, Mytilus galloprovincialis. The presence of resistant (less susceptible to enzyme cleavage) site repeating unit in the carbohydrate backbone of HA is discussed in relation with the T/ H values experimentally determined by HPCE.

Selective metallic tube reactivity in the solution-phase osmylation of single-walled carbon nanotubes.

Single-walled carbon nanotubes have been reacted with osmium tetroxide (OsO(4)) in solution in the presence of O(2) and UV irradiation at 254 nm. We observe one main structural motif, namely thickly coated nanotube structures, densely covered with OsO(2), consisting of multiple bundles of derivatized tubes. In a few instances, bridging uncoated tubes, connecting these thickly coated structures, incorporate a number of smaller nanotube bundles, projecting out from the larger functionalized aggregates of tubes. It is believed that OsO(2) (a) initially forms on the nanotubes by the preferential covalent sidewall functionalization of metallic nanotubes and (b) subsequently self-aggregates. The formation of an intermediate charge-transfer complex is likely the basis for the observed selectivity and reactivity of metallic tubes. Extensive characterization of these osmylated adducts has been performed using a variety of electron microscopy and optical spectroscopy techniques.

Determination of gold by electrothermal atomic absorption spectrometry after electrodeposition on a graphite tube

The inner wall of a graphite tube served as the surface for the adsorptive accumulation and for the electrodeposition of gold from a solution. A flow-through cell was constructed. After the deposition step, the graphite tube was placed into the graphite furnace and an atomization program was applied. To reach the best results, the electrodeposition conditions, such as the medium, deposition potential or current and the flow rate of solution, were optimized. As the working electrodes, pyrolytic graphite coated tubes, uncoated electrographite tubes and tubes covered by elemental palladium were used. This palladium surface was obtained by electrodeposition of palladium prior to gold deposition. For this surface and 3 ml of solution, the sensitivity of determination was 50 times higher than that of the direct sampling of 20 μl solution into a pyrolytic graphite coated tube. The procedure was applied to the determination of gold in river waters.

Tissue adhesion to bioactive glass-coated silicone tubing in a rat model of peritoneal dialysis catheters and catheter tunnels

Silicone peritoneal dialysis catheters do not develop tissue ingrowth, lack a mechanical barrier to periluminal bacterial migration and need cuffs for anchorage. We hypothesized that a bioactive glass coating composed of silicon, calcium, sodium and phosphorous oxides would cause a beneficial tissue reaction causing catheter adhesion, and tested this in a rat model. A hexane solvent-based method of coating silicone tubes with Bioglass powder was used, which maintained flexibility, and then the ultrastructure was confirmed with scanning electron microscopy (EM). Segments 2.5 cm were implanted subcutaneously in 8 Sprague-Dawley rats, with uncoated tubes as a contralateral control, and histology was done at 2, 4 and 6 weeks, including special stains and EM. The uncoated segments grossly had no adherence to surrounding tissue, and were physically separate from a thin fibrous capsule of approximately 50 micro width. Trichrome stains demonstrated the capsule was rich in collagen. There was minimal adjacent tissue reaction. In contrast, the coated tubes were palpably fixed to the soft tissues, and sections demonstrated an adjacent prominent layer of macrophages and multinucleated giant cells. Small numbers of lymphocytes were noted. This cellular reaction increased over the 6-week implant duration, and was also associated with neovascularization of the tissue adjacent to the segments (33 vessels in coated vs. 20 in controls per x 200 field, P < 0.0001). Many refractile silicone particles and prominent multinucleated giant cells were present, with small numbers of lymphocytes and macrophages. Stains showed scattered discontinuous calcific deposits. These findings are consistent with reports that the Bioglass(R) silicon oxide leads to the formation of a layer of hydroxyapatite, which binds to collagen and induces a tissue cellular reaction. In summary, bioactive glass coatings can improve the tissue retention of silicone tubing by promoting adhesion by collagen and cell proliferation, and are promising for future studies of peritoneal dialysis catheters.

Durability of the binding inhibition of albumin coating on tympanostomy tubes

Objective: Occlusion and prolonged otorrhea are typical problems associated with the use of middle-ear ventilation tubes. Albumin coating of ventilation tubes has been introduced to prevent tube occlusions by granulation tissue, blood clot, or pus. In this study, the durability of the binding inhibition (BI) of fibronectin was examined on the tube surface in albumin-coated tubes in different environments during an 8-month trial. Methods: Human serum albumin (HSA) was used to coat silicone tympanostomy tubes. Fibronectin, a typical adhesive protein in serum and exudates, was used as a model representative of exudates of the ear. The durability of BI of this glue protein on the tube surface was tested in different time periods with radiolabelled fibronectin. Scanning electron microscopy (SEM) was performed on the tubes. Results: The BI of fibronectin, achieved with the albumin coating, was still strong after 8 months of storage at +4 °C. A slight decline in BI was noted between the first and third months of storage at +37 °C. A significant difference between HSA-coated and uncoated tympanostomy tubes was noted in SEM. The uncoated surface generally appeared to be rougher than that of HSA-coated tubes when either titanium or silicone tubes were tested. Conclusions: Albumin coating markedly inhibits the binding of fibronectin on tube surfaces in vitro. A clear BI achieved by albumin coating on tube surfaces was shown to persist throughout an 8-month trial, although some reduction of the BI was seen over time. The result emphasizes the role of albumin coating in preventing the adherence of foreign material on tympanostomy tubes. No advantage was achieved by using a cross-linking chemical in the albumin coating.

Zirconium–iridium coating as a permanent modifier for determination of tin in stream sediment, oyster tissue and total diet slurries by electrothermal atomic absorption spectrometry

A slurry atomization procedure has been developed for the determination of total tin in different types of environmental samples such as stream sediment, oyster tissue and total diet using a Zr–Ir permanent chemical modifier and transverse heated electrothermal atomic absorption spectrometry (THETAAS). Reference materials such as GBW07312 Stream Sediment, NIST SRM 1566a Oyster Tissue and NIST SRM 1548 Total Diet were used to validate the method. Slurries were prepared in a mixture of 1% v/v HNO3, 2% v/v HCl and 0.2% Triton X-100 solution by using magnetic stirring and ultrasonication. Addition of Triton X-100 after sonication of the slurries rather than before was found to improve the precision of measurement. With the Zr–Ir-coated tube the characteristics mass obtained was 38 ± 2 pg, which is an improvement of nearly five times compared to using an uncoated tube. The tube lifetime using aqueous standards and slurries was nearly 500 atomization cycles. The Zr–Ir permanent chemical modifier was found to effectively reduce the interference effects from chloride, phosphate and silica, as nearly 90–100% recovery was obtained in the presence of 100 μg of the matrix. In the presence of 100 μg of sulfide, aluminum nitrate and sodium silicate, 30–60% recovery was obtained, indicating the presence of matrix interferences.

Effective Medium Calculations of the Electromagnetic Behavior of Single Walled Carbon Nanotube Composites

ABSTRACTDielectric properties of single walled carbon nanotube assemblies were calculated with an effective medium approximation at frequencies from 200 MHz to 200 GHz. The model treats the carbon nanotubes as layered cylinders, each with a core, a graphene layer and an outer layer, to investigate the dielectric properties of coated and filled nanotubes. The graphene and metal layer properties were modeled with a Drude approximation based on literature data. A generalized Bruggeman model was then used to determine the macroscopic behavior of the modified carbon nanotubes in a composite structure as a function of volume fraction, frequency, and aspect ratio. The depolarization factors in this model were scaled by the normalized effective permittivity to better account for percolation behavior. The model showed a wide variety of frequency dependent dielectric properties. Uncoated tubes were calculated to form highly conductive materials at volume fractions of just a few percent and metal-coated tubes enhanced the conductivity by an order of magnitude. Calculations of nanotubes with insulating coatings showed that high dielectric constants with moderate to low dielectric loss were possible.

Experimental investigation of the control of bacterial community composition in macrofaunal burrows

The burrows and tubes of infauna are complex and dynamic systems that promote sig- nificant heterogeneity in the ecological and geochemical properties of benthic systems. We experi- mentally evaluated the extent to which behaviors of macrofauna, including ventilation activity, the residence times of tubes in sediments and tube composition, influence the development and succes- sion of microbial communities which line macrofaunal burrows (i.e. the burrow microbial biofilm). Our experiments used a burrow mimic system, which allowed manipulation of some biological and environmental factors while holding other factors constant. The biofilm microbial community was assessed using phospholipid fatty acid (PLFA) analysis, a sensitive measure of microbial biomass and a significant tool in the identification of some taxonomic and functional groups of microorganisms in marine systems. Results suggest that the burrow mimics supported the development of microbial assemblages with phospholipid signatures that were both similar to those found in natural burrows and responsive to experimental manipulation. Burrow mimic composition significantly affected PLFA signatures, within the range of compounds and concentrations observed in natural systems. Tubes that were coated with an organic polymer were characterized by lower microbial biomass than uncoated tubes and also exhibited a substantially different PLFA signature. The residence time of tube mimics in sediments also affected the PLFA signature. Tubes with a longer residence time were characterized by higher microbial biomass, and a distinct anaerobe signature, relative to tube mimics having shorter residence times. Thus, a distinct successional sequence was observed. Surprisingly, irrigation frequency, i.e. the rate at which burrows are renewed with fresh, oxic overlying water and rid of metabolic byproducts and other solutes from the host organism and surrounding sediments, had minor effects on PLFA signature within the burrow biofilm. Our results suggest that the proper- ties of the burrow microenvironment exert fundamental controls on microbial community composi- tion in burrow biofilms and are likely to influence biogeochemical processes over short length scales in nearshore systems.

Fretting damage of TiN coated zircaloy-4 tube

Fretting has been reported and investigated for over 50 years. However, it is still one of the modern plagues for several industrial machineries. Especially, fretting of fuel rod cladding material, zircaloy-4 tube, in pressurized water reactor (PWR) must be reduced and avoided. Thin hard coatings are employed to improve the tribological properties such as friction and wear of conventional engineering materials. Among these coatings, physical vapor deposition (PVD) TiN coating is probably one of the most frequently and successfully used PVD coatings for the mitigation of fretting wear. Therefore, in this study a fretting wear experiment was performed using TiN coated zircaloy-4 tube as the fuel rod cladding material and uncoated zircaloy-4 tube as one of the grids. The fretting tester was designed and manufactured for this experiment. The number of cycles, slip amplitude and normal load were selected as main factors of fretting. The type of contact was cylinder-to-cylinder contact. The worn surface was observed by optical microscope, 3-D surface measuring instrument and scanning electron microscope (SEM). The results of this research showed that the wear volume of TiN coated zircaloy-4 tube decreased about 1.2–3 times more than uncoated tube and wear mechanisms were brittle fracture, fatigue fracture, adhesion, abrasion and oxidation.

New method for coating tympanostomy tubes to prevent tube occlusions

Objective: tympanostomy tube insertion is currently the most common surgical procedure requiring general anesthesia performed on children. Occlusion of the tube and prolonged otorrhea through the tube are typical problems associated with the use of middle-ear ventilation tubes. In this study, a new method for coating ventilation tubes is introduced that prevents occlusion of the tube lumen by granulation tissue, blood clot or pus. Methods: human serum albumin (HSA) was used to coat standard tympanostomy tubes of different materials. Fibronectin, a typical protein in serum and exudates and one of the most adhesive glycoproteins, was used as a model representative of exudates of the ear. Results: when compared with the binding on uncoated tubes, the binding of fibronectin on HSA-coated tubes was inhibited from 59 to 85%, depending on the tube material used. Conclusions: HSA-coating markedly reduced the binding of fibronectin on tube surfaces in vitro. The study shows the potential role of HSA-coating in preventing the adherence of foreign material to tympanostomy tubes and reducing tube occlusions.

Experimental Investigation of Fretting Mechanisms of TiN Coated Fuel Rod Cladding Materials(Tribology)

The fretting characteristics of TiN coated Zircaloy-4 tube were investigated experimentally. The fretting experiment was performed using TiN coated Zircaloy-4 tube as the fuel rod cladding material and uncoated Zircaloy-4 tube as one of grids. TiN coating is probably one of the most frequently and successfully used PVD coatings for the mitigation of fretting. In this study, TiN coating by PVD was employed for improvement of Zircaloy-4 tube fretting characteristics. The fretting tester was designed and manufactured for this experiment. The number of cycles, slip amplitude and normal load were selected as main factors of fretting. The results of this research showed that the wear volume of TiN coated Zircaloy-4 tube increased as number of cycles, normal load and slip amplitude increase but the quantity of volume was lower than the case of uncoated Zircaloy-4 tube pairs.

Thermal modeling of various thermal barrier coatings in a high heat flux rocket engine

One- and two-dimensional thermal models were developed to predict the thermal response of tubes with and without thermal barrier coatings (TBCs) tested for short durations in a H 2/O 2 rocket engine. Temperatures were predicted using median thermophysical property data for traditional air plasma sprayed ZrO 2–Y 2O 3 TBCs, as well as air plasma sprayed and low pressure plasma sprayed ZrO 2–Y 2O 3/NiCrAlY cermet coatings. Good agreement was observed between predicted and measured metal temperatures. It was also shown that the variation in the reported values of the thermal conductivity of plasma sprayed ZrO 2–Y 2O 3 coatings can result in temperature differences of up to 180°C at the ceramic/metal interface. In contrast, accounting for the presence of the bond coat or radiation from the ceramic layer had only a small effect on substrate temperatures (<20°C). The thermal models were also used to show that for the short duration test conditions of this study, a 100 μm thick ZrO 2–Y 2O 3 coating would provide a metal temperature benefit of approximately 300°C over an uncoated tube while a 200 μm thick coating would provide a benefit greater than 500°C. The difference in the thermal response between tubes and rods was also predicted and used to explain the previously-observed increased life of TBCs on rods over that on tubes.

Extracorporeal circulation can induce hypotension by both blood-material contact and pump-induced platelet aggregation

Objective: Use of extracorporeal systems in cardiopulmonary bypass and dialysis induces vascular reactions, which can lead to hypotension and lung edema. Methods: To study the contribution of blood-material contact and use of a roller pump, as well as prevention of their adverse effects, we perfused a rat hind leg with a tube connecting a carotid and a femoral artery. Results: Autoperfusion of an uncoated tube caused a fall of aortic pressure and femoral resistance to 66% ± 16% and 76% ± 15%, respectively, of their initial values within 2 hours, whereas in control animals without a shunt, these variables hardly changed (to 94% ± 2.8% and 99% ± 2.8%, respectively). Lung water content became significantly higher than that found in control animals (79.4% ± 1.50% versus 77.0% ± 1.67%). If we coated the tube with albumin, these changes were largely prevented. When the coated tube was placed in a roller pump, aortic pressure and femoral resistance immediately fell to 79% ± 17.2% and 63% ± 13.5%, respectively, whereas lung water content did not increase. The vasodilation was caused by platelet aggregation and could be prevented with aurintricarboxylic acid, which inhibits shear-induced platelet aggregation by blocking the binding of von Willebrand factor to platelet glycoprotein Ib receptors. Conclusions: Extracorporeal circulation may induce hypotension and lung edema by means of blood-material contact. Hypotension can be prevented by coating the system with albumin but can still result from pump-induced platelet aggregation. (J Thorac Cardiovasc Surg 2000;120:12-9)

Chemical reactions of tellurium in graphite tubes of atomic absorption spectrometry

The chemical reactions of tellurium were investigated in uncoated, pyrolytic graphite-coated, and zirconium-treated polycrystalline electrographite tubes. After drying, tellurium is present as TeO 2, which is reduced by the graphite to the volatile suboxide TeO. This molecule was detected in the gas phase by molecular absorption spectroscopy. In coated tubes, this reduction process occurs at lower temperatures compared to uncoated and Zr-treated tubes, and shows a faster reaction rate. The suboxide is reduced to elemental Te on collision with the graphite tube wall. This transport process via the gas phase was observed by vaporization from L’vov platforms and subsequent separate atomization from wall and platform. In uncoated tubes, tellurium could be stabilized to temperatures above 1200°C due to intercalation, which was proven by re-oxidation experiments.

Reduced thrombus formation by hyaluronic acid coating of endovascular devices.

Biocompatible stent coatings may alleviate problems of increased (sub)acute thrombosis after stent implantation. Hyaluronic acid (HA), a ubiquitous, nonsulfated glycosaminoglycan, inhibits platelet adhesion and aggregation and prolongs bleeding when administered systemically. However, the effects of immobilized HA for reducing stent platelet deposition in vivo are unknown. We therefore quantified the antithrombotic effects of coating stainless steel stents and tubes with HA using an established baboon thrombosis model under physiologically relevant blood flow conditions. HA-coated and uncoated (control) stents (3.5 mm in diameter, n=32) and stainless steel tubes (4.0 mm in diameter, n=18) were deployed into exteriorized arteriovenous shunts of conscious, nonanticoagulated baboons. Accumulation of (111)In-radiolabeled platelets was quantified by continuous gamma-camera imaging during a 2-hour blood exposure period. HA coating resulted in a significant reduction in platelet deposition in long (4 cm) tubes (0.24+/-0.15 x 10(9) versus 6.12+/-0.49 x 10(9) platelets; P<0.03), short (2 cm) stainless steel tubes (0.18+/-0.06 x 10(9) versus 3.03+/-0.56 x 10(9) platelets; P<0.008), and stents (0.82+/-0.20 x 10(9) versus 1.83+/-0. 23 x 10(9) platelets; P<0.02) compared with uncoated control devices. Thus, HA coating reduces platelet thrombus formation on stainless steel stents and tubes in primate thrombosis models. These results indicate that immobilized HA may represent an attractive strategy for improving the thromboresistance of endovascular devices.

Pump-induced platelet aggregation in albumin-coated extracorporeal systems

Objective: Coating of extracorporeal systems with heparin does not prevent platelet activation and subsequent bleeding disorders. We investigated whether this could be due to elevated shear stress caused by a roller pump. Methods: Human or rat blood was made to flow through an uncoated or an albumin-coated medical polyvinyl chloride tube with or without a roller pump. Aggregation of platelets in the tubing was recorded continuously with a photometric device. Results: Although in vitro gravitational flow in uncoated tubes caused immediate platelet aggregation and platelet loss, this remained absent in coated tubes. When the pump was started in experiments with a coated tube strong platelet aggregation was observed and platelet count fell within 5 minutes to 78% ± 2% and 71% ± 3% of control values in human and rat blood, respectively. In vivo, no aggregation was observed during spontaneous flow in rats with an albumin-coated tube running from the carotid artery to the femoral artery, but aggregation started as soon as the blood was pumped. Pump-induced platelet aggregation, both in vitro and in vivo, could be prevented with aurintricarboxylic acid, which specifically inhibits shear-induced platelet aggregation as has recently been shown. Pump perfusion of blood in an uncoated tube did not elicit platelet aggregation. Conclusions: Pump perfusion of blood in coated systems elicits shear-induced platelet aggregation, which may be prevented by administration of substances that block the binding of von Willebrand factor to glycoprotein Ib receptors on the platelets. The effects of pumping on platelets are masked in uncoated circuits because of the dominant influence of blood-material contact. (J Thorac Cardiovasc Surg 1999;118:946-52)

Local drug delivery of Argatroban from a polymeric‐metallic composite stent reduces platelet deposition in a swine coronary model

Thrombus formation after intracoronary stent implantation provides a stimulus for neointimal hyperplasia and if excessive can result in stent thrombosis. We tested the hypothesis that local delivery of an antithrombin drug from a polymeric-metallic stent inhibits platelet thrombus formation. An uncoated metal slotted tube, a jellyroll slotted metal stent with an Argatroban-loaded polymeric sleeve, and a jellyroll slotted metal stent with a drug-leached polymeric sleeve were randomly deployed into the coronary arteries of eight juvenile farm swine. Platelet deposition in the stented segments was determined at 2 hr using autologous 111Indium oxime-labeled platelets. Platelet deposition was significantly less in the Argatroban-loaded stents compared to the Argatroban-leached stents (1.40 × 108 platelets/cm2 vs. 26.8 × 108 platelets/cm2; P = 0.005). When corrected for differences in the metal surface area exposed to blood, platelet deposition was significantly lower in the Argatroban-loaded stent (1.74 ± 1.95 × 108/cm2) compared to the Argatroban-leached stent (33.5 ± 39.1 × 108/cm2; P = 0.005) and the uncoated metal stent (36.2 ± 73.3 × 108/cm2; P = 0.006). In this coronary stent thrombosis model Argatroban has local antithrombotic properties when delivered with a polymer-metallic stent. Improved polymeric designs may reduce risk of thrombus deposition at the site of stent implantation. Cathet. Cardiovasc. Intervent. 46:503–507, 1999. © 1999 Wiley-Liss, Inc.

Local drug delivery of Argatroban from a polymeric-metallic composite stent reduces platelet deposition in a swine coronary model

Thrombus formation after intracoronary stent implantation provides a stimulus for neointimal hyperplasia and if excessive can result in stent thrombosis. We tested the hypothesis that local delivery of an antithrombin drug from a polymeric-metallic stent inhibits platelet thrombus formation. An uncoated metal slotted tube, a jellyroll slotted metal stent with an Argatroban-loaded polymeric sleeve, and a jellyroll slotted metal stent with a drug-leached polymeric sleeve were randomly deployed into the coronary arteries of eight juvenile farm swine. Platelet deposition in the stented segments was determined at 2 hr using autologous 111Indium oxime-labeled platelets. Platelet deposition was significantly less in the Argatroban-loaded stents compared to the Argatroban-leached stents (1.40 x 10(8) platelets/cm2 vs. 26.8 x 10(8) platelets/cm2; P=0.005). When corrected for differences in the metal surface area exposed to blood, platelet deposition was significantly lower in the Argatroban-loaded stent (1.74+/-1.95 x 10(8)/cm2) compared to the Argatroban-leached stent (33.5+/-39.1 x 10(8)/cm2; P=0.005) and the uncoated metal stent (36.2+/-73.3 x 10(8)/cm2; P=0.006). In this coronary stent thrombosis model Argatroban has local antithrombotic properties when delivered with a polymer-metallic stent. Improved polymeric designs may reduce risk of thrombus deposition at the site of stent implantation.