scholarly journals Strain-induced accelerated asymmetric spatial degradation of polymeric vascular scaffolds

2018 ◽  
Vol 115 (11) ◽  
pp. 2640-2645 ◽  
Author(s):  
Pei-Jiang Wang ◽  
Nicola Ferralis ◽  
Claire Conway ◽  
Jeffrey C. Grossman ◽  
Elazer R. Edelman
Keyword(s):  
Structural Integrity ◽  
Clinical Performance ◽  
Chemical Degradation ◽  
Metal Stents ◽  
Research Strategies ◽  
Localized Deformation ◽  
Polymeric Scaffolds ◽  
Vascular Scaffolds ◽  
Catastrophic Fracture ◽  
Structural Irregularities

Polymer-based bioresorbable scaffolds (BRS) seek to eliminate long-term complications of metal stents. However, current BRS designs bear substantially higher incidence of clinical failures, especially thrombosis, compared with metal stents. Research strategies inherited from metal stents fail to consider polymer microstructures and dynamics––issues critical to BRS. Using Raman spectroscopy, we demonstrate microstructural heterogeneities within polymeric scaffolds arising from integrated strain during fabrication and implantation. Stress generated from crimping and inflation causes loss of structural integrity even before chemical degradation, and the induced differences in crystallinity and polymer alignment across scaffolds lead to faster degradation in scaffold cores than on the surface, which further enlarge localized deformation. We postulate that these structural irregularities and asymmetric material degradation present a response to strain and thereby clinical performance different from metal stents. Unlike metal stents which stay patent and intact until catastrophic fracture, BRS exhibit loss of structural integrity almost immediately upon crimping and expansion. Irregularities in microstructure amplify these effects and can have profound clinical implications. Therefore, polymer microstructure should be considered in earliest design stages of resorbable devices, and fabrication processes must be well-designed with microscopic perspective.

scholarly journals Multiplicity of morphologies in poly (l-lactide) bioresorbable vascular scaffolds

2016 ◽  
Vol 113 (42) ◽  
pp. 11670-11675 ◽  
Author(s):  
Artemis Ailianou ◽  
Karthik Ramachandran ◽  
Mary Beth Kossuth ◽  
James Paul Oberhauser ◽  
Julia A. Kornfield
Keyword(s):  
Balloon Catheter ◽  
Metal Stents ◽  
Late Stent Thrombosis ◽  
Bioresorbable Vascular Scaffold ◽  
Promising Alternative ◽  
Vascular Scaffolds ◽  
Bioresorbable Vascular Scaffolds ◽  
Brittle Polymer ◽  
Micrometer Scale ◽  
Strength And Ductility

Poly(l-lactide) (PLLA) is the structural material of the first clinically approved bioresorbable vascular scaffold (BVS), a promising alternative to permanent metal stents for treatment of coronary heart disease. BVSs are transient implants that support the occluded artery for 6 mo and are completely resorbed in 2 y. Clinical trials of BVSs report restoration of arterial vasomotion and elimination of serious complications such as late stent thrombosis. It is remarkable that a scaffold made from PLLA, known as a brittle polymer, does not fracture when crimped onto a balloon catheter or during deployment in the artery. We used X-ray microdiffraction to discover how PLLA acquired ductile character and found that the crimping process creates localized regions of extreme anisotropy; PLLA chains in the scaffold change orientation from the hoop direction to the radial direction on micrometer-scale distances. This multiplicity of morphologies in the crimped scaffold works in tandem to enable a low-stress response during deployment, which avoids fracture of the PLLA hoops and leaves them with the strength needed to support the artery. Thus, the transformations of the semicrystalline PLLA microstructure during crimping explain the unexpected strength and ductility of the current BVS and point the way to thinner resorbable scaffolds in the future.

Fracture Mechanics Aspects of the Structural Integrity Technology of Spherical Aluminum Containment Vessels for LNG Tankers

1980 ◽  
Vol 102 (3) ◽  
pp. 303-314 ◽  
Author(s):  
J. G. Kaufman ◽  
R. J. Bucci ◽  
R. A. Kelsey
Keyword(s):  
Fracture Mechanics ◽  
Experimental Approach ◽  
Structural Integrity ◽  
Fatigue Loading ◽  
Aluminum Alloy 5083 ◽  
Spherical Tank ◽  
Tank Design ◽  
Stressed Region ◽  
Catastrophic Fracture ◽  
Mechanics Concepts

The Kvaerner-Moss spherical tank design offers significant economic advantage for the shipboard transport of liquefied natural gas. An analytical and experimental approach based on fracture mechanics concepts was used to assist the designer in providing answers to the following basic questions: (1) Might a discontinuity smaller than detectable by nondestructive inspection lead to catastrophic fracture; (2) How fast would such a discontinuity grow under fatigue loading likely to occur during the lifetime of the tank; (3) Could a fatigue crack growing part way through the tank wall precipitate catastrophic fracture before it grows through the wall and is detected as a leak; and (4) If leakage develops, how much time is available to get the ship safely to port for discharge and repair? Both “critical” locations in the tank, i.e., the highest stressed region of the membrane and the equatorial ring, are examined. Available data indicating the safety of spherical tanks fabricated of aluminum alloy 5083-0 is documented.

scholarly journals Determination of thickness and quality of refractory linings in industrial furnaces using acousto ultrasonic echo

2021 ◽  
Author(s):  
Gary Walters
Keyword(s):  
Structural Integrity ◽  
Refractory Lining ◽  
Production Optimization ◽  
Chemical Degradation ◽  
Laboratory Measurements ◽  
Destructive Testing ◽  
Transfer Capability ◽  
Ultrasonic Echo ◽  
Metallurgical Furnaces ◽  
Thickness Measurements

Refractory linings in metallurgical furnaces undergo deterioration and wearing with time. The deterioration is caused mainly by thermomechanical mechanisms leading to cracks, chemical degradation and loss of heat transfer capability. Any sudden failure of the lining is dangerous and could affect the structural integrity of the furnace, leading to production loss and costly refurbishment. Non-destructive testing (NDT) and monitoring of refractory lining would lead to better safety, longer use of the vessel, production optimization, controlled maintenance and increased production. Thickness measurements and monitoring of the refractory lining in operating furnaces is possible using Acousto Ultrasonic -Echo (AU-E) technique. This technique uses stress waves of both acoustic and ultrasonic ranges in order to determine thickness and integrity. This thesis presents the details of AU-E technique in addition to laboratory measurements to determine parameters leading to the in-situ measurements. Finally, three case studies are presented to substantiate the theoretical and laboratory measurements.

scholarly journals Impact of statins on vascular scaffolds response in porcine carotid arteries

2021 ◽  
Vol 7 (2) ◽  
pp. 101-104
Author(s):  
Sabine Kischkel ◽  
Niels Grabow ◽  
Carsten M. Bünger ◽  
Anja Püschel
Keyword(s):  
Carotid Arteries ◽  
Oral Treatment ◽  
Vascular Inflammation ◽  
Bare Metal Stents ◽  
Metal Stents ◽  
Preclinical Model ◽  
Bare Metal ◽  
Polymer Scaffolds ◽  
Left Common Iliac Artery ◽  
Polymeric Scaffolds

Abstract Surgical treatments of arterial occlusive disease with fully absorbable polymeric scaffolds, as a potential alternative to permanent metallic stents, are increasingly penetrating the clinical field. An addition part of the management of patients suffering from vascular diseases is the administration of statins. In this study, absorbable x-ray marked PLLA-based polymer scaffolds and permanent bare-metal stents (BMS) were implanted interventionally into both common carotid arteries (CCA) of 6 healthy female pigs via the left common iliac artery (8F-sheath). The pigs were administered dual antiplatelet drugs oral starting 3 days before the procedure until the end of the study. In Addition, the pigs received atorvastatin orally, beginning 5 days prior to surgery and lasting until the study ended. Stented CCA segments were explanted after 4 weeks, and processed for quantitative histomorphometry, and estimation of vascular inflammation and injury scores. Polymer scaffolds showed a decreased residual lumen area and higher stenosis after 4 weeks (6.41 ± 0.83 mm² and 40.52 ± 5.01%) as compared to the bare-metal reference stent (15.17 ± 0.896 mm² and 7.80 ± 0.88%). After 4 weeks, inflammation score were higher in the polymer group (1.30 ± 0.37) compared to the BMS group (0.42 ± 0.18). In contrast, the BMS showed a slightly elevated vascular injury score (0.85 ± 0.12), as compared to the polymer (0.60 ± 0.23) group. In this preclinical model, the new absorbable polymeric scaffolds showed similar technical feasibility and safety for vascular application as the permanent metal stents. Although no positive trends were observed with oral treatment with atorvastatin, further optimization with a dual-loaded coating is still reasonable. In addition, reduced strut thickness of the polymer scaffolds would have potential to positively impact tissue ingrowth between struts and should be considered in future work on stent design.

Vollständig resorbierbare Stents – eine neue Ära in der Behandlung der koronaren Herzkrankheit?

Praxis ◽  
2017 ◽  
Vol 106 (2) ◽  
pp. 85-89
Author(s):  
Zaid Sabti ◽  
Raban Jeger
Keyword(s):  
Bare Metal Stents ◽  
Drug Eluting Stents ◽  
Metal Stents ◽  
Bare Metal ◽  
Vascular Scaffolds ◽  
Drug Eluting ◽  
Bioresorbable Vascular Scaffolds

Zusammenfassung. Die perkutane Ballonangioplastie revolutionierte die Behandlung der koronaren Herzkrankheit. Der Einsatz von Gefässstützen (Stents) setzte diese Revolution fort. Nach den reinen Metallstents (Bare metal stents, BMS) und den Medikamenten-beschichteten Stents (drug-eluting stents, DES) folgen nun bioresorbierbare Stents (bioresorbable vascular scaffolds, BVS). Im Gegensatz zu den ersten zwei Stent-Generationen werden die BVS nach einer bestimmten Zeit vollständig abgebaut und versprechen eine Antwort für bisher ungelöste Probleme von BMS und DES.

Targeting Problems of Composite Failure

2009 ◽  
Vol 417-418 ◽  
pp. 37-40 ◽  
Author(s):  
Peter W.R. Beaumont
Keyword(s):  
Life Expectancy ◽  
Stress Corrosion Cracking ◽  
Large Scale ◽  
Structural Integrity ◽  
Engineering Structures ◽  
Composite Failure ◽  
Long Life ◽  
Catastrophic Fracture ◽  
Materials Used ◽  
Integrity Analysis

Predicting precisely where a crack will develop in a material under stress and exactly when in time catastrophic fracture of the component will occur is one the oldest unsolved mysteries in the design and building of large-scale engineering structures. Fitness considerations for long-life implementation of aerospace composites include understanding phenomena such as fatigue, creep and stress corrosion cracking that affect reliability, life expectancy, and durability of structure. Structural integrity analysis treats the design, the materials used, and figures out how best components and parts can be joined; furthermore, SI takes into account service duty.

scholarly journals Everolimus-eluting bioresorbablecoronary scaffold in Asian patients; a 2-yearfollow-up

2020 ◽  
pp. 1-11
Author(s):  
Muhammad Abdul Salam Azad ◽  
Uzma Gul ◽  
Asim Javed
Keyword(s):  
Case Series ◽  
Bare Metal Stents ◽  
Metal Stents ◽  
Asian Patients ◽  
Implantation Techniques ◽  
Bioresorbable Stent ◽  
Vascular Scaffolds ◽  
Drug Eluting ◽  
Artery Disease ◽  
Absorb Bvs

Abstract Indo-Pakistan population has one of the highest risk of coronary artery disease(CAD) in the world.1Percutaneous interventions with the use of stents has been the mainstay of treatment for CAD, evolving from balloon angioplasty to bare metal stents and then to drug eluting stents. However, there are a few drawbacks related to the metal implant in the coronary, leading to the development of bio-resorbable vascular scaffolds(BVS). This case series studies the implantation techniques and 24 month clinical outcome of bioresorbable stent Absorb at Rawalpindi Institute of Cardiology. From November 1, 2013 till June 30, 2018. Fifty patients undergoing angioplasty with Absorb BVS as elective or primary PCI were enrolled. Case selection was at the discretion of the operator. Patients were followed up clinically. Repeat angiogram was conducted if clinically indicated.  Continuous...  

scholarly journals Crimping-induced structural gradients explain the lasting strength of poly l-lactide bioresorbable vascular scaffolds during hydrolysis

2018 ◽  
Vol 115 (41) ◽  
pp. 10239-10244 ◽  
Author(s):  
Karthik Ramachandran ◽  
Tiziana Di Luccio ◽  
Artemis Ailianou ◽  
Mary Beth Kossuth ◽  
James P. Oberhauser ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Heart Disease ◽  
Morphological Changes ◽  
Metal Stents ◽  
Radial Load ◽  
Late Stent Thrombosis ◽  
X Ray ◽  
Radial Strength ◽  
Vascular Scaffolds ◽  
Bioresorbable Vascular Scaffolds

Biodegradable polymers open the way to treatment of heart disease using transient implants (bioresorbable vascular scaffolds, BVSs) that overcome the most serious complication associated with permanent metal stents—late stent thrombosis. Here, we address the long-standing paradox that the clinically approved BVS maintains its radial strength even after 9 mo of hydrolysis, which induces a ∼40% decrease in the poly l-lactide molecular weight (Mn). X-ray microdiffraction evidence of nonuniform hydrolysis in the scaffold reveals that regions subjected to tensile stress during crimping develop a microstructure that provides strength and resists hydrolysis. These beneficial morphological changes occur where they are needed most—where stress is localized when a radial load is placed on the scaffold. We hypothesize that the observed decrease in Mn reflects the majority of the material, which is undeformed during crimping. Thus, the global measures of degradation may be decoupled from the localized, degradation-resistant regions that confer the ability to support the artery for the first several months after implantation.

scholarly journals Structural integrity of engineering composite materials: a cracking good yarn

2016 ◽  
Vol 374 (2071) ◽  
pp. 20160057 ◽  
Author(s):  
Peter W. R. Beaumont ◽  
Costas Soutis
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Large Scale ◽  
Structural Integrity ◽  
High Efficiency ◽  
Human Life ◽  
Engineering Structures ◽  
Catastrophic Fracture ◽  
Materials Used ◽  
Integrity Analysis

Predicting precisely where a crack will develop in a material under stress and exactly when in time catastrophic fracture of the component will occur is one the oldest unsolved mysteries in the design and building of large-scale engineering structures. Where human life depends upon engineering ingenuity, the burden of testing to prove a ‘fracture safe design’ is immense. Fitness considerations for long-life implementation of large composite structures include understanding phenomena such as impact, fatigue, creep and stress corrosion cracking that affect reliability, life expectancy and durability of structure. Structural integrity analysis treats the design, the materials used, and figures out how best components and parts can be joined, and takes service duty into account. However, there are conflicting aims in the complete design process of designing simultaneously for high efficiency and safety assurance throughout an economically viable lifetime with an acceptable level of risk. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

scholarly journals When to Use Bioresorbable Vascular Scaffolds

2017 ◽  
Vol 11 (1) ◽  
pp. 25 ◽  
Author(s):  
Xiaoyu Yang ◽  
Mohamed Ahmed ◽  
Donald E Cutlip ◽  
◽  
◽  
...  
Keyword(s):  
Bare Metal Stents ◽  
Percutaneous Treatment ◽  
The United States ◽  
Lessons Learned ◽  
High Rate ◽  
Drug Eluting Stent ◽  
Metal Stents ◽  
Scaffold Thrombosis ◽  
Vascular Scaffolds ◽  
Bioresorbable Vascular Scaffolds

The development of the drug eluting stent (DES) was an important milestone in percutaneous treatment of coronary artery disease. The DES overcomes vessel recoil and restenosis to decrease the high rate of target lesion revascularization associated with balloon angioplasty and bare metal stents. Despite these benefits, the DES has an ongoing risk of stent-related complications because of permanent implantation of a foreign body and restriction of vascular vasomotion. Bioresorbable vascular scaffolds (BVS) are designed to provide mechanical support and drug delivery similar to the DES, followed by complete resorption over several years. Recent trials have demonstrated clinical non-inferiority of the BVS compared with contemporary DES, although certain clinical outcomes are concerning, particularly with regard to higher rates of scaffold thrombosis. The theoretical long-term benefits are promising, but remain unproven. Early adoption of this new technology in the United States should apply the lessons learned regarding rigorous strategies to decrease adverse events, including careful patient and lesion selection and meticulous implantation techniques.

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