Stent Material Research Articles

A viewpoint on material and design considerations for oesophageal stents with extended lifetime

Oesophageal stents are meshed tubular implants designed to maintain patency of the oesophageal lumen and attenuate the symptoms of oesophageal cancer. Oesophageal cancers account for one in twenty cancer diagnoses and can lead to dysphasia, malnutrition and the diminishment of patient quality of life (QOL). Self-expanding oesophageal stents are the most common approach to attenuate these symptoms. Recent advances in oncological therapy have enabled patient survival beyond the lifetime of current devices. This introduces new complications for palliation, driving the need for innovation in stent design. This review identifies the factors responsible for stent failure. It explores the challenges of enhancing the longevity of stent therapies and outlines solutions to improving clinical outcomes. Discussions focus on the role of stent materials, construction methods, and coatings upon device performance. We found three key stent enhancement strategies currently used; material surface treatments, anti-migratory modifications, and biodegradable skeletons. Furthermore, radioactive and drug eluting stent designs were identified as emerging novel treatments. In conclusion, the review offers an overview of remaining key challenges in oesophageal stent design and potential solutions. It is clear that further research is needed to improve the clinical outcome of stents and patient QOL.

Adverse events associated with AXIOS stents: Insights from the manufacturer and user facility device experience database.

ABSTRACTBackground and Objectives:The AXIOS stent is indicated for transgastric or transduodenal drainage of symptomatic pancreatic pseudocysts and symptomatic walled off necrosis. The AXIOS stent functions as a conduit which allows solid and liquid pancreatic fluid collections (PFC) contents to pass into the luminal GI tract and also allows the passage of standard and therapeutic endoscopes into the PFC to perform endoscopic debridement. We aim to investigate the number and type of complications associated with AXIOS stents.Materials and Methods:We analyzed postmarketing surveillance data from the Food and Drug Administration Manufacturer and User Facility Device Experience (MAUDE) database January 2016 to February 2021.Results:During the study period, approximately 588 reports with 579 device issues and 250 patient complications were identified. Most device complications were due to stent positioning problems or stent malpositioning (n = 206; 35.6%), followed by stent migration (n = 72; 12.4%), premature deployment (n = 61; 10.5%), material integrity (n = 56; 9.6%), deployment failure (n = 47; 8.1%), and difficulty removing the stent (n = 45; 7.7%). The most reported patient adverse events were hemorrhage/bleeding (n = 81; 32.4%), perforation (n = 26; 10.4%), pain (n = 22; 8.8%), unspecified infection (n = 20; 8.0%), and death (n = 17; 6.8%).Conclusions:Findings from the MAUDE database highlight patient and device complications which endoscopists should be aware of before AXIOS stent placement.

Transcatheter Approaches to Palliation for Tetralogy of Fallot.

To this day, controversy still exists regarding the optimal method to treat symptomatic neonates and infants with Tetralogy of Fallot (TOF). Symptomatic (severely cyanotic or ductal dependent) infants with TOF can undergo either a staged repair approach (consisting of initial palliation followed by complete repair) or primary repair. Traditionally, initial palliative procedures have been surgical, for example placement of a Blalock-Taussig-Thomas (BTT) shunt. Recent advances in technology have facilitated the introduction of catheter-based procedures as palliative techniques, for example, patent ductus arteriosus (PDA) stenting and right ventricular outflow tract (RVOT) stenting as more durable solutions than balloon pulmonary valvuloplasty (BPV). In this article, we discuss the rationale for these procedures, technical aspects of these procedures and outcomes data compared to traditional surgical procedures. Recent data have suggested that RVOT and PDA stenting procedures offer many advantages over traditional surgical palliative procedures as palliative methods in this patient population. This comes at a cost of increased reintervention burden, which may be considered part of the overall treatment strategy in smaller neonates and can be minimized with a focus on technical aspects and overall treatment strategies. Advanced surgical techniques are required at the eventual complete repair to negotiate removal of stent material and pulmonary artery reconstruction in some instances. Further adoption of catheter based palliative procedures for infants with symptomatic TOF has the potential to tip the outcomes towards favoring a staged approach, particularly in high-risk infants.

Improved Corrosion Resistance and Repellency to the Body Fluids by Thin-Film Dlc and Swcnt Coating of the Stent Materials

Improved Corrosion Resistance and Repellency to the Body Fluids by Thin-Film Dlc and Swcnt Coating of the Stent Materials

Biomedical Material for Stent Application: Current Status and Future Challenges

Cardiovascular disease is the leading cause of death worldwide. Arterial stenting as a transluminal angioplasty procedure allows re-opening of narrowed vessels and restoring normal blood flow with stent placement. The development of stents ed at the end of 19 century with bare-metal stents (BMS). Now, it has been based on the application of biodegradable or natural decomposed and coated stents. The coated stent has been found to improve BMS properties in terms of biocompatibility, cytotoxicity, and better mechanical and biophysical properties. Also, a biodegradable stent may support the blood micro-vessel during the estimated period of time before downgraded constituents. The biodegradable stent also allows a reinsertion for several months to improve the vessel wall's quality. This paper describes the possible materials for stents and their properties such as design criteria, degradation behavior, disadvantages, and advantages with clinical and preclinical trials to date. Stent degradation allows reinsertion of the stent after several months and improves the vessel wall quality. This paper focuses on developing materials for stents, which describe the possible materials for stents and their properties. Furthermore, the current clinical trial of the new proposed stent will also be highlighted.

Zn-Mg-WC Nanocomposites for Bioresorbable Cardiovascular Stents: Microstructure, Mechanical Properties, Fatigue, Shelf Life, and Corrosion.

Zinc (Zn) and Zn alloys have been studied as potential materials for bioresorbable stents (BRSs) in the last decade due to their favorable biodegradability and biocompatibility. However, most Zn alloys lack the necessary combination of strength, ductility, fatigue resistance, corrosion rate (CR), and thermal stability needed for such applications. In this study, nanoparticles made of tungsten carbide (WC) were successfully incorporated into Zn alloyed with 0.5 wt % magnesium (Mg) and evaluated for their suitability for BRS applications. Specifically, the resulting Zn-0.5Mg-WC nanocomposite's microstructure, mechanical properties, in vitro CR, and thermal stability were evaluated. The Zn-0.5Mg-WC nanocomposite had excellent mechanical strength [ultimate tensile strength (UTS) > 250 MPa], elongation to failure (>30%), and a suitable in vitro CR (∼0.02 mm/y) for this clinical application. Moreover, the Zn-0.5Mg-WC nanocomposite survived 10 million cycles of tensile loading (stress ratio, R = 0.053) when the maximum stress was 80% of the yield stress. Its ductility was also retained during a 90-day thermal stability study, indicating an excellent shelf life. Stent prototypes were fabricated using this composition and were successfully deployed during bench testing without fracture. These results show that the Zn-0.5Mg-WC nanocomposite is a promising material for BRS applications. In vivo studies are underway to validate both biocompatibility, stent function, and degradation.

Factors Associated With Noninfectious Fever After Endovascular Aortic Aneurysm Repair

Purpose: The post–endovascular abdominal aortic aneurysm repair (EVAR) inflammatory response, which is very often associated with fever, has been ascribed to a wide range of proinflammatory mediators and operative events. The aim of this study was to evaluate the impact of such factors in the development of fever of noninfectious origin after elective EVAR. Materials and Methods: A retrospective analysis of prospectively collected data of patients treated with standard elective EVAR between February 2017 and December 2020 was undertaken. The database included patients’ demographics and comorbidities, as well as laboratory inflammatory markers (white blood cell count, neutrophils, and C-reactive protein [CRP]) and anatomical characteristics (sac diameter, inferior mesenteric artery [IMA] patency and diameter, number of patent lumbar arteries, internal iliac artery [IIA] patency or occlusion). Intraoperative details, such as type of stent graft material and IIA overstenting, were also analyzed. Patients with infectious postoperative complications or previously receiving systemic anti-inflammatory medication were excluded. Statistical analysis was performed by SPSS 22.0 for Windows software (IBM Corp, Armonk, New York). Results: From 332 patients treated with elective EVAR between 2017 and 2020, 268 patients (all men) were included in the analysis. The mean age was 72.1±7.5 years and the mean aneurysm diameter was 59.1±12.1 mm. Seventeen patients were excluded due to a known infection site. From the study cohort, 114 (42.5%) patients presented with fever. Multivariate regression analysis confirmed that the occlusion of IMA ≥5 mm (p<0.008) and higher CRP (p<0.001) were independent factors associated with postoperative fever. A subanalysis was performed only on patients with patent IMA before EVAR. In the multivariate regression analysis of this subgroup, IMA ≥5 mm (p=0.008), presence of dyslipidemia (p=0.037), and higher CRP (p<0.001) were related to fever. Conclusion: Occlusion of an existing wide (≥5 mm) and patent IMA prior to EVAR may contribute to the development of post-EVAR pyrexia. The CRP is a reliable marker for post-EVAR fever. Further prospective studies are needed to corroborate these findings.

Cell-Material Interactions in Direct Contact Culture of Endothelial Cells on Biodegradable Iron-Based Stents Fabricated by Laser Powder Bed Fusion and Impact of Ion Release.

Additive manufacturing is a promising technology for the fabrication of customized implants with complex geometry. The objective of this study was to investigate the initial cell-material interaction of degradable Fe-30Mn-1C-0.02S stent structures in comparison to conventional 316L as a reference, both processed by laser powder bed fusion. FeMn-based alloys have comparable mechanical properties with clinically applied AISI 316L for a corrosion-resistant stent material. Different corrosion stages of the as-built Fe-30Mn-1C-0.02S stent surfaces were simulated by pre-conditioning in DMEM under cell culture conditions for 2 h, 7 days, and 28 days. Human umbilical vein endothelial cells (HUVECs) were directly seeded onto the pre-conditioned samples, and cell viability, adherence, and morphology were analyzed. These studies were accompanied by measurements of iron and manganese ion release and Auger electron spectroscopy to evaluate the influence of corrosion products and degradation on the cells. In the initial phase (2 h of pre-conditioning), HUVECs were able to attach but the cell number decreased over the cultivation period of 14 days and the CD31 staining pattern of intercellular contacts was disordered. At later time points of corrosion (7 and 28 days of pre-conditioning), CD31 staining was distinctly located at the intercellular contacts, and the cell density increased after seeding and was stable for up to 14 days. Formation of a complex degradation layer, which had a composition and thickness dependent on the pre-conditioning time, led to a reduced ion release and finally showed a positive effect on cell survival. Concluding, our data suggest the suitability of Fe-30Mn-1C-0.02S for in vivo applications.

Endoscopic esophageal stenting in combination with chemoradiation therapy: A review

Esophageal stenting is undoubtedly an effective method of choice for resolving malignant dysphagia in the presence of esophageal cancer. Nevertheless, the implantation of esophageal stents for malignant pathology is only a way to achieve adequate oral nutrition, which, unfortunately, does not increase the life expectancy in incurable patients. Early studies on the combination of chemoradiation therapy and stent implantation reported a relatively high rate of complications. Therefore, such therapeutic combinations have not been introduced into widespread practice. Nevertheless, to date, there is no convincing clinical data on the results of a combination of stenting methods and chemoradiation therapy, as well as their effect on the incidence of possible complications. Recent research has shown a very encouraging prospect. The combination of these techniques can increase life expectancy in incurable patients through continuous improvements in stent materials and designs.

Corrosion behavior of a non-equiatomic CoCrFeNiTi high-entropy alloy: A comparison with 304 stainless steel in simulated body fluids

A new type of non-equiatomic Co40Fe35Cr16Ni8Ti1 HEA was designed and synthesized, and its corrosion resistance was compared with 304 SS in Hank's simulated body fluids to verify its feasibility as an alternative for existing coronary stent materials. Electrochemical tests showed that the corrosion current density of Co40Fe35Cr16Ni8Ti1 HEA was 10−6 in order of magnitude, which was about 1/6 of that of 304 SS, and the impedance value of Co40Fe35Cr16Ni8Ti1 HEA was 105 in order of magnitude, which was about 7 times that of 304 SS. Scanning electron microscopy testing showed that after 120 h of continuous salt spray corrosion, the surface of 304 SS showed obvious corrosion morphology compared with Co40Fe35Cr16Ni8Ti1 HEA, and it was corroded with clear grain boundaries. After 6 h of potentiostatic polarization, a passive film was formed on the surfaces of Co40Fe35Cr16Ni8Ti1 HEA and 304 SS respectively, and the composition of the passive film of the two materials was analyzed by X-ray electron spectroscopy. Compared with 304 SS, the passive film formed on Co40Fe35Cr16Ni8Ti1 HEA is rich in Co and Cr elements, and the high Content of Cr and Ni makes Co40Fe35Cr16Ni8Ti1 HEA have higher corrosion resistance in Hank simulated body fluid. The high content of Fe2+ oxide in the passive film is the main reason why 304 SS is less resistant to corrosion than Co40Fe35Cr16Ni8Ti1 HEA in Hank's simulated body fluid.

The evolution of the structure and mechanical properties of fully bioresorbable polymer-glass composites during degradation

Fully bioresorbable polymer matrix composites have long been considered as potential orthopaedic implant materials, however their combination of mechanical strength, stiffness, ductility and bioresorbability is also attractive for cardiac stent applications. This work investigated reinforcement of polylactide-based polymers with phosphate glasses, addressing key drawbacks of current polymer stents, and examined the often-neglected evolution of structure and mechanical properties during degradation. Incorporation of 15–30 wt% phosphate glass led to modulus increases of up to 80% under simulated body conditions, and 15 wt% glass composites retained comparable ductility to pure polymers, crucial for stent applications where ductility and stiffness are required. Two-stage degradation was observed, dominated by interfacial water absorption and glass dissolution. Polymer embrittlement mechanisms (crystallisation, enthalpy relaxation) were suppressed by glass addition, allowing composites to achieve a more controlled loss of mechanical properties during degradation, which could allow gradual transfer of loading to newly healed tissue. These results provide a valuable new system for understanding the structural and mechanical changes occurring during degradation of fully bioresorbable polymer matrix composites, providing important new data to underpin the design of effective cardiac stent materials.

Intraoperative video showing the sequence of the operation highlighting the removal of the stent and infected material and further reconstruction of the aortic arch, proximal descending thoracic aorta and supra-aortic trunks using a Thoraflex PlexusTM (Terumo Aortic, Vascutek) with cardiopulmonary bypass, moderate hypothermic circulatory arrest and antegrade cerebral perfusion.

Intraoperative video showing the sequence of the operation highlighting the removal of the stent and infected material and further reconstruction of the aortic arch, proximal descending thoracic aorta and supra-aortic trunks using a Thoraflex PlexusTM (Terumo Aortic, Vascutek) with cardiopulmonary bypass, moderate hypothermic circulatory arrest and antegrade cerebral perfusion.

Stent encrustation or fragmentation? A case report of post stent removal encrustation in postpartum woman and literature review

BackgroundUreteral stents are commonly used in the field of urology to relieve ureteral obstruction. However, complications relating to ureteral stent use, such as encrustation continue to occur, especially with prolonged indwell time.Case presentationHere we present a 37-year-old postpartum woman with a foreign body in her bladder after removing a ureteral stent 1 month before. She insisted that the foreign body was the fragment of stent and asked for medical malpractice indemnity payments while the surgeon of her insisted that the stent was intact during the procedure. Finally, the foreign body was confirmed as an encrustation by cystoscopy and the patient received 10,000 yuan ($ 1500) as indemnity payments after encrustation removal.ConclusionIn the absence of guidelines, stent indwelling time vary with centers’ habits, stent materials and patient’s education. Early detection of stent encrustation and timely removal of the encrusted stent are still the best way to avoid stent retention. Violent stent removal is of danger and not recommended in any case.

In-vivo evaluation of molybdenum as bioabsorbable stent candidate

Biodegradable stents have tremendous theoretical potential as an alternative to bare metal stents and drug-eluting stents for the treatment of obstructive coronary artery disease. Any bioresorbable or biodegradable scaffold material needs to possess optimal mechanical properties and uniform degradation behavior that avoids local and systemic toxicity. Recently, molybdenum (Mo) has been investigated as a potential novel biodegradable material for this purpose. With its proven moderate degradation rate and excellent mechanical properties, Mo may represent an ideal source material for clinical cardiac and vascular applications. The present study was performed to evaluate the mechanical performance of metallic Mo in vitro and the biodegradation properties in vivo. The results demonstrated favorable mechanical behavior and a uniform degradation profile as desired for a new generation ultra-thin degradable endovascular stent material. Moreover, Mo implants in mouse arteries avoided the typical cellular response that contributes to restenosis. There was minimal neointimal hyperplasia over 6 months, an absence of excessive smooth muscle cell (SMC) proliferation or inflammation near the implant, and avoidance of significant harm to regenerating endothelial cells (EC). Qualitative inspection of kidney sections showed a potentially pathological remodeling of kidney Bowman's capsule and glomeruli, indicative of impaired filtering function and development of kidney disease, although quantifications of these morphological changes were not statistically significant. Together, the results suggest that the products of Mo corrosion may exert beneficial or inert effects on the activities of inflammatory and arterial cells, while exerting potentially toxic effects in the kidneys that warrant further investigation.

State of the Science in Tracheal Stents: A Scoping Review.

Recent material science advancements are driving tracheal stent innovation. We sought to assess the state of the science regarding materials and preclinical/clinical outcomes for tracheal stents in adults with benign tracheal disease. A comprehensive literature search in April 2021 identified 556 articles related to tracheal stents. One-hundred and twenty-eight full-text articles were reviewed and 58 were included in the final analysis. Datapoints examined were stent materials, clinical applications and outcomes, and preclinical findings, including emerging technologies. In the 58 included studies, stent materials were metals (n=28), polymers (n=19), coated stents (n=19), and drug-eluting (n=5). Metals included nitinol, steel, magnesium alloys, and elgiloy. Studies utilized 10 different polymers, the most popular included polydioxanone, poly-l-lactic acid, poly(d,l-lactide-co-glycolide), and polycaprolactone. Coated stents employed a metal or polymer framework and were coated with polyurethane, silicone, polytetrafluoroethylene, or polyester, with some polymer coatings designed specifically for drug elution. Drug-eluting stents utilized mitomycin C, arsenic trioxide, paclitaxel, rapamycin, and doxycycline. Of the 58 studies, 18 were human and 40 were animal studies (leporine=21, canine=9, swine=4, rat=3, ovine/feline/murine=1). Noted complications included granulation tissue and/or stenosis, stent migration, death, infection, and fragmentation. An increasing diversity of materials and coatings are employed for tracheal stents, growing more pronounced over the past decade. Though most studies are still preclinical, awareness of tracheal stent developments is important in contextualizing novel stent concepts and clinical trials. Laryngoscope, 132:2111-2123, 2022.

Polymer selection for Eustachian tube stent application based on mechanical, thermal and degradation behavior

Abstract The novel concept of stenting the Eustachian tube was established to provide an effective and safe therapy of Eustachian tube dysfunction. Biodegradable polymer stents are being developed to restore impaired tube function. As the supporting effect may be required for different time periods, PLA-co-PEG copolymers, PLLGA, PDLLA and PDS, having shorter degradation times compared to PLLA, were evaluated as potential stent materials. Since tensile tests and thermal analyses of solvent cast films from PLA-co-PEG copolymers showed comparable properties to PLLA, stent samples were manufactured from these materials. Mechanical stent testing revealed an increase of elastic recoil and slight decrease of collapse pressure compared to PLLA. In a short term accelerated degradation study a considerable percentage molar mass reduction and an increasing degree of crystallinity depending on PEG content was found. Based on the results obtained, the tested polymers offer a promising, faster degradable alternative to the established stent material PLLA.

Research and development strategy for biodegradable magnesium-based vascular stents: a review.

ABSTRACTMagnesium alloys are an ideal material for biodegradable vascular stents, which can be completely absorbed in the human body, and have good biosafety and mechanical properties. However, the rapid corrosion rate and excessive localized corrosion, as well as challenges in the preparation and processing of microtubes for stents, are restricting the clinical application of magnesium-based vascular stents. In the present work we will give an overview of the recent progresses on biodegradable magnesium based vascular stents including magnesium alloy design, high-precision microtubes processing, stent shape optimisation and functional coating preparation. In particular, the Triune Principle in biodegradable magnesium alloy design is proposed based on our research experience, which requires three key aspects to be considered when designing new biodegradable magnesium alloys for vascular stents application, i.e. biocompatibility and biosafety, mechanical properties, and biodegradation. This review hopes to inspire the future studies on the design and development of biodegradable magnesium alloy-based vascular stents.

Raman Spectroscopy as a Novel Method for the Characterization of Polydioxanone Medical Stents Biodegradation.

Polydioxanone (PPDX), as an FDA approved polymer in tissue engineering, is an important component of some promising medical devices, e.g., biodegradable stents. The hydrolytic degradation of polydioxanone stents plays a key role in the safety and efficacy of treatment. A new fast and convenient method to quantitatively evaluate the hydrolytic degradation of PPDX stent material was developed. PPDX esophageal stents were degraded in phosphate-buffered saline for 24 weeks. For the first time, the changes in Raman spectra during PPDX biodegradation have been investigated here. The level of PPDX hydrolytic degradation was determined from the Raman spectra by calculating the area under the 1732 cm−1 peak shoulder. Raman spectroscopy, unlike Fourier transform infrared (FT-IR) spectroscopy, is also sensitive enough to monitor the decrease in the dye content in the stents during the degradation. Observation by a scanning electron microscope showed gradually growing cracks, eventually leading to the stent disintegration. The material crystallinity was increasing during the first 16 weeks, suggesting preferential degradation of the amorphous phase. Our results show a new easy and reliable way to evaluate the progression of PPDX hydrolytic degradation. The proposed approach can be useful for further studies on the behavior of PPDX materials, and for clinical practice.

Fluid-Structure Interaction in Coronary Stents: A Discrete Multiphysics Approach

Stenting is a common method for treating atherosclerosis. A metal or polymer stent is deployed to open the stenosed artery or vein. After the stent is deployed, the blood flow dynamics influence the mechanics by compressing and expanding the structure. If the stent does not respond properly to the resulting stress, vascular wall injury or re-stenosis can occur. In this work, a Discrete Multiphysics modelling approach is used to study the mechanical deformation of the coronary stent and its relationship with the blood flow dynamics. The major parameters responsible for deforming the stent are sorted in terms of dimensionless numbers and a relationship between the elastic forces in the stent and pressure forces in the fluid is established. The blood flow and the stiffness of the stent material contribute significantly to the stent deformation and affect its rate of deformation. The stress distribution in the stent is not uniform with the higher stresses occurring at the nodes of the structure. From the relationship (correlation) between the elastic force and the pressure force, depending on the type of material used for the stent, the model can be used to predict whether the stent is at risk of fracture or not after deployment.

Influence of bovine serum albumin on corrosion behaviour of pure Zn in phosphate buffered saline

Zinc (Zn) and its alloys have received increasing attention as new alternative biodegradable metals. However, consensus has not been reached on the corrosion behaviour of Zn. As cardiovascular artery stent material, Zn is supposed to contact with plasma that contains inorganic salts and organic components. Protein is one of the most important constitute in the plasma and could adsorb on the material surface. In this paper, bovine serum albumin (BSA) was used as a typical protein. Influences of BSA on pure Zn corrosion in phosphate buffered saline is investigated as a function of BSA concentrations and immersion durations by electrochemical techniques and surface analysis. Results showed that pure Zn corrosion was progressively accelerated with BSA concentrations (ranging from 0.05 to 5 g L−1) at 0.5 h. With time evolves, formation of phosphates as corrosion product was delayed by BSA adsorption, especially at concentration of 2 g L−1. Within 48 h, the corrosion of pure Zn was alleviated by BSA at concentration of 0.1 g L−1, whereas the corrosion was enhanced after 168 h. Addition of 2 g L−1 BSA has opposite influence on the pure Zn corrosion. Furthermore, schematic corrosion behaviour at protein/Zn interfaces was proposed. This work encourages us to think more about the influence of protein on the material corrosion and helps us to better understand the corrosion behaviour of pure Zn.