Editor's Choice -- Type IIIb Endoleaks: Fabric Perforations of Explanted New Generation Endoprostheses.

OBJECTIVE: To analyse explanted endografts (EGs) and describe fabric degradation responsible for type IIIb endoleaks. METHODS: As part of the European collaborative retrieval programme, 32 EGs with fabric defects on macroscopic evaluation were selected. The explanted EGs were processed and studied based on the ISO 9001 certified standard protocol. It includes instructions on the collection, transportation, cleaning, and examination of explanted material. The precise analysis was performed with a digital microscope of 20 - 200 times magnification. Possible perforation mechanisms were assessed in stress tests. RESULTS: The median time to explantation of the 32 EGs was 54 months. The explants included 65 separate EG modules, with 46 (70.8%) having a combined 388 fabric perforations. Each EG had a median of 4.79 mm2 (interquartile range [IQR] 9.86 mm2) of cumulated hole area (an average of 0.13% of an EG's area). There were 239 (61.6%) expanded polytetrafluoroethylene (ePTFE; 11 EGs) and 149 (38.4%) polyethylene terephthalate (PET; 21 EGs) fabric ruptures, with no difference in hole distribution between these types of material. Overall, 126 (32.5%) stent related and 262 (67.5%) non-stent related fabric perforations were identified. Perforations caused by fabric fatigue in ePTFE (151, 63.2%) and material kinking in PET (41, 27.5%) were the most common. The stent related perforations were larger in size (0.80 mm2) than non-stent related perforations (0.19 mm2); p < .001. Wider interstent spaces and prolonged implantation duration were associated with an increased risk of stent related perforation development; p < .001 and p = .004, respectively. Large stent related perforations were also detected in the short term, suggesting mechanical issues as underlying causes. CONCLUSION: The fabric of EGs may degrade and lead to the development of perforations. The largest perforations are stent related. Their occurrence and size depend on the implantation time and the EG shape affected by arterial tortuosity. The conclusions are limited to the samples from a select explant group.

Mechanical Performance Assessment of Physician Modified Aortic Stent Graft.

OBJECTIVE: This study aimed to compare various fenestration configurations of physician modified aortic stent grafts in order to identify which design parameters have a significant influence on the mechanical behaviour of the fenestration. METHODS: the fenestration configurations were considered according to different manufacturing parameters: cutting technique, fenestration reinforcement, suture material, reinforcement loop design, and number of suture points. The performance of the graft/bridging stent assembly was assessed at various levels: (1) branch pull out force; (2) fenestration enlargement and rupture strength; (3) balloon angioplasty resistance; and (4) behaviour under cyclic fatigue. RESULTS: Sixty manual fenestrations were created. The tests performed on the fenestrations had several main findings. First, reinforcement increased the radial force on the branch, which increased the pull out force; this may limit migration of the bridging stent in vivo. The phenomenon was amplified with a snare reinforced fenestration, which seemed to be the most efficient. Moreover, increasing the number of suture passes also appeared to increase the branch extraction force securing the assembly. The enlargement tests showed that non-reinforced fenestrations had the weakest radial strength. This was confirmed with the balloon angioplasty test, which showed that these latter specimens undergo the most significant textile degradation. After fatigue tests, all fenestrations were larger, showing that elastic recoil was incomplete in all samples. The largest recoil was observed in the non-reinforced ophthalmological cautery (OC) fenestrations (40%). Regarding the behaviour of the samples up to rupture, all samples behaved in a similar way; however, the double loop fenestration strength level was the highest. CONCLUSION: This study demonstrated that the snare double loop reinforcement has an advantage regarding durability of the graft branch assembly. Moreover, non-reinforced fenestrations show signs of weakness and lack of stability, which questions the in situ or laser fenestration procedures.

Mechanical Behaviour of Fenestrations in Current Aortic Endografts.

OBJECTIVE: The aim of this study was to assess the mechanical characteristics of current commercially available fenestrated endografts (FE). The performance of the fenestrations according to the design were compared as the relationship between a bridging covered stent graft (CSG) and the fenestration. METHODS: A total of 21 Zenith (Cook Medical, Bloomington, IN, USA) and 17 Anaconda (Terumo Company, Inchinnan, UK) fenestrations were studied. Radial extension tests were performed, inserting two half cylinders spaced up to 2 mm in a 7 mm diameter fenestration from each device. Branch pull out force was measured to test the stability of the assembly with a calibrated 8 mm branch and two CSGs: Advanta V12 (Atrium Medical; Hudson, NH, USA) and BeGraft Peripheral Stent Graft (Bentley InnoMed GmbH, Hechingen, Germany). A branch was inserted in both the 7 mm diameter fenestrations and in a control 7 mm fenestration. Fatigue tests were performed on the devices to assess long term outcomes of the endograft. RESULTS: Over a 2 mm vertical displacement, the resulting loading curves look similar for both devices. The force value level was 33.4 ± 6.9 N for the Cook fenestration and 54.45 ± 18 N for the Anaconda fenestration (p = .001). With respect to an 8 mm calibrated branch, the required extraction strength from the fenestration was statistically significantly greater with the Anaconda device (9.5 ± 4.7 N vs. 4.49 ± 0.28 N; p = .001). The required strength to extract the V12 CSG from a control cylindered shape was statistically significantly higher than for the BeGraft CSG (6.75 ± 2.86 N vs. 1.83 ± 0.67 N; p = .003). The surface area of the fenestration of the Cook device was increased with cycling (7 200 cycles) compared with the Anaconda device (15.5% vs. 6.5% hole surface area increase). CONCLUSION: The mechanical performance of the fenestration can be fine tuned by considering its design. A CSG optimising the performance of the fenestration and the CGS-fenestration interface could reduce the risk of leakage in clinical practice.

Comprehensive Review of Physician Modified Aortic Stent Grafts: Technical and Clinical Outcomes.

OBJECTIVE: Physician modified stent grafts (PMSGs) present satisfactory results in selected cases of complex aortic pathologies. However, the technique lacks standardisation and depends on the surgeon and aortic segment. The aim of this article is to review comprehensively the technical details and clinical results of PMSGs related to patients with pathology in all aortic locations. METHODS: A MEDLINE search (last search 20 April 2020) identified 20 relevant papers in the English language published over the last 20 years evaluating clinical outcomes after a PMSG and specifying the technical details to design it. RESULTS: Seven hundred and eleven patients were included in the analyses, with 59% being operated on as an emergency. Ninety-two per cent of abdominal aortic segment PMSGs (A-PMSGs) were performed either as an emergency or before 2012. The main indications were available in 670 cases; 435 were degenerative aneurysms (64.9%) and 171 were aortic dissections (25.5%). Most of the endografts used were composed of polyethylene terephthalate, except for the Ankura (expanded polytetrafluoroethylene [Lifetech Scientific, Shenzhen, China]; n = 50, 7.5%). The Valiant (Medtronic, Minneapolis, MN, USA) represented 65% (n = 169) of aortic arch PMSGs (aa-PMSGs) and the Zenith platform (Cook Medical, Bloomington, IN, USA) 51% (n = 139) of A-PMSGs. A snare was used to reinforce the fenestration in 458 PMSGs (66%) and a cautery device cut the fenestration in 484 (75%) PMSGs. No bridging stent was used in 47 (7.0%) PMSGs (these aa-PMSGs had large fenestrations). Technical success ranged from 87.5% to 100% and 30 day mortality from 0% to 8%. Primary branch patency ranged from 96.3% to 100% at 12 month follow up. Zero to 14% of patients experienced type 3 or type 1 endoleak at 14.8 month follow up. CONCLUSION: PMSG is a useful technique, particularly when validated treatments are not available. However, it is a non-standardised technique and the long term consequences of modifications remain unknown.

Compliance of Textile Vascular Prostheses Is a Fleeting Reality.

OBJECTIVE: Compliance is considered to be a major property influencing the long term performances of synthetic vascular substitutes that could play a role in anastomotic false aneurysm and intimal hyperplasia stenosis onset. Over the last decades, manufacturers have tried to develop substitutes that mechanically mimic arterial properties and avoid a compliance mismatch at the anastomoses in particular. However, data are missing about how initial compliance properties could change with time. The goal of this study was to evaluate how the compliance of vascular grafts evolves under cyclic loading conditions in vitro. METHODS: The compliance of three different models of commercially available textile polyethylene terephthalate (PET) grafts was evaluated. Tests were performed with and without their original coating. Compliance was assessed with a specific device dedicated to measure the deformations undergone by a graft under cyclic pressure loading conditions, using image analysis software. In each experiment, image analysis was performed under 60 and 140 mmHg pressure loading conditions at loading start (H0) and after three, six, and 24 h (H3, H6, H24) loading time. Average radial, longitudinal, and volumetric compliance was calculated from the obtained images. RESULTS: Twenty-four samples were tested. Results demonstrate that all values decreased significantly within only a few hours. On average, the loss of compliance after 3 h of cyclic loading ranged on average from 35% for longitudinal compliance to 39% for radial compliance and 37% (p < .050) for volume compliance. After 24 h, the loss of radial, longitudinal and volume compliance was respectively 63 ± 3%, 60.5 ± 2% and 61 ± 7%. CONCLUSION: In this in vitro model, PET graft compliance has already decreased significantly within 3 h. The rapid loss of compliance identified in this experimental study helps explain the mismatch mentioned in clinical observations.

Laser Uses in Noncoronary Arterial Disease.

BACKGROUND: In the past decade, excimer laser angioplasty (ELA) has emerged in the field of peripheral artery disease (PAD). Laser indications now extend to off-label uses, such as in situ fenestration of aortic endograft. The aim of this study was to review the different therapeutics applications of lasers in arterial disease treatment. METHODS: We reviewed the English-language literature using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. We selected 106 relevant papers. We excluded unrelated papers (n = 67), letters and commentaries (n = 6), and review articles (n = 7), leaving 26 articles to form the basis of this review. RESULTS: A total of 18 articles were included in the analysis of ELA applications in PAD. Nine articles were related to atherosclerotic plaques. With a mean follow-up of 15 ± 7 months, primary patency was 65% ± 20%. The mean distal embolism rate during the procedure was 5%. Eight more articles focused on in-stent restenosis. The mean technical success was 98%, and the rate of distal embolism during the procedure was 9%. With a mean follow-up of 10 ± 4 months, primary patency was 68% ± 18%. Eight articles described "off-label" excimer laser indications in endovascular therapy, including 5 papers regarding in situ fenestrations for complex aortic aneurysms. CONCLUSION: Laser atherectomy and laser-assisted techniques are an important part of a vascular surgeon and interventionalist's armamentarium.

Explanted Vascular and Endovascular Graft Analysis: Where Do We Stand and What Should We Do?

OBJECTIVE/BACKGROUND: Since the late 1950s, major advances in vascular surgical practice have been closely associated with the introduction of novel vascular implants. These devices have been constructed from a variety of materials and have been designed to be implanted in several different ways. Despite a rigorous regulatory process, regular failures continue to be observed. A systematic review of the literature and of the Geprovas registry was performed in order to improve understanding of the failures. METHODS: A systematic review was performed via a search of the MEDLINE and Embase databases. Full text, English, German, or French language studies without any chronological limit were included. The reference lists of included studies, as well as the first 20 related items, were scanned for other potentially relevant studies. RESULTS: Data extraction allowed the evaluation of 184 publications; 72 publications met the inclusion criteria. Only 12 publications reported sufficient data for structural, histopathological, and epidemiological analysis. However, explant analysis allowed the understanding of degenerative phenomena: "warp knitted" replaced "weft knitted" polyethylene terephthalate grafts, decreasing the risk of dilatation or rupture; inter-nodal distance was modified in order to improve polytetrafluoroethylene graft incorporation capacities; and index of saturation, endograft fabric/stent interactions, and stent fatigue phenomena have been extensively studied in an attempt to improve endovascular device durability. CONCLUSION: A general lack of depth of reporting of explants remains. Dedicated systematic explant analysis programs are the key to improving the performance of future generations of devices.

How Compression Inside a Delivery System can Degrade the Cover of Aortic Endografts.

BACKGROUND: The goal of the present study was to identify the potential degradations undergone by textile endoprostheses (EPs) over the crimping process related to the catheter insertion purpose. In particular, we studied how the device design parameters can influence the wrinkling of the textile material, assuming that wrinkling induces stress concentration and may jeopardize the lifetime of the device. MATERIALS AND METHODS: Custom-designed EPs were obtained from various stent designs and textile constructions. Monofilament and multifilament materials were considered for the cover. Stent segment size, distance, and wire diameter were considered as variable for the stent. The EPs of 26-mm diameter were then crimped in a mock transparent 6-mm diameter catheter sheath for 8 and 30 days duration. After releasing the EPs from the sheath, the textile cover was characterized for roughness properties to identify the crease level induced on the surface by crimping. RESULTS: Results brought out that the monofilament material was characterized by a larger number of deeper creases in the zones where the stent was in contact with the cover. Conversely, the multifilament was more folded in the zones between stent segments. Moreover, it appeared that the stent design influenced the creases' topography. The textile seemed to be less prone to heavy wrinkling with stent segments made from larger wire diameter and larger segment size. Regarding the crimping duration, it came out that a longer stay in the sheath tends to promote more significant wrinkling. CONCLUSIONS: In this work, it was shown that wrinkling of the textile cover occurs in the EPs already at crimping level. However, an appropriate design of the EPs should limit the phenomenon and improve the performances of the EPs.

Evaluation of Nitinol Stents Using a 3-Dimensional Printed Superficial Femoral Artery Model: A Preliminary Study.

BACKGROUND: Mechanical tests assessing Nitinol stents used for the superficial femoral artery (SFA) are designed without taking into account their deployment environments. The objectives of this study were (1) to create normal and pathologic femoral artery models, (2) to run mechanical tests reproducing the stresses of the SFA, and (3) to study and compare Nitinol stents in those conditions. METHODS: Femoral artery models with identical mechanical properties to the SFA were created using the 3-dimensional printing technology. Those models were designed with and without an asymmetric focal 50% stenosis. Three mechanical tests (bending-compression, bending-compression-torsion, and multiple bending tests) were created and 1 flexible stent was tested, of 6 and 7-mm diameter. Three samples of the stent, LifeStent (Bard(®)), were deployed and tested in the models. Stents alone were evaluated in the same conditions. The analysis focused on the comparison of rheologic curves, level of kink, and the energy deployed for each stent to kink. RESULTS: In the 3 tests, all stents deployed in the models presented a kink during their evaluation. When tested alone, during the compression-bending and bending-compression-torsion tests, no plicature was observed. During the multiple bending test, the energy deployed to plicature for the stent tested alone was of 1.4 ± 0.10 and 2.84 ± 0.1 J compared with 9.7 ± 0.6 and 8.25 ± 0.6 J when deployed in the model for the Lifestent 6 × 80 and 7 × 80 mm, respectively. For all of these 3 tests, 6-mm diameter stents exhibited a level of kink and energy of kink higher than 7 mm stents. The behavior of the stents changed in the stenosed model whatever diameter is taken into account. Analysis of the rheologic curves showed a decrease in the inflection of the curve related to the plication. In the bending-compression test, the presence of a stenosis lead to an early plication of the model, with less deployed kinking energy whereas in the bending, compression, and torsion test, this earliness was absent. CONCLUSIONS: This study permitted the creation of a mechanical test platform evaluating Nitinol stents in bending situations. It tends to confirm the mechanical deleterious effect of excessive oversizing. This study confirms the necessity to evaluate Nitinol stents in their deployment environments.

Learning Curve of Robotic-Assisted Anastomosis: Shorter than the Laparoscopic Technique? An Educational Study.

BACKGROUND: Achieving aortic anastomosis in laparoscopic surgery remains a technical challenge. The Da Vinci robot could theoretically counteract this issue by minimizing the technical challenge. The aim of this study was to compare the learning curves of performing vascular anastomoses by trainees without any experience using purely laparoscopic versus robotic-assisted techniques. METHODS: Surgery residents were randomly included in the laparoscopic group (group A, n = 3) and the robotic group (group B, n = 3). They performed 10 end-to-end anastomoses on 18-mm-diameter tubular expanded polytetrafluoroethylene grafts. The parameters recorded were duration to complete the anastomosis and an indirect sealing quality evaluation (ISQE) defined as the following ratio: number of stitches with a distance of less than 4 mm/total number of stitches. RESULTS: The mean duration to perform the anastomosis decreased from 2340 s (±64) for the first anastomosis to 651 s (±248) for the last in group A (P < 0.05) and from 1989 s (±556) to 801 s (±120) in group B (P < 0.05). The mean ISQE increased from 74% (±18) for the first anastomosis to 98% (±3) for the last in group A (P < 0.05) and decreased from 100% to 98% (±2) in group B (nonsignificant). The mean duration to perform the first anastomosis was lower in group B than in group A (P < 0.05). The mean duration to perform the last anastomosis was not significantly different between the groups. Sealing tended to be better in group B for the first anastomosis compared with group A. CONCLUSIONS: Minimally invasive laparoscopic technique training demonstrates a learning curve to perform vascular anastomoses. The robotic-assisted technique tended to improve suturing skills and should be considered as a valuable tool to reduce the technical learning curve.

Relation between tensile tests and compliance in polyester textile vascular prostheses.

BACKGROUND: Compliance is one of the mechanical features of a vascular prosthesis (VP) that influences its performances. The goal of the present in vitro study was to attempt characterizing textile VP compliance through mechanical tests proposed in the standards. METHODS: Three different models of commercially available knitted VP (P1, P2, and P3) were studied using longitudinal and circumferential traction tests on coated and uncoated samples. Five samples of each model were considered for each test. The Young modulus was then calculated to indirectly predict the longitudinal and radial compliance of the VP. Moreover, actual compliance was measured on a specific device that regulates the intraluminal pressure of a fluid maintained in the tested VP at 37°C. VP dilatation under pressure load was measured with a digital camera system. RESULTS: The Young modulus variations from one VP to the other were compared with the differences between effective compliance values at radial, longitudinal, and volume level. Although the presented results show differences among the VP, one can observe that the graft materials' Young modulus and the compliance properties are linked together in general. CONCLUSIONS: Although VPs are subjected to multidirectional stresses ex vivo, unidirectional standard mechanical tests, through the measurement of the materials Young modulus, can help predicting their compliance, however, in a limited frame.

Textile heart valve: first in-vivo experiment in the aortic position.

Non-invasive aortic valve implantation has become an alternative technique to surgical valve replacement in patients at high risk for open-chest surgery. With over 100,000 procedures already performed clinically, the technology is expected to involve less-critical patients in future. Whereas, biological valve tissue is a fragile material when folded for low-diameter catheter insertion purposes, textile polyester is a less-fragile material and may offer an alternative material to replace valve leaflets. One issue related to textile is the porosity of the material, which may induce exaggerated tissue ingrowth. Today, data relating to interactions between living tissues and fabrics used as valve materials are available only in the mitral position. Hence, the study aim was to observe the interaction pattern when the valve is implanted in the aortic position, and to assess the influence of sinus whirls on this pattern.

Surface treatment of PET multifilament textile for biomedical applications: roughness modification and fibroblast viability assessment.

OBJECTIVES: The aim of this study was to investigate the potential of tuning the topography of textile surfaces for biomedical applications towards modified cell-substrate interactions. METHODS: For that purpose, a supercritical Nitrogen N2 jet was used to spray glass particles on multi-filament polyethylene terephthalate (PET) yarns and on woven fabrics. The influence of the jet projection parameters such as the jet pressure (P) and the standoff distance (SoD) on the roughness was investigated. RESULTS: The impact of the particles created local filament ruptures on the treated surfaces towards hairiness increase. The results show that the treatment increases the roughness by up to 17 % at P 300 bars and SoD 300 mm while the strength of the material is slightly decreased. The biological study brings out that proliferation can be slightly limited on a more hairy surface, and is increased when the surface is more flat. After 10 days of fibroblast culture, the cells covered the entire surface of the fabrics and had mainly grown unidirectionally, forming cell clusters oriented along the longitudinal axis of the textile yarns. Clusters were generated at yarn crossings. CONCLUSIONS: This approach revealed that the particle projection technology can help tuning the cell proliferation on a textile surface.

Medical textile implants: hybrid fibrous constructions towards improved performances.

OBJECTIVES: One main challenge for textile implants is to limit the foreign body reaction (FBR) and in particular the fibrosis development once the device is implanted. Fibrotic tissue in-growth depends on the fiber size, the pore size, and the organization of the fibrous construction. Basically, non-woven fibrous assemblies present a more favorable interface to biological tissues than do woven structures. However, they are mechanically less strong. In order to combine both strength and appropriate topography properties, the design of a hybrid fibrous construct was considered and discussed in this work. METHODS: Two polyethylene terephthalate (PET) weaves (satin and plain) were assembled with a non-woven PET mat, using an ultrasound welding process. RESULTS: The physical and mechanical properties of the construction as well as its ability to interact with the biological environment were then evaluated. In particular, the wettability of the obtained substrate as well as its ability to interact with mesenchymal stem cells (MSC) at 24 h (adhesion) and 72 h (proliferation) in vitro were studied. CONCLUSIONS: The results show that the non-woven layer helps limiting cell proliferation in the plain weave construction and promotes conversely proliferation in the satin construction.

Textile heart valve prosthesis: from fabric design criteria to early in-vivo performances.

BACKGROUND AND AIM OF THE STUDY: Percutaneous aortic valve implantation has become an alternative technique to surgical valve replacement in patients at high risk for open-chest surgery. Biological valve tissue is, however, a fragile material when folded for small-diameter catheter insertion purposes. Textile polyester is a less fragile material, and could be an alternative replacement for the valve leaflets. The dynamic performances obtained in vitro with a valve prosthesis made from textile have proven in previous studies to be satisfactory. However, as textile is a porous material the interaction processes between the fabric leaflet surfaces and living tissues remain unknown. The study aim was to discuss the fabric design criteria which are best suited to clinical application. METHODS: An appropriate design provided strength, limited porosity and low bulk to the fabric, which was particularly suited for small-diameter catheter insertion purposes. The in-vivo behavior of a non-coated polyester textile valve prototype was then studied in the mitral position in a sheep model. RESULTS: The results showed that limited tissue ingrowth occurred, and Ca deposits tended to stiffen the fabric leaflets after a two-month implantation period, which was not compatible with the survival of the animal. CONCLUSION: The initial results obtained with this non-coated polyester textile valve confirmed that this revolutionary fabric is worthy of further investigation.

Mechanical Comparison between Fenestrated Endograft and Physician-Made Fenestrations.

INTRODUCTION: A fenestrated endograft (FE) is the first-line endovascular option for juxta and pararenal abdominal aortic aneurysms. A physician-modified stent-graft (PMSG) and laser in situ fenestration (LISF) have emerged to circumvent manufacturing delays, anatomic standards, and the procedure's cost raised by FE. The objective was to compare different fenestrations from a mechanical point of view. METHODS: In total, five Zenith Cook fenestrations (Cook Medical, Bloomington, IN, USA) and five Anaconda fenestrations (Terumo Company, Inchinnan, Scotland, UK) were included in this study. Laser ISF and PMSG were created on a Cook TX2 polyethylene terephthalate (PET) cover material (Cook Medical, Bloomington, IN, USA). In total, five LISFs and fifty-five PMSG were created. All fenestrations included reached an 8 mm diameter. Radial extension tests were then performed to identify differences in the mechanical behavior between the fenestration designs. The branch pull-out force was measured to test the stability of assembling with a calibrated 8 mm branch. Fatigue tests were performed on the devices to assess the long-term outcomes of the endograft with an oversized 9 mm branch. RESULTS: The results revealed that at over 2 mm of oversizing, the highest average radial strength was 33.4 ± 6.9 N for the Zenith Cook fenestration. The radial strength was higher with the custom-made fenestrations, including both Zenith Cook and Anaconda fenestrations (9.5 ± 4.7 N and 4.49 ± 0.28 N). The comparison between LISF and double loop PMSG highlighted a higher strength value compared with LISF (3.96 N ± 1.86 vs. 2.7 N ± 0.82; p= 0.018). The diameter of the fenestrations varied between 8 and 9 mm. As the pin caliber inserted in the fenestration was 9 mm, one could consider that all fenestrations underwent an "elastic recoil" after cycling. The largest elastic recoil was observed in the non-reinforced/OC fenestrations (40%). A 10% elastic recoil was observed with LISF. CONCLUSION: In terms of mechanical behavior, the custom-made fenestration produced the highest results in terms of radial and branch pull-out strength. Both PMSG and LISF could be improved with the standardization of the fenestration creation protocol.

Calcification of Synthetic Vascular Grafts: A Systematic Review.

Objective: Calcification of vascular grafts, including polyethylene terephthalate (PET) and expanded polytetrafluoroethylene (ePTFE) grafts may contribute to graft failure, but is under reported. The aim of this study was to review the literature to assess whether vascular graft calcification is deleterious to vascular graft outcomes. Data sources: The Medline and Embase databases were searched. Review methods: A systematic literature search according to PRISMA Guidelines was performed using a combined search strategy of MeSH terms. The MeSH terms used were "calcification, physiologic", "calcinosis", "vascular grafting", "blood vessel prosthesis", "polyethylene terephthalates", and "polytetrafluoroethylene". Results: The systematic search identified 17 cases of PET graft calcification and 73 cases of ePTFE graft calcification over a 35 year period. All cases of PET graft calcification were reported in grafts explanted for graft failure. The majority of cases of ePTFE graft calcification were unexpectedly noted in grafts used during cardiovascular procedures and subsequently removed. Conclusion: Calcification of synthetic vascular grafts is under reported but can compromise the long term performance of the grafts. More data, including specific analysis of radiological findings as well as explant analysis are needed to obtain a more sensitive and specific analysis of the prevalence and incidence of vascular graft calcification and the impact of calcification on synthetic graft outcomes.

Degradation phenomena on last generations of polyethylene terephthalate knitted vascular prostheses.

Objectives: The aim of this study was to analyze a series of new generations of explanted knitted polyethylene terephthalate (PET) vascular grafts (VGs) presenting nonanastomotic degradations according to preoperative computed tomography angiography (CTA) when available in order to better understand the mechanisms leading to rupture. Methods: Explanted knitted PET VGs were collected as part of the Geprovas European Collaborative Retrieval Program. VGs implanted after 1990 presenting a nonanastomotic rupture of the fabric were included. Clinical data and pre-explantation CTA data when available were retrieved for each VG. The ruptures were characterized by macroscopic examination and optical microscopy according to a standardized protocol. Results: Nineteen explants were collected across 11 European centers, 13 were implanted as infrainguinal bypasses, 3 at the aortic level, and 1 as an axillobifemoral bypass. The mean implantation duration was 9.2 years. Pre-explantation CTA data were available for 8 VGs and showed false aneurysms at the adductor canal level on 4 VGs, at the inguinal ligament level on 2 VGs, and in the proximal or middle third thigh level on 3 VGs. Examination revealed longitudinal ruptures on 9 explanted VGs (EVGs), transversal ruptures on 15 EVGs, 45°-oriented ruptures on 5 EVGs, V-shaped ruptures on 7 EVGs, and punctiform ruptures on 2 EVGs. Ruptures involved the remeshing line on 11 EVGs, the guideline on 10 EVGs, and the crimping valley on 15 EVGs.At the microscopic level, two main degradation phenomena could be identified: a decrease in the density of the meshing and local ruptures of the PET fibers. Fourteen EVGs presented a loosening of the remeshing line and 17 EVGs an attenuation of the crimping. Conclusions: New-generation PET VG degradation seems to result from both anatomic constraints and intrinsic textile structure phenomena.

Non-woven textiles for medical implants: mechanical performances improvement.

Non-woven textile has been largely used as medical implant material over the last decades, especially for scaffold manufacturing purpose. This material presents a large surface area-to-volume ratio, which promotes adequate interaction with biological tissues. However, its strength is limited due to the lack of cohesion between the fibers. The goal of the present work was to investigate if a non-woven substrate can be reinforced by embroidery stitching towards strength increase. Non-woven samples were produced from both melt-blowing and electro-spinning techniques, reinforced with a stitching yarn and tested regarding several performances: ultimate tensile strength, burst strength and strength loss after fatigue stress. Several stitching parameters were considered: distance between stitches, number of stitch lines (1, 2 or 3) and line geometry (horizontal H, vertical L, cross X). The performance values obtained after reinforcement were compared with values obtained for control samples. Results bring out that reinforcement can increase the strength by up to 50% for a melt-blown mat and by up to 100% for an electro-spun mat with an X reinforcement pattern. However, after cyclic loading, the reinforcement yarn tends to degrade the ES mat in particular. Moreover, increasing the number of stitches tends to fragilize the mats.

Quantifying the Functional Stiffness of Pullthrough Wires Used for Endovascular Aneurysm Repairs Using Comparative Tension Dynamometry.

Objective: There are only few studies on the stiffness of guidewires used to deliver devices during endovascular procedures, particularly abdominal/thoracic endovascular aneurysm repair. In certain situations, tensioned pullthrough wires are also used, but no studies have examined their effective/functional stiffness. The objective of this study was to assess the radial stiffness characteristics of pullthrough wires compared with standard stiff wires. Methods: Two types of stiff guidewires (Lunderquist Extra-Stiff and Amplatz Super Stiff; 0.035″ × 260 cm), were compared with a floppy guidewire (Radifocus Stiff M; 0.035″ × 260 cm) in two configurations: standard (non-tensioned) and pullthrough (tensioned). Radial stiffness was defined as the peak deformation force (PDF; newtons [N]) needed to deform the wires on an electromechanical dynamometer; data were logged on proprietary dynamometric software and peak load values assessed per wire. Three experimental runs were performed on three fresh sets of each wire per configuration. PDFs from straight configuration to midwire deformation at 15 mm were translated into Microsoft Excel for statistical analysis in Minitab 19 for Windows. Results: Mean ± SD PDFs were 7.83 ± 0.23 N for the Lunderquist and 9.87 ± 0.92 N for the Amplatz. This was 7.84 ± 0.52 N for the Radifocus wire in standard configuration, which increased to 15.48 ± 0.33 N when the Radifocus wire was in pullthrough configuration. This was significantly higher than both the Lunderquist and Amplatz Super Stiff wires (p < .001, one way analysis of variance). Conclusion: This study affirmed that a pullthrough wire becomes functionally more rigid than typical stiff wires used for endovascular procedures, and it is this stiffness that allows device delivery.