Zinc Exhibits Ideal Physiological Corrosion Behavior for Bioabsorbable Stents (original) (raw)
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New approaches in evaluating metallic candidates for bioabsorbable stents
Emerging Materials Research, 2012
A series of unconventional approaches has been developed at Michigan Technological University, which is able to screen candidate materials for use in bioabsorbable (or bioresorbable) stents by reducing the scale of necessary animal studies and the complexity of biocorrosion analyses. Using a novel in vivo approach, materials formed into a simplified wire geometry were implanted into the wall of the abdominal aorta of rodents for several weeks or months to measure the extent of in vivo degradation, quantify mechanical strength over time, characterize the resulting products, and assess biocompatibility. An in vitro method was developed to identify bioabsorbable candidate materials, reproduce the corrosion products formed in vivo, and predict the degradation rate of stent materials. To accomplish this goal, wires were encapsulated in an extracellular matrix and corroded in cell culture media in vitro. Encapsulation of the wires in vitro was necessary in order to mimic in vivo stent encapsulation within a neo-intima. Alternatively, accelerated in vitro corrosion for materials with very low corrosion rates was accomplished by exposing fibrin-coated wires to a steady flow of cell culture media. After in vivo and in vitro tests, wires were subjected to tensile testing to quantify the rate of material degradation and loss of mechanical strength.
In-vivo corrosion and local release of metallic ions from vascular stents into surrounding tissue
The Journal of invasive cardiology, 2010
To evaluate retrieved bare metal vascular stents and surrounding tissue. Limited information is available regarding the condition of stent surfaces and their interaction with vascular tissue following implantation. Corrosion of stents presents two main risks: release of metallic ions into tissue and deterioration of the mechanical properties of stents which may contribute to fracture. Release of heavy metal ions could alter the local tissue environment leading to up-regulation of inflammatory mediators and promote in-stent restenosis. Nineteen cases were collected from autopsy, heart explants for transplant, and vascular surgery (23 vessels containing 33 bare metal stents). A method was developed for optimal tissue dissolution and separation of the stent/tissue components without inducing stent corrosion. When available, chemical analysis was performed to assess metallic content in both the control and dissolved tissue solutions. Electron microscopy and digital optical microscopy im...
Biodegradable Metal Stents: A Focused Review on Materials and Clinical Studies
Journal of Biomaterials and Tissue Engineering, 2014
Coronary artery disease (CAD) is the most common type of heart disease caused by plaque building up along the inner walls of coronary arteries which narrows the lumen and reduces blood flow. Stenting is the current standard procedure to treat the disease by opening the narrowed arteries and restoring the blood flow. Stenting has been revolutionary evolved from the use of bare metal stents made of corrosion resistant alloys to the incorporation of anti-proliferative drugs in the drug eluting stents. Despite the advantages and limitation of the current stent technology, the permanent presence of stents in the arteries is questionable, especially for some applications, including pediatric, in presence of collateral arteries, and others. Biodegradable stents, designed to support the arterial wall and disappear after its remodelling, therefore constitute an interesting choice, possibly representing the next revolutionary treatment of CAD. Magnesium, iron, zinc and their alloys are among metals have been proposed as biodegradable stent materials. These metals are designed to degrade in vivo through corrosion process without posing toxicity problems to the body and called as biodegradable metals. Stents made of magnesium and its alloys have been the most studied, developed and reached clinical trials in humans, followed by those made of iron which reached in vivo studies in animals. Meanwhile, zinc is just recently proposed with only few studies have been reported. This papers presents a focused review on the development of biodegradable metals for stents.
Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2010
Limited information exists regarding the in vivo stability of endovascular stents. Nine excised human vascular segments with implanted stents (n ¼ 16) manufactured from stainless steel, nickel-titanium, tantalum, and cobalt-based alloys were analyzed. The stent/tissue components were separated using an established tissue dissolution protocol and control and explanted stents were evaluated by digital optical and electron microscopy. Metallic content in surrounding tissues was measured by mass spectroscopy. Surface alterations, consistent with corrosion mediated by electrochemical and mechanical factors, were observed in 9 of the 16 explanted stents and were absent from control stents. Tissue dissolved from around corroded stents corresponded with a higher metallic content. The effect of these changes in the microtopography of stents on their mechanical properties (fatigue strength and fracture limit) in addition to the potential for released metallic debris contributing to the biological mechanisms of in-stent restenosis supports the need for further investigations. V C 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 95B: 225-238, 2010.
Short-Term Effects of Biocorrodible Iron Stents in Porcine Coronary Arteries
Journal of Interventional Cardiology, 2008
Background: Biocorrodible iron stents carry the potential to overcome limitations, such as chronic inflammation and premature recoil, posed by biodegradable polymer and magnesium alloy stents. This study aimed to test the safety and efficacy of biocorrodible iron stents in porcine coronary arteries. Methods: Iron stents and cobalt chromium stents were randomly deployed in the coronary arteries of juvenile domestic pigs. Animals were sacrificed at 28 days, and the vessels were fixed and processed for histochemistry. Results: At 28 days, iron stents started to show signs of degradation without evidence of stent particle embolization or thrombosis without traces of excess inflammation, or fibrin deposition. At 28 days, the surface of the iron stent struts was black to brown and the vascular wall adjacent to the iron stent had a brownish tinge. There were no statistically significant differences in any of the measured parameters between segments implanted with iron and cobalt chromium stents. There were also no adverse effects in the persistent areas. Conclusion: The current study demonstrates that stents made of biocorrodible iron are safe. In some of the measured parameters, such as intimal thickness, intimal area, and percentage occlusion, there was a trend in favor of the iron stents.
Journal of the Mechanical Behavior of Biomedical Materials, 2019
Intra-arterial stenosis due to atherosclerosis is often treated with endovascular balloon dilatation with a metal stent. Restenosis is common and is frequently treated with a new stent placed inside the existing one or the stents are placed with overlap to cover a larger area of the vessels. Observations of stent fractures, stent compression, accumulation of immunocompetent cells around stents have suggested the possibility of immunologic reactions to substances released from stents. An accelerated corrosion model was developed to study corrosion behaviour of commonly used surgical peripheral stents. Single nitinol stents (n = 6), connected stents of the same material (stent-in-stent, both nitinol, n = 7) and connected stents of dissimilar alloys (Nitinol with stainless steel stent inside, n = 7) were investigated. The stents were subjected to mechanical pulsatile radial strain (up to 8% strain at 1 Hz) and electrochemical stress (+112 mV vs. SCE). The release of nickel and titanium ions was compared. Scanning electron images were obtained. There was a higher release of nickel when combining two similar (range: 1382-8018 μg/L, p = 0.0012) and dissimilar (range: 170-2497 μg/L, p = 0.0023) stents compared to single stents (range: 0.4-216 μg/L). The concentration of titanium was low (range: 1.6-98.4 μg/L) with only a difference between the single and two similar stents (p = 0.0047). Deposits of corrosion products were clearly visible after fretting and pitting corrosion mainly on the Nitinol stents. Several mesh wires were fractured. The study demonstrated that mechanical strain combined with weak electric potential resulted in pronounced corrosion and fracture of stents, especially with overlapping stents. Single stents after pulsatile load released the lowest amount of ions. The combination of stents of the same material (Nitinol) had the highest release of metal ions.
Acta Biomaterialia, 2010
In the search for a metallic material showing moderate and uniform degradation for application as degradable cardiovascular stents, electroformed iron (E-Fe) was evaluated by in vitro degradation and cell viability tests. Static immersion and dynamic degradation were used to evaluate degradation rate and mechanism, while cell viability assay was used to assess cytotoxicity. The results were compared with those of iron fabricated by casting and thermomechanical treatment previously investigated as a stent material. Electroformed iron showed faster degradation than iron fabricated by casting (0.25 vs. 0.14 mm year À1 ), with a uniform degradation mechanism. Cell viability results showed that E-Fe did not result in a decrease in metabolic activity when exposed to primary rat smooth muscle cells. However, it caused a decrease in cell proliferation activity which could be beneficial for the inhibition of in-stent restenosis.
Corrosion test of overlapping coronary artery stents made of different materials
Materials Today: Proceedings, 2018
Coronary stents are widely used for the treatment of ischemic heart disease. After implantation the stent remains in the body. Due to the differences in coronary flow, shear stress and turbulences bifurcation lesions are common anatomy features of the human coronary tree. In the case of bifurcation lesions or severe stenosis, several stents are implanted in the same vessel segment, dilating them into each other. The blood flow in the vessel provides ideal environment for corrosion damage processes. During bifurcation stenting physicians can dilate two stents into each other made of a different material (with distinct normal potentials). In this case galvanic or crevice corrosion can occur, so special attention was paid to this field. In this study corrosion behavior of overlapping CoCr and PtCr coronary stents are described.
Metallic zinc exhibits optimal biocompatibility for bioabsorbable endovascular stents
Materials Science and Engineering: C, 2015
Although corrosion resistant bare metal stents are considered generally effective, their permanent presence in a diseased artery is an increasingly recognized limitation due to the potential for long-term complications. We previously reported that metallic zinc exhibited an ideal biocorrosion rate within murine aortas, thus raising the possibility of zinc as a candidate base material for endovascular stenting applications. This study was undertaken to further assess the arterial biocompatibility of metallic zinc. Metallic zinc wires were punctured and advanced into the rat abdominal aorta lumen for up to 6.5 months. This study demonstrated that metallic zinc did not provoke responses that often contribute to restenosis. Low cell densities and neointimal tissue thickness, along with tissue regeneration within the corroding implant, point to optimal biocompatibility of corroding zinc. Furthermore, the lack of progression in neointimal tissue thickness over 6.5 months or the presence of smooth muscle cells near the zinc implant suggest that the products of zinc corrosion may suppress the activities of inflammatory and smooth muscle cells.