Alloy Stent Research Articles

Optimal Use of Temporary Clip Application during Aneurysm Surgery - In Search of the Holy Grail.

Temporary clips are invaluable safety tools during the clipping of an aneurysm. Controversies regarding maximum permissible duration and safety, however, remain unanswered. This descriptive narrative attempts to review the literature to provide valuable insights on controversies clouding the use of temporary clips among neurosurgeons. Popular databases, including Pub Med, Medline/Medscape, Scopus, Cochrane, Embase, Google Scholar, were searched to find available literature on temporary clips. The searched MeSH terms were “Temporary Clip,” “Temporary Clipping,” “Cerebral Aneurysm,” and “Aneurysm.” Temporary clips have been in use since 1928 and have undergone considerable structural and technical modifications. A temporary clip's optimal safety limit is not yet defined with literature evidence ranging from immediate to 93 min. It is not yet definite whether temporary clips application aggravates vasospasm, but emergency temporary clips application, especially in poor-grade aneurysmal subarachnoid hemorrhage patients, is associated with poor outcomes. A temporary clip needs to be applied with caution in patients treated earlier by endovascular technique and having indwelling stents. Nitinol Stent is feasible, while a Cobalt-Chromium alloy stent does not get occluded and gets deformed under the closing pressure of a temporary clip. Although a temporary clip application is a fundamental strategy during the clipping of an aneurysm; the exact safe duration remains to be decided in randomized control trials. Their utility for the shorter duration is beneficial under un-conclusive evidence of neuroprotective agents and intraoperative monitoring. Neurosurgeons need to consider all aspects of their pros and cons for optimal use.

Magnesium alloy stents: A friend or foe of coronary in-stent restenosis?

Coronary artery disease (CAD) is regarded as the principal cause of cardiovascular diseases and one of the leading causes of mortality. In order to alleviate the risk of CAD, percutaneous coronary intervention (PCI) and stent implantation have recently been applied. In particular, Mg alloy (Mg-alloy) stents (MAS) have been used as clinical routine for the treatment of CAD. However, emerging evidence suggests that this treatment strategy is substantially associated with coronary in-stent restenosis (ISR), which remains the main cause of unintentional and repeat drug-eluting stent (DES) interventions in the United States. In this regard, understanding of MAS as friend or foe of ISR treatment is needed to establish the exact mechanism underlying this condition. This mini review therefore aimed to provide an integrated view on the existing findings of the relationship between MAS and ISR. The understanding of MAS as either a friend or foe is crucial for the management of ISR, which is reported to be very challenging amidst lack of effective therapeutic options.

The biological responses and mechanisms of endothelial cells to magnesium alloy.

Due to its good biocompatibility and degradability, magnesium alloy (Mg alloy) has shown great promise in cardiovascular stent applications. Rapid stent re-endothelialization is derived from migrated and adhered endothelial cells (ECs), which is an effective way to reduce late thrombosis and inhibit hyperplasia. However, fundamental questions regarding Mg alloy affecting migration and adhesion of ECs are not fully understood. Here, we evaluated the effects of Mg alloy on the ECs proliferation, adhesion and migration. A global gene expression profiling of ECs co-culturing with Mg alloy was conducted, and the adhesion- and migration-related genes were examined. We found that Mg alloy had no adverse effects on ECs viability but significantly affected ECs migration and adhesion. Co-cultured with Mg alloy extract, ECs showed contractive adhesion morphology and decreased motility, which was supported by the down-regulation of adhesion-related genes (Paxillin and Vinculin) and migration-related genes (RAC 1, Rho A and CDC 42). Accordingly, the re-endothelialization of Mg alloy stent was inhibited in vivo. Our results may provide new inspiration for improving the broad application of Mg alloy stents.

Finite element modeling of shape memory alloy stent insertion in the vessel with consideration of vessel damage

One of the common methods to resolve artery stenosis is the insertion of a shape memory alloy stent in the artery. The use of shape memory alloys in the manufacturing of self-expandable stent has expanded because of the superelastic behavior of this alloy. In this paper, we simulated a shape memory alloy stent insertion in an artery to explore stress and damage effects arising from the stent insertion on the artery by using ABAQUS software. To simulate the mechanical behavior of artery, we considered the effect of the inelastic arterial properties (stress softening and recoverable inelastic deformation) that activated under supraphysiological loading in the stenting process, and to simulate stent behavior, the Souza model is used. These two models were applied in ABAQUS by UMAT codes. By using the damage model, the amount of damage in the artery, which is one of the factors of restenosis, is investigated. Also, in this paper, we have used real diseased artery geometry, which was specified from high-resolution magnetic resonance images, therefore the analysis is more in line with reality and it is possible to determine the location of the maximum stress and damage in the artery.

Damage evolution of biodegradable magnesium alloy stent based on configurational forces

Magnesium alloy has attracted most of the recent attention as a candidate for stent material due to their biocompatible and biodegradable nature. However, their corrosion behavior in the human body is still a major issue in research today. In this paper, a strategy to simulate damage evolution in biodegradable magnesium alloy stent is given by introducing a configurational damage model. In the framework of continuum thermodynamics, one can characterize the development and evolution of local damage of materials by establishing internal variables in phenomenological method. We believe that corrosion can damage alloy in two different ways: surface corrosion and stress corrosion. Surface corrosion is described using uniform damage, when the structure is exposed in a corrosion environment; Configurational force is used to describe stress corrosion when the structure is exposed in a stimulating environment. We then select global damage and radial resistance force to perform the changes of macroscopic mechanical properties during stent degradation. Finally, the well performance of the proposed model is demonstrated through several numerical examples. This model has the potential to assist stent design and development in the future.

Computational Modeling of the Corrosion Process and Mechanical Performance of Biodegradable Stent

Magnesium alloy stents have drawn increasing research interest in recent years owing to their biodegradable behaviors. As dissolved by corrosion, mass of the magnesium alloy stents decreases with time, allowing mechanical load to gradually transfer to the surrounding tissues. This work aimed to develop a numerical model based on Continuum Damage Mechanics (CDM) combining pitting corrosion and stress corrosion crack to better predict the degradation behavior of biodegradable magnesium alloy stent. It was applied in coronary stents through finite element method compared with the use of single pitting corrosion model. The results indicated that addition of stress corrosion attack accelerated the degradation rate and support performance loss of stent compared with single pitting corrosion. The proposed model would bring new sights to simulation and serve the design of magnesium alloy stents.

In vitro corrosion properties of HTHEed Mg-Zn-Y-Nd alloy microtubes for stent applications: Influence of second phase particles and crystal orientation

Magnesium (Mg) alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability. However, in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion, which is limiting their widespread application. To solve the problem of uneven degradation of stents, a HTHE (long-time and high-temperature heat treatment, large-reduction-ratio hot extrusion) process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study. The heat treatment is to dissolve alloying elements and reduce the size of SPPs, and the hot extrusion is to acquire fine-grained and strongly textured microtubes. The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes. After hot extrusion, microtubes show strong texture with basal plain oriented parallel to the longitudinal section (LS). The corrosion testing indicates that severe localized corrosion occurs on the cross section (CS) while localized corrosion is alleviated on the LS. Based on the different corrosion properties of the LS and CS, HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents.

The optimal structural analysis of cobalt-chromium alloy (L-605) coronary stents

A coronary stent is a conventional medical device used in percutaneous coronary intervention (PCI), and its mechanical properties have become one of the critical factors to determine the effect of surgical treatment. Based on the existing cobalt-chromium (CO-Cr) alloy L605 coronary stent, this paper established an integrated finite element model of the stent-balloon-compression shell to simulate the stent bundle expansion test and crush resistance test with parallel plates. We verified the accuracy of the analytical model by comparing the simulation results with experimental results. The effects of different parameters on the axial retraction performance, the expansion uniformity, and the flexibility of the stent are analyzed by using the support body dimension and connector form as parameters. The results demonstrate that increasing the number and length of the circumferential support can improve the axial retraction performance, expansion uniformity, and the form of the connector has a significant influence on the flexibility of the stent. Finally, the optimized CO-Cr alloy stent with improved comprehensive indicators is described.

Biodegradable JDBM coating stent has potential to be used in the treatment of benign biliary strictures

In our previous study, to find out the optimal alloy suitable for biliary surgery, magnesium alloy Jiao Da Bio-magnesium (denoted as JDBM) alloy, Zn–3Cu alloys, and their respective coating (MgF2–PDLLA) products were produced for our research. We found that JDBM seems to be a potential material for clinical biliary stent application due to its uniform degradation and good compatibility. In order to apply the JDBM alloy to treat benign bile duct stricture, our group prepared the bare JDBM and its coating product into finished stents by mesh weaving carving technology and conducted the mechanical property tests, degradation tests and biocompatibility tests. During the mechanical property tests, we found the bare JDBM stent was more suitable than titanium alloy stent when applies to the bile duct, and the coating of the JDBM coating stent has no effect on its mechanical properties. Our in vitro and in vivo experiments revealed that the degradation rate of the JDBM coating stent is lower than that of the JDBM stent, and both stents were biosafe. Thus, there is promise for JDBM coating stents for the treatment of benign biliary strictures.

Technical Feasibility and Histological Analysis of Balloon-Expandable Metallic Stent Placement in a Porcine Eustachian Tube

There is a clinical need to develop a stent to treat obstructive and refractory Eustachian tube dysfunction (ETD) after balloon Eustachian tuboplasty. An animal model for stent placement in the Eustachian tube (ET) is needed to develop optimal designs and materials, as stents for ETD have not been clinically applied. The purpose of this study was to evaluate the technical feasibility of stent placement and histological changes in a porcine ET model. Six ETs were evaluated in three pigs. Cobalt–chrome alloy stents with two different diameters were placed in the left and right ET of each animal (right, 3.5 mm; left, 2.5 mm). The outcomes were assessed by endoscopic and fluoroscopic imaging during the procedure, computed tomography after the procedure, and by histological examinations. Stent placement was technically successful in all specimens after metallic guiding sheaths were located in the nasopharyngeal end of the ET. The mean luminal diameters of the proximal, middle, and distal portions of the larger stents in the right ETs were 3.48 mm, 2.54 mm, and 2.15 mm, respectively. In the left ETs using smaller stents, these values were 2.49 mm, 1.73 mm, and 1.42 mm, respectively. The diameters of the inserted stents differed by stent location and the original diameter. Histological findings showed tissue hyperplasia with severe inflammatory cell infiltration at 4 weeks after stent placement. In conclusion, stent placement into the porcine ET was technically feasible, and stent-induced tissue hyperplasia was significantly evident. The luminal configuration of the placed ET stent changed according to its non-elastic nature and anatomical features of the porcine ET. Using this model, ET stents of various materials and designs with anti-inflammatory or anti-proliferative drugs can be optimized for future treatments of ET dysfunction.

Final 5-Year Results in Randomized Japanese Patients Implanted With a Thin-Strut, Bioabsorbable, Polymer-Coated, Everolimus-Eluting SYNERGY Stent (From the EVOLVE II Study).

Background: SYNERGY is a thin-strut, platinum-chromium metal alloy stent with an ultrathin abluminal everolimus-eluting bioabsorbable polymer. EVOLVE II was a global randomized controlled trial that enrolled 1,684 patients treated with either a SYNERGY or durable polymer PROMUS Element Plus (PE+) everolimus-eluting stent, including 155 patients from Japanese sites. This substudy analyzed 5-year clinical outcomes in the Japanese and non-Japanese cohorts.Methods and Results: Patients aged ≥18 years with ≤3 native coronary artery lesions (reference vessel diameter ≥2.25–≤4.00 mm; length ≤34 mm) in ≤2 major vessels were randomized 1 : 1 to receive either SYNERGY (n=74 patients in Japan) or PE+ (n=81 patients in Japan). Five-year target lesion failure (TLF) was observed in 8.3% SYNERGY- and 11.2% PE+-treated patients (P=0.54). There were no cardiac deaths, and rates of target lesion revascularization and myocardial infarction were comparable between treatment arms. One patient in the SYNERGY arm experienced a very late definite stent thrombosis (ST); no ST occurred in the PE+ arm (P=0.30). Despite differences in baseline clinical and lesion characteristics, the 5-year TLF rates were not significantly different in SYNERGY-treated patients either in (8.3%) or outside (14.8%) Japan (P=0.14).Conclusions: In Japanese patients with coronary artery disease, SYNERGY showed comparable efficacy to PE+, with low rates of adverse events over 5 years. Similarly, 5-year clinical outcomes were favorable in Japanese vs. non-Japanese patients implanted with SYNERGY.

Designing HA/PEI nanoparticle composite coating on biodegradable Mg–Zn–Y-Nd alloy to direct cardiovascular cells fate

Biodegradable magnesium (Mg) alloy as a new generation of cardiovascular stent material has attracted great attention. However, the problems of excessive degradability and lack of corresponding biological functions of Mg alloys still need to be solved urgently. In the present study, series of hyaluronic acid (HA)/polyethyleneimine (PEI) nanoparticles (NP) with optimized parameters were designed and fixed on the fluorination/poly-dopamine (PDA) treated Mg–Zn–Y-Nd alloy to prepare a multi-functional composite coating. Our data indicated that the HA/PEI NPs composite coatings greatly improved the corrosion resistance and biological functions of the Mg–Zn–Y-Nd alloy. We hope this technology contribute to better feasibility of the new generation of biodegradable Mg alloy stents.

Cellular response of biodegradable AZ31 magnesium alloy stent in artery

Because of the increasing incidence of coronary artery disease, the use of cardiovascular stents is gradually increasing. In percutaneous coronary intervention, advantage of bioresorbable stent is that the stent does not remain in the human body after completing the necessary mechanical support to ensure the blood vessel open, and finally degrades into harmless molecules. Compared with bare stents, which require long-term retention in the body, the incidence of restenosis in stent or late stent thrombosis was lower. Current biodegradable stent mainly include polymers, biodegradable stents and metal alloy stent. Magnesium-based stent degradation and its copolymers are used in the application of biological absorbable stents and attract the attention of researchers.

Intraluminal Titanium Alloy Stent to Prevent Tracheal Stenosis in Tracheal Anastomosis.

Tracheal stenosis can cause respiratory problems in mature, small-breed dogs. This study aimed to evaluate the placement of an intratracheal titanium alloy stent to prevent tracheal stenosis in canine tracheal anastomosis. The self-expandable intratracheal stent was an alloy of nickel and titanium, at the same atomic ratio. Vital signs and respiratory patterns, C-reactive protein, radiography, computed tomography, and endoscopy results after intraluminal stenting were assessed for 3-5 months. No dogs showed evidence of intraluminal tracheal stenosis or tracheitis in the region of stent insertion on tracheoscopy and computed tomography after tracheal stent placement. After 1-2 weeks of tracheal stent placement, all dogs resolved coughing and dyspnea signs and resumed normal activities. The intratracheal stent showed no movement or deformation in the trachea, and had flexibility and an appropriate radial force. Therefore, titanium alloy tracheal stents are useful in stenotic operations for tracheal reconstruction.

Immobilization of bioactive complex on the surface of magnesium alloy stent material to simultaneously improve anticorrosion, hemocompatibility and antibacterial activities

Magnesium alloy represents one of the most potential biodegradable vascular stent materials due to its good biodegradability, biocompatibility and suitable mechanical properties, whereas the rapid degradation in physiological environment and the limited biocompatibility remain the challenges. In this study, graphene oxide (GO) was firstly functionalized by chitosan (GOCS), followed by loading zinc ions and propranolol to obtain GOCS@Zn/Pro complex, which was finally covalently immobilized on the self-assembled modified magnesium alloy surface to enhance the corrosion resistance and biocompatibility. The multi-functional coating can significantly improve the corrosion resistance and reduce the degradation rate of the magnesium alloy. Furthermore, the coating can significantly inhibit platelet adhesion and activation, reduce hemolysis rate, prolong activated partial thromboplastin time (APTT), and thus improve the blood compatibility of the magnesium alloy. In addition, the modified magnesium alloy can not only significantly promote the endothelial cell adhesion and proliferation, up-regulate the expression of vascular endothelial growth factor (VEGF) and nitric oxide (NO), but also endow the materials with good antibacterial properties. Therefore, the method of the present study can be used to modify magnesium alloy stent materials to simultaneously enhance corrosion resistance and blood compatibility, promote endothelialilization, and inhibit infections.

Determination of the Entire Stent Surface Area by a New Analytical Method

Stenting is a widely used treatment procedure for coronary artery disease around the world. Stents have a complex geometry, which makes the characterization of their corrosion difficult due to the absence of a mathematical model to calculate the entire stent surface area (ESSA). Therefore, corrosion experiments with stents are mostly based on qualitative analysis. Additionally, the quantitative analysis of corrosion is conducted with simpler samples made of stent material instead of stents, in most cases. At present, several methods are available to calculate the stent outer surface area (SOSA), whereas no model exists for the calculation of the ESSA. This paper presents a novel mathematical model for the calculation of the ESSA using the SOSA as one of the main parameters. The ESSA of seven magnesium alloy stents (MeKo Laser Material Processing GmbH, Sarstedt, Germany) were calculated using the developed model. The calculated SOSA and ESSA for all stents are 33.34%(±0.26%) and 111.86 mm (±0.85 mm), respectively. The model is validated by micro-computed tomography (micro-CT), with a difference of 12.34% (±0.46%). The value of corrosion rates calculated using the ESSA computed with the developed model will be 12.34% (±0.46%) less than that of using ESSA obtained by micro-CT.

A Mini Review on Biodegradable Magnesium Alloy Vascular Stent

Biodegradable magnesium alloy stents are a new generation of vascular stents which can open up blocked blood vessels at an early stage, then degrade and be absorbed by the body at a suitable rate after the vascular has been repaired. Mg alloys are excellent materials for vascular stents benefit from their sufficient mechanical properties and good biocompatibility. At present, Mg alloy is also used as a green material in the research of vascular stents due to its biodegradable property. In this paper, based on the research situation of degradable Mg alloy stents in recent years, the research history, degradation mechanism, structural design and basic research experiments of Mg alloy stents are reviewed.

Improved Transcatheter aortic valve implantation for aortic regurgitation using a new-type stent: the first preclinical experience

BackgroundIn this study, we sought to evaluate the feasibility of improved transcatheter aortic valve implantation (TAVI) in noncalcified aortic valve by using the novel concept of double-layer ChenValve prosthesis. TAVI was initially considered as an alternative treatment for high-risk patients with aortic stenosis. However, non noncalcified aortic valve disease was considered as a contraindication to TAVI.MethodsChenValve prosthesis, which consisted of a self-expanding Nitinol ring, a balloon-expandable cobalt-chromium alloy stent and a biological valve, was implanted at the desired position under fluoroscopic guidance in a transapical approach through a 20F sheath in 10 goats. Aortic angiography was performed to measure the diameter of the aotic annulus and assess the performance of the artificial valve. The ultrasound was used to evaluate the regurgitation or paravalvular leakage and trans-prosthetic vascular flow velocity postoperatively. The aortogram and transthoracic echocardiography were applied to observe whether the valve stent was implanted at the desired position.ResultsChenValve prosthesis was successfully transppical implanted in all animals. The aortogram and transthoracic echocardiography performed immediately after implantation revealed that the valve stent was implanted at the desired position. There was no significant paravalvular leakage, obstruction of coronary artery ostia, stent malpositioning or dislodgement occurred.ConclusionsThis preliminary trial with the novel double-layer ChenValve prosthesis demonstrated the feasibility of improved TAVI in noncalcified aortic valve. The mechanism of Nitinol ring-guided locating the aortic sinus enables us to anatomically correct position the artifact valve. This improved strategy seems to make the TAVI process more safe and repeatable in noncalcified aortic valve.

An asymmetric surface coating strategy for improved corrosion resistance and vascular compatibility of magnesium alloy stents

Magnesium (Mg) and its alloys are promising materials for biodegradable drug-eluting stent applications, but their rapid corrosion remains a major challenge for clinical practice. Considerable efforts have been made to develop an efficient surface coating that can provide higher Mg stent corrosion resistance, sustained drug-delivery capability, and vascular compatibility. Herein, we introduce poly(ether imide) (PEI) and poly(lactic-co-glycolic acid) (PLGA) as surface coating polymers for WE43 Mg-alloy stent. Using a sequential spray-coating method, we developed a novel asymmetric stent coating comprising an inner surface coated with a PEI single layer and outer/side surfaces coated with sirolimus-loaded PLGA/PEI double layers. PEI coating layer has excellent adhesiveness to WE43 surface and considerably improves WE43 corrosion resistance and in vitro endothelial cell compatibility. PLGA/PEI double coating layer ensures a low release rate of sirolimus and stable surface morphology during drug-release process. Only vascular smooth muscle cells are directly affected by sirolimus owing to the asymmetric geometry of PLGA/PEI double coating, which has a satisfactory anti-proliferation effect. These results indicate that the developed asymmetrically PEI- and PLGA/PEI-coated WE43 stents have significant potential for achieving enhanced re-endothelialization and suppressed in-stent restenosis in vascular stent applications.

Microstructure and performance of biodegradable magnesium alloy tubes fabricated by local-heating-assisted dieless drawing

Abstract Magnesium (Mg) alloy stents are expected to be the next generation of stents because of good biocompatibility and biodegradability. Compared with cold drawing, dieless drawing with local heating is an effective method for manufacturing the Mg alloy microtubes since a large reduction in area can be achieved in a single pass. However, the microstructure and properties of dieless drawn tubes have not been clarified, leading to the problems in practical application of dieless drawn tubes. In this study, the microstructure and performance of dieless drawn tubes are clarified. The results show that temperature and speed in the dieless drawing process are two factors in determining the grain size of dieless drawn tubes since decreasing the temperature or increasing the speed promotes the generation of fine-grained microstructure. Twins are also generated during the dieless drawing process, which 1) disintegrates grains leading to refinement and 2) causes Hall–Petch law effect on dieless drawn tubes. Tensile tests show that grain size is the main factor in determining the mechanical properties of dieless drawn tubes, namely, 0.2% proof stress 135–180 MPa, ultimate tensile strength (UTS) 200–250 MPa, and elongation 8–12%. In 0.9 wt% NaCl solution, localized corrosion is the key factor in initiating the corrosion of dieless drawn tubes, but refined grains and fewer twins can alleviate local corrosion. These results imply that dieless drawn tubes are promising in the clinical application of Mg alloy stents for cardiovascular disease.