Fatigue and durability of Nitinol stents

Nitinol self-expanding stents are effective in treating peripheral artery disease, including the superficial femoral, carotid, and renal arteries. However, fracture occurrences of up to 50% have been reported in some stents after one year. These stent fractures are likely due to in vivo cyclic displacements. As such, the cyclic fatigue and durability properties of Nitinol-based endovascular stents are discussed in terms of an engineering-based experimental testing program. In this paper, the combined effects of cardiac pulsatile fatigue and stent-vessel oversizing are evaluated for application to both stents and stent subcomponents. In particular, displacement-controlled fatigue tests were performed on stent-like specimens processed from Nitinol microtubing. Fatigue data were collected with combinations of simulated oversizing conditions and pulsatile cycles that were identified by computer modeling of the stent that mimic in vivo deformation conditions. These data are analyzed with non-linear finite element computations and are illustrated with strain-life and strain-based constant-life diagrams. The utility of this approach is demonstrated in conjunction with 10 million cycle pulsatile fatigue tests of Cordis SMART Control^® Nitinol self-expanding stents to calculate fatigue safety factors and thereby predict in vivo fatigue resistance. These results demonstrate the non-linear constant fatigue-life response of Nitinol stents, whereby, contrary to conventional engineering materials, the fatigue life of Nitinol is observed to increase with increasing mean strain.     

An intriguing design concept to enhance the pulsatile fatigue life of self-expanding stents

Intravascular stenting has emerged as the primary treatment for vascular diseases and has received great attention from the medical community since its introduction two decades ago. The endovascular self-expanding stent is used to treat peripheral artery diseases; however, once implanted, these stents suffer from various cyclic motions caused by pulsatile blood pressure and daily activities. Due to this challenging environment, fatigue performance has become a critical issue for stent design. In this paper, a simple yet intriguing concept of stent design aimed at enhancing pulsatile fatigue life is investigated. The concept of this design is to shift the highly concentrated stresses/strains away from the crown and re-distribute them along the stress-free bar arm by tapering its strut width. Finite element models were developed to evaluate the mechanical integrity and pulsatile fatigue resistance of the stent to various loading conditions. Results show that the fatigue safety factor jumped to 2.5–3.0 times that of the standard stent with constant strut width. This is astonishing considering that the stent profile and scaffolding were not compromised. The findings of this paper provide an excellent approach to the optimization of future stent design to greatly improve stent fatigue performance.     

The consequences of the mechanical environment of peripheral arteries for nitinol stenting

The use of stents in peripheral arteries has not been as successful as in coronary arteries, with high rates of restenosis and stent fracture common. Normal joint flexion induces a range of forces on the arteries, which has an unknown effect on the outcomes of stenting. The objective of this study is to determine how physiological levels of vessel bending and compression following stent implantation will influence the magnitude of stent stresses and hence the risks of fatigue fracture. A further objective is to compare how this mechanical environment will influence arterial stresses following implantation of either stainless steel or nitinol stents. To this end, models of both nitinol and stainless steel stents deployed in peripheral arteries were created, with appropriate loading conditions applied. At high levels of bending and compression, the strain amplitude threshold value for fatigue failure is exceeded for nitinol stents. Bending was predicted to induce high stresses in the artery following stenting, with higher arterial stresses predicted following implantation of a stainless steel stent compared to a nitinol stent. Both bending and compression may contribute to stent fracture by increasing the strain amplitude within the stent, with the dominant factor dependant on location within the arterial tree. For the specific stent types investigated in this study, the model predictions suggest that compression is the dominant mechanical factor in terms of stent fatigue in the femoral arteries, whereas bending is the most significant factor in the popliteal artery. To increase fatigue life and reduce arterial injury, location specific stent designs are required for peripheral arteries.     

Methods for Quantifying Three-Dimensional Deformation of Arteries due to Pulsatile and Nonpulsatile Forces: Implications for the Design of Stents and Stent Grafts

The knowledge of dynamic changes in the vascular system has become increasingly important in ensuring the safety and efficacy of endovascular devices. We developed new methods for quantifying in vivo three-dimensional (3D) arterial deformation due to pulsatile and nonpulsatile forces. A two-dimensional threshold segmentation technique combined with a level set method enabled calculation of the consistent centroid of the cross-sectional vessel lumen, whereas an optimal Fourier smoothing technique was developed to eliminate spurious irregularities of the centerline connecting the centroids. Longitudinal strain and novel metrics for axial twist and curvature change were utilized to characterize 3D deformations of the abdominal aorta, common iliac artery, and superficial femoral artery (SFA) due to musculoskeletal motion and deformations of the coronary artery due to cardiac pulsatile motion. These illustrative applications show the significance of each deformation metric, revealing significant longitudinal strain and axial twist in the SFA and coronary artery, and pronounced changes in vessel curvature in the coronary artery and in the inferior region of the SFA. The proposed methods may aid in designing preclinical tests aimed at replicating dynamic in vivo conditions in the arterial tree for the purpose of developing more durable endovascular devices including stents and stent grafts.     

The role of vascular calcification in inducing fatigue and fracture of coronary stents

Traditional approaches for in-vitro pulsatile and fatigue testing of endovascular stents do not take into consideration the pathologies of the stented vessel and their associated biomechanical effects. One important pathology is calcification, which may be capable of inducing changes in the vessel wall leading to inhomogeneous distribution of stresses combined with wall motion during the cardiac cycle. These local property changes in the region adjacent to stents could directly influence in-vivo stent performance. Seven cases containing a total of 18 stents were obtained from autopsy. Radiographs were evaluated and vessels were sectioned for histology and stent topographical analysis. Stents were retrieved by chemical removal of surrounding tissue and surfaces were evaluated using 3D digital optical and scanning electron microscopy for biomechanical abrasion and fracture features. Pathologic complications such as restenosis and thrombus formation were assessed from histological sections. Direct evidence of fracture was found in 6 of the 7 cases (in 12 out of 18 stents; 9 drug eluting and 3 bare metal). The degree of stent alterations was variable, where separation of segments due to fracture occurred mostly in drug-eluting stents. All fracture surfaces were representative of a high cycle fatigue mechanism. These fractures occurred in complex lesions involving the presence of diffuse calcification alone, or in combination with vessel angulations and multiple overlapping stents. Morphologic analysis of tissue at or near some fracture sites showed evidence of thrombus formation and/or neointimal tissue growth.     

Cell Area and Strut Distribution Changes of Bent Coronary Stents： A Finite Element Analysis

Coronary stents are metal coils or mesh tubes delivered to blocked vessels through catheters, whic Recently, special drugs h are expanded by balloons to reopen and scaffold target vessels. are carried by stents （drug-eluting stents） to further reduce instent restenosis rate after stenting procedure. However, continual study on biomechanical characteristics of stents is necessary provide a more suitable drug loading for better interactions between stents and tissue, or to platform for drug-eluting stents. The purpose of this paper is to show how finite element methods can be used to study cell area and strut distribution changes of bent coronary stents. A same bending deformation was applied to two commercial coronary stent models by a rigid curved vessel. Results show that the stent design influenced the changes of cell area and strut distribution under bending situation. The stent with links had more cell area changes at outer curvature, and the stent with peak-peak （ 〉 〈 ） strut design could have strut contact and overlapping at inner curvature. In conclusion, this finite element method can be used to study and compare cell area and strut distribution changes of bent stents, and to provide a convenient tool for designers in testing and improving biomechanical characteristics of new stents.     

A Novel Carotid Covered Stent Design: In Vitro Evaluation of Performance and Influence on the Blood Flow Regime at the Carotid Artery Bifurcation

In the present study, a novel carotid covered stent design has been developed. Prototypes of different geometrical design parameters have been fabricated and their performance has been evaluated in vitro under physiological pulsatile flow condition, utilizing flow visualization (dye injection), and particle image velocimetry techniques. These evaluations include the assessment of emboli prevention capability, side-branch flow preservation, and influence on the branch flow pattern and velocity field. The novel covered stents demonstrated significantly higher emboli prevention capability than the corresponding bare metal stent, while preserving more than 83% of the original flow of the external carotid artery (ECA). Flow in the ECA through these covered stents was uniform without evidence of undesirable flow recirculation and reversed flow that might predispose the vessel wall to post-stenting intimal thickening and atherosclerotic plaque formation. This study demonstrated the potential of these novel covered stent designs for the treatment of carotid atherosclerotic stenosis. However, further computational and in vivo investigations of hemodynamics, biological effects, and mechanical performance of this covered stent design is warranted.     

An equivalent strain/Coffin-Manson approach to multiaxial fatigue and life prediction in superelastic Nitinol medical devices

Medical devices, particularly endovascular stents, manufactured from superelastic Nitinol, a near-equiatomic alloy of Ni and Ti, are subjected to complex mixed-mode loading conditions in vivo, including axial tension and compression, radial compression, pulsatile, bending and torsion. Fatigue lifetime prediction methodologies for Nitinol, however, are invariably based on uniaxial loading and thus fall short of accurately predicting the safe lifetime of stents under the complex multiaxial loading conditions experienced physiologically. While there is a considerable body of research documented on the cyclic fatigue of Nitinol in uniaxial tension or bending, there remains an almost total lack of comprehensive fatigue lifetime data for other loading conditions, such as torsion and tension/torsion. In this work, thin-walled Nitinol tubes were cycled in torsion at various mean and alternating strains to investigate the fatigue life behavior of Nitinol and results compared to equivalent fatigue data collected under uniaxial tensile/bending loads. Using these strain-life results for various loading modes and an equivalent referential (Lagrangian) strain approach, a strategy for normalizing these data is presented. Based on this strategy, a fatigue lifetime prediction model for the multiaxial loading of Nitinol is presented utilizing a modified Coffin-Manson approach where the number of cycles to failure is related to the equivalent alternating transformation strain.     

Alteration of hemodynamics in aneurysm models by stenting: Influence of stent porosity

Recent developments in minimally invasive approach to cerebrovascular diseases include the placement of stents in arteries for treatment of aneurysms. Preliminary clinical observations and experimental studies have shown that intravascular stents traversing the orifice may lead to thrombosis and subsequent occlusion of the aneurysm. The alterations in vessel local hemodynamics due to the introduction of a stent are not yet well understood. We investigated changes in local hemodynamics resulting from stent implantation. Pulsatile flow patterns in an experimental flow appraratus were visualized using laser-induced fluorescence of rhodamine dye. The test cells were constructed in a rectangular shape to facilitate an undisturbed longitudinal view of flow patterns in parent vessel and aneurysm models with and without porous stents. Woven nitinol stents of various porosities (76%, 80%, 82%, and 85%) were investigated. The selected fluid dynamic similarity parameters (Reynolds and Womersley numbers) represented conditions usually found in high-flow, larger arteries in humans (such as the carotid artery) and low-flow, smaller arteries (such as the vertebral artery). The mean Reynolds number for the larger arteries was 180, with maximum/minimum values of 490/−30 and the Womersley number was 5.3. The mean Reynolds number for the smaller arteries was 90, with maximum/minimum values of 230/2, and the Womersley number was 2.7. For the larger arteries modeled, placement of a stent of the lowest porosity across the aneurysm orifice resulted in reduction of aneurysmal vortex speed and decreased interaction with parent vessel flow. For smaller arteries, a stent of the same porosity led to a substantial reduction of parent vessel/aneurysmal flow interaction and the appearance of a nonrecirculating crescent of fluid rich in rhodamine dye in the aneurysm dome. Our results can help explainin vivo thrombus formation within an aneurysm after placement of a stent that is compatible with local hemodynamics.     

Modeling of Size Dependent Failure in Cardiovascular Stent Struts under Tension and Bending

Cardiovascular stents are cylindrical mesh-like metallic structures that are used to treat atherosclerosis. The thickness of stent struts are typically in the range of 50–150 μm. At this microscopic size scale, the tensile failure strain has been shown to be size dependent. Micromechanically representative computational models have captured this size effect in tension. In this paper polycrystalline models incorporating material fracture are used to investigate size effects for realistic stent strut geometries and loading modes. The specific loading a stent undergoes during deployment is uniquely captured and the implications for stent design are considered. Fracture analysis is also performed, identifying trends in terms of strut thickness and loading type. The results show, in addition to the size effect in tension, further size effects in different loading conditions. The results of the loading analyses are combined to produce a tension and bending failure graph. This design safety diagram is presented as a tool to predict failure of stent struts. This study is particularly significant given the current interest in producing smaller stents.     

Linear and nonlinear viscoelastic modeling of aorta and carotid pressure-area dynamics under in vivo and ex vivo conditions

A better understanding of the biomechanical properties of the arterial wall provides important insight into arterial vascular biology under normal (healthy) and pathological conditions. This insight has potential to improve tracking of disease progression and to aid in vascular graft design and implementation. In this study, we use linear and nonlinear viscoelastic models to predict biomechanical properties of the thoracic descending aorta and the carotid artery under ex vivo and in vivo conditions in ovine and human arteries. Models analyzed include a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (an arctangent and a sigmoid model) that relate changes in arterial blood pressure to the vessel cross-sectional area (via estimation of vessel strain). These models were developed using the framework of Quasilinear Viscoelasticity (QLV) theory and were validated using measurements from the thoracic descending aorta and the carotid artery obtained from human and ovine arteries. In vivo measurements were obtained from 10 ovine aortas and 10 human carotid arteries. Ex vivo measurements (from both locations) were made in 11 male Merino sheep. Biomechanical properties were obtained through constrained estimation of model parameters. To further investigate the parameter estimates, we computed standard errors and confidence intervals and we used analysis of variance to compare results within and between groups. Overall, our results indicate that optimal model selection depends on the artery type. Results showed that for the thoracic descending aorta (under both experimental conditions), the best predictions were obtained with the nonlinear sigmoid model, while under healthy physiological pressure loading the carotid arteries nonlinear stiffening with increasing pressure is negligible, and consequently, the linear (Kelvin) viscoelastic model better describes the pressure–area dynamics in this vessel. Results comparing biomechanical properties show that the Kelvin and sigmoid models were able to predict the zero-pressure vessel radius; that under ex vivo conditions vessels are more rigid, and comparatively, that the carotid artery is stiffer than the thoracic descending aorta; and that the viscoelastic gain and relaxation parameters do not differ significantly between vessels or experimental conditions. In conclusion, our study demonstrates that the proposed models can predict pressure–area dynamics and that model parameters can be extracted for further interpretation of biomechanical properties.     

Virtual optimization of self-expandable braided wire stents

At present, the deployment of self-expandable braided stents has become a common and widely used minimally invasive treatment for stenotic lesions in the cardiovascular, gastrointestinal and respiratory system. To improve these revascularization procedures (e.g. increase the positioning accuracy) the optimal strategy lies in the further development of the stent design. In the context of optimizing braided stent designs, computational models can provide an excellent research tool complementary to analytical models. In this study, a finite element based modelling strategy is proposed to investigate and optimize the mechanics of braided stents. First a geometrical and finite element model of a braided Urolume endoprosthesis was built with the open source pyFormex design tool. The results of the reference simulation of the Urolume stent are in close agreement with both analytical and experimental data. Subsequently, a simplex-based design optimization algorithm automatically adjusts the reference Urolume geometry to facilitate precise positioning by reducing the foreshortening with 20% while maintaining the radial stiffness. Therefore, the proposed modelling strategy appears to be a promising optimization methodology in braided stent design.     

Effects of through-hole drug reservoirs on key clinical attributes for drug-eluting depot stent

Atherosclerosis, a condition related to cholesterol build-up and thickening of the inner wall of the artery, narrows or occludes the artery lumen. The drug-eluting stent is a major breakthrough for the treatment of such coronary artery diseases. In recent years, another innovative variation of the drug-eluting stent with drug reservoirs has been introduced. It allows programmable drug delivery with spatial and temporal control and has several potential advantages over traditional drug-eluting stents. However, creating such reservoirs on the stent struts may weaken the stent scaffolding and compromise its mechanical integrity. In this paper, the effects of these micro-sized through-hole drug reservoirs on several key clinically relevant functional attributes of the depot stent were investigated. Finite element models were developed to predict the mechanical integrity of a balloon-expandable stent at various stages such as manufacturing and deployment, as well as the stent radial strength and fatigue life.Results show that (1) creating drug reservoirs on a stent could impact the stent fatigue resistance to some degree; (2) drug reservoirs on the stent crowns led to much greater loss in all key clinical attributes than reservoirs on other locations; (3) reservoir shape change resulted in little differences in all key clinical attributes; (4) for the same drug loading capacity, larger and fewer reservoirs yielded lower equivalent plastic strain and radial strength but higher fatigue safety factor; and (5) the proposed depot stent was proven to be a feasible design. Its total drug capacity could be tripled with acceptable marginal trade-off in key clinical attributes. These results can serve as the guidelines to help future stent designs to achieve the best combination of stent mechanical integrity and smart drug delivery in the future, thereby opening up a wide variety of new treatment potentials and opportunities.     

Simulation of longitudinal stent deformation in a patient-specific coronary artery

In percutaneous coronary intervention (PCI), stent malapposition is a common complication often leading to stent thrombosis (ST). More recently, it has also been associated with longitudinal stent deformation (LSD) normally occurring through contact of a post balloon catheter tip and the protruding malapposed stent struts.The aim of this study was to assess the longitudinal integrity of first and second generation drug eluting stents in a patient specific coronary artery segment and to compare the range of variation of applied loads with those reported elsewhere. We successfully validated computational models of three drug-eluting stent designs when assessed for longitudinal deformation. We then reconstructed a patient specific stenosed right coronary artery segment by fusing angiographic and intravascular ultrasound (IVUS) images from a real case. Within this model the mechanical behaviour of the same stents along with a modified device was compared. Specifically, after the deployment of each device, a compressive point load of 0.3 N was applied on the most malapposed strut proximally to the models. Results indicate that predicted stent longitudinal strength (i) is significantly different between the stent platforms in a manner consistent with physical testing in a laboratory environment, (ii) shows a smaller range of variation for simulations of in vivo performance relative to models of in vitro experiments, and (iii) the modified stent design demonstrated considerably higher longitudinal integrity. Interestingly, stent longitudinal stability may differ drastically after a localised in vivo force compared to a distributed in vitro force.     

典型胸主动脉裸支架的力学性能

目的 研究两种胸主动脉镍钛裸支架（Ze、Fa支架）的力学性能,为裸支架的设计和临床选择提供理论依据。方法建立两种裸支架的有限元模型和实物模型。分别完成两种裸支架弯曲、径向力和模拟使用的有限元分析,并进行对应的实物模型测试。通过实测结果验证有限元分析的准确性,预测支架植入后血管的应力和应变。结果 有限元分析表明,Ze、Fa支架弯曲90°时截面扁平率分别为3.83%和18.83%（实测为8.57%和14.27%）,弯曲180°时截面扁平率分别为12.02%和23.72%（实测为14.37%和23.35%）。Ze、Fa支架在心脏收缩期最大径向力分别为33、429 N/m（实测为31、433 N/m）,在心脏舒张期最大径向力分别为27、146 N/m（实测为29、179 N/m）。Ze、Fa支架在植入后对血管造成的最大应力分别为4、18 kPa,最大应变分别为4.17%和13.92%,最大直径扩张率分别为103%和898%。有限元分析和实测结果无显著性差异（P>0.05）。结论Ze、Fa支架植入后对健康血管造成的最大应力、应变在许可范围内。Ze支架的弯曲性能较优,适合被植入弯曲血管。Ze支架径向力较弱,适合被作为仅提供内膜支撑的Petticoat支架。较强的径向力有助于加强Fa支架在血管内的稳定性,降低脊髓缺血风险,故Fa支架适合被作为限制性裸支架。     

新型可降解锌合金支架的结构设计及其力学性能分析

目的对比分析一款新结构可降解支架和传统结构可降解支架力学性能和对狭窄血管的治疗效果。方法利用有限元数值模拟,将新结构支架和传统结构支架分别植入直径狭窄为30%的血管,对比分析两种支架的支撑性能及其对狭窄血管重构的影响。结果与传统结构支架相比,新结构支架的径向回弹率和狗骨头率分别降低了26.6%和34.7%。此外,植入新结构支架的狭窄血管回弹较小,拥有更平滑更大的管腔。结论对比传统结构支架,新结构支架具有更高的支撑性能,对狭窄血管的治疗效果更佳。具有高支撑性能的新结构支架有望成为临床介入治疗设备的新选择。     

药物洗脱冠状动脉支架系统动物实验研究

目的通过观察在猪动脉中置人心畅可降解聚合物涂层药物洗脱冠状动脉支架（天津百畅公司开发）及对照组支架后的植入后管腔丢失、内皮化、炎症反应、损伤及血栓形成情况来评价国产可降解聚合物涂层药物洗脱支架临床应用的可行性。方法将2种共60枚支架分别置入30头猪冠状动脉的前降支、回旋支以及右冠状动脉。支架植入后的2,5,12,25周,将不同数量的猪处死行组织形态学检查,观察炎症、血栓形成情况和内皮化评价。结果支架置入术后的冠脉通畅,无明显狭窄;支架贴血管内壁良好,血管内腔表面光滑;2种支架均无血栓形成,心畅可降解聚合物涂层药物洗脱支架炎症反应及内皮化与对照组无明显差异,其管腔丢失较对照组轻或无明显差异。结论实验提示心畅可降解聚合物涂层药物洗脱支架置入后有良好的血液相容性,生物性能稳定,支架内表面迅速内皮化,血管有良好的开通率。说明可降解聚合物涂层药物洗脱支架是安全、有效的。     

冠脉支架设计的材料适应性研究

目的 基于一种确定的冠脉支架设计,分析不同材料的适应性,建立支架设计-材料选择的评价方法。 方法针对可能应用的 5 种支架材料,利用有限元数值模拟方法分析支架在血管中的扩张性能,考察支架设计和材料的安全性及可用性。 针对不可降解材料重点考察支架在长期植入后的耐疲劳性能;对可降解材料分析其降解过程中 的支撑力变化,明确支架所能提供的支撑力的规律。 结果 针对确定的冠脉支架设计,模拟显示 316L 不锈钢和L605 钴铬合金支架的径向回弹率分别是 26% 和 19% ,轴向缩短率分别为 0. 22% 和 0. 28% ,最大等效应力分别为551. 2、829. 1 MPa,疲劳动态安全系数分别为 1. 36 和 1. 67,针对可降解材料 AZ31 镁合金、铁和左旋聚乳酸(PLLA),基于该设计的支架的模拟破坏时间分别为 30 h 和 180、270 d。 结论 基于本文的支架设计,L605 钴铬合金具有最佳的扩张性能和耐疲劳性能,可以满足临床需求。 相较于 AZ31 的快速降解破坏,铁支架和 PLLA 支架的力学性能接近,但仍需结构优化后才能满足临床需求。 有限元数值模拟,尤其是扩张性能和耐疲劳性能分析,可以有效模拟支架力学行为,并为支架制造材料选择和设计优化提供依据。     

<Emphasis Type="Italic">In Vitro</Emphasis> Comparison of the Effect of Stent Configuration on Wall Shear Stress Using Time-resolved Particle Image Velocimetry

Time resolved particle image velocimetry was used to measure wall shear stress (WSS) and oscillatory shear index (OSI) within a 3.0 mm diameter compliant vessel model implanted with an Abbott Vascular XIENCE V^® stent in five configurations: baseline, over-expanded, increased vessel diameter, two overlapped stents, and increased stent length. Flow through unstented vessels was also tested for comparison. Flow conditions featured a realistic coronary pressure-flow offset and reversal at average flow rates corresponding to resting (Re = 160, f = 70 bpm) and exercise conditions (Re = 300, f = 120 bpm). Comparisons revealed that the WSS was similar for all cases behind the first strut and downstream of the device, indicating that changes in configuration have little effect downstream. However, there were notable differences within each stent revealing reduced WSS values for all cases due to the stent-imposed expansion of the vessel wall (0.20–9.29 dynes/cm² for Re = 160 and d = 3.0 mm). Over-expanding the stent with a second balloon affected the alignment of the stent geometry, and led to higher WSS at the inlet and lower values at mid-stent. The overlapped stents showed disturbed flow and a WSS deficit region downstream of the overlapped region. Analysis of the longer stent showed that the WSS within the vessel recovers with distance. An overall correlation was noted between decreased WSS values and elevated OSI. Results of this study are important because decreased WSS has been implicated in endothelial cell changes and increased restenosis, and clinical research has shown that a link exists between deployment configurations and negative patient outcomes.     

A 5-fluorouracil-loaded polydioxanone weft-knitted stent for the treatment of colorectal cancer

In-stents restenosis caused by tumour ingrowth is a major problem for patients undergoing stent displacement because the conventional stents often lack a sustained anti-tumour capability. The aim of this paper was to develop a weft-knitted polydioxanone stent which can slow release 5-fluorouracil (5-FU). In order to determine the most suitable drug concentration, the 5-FU safe concentration in vivo and appropriate loading percentage in the membranes were investigated, and then 5-FU-loaded poly-l-lactide membranes at concentration of 3.2%, 6.4% and 12.8% were coated onto the stent using electro-spinning method, respectively. The morphology, chemical structure and in vitro drug release property of the coating membranes were subsequently examined. Their anti-tumour activity and mechanism were assessed in vitro and in vivo using a human colorectal cancer cell line HCT-116 and tumour-bearing BALB/c nude mice. The half maximal inhibitory concentration (IC₅₀) and the median lethal dose (LD₅₀) demonstrated that the 6.4% and 12.8% membranes had better anti-tumour effects than pure 5-FU due to the sustainable drug releasing property of the coated membranes on the stent. The membranes possessing appropriate drug loading doses, such as 6.4% or 12.8% also provided better anti-in-stents restenosis effects than other groups tested. Therefore, it is concluded that the drug-loaded stents have great potential for the use in the treatment of intestinal cancers in the future.