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 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.

scholarly journals Materials and Manufacturing Technologies Available for Production of a Pediatric Bioabsorbable Stent

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Ryan D. Alexy ◽  
Daniel S. Levi
Keyword(s):  
Congenital Heart Disease ◽  
Heart Disease ◽  
Congenital Heart ◽  
Coarctation Of The Aorta ◽  
Pulmonary Artery Stenosis ◽  
Metal Stents ◽  
Surgical Removal ◽  
Vessel Growth ◽  
Radial Strength ◽  
Manufacturing Technologies

Transcatheter treatment of children with congenital heart disease such as coarctation of the aorta and pulmonary artery stenosis currently involves the use of metal stents. While these provide good short term results, there are long term complications with their use. Children outgrow metal stents, obligating them to future transcatheter dilations and eventual surgical removal. A bioabsorbable stent, or a stent that goes away with time, would solve this problem. Bioabsorbable stents are being developed for use in coronary arteries, however these are too small for use in pediatric congenital heart disease. A bioabsorbable stent for use in pediatric congenital heart disease needs to be low profile, expandable to a diameter 8 mm, provide sufficient radial strength, and absorb quickly enough to allow vessel growth. Development of absorbable coronary stents has led to a great understanding of the available production techniques and materials such as bioabsorbable polymers and biocorrodable metals. Children with congenital heart disease will hopefully soon benefit from the current generation of bioabsorbable and biocorrodable materials and devices.

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.

The DESolve® novolimus bioresorbable scaffold

2021 ◽  
Author(s):  
Pierluigi Demola ◽  
Francesco Meucci ◽  
Miroslava Stolcova ◽  
Carlo Di Mario ◽  
Alessio Mattesini
Keyword(s):  
Polymer Scaffold ◽  
Bioresorbable Scaffold ◽  
Incomplete Stent Apposition ◽  
Radial Strength ◽  
Vessel Patency ◽  
Vascular Scaffolds ◽  
Bioresorbable Vascular Scaffolds ◽  
Controversial Topic ◽  
Long Term Impact

A longtime aspiration of interventional cardiologists remains to improve the long-term impact of stent permanence in coronaries to restore original vessel patency and physiological endothelium response. Bioresorbable vascular scaffolds were considered revolutionary in coronary devices, but several trials were disappointing; thus, the challenge in this field remains. DESolve is a novolimus-eluting poly-L lactide-based polymer scaffold that dissolves through a bio-reabsorption mechanism, vanishing completely in 2 years. Its ability to supply the necessary radial strength to support the vessel for the critical early months after delivery is an important feature showing a unique self-correction property, which reduces incomplete stent apposition. Overexpansion has a good, safe margin with DESolve. This review aims to provide an overview of this controversial topic.

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.

scholarly journals Bioresorbable Vascular Scaffolds—Dead End or Still a Rough Diamond?

2019 ◽  
Vol 8 (12) ◽  
pp. 2167 ◽  
Author(s):  
Mateusz P. Jeżewski ◽  
Michał J. Kubisa ◽  
Ceren Eyileten ◽  
Salvatore De Rosa ◽  
Günter Christ ◽  
...  
Keyword(s):  
Second Generation ◽  
Cardiac Events ◽  
Vasomotor Function ◽  
Dead End ◽  
Radial Strength ◽  
Vessel Patency ◽  
Vascular Scaffolds ◽  
Drug Eluting ◽  
Bioresorbable Vascular Scaffolds ◽  
First And Second Generation

Percutaneous coronary interventions with stent-based restorations of vessel patency have become the gold standard in the treatment of acute coronary states. Bioresorbable vascular scaffolds (BVS) have been designed to combine the efficiency of drug-eluting stents (DES) at the time of implantation and the advantages of a lack of foreign body afterwards. Complete resolution of the scaffold was intended to enable the restoration of vasomotor function and reduce the risk of device thrombosis. While early reports demonstrated superiority of BVS over DES, larger-scale application and longer observation exposed major concerns about their use, including lower radial strength and higher risk of thrombosis resulting in higher rate of major adverse cardiac events. Further focus on procedural details and research on the second generation of BVS with novel properties did not allow to unequivocally challenge position of DES. Nevertheless, BVS still have a chance to present superiority in distinctive indications. This review presents an outlook on the available first and second generation BVS and a summary of results of clinical trials on their use. It discusses explanations for unfavorable outcomes, proposed enhancement techniques and a potential niche for the use of BVS.

The External Shape of Human γ GI Immunoglobulin from Crystal Sections

1971 ◽  
Vol 29 ◽  
pp. 428-429
Author(s):  
L. W. Labaw
Keyword(s):  
Molecular Weight ◽  
Sodium Phosphate ◽  
Osmium Tetroxide ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray ◽  
Large Molecular Weight ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Crystallographic Axes

Crystals of a human γGl immunoglobulin have the external morphology of diamond shaped prisms. X-ray studies have shown them to be monoclinic, space group C2, with 2 molecules per unit cell. The unit cell dimensions are a = 194.1, b = 91.7, c = 51.6Å, 8 = 102°. The relatively large molecular weight of 151,000 and these unit cell dimensions made this a promising crystal to study in the EM.Crystals similar to those used in the x-ray studies were fixed at 5°C for three weeks in a solution of mother liquor containing 5 x 10-5M sodium phosphate, pH 7.0, and 0.03% glutaraldehyde. They were postfixed with 1% osmium tetroxide for 15 min. and embedded in Maraglas the usual way. Sections were cut perpendicular to the three crystallographic axes. Such a section cut with its plane perpendicular to the z direction is shown in Fig. 1.This projection of the crystal in the z direction shows periodicities in at least four different directions but these are only seen clearly by sighting obliquely along the micrograph.

The Collagenic Molecular Structural Unit of Solid State Complexes

1971 ◽  
Vol 29 ◽  
pp. 478-479
Author(s):  
Kenneth M. Richter ◽  
John A. Schilling
Keyword(s):  
Molecular Weight ◽  
Solid State ◽  
Structural Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Naoh Treatment

The structural unit of solid state collagen complexes has been reported by Porter and Vanamee via EM and by Cowan, North and Randall via x-ray diffraction to be an ellipsoidal unit of 210-270 A. length by 50-100 A. diameter. It subsequently was independently demonstrated by us in dog tendon, dermis, and induced complexes. Its detailed morphologic, dimensional and molecular weight (MW) aspects have now been determined. It is pear-shaped in long profile with m diameters of 57 and 108 A. and m length of 263 A. (Fig. 1, tendon, KMnO4 fixation, Na-tungstate; Fig. 2a, schematic of unit in long, C, and x-sectional profiles of its thin, xB, and bulbous, xA portions; Fig. 2b, tendon essentially unmodified by ether and 0.4 N NaOH treatment, Na-tungstate). The unit consists of a uniquely coild cable, c, of ṁ 22.9 A. diameter and length of 2580-3316 A. The cable consists of three 2nd-strands, s, each of m 10.6 A.

Examination of Rabbit Fc Crystals

1968 ◽  
Vol 26 ◽  
pp. 140-141
Author(s):  
J. P. Robinson ◽  
P. G. Lenhert
Keyword(s):  
Molecular Weight ◽  
Flat Plate ◽  
Phosphate Buffer ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutral Ph ◽  
Small Crystals ◽  
Carbon Coated ◽  
Diffraction Patterns

Crystallographic studies of rabbit Fc using X-ray diffraction patterns were recently reported. The unit cell constants were reported to be a = 69. 2 A°, b = 73. 1 A°, c = 60. 6 A°, B = 104° 30', space group P21, monoclinic, volume of asymmetric unit V = 148, 000 A°3. The molecular weight of the fragment was determined to be 55, 000 ± 2000 which is in agreement with earlier determinations by other methods.Fc crystals were formed in water or dilute phosphate buffer at neutral pH. The resulting crystal was a flat plate as previously described. Preparations of small crystals were negatively stained by mixing the suspension with equal volumes of 2% silicotungstate at neutral pH. A drop of the mixture was placed on a carbon coated grid and allowed to stand for a few minutes. The excess liquid was removed and the grid was immediately put in the microscope.

Monitoring Polymer-Assisted Mechanochemical Cocrystallisation Through in Situ X-Ray Powder Diffraction

2020 ◽  
Author(s):  
Luzia S. Germann ◽  
Sebastian T. Emmerling ◽  
Manuel Wilke ◽  
Robert E. Dinnebier ◽  
Mariarosa Moneghini ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Powder Diffraction ◽  
Reaction Rate ◽  
Polymer Additives ◽  
Time Resolved ◽  
X Ray

Time-resolved mechanochemical cocrystallisation studies have so-far focused solely on neat and liquid-assisted grinding. Here, we report the monitoring of polymer-assisted grinding reactions using <i>in situ</i> X-ray powder diffraction, revealing that reaction rate is almost double compared to neat grinding and independent of the molecular weight and amount of used polymer additives.<br>

Sign in / Sign up

Export Citation Format

Share Document