Search

Laser-based metal powder bed fusion (PBF-LB/M) offers great potential for producing complex and filigree sub-millimetre parts with customised shapes, such as patient-specific vascular stents. However, stent fabrication via PBF-LB/M encounters fundamental challenges, including dimensional limitations, poor surface quality, difficult support structure handling and geometrical deviations. This study addresses these challenges by investigating the potential and limitations of a novel hybrid post-processing approach. This technique uses the combination of electrochemical polishing and chemical etching and is investigated from process and design perspectives, to emphasise the interactions between the two. With the systematic application of hybrid post-processing, the strut thickness and the surface roughness were substantially reduced. Moreover, it enabled the successful removal of part-internal support structures. Furthermore, angle and orientation-dependent geometrical deviations could be compensated, highlighting the potential of achieving homogenous strut thicknesses within parts containing variable overhang angles. This study demonstrates that the usage of hybrid (electro)chemical post-processing methods with specifically tailored process parameters is a promising approach for overcoming the design- and process-related challenges in PBF-LB/M manufactured sub-millimetre parts. [ABSTRACT FROM AUTHOR]

Biodegradable metals offer a promising means to ameliorate many of the long-term risks associated with vascular devices made of conventional biostable stent metals. While numerous biodegradable metal alloys have been developed and characterized in animal models, knowledge of their blood reactivity and thrombogenicity remains unknown. Metal hemocompatibility is particularly valuable because current generation drug-eluting stents pose a significant long-term thrombosis risk. In this study, four pure metals, widely used as degradable base materials (Fe, Zn, Mg, and Mo), and three alloys commonly used in cardiovascular devices [NiTi, CoCr, and stainless steel (SS)] were evaluated. This work examined how each of these metals activate platelets, coagulation factors, and inflammation using in vitro hemocompatibility assays and a clinically relevant ex vivo non-human primate arteriovenous shunt model. Testing found that while all metals promoted a downstream activation of platelets and coagulation in flowing whole blood, platelet and fibrin attachment to Mg was markedly reduced. Additionally, Fe and Mo trended toward higher platelet attachment and contact pathway activation. Overall, the results suggest that Mg may delay clot initiation, but not eliminate clot formation, indicating the importance of understanding thrombosis in Mg alloys that are currently being developed for clinical use as biodegradable stents.

In this manuscript we present a mathematical theory and a computational algorithm to study optimal design of mesh-like structures such as metallic stents by changing the stent strut thickness and width to optimize the overall stent compliance. The mathematical constrained optimization problem is to minimize the “compliance functional” over a closed and bounded set of constraints. The compliance functional is the stent's overall elastic energy. The constraints are the minimal and maximal strut thickness, and a given fixed volume of the stent material. We prove the existence of a minimizer, thereby proving that the constrained optimization problem has a solution. A numerical scheme based on an iteration procedure is introduced, and implemented within a Finite Element Method framework. Optimal design of three different stent prototypes is considered: (1) a single zig-zag ring, which can be found in many complex stent designs on the US market as a basic cell in the modular stent design, (2) a Palmaz–Schatz type stent consisting of 6 zig-zag rings, and (3) a Cypher(TM) type stent consisting of zig-zag rings with sinusoidal connectors. Several interesting optimization solutions are found, some of which have already been implemented in the design of the currently available stents on the US market. The resulting computational algorithm is compared to a Genetic Algorithm, and it is shown that our computational approach outperforms the Genetic Algorithm in the following three key aspects: (1) computation time, (2) accuracy, and (3) maintaining the symmetry of the solution.

The radial strength of balloon expandable stents represents a key property for a successful recanalization of sclerotic blood vessels. This study focuses on the most commonly used method for investigation of radial strength and radial stiffness via segmented head test setup. A custom made user software was used for evaluation of the radial force curves considering requirements of international standards such as ASTM F3067. Contributing factors during measurement such as friction and test setup deformation as well as the single cycle and multi cycle approach were addressed and discussed.

Magnesium alloy, as a new material for vascular stents, possesses excellent mechanical properties, biocompatibility, and biodegradability. However, the mechanical properties of magnesium alloy stents exhibit relatively inferior performance compared to traditional metal stents with identical structural characteristics. Therefore, improving their mechanical properties is a key issue in the development of biodegradable magnesium alloy stents. In this study, three new stent structures (i.e., stent A, stent B, and stent C) were designed based on the typical structure of biodegradable stents. The changes made included altering the angle and arrangement of the support rings to create a support ring structure with alternating large and small angles, as well as modifying the position and shape of the link. Using finite element analysis, the compressive performance, expansion performance, bending flexibility performance, damage to blood vessels, and hemodynamic changes of the stent were used as evaluation indexes. The results of these comprehensive evaluations were utilized as the primary criteria for selecting the most suitable stent design. The results demonstrated that compared to the traditional stent, stents A, B, and C exhibited improvements in radial stiffness of 16.9%, 15.1%, and 37.8%, respectively; reductions in bending stiffness of 27.3%, 7.6%, and 38.1%, respectively; decreases in dog-boning rate of 5.1%, 93.9%, and 31.3%, respectively; as well as declines in the low wall shear stress region by 50.1%, 43.8%, and 36.2%, respectively. In comparison to traditional stents, a reduction in radial recoiling was observed for stents A and C, with decreases of 9.3% and 7.4%, respectively. Although there was a slight increase in vessel damage for stents A, B, and C compared to traditional stents, this difference was not significant to have an impact. The changes in intravascular blood flow rate were essentially the same after implantation of the four stents. A comparison of the four stents revealed that stents A and C exhibited superior overall mechanical properties and they have greater potential for clinical application. This study provides a reference for designing clinical stent structures. [ABSTRACT FROM AUTHOR]

Metamaterials are a group of materials/structures which possess novel behaviors not existing in nature. The metamaterials include electromagnetic metamaterials, acoustic metamaterials, mechanical metamaterials, etc. among which the mechanical metamaterials are widely used in the field of biomedical engineering. The mechanical metamaterials are the ones that possess special mechanical behaviors, e.g., lightweight, negative Poisson’s ratio, etc. In this paper, the commonly used mechanical metamaterials are reviewed and their applications in the field of biomedical engineering, especially in bone tissue engineering and vascular stent, are discussed. Finally, the future perspectives of this field are given.

Shape memory polymers (SMPs) are smart materials that can alter their shape from a temporary shape to a permanent shape upon external stimuli. This unique property of SMP has shown enormous potential and breakthrough discoveries in biomedical engineering. A significant number of SMP based research publications in the recent past have demonstrated the researchers’ thirst to introduce SMP based devices to the biomedical fields. SMPs favour minimally invasive surgeries and showed enormous potential in vascular stents. However, SMP-based vascular stents have not been realised to date, indicating a lack of high-quality research outputs. Most studies either repeat or provide only minor extensions to ongoing research. This article reviews SMP materials used for vascular stent development and briefly introduces SMP, architecture, and history.Followed by SMP vascular stent fabrication methods, responsive physical behaviour, the performance of the vascular stents, limitations, and vitro and vivo clinical results. Finally, challenges and future directions of SMP vascular stents are identified and highlighted.

In the world, one of the leading causes of death is coronary artery disease (CAD). There are several ways to treat this disease, and stenting is currently the most appropriate way in many cases. Nowadays, the use of stents has rapidly increased, and they have been introduced in various models, with different geometries and materials. To select the most appropriate stent required, it is necessary to have an analysis of the mechanical behavior of various types of stents. The purpose of this article is to provide a complete overview of advanced research in the field of stents and to discuss and conclude important studies on different topics in the field of stents. In this review, we introduce the types of coronary stents, materials, stent processing technique, stent design, classification of stents based on the mechanism of expansion, and problems and complications of stents. In this article, by reviewing the biomechanical studies conducted in this field and collecting and classifying their results, a useful set of information has been presented to continue research in the direction of designing and manufacturing more efficient stents, although the clinical-engineering field still needs to continue research to optimize the design and construction. The optimum design of stents in the future is possible by simulation and using numerical methods and adequate knowledge of stent and artery biomechanics.

Vascular stent implantation has become an important choice for the treatment of severe cardiovascular and cerebrovascular blockage. Rational design is vital to ensure the mechanical properties of the vascular stents, which are important both to the implantation and service as for clinical treatment of coronary heart disease. Therefore we proposed a wholly new non-uniform honeycomb stent E and compared with an inverted honeycomb-like shaped stent F and a honeycomb-like shaped stent G. To evaluate their properties, a finite element method (FEM) was used to simulate the implantation process (crimp, crimp recoil, expand, and expand recoil) of these three different kinds of stents. Results showed that the stent E exhibits better mechanical behaviour than the other two stents F and G as far as radial strength and axial shortening performances and that the distribution of equivalent stress among the stent E is more uniform than that among the other two stents F and G. After that, a three-point bending method was used to study the bending flexibility of these three vascular stents. Stent E shows high bending stiffness compared with stents F and G due to the existence of additional support bridges in its structure. This study can be helpful to the rational design of optimizable PLA stents for its practical clinical performance and therefore possibly improve the prognosis of patients. [ABSTRACT FROM AUTHOR]

The shape memory properties (SMP) of long‐chain branched poly(lactic acid) (b‐PLA) vascular stent prepared through 3D‐printed technologies are studied by comparison with PLA. SMP is expected to endow vascular stent smart properties of self‐expanding stent, which could self‐expand and support the stenosis after reaching the lesion. The shape recovery rate of the b‐PLA samples at 60°C reaches to 93%, which is much higher than that of the PLA samples with 26%. The two‐cycle deformation‐recovery test of dynamic mechanical analysis (DMA) shows that the shape recovery rate of b‐PLA samples at 60°C reaches 98% in the first and second cycle, suggesting the good SMP. Meanwhile, the 3D‐printed b‐PLA vascular stent could recover to initial shape within 22 s, while the PLA vascular stent could not recover to initial shape after shape deformation at 60°C. Furthermore, Two‐dimensional wide‐angle X‐ray diffraction analysis (2D‐WXRD) diffraction results confirm that both PLA and b‐PLA samples exhibit two bright diffraction spots of (200)/(100) plane, and 2D‐SAXS scattering patterns changed from uniform scattering rings to the spindle‐shaped pattern after shape deformation. After shape recovery at 60°C, the 2D‐WXRD diffraction and two‐dimensional small‐angle X‐ray scattering analysis (2D‐SAXS) scattering patterns of the PLA samples remain no change, while b‐PLA samples recover to initial patterns and exhibit diffuse diffraction rings and uniform scattering rings, respectively, long period (Lac) decrease and lamellae thickness (Lc) maintain constant. The above results verify the excellent SMP of b‐PLA vascular stent as well as self‐expandable properties, which mainly ascribing to the combined action of branched entanglement points and lamellae as stationary phase. Besides, cell counting kit‐8 (CCK‐8) assays, cell live/dead staining and cell nuclei/cytoskeleton staining prove the good cell compatibility of b‐PLA stent before and after SMP. [ABSTRACT FROM AUTHOR]

In recent years, an increase in cardiovascular diseases (CVD) has been observed, constituting a global health concern, owing to a steady escalation in patient numbers. For pro-long-life services in patients, the mechanical properties, biocompatibility, and degradation behaviors of metallic vascular stents should be significantly considered during the design and manufacturing progress. In particular, biodegradable metal-based vascular stents offer initial mechanical support for cardiovascular lesions and self-degradation during vascular remodeling, thereby obviating the necessity for subsequent surgeries. Biodegradable metallic vascular stents are regarded as a prominent direction for the future development of biodegradable vascular stents (BVS), owing to their distinctive capacity for spontaneous degradation and their superior mechanical properties, which confer significant benefits upon a broader demographic afflicted by cardiovascular disease. Currently, magnesium (Mg), iron (Fe), and zinc (Zn)-based alloys are the focus of extensive research in the field of cardiovascular biodegradable materials. This paper is dedicated to delineating the benefits and limitations of three metal alloys in cardiovascular stent applications, focusing on their mechanical performance and degradation characteristics. Furthermore, a discussion on their performance within in vitro experiments, animal trials, and clinical translation is encompassed. The performance evaluation of a prospective novel biodegradable material, molybdenum (Mo), is elucidated. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) are smart materials that can alter their shape from a temporary shape to a permanent shape upon external stimuli. This unique property of SMP has shown enormous potential and breakthrough discoveries in biomedical engineering. A significant number of SMP based research publications in the recent past have demonstrated the researchers' thirst to introduce SMP based devices to the biomedical fields. SMPs favour minimally invasive surgeries and showed enormous potential in vascular stents. However, SMP-based vascular stents have not been realised to date, indicating a lack of high-quality research outputs. Most studies either repeat or provide only minor extensions to ongoing research. This article reviews SMP materials used for vascular stent development and briefly introduces SMP, architecture, and history. Followed by SMP vascular stent fabrication methods, responsive physical behaviour, the performance of the vascular stents, limitations, and vitro and vivo clinical results. Finally, challenges and future directions of SMP vascular stents are identified and highlighted. [ABSTRACT FROM AUTHOR]

BACKGROUND: As a new generation of biodegradable materials, magnesium alloy has good mechanical properties, biocompatibility, and degradability, which is one of the research hotspots in the field of biomaterials. OJECTIVE: To summarize current status and problems of magnesium alloy biomaterials in animals in recent years. METHODS: The articles were searched by using the databases of PubMed and CNKI. The key words were “metal biomaterials, degradable metals, magnesium alloy materials, magnesium-based implants, vascular stents, animal experiment, corrosion rate, biosafety” in Chinese and in English. As a result, 70 articles were applied after reading and analyzing the titles and abstracts of the articles published between January 2016 and June 2021. RESULTS AND CONCLUSION: (1) The safety and degradation rate of magnesium alloy are the main influencing factors for its clinical application as a biodegradable biomedical material. (2) Magnesium alloy has great potential in internal fixation of fracture, repair of bone defect after bone tumor operation, ligament fixation and coronary artery stenosis as vascular stent. Magnesium alloy has excellent histocompatibility and no potential safety hazard in short-term application, but there is still no long-term biosafety research result. (3) The magnesium alloy stent can support blood vessels in the early stage of vascular lesion. After the normal function of the blood vessels in this part is restored, the stent is absorbed and metabolized by the body. When the vascular stenosis and obstruction occur again, the magnesium alloy stent can be implanted again to achieve the purpose of repeated repair. (4) At present, magnesium alloy has become a hot material in the field of medical device research, but the current research results are only obtained in animal experiments or small-sample clinical trials. (5) At present, researchers have basically reached a consensus that magnesium alloy alloying, surface treatment and preparation of composite materials can effectively solve its safety problems and the defects of fast degradation rate. However, previous studies have shown that there is still a lack of standardized reference standards for animal selection, implant preparation, and evaluation methods in magnesium alloy experiments. (6) Therefore, it is necessary to perfect and formulate relevant reference standards for magnesium alloy experiments in the future for the development of rigorous and good preclinical research, which will also provide strong theoretical support for the effectiveness and safety evaluation of magnesium alloy materials. [ABSTRACT FROM AUTHOR]

Today, it takes ten to twelve years on average to complete a clinical trial before a new drug is approved and brought to market. Moreover, the evaluation of the efficacy and safety of drugs or devices has been performed in the linear and sequential manner with limited change over the past decade. The InSilc project is an EU funded project (www.insilc.eu) within which the InSilc platform was developed to design, develop and assess coronary stents. The InSilc platform contains the following modules: Mechanical Modelling Module, 3D Reconstruction and Plaque Characterization Tool, Deployment Module, Fluid Dynamics Module, Drug Delivery Module, Degradation Module, Myocardial Perfusion Module, Virtual Population Physiology and Virtual Population Database. We analysed the cost of three different in silico scenarios for clinical study. In Scenario 1, two different stent designs are compared according to the ISO standard for in silico mechanical tests. Scenario 2 predicts the stenting outcome for a virtual anatomy where design/material could be changed. Scenario 3 compares two stents using the same virtual anatomies from the Virtual vessel database. Cost-effectiveness analysis was performed for real clinical trials with metallic and BVS stent and in silico clinical trials. It was observed that in silico clinical trials are almost 90 times cheaper than real clinical trials for 1000 patients. In silico clinical trials will not completely replace real clinical studies, but the evidence shows that they can significantly reduce the cost of a real clinical study which will open a new avenue for future hybrid real and in silico clinical trials. [ABSTRACT FROM AUTHOR]

One of the leading causes of death is cardiovascular disease, and the most common cardiovascular disease is coronary artery disease. Percutaneous coronary intervention and vascular stents have emerged as a solution to treat coronary artery disease. Nowadays, several types of vascular stents share the same purpose: to reduce the percentage of restenosis, thrombosis, and neointimal hyperplasia and supply mechanical support to the blood vessels. Despite the numerous efforts to create an ideal stent, there is no coronary stent that simultaneously presents the appropriate cellular compatibility and mechanical properties to avoid stent collapse and failure. One of the emerging approaches to solve these problems is improving the mechanical performance of polymeric bioresorbable stents produced through additive manufacturing. Although there have been numerous studies in this field, normalized control parameters for 3D-printed polymeric vascular stents fabrication are absent. The present paper aims to present an overview of the current types of stents and the main polymeric materials used to fabricate the bioresorbable vascular stents. Furthermore, a detailed description of the printing parameters' influence on the mechanical performance and degradation profile of polymeric bioresorbable stents is presented. [ABSTRACT FROM AUTHOR]

Metallic stents have been largely used over the last decades to treat vascular diseases like coronary artery or peripheral vessel stenosis. Although they remain the gold standard for vascular treatment, they are subjected to in‐vivo complications such as corrosion, structural failure, fractures, and re‐stenosis due especially to the material which is used. Polymer material being less rigid than metallic material could be a potential solution and would help limiting these issues especially in peripheral vessels where flexibility is required. Among polymeric materials, polyethylene terephthalate (PET) has been used to develop stents of this study, since its biocompatibility has already been proven especially in the field of cardiovascular applications. Moreover, to guarantee flexibility, braiding technology has been used to manufacture the samples. The goal of this work was to evaluate PET‐braided stents behavior under accelerated fatigue up to 105 cycles. The effect of fatigue on the radial compression strength was then investigated and the material surface was examined by SEM to identify locations of structural failure. The effect of the different manufacturing parameters (braiding angle, braiding pattern, stent diameter, and wire diameter) on the fatigue behavior was also assessed. Results show that stents have a good elastic recovery of their diameters after fatigue despite the friction that occurred between the filaments. Moreover, fatigue loading induces radial strength loss in all stents. However, this loss varies according to the stent design. In addition, no wire fracture has been reported. It comes out from the study that PET‐braided stents show suitable mechanical behavior over accelerated fatigue loading up to 105 cycles and that their braiding parameters have a huge impact on their performances. [ABSTRACT FROM AUTHOR]

Biosafety of AZ31B magnesium (Mg) alloy and the effect of its degradation products on tissues, organs, and whole systems are highly needed to be evaluated before clinical application. This study serves a wide variety of safety evaluations of biodegradable AZ31B alloy on nerve cells. As a result of this in vitro study, the maximum aluminum (Al) ion and Mg ion concentrations in the medium were estimated to be 22 μmol/L and 2.75 mmol/L, respectively, during degradation. In addition, the corresponding cell mortality was observed to be 36% and lower than 5% according to the resistance curves of the cell to Mg and Al ions. Furthermore, the maximum Al ion and Mg ion concentrations in serum and cerebrospinal fluid were detected to be 26.1 μmol/L and 1.2 mmol/L, respectively, for 5 months implantation. Combining the result of in vivo dialysis with the result of ion tolerance assay experiments, the actual death rate of nerve cells is estimated between 4 and 10% in vivo, which is lower than the result of in vitro cytotoxicity evaluation. Moreover, no psychomotor disability during clinical studies is observed. Consequently, stent made of AZ31B alloy with surface treatment is feasible for carotid artery stenosis, and it is safe in terms of cell viability on the nervous system. [ABSTRACT FROM AUTHOR]

Abstract BACKGROUND: With the increasing incidence of vascular diseases, the clinical application of vascular stents combined with minimally invasive treatment surgery is widely used. OBJECTIVE: To describe the research background, performance requirements, types, raw materials, production and modification techniques of endovascular stents, and analyze the complications and improvement methods after the endovascular stent implanted in the human body. METHODS: The databases of CNKI and Web of Science were searched, and the search time period was from 2005 to 2020. The key words were “vascular stent, aneurysm, endovascular exclusion, research status” in English and Chinese. RESULTS AND CONCLUSION: The use of endovascular stents combined with minimally invasive treatment for aneurysms is very important in clinic. Traditional vascular stents cannot have good long-term patency rate, durability, anti-thrombosis and anti-tumor functions at the same time; it should be systematically designed and improved from the aspects of structural design, endothelialization, and functional modification of high effective drug release. The study of endovascular stents is a cutting-edge research involving multidisciplinary interdisciplinary research. To develop vascular stents with more biocompatible, more stable, and lower costs, the collaborative innovation of a multidisciplinary team of talents in biological materials, engineering technology and clinical medicine is important, so as to contribute to the medical cause of human beings. [ABSTRACT FROM AUTHOR]

In case of cardiovascular implants classified as class III medical products there is a specific responsibility for manufacturers as well as regulatory authorities to follow international standards to guarantee for safety and efficacy. Fast developments of science and technology as well as novel clinical findings create permanent needs to match the standardization. Therefore, a set of international standards is analyzed with respect to their use for particular coronary drug-eluting stents and artificial heart valves. It was found that standards (ISO, ASTM) exist for general requirements on passive implants, but also specifically relate to arterial stents, stent grafts, bioresorbable and drug-eluting stents, as well as artificial heart valves. New work items address new methods for characterization of coating integrity, particulate matter and simulated use testing. European Medical Device Regulation (MDR) requires technical expertise and capacity at Notified Bodies supported by independent test laboratories. Generally, the interest in standardization from industry, test laboratories and authorities is high, but more input from medical experts would further improve the value of standardization and its relevance for safe and even more effective implants.

One of the leading causes of death is cardiovascular disease, and the most common cardiovascular disease is coronary artery disease. Percutaneous coronary intervention and vascular stents have emerged as a solution to treat coronary artery disease. Nowadays, several types of vascular stents share the same purpose: to reduce the percentage of restenosis, thrombosis, and neointimal hyperplasia and supply mechanical support to the blood vessels. Despite the numerous efforts to create an ideal stent, there is no coronary stent that simultaneously presents the appropriate cellular compatibility and mechanical properties to avoid stent collapse and failure. One of the emerging approaches to solve these problems is improving the mechanical performance of polymeric bioresorbable stents produced through additive manufacturing. Although there have been numerous studies in this field, normalized control parameters for 3D-printed polymeric vascular stents fabrication are absent. The present paper aims to present an overview of the current types of stents and the main polymeric materials used to fabricate the bioresorbable vascular stents. Furthermore, a detailed description of the printing parameters’ influence on the mechanical performance and degradation profile of polymeric bioresorbable stents is presented.

Using pyromelliticdianhydride (PMDA) and polyfunctional epoxy ether (PFE) as branching agent, long chain branching stereocomplex poly(L‐lactide)s and poly(D‐lactide)s was prepared by reactive processing, respectably. Then stereocomplex poly(lactide)s of long chain branching PLLA and PDLA (sc‐PLA/BA) was prepared by solution blending and its fabricated the vascular stents via 3D‐printing.The effects of branching structure on melt crystallization behavior of sc‐PLA/BA investigated by DSC. The influence of the branching agent content on the crystallization ability of samples shows a bell‐shaped relationship, there is a maximum point when the branching agent content is1.5 wt%. When the branching agent content is less than 1.5 wt%, the crystallization ability of the sample increased with the increasing of branching agent content. When the branching agent content exceeded than 1.5 wt%, the crystallization ability of the samples decreased with branching agent content increasing. Such behavior is as the linear PLA branched to dendrite configuration, the enrichment of segments around branching structure within branched chains promoted its nucleation. But the high degree of branching caused inter‐ or intrachians entanglement which obstructed the segments movement and growth into the crystals. The half‐time of crystallization (t1/2) of the samples decreased from 6 minutes for initial sc‐PLA/BA‐0 to 3 minutes of sc‐PLA/BA‐1.5 wt% at 163°C. POM results indicated that nucleation density of sc‐PLA/BA significantly increased with the branching agent increasing. Moreover, mechanical testing demonstrated that forming branching structure could be an effective modification of the mechanical properties for sc‐PLA, its tensile strength and modulus increases from 57.3 MPa and 2.02 GPa to 70.4 MPa and 3.31 GPa, respectively. TGA results analyzed by FWO method and Kissinger method, indicated the apparent activation energy of sc‐PLA/BA samples increases from 96.8 to 113.3 kJ/mol, suggesting the improvement of heat resistance. The CCK‐8 assay, ALP assay and cell Live/Dead assay results indicated that sc‐PLA with branching structure presented very low cell cytotoxicity. Therefore, the long chain branching sc‐PLA matrix with branching agent could effectively improve its crystallization abilities, mechanical properties, heat resistance and biocompatibilities. [ABSTRACT FROM AUTHOR]

Percutaneous coronary intervention (PCI) with stent implantation is one of the most effective treatments for cardiovascular diseases (CVDs). However, there are still many complications after stent implantation. As a medical device with a complex structure and small size, the manufacture and post-processing technology greatly impact the mechanical and medical performances of stents. In this paper, the development history, material, manufacturing method, and post-processing technology of vascular stents are introduced. In particular, this paper focuses on the existing manufacturing technology and post-processing technology of vascular stents and the impact of these technologies on stent performance is described and discussed. Moreover, the future development of vascular stent manufacturing technology will be prospected and proposed.

Magnesium alloys are promising cardiovascular stent materials due to the favourable physical properties and complete biodegradability in vivo. However, the rapid degradation, poor cytocompatibility and tendency of thrombogenesis hinder practical clinical applications. In order to solve these problems, a facile and highly efficient strategy of alkali treatment combined with subsequent layer-by-layer assembly was used to fabricate a multifunctional coating. A bottom layer hydroxyl (–OH) with negative charge after alkali treatment first formed a solid bond with magnesium matrix to provide a rough outer surface for the further immobilization of functional biomolecules. Afterwards, polydopamine and hyaluronic acid were successively immobilized on alkali-treated magnesium surface via strong electrostatic adsorption and covalent bonding between carboxyl group of hyaluronic acid and amine or hydroxyl of polydopamine to form magnesium/OH/polydopamine/hyaluronic acid. Hydroxyl significantly improves the corrosion resistance while polydopamine and hyaluronic acid layers act as a further barrier to provide better anticorrosion. A balance between biocompatibility and antithrombogenicity has been achieved by adjusting the content of hyaluronic acid on polydopamine surface. The multifunctional magnesium/OH/polydopamine/hyaluronic acid coating with lower hyaluronic acid concentrations expose more active sites of polydopamine molecules to promote endothelial cell proliferation while retaining the intrinsic antithrombogenic function of hyaluronic acid to offer a potential application for vascular stents. [ABSTRACT FROM AUTHOR]

Improving the surface properties of vascular stents to accelerate endothelialization in vivo could play an important role in minimizing the risk of late thrombosis. We previously showed that mussel adhesive protein fused with VE‐cadherin extracellular domain (VE‐M) specifically triggered endothelial cell adhesion in vitro. In this study, using stent implants coated with VE‐M, we evaluated the clinical applicability of VE‐M in endothelialization recovery in vivo. First, we explored the effect of VE‐M on hemocompatibility and tight junctions between endothelial cells (ECs) in vitro. VE‐M significantly inhibited platelet adhesion and promoted EC proliferation. Furthermore, VE‐M drastically increased the centralization of F‐actin in human umbilical vein endothelial cells (HUVECs) along the cell contacts, reduced fluorescein isothiocyanate (FITC)—dextran transport across the HUVECs, and elevated expression levels of tight junction proteins (TJPs) in ECs. We then evaluated the effect of VE‐M on endothelialization recovery in vivo through implantation of vascular stents. At 1 day after implantation, stents coated with VE‐M recruited more endothelial progenitor cells (EPCs) than bare stents. At 7 days after implantation, VE‐M stents had a greater coverage of ECs than bare stents. At 1 month after implantation, ECs on VE‐M stents were appropriately elliptical in morphology and closely resembled physiological morphology. Hematoxylin‐eosin (HE) staining revealed little in‐stent neointima formation on VE‐M stents, and SEM images revealed that smooth endothelium had formed on VE‐M stents without adherent platelets. Taken together, these findings indicate that VE‐M accelerates in vivo endothelialization of vascular stents via recruitment of EPCs and promotes endothelium formation and could be explored as a potential bioactive coating for vascular implant. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:94–103, 2020. [ABSTRACT FROM AUTHOR]

We develop a novel mathematical and computational framework for geometric optimization of mesh-like devices such as stents, based on modeling mesh-like structures as networks of one-dimensional curved rods. To simplify calculations, the curved rods are approximated by piecewise straight rods. Constrained optimization problems for different cost functionals are stated and mathematically analyzed. The cost functionals considered include: (1) stents' compliance, (2) L 2 norm of displacement, (3) L 2 norm of contact moment (which is related to fatigue), and (4) multicriteria optimization in which stents are optimized to achieve maximal radial stiffness and minimal bending rigidity. The optimization parameters are stent's vertices, namely, the location of points where the stent struts meet. Existence of solutions to the mathematically posed optimization problems is obtained, and a numerical method based on the gradient descent algorithm is proposed to find the solutions. Three representative stents' geometries are numerically analyzed to show that the optimization algorithms provide tangible solutions. The stent geometries considered are those of Palmaz type stents, single zig-zag stent rings, and Express type stents. Interesting findings are obtained, including several new stent designs. Several optimized stents are presented, including an optimized Palmaz stent with a reduction in contact moment of 30%, and optimized Express and Palmaz stents with a reduction in compliance by more than 70%. • A mathematical framework is developed for optimization of mesh-like devices (e.g. stents) modeled as networks of 1D rods. • Constrained optimization problems for different cost functionals are stated and mathematically analyzed. • The cost functions include compliance, displacement and contact moment (fatigue), optimization parameters are stent's vertices • Existence of solutions is obtained, and a numerical method based on gradient descent is developed. • Simulations provide new optimized geometries obtained from Palmaz-type and Express-type stents. [ABSTRACT FROM AUTHOR]

Titanium alloys are widely used for biomedical applications due to their good biocompatibility. Nevertheless, they cannot be used for balloon expandable stents due to a lack of ductility compared to cobalt-chromium (Co-Cr) alloys and stainless steels. In this study, a new highly deformable Ti-16Nb-8Mo alloy was designed for such an application. However, the biological performance of a stent material is strongly influenced by the effect exerted on the behavior of endothelial cells. Therefore, the cellular responses of human umbilical vein endothelial cells (HUVECs), including morphological characteristics, cell viability and proliferation, and functional markers expression, were investigated to evaluate the biocompatibility of the alloy in the present study. The in vitro results demonstrated the suitability of this alloy for use as endovascular stents.

Over the last decades, stents have been largely used to treat vascular diseases such as coronary artery or peripheral vessel stenosis. Among the solutions which are commercially available to treat vascular stenosis, metallic stents represent the gold standard. However, issues such as restenosis, corrosion and fractures have been reported with these devices and are especially due to the material which is used. Braided polymeric stents could present an alternative to replace metallic stents especially in peripheral vessels where flexibility is required. Among polymeric materials, polyethylene terephthalate (PET), could be a good candidate as its biocompatibility has already been widely proven especially in the field of cardiovascular applications. Moreover, braided devices have been already used for the stenting of peripheral zones, providing locally outstanding flexibility due to the discontinuity of these structures. The goal of this work was to evaluate the radial strength and the recovery performances of polymeric braided stents made from PET monofilaments. In particular, the behavior of these stents under repeated cyclic radial compression loading was assessed and compared to results obtained with a metallic braided stent of same diameter. Results show that polymeric braided stents provide 100% elastic recovery after 20% diameter compression over 2000 repetitive loading cycles. However, radial strength goes slightly down with cycling, which points out that friction occurs in the braid. It comes out from the study that a braided polymer stent shows suitable mechanical behavior compared to a metallic stent over cyclic loading up to 2000 cycles. Moreover, it is shown that the mechanical behavior of these stents depend highly on the braid angle. [ABSTRACT FROM AUTHOR]

In this study, we designed a double layer-coated vascular stent of 316L stainless steel using an ultrasonic spray system to achieve both antiproliferation and antithrombosis. The coating included an inner layer of graphene oxide (GO) loaded with docetaxel (DTX) and an outer layer of carboxymethyl chitosan (CMC) loaded with heparin (Hep). The coated surface was uniform without aggregation and shedding phenomena before and after stent expanded. The coating treatment was able to inhibit the adhesion and activation of platelets and the proliferation and migration of smooth muscle cells, indicating the excellent biocompatibility and antiproliferation ability. The toxicity tests showed that the GO/DTX and CMC/Hep coating did not cause deformity and organ abnormalities in zebrafish under stereomicroscope. The stents with GO double-layer coating were safe and could effectively prevent thrombosis and in-stent restenosis after the implantation into rabbit carotid arteries for 4–12 weeks. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Technologies / Materiali in Tehnologije is the property of Institute of Metals & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The kink behavior of vascular stents is of particular interest for clinicians, stent manufacturers and regulatory as a kinked stent generates a lumen loss in the stented vessel and can lead to in-stent restenosis. In this study methods to determine the kink resistance of stents and stent delivery systems according to the ISO 25539-2 and FDA guidance no. 1545 were presented. The methods are applicable for balloon expandable stents as well as for self-expanding stents and determine the lumen loss and residual diameter change dependent on the specific bending radius.

Endovascular stents are exposed to cyclic loads resulting from daily activity and pulsatile arterial blood pressure. DIN EN ISO 25539-2 and FDA guideline 1545 recommend durability testing, exposing stents to physiological cyclic loads for a 10 year equivalent. For accelerated testing, the simulated deformation has to be comparable to physiological in-vivo deformation. A new test setup is presented to determine diameter deformation of vascular stents during fatigue testing with radial loading.

Bioresorbable scaffolds (BRS) were developed as an alternative to drug-eluting stents (DES) to facilitate vessel restoration and reduce the risk of future adverse events. However, recent meta-analyses and "real-world" registries have raised some concern about the safety of this novel technology, especially due to an increased risk of thrombosis within the first weeks of scaffold implantation. These devices appear to be less forgiving to poor implantation strategies when compared to contemporary DES. Moreover, problems with the first generation of these devices--bulky struts and high crossing prolife, prolonged resorption time, lack of x-ray visibility, and limited tolerance to postdilation--have restricted their clinical application and negatively impacted their short- to mid-term safety performance. However, the potential for long-term improvements has encouraged further research into strategies to overcome these limitations, and potentially safer next-generation devices are already undergoing in-human clinical evaluations. Based on the current literature and our center's experience with these devices, this review discusses various approaches to optimize BRS implantation, drawbacks related to current-generation BRS, and potentially advantageous features of three next-generation scaffold systems. [ABSTRACT FROM AUTHOR]

Laser cutting is a key technology for the medical devices industry, providing the flexibility, and precision for the processing of sheets, and tubes with high quality features. In this study, extensive experimentation was used to evaluate the effect of fiber laser micro-cutting parameters over average surface roughness (Ra) and back wall dross (Dbw) in AISI 316L stainless steel miniature tubes. A factorial design analysis was carried out to investigate the laser process parameters: pulse frequency, pulse width, peak power, cutting speed, and gas pressure. A real laser beam radius of 32.1 μm was fixed in all experiments. Through the appropriate combination of process parameters (i.e., high level of pulse overlapping factor, and pulse energy below 32 mJ) it was possible to achieve less than 1 μm in surface roughness at the edge of the laser-cut tube, and less than 3.5% dross deposits at the back wall of the miniature tube. [ABSTRACT FROM AUTHOR]

Vascular stents are general medical devices of class III or IIb, which are placed along the walls of the constricted coronary and peripheral blood vessels thus keeping them viable. According to the mechanism of expansion, stents may be balloon-expandable or self-expanding. Depending on the geometry they can be classified into: coil stents, open-cell modular stents and multi-cell closed cell stents. The most important characteristic of vascular stents is their flexibility, but a number of additional requirements must also be met: high radial strength, low elastic deformation, small diameter, the possibility of monitoring through the bloodstream, minimum subsequent shortening, minimum elastic longitudinal deformation, and the optimal retention at target site. Materials for production of stents must be biologically inert, visible by radiological techniques, biocompatible, corrosion-resistant and resistant to stress due to blood flow. The most significant adverse event after stent implantation is the occurrence of restenosis, which is most efficiently overcome by the application of drug releasing stents. These stents are composed of three parts: stent platform, drug carrier and a drug that inhibits neointimal hyperplasia - paclitaxel and limuses (sirolimus, everolimus, zotarolimus, tacrolimus, pimecrolimus, etc.). In recent years, stents with surfaces coated with substances that accelerate endothelialisation and thus reduce thrombosis have been developed. The latest approach is represented by a stent with the lumen coated with CD34 antibody, and the outer side coated with sirolimus. By using these devices a double effect is achieved: acceleration of endothelialisation and inhibition of neointimal hyperplasia.

Cobalt chromium (CoCr) alloy tubes have been widely used in manufacturing of vascular stents, due to their excellent bio-mechanical properties, especially their high strength. In recent years, fiber lasers have been used in the micro-machining of vascular stents, given their better cutting quality than neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. A comparison study of CoCr fiber laser cutting with oxygen and argon is presented, and the differences, such as surface topography, chemical composition, and kerfs geometry, between the oxygen cuts and argon cuts are studied. Three types of topographies are obtained for the oxygen cuts, and the underlying reason for the different topographies are discussed. The influences of key parameters including power, repetition rate, pulse width, and cutting speed on the cutting quality are analyzed. The present research can also provide an optimization guideline for the micro-profiling of CoCr vascular stents. [ABSTRACT FROM AUTHOR]

Medical implants made of biodegradable materials could be advantageous for temporary applications, such as mechanical support during bone-healing or as vascular stents to keep blood vessels open. After completion of the healing process, the implant would disappear, avoiding long-term side effects or the need for surgical removal. Various corrodible metal alloys based on magnesium, iron or zinc have been proposed as sturdier and potentially less inflammatory alternatives to degradable organic polymers, in particular for load-bearing applications. Despite the recent introduction of magnesium-based screws, the remaining hurdles to routine clinical applications are still challenging. These include limitations such as mechanical material characteristics or unsuitable corrosion characteristics. In this article, the salient features and clinical prospects of currently-investigated biodegradable implant materials are summarized, with a main focus on magnesium alloys. A mechanism of action for the stimulation of bone growth due to the exertion of mechanical force by magnesium corrosion products is discussed. To explain divergent in vitro and in vivo effects of magnesium, a novel model for bacterial biofilm infections is proposed which predicts crucial consequences for antibacterial implant strategies.

Laser cutting is a key technology for the medical devices industry, providing the flexibility, and precision for the processing of sheets, and tubes with high quality features. In this study, extensive experimentation was used to evaluate the effect of fiber laser micro-cutting parameters over average surface roughness ( R a ) and back wall dross ( D bw ) in AISI 316L stainless steel miniature tubes. A factorial design analysis was carried out to investigate the laser process parameters: pulse frequency, pulse width, peak power, cutting speed, and gas pressure. A real laser beam radius of 32.1 μm was fixed in all experiments. Through the appropriate combination of process parameters (i.e., high level of pulse overlapping factor, and pulse energy below 32 mJ) it was possible to achieve less than 1 μm in surface roughness at the edge of the laser-cut tube, and less than 3.5% dross deposits at the back wall of the miniature tube.

In this paper, a robust constitutive model adapted to a 3D beam theory in the finite strain regime is proposed to simulate thermo-mechanical behaviors of shape memory alloys (SMAs) under triaxial normal-shear loadings. For the first time, four internal parameters are considered to capture martensitic transformation, orientation/reorientation of martensite variants, normal-shear deformation coupling, and asymmetric/anisotropic strain generation in polycrystalline SMAs. Solution algorithms of the model are presented for stress- and strain-control cases based on the elastic-predictor inelastic-corrector return mapping process. To develop the Cauchy-Green deformation tensor, a 3D exact displacement field is proposed based on the centroid movements and rotations of the cross-section. A finite element formulation along with the Newton-Raphson and Riks techniques is also established to trace the non-linear equilibrium path of 3D SMA beam structures in the large defamation regime. Higher-order shape functions are also considered to avoid shear and membrane locking issues. To explore and demonstrate the capabilities of the proposed model, the results of the triaxial and 3D SMA constitutive models are compared with existing experimental results on uniaxial tension, and combined tension-torsion tests. Afterwards, the results of 3D solid element and proposed 3D beam element are compared with experimental results of deep stretch SMA helical springs under three loading/unloading cycles. An excellent qualitative and quantitative correlation is observed between numerical and experimental results verifying the model accuracy and the solution procedure. The combination of the proposed triaxial SMA constitutive model with 3D beam theory leads to a significant reduction in computational time and storage requirements without any accuracy loss. Extra simulations are then conducted for a simplified model of a 3D biomedical vascular SMA stent under various loading/unloading conditions. The simulations reveal that the new 3D finite-strain SMA-beam element is well appropriate for modeling of 3D spatial lattice-based stents. Due to simplicity and accuracy, the 3D SMA beam model could serve in future efforts for a computationally efficient modeling of large defamations of complicated 3D SMA structures with 2D members (e.g., SMA lattices). [Display omitted] • A robust constitutive model is developed to simulate behaviors of SMAs under triaxial normal-shears loadings. • The solution algorithms combined is extended to trace the non-linear equilibrium path of 3D SMA beam structures. • The results of present 3D Beam model has been compared with existing experimental results as well as 3D solid elements. • A good qualitative and quantitative correlation is observed between numerical and experimental results. • The proposed triaxial SMA beam model leads to a significant reduction in computational time without loss inaccuracy. [ABSTRACT FROM AUTHOR]

This study aims to develop reticular, tubular polyvinyl alcohol (PVA) vascular stents, and then examines their structure and properties. PVA fibers are knitted, followed by being immersed in a polycaprolactone (PCL) solution and thermally treated in order to form vascular stents. The test results indicate that the combination of a loop structure of knits and the PCL film that is adhered to fibers can effectively form elastic, compression-resistant PVA vascular stents. The vascular stents retain a stabilized path after an in vitro degradation, and thus this study successfully creates the desired elastic PVA vascular stents. [ABSTRACT FROM AUTHOR]

Using revised simulated body fluid (r-SBF), the electrochemical corrosion behavior of an Nb–60Ta–2Zr alloy for MRI compatible vascular stents was characterized in vitro. As indicated by XPS analysis, the surface passive oxide film of approximately 1.3 nm thickness was identified as a mixture of Nb 2 O 5 , Ta 2 O 5 and ZrO 2 after immersion in the r-SBF. The Nb–60Ta–2Zr alloy manifests a low corrosion rate and high polarization resistance similar to pure Nb and Ta, as shown by the potentiodynamic polarization curves and EIS. Unlike 316L stainless steel and the L605 Co–Cr alloy, no localized corrosion has been detected. Semiconducting property of passive film on the Nb–60Ta–2Zr alloy was identified as the n-type, with growth mechanism of high-field controlled growth. The excellent corrosion resistance in simulated human blood enviroment renders the Nb-60Ta-2Zr alloy promising as stent candidate material. [ABSTRACT FROM AUTHOR]