Stainless Steel Stents Research Articles

Effective Adsorption of Functional Biological Macromolecules on Stainless Steel Surface with Micro/Nanoporous Texture

Stainless steel (AISI 316L) is commonly used as a material in medical devices. Modification of the metal surface with bioactive molecules and/or nanoparticles to develop next-generation smart biomaterial, e.g., cardiovascular stents, has recently attracted great attention. The present work investigated adsorption of antibodies and enzymes on micro/nanoporous 316L stainless steel compared with that on smooth and gold-coated stainless steel surfaces. The experimental results showed that the micro/nanoporous stainless steel surface produced by electrochemical erosion can adsorb a large amount of proteins (antibodies or horse radish peroxidase (HRP)), with comparable or better results than the sputtered-gold surface. Washes with surfactants (e.g., 10% bull serum albumin (BSA) or 0.2% Tween 20 solution) did not remove the enzymes/antibodies. In contrast, pretreatment of the metal plates with 5% Tween 20 halved antibody adsorption but did not affect adsorption of HRP. The wettability of the porous metal surface coated with proteins depended on the protein species and amount of protein adsorbed. The 1595 Acta Phys. ⁃Chim. Sin. 2013 Vol.29 protein-coated porous surface was hydrophilic (water contact angle<50°), which should make it biocompatible. The proteins on the micro/nanoporous stainless steel surface retained their high biological activity; in particular, micro/nanoporous stainless steel stents modified with an anti-CD34 antibody using the present method can effectively and selectively capture KG-1 cells. Our work provides a basis for developing novel polymer-free, smart, economic biomaterials with stainless steel for biomedical applications.

Magnetizable Duplex Steel Stents Enable Endothelial Cell Capture

Emerging medical nanotechnology applications often utilize magnetic forces to guide the movement of superparamagnetic particle linked cells and drugs in order to achieve a therapeutic effect. Superparamagnetic particle labeled endothelial cells have previously been captured on the surface of prototype nickel-plated stents in proof of concept studies. Facilitated endothelialization may help improve the healing of stented arteries and reduce the risk of stent thrombosis and restenosis. Extensive evaluation of candidate materials led to the development of a magnetizable 2205 duplex stainless steel stent. Magnetic field strengths of approximately 630 mG were induced within these stents by holding them in close proximity to a 0.7 T rare earth magnet. The magnetic field strength was reliably maintained over several days, but was partially reduced upon mild mechanical shock or plastic deformation. Mechanical testing demonstrated that stents could withstand crimping and expansion necessary for vascular implantation; however, magnetic field strength was significantly reduced. When placed in an endothelial cell suspension of 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cells/mL, magnetized stents captured approximately 310 cells/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> compared to approximately 35 cells/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for non-magnetized control stents. These data provide quantitative support to the observation that low level magnetization of stents may be adequate to attract labeled, autologous, blood-derived endothelial outgrowth cells following stent placement. This, in turn, may lead to more rapid and complete healing of stented arteries with a concomitant improvement in stent performance.

Study on Kinetics and Biocompatibility Evaluation of Multiple Polymer Layer with Biochemical Material Properties in Drug-Eluting Stent

The Paclitaxel-eluting stents (PTX) with three-layered polymer coating were studied in this work. The PLGA (polylactic acid-co-glycolic acid) with 15 percent PEG (poly ethylene glycol) concentration in blend have been applied for preparing multiple layer drug carrier and fabricated on the surface of 316L stainless steel stents by ultrasonic atomization spraying method. The Paclitaxel was explored in doses: (~255μg) for single layer coated PTX (30 wt%), and (~275μg) for multiple layer coated PTX in accordance. Pre- and post-expansion surface morphologies of multiple layer stent were examined by scanning electron microscopy (SEM). The Paclitaxel release kinetics was studied by comparative method of release profiles of single layer PTX with 3-layered polymer coated PTX. The biocompatibility by hemolysis ratio and dynamic clotting time with platelet adhesion measurements also was investigated.

&lt;i&gt;In Vitro&lt;/i&gt; Drug Release and Hemocompatibility of Biodegradable Plga/Peg Coated Paclitaxel-Eluting Stents

The Paclitaxel-eluting stents (PTX) with biodegradable copolymer coating were studied in investigations. The polymer blend composition of PLGA (polylactic acid-co-glycolic acid) and PEG (poly ethylene glycol) have been applied as drug carrier and fabricated on the surface of 316L stainless steel stents by ultrasonic atomization spraying method. Were explored three doses: low-dose (~80μg per stent, 10 wt%), moderate-dose (~150μg per stent , 20 wt%), and high-dose (~220μg per stent , 30 wt%). The weight ratio of Paclitaxel to PLGA/PEG blends was 10:90, 20:80, and 30:70. Pre- and post-expansion surface morphologies of the Paclitaxel-eluting copolymer coating stents were examined by scanning electron microscopy (SEM). The quantitative analysis of Paclitaxel release in vitro and hemocompatibility by hemolysis ratio and dynamic clotting time measurement also were investigated.

Changes in Coronary Angulation After Bioresorbable Vascular Scaffold and Cobalt-Chromium and Stainless Steel Stent Implantation

ABSTRACT Background The conformability of the stent, defined as the adaptation of the prosthesis to the natural shape of the vessel, is the major cause of geometrical changes after stenting and is influenced by the stent material and design. It may be assessed by measuring changes in the curvature and the angulation of the treated segment after stent implantation. The objective of this study was to compare changes in coronary angulation after implantation of the bioresorbable vascular scaffold (BVS) and cobalt-chromium and stainless steel metal platforms used in second-generation drug-eluting stents. Methods In this retrospective analysis, 50 patients with single de novo lesions in native coronary arteries and diameter between 2.5 and 3.5 mm and length up to 23 mm were included. Twenty-five patients were treated with BVS and 25 patients were treated with cobalt-chromium (n = 12) or stainless steel (n = 13) platforms. Angulation was measured using a dedicated quantitative angiography analysis software. Results Vessel angulation significantly changed after device implantation. In the group submitted to the implantation of metal platforms there was greater coronary angulation change when compared to the group treated with BVS (41.6% vs. 14.9%; P Conclusions In this preliminary assessment, the BVS produced a smaller coronary angulation change. The clinical impact of this finding must be prospectively investigated in a larger and more complex cohort.

Study of drug-eluting coating on metal coronary stent

Drug-eluting stent has been proved to decrease the restenosis caused by the stent implantation, owing to the existence of a drug-eluting coating on the stent. For ensuring the effectivity and security of the drug-eluting stent during the service period, the uniform surface, good deformation and stabilized drug release behavior of the stents should be satisfied. In this study, the performances mentioned were studied on stainless steel stents. The results showed that the surface morphology of the coating was affected by the sorts of solvent, the parameters of the spraying process and the addition of the plasticizer. The drug-eluting profile of the coating was influenced by the plasticizer content and PLGA/drug ratio of the coating. Meanwhile, the plasticizer as an additional agent obviously increased the deformation performance of the coating. Optimized parameters for preparation of the drug-eluting coating were investigated to obtain a drug-eluting coating with good integrated performances.

Nickel-free stainless steel avoids neointima formation following coronary stent implantation

SUS316L stainless steel and cobalt–chromium and platinum–chromium alloys are widely used platforms for coronary stents. These alloys also contain nickel (Ni), which reportedly induces allergic reactions in some subjects and is known to have various cellular effects. The effects of Ni on neointima formation after stent implantation remain unknown, however. We developed coronary stents made of Ni-free high-nitrogen austenitic stainless steel prepared using a N2-gas pressurized electroslag remelting (P-ESR) process. Neointima formation and inflammatory responses following stent implantation in porcine coronary arteries were then compared between the Ni-free and SUS316L stainless steel stents. We found significantly less neointima formation and inflammation in arteries implanted with Ni-free stents, as compared to SUS316L stents. Notably, Ni2+ was eluted into the medium from SUS316L but not from Ni-free stainless steel. Mechanistically, Ni2+ increased levels of hypoxia inducible factor protein-1α (HIF-1α) and its target genes in cultured smooth muscle cells. HIF-1α and their target gene levels were also increased in the vascular wall at SUS316L stent sites but not at Ni-free stent sites. The Ni-free stainless steel coronary stent reduces neointima formation, in part by avoiding activation of inflammatory processes via the Ni-HIF pathway. The Ni-free-stainless steel stent is a promising new coronary stent platform.

Quantitative determination of magnetic force on a coronary stent in MRI

To introduce an analytical method for a quantitative determination of magnetic force on a coronary stent in the magnetic resonance imaging (MRI) magnet that is generally applicable to metallic implants. Magnetic forces on metallic implants in the MRI magnets are traditionally determined empirically by measuring deflection from the vertical plane at the central axis of the magnet and at the point of the largest force along the longitudinal axis of the magnet. Magnetic and chemical characterization of the stents was performed by a commercial magnetometer and energy-dispersive X-ray spectroscopy. Magnetic force on the stents fabricated of paramagnetic alloys (surgical stainless steel and cobalt-chromium) was determined by measuring the stent's magnetic dipole moment and employing the on-axis magnetic field profile of an MRI magnet. The maximum force on the stainless steel stent was found to be F(S,max) = 0.18 mN, whereas on the cobalt-chromium stent it was F(C,max) = 0.06 mN. The magnetic force on the investigated paramagnetic stents is even smaller than the gravitational force acting on the stents in the Earth's gravity field, so that it has no physiological impact on the stented vessels.

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The ability of three different intravascular stents (Gianturco-Roubin, Palmaz-Schatz, and CV Rad), and two different metals (stainless steel and tantalum) to resist vasoconstriction was evaluated in an intact artery ex vivo model.Stents were deployed in 21 rabbit thoracic aortae and five dog carotid arteries, which were constricted with phenylephrine and serotonin, respectively. Vasoconstriction was measured with the use of high-frequency ultrasonic imaging.The maximal vasoconstriction of the control segment was 37.7% ± 2.6 with rabbit aortae and 36.3% ± 4.1 with dog carotid arteries, while the average maximal constriction for all segments in which stents were placed was 5.7% ± 1.1 (P < .01). The maximal constriction of the Gianturco-Roubin stainless steel stent was 9.4% ± 2.7 versus 7.9% ± 1.6 with the tantalum version (P = .65). Both designs showed somewhat greater constriction compared with either the Palmaz-Schatz (3.3% ± 0.9) or the CV Rad (1.4% ± 1.1) stents.Although all of the stents tested substantially resist arterial vasoconstrictive forces, the Palmaz-Schatz and CV Rad stents resist vasoconstriction to a greater degree than the Gianturco-Roubin stents. Tantalum and stainless steel stents of the same design (Gianturco-Roubin) appear similar in their ability to resist vasoconstrictive forces.

Deformation of a Transapical Aortic Valve After Cardiopulmonary Resuscitation: A Potential Risk of Stainless Steel Stents

![Figure][1] [![Graphic][3] ][3] We show autopsy images of a deformed Edwards Sapien XT (Edwards Lifesciences Corp., Irvine, California) valve from a patient requiring cardiopulmonary resuscitation (CPR) 5 days after uneventful transapical valve implantation. Postoperative

How to design the optimal self-expandable oesophageal metallic stents: 22 years of experience in 645 patients with malignant strictures

To evaluate the clinical efficacy and safety of self-expandable metallic stent (SEMS) placement for malignant oesophageal strictures and their relationship with stent designs. Seven generations of SEMS were used to treat 645 consecutive patients with oesophageal strictures. Logistic regression models were constructed to identify predictive factors associated with complications. Stent placement was technically successful in 641 of 645 patients (99.4%). The clinical success rate was 95.5%. There were 260 (40.3%) complications after stent placement. Due to complications, 68 stents were removed; 66 of 68 stents (97.1%) were removed successfully. Stainless steel (SS) stents (odds ratio [OR] 4.18; 95% confidence interval [CI] 2.10, 8.32) and radiation therapy (RT) before stent placement (OR 4.23; CI 2.02, 8.83) were significantly associated with severe pain. Flared ends (OR 9.63; CI 3.38, 27.43), stricture length <6 cm (OR 2.01; CI 1.13, 3.60), and a stent diameter <18 mm (OR 3.00; CI 1.32, 6.84) were predictive factors of stent migration. Polyurethane membranes were associated with more frequent tumour ingrowth than polytetrafluoroethylene (PTFE) membranes (P = 0.002). Despite the relatively high complication rate, retrievable self-expandable PTFE-covered nitinol stents equipped with a head and a tail appeared to be an effective treatment for malignant oesophageal strictures.

Fabrication of biofunctional stents with endothelial progenitor cell specificity for vascular re-endothelialization

Endothelial progenitor cells (EPCs) have been identified as a crucial factor for re-endothelialization after stenting, resulting in the prevention of stent thrombosis and neointimal hyperplasia. Because EPCs can be introduced by antibody–antigen interactions, the suitable choice of antibody and the biocompatible surface modification technology including antibody immobilization are essential for developing an EPC-capturing stent. In this study, we fabricated a biofunctional stent with EPC specificity by grafting a hydrophilic polymer and consecutively immobilizing the antibody against vascular endothelial cadherin (VE-cadherin) which is one of the specific EPC surface markers. The surface of a stainless steel stent was sequentially modified by acid-treatment, silanization and covalent attachment of polymers not only to improve biocompatibility but also to introduce functional groups on the stent surface. The surface-modified stent immobilized anti-VE-cadherin antibodies, and the EPCs were remarkably captured whereas THP-1s, human acute monocytic leukemia cells, were not adsorbed on the stent. Furthermore, we confirmed that the recruited EPCs developed the endothelial cell layers on the antibody-conjugated stent. These positive in vitro results will encourage the extensive application of biofunctional surface modification technology for a variety of medical devices.

Comparison of endothelialization and neointimal formation with stents coated with antibodies against CD34 and vascular endothelial-cadherin

Vascular endothelial-cadherin (VE-cadherin) is exclusively expressed on the late endothelial progenitor cells (EPC). Therefore, VE-cadherin could be an ideal target surface molecule to capture circulating late EPC. In the present study, we evaluated whether anti-VE-cadherin antibody-coated stents (VE-cad stents) might accelerate endothelial recovery and reduce neointimal formation more than anti-CD34 antibody-coated stents (CD34 stents) through the superior ability to capture the late EPC. The stainless steel stents were coated with anti-human VE-cadherin antibodies or anti-human CD34 antibodies under the same condition. In vitro, VE-cad stents showed higher number of adhering EPC (823.6 ± 182.2 versus 379.2 ± 137.2 cells per HPF, p < 0.001). VE-cad stents also demonstrated better specific capturing of cells with endothelial lineage markers than CD34 stents did in flow cytometric analysis. VE-cad stents showed more effective re-endothelialization after 1 h, 24 h, and 3 days in vivo. At 42 days, VE-cad stents demonstrated significantly smaller neointima area (0.92 ± 0.38 versus 1.24 ± 0.41 mm2, p = 0.002) and significantly lower PCNA positive cells in neointima (1684.8 ± 658.8/mm2 versus 2681.7 ± 375.1/mm2, p = 0.008), compared with CD34 stents. In conclusion, VE-cad stents captured EPC and endothelial cells more selectively in vitro, accelerated re-endothelialization over stents, and reduced neointimal formation in vivo, compared with CD34 stents.

Reocclusion caused by stent fracture implanted in the subclavian artery ostium: a case report

A 47year-old male, a woodcutter by profession, complained of severe pain in the left arm during physical stress. Eighteen months ago, a balloon-expandable stainless steel stent had been implanted in the left subclavian artery ostium. The angiography revealed a stent fracture at the origin of the left subclavian artery, this condition led to a re-obstruction of the stent. After the insertion of a self-expandable Nitinol stent, the side differences of arterial pressure and the symptoms disappeared. This is the first reported case of a stent fracture inserted at the origin of the subclavian artery without severe calcification.

Assessment of a transcatheter heart valve prosthesis with multidetector computed tomography: in vitro and in vivo imaging characteristics

Multidetector-row computed tomography (MDCT) image quality (IQ) of the commonly implanted Sapien prosthesis was assessed both in vitro and in vivo. The prosthesis was imaged in an in vitro model with a 256-slice CT system under pulsatile conditions using three protocols (1) retrospectively ECG-gating at 120 kV/600 mAs and (2) 140 kV/406 mAs, and (3) prospective triggering at 120 kV/210 mAs (10 acquisitions per protocol). After reconstruction in three perpendicular planes, IQ of the supra-,peri-,sub-,and intraprosthetic as well as leaflet regions was scored on a four-point scale (1 = non-diagnostic, 2 = moderate, 3 = good and 4 = excellent) by two observers. IQ was also assessed for twenty-one post-operative scans. The in vitro scans of the two retrospective protocols and twenty-one in vivo scans were analyzed during systole and diastole. The prospectively triggered scans were analyzed during diastole. Except for the valve leaflets in 5 systolic reconstructions, the in vitro scores were moderate to excellent. In vivo, 7 systolic and 3 diastolic reconstructions of the valve leaflets were non-diagnostic as well as 3 peri-prosthetic regions in diastole. All other scores were moderate to excellent. The Sapien prosthesis surrounded by a radiopaque stainless steel stent can be visualized with MDCT with moderate to good IQ, except for the valve leaflet region that has generally non-diagnostic or moderate IQ.

Mussel‐Inspired Coating of Polydopamine Directs Endothelial and Smooth Muscle Cell Fate for Re‐endothelialization of Vascular Devices

Polydopamine (PDAM), a mussel adhesive protein inspired coating that can be easily deposited onto a wide range of metallic, inorganic, and organic materials, gains interest also in the field of biomaterials. In this work, PDAM is applied as coating on 316L stainless steel (SS) stents and the response of cells of the blood vessel wall, human umbilical vein endothelial cell (HUVEC), and human umbilical artery smooth muscle cell (HUASMC) as predictors for re-endothelialization is tested. It is found that the PDAM-modified surface significantly enhances HUVEC adhesion, proliferation, and migration, release of nitric oxide (NO), and secretion of prostaglandin I(2) (PGI(2) ). Additionally, the PDAM-modified surface shows a remarkable ability to decrease the adhesion and proliferation of HUASMCs. As a blood-contacting material, the PDAM tends to improve the hemocompatibility compared with the substrate 316L SS. It is noteworthy that the PDAM coating shows good resistance to the deformation behavior of compression and expansion of a stent. These data suggest the potential of PDAM as a blood-contacting material for the application in vascular stents or grafts.

Impact of Parallel Micro-Engineered Stent Grooves on Endothelial Cell Migration, Proliferation, and Function

Stent luminal surface characteristics influence surface endothelialization. We hypothesize that luminal stent microgrooves created in the direction of coronary flow accelerate endothelial cell migration, resulting in lower levels of neointimal formation. Surface coverage efficiency was evaluated in vitro by allowing human aortic endothelial cells (HAEC) to migrate onto microgrooved (G) or smooth (NG) surfaces. HAEC functionality was assessed by proliferation rate, apoptosis rate, nitric oxide production, and inflammatory markers TNF-α and VCAM-1 expression. Early endothelialization and restenosis studies were performed using the porcine coronary injury model. Stainless steel stents of identical design with (GS) and without (NGS) luminal microgrooves were used. The commercially available Multi-Link Vision (MLVS) stent of identical design was used as a control. The degree of GS and NGS surface endothelialization was compared at 3 days. Biocompatibility and tissue response outcomes were evaluated at 28 days. The in vitro study demonstrated that at 7 days the presence of surface microgrooves increased HAEC migration distance >2-fold. Cell proliferation rate and nitric oxide production were increased and apoptosis rate was decreased. There was no difference in inflammatory marker expression. At 3 days, coronary artery stent endothelialization was significantly increased in GS compared with NGS (81.3% versus 67.5%, P=0.0002). At 28 days, GS exhibited lower neointimal thickness compared with either NGS (21.1%, P=0.011) or MLVS (40.8%, P=0.014). Parallel microgrooves on coronary stent luminal surfaces promote endothelial cell migration and positively influence endothelial cell function, resulting in decreased neointimal formation in the porcine coronary injury model.

Fatigue life assessment of cardiovascular balloon-expandable stents: A two-scale plasticity–damage model approach

Cardiovascular disease has become a major global health care problem in the present decade. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, as a result of the high number of cyclic loads these devices are subjected to in vivo, numerical approaches for fatigue life assessment of stents has gained special interest in the engineering community. Numerical fatigue predictions can be used to modify the design and prevent failure, without making and testing numerous physical devices, thus preventing from undesired fatigue failures. This work presents a fatigue life numerical method for the analysis of cardiovascular balloon-expandable stainless steel stents. The method is based on a two-scale continuum damage mechanics model in which both plasticity and damage mechanisms are assumed to take place at a scale smaller than the scale of the representative volume element. The fatigue failure criterion is based on the Soderberg relation. The method is applied to the fatigue life assessment of both PalmazShatz and Cypher stent designs. Validation of the method is performed through comparison of the obtained numerical results with some experimental results available for the PalmazShatz stent design. The present study gives also possible directions for future research developments in the framework of the numerical fatigue life assessment of real balloon-expandable stents.

Endothelial Progenitor Cell Capture Stent: Safety and Effectiveness

The endothelial progenitor cell (EPC) capture stent is an innovative device that makes use of the ability of bone marrow-derived EPCs to migrate to injured arterial segments to facilitate healing. The EPC antibody surface, consisting of a covalently coupled polysaccharide intermediate coating with anti-human CD34 antibodies, is attached to a stainless steel stent. Upon stent placement, the anti-human CD34 antibodies will attract circulating EPCs, which are expected to develop into mature functional endothelium. This accelerated healing strategy aims to lower the risk of restenosis and stent thrombosis, as well as obviate prolonged dual antiplatelet therapy. Since the first-in-man study in 2003, a number of small-to-medium size registry and postmarketing studies that confirmed the good safety profile of the EPC capture stent have been published. However, due to lack of large-scale randomized trials, its effectiveness, compared with bare metal stents and drug-eluting stents, cannot be ascertained. Based on restudy angiographic data, instent late loss was approximately 0.7-0.9 mm, which compares unfavorably with that of drug-eluting stents. In order to improve the effectiveness of the EPC capture stent in reducing restenosis--while maintaining its pro-healing property--a bioengineered sirolimus-eluting stent known as the Combo stent was recently designed to combine the EPC capture technology with the abluminal elution of sirolimus. Data from animal studies have been encouraging. The first-in-man study of the Combo stent has been completed and results were presented.

Micromechanical methodology for fatigue in cardiovascular stents

A finite element based micromechanical methodology for cyclic plasticity and fatigue crack initiation in cardiovascular stents is presented. The methodology is based on the combined use of a (global) three-dimensional continuum stent-artery model, a local micromechanical stent model, the development of a combined kinematic–isotropic hardening crystal plasticity constitutive formulation, and the application of microstructure sensitive crack initiation parameters. The methodology is applied to 316L stainless steel stents with random polycrystalline microstructures, based on scanning electron microscopy images of the grain morphology, under realistic elastic–plastic loading histories, including crimp, deployment and in vivo systolic–diastolic cyclic pressurisation. Identification of the micromechanical cyclic plasticity and failure constants is achieved via application of an objective function and a unit cell representative volume element for 316L stainless steel. Cyclic stent deformations are compared with the J2-predicted response and conventional fatigue life prediction techniques. It is shown that micromechanical fatigue analysis of stents is necessary due to the significant predicted effects of material inhomogeneity on micro-plasticity and micro-crack initiation.