316L Stainless Steel Stents Research Articles

Corrosion resistance improvement for 316L stainless steel coronary artery stents by trimethylsilane plasma nanocoatings.

To improve their corrosion resistance and thus long-term biocompatibility, 316L stainless steel coronary artery stents were coated with trimethylsilane (TMS) plasma coatings of 20-25 nm in thickness. Both direct current (DC) and radio-frequency (RF) glow discharges were utilized for TMS plasma coatings and additional NH₃/O₂ plasma treatment to tailor the surface properties. X-ray photoelectron spectroscopy (XPS) was used to characterize the coating surface chemistry. It was found that both DC and RF TMS plasma coatings had Si- and C-rich composition, and the O- and N-contents on the surfaces were substantially increased after NH₃/O₂ plasma treatment. Surface contact angle measurements showed that DC TMS plasma nanocoating with NH₃/O₂ plasma treatment generated very hydrophilic surface. The corrosion resistance of TMS plasma coated stents was evaluated through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The potentiodynamic polarization demonstrated that the TMS plasma coated stents imparted higher corrosion potential and pitting potential, as well as lower corrosion current densities as compared with uncoated controls. The surface morphology of stents before and after potentiodynamic polarization testing was analyzed with scanning electron microscopy, which indicated less corrosion on coated stents than uncoated controls. It was also noted that, from EIS data, the hydrophobic TMS plasma nanocoatings showed stable impedance modulus at 0.1 Hz after 21 day immersion in an electrolyte solution. These results suggest improved corrosion resistance of the 316L stainless steel stents by TMS plasma nanocoatings and great promise in reducing and blocking metallic ions releasing into the bloodstream.

GW24-e1819 Experiment of cellular repressor of E1A-stimulated genes (CREG) delivery via nanoporous stent in a porcine coronary mode

ObjectivesIn this study we investigate the In vitro pharmacokinetic of nanoporous CREG eluting-stent (CREGES) and evaluate the efficacy and safety of nanoporous CREGES in inhibiting neointima proliferation in porcine coronary...

Finite Element Model and Fluid-Structure Interaction Analysis of the Intravascular Stent

The 316L stainless steel stent was analyzed about the effect on interaction with plaque and vessels and blood flow during and after implantation using finite element method (FEM) and computational fluid dynamics (CFD). The results showed that tilted ends are likely to damage the intima which may stimulate thrombus formation and neointimal hyperplasia and will cause the restenosis. Stagnant zones formed by the stent may cause the backflow phenomenon, which also contribute to the important elements of in-stent restenosis (ISR).

In vitro study on the feasibility of magnetic stent hyperthermia for the treatment of cardiovascular restenosis

Thermal treatment or hyperthermia has received considerable attention in recent years due to its high efficiency, safety and relatively few side-effects. In this study, we investigated whether it was possible to utilize targeted thermal or instent thermal treatments for the treatment of restenosis following percutaneous transluminal coronary angioplasty (PTCA) through magnetic stent hyperthermia (MSH). A 316L stainless steel stent and rabbit vascular smooth muscle cells (VSMCs) were used in the present study, in which the inductive heating characteristics of the stent under alternative magnetic field (AMF) exposure, as well as the effect of MSH on the proliferation, apoptosis, cell cycle and proliferating cell nuclear antigen (PCNA) expression of the rabbit VSMCs, were evaluated. The results demonstrated that 316L stainless steel coronary stents possess ideal inductive heating characteristics under 300 kHz AMF exposure. The heating properties were shown to be affected by the field intensity of the AMF, as well as the orientation the stent axis. MSH had a significant effect on the proliferation and apoptosis of VSMCs, and the effect was temperature-dependent. While a mild temperature of 43°C demonstrated negligible effects on the growth of VSMCs, MSH treatment above 47°C effectively inhibited the VSMC proliferation and induced apoptosis. Furthermore, a 47°C treatment exhibited a significant and long-term inhibitory effect on VSMC migration. The results strongly suggested that MSH may be potentially applied in the clinic as an alternative approach for the prevention and treatment of restenosis.

Surface Modification of Coronary Stents for Intravascular Gene Delivery

The present study investigated a novel surface modification on metal coronary stent for antibody immobilization. Methods: 316L stainless steel stents were surface modified with protein coatings. An Anti-DNA antibody was covalently bound to the protein surface using a bi-functional cross-linking agent SPDP. The artwork and binding stability of protein coatings were evaluated by in-vitro eluting. The feasibility and stability of anti-DNA antibody covalently bound to the stent were evaluated by means of 125I labeling. Results: We observed that pre-treating the steel surface using diluted HCL and increasing the ratio of cross-linking agent caused significantly increased binding stability of the protein coatings (p﹤0.001). The amount of chemically coupled antibody on the stents was 8 times higher than that of physically absorbed control stents. The stability of chemically coupled antibody on the stent was significantly better than physically absorbed control. Conclusion: It is concluded that we optimized the technique of protein coating on stainless steel and achieved stable anti-DNA antibody immobilization, therefore enabled efficient and highly localized non-viral gene delivery.

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.

<i>In Vitro</i> 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.

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.

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.

Mesenchymal stem cell seeding promotes reendothelialization of the endovascular stent

This study is designed to make a novel cell seeding stent and to evaluate reendothelialization and anti-restenosis after the stent implantation. In comparison with cell seeding stents utilized in previous studies, Mesenchymal stem cells (MSCs) have advantages on promoting of issue repair. Thus it was employed to improve the reendothelialization effects of endovascular stent in present work. MSCs were isolated by density gradient centrifugation and determined as CD29(+) CD44(+) CD34(-) cells by immunofluorescence and immunocytochemistry; gluten and polylysine coated stents were prepared by ultrasonic atomization spray, and MSCs seeded stents were made through rotation culture according to the optimized conditions that were determined in previous studies. The results from animal experiments, in which male New Zealand white rabbits were used, show that the reendothelialization of MSCs coated stents can be completed within one month; in comparison with 316L stainless steel stents (316L SS stents) and gluten and polylysine coated stents, the intimal hyperplasia and in-stent restenosis are significantly inhibited by MSCs coated stents. Endovascular stent seeded with MSCs promotes reendothelialization and inhibits the intimal hyperplasia and in-stent restenosis compared with the 316L SS stents and the gluten and polylysine coated stents.

Corrosion Resistance of Ti-O Film Modified 316L Stainless Steel Coronary Stents In Vitro

This article dealt with improving corrosion resistance of stent modified using Ti-O film. Ti-O films of various thicknesses were grown on the surface of 316L stainless steel (SS) stents by metal vacuum arc source deposition technology, and the phase composition, the thickness and the adhesion between films and substance were investigated by micro-x-ray diffraction (Micro-XRD), surface profilometer, and scanning electron microscopy (SEM) separately. The corrosion resistance of modified stent was assessed by polarization test in phosphate buffered solution (37 ± 1 °C). The result shows that the Ti-O films were very smooth and uniform. There were not any cracks and delaminations after dilation by angioplasty, the adhesion between Ti-O film and stent is satisfactory. The open circuit potential (OCP) of the Ti-O film modified stents was higher than that of the bare stents; it shows that the electrochemical stability of modified stents was more than bare stents. The polarization test result indicates that the passivation stability and anti-breakdown performance of Ti-O film stents had better than bare stents, and no pitting was observed on the surface of both modified stents, but the local film striations were found on the stent surface of the thicker film, which indicated that the Ti-O film stents with certain thickness has good corrosion resistance.

In vitro biocompatibility of plasma-aided surface-modified 316L stainless steel for intracoronary stents

316L-type stainless steel is a raw material mostly used for manufacturing metallic coronary stents. The purpose of this study was to examine the chemical, wettability, cytotoxic and haemocompatibility properties of 316L stainless steel stents which were modified by plasma polymerization. Six different polymeric compounds, polyethylene glycol, 2-hydroxyethyl methacrylate, ethylenediamine, acrylic acid, hexamethyldisilane and hexamethyldisiloxane, were used in a radio frequency glow discharge plasma polymerization system. As a model antiproliferative drug, mitomycin-C was chosen for covalent coupling onto the stent surface. Modified SS 316L stents were characterized by water contact angle measurements (goniometer) and x-ray photoelectron spectroscopy. C1s binding energies showed a good correlation with the literature. Haemocompatibility tests of coated SS 316L stents showed significant latency (t-test, p < 0.05) with respect to SS 316L and control groups in each test.

A.R.T.: concept of a bioresorbable stent without drug elution

Why bioresorbable stents? More than 20 years ago, interventional cardiology was launched by Andreas Gruntzig, introducing a revolutionary innovation, i.e., percutaneous balloon angioplasty1. The 316L stainless steel stent was initially introduced to tackle acute closure secondary to dissections following balloon angioplasty. In fact, the stent not only resolved the acute complications, but also appeared to be the appropriate response to the midterm complication, i.e., restenosis2,3. Indeed, the principal mechanism of restenosis after balloon angioplasty appeared to be related to chronic constrictive remodelling as a negative component of the healing process4-6. Nevertheless, the permanent (316L stainless steel) stent was the origin of a new disease, in-stent restenosis, corresponding to a foreign body reaction. Drug eluting stents were conceived to skip this particular healing process via cell cycle-inhibiting drugs in order to prevent in-stent restenosis. However, these drugs were cytotoxic, not only against smooth muscle cells, but also endothelial cells leading to late stent thrombosis and/or restenosis7,8. So, by inhibiting this inescapable healing process, we have delayed the occurrence of complications. The approach of Arterial Remodelling Technologies (A.R.T.) is to consider that the error resides in the discrepancy between the healing duration (i.e., a few months) and the immortal half life of the metallic stent, the source of new complications when it is no longer necessary: the bioresorbable stent acts as a transitory cast, scaffolding the artery wall during the healing process. Moreover, the healing process will induce endothelial coverage, a mandatory step for the midand long-term follow-up that will simplify one of the issues of drug eluting stents, i.e., expensive and prolonged dual antiplatelet therapy reducing the quality of life. The degradation of the bioresorbable stent will result in stent fragmentation, stopping the perpetual mechanico-genic stimulus produced by the stent’s overstretching of the arterial wall after the healing process. This can then restore the remodelling capacities of the artery wall itself, thus preserving its future, avoiding a growing accumulation of metal in the arteries9,10. Last but not least, the bioresorbable stent will not impair vasomotion after healing, namely at its extremities.

XPS, AES, and Electrochemical Study of Iridium Oxide Coating Materials for Cardiovascular Stent Application

The surface composition and morphology of iridium oxide (IrO2) coatings prepared by a multi-step physical vapor deposition process on 316L stainless steel stent substrates has been investigated by XPS, AES, and FESEM. The obtained data show that even though the morphologies of iridium oxide films produced within the examined range of PVD process parameters are almost identical, there is a difference in their surface composition, in particular in the ratios of Ir-O σ and Ir=O π bonds. A correlation between the surface stoichiometries of the IrO2 films and their electrochemical CV and EIS responses has been established. The observed differences in the O 1s photoemission line shape of the investigated iridium oxide films were strikingly reflected in their voltammetric curve features. The implication of these finding on the mechanism of the catalytic decomposition of hydrogen peroxide by IrO2 is discussed.

Electrochemical and SEM Characterization of Gold-Coated Stents In Vitro

The inert properties of gold make it a useful material for implants. Gold was applied as a coating on 316L stainless steel stents to improve the radiopacity and to provide better thrombogenic resistance and a lower degree of restenosis after deployment. Reports of clinical trials using gold-coated stents showed controversial results. A detailed examination of gold-coated stents was designed to understand the influence of surface conditions on the electrochemical properties in vitro. Corrosion resistance of gold-coated stents was investigated by cyclic polarization, and potentiostatic control. Surface morphologies of gold-coated stents in as-received condition, postinflated condition, and after cyclic polarization were characterized by scanning electron spectroscopy (SES). X-ray mapping identified elemental distribution. Results found severe defects in the gold-coating in the as-received condition, cracks and wrinkles on inflated gold-coated stents, and severe corrosion after cyclic polarization. Leaching of metallic ions in Ringer’s solution was possible.

Drug-Eluting Stent-Induced Left Anterior Descending Coronary Artery Aneurysm: Repair by Pericardial Patch—Where Are We Headed?

Deployment of drug-eluting stents has been associated with late thrombosis and restenosis on withdrawal of antiplatelet agents. We report a complication of inflammation and localized coronary artery aneurysms immediately adjacent to the stent after 4 years of implantation. Late chronic inflammatory responses may evolve for up to 4 years after sirolimus-eluting stent implantation and can cause weakening, erosion, and aneurysms of the coronary arteries.

Preparation, characterization and anticoagulation of curcumin-eluting controlled biodegradable coating stents

Curcumin is pharmaceutically active in many ways, having properties including anticoagulation, anti-proliferation, anti-inflammatory, and may be used to fabricate drug-eluting stents to treat in-stent restenosis after stent implantation. Here we describe our investigations of curcumin-eluting PLGA coatings formed using the biodegradable polymer PLGA (polylactic acid-co-glycolic acid) as drug carrier and uniformly fabricated on the surface of 316L stainless steel stents by an ultrasonic spray method. Three doses were explored — low dose (∼ 140 μg per stent or 115 μg/cm 2), moderate dose (∼ 280 μg per stent or 230 μg/cm 2), and high dose (∼ 490 μg per stent or 408 μg/cm 2). Pre- and post-expansion morphologies of the stent coating were examined by optical microscopy (OM) and scanning electron microscopy (SEM), indicating that the coating not only was very smooth and uniform but also had the ability to withstand the compressive and tensile strains imparted without cracking from the stent during the expansion process. Atomic force microscopy (AFM) images indicated the topography of the PLGA-only and moderate dose curcumin-eluting stent that showed an average roughness below 1 nm; no drug particles could be seen on the stent surface, indicating that curcumin can be mixed with PLGA at the molecular level using an ultrasonic atomization spray method. The structure of the coating films was characterized by Fourier Transform Infrared (FTIR) spectroscopy and X-ray electron spectroscopy (XPS), with results suggesting that there was no chemical reaction between curcumin and the drug. The results of in vitro measurements of drug release from curcumin-eluting stents showed that all the curcumin-eluting stents studied exhibited a nearly linear sustained-release profile with no significant burst releases within the measurement period. The in vitro anticoagulation behavior of curcumin-eluting stents was investigated by static platelet adhesion and APTT (activated partial thromboplastin time) tests, revealing that the anticoagulation properties of curcumin-eluting stents are superior to those for stainless steel stents and PLGA-only-coated stents. The anticoagulation behavior of curcumin stents improved significantly as the drug dose was increased.

Stability of passivated 316L stainless steel oxide films for cardiovascular stents

Passivated 316L stainless steel is used extensively in cardiovascular stents. The degree of chloride ion attack might increase as the oxide film on the implant degrades from exposure to physiological fluid. Stability of 316L stainless steel stent is a function of the concentration of hydrated and hydrolyated oxide concentration inside the passivated film. A high concentration of hydrated and hydrolyated oxide inside the passivated oxide film is required to maintain the integrity of the passivated oxide film, reduce the chance of chloride ion attack, and prevent any possible leaching of positively charged ions into the surrounding tissue that accelerate the inflammatory process. Leaching of metallic ions from corroded implant surface into surrounding tissue was confirmed by the X-ray mapping technique. The degree of thrombi weight percentage [W(ao): (2.1 +/- 0.9)%; W(ep): (12.5 +/- 4.9)%, p < 0.01] between the amorphous oxide (AO) and the electropolishing (EP) treatment groups was statistically significant in ex-vivo extracorporeal thrombosis experiment of mongrel dog. The thickness of neointima (T(ao): 100 +/- 20 microm; T(ep): 500 +/- 150 microm, p < 0.01) and the area ratio of intimal response at 4 weeks (AR(ao): 0.62 +/- 0.22; AR(ep): 1.15 +/- 0.42, p < 0.001) on the implanted iliac stents of New Zealand rabbit could be a function of the oxide properties.

Iliac Anastomotic Stenting With a Biodegradable Poly-L-Lactide Stent: A Preliminary Study After 1 and 6 Weeks

To assess the technical feasibility, thrombogenicity, and biocompatibility of a new biodegradable poly-L-lactic acid (PLLA) anastomotic stent. A polytetrafluoroethylene bifurcated graft was implanted in 17 pigs through a midline abdominal incision. After transverse graft incision, 17 316L stainless steel stents and 17 PLLA stents were randomly implanted at both iliac anastomotic sites and deployed with a 6-mm balloon under direct vision without angiography. Intended follow-up was 1 week in 6 pigs receiving oral acetylsalicylic acid (ASA) and in 7 pigs receiving ASA/clopidogrel; 4 pigs receiving ASA/clopidogrel were followed for 6 weeks. At the end of the study, the segments containing the stents were surgically explanted and processed for histology to measure the mean luminal diameter, intimal thickness, and the vascular injury and inflammation scores. Initial technical success of stent placement was achieved in all animals without rupture of the suture. Two pigs died (unrelated to the stent) at 3 days after operation (1 in groups A and B). At 1 week, all PLLA stents showed thrombotic occlusion with the use of ASA alone. In contrast, all PLLA stents remained patent with concurrent administration of ASA/clopidogrel. All metal stents were patent regardless of the antiplatelet regimen. The mean luminal diameter of patent PLLA stents (4.13+/-0.17 mm) was comparable to metal stents (4.27+/-0.35 mm, p=0.78) at 1 week, but significantly diminished at 6 weeks (3.21+/-0.44 versus 4.19+/-0.18 mm, p=0.005). Histological analysis showed no signs of excessive recoil. PLLA stents induced a higher inflammation score (1.79+/-0.56) and more intimal hyperplasia (0.34+/-0.11 mm) compared to metal stents [1.27+/-0.44 mm (p<0.001) and 0.18+/-0.04 mm (p=0.006), respectively] at 6 weeks. Vascular injury was comparable between PLLA and metal stents. Biodegradable PLLA stents showed higher thrombogenicity and reduced patency compared to metal stents during early follow-up. Although ASA and clopidogrel prevented thrombotic occlusion, the increased inflammatory response and neointima formation remain major concerns of PLLA stents. A solution to this problem might be the incorporation of anti-inflammatory drugs into the PLLA stent.

Estudo da resposta tissular à endoprótese recoberta de jugular bovina em veia cava inferior de suínos

OBJETIVO: Avaliar a resposta tissular a uma endoprótese, com cobertura biológica heteróloga, implantada em veia cava inferior de suínos. MÉTODO: Desenvolvemos uma endoprótese auto-expansível, revestida com um segmento de jugular bovina, conservada por processo L-hydro e suturada em um stent de aço inoxidável 316L. O dispositivo introdutor utilizado foi a bainha de liberação da endoprótese aórtica Taheri-Leonhardt (Flórida, EUA). Foram implantadas endopróteses em 10 suínos, todas na veia cava infra-renal. Os animais foram submetidos à flebografia peroperatória. À necropsia, após 2 meses, cada endoprótese foi retirada em bloco e analisada macroscopicamente, visando a avaliação da perviedade, aderência aos tecidos vizinhos e incorporação à parede venosa; e, histopatologicamente, visando a resposta histológica ao enxerto. RESULTADOS: Na análise macroscópica, todas as endopróteses encontravam-se pérvias e totalmente incorporadas à parede venosa, porém seis apresentavam trabeculações grosseiras no seu interior e quatro algum grau de fibrose perivascular. Três animais desenvolveram linfocele, uma retroperitoneal e as outras na parede abdominal. No estudo histopatológico, observamos reação inflamatória granulomatosa tipo corpo estranho em todos os casos, sendo predominante na camada média (80%). CONCLUSÃO: O modelo estudado apresentou baixa trombogenicidade, corroborando com a eficácia do meio de conservação e material escolhidos; porém, baixa biocompatibilidade, provavelmente pelo obstáculo imunológico dos xenoenxertos e resposta tissular exagerada do território venoso.