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The stent-graft has always been a key device in endovascular treatments. However, most stents are integrated with graft by sutures, which may fracture or untie, leading to implant failure. This study reports a new sutureless composite stent-graft fabricated by braiding technology, which can combine various materials. The proposed sutureless braided...
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... wires were used as the core yarns and wrapped by PET multi- filament yarns with fineness ranged from 100D to 200D in a regular braiding structure (Figure 1). Before braid- ing, all NiTi wires were exposed to heat setting by the customized mold (Figure 2) at 600 C for 5 min to form a stable helix shape. 26,27 The characteristics of bare and covered NiTi yarns are listed in Table 1. ...
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The novel braided composite stent (BCS), woven with both nitinol wires and polyethylene terephthalate (PET) strips, were characterized and compared with the braided nitinol stent in the same weaving pattern. Finite element models simulating the stent compression and bending were developed to quantify its radial strength and longitudinal flexibility...
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... (iii) SEM image of ePTFE for node-fibril microstructure representation (scale bar: 10 μm); [41] b) Schematic of the braiding process (blue line denotes PET fibers and red line denotes covered NiTi yarns), [82] and fabricated SGs with different parameters. [81] Left: Reproduced with permission. [82] Copyright 2018, Elsevier Ltd., Right: Reproduced with permission. ...
... [82] Copyright 2018, Elsevier Ltd., Right: Reproduced with permission. [81] Copyright 2017, SAGE Publications. c) Production of the small caliber electrospun SG and SEM image of the graft (scale bar:10 μm). ...
... The low porosity in the braided structure can play the shielding role of the SG without the need for a graft cover. [81,82] Due to the increased stent stiffness (radial and longitudinal), host artery hemodynamics can be negatively influenced by the noncompliant behavior of the implanted region, resulting in an overall pressure drop and an increase in pulse-wave velocity. [50] The concept of a braided stent entered a new era with the commercialization of the multilayer flow modulator (MFM; Cardiatis, Isnes, Belgium), bringing a new paradigm and shifting the focus of treatment from traditional aneurysm exclusion (physical barrier) to reconstruction of the parent vessel (functional barrier). ...
Endovascular treatment of aortic disorders has gained wide acceptance due to reduced physiological burden to the patient compared to open surgery, and ongoing stent‐graft evolution has made aortic repair an option for patients with more complex anatomies. To date, commercial stent‐grafts are typically developed from established production techniques with simple design structures and limited material ranges. Despite the numerous updated versions of stent‐grafts by manufacturers, the reoccurrence of device‐related complications raises questions about whether the current manfacturing methods are technically able to eliminate these problems. The technology trend to produce efficient medical devices, including stent‐grafts and all similar implants, should eventually change direction to advanced manufacturing techniques. It is expected that through recent advancements, especially the emergence of 4D‐printing and smart materials, unprecedented features can be defined for cardiovascular medical implants, like shape change and remote battery‐free self‐monitoring. 4D‐printing technology promises adaptive functionality, a highly desirable feature enabling printed cardiovascular implants to physically transform with time to perform a programmed task. This review provides a thorough assessment of the established technologies for existing stent‐grafts and provides technical commentaries on known failure modes. They then discuss the future of advanced technologies and the efforts needed to produce next‐generation endovascular implants.
... The preparation of braided stent-grafts was reported before. 21 Briefly, biomedical grade polyethylene terephthalate (PET) multifilament yarns of 200D/135f were braided with 0.12 mm nitinol (NiTi) wires (Peier Tech and Luminous Company, China) on 32-bobbin braiding machines at Donghua University (China). Four NiTi wires were used as mechanical supports, and PET multifilament yarns were adopted as the graft. ...
... Four NiTi wires were used as mechanical supports, and PET multifilament yarns were adopted as the graft. 21 To keep a consistent stent-graft inner diameter, a mold with an outer diameter of 4 mm was applied. After braiding, stentgrafts were annealed in air for 10 min at 180°C (Shanghai Yiheng Co., Ltd., China). ...
... Radial and longitudinal mechanical properties of all stentgrafts were determined by the compression instrument (Model LLY-06D, Laizhou, Co., Ltd., China). As described in a previous report, 21 the compression force was measured by the parallel plate method. The presser foot moved at a velocity of 15 mm/min. ...
Stents or stent-grafts are often functionalized with films to enhance cell/surface interactions and improve endothelialization. However, continuous or film coatings by common surface modification tactics may preclude cells from migrating along the thickness direction and may change the physical characteristics of stent-grafts. Here, polydopamine nanoparticles (PDA-NPs) are attached on braided stent-grafts tightly, forming a nano structure on micro filaments. They also serve as the anchor for bioactive REDV peptides immobilization to promote endothelia cells (ECs) activities. The results show that braided stent-grafts decorated with PDA-NPs and REDV demonstrate excellent endothelialization performance and hemocompatibility due to the micro/nano structure formed and REDV affinity to ECs. The physical properties of stent-grafts are also not compromised. A potential surface modification strategy for scaffold applications is illustrated.
... Parallel plate measurement is defined as an effective method to evaluate the compression resistance characteristics of cardiovascular stents according to ISO 25539-2012 (Standards). A customized com- pression resistance instrument (Model LLY-06D, Laizhou, Co., Ltd., China) was used ( Xue et al., 2017). The prototype stent was firstly compressed to 50% of its outer diameter. ...
... Parallel plate measurement is primarily adopted to evaluate the compression characteristics of cardiovascular stents (Standards, 2012) and conducted by a customized apparatus (Model LLY-06D, Laizhou, Co., Ltd, China) in this study (Xue et al., 2017). The upper plate firstly went down to compress prototype stents until 50% deformation of outer diameter and then went up to out of touch with stents after 30 s. Keeping unloading for 30 s, the upper plate went down again to touch the stents. ...
Polymeric bioresorbable stents (BRSs) can eliminate the long-term stent restenosis by degrading after vascular remolding and have been recommended for the congenital heart disease treatment. However, the mechanical weakness remains one of main inferiorities of their applications. So, the aim of this study was to develop mechanically reinforced bioresorbable stents (MRBSs) based on poly(p-dioxanone) (PPDO) monofilaments and braiding technology. Axial runners were introduced and MRBSs showed greatly higher compression force and relatively lower viscous performance, as well as longer mechanical stability during degradation, compared with controls. Besides, stent compression behaviors were analyzed experimentally and numerically to investigate their deformation mechanisms. The results showed increased contacting points and friction force among yarns in MRBSs. Also, the skeleton formed in MRBSs attributed to higher yarn bending degree, strain energy and better structure stability during compression. Combined with the non-linear PPDO material stress-strain ratio and thermodynamic theory, yarn based stent compression modes were discussed. In addition, the autocatalysis and nonrandom chain scission degradation behaviors of MRBSs were revealed.
... Due to its special structure, the braided stent-graft can easily keep its original pattern after deformations and is of high flexibility suitable for curved arteries (Isayama et al., 2009). We developed a composite braided stent-graft that incorporated Nitinol (NiTi) wires and polyethylene terephthalate (PET) multifilament yarns in our former research (Xue et al., 2017b). And that braided structure with low porosity can play the role of the stent-graft without using a cover. ...
... We have reported the fabrication of braided stent-grafts in our former research (Xue et al., 2017a(Xue et al., , 2017b. Briefly, biomedical-grade polyethylene terephthalate (PET) multifilament yarns of 900D/288 F (Suzhou Suture Needle Company, Suzhou, China) and Nitinol (NiTi) wires with the diameter of 0.2 mm (Winbond New Material Technology Co., Ltd, Wuxi, China) were adopted. ...
... Wires interact by the friction force, leading to highly flexible stent-grafts. In our former researches (Xue et al., 2017b), we took the advantage of braiding structures and developed composite braided stent-grafts by PET multifilament and NiTi wires. In this work, we highlighted the importance of blood permeability and microthrombus transfer performance of stent-grafts and provided an evaluation methodology. ...
Endoleak and luminal loss related to blood permeation and microthrombus migration remain the main challenges in the aneurysm treatment, although stent-grafts have been widely applied. Stent-grafts provide a boundary to shield blood and microemboli transport, which are correlated with their mass transfer performance. Water permeability of vascular prostheses with woven and knitted structures has been analyzed and documented by many researchers, as well as oxygen and protein transfer. However, it is almost a total lack of blood and microemboli transfer along the braided stent-graft thickness direction. In this research, we provided a methodology for the vascular prostheses mass transfer evaluation. Braided stent-grafts in our former research were conducted on a self-developed testing system to investigate their blood permeability and microthrombus transfer behaviors. The pressure along wall thickness direction can be changed. Analytical models were also established based on pore parameters, making them applicative to different structures. Results revealed that the mass transfer behavior of stent-grafts was positively affected by porosity and pore diameter while negatively influenced by their thickness.
... Parallel plate measurement is defined as an effective method to evaluate the compression resistance characteristics of cardiovascular stents according to ISO 25539-2012 (Standards). A customized com- pression resistance instrument (Model LLY-06D, Laizhou, Co., Ltd., China) was used ( Xue et al., 2017). The prototype stent was firstly compressed to 50% of its outer diameter. ...
Stents are vital devices to treat vascular stenosis in pediatric patients with congenital heart disease. Bioresorbable stents (BRSs) have been applied to reduce challenging complications caused by permanent metal stents. However, it remains almost a total lack of BRSs with satisfactory compression performance specifically for children with congenital heart disease, leading to importantly suboptimal effects. In this work, composite bioresorbable prototype stents with superior compression resistance were designed by braiding and annealing technology, incorporating poly (p-dioxanone) (PPDO) monofilaments and polycaprolactone (PCL) multifilament. Stent prototype compression properties were investigated. The results revealed that novel composite prototype stents showed superior compression force compared to the control ones, as well as recovery ability. Furthermore, deformation mechanisms were analyzed by computational simulation, which revealed bonded interlacing points among yarns play an important role. This research presents important clinical implications in bioresorbable stent manufacture and provides further study with an innovative stent design.
... The main objective of this study was to further the application of bending fatigue in stent-grafts, as well as the relationship between their design and bending durability. In our former study, we have developed a sutureless composite stent-graft that incorporates Nitinol (NiTi) yarns and polyethylene terephthalate (PET) multifilament yarns based on braiding technology, which is aimed at peripheral arteries (Xue et al., 2017). We hereby provided a stent-graft bending lifetime evaluation methodology in vitro. ...
... However, the diamond-shaped buckling and neck propagation in SG B , associated with friction force between NiTi yarn and NiTi yarn, contain not only inplane yarn dislocation but also out-plane buckling. We have verified higher value of friction force between NiTi yarn and NiTi yarn (the friction force between NiTi yarn and NiTi yarn was 23.49 cN and the friction force between NiTi yarn and PET was 10.87 cN) (Xue et al., 2017). Energy absorption of the diamond-shaped buckling includes bending the tube into a flat plate, and bending inclined and circumferential hinges at edges of triangles, which dissipate more energy (Harte and Fleck, 2000). ...
Stent-grafts in peripheral arteries suffer from complex cyclic loadings in vivo, including pulsatile, axial bending and torsion. Normal fatigue durability evaluation technologies, however, are majorly based on pulsation and thus are short of accuracy under the complicated stress conditions experienced physiologically. While there is a little research focused on the cyclic fatigue of stent-grafts in bending, it remains an almost total lack of deformation or fatigue mechanisms. In this work, composite braided stent-grafts incorporating Nitinol (NiTi) yarns and polyethylene terephthalate (PET) multifilament yarns were cycled in bending by the self-developed testing system to investigate their deformation behaviors. Deformation mechanisms at the yarn level were discussed, and NiTi yarn crossover structure was considered the primary factor affecting the deformation modes. Four yarn-crossover-based deformation modes (accordion buckling, diamond-shaped buckling, neck propagation and microbuckling) revealed the mechanisms of energy absorption of braided stent-grafts on the mesoscopic scale. Further, mechanical modes were applied to help regulate stent designs.
Stent insertion can serve as an effective therapy method for patients with esophageal stricture but stents with inappropriate mechanical properties lead to restenosis. To prepare a stent matching the esophageal environmental mechanics, both the NiTi spring yarn and polyester multifilament were used to produce seven kinds of stents by braiding technology. The mechanical properties of the stents were tested including compression, flexibility, and antimigration behavior. Results showed that three different parameters including spring consistency with tracks, spring content, and spring pitch altered the effective number of coils and elastic modulus, and affected the compression strength, flexibility and migration resistance of the stent. In particular, the integrated braided stent with full consistency, 12 NiTi spiral yarns, and spring pitch of 1.00 mm had the best mechanical properties among all the prototypes in this research. The compression strength, bending strength, and migration resistance were 1048.75 cN, 46.35 cN, and 3.74 N, respectively. In summary, this research presents a new preparation method for esophageal stent manufacture in the treatment of inoperable esophageal malignancies.
Poly(L-lactic acid) (PLLA) braided stents have superior biocompatibility and flexibility, substituting metal stents in peripheral blood vessels. However, the radial supporting capacity of PLLA braided stent should be improved to bear the dynamic load from the peripheral artery. This paper evaluated the radial support performance of PLLA braided stents with different braiding angles after the radial cyclic loads test. The results indicate that braiding angle of stents is an important parameter affecting its ability to resist radial cyclic loads. The stent with a smaller braiding angle has better initial radial support but insufficient durability, while the stent with a larger braiding angle could maintain adequate radial support and suitable ability to resist radial cyclic loads. The theoretical analysis, verified by observing the surface morphology of filament crossover points, found that filaments of the stents with smaller braiding angles have more significant axial displacement and axial rotation angle during radial compression, which made the friction phenomenon more intense and led to insufficient ability to resist radial cyclic loads. This study could provide a meaningful idea for preparing biodegradable braided stents with suitable ability to resist radial cyclic loads.
