Alloy Stent Research Articles

Study on surface quality and mechanical properties of micro-milling WE43 magnesium alloy cardiovascular stent

Traditional laser processing technique is mainly applied for cardiovascular stent manufacture, especially for materials with high mechanical properties and high melting point, while it usually produces problems such as material ablation and defects during finish machining process. Magnesium alloy, as material candidate for bioresorbable cardiovascular stent, has low melting and ignition point, high oxidizability property. Laser processing technique scarcely meets the requirements of high surface quality of magnesium alloy cardiovascular stents, this paper firstly develops a five-axis micro-milling technique to fabricate magnesium alloy cardiovascular stents. Milling orthogonal test was carried out to obtain the optimal finish machining parameters, and then a novel stent machining process was established. The processed stent has an inner diameter of 1.5 mm, a thickness of 80 μm and a length of 8 mm with a U-bend width of 100 μm and a link strut width of 70 μm, and the optimal finish processing parameters was set up with the main spindle speed of 30,000 rpm, feed speed 200 mm/min, cutting width 50 μm and cutting depth 40 μm. The dimensional accuracy and surface topography of the magnesium alloy stent were measured and characterized, and results showed that the dimensional accuracy was within 0.01 mm, and the machined stent achieved better surface quality without obvious processing defects such as pits, grooves and pores while comparing with the stent under original processing parameters. In order to evaluate the radial support performance of the stent, the radial compression and expansion experiments and simulations were conducted, respectively. Results showed that the maximum diameter error in the experiment and simulation was 13.35 %, and the radial recoiling error was 16.79 %. This work provides a potential stent manufacture technique in the development and clinical application of bioresorbable magnesium alloy stent.

Impact of Two Urethral Stent Types on Complications after One-Stage Hypospadias Repair Using the Duckett Procedure.

The authors evaluated whether the new nickel-titanium alloy stent (NTAS) is superior to the traditional silicone stent used in hypospadias repair surgery in preventing complications such as urinary fistula. This retrospective cohort study included 576 patients with hypospadias who underwent NTAS or traditional silicone stent placement after hypospadias surgery between March of 2002 and August of 2019. The primary outcome was the rate of urinary fistula occurrence at 4 weeks (stent removal time), and the secondary outcomes were the rate of other complications, such as urethral stricture, urethral diverticulum, infection, and so on. The occurrence of complications in both groups was compared, and the important contributing factors of urinary fistula and urethral stricture were determined. Among 576 patients, 398 were assigned to the NTAS group, and 178 were assigned to the silicone group. Thirty-five patients in the NTAS group and 30 in the silicone group developed urinary fistula, with a rate of 8.8% and 16.9%, respectively ( P = 0.005). Subgroup analysis showed that the differences were mainly in preschool patients (6 years or younger) ( P = 0.004) and those with the penile type of hypospadias ( P = 0.008). In addition, urethral stricture complicated five patients in the NTAS group and two in the silicone group, with a rate of 1.3% and 1.1%, respectively ( P = 1.000). Logistic regression showed that hypospadias type ( P = 0.001) and stent type ( P = 0.001) are the important risk factors for urethral fistula. The NTAS reduced the occurrence of urinary fistula complications after hypospadias repair in preschool patients, and can be presented as a better choice for hypospadias surgery. Therapeutic, III.

Copper-loaded chitosan coating for improved in-vitro corrosion resistance and endothelialization of magnesium alloy stents

For degradable magnesium alloy stents, excellent corrosion resistance and rapid endothelialization are two essential properties. In this paper, we plan to use a copper-loaded chitosan coating to accelerate the endothelialization process of the stent, which not only improves the biocompatibility of the magnesium alloy stent, but also its corrosion resistance by improving the service environment in vivo. Copper is an impurity in magnesium alloys, so how copper-containing coatings affect the corrosion resistance of magnesium alloy stents is the focus of this paper. The corrosion properties of the material were characterized by electrochemical experiments, immersion experiments, and in vitro cellular experiments characterized the effect of the copper-loaded coating on endothelial cells. The results showed that the Icorr of the copper-loaded chitosan coated sample and the Icorr of the unloaded copper chitosan coated sample were both in the order of 10−8, and the decrease of the corrosion resistance of the magnesium alloy by the copper-containing chitosan composite coating was not significant, and it still had a protective effect on the magnesium alloy substrate. During the immersion process, magnesium and copper ions were slowly released, followed by the hydrogen released. In addition, the weight loss rate of different coated samples presented the tendency of slower at inital, faster at last, and the weight loss rate of 0.041% for the copper-loaded chitosan coated sample was not significantly different from that of 0.035% for the unloaded copper coating group, after 28 days of immersion. The in vitro degradation products of the copper-loaded composite coating on the surface of magnesium alloy were also analyzed by XRD and EPMA, which included Mg(OH)2, Mg3(PO4)2 and Ca3(PO4)2; in addition the degradation process was analyzed. The cellular experiments results showed that the copper-loaded magnesium alloy had a proliferation rate of 243.0% for endothelial cells, which indicated that the copper-loaded coating could endow magnesium alloy stent a good biofunctional properties.

Improvement of TiN coating on comprehensive performance of NiTi alloy braided vascular stent

In order to improve the wear and corrosion resistance of Ni–Ti alloy-based braided stent, High-temperature nitriding technology was used to prepare the TiN coating with different process parameters. Based on the systematic evaluation of nano-mechanical properties, tribological properties, electrochemical corrosion properties, nickel ion release properties and cytotoxicity, the feasibility of the application of the TiN coating in braided peripheral vascular stents was explored. The results showed that TiN coating included the TiN layer of about 1μm and nitrided layer of 50μm under the process parameters of 800 °C and 1h. The nano hardness and elastic modulus for TiN film were 20.50GPa and 281.66GPa, respectively. TiN coating can not only significantly reduce the friction coefficient in dry sliding and lubrication state, but also greatly reduce the wear rate such as by three orders of magnitude in dry sliding condition. TiN film reduced the icorr value with a reduction amount of 75.1%, with the value of 8.41 × 10−8 and 2.09×10−8A/cm2 for NiTi and TiN, respectively. After 28 days of soak experiment in phosphate buffer solution, the total nickel ion release amount of sample TiN#4 and bare NiTi were 0.094 and 1.452ng/m, which was reduced by 93.5%. The relative cell proliferation rate results showed that TiN samples all exceeded 90%, which mean that the cytotoxicity grade was 0. Based on the above results, TiN showed good nano-mechanical, tribological, electrochemical corrosion, nickel ion release and cytotoxity properties, and was expected to be used as a protective layer on the surface of Ni–Ti alloy stent.

A Preliminary Study on the Morphological Changes of an NiTi-Shaped Memory Alloy Stent in the Vertebral Body.

At present, the most commonly used filler polymethyl methacrylate (PMMA) has the disadvantages of monomer toxicity, heat and leakage, and cannot be applied in young people. Therefore, finding a minimally invasive and good tissue-compatible alternative material has been a research hotspot in spine surgery in recent years. The aim of this study is to explore whether the memory alloy stent can avoid the complications of bone cement or not. Four non-adjacent vertebral bodies of the thoracic and lumbar spine in the 18 10-month-old pigs were selected as the surgical site and were randomly divided into the scaffold group and the bone cement group. The memory alloy scaffold and PMMA (polymethyl methacrylate) bone cement were placed via percutaneous puncture, and intraoperative fluoroscopy and micro-CT were used to observe the changes in the height of scaffolds and bone cement in the vertebral body immediately, 6 weeks, and 12 weeks after operation, the microstructural parameters of the bone trabeculae (bone volume fraction, bone surface volume ratio, bone trabeculae number) were also measured. The memory alloy stent could expand in the vertebral body, and its height gradually increased with time; additionally, the height of the bone cement mass did not change with time (p=0.00). New bone trabeculae could grow into the scaffold along the gap, and the volume fraction of bone, the volume ratio of bone surface area, and the number of bone trabeculae increased gradually (p=0.00). However, the volume fraction of bone, the volume ratio of bone surface area, and the number of trabeculae in the cement block decreased gradually (p=0.00). Memory alloy scaffolds have dynamic expansion characteristics in vivo, which can effectively avoid the complications of bone cement. Thus, it is beneficial to explore this minimally invasive treatment for vertebral compression fractures.

A novel MgF2/PDA/S-HA coating on the bio-degradable ZE21B alloy for better multi-functions on cardiovascular application

Recently, functional molecules such as Polydopamine (PDA), Hyaluronic Acid (HA) and heparin have been widely studied in the field of surface modification of magnesium (Mg) alloy stents for better degradation behavior and biocompatibility, but their further application is limited by undesirable anticoagulant function, uncontrollable degradation and easy bleeding, respectively. Regarding to this consideration, a magnesium Fluoride/Polydopamine/Sulphonated hyaluronic acid (MgF 2 /PDA/S-HA) composite coating was successfully prepared by applying S-HA with sulfur content of 9.71 wt% on the surface of ZE21B alloy in this study. The results showed that the composite coating with a unique mesh structure not only inherited the anticoagulant effect of sulfonic acid group and the excellent cyto-compatibility of S-HA with high sulfur content, but also significantly improved the corrosion performance of ZE21B alloy. These results indicate a great application potential of the composite coating in the field of cardiovascular biomaterials.

Biomechanical characteristics of self-expanding sinus stents during crimping and deployment_A comparison between different biomaterials

Self-expanding sinus stents are often used in functional endoscopic sinus surgery to treat inflamed sinuses. The PROPEL self-expanding sinus stent offers mechanical support to the sinus cavity to prevent restenosis. The stent is made of a bioabsorbable material (PLGA) that disappears after wound healing. However, complications such as foreign body sensation and severe stent migration/expulsion have been reported after implantation. Little is known about the contact characteristics of self-expanding sinus stents from when the stent is crimped into the insertion device through to deployment into the sinus cavity. This current study developed a test platform to analyze the biomechanical behavior of the stent during this process. Three common bioabsorbable materials, PLGA, PCL and Mg alloy, were evaluated to understand how the choice of material affects the biomechanical characteristics of self-expanding sinus stents. The results showed that the material can have a considerable influence on the contact characteristics during crimping and deployment. When crimped, the PLGA and Mg alloy stents showed much higher plastic strain and contact stress than the PCL stent. When deployed, the PCL stent had the largest contact area (4.3 mm2) and the lowest contact pressure (0.1 MPa) on the inner surface of the sinus canal. The results indicate that PCL could be a suitable choice for self-expanding sinus stents. This current study provides a method for observing the biomechanical characteristics of sinus stents during stent crimping and deployment.

Recent advances in surface endothelialization of the magnesium alloy stent materials

Magnesium and its alloy have good mechanical properties and biodegradability, and have become the hotspot of the next-generation biodegradable vascular stent materials. However, their rapid degradation in vivo and poor biocompatibility are still the bottlenecks of clinical applications for the cardiovascular stents. In particular, how to induce the repair and regeneration of the vascular endothelial with normal physiological functions on the surface of the magnesium alloy stent materials represents the key to its clinical application in the field of cardiovascular stents. It has been believed that it is an ideal way to completely solve the postoperative complications through constructing the multifunctional anti-corrosive bioactive coating on the magnesium alloy surface to induce the formation of vascular endothelium with normal physiological functions. However, how to construct a corrosion-resistant multifunctional bioactive coating with the good endothelial regeneration abilities on the magnesium alloy surface still faces a great challenge. This paper mainly focused on highlighting and summarizing the recent advances in the surface endothelialization of the magnesium alloy materials for the vascular stent, including the bio-inert coating, in-situ immobilization of bioactive molecules on the surface, polymer coating loaded with bioactive factors, novel multifunctional polymer coating, bioactive micropatterns, bioactive layer with glycocalyx-like structure, NO-releasing coating and bioactive sol-gel coating. The advantages and disadvantages of these strategies were discussed and analyzed. Finally, in the senses of future development and clinical application, this paper analyzed and summarized the development direction and prospect of surface endothelialization of the magnesium alloy vascular stents. It is anticipated that this review can give the new cues to the surface endothelialization of the cardiovascular magnesium alloy stents and promote future advancements in this field.

A compound Schiff base coating on biomedical magnesium alloy for enhanced corrosion resistance and biocompatibility

The rapid degradation and delayed endothelialization of magnesium (Mg) alloys are the bottlenecks that limit their application in the direction of cardiovascular stents. In the previous work, we have reported a novel compound coating composed of three newly synthesized Schiff bases which significantly improved the corrosion resistance of the Mg alloy. However, the effect of electrostatic spraying time on the physicochemical properties, corrosion resistance and biocompatibility of the compound coating has not been systematically explored. In the present study, the compound Schiff base coating was electrostatic-sprayed on to the Mg alloy surface with 1.0 ​min (CP-1.0), 1.5 ​min (CP-1.5), 2.0 ​min (CP-2.0) and 2.5 ​min (CP-2.5), respectively. Our data suggested that CP-1.5 possessed more homogeneous surface, better corrosion resistance, stronger hemocompatibility and pro-endothelialization ability. Our study may give inspiration for designing the special coatings only for the biodegradable Mg alloy stents for vascular application.

Corrosion resistance evaluation of biodegradable magnesium alloy vascular stents optimized by mechanical adapted polymer coating strategy

Surface modification coating of magnesium alloy stents as a physical barrier is to inhibit the corrosive medium from contact with matrix. In view of the complex deformation behavior of stent, mechanical adopted polymer coating strategy was considered in our work. Here, a relatively high plasticity polymer- poly(butyl acrylate) (PBA) was applied as the outer protective layer on the surface of magnesium alloy discs and stents through a dip-coating method and ultrasonic spraying system respectively. Compared with low plasticity poly(d,l-lactide) (PDLLA) control group, mechanical property of PBA polymer film were detected, furthermore, the static corrosion behaviors of PBA/MgF2 flake samples were investigated by electrochemical and immersion tests for a period time. The morphologies and degradation behaviors of stents after grip-expansion were conducted to explore the mechanical adaptability of PBA/MgF2 coating with magnesium alloy stent. PBA/MgF2 composite coating could improve the corrosion resistance of both static and deformed magnesium alloys, exhibiting a long-term protection. Especially, PBA-coated stent maintained the structural integrity and a relatively smooth surface after 21 days of service. Therefore, it is inferred that a coating material with high elongation at break is more mechanical adaptability with stent deformation to reduce the degradation rate of magnesium alloy stents.

Dual strengthened corrosion control of biodegradable coating on magnesium alloy for vascular stent application

Recently, magnesium alloy vascular stents have aroused great attraction because of their biodegradability and good mechanical properties. However, the rapid degradation of magnesium alloy stents causes their premature collapse in clinical application. So far, there have been few magnesium alloy stent systems that achieved sufficient support time by using biodegradable coating. In this paper, a dual strengthened biodegradable coating on a AZ31b magnesium alloy stent was suggested to achieve stronger adhesion and lower water permeability. The composite coating consisted of a magnesium hydrate - magnesium fluoride (Mg(OH)2-MgF2) inorganic base layer constructed by a simple two-step solution immersion and a graphene oxide - poly(trimethylene carbonate) outer layer prepared by ultrasonic spraying. The biodegradable composite coating modified magnesium alloy exhibited an extremely low corrosion current density of 4.3 × 10−10 A·cm−2, which is five orders of magnitude lower than the unmodified magnesium alloy. In vitro immersion tests revealed that the modification can effectively reduce the corrosion rate of the magnesium alloy stent, and the modified magnesium alloy stent can support at least 8 weeks. Furthermore, in vitro biological experiment revealed the modification of the composite coating improved the biocompatibility and ensured good microenvironment for vascular repair. These results suggest that the biodegradable composite coating has great potential for application in vascular stent.

Strengthened corrosion control of biodegradable poly(trimethylene carbonate) coating on bioabsorbable Mg alloy by introducing graphene oxide

Corrosion control of bioabsorbable Mg alloy stents is an attractive topic in recent years. Biodegradable polymer modification is a potential anti-corrosion method, but cannot achieve the desired corrosion protection due to the high water permeability of biodegradable polymers. In this study, a strengthened corrosion control strategy is proposed: Graphene oxide (GO) was introduced into a poly(trimethylene carbonate) (PTMC) coating to improve its anti-corrosion performance. GO/PTMC composite coatings with different GO contents were applied to AZ31b Mg alloy surfaces, and the effect of GO content (0, 0.2, 1, 3, 6, and 10 wt%) on surface characteristics, corrosion resistance, and in vitro biosafety was investigated. The results showed that the increase of GO content in the PTMC coating (<6 wt%) could improve its corrosion resistance by prolonging the permeation path of solution. Meanwhile, the addition of GO (<6 wt%) had little negative effects on cytocompatibility and hemocompatibility. However, when the addition of GO exceeded 6 wt%, GO aggregated on the coating surface, resulting in the formation of new defects and a rapid decrease in corrosion resistance. The optimized sample (GO content: 6 wt%) had the highest impedance modulus of 8.9 × 107 Ω·cm2 at 0.1 Hz and good in vitro biocompatibility, which shows great potential for application in vascular stents.

In vitro application of drug-loaded hydrogel combined with 3D-printed porous scaffolds

Titanium mesh and three-dimensional titanium alloy scaffolds play a key role in addressing oral and maxillofacial bone defects, which can provide a specific environment and structure for bone growth and development. The two main causes of implant surgery failure are aseptic loosening and bacterial-induced implant-associated infections. To make bone defect implants effective for a long time, the ideal scaffold should take into account the two functions of osseointegration and anti-infection. Therefore, on the basis of the low-elastic-modulus Ti-10Ta-2Nb-2Zr (TTNZ) alloys developed by the research group in the early stage, this study intends to combine the vancomycin-loaded hydrogel with the 3D-printed through-hole porous titanium alloy scaffold to endow 3D-printed TTNZ scaffolds with antibacterial properties. The antibacterial properties of the complex were investigated by the zone of inhibition test and the adhesion/free antibacterial test. The effects of the composite system on osseointegration were investigated from the aspects of cell adhesion, cell proliferation and osteogenesis-related gene expression. The results showed that loading 2.5 wt.% and 5 wt.% vancomycin did not affect the structure of chitosan–hyaluronic acid hydrogel. The properties of the hydrogels were examined by scanning electron microscopy, Fourier-transform infrared, degradation experiment in vitro and vancomycin release experiment in vitro. When combined with porous scaffolds, the drug-loaded hydrogels exhibited slower drug release rates and longer release times. In addition, in vitro studies found that the TTNZ scaffolds loaded with 5 wt.% vancomycin had a certain effect on the expression of osteogenesis-related genes in cells, but the antibacterial effect was the best. The porous scaffolds loaded with 2.5 wt.% vancomycin hydrogel TTNZ scaffolds did not inhibit cell proliferation, adhesion, alkaline phosphatase activity, and osteogenesis-related gene ex-pression, but the antibacterial effect on free bacteria was not as good as that of TTNZ scaffolds loaded with 5 wt.% vancomycin. This study, complementing the advantages of the two and controlling the local release rate of vancomycin, provides a new idea for future 3D printing of titanium alloy stents for anti-infection.

Experimental study of a heparin-coated venous stent fabricated by atomic layer deposition.

To evaluate the safety and efficacy of heparin-coated venous stents in animals. We used atomic layer deposition technology to obtain a heparin coating with good stability and then prepared a heparin-coated venous stent based on this technology. The experimental stents were prepared according to the diameter of the rabbit inferior vena cava and were divided into Ni-Ti alloy stent group, Ni-Ti-Al2O3 stent group and Ni-Ti-Al2O3-Heparin stent group. 3 days, 7 days and 14 days after stent implantation, the materials were collected, and the three groups of stents were observed by hard tissue section pathology, immunohistochemistry and scanning electron microscope to observe the differences in vascular wall inflammation, thrombosis, lumen stenosis and vascular intima regeneration. The experiment confirmed the safety of the heparin-coated stent in vivo. Compared with the control group, the experimental group showed a high degree of vascular endothelialization and an intact neointimal structure 14 days after implantation. The long-term safety and biological effects of heparin-coated venous stents in animals require further study.

Heating of metallic biliary stents during magnetic hyperthermia of patients with pancreatic ductal adenocarcinoma: an in silico study

Objective To investigate the eddy current heating that occurs in metallic biliary stents during magnetic hyperthermia treatments and to assess whether these implants should continue to be an exclusion criterion for potential patients. Methods Computer simulations were run on stent heating during the hyperthermia treatment of local pancreatic tumors (5–15 mT fields at 300 kHz for 30 min), considering factors such as wire diameter, type of stent alloy, and field orientation. Maxwell’s equations were solved numerically in a bile duct model, including the secondary field produced by the stents. The heat exchange problem was solved through a modified version of the Pennes’ bioheat equation assuming a temperature dependency of blood perfusion and metabolic heat. Results The choice of alloy has a large impact on the stent heating, preferring those having a lower electrical conductivity. Only for low field intensities (5 mT) and for some of the bile duct tissue layers the produced heating can be considered safe. The orientation of the applied field with respect to the stent wires can give rise to the onset of regions with different heating levels depending on the shape that the stent has finally adopted according to the body’s posture. Bile helps to partially dissipate the heat that is generated in the lumen of the bile duct, but not at a sufficient rate. Conclusion The safety of patients with pancreatic cancer wearing metallic biliary stents during magnetic hyperthermia treatments cannot be fully assured under the most common treatment parameters.

One-step fabrication of self-healing poly(thioctic acid) coatings on ZE21B Mg alloys for enhancing corrosion resistance, anti-bacterial/oxidation, hemocompatibility and promoting re-endothelialization

Coating magnesium (Mg) alloy stents with biodegradable polymeric materials can address the problems of thrombosis, inflammation, and restenosis caused by poor corrosion resistance and delayed endothelialization; however, these commonly used polymer coatings and their degradation products have no therapeutic effect and sometimes bring extra-side effects. Herein, to develop a polymeric coating with an additional therapeutic effect from that of the polymer itself, a poly(thioctic acid)-based homopolymer was simply synthesized via solvent-free thermal polymerization (containing Zn2+ ions) of thioctic acid (TA), a bioactive ingredient originating from the human body. A Poly(TA-Zn) coating was fabricated on alkali-heat (Mg(OH)2) treated ZE21B alloys via a one-step method, followed by conjugating REDV peptides, to simultaneously enhance the corrosion resistance and re-endothelialization process. Surface characterization and performance were comprehensively investigated. Molecular dynamics (MD) simulations demonstrate that the Zn-O coordination bonds formed between Zn2+ ions and carboxylic groups can inhibit the depolymerization of the Poly(TA-Zn) polymer. SEM micrographs show that the Poly(TA-Zn) coating is homogeneous and has a thickness of 45.03 ± 4.85 μm, and this coating is sturdily bonded to the Mg(OH)2 modified ZE21B substrate. Electrochemical and immersion tests show that the Poly(TA-Zn) sample provides good corrosion protection for ZE21B substrates because of its excellent self-healing properties, and it exhibits superior anti-bacterial/oxidation properties. After immobilizing REDV peptides, Poly(TA-Zn)-REDV samples can substantially hinder platelet adhesion/activation, reduce hemolysis rate, selectively promote the proliferation of endothelial cells and inhibit the growth of smooth muscle cells, thereby improving the anti-coagulation and re-endothelialization ability of Mg substrates.

A Biocompatibility Study of Plasma Nanocoatings onto Cobalt Chromium L605 Alloy for Cardiovascular Stent Applications.

The objective of this study was to evaluate the biocompatibility of trimethylsilane (TMS) plasma nanocoatings modified with NH3/O2 (2:1 molar ratio) plasma post-treatment onto cobalt chromium (CoCr) L605 alloy coupons and stents for cardiovascular stent applications. Biocompatibility of plasma nanocoatings was evaluated by coating adhesion, corrosion behavior, ion releasing, cytotoxicity, and cell proliferation. Surface chemistry and wettability were studied to understand effects of surface properties on biocompatibility. Results show that NH3/O2 post-treated TMS plasma nanocoatings are hydrophilic with water contact angle of 48.5° and have a typical surface composition of O (39.39 at.%), Si (31.92 at.%), C (24.12 at.%), and N (2.77 at.%). The plasma nanocoatings were conformal to substrate surface topography and had excellent adhesion to the alloy substrates, as assessed by tape test (ASTM D3359), and showed no cracking or peeling off L605 stent surfaces after dilation. The plasma nanocoatings also improve the corrosion resistance of CoCr L605 alloy by increasing corrosion potential and decreasing corrosion rates with no pitting corrosion and no mineral adsorption layer. Ion releasing test revealed that Co, Cr, and Ni ion concentrations were reduced by 64–79%, 67–69%, and 57–72%, respectively, in the plasma-nanocoated L605 samples as compared to uncoated L605 control samples. The plasma nanocoatings showed no sign of cytotoxicity from the test results according to ISO 10993-05 and 10993-12. Seven-day cell culture demonstrated that, in comparison with the uncoated L605 control surfaces, the plasma nanocoating surfaces showed 62 ± 7.3% decrease in porcine coronary artery smooth muscle cells (PCASMCs) density and had comparable density of porcine coronary artery endothelial cells (PCAECs). These results suggest that TMS plasma nanocoatings with NH3/O2 plasma post-treatment possess the desired biocompatibility for stent applications and support the hypothesis that nanocoated stents could be very effective for in-stent restenosis prevention.

Enhanced corrosion resistance and biocompatibility of an elastic poly (butyleneadipate-co-terephthalate) composite coating for AZ31 magnesium alloy vascular stents

Surface modification has been considered to provide an effective solution to the poor corrosion resistance of magnesium alloys. A large number of relevant studies have demonstrated that various protective coatings can reduce the degradation rate of magnesium alloys, but most of them are for magnesium alloy materials and devices without deformation. For biodegradable magnesium alloy stents, the selection of protective coating is vitally important due to the residual stress during implantation and cyclic loading after implantation. Therefore, compared with commonly used poly-D,l-lactide (PDLLA), a reliable protection was proposed on HF-treated Mg alloy via application of poly(butyleneadipate-co-terephthalate) (PBAT) with high elongation at break in this paper. In the long term, the corrosion resistance of PBAT-F coating of both flake samples and stents was decisively superior to PDLLA, which could be attributed to its outstanding barrier performance and mechanical properties. Simultaneously, PBAT composite coating exhibited better hemocompatibility and higher cell proliferation rates. The above results show that PBAT is an excellent coating material for vascular stents whereas PBAT composite coating could be a promising candidate as a protective coating for Mg stents.

Mechanical and hydrodynamic effects of stent expansion in tapered coronary vessels

Percutaneous coronary intervention (PCI) has become the primary treatment for patients with coronary heart disease because of its minimally invasive nature and high efficiency. Anatomical studies have shown that most coronary vessels gradually shrink, and the vessels gradually become thinner from the proximal to the distal end. In this paper, the effects of different stent expansion methods on the mechanical and hemodynamic behaviors of coronary vessels and stents were studied. To perform a structural-mechanical analysis of stent implantation, the coronary vessels with branching vessels and the coronary vessels with large bending curvature are selected. The two characteristic structures are implanted in equal diameter expansion mode and conical expansion mode, and the stress and mechanical behaviors of the coronary vessels and stents are analyzed. The results of the structural-mechanical analysis showed that the mechanical behaviors and fatigue performance of the cobalt-chromium alloy stent were good, and the different expansion modes of the stent had little effect on the fatigue performance of the stent. However, the equal diameter expansion mode increased distal coronary artery stress and the risk of vascular injury. The computational fluid dynamics analysis results showed that different stent expansion methods had varied effects on coronary vessel hemodynamics and that the wall shear stress distribution of conical stent expansion is more uniform compared with equal diameter expansion. Additionally, the vortex phenomenon is not apparent, the blood flow velocity is slightly increased, the hydrodynamic environment is more reasonable, and the risk of coronary artery injury is reduced.

Five-year comparative study of thin-strut rapamycin-eluting bioabsorbable scaffold with metallic drug-eluting stent in porcine coronary artery.

ObjectivesUsing quantitative coronary angiography (QCA), optical coherence tomography (OCT), histomorphometry, and pharmacokinetics, this study tried to evaluate the safety and efficacy of Biomagic rapamycin-eluting bioabsorbable scaffold (BVS) in non-atherosclerotic porcine coronary arteries.BackgroundBiomagic BVS is a new generation of thin-strut bioabsorbable scaffold. We conducted comparative study detailing pathological response, safety and efficacy of Biomagic BVS and the Firebird2 rapamycin-eluting cobalt-based alloy stent (DES) in a porcine coronary artery model. The animals were followed up at 14 days, 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months after stent implantation.MethodsA total of 143 devices (95 Biomagic and 48 Firebird2) were implanted in 2 or 3 main coronary arteries of 76 nonatherosclerotic swine and examined by QCA, OCT, light microscopy, and pharmacokinetics analyses at various time points.ResultsVascular responses to Biomagic and Firebird2 were largely comparable at all time points, with struts being sequestered within the neointima. The degree of inflammation of both devices was mild to moderate, although the Biomagic score was higher at 14 days to 24 months. However, there was no statistical difference between the two groups except 14 days. At each follow-up time point, the percentage of area stenosis in the Biomagic group was greater than that in the Firebird 2 group, but there was no statistical difference between the two groups at 3 and 12 months. The extent of fibrin deposition was similar between Biomagic and Firebird2, which peaked at 1 month and decreased rapidly thereafter. Pharmacokinetic study showed that coronary tissue sirolimus concentration remained above 2 ng/mg of tissue at 28 day. Histomorphometry showed expansile remodeling of Biomagic-implanted arteries starting after 12 months, and lumen area was significantly greater in Biomagic than Firebird2 at 36 and 42 months. These changes correlated with dismantling of Biomagic seen after 12 months. OCT images confirmed that degradation of Biomagic was complete by 36 months.ConclusionsBiomagic demonstrates comparable long-term safety to Firebird2 in porcine coronary arteries with mild to moderate inflammation. Although Biomagic was associated with greater percent stenosis relative to Firebird2 within 36 months, expansile remodeling was observed after 12 months in Biomagic with significantly greater lumen area at ≥36 months. Scaffold resorption is considered complete at 36 months.