Biodegradable Cardiovascular Stents Research Articles

Research on theoretical and experimental investigations of burr formation mechanism in micro-milling process of medical ploy-l-lactide

Medical grade poly-l-lactide (PLLA) has been widely applied for medical devices and consumables, e.g. biodegradable cardiovascular stents and surgical thread, due to its excellent biocompatibility. High-speed micro-milling technology shows great potential in high-precision and high-quality manufacturing of material PLLA, while it usually produces problems such as material burrs and defects. There is few research and analysis on the material removal mechanism and theory in the micro-milling process of polymers, and thus this paper aims to investigate the burr formation mechanism and processing quality in micro-milling process of medical PLLA. Firstly, a novel thermal-mechanical coupled theoretical model was proposed by considering the minimum cutting thickness and cutting-edge radius size effects, which can reveal the plastic flow law during micro-milling process of polymer material. This model was used to calculate the burr width at up and down milling sides of cutting area. Then material characterization and micro-milling experiments on two types of PLLA with different molecular weights were carried out to validate the established theoretical model, and further the micro-milling parameters were optimized to achieve the control of material burr formation and growth. As a result, a cardiovascular stent was fabricated by micro-milling with the optimized parameters (spindle speed of 25,000 rpm, feed rate of 100 mm/min and axial depth of cut of 5 μm), and the stents obtained significantly high surface quality. These results suggest that the proposed theoretical model has great advantages in the high-quality micro-milling of medical material PLLA. This work provides a potential stent manufacture technique in the development and clinical application of bioresorbable polymeric stents.

Comparative Investigation of the Corrosion Behavior and Biocompatibility of the Different Chemical Conversion Coatings on the Magnesium Alloy Surfaces

Due to their good biodegradability and biocompatibility, magnesium alloys are widely favored as the potential candidate for the biodegradable cardiovascular stent. However, the rapid degradation and the limited biocompatibility in vivo remain the main bottlenecks that inhibit their clinical applications. The construction of the chemical conversion coating on the magnesium alloy surface represents one of the effective strategies to control the degradation rate and enhance the biocompatibility. In the present study, the different chemical conversion layers were prepared on the magnesium alloy surface by chemical conversion treatment, including sodium hydroxide (NaOH), hydrofluoric acid (HF), phosphoric acid (H3PO4) and phytic acid (C6H18O24P6) treatment, and the corrosion behaviors and biocompatibility of the chemical conversion layers were comparatively investigated in detail. The results showed that the different chemical treatments can produce the different conversion layers on the magnesium alloy surfaces with a variety of physicochemical characteristics, corrosion resistance and biocompatibility, and all treatments can enhance the corrosion resistance to varying degrees. The hydrophilicity and corrosion resistance of the sodium hydroxide-treated magnesium alloy were the best among all the materials. Although the hydrofluoric acid-treated magnesium alloy had produced a hydrophobic coating, the corrosion resistance still needed to be improved. Magnesium alloys treated by sodium hydroxide showed a selective promotion of albumin adsorption, while the other samples simultaneously promoted albumin and fibrinogen adsorption. For the blood compatibility, the hemolysis rates of all of the treated materials were reduced to below 5%. The samples treated by phytic acid had the smallest hemolysis rate, and the NaOH-treated magnesium alloy had the least amount of platelet adhesion and activation. An appropriate microenvironment for cell growth could be achieved by the chemical conversion treatment, according to the results of the endothelial cell adhesion and proliferation, and the NaOH-treated surface showed the best endothelial cell growth behaviors among all of the samples. In summary, the corrosion resistance and biocompatibility of the magnesium alloy were significantly improved by the sodium hydroxide treatment, and thus this treatment can be used as a pretreatment for the surface modification of the magnesium alloy in order to further enhance the biocompatibility when used as the cardiovascular implants.

Zinc Ion-crosslinked polycarbonate/heparin composite coatings for biodegradable Zn-alloy stent applications

Zinc and its alloys are the best candidates for biodegradable cardiovascular stents due to their good corrosion rate and biocompatibility in vasculature. However, the cytotoxicity caused by the rapid release of zinc ions during the initial degradation stage and the lack of an anticoagulant function are huge challenges for their practical clinical applications. In this work, we developed a zinc ion-crosslinked polycarbonate/heparin composite coating via electrophoretic deposition (EPD) to improve the biocompatibility and provide anticoagulant functions for Zn-alloy stents. Both electrochemical tests and in vitro immersion tests demonstrated an enhanced corrosion resistance and lower Zn ion release rate of the coated Zn alloys. Enhanced adhesion and proliferation of endothelial cells on coated Zn alloys were also observed, indicating faster reendothelialization than that on bare Zn alloys. Moreover, the surface erosion of the composite coating led to the uniform and long-term release of heparin, which remarkably inhibited the adhesion and activation of platelets, and may have endowed the coated Zn-alloy stents with long-term anticoagulant functions.

Mechanical characteristics and biocorrosion behaviour of AS-CAST Zn-3Cu-Al alloys for cardiovascular bioabsorbable devices

In this study, the biomechanical and biocorrosion behaviour of as-cast Zn-3Cu-xAl (x = 0, 1, and 2 wt%) alloys for potential application as biodegradable cardiovascular stents was investigated. The alloys were manufactured by liquid metallurgy processing employing metal casting practices, while Scanning electron microscopy (SEM), X-ray diffractometry (XRD), hardness, tensile properties, fracture toughness, and invitro biodegradation rate evaluation in physiological saline solution (0.9% w/v sodium chloride and 5% w/v glucose), were yardsticks used to assess the alloys’ material characteristics. The results show that alloys all consist predominantly of ƞ Zn solid solution phase; while Cu5Zn8; Al4Cu9; and Al4Cu9, AlCu; were the intermetallic phases also identified as complementary phase constituents in the Zn-3Cu, Zn-3Cu-1Al, and Zn-3Cu-2Al alloys, respectively. The 1 and 2 wt% addition of Al in the Zn-3Cu alloy system, resulted in 4.52 and 21.89% increase in hardness, 4.46 and 35.17% increase in ultimate tensile strength, 5.09 and 36.88% increase in specific strength, 2.18 and 34.74% increase in fracture toughness, but 10.5 and 16.6% decrease in percentage elongation, respectively. The improved strength characteristics of the alloy compositions containing Al were attributed to matrix strengthening (due to solid solution strengthening), phase hardening and particle hardening effects (from the intermetallic phases) facilitated by the Al addition. Furthermore, the rate of in vitro corrosion decreased for the alloy compositions containing Al in comparison to the Zn-3Cu alloy, with the Zn-3Cu-1Al composition exhibiting the least biodegradation rate. The strength, toughness, ductility and biocorrosion property balance exhibited by the Zn-3Cu-1Al and Zn-3Cu-2Al alloy compositions make them promising candidates for further consideration for cardiovascular stent applications.

High-Efficient Vacuum Ultraviolet-Ozone Assist-Deposited Polydopamine for Poly(lactic-co-glycolic acid)-Coated Pure Zn toward Biodegradable Cardiovascular Stent Applications.

Zinc is a prospective metal for biodegradable cardiovascular stent applications, but the excessively released Zn2+ during degradation remains a huge challenge in biocompatibility. Considerable efforts have been made to develop a high-efficient surface modification method, while maintaining adhesion strength, mechanical support, and vascular compatibility. Biomimetic polydopamine (PDA) can adhere to Zn tightly, subsequently achieving robust chemical bonds with poly(lactic-co-glycolic acid) (PLGA) coating. However, the deposition of PDA on Zn depends on the controlled conditions such as a sensitive pH and a long period of time. Herein, we introduce vacuum ultraviolet-ozone (VUV/O3) assist-deposition technology to accelerate the polymerization of PDA on pure Zn, which shortens the process to 40 min at a moderate pH of 8.5 and improves the deposition rate by 1-2 orders of magnitude under sufficient active oxygen species (ROS). Additionally, PLGA/PDA coating enhances the corrosion resistance, and their effective protection maintains the mechanical properties after long-term corrosion. Moreover, the controlled Zn2+ release contributes to the superior in vitro biocompatibility, which inhibits the hemolysis rate and smooth muscle cell (SMC) proliferation. The enhanced endothelial cell (EC) proliferation is promising to promote the re-endothelialization, avoiding in-stent restenosis and neointimal hyperplasia. Such modified Zn might be a viable candidate for the treatment of cardiovascular diseases.

Characterization of nano precipitate phase in an as-extruded Zn-Cu alloy

Zn-Cu-based alloys are an important alloy series and show promising application prospect for biodegradable cardiovascular stents due to their excellent anti-self-aging property and combination of strength and ductility as well as good biocompatibility. Generally, nano-precipitates are an effective way to strengthen these alloys. In Zn-Cu-based alloys, only the second phases with submicron or micron size were observed in previous investigations. Here nanosized precipitates in an as-extruded Zn-2.0wt.%Cu alloy were first characterized using transmission electron microscopy, and identified as the ε (CuZn4) phase enriched Cu element with a hexagonal structure, which present with a rod shape and are symmetrically distributed along the [022¯1]η direction at a specific angle with the basal plane of the matrix. The nano-precipitates exhibit an approximately coherent interface with the matrix. The shape and orientation relationship with the matrix of these nano-precipitates were analyzed based on free energy minimization.

Non-destructive corrosion study on a magnesium alloy with mechanical properties tailored for biodegradable cardiovascular stent applications

An Mg-2Zn-0.6Zr-0.6Nd alloy for biodegradable cardiovascular stent applications was prepared through indirect extrusion. The alloy exhibited a superior combination of tensile yield strength (TYS), ultimate tensile strength (UTS) and elongation (EL) of about 269 MPa, 298 MPa and 25.6 %, respectively. In addition, the non-destructive electrochemical frequency modulation (EFM) technique was used for the first time to investigate the corrosion behavior of Mg alloys combined with electrochemical impedance spectroscopy (EIS) in Dulbecco’s Modified Eagle’s Medium (DMEM) and in Hank’s solution. Compared with the corrosion rate of 0.07 mm/year in Hank’s solution, lower corrosion rate of 0.03 mm/year was achieved in DMEM. The significant differences between the corrosion rate trends were discussed and related with the composition of the corrosion layer formed. Depending on the biomimetic fluids tested, different corrosion products were precipitated on the alloy’s surface: a compact and homogeneous layer of MgxCay(PO4)z and Zn(OH)2 and organic compounds was formed in DMEM, whereas a partial coverage of MgxCay(PO4)z and Mg(OH)2 was formed in Hank’s solution.

Are Fe-Based Stenting Materials Biocompatible? A Critical Review of In Vitro and In Vivo Studies.

Fe-based materials have increasingly been considered for the development of biodegradable cardiovascular stents. A wide range of in vitro and in vivo studies should be done to fully evaluate their biocompatibility. In this review, we summarized and analyzed the findings and the methodologies used to assess the biocompatibility of Fe materials. The majority of investigators drew conclusions about in vitro Fe toxicity based on indirect contact results. The setup applied in these tests seems to overlook the possible effects of Fe corrosion and does not allow for understanding of the complexity of released chemical forms and their possible impact on tissue. It is in particular important to ensure that test setups or interpretations of in vitro results do not hide some important mechanisms, leading to inappropriate subsequent in vivo experiments. On the other hand, the sample size of existing in vivo implantations is often limited, and effects such as local toxicity or endothelial function are not deeply scrutinized. The main advantages and limitations of in vitro design strategies applied in the development of Fe-based alloys and the correlation with in vivo studies are discussed. It is evident from this literature review that we are not yet ready to define an Fe-based material as safe or biocompatible.

Systematical evolution on a Zn-Mg alloy potentially developed for biodegradable cardiovascular stents.

To reduce the long-term side effects of permanent metallic stents, a new generation of cardiovascular stents called "biodegradable stents" is being extensively developed. Zinc has been considered as a promising candidate material for biodegradable cardiovascular stents due to its excellent biocompatibility and appropriate biodegradability. However, weak mechanical properties limit its further clinic application. In this study, hot extruded pure Zn and Zn-0.02 Mg alloy were prepared. Compared with pure Zn, Zn-0.02 Mg alloy showed more homogeneous microstructure, much smaller grain size and higher mechanical strength. Zn-0.02 Mg alloy presented uniform corrosion morphologies during the immersion process, and its corrosion rates was higher than that of pure Zn. Hemocompatibility results showed that the Zn-based alloy had extremely low hemolysis rate (0.74 ± 0.15%) and strong inhibitory effect on blood coagulation, platelet adhesion and aggregation. Zn-0.02 Mg alloy also exhibited excellent cytocompatibility. Its extracts could significantly promote the proliferation of endothelial cells. Moreover, the antibacterial activities of the Zn-based alloy were demonstrated by spread plate assay, live/dead viability assay and bacterial morphology observation. These results indicate that the extruded Zn-0.02 Mg alloy has a potential in biodegradable cardiovascular stents.

Influence of the electrosynthesis conditions on the spontaneous release of anti-inflammatory salicylate during degradation of polypyrrole coated iron for biodegradable cardiovascular stent

In this work, the spontaneous release of anti-inflammatory salicylate from polypyrrole (PPy) coated iron has been studied during degradation of the material in phosphate buffer saline at 37 °C. The sodium salicylate was incorporated into PPy in a one-step electropolymerization process. The influence of the synthesis conditions such as sodium salicylate concentration, pyrrole concentration and deposition charge on drug release profile has been investigated. The morphology, surface roughness and redox properties of PPy/Fe have been also studied. The drug release was studied by UV–Vis spectrophotometer with flow cuvette connected to the electrochemical cell, which provided continuous study of the released dopant. As a result, reliable and quantitative study of salicylate release from PPy coated iron was attained. Depending on the synthesis conditions the concentration of the salicylate released was in the range of 83–183 μM cm−2 after 21 h of immersion. The rate of drug release of 10–11 μM h−1 was the highest at the beginning after immersion (1–2 h), then it gradually decreased and finally it reached the lowest value of approximately 0.3 μM h−1 at the end of the process.”

Serum albumin can influence magnesium alloy degradation in simulated blood plasma for cardiovascular stenting

Magnesium (Mg) alloys are promising materials for biodegradable cardiovascular stents due to their good biocompatibility and low thrombogenicity. Since dissolved Mg is unlikely to cause any adverse effects, magnesium materials become safe choice in humans. Herein, we report on the in vitro degradable properties of a new bioresorbable implant for conceivable cardiovascular stent application, namely AZ80 magnesium alloy. The degradation behavior in simulated blood plasma (SBP) without and with 5_ 40 g/L bovine serum albumin (BSA) was assessed using open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The results show that degradation susceptibility of the alloy at any exposure period depends very much on the surrounding electrolyte composition. Additions of 10_20 g/L BSA doses in SBP fluid lead to decrease the susceptibility of the alloy degradation due to forming an integrated protective adsorbed layer on the surface. Plausible explanations were given for the stimulating effect induced by BSA at concentrations lower than 10 g/L or higher than 20 g/L. The synergistic influence of the negatively charged adsorbed albumin molecules at the physiological concentration (40 g/L) and Cl− ions in the contacting medium was also investigated. The electrochemical results are very consistent with SEM and EDX surface analyses, as well as the antibacterial efficiency of the alloy.

A feasibility study of using biodegradable magnesium alloy in glaucoma drainage device.

Technological advances in glaucoma have challenged the traditional treatment paradigm. Historically incisional surgery has been used in cases of advanced disease and/or uncontrolled intraocular pressures resistant to medical or laser interventions. More recently, perhaps due to advancements in imaging, surgery has been suggested to be beneficial earlier in the treatment paradigm. Despite these trends, surgical manipulation of the tissues and unpredictability of wound healing continue to result in surgical failure. Magnesium is an essential element for human body and plays a critically important role in maintaining the functional and structural integrity of several tissues, including the eye. Due to several of its advantageous properties such as non-toxicity, biodegradability, and high biological compatibility, magnesium alloy has attracted great attention as a novel biomaterial. Biodegradable cardiovascular stents made of magnesium alloy have already been introduced into clinical practice. The purpose of this review is to determine if bioabsorbable magnesium alloys can be utilized as a promising candidate for the development of a new generation of glaucoma surgical assistive devices.

Tailoring the electrochemical degradation of iron protected with polypyrrole films for biodegradable cardiovascular stents

The degradation of polypyrrole (PPy) coated iron is studied in phosphate buffer saline solution at 37°C by odd random phase multisine electrochemical impedance spectroscopy (ORP-EIS). PPy is electropolymerized with anti-inflammatory salicylates incorporated in the film, as a drug release system. The modelling of EIS over time provides the quantitative description of the corrosion behaviour of the material. Thus, the reliable analysis of the degradation stages of PPy coated iron is attained. The outcome of the present study shows that the degradation of iron can be tailored by tuning the properties of the PPy coating for possible medical applications.

Biphasic responses of human vascular smooth muscle cells to magnesium ion

Magnesium-based alloys are promising in biodegradable cardiovascular stent applications. The degradation products of magnesium stents may have significant impacts on the surrounding vascular cells. However, knowledge on the interactions between magnesium ion and vascular cells at the molecular and cellular levels is still largely missing. Vascular smooth muscle cell (SMC) plays an important role in the pathogenesis of restenosis and wound healing after stent implantation. This study evaluated the short-term effects of extracellular magnesium ion (Mg(2+)) on the cellular behaviors of SMCs. Cellular responses to Mg(2+) were biphasic and in a concentration-dependent manner. Low concentrations (10 mM) of Mg(2+) increased cell viability, cell proliferation rate, cell adhesion, cell spreading, cell migration rate, and actin expression. In contrast, higher concentrations (40-60 mM) of Mg(2+) had deleterious effects on cells. Gene expression analysis revealed that Mg(2+) altered the expressions of genes mostly related to cell adhesion, cell injury, angiogenesis, inflammation, coagulation, and cell growth. Finding from this study provides some valuable information on SMC responses toward magnesium ions at the cellular and molecular levels, and guidance for future controlled release of magnesium from the stent material.

Corrosion Effects of Electrolytic Biocomposites Coated Magnesium on Endolithial Cell Viability

Though the degradable magnesium alloy used to construct an absorbable stent could be another candidate, its poor corrosion resistance is relatively a serious impediment against wider applications of magnesium alloy[1]. In this study, the coatings of zirconia (ZrO2) bottom layer and calcium phosphate (CaP) top layer are carried out on pure magnesium specimens by electrolytic deposition and subsequent annealing, leading to the corrosion current density reduced from 13.3 to 3.86 μA/cm2 derived by potentiodynamic polarization tests in artificial blood plasma at 37 °C. Furthermore, calcium phosphate (CaP), gelatin (Gel) and heparin (Hep) are co-deposited on post CaP/ZrO2 coated specimens in order to fabricate the heparin sustaining release system for promoting the hemocompatibility of magnesium. Heparin loaded composite coatings are analyzed by X-Ray diffractometry (XRD), field emission scanning electron microscope (FESEM), focused ion beam (FIB) system, toluidine blue colorimetric assay, UV-visible spectrometer, and indirect endothelial cell viability tests. The drug content increases from 243.56±55.18 μg/cm2 for single layer (CaP-Hep) to 484.19±19.26 μg/cm2 for multilayer (CaP-Gel-Hep/CaP-Hep/CaP/ZrO2) and the sustaining release of the latter lasting for more than 28 days compared with that of the former for 1 day in PBS solution. The cell viability, related to Mg2+ ions in medium extracts which are still toxic to endothelial cells at high concentrations, is 63 % for the uncoated, 97 % for the ZrO2 coated, and 110 % for the CaP/ZrO2 and CaP-Gel-Hep/CaP-Hep/CaP/ZrO2 coated specimens compared with 100 % for the negative control. All results indicate that ZrO2 coated, CaP/ZrO2 coated, and CaP-Gel-Hep/CaP-Hep/CaP/ZrO2coated magnesium specimens are potential for biodegradable cardiovascular stents. Acknowlegement The authors are grateful for the support of this research by the National Science Council,Republic of China (Taiwan) under contract No. NSC 102-2221-E-005-027-MY3. [1]M.J. Wang, C.F. Li, S.K. Yen, Electrolytic MgO/ZrO2 duplex-layer coating on AZ91D magnesium alloy for corrosion resistance, Corrosion Science, 76 (2013) 142-153.

Microscopic bio‐corrosion evaluations of magnesium surfaces in static and dynamic conditions

Biodegradable materials including biodegradable metals are continuously being investigated for the development of next generation cardiovascular stents. Predictive in vitro tests are needed that could evaluate potential materials while simulating in vivo conditions. In this manuscript we report the microscopic bio-corrosion evaluations of magnesium surfaces in static and dynamic conditions. A corrosion test bench was designed and fabricated and static and dynamic corrosion tests were carried out with samples of magnesium alloy. The fluid wall shear stress equation and the Churchill's friction factor equation were used to calculate the fluid velocity required to generate the desired shear stress on samples in the test bench. Static and dynamic corrosion tests at 24 and 72 h were carried out at 0.88 Pa shear stress mimicking the in vivo shear stress. Microscopic evaluations of the corroded surfaces were carried out by optical, scanning electron microscopy and energy dispersive X-ray spectroscopy to evaluate the corrosion behaviour and surface properties of the test samples. The surface and interface analysis of magnesium samples post test indicated that dynamic conditions prevented the build-up of corrosion by-products on the sample surface and the corrosion mechanism was uniform as compared to static conditions. The use of a masking element to restrict the exposed area of the sample didn't result in increased corrosion at the boundary. Thus, we have demonstrated the feasibility of the designed test bench as a viable method for bio-corrosion surface analysis under dynamic corrosion conditions for potential biodegradable cardiovascular stent materials.

Biodegradable magnesium coronary stents: material, design and fabrication

Biodegradable cardiovascular stents in magnesium (Mg) alloys constitute a promising option for a less intrusive treatment, due to their high compatibility with the body tissue and intrinsic dissolution in body fluids. The design and fabrication aspects of this medical device require an integrated approach considering different aspects such as mechanical properties, corrosion behaviour and biocompatibility. This work gathers and summarises a multidisciplinary work carried out by three different research teams for the design and fabrication of Mg stents. In particular, the paper discusses the design of the novel stent mesh, the deformability study of the Mg alloys for tubular raw material and laser microcutting for the realisation of the stent mesh. Although, the results are not fully validated as the device has not been fully tested, they show the feasibility of the used approaches, as the first prototype stents in Mg alloy were produced successfully.

In vitro degradation behavior and biocompatibility of Mg–Nd–Zn–Zr alloy by hydrofluoric acid treatment

In this paper, Mg–Nd–Zn–Zr alloy (denoted as JDBM) coated with hydrofluoric acid (HF) chemical conversion film (MgF2) was researched as a potential biodegradable cardiovascular stent material. The microstructures, in vitro degradation and biocompatibility were investigated. The field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) showed that a compact MgF2 film was formed on the surface of JDBM. The corrosion rate decreased in artificial plasma from 0.337 to 0.253mm·y−1 and the electrochemical measurement demonstrated that the corrosion resistance of JDBM alloy could be obviously improved due to the protective MgF2 film on the surface of the substrate. Meanwhile, the hemolysis ratio of JDBM decreased from 52.0% to 10.1% and the cytotoxicity met the requirement of cellular application after HF treatment. In addition, JDBM and MgF2 film showed good anti-platelet adhesion, which is a very favorable property for implant material in contact with blood directly.

Tissue response to poly( l-lactic acid)-based blend with phospholipid polymer for biodegradable cardiovascular stents

A temporary cardiovascular stent device by bioabsorbable materials might reduce late stent thrombosis. A water-soluble amphiphilic phospholipid polymer bearing phosphorylcholine groups (PMB30W) was blended with a high-molecular-weight poly( l-lactic acid) (PLLA) to reduce unfavorable tissue responses at the surface. The PLLA implants and the polymer blend (PLLA/PMB30W) implants were inserted into subcutaneous tissues of rats, the infrarenal aorta of rats, and the internal carotid arteries of rabbits. After 6 months subcutaneous implantation, the PLLA/PMB30W maintained high density of phosphorylcholine groups on the surface without a significant bioabsorption. After intravascular implantation, the cross-sectional areas of polymer tubing with diameters less than 1.6 mm were histomorphometrically measured. Compared to the PLLA tubing, the PLLA/PMB30W tubing significantly reduced the thrombus formation during 30 d of implantation. Human peripheral blood mononuclear cells were cultured on the PLLA and the PLLA/PMB30W to compare inflammatory reactions. Enzyme-linked immunosorbent assay quantified substantially decreased proinflammatory cytokines in the case of the PLLA/PMB30W. They were almost the same level as the negative controls. Thus, we conclude that the phosphorylcholine groups could reduce tissue responses significantly both in vivo and in vitro, and the PLLA/PMB30W is a promising material for preparing temporary cardiovascular stent devices.

Electroformed iron as new biomaterial for degradable stents: Development process and structure–properties relationship

An electroforming technique was developed for fabricating iron foils targeted for application as biodegradable cardiovascular stent material. The microstructure, mechanical properties and corrosion of electroformed iron (E-Fe) foils were evaluated and compared with those of pure iron made by casting and thermomechanical treatment (CTT-Fe), with 316L stainless steel (316L SS) and with other candidate metallic materials for biodegradable stents. Electron backscattered diffraction revealed an average grain size of 4 μm for E-Fe, resulting in a high yield (360 MPa) and ultimate tensile strength (423 MPa) being superior to those of other metallic biodegradable stent materials. Annealing at 550 °C was found to improve the ductility of the E-Fe from 8% to 18%. The corrosion rate of E-Fe in Hanks’ solution, measured by potentiodynamic polarization, was higher than that of CTT-Fe, which had been found to have a slow in vivo degradation. The results showed that E-Fe possesses fine-grain microstructure, suitable mechanical properties and moderate corrosion rate as a degradable stent material.