Nano- and Micro-Scale Adhesion in Drug-eluting Stents

2009 ◽  
Vol 1239 ◽  
Author(s):  
Ting Tan ◽  
Juan Meng ◽  
Nima Rahbar ◽  
Hannah Li ◽  
George Papandreou ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Computational Study ◽  
Interfacial Fracture ◽  
Drug Eluting Stents ◽  
Pure Mode ◽  
Force Microscopy ◽  
Atomic Force ◽  
Drug Eluting ◽  
Model Drug ◽  
Mechanics Concepts

AbstractThis paper presents a combined experimental and theoretical/computational study of adhesion and interfacial fracture between multilayers in a CYPHER® model drug eluting stents (DES). Atomic Force Microscopy (AFM) is used to obtain pull-off forces between coated AFM tips and substrates that simulate the bimaterial surfaces in the DES. Adhesion theories and fracture mechanics concepts are then applied to obtain estimates of the fracture toughness over a range of mode mixities between pure mode I and pure mode II. The trends in the estimates are shown to be in good agreement with experimental measurements of interfacial fracture toughness obtained from Brazil disk specimens over the same range of mode mixities.

Adhesion and interfacial fracture in drug-eluting stents

2010 ◽  
Vol 25 (4) ◽  
pp. 641-647 ◽  
Author(s):  
Juan Meng ◽  
Argjenta Orana ◽  
Ting Tan ◽  
Kurt Wolf ◽  
Nima Rahbar ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Interfacial Fracture ◽  
Drug Eluting Stent ◽  
Mode Mixity ◽  
Parylene C ◽  
Energy Release Rates ◽  
Drug Eluting ◽  
Model Drug ◽  
Experimental And Theoretical Studies ◽  
Initial Cracks

This paper presents experimental and theoretical studies of the adhesion between the drug-eluting layer and a Parylene C primer layer in coatings present on a model drug-eluting stent. To quantify adhesion, Brazil nut sandwich specimens were prepared mimicking the layers of this coating. These samples were stressed to fracture, and the resulting initial cracks at the Parylene C/drug interface were used to measure the dependence of interfacial fracture energy of mode mixity. The mating fracture surfaces were then analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The interfacial energy release rates were obtained over a wide variety of mode mixities. Adhesion and fracture mechanics models were then used to estimate the mode mixity dependency of interfacial fracture toughness. Fracture toughness was found to be larger under higher mode mixity than that under lower mixity and the analytical model showed close agreement with experimental results.

scholarly journals Nanohydrogels Based on Self-Assembly of Cationic Pullulan and Anionic Dextran Derivatives for Efficient Delivery of Piroxicam

Pharmaceutics ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 622 ◽  
Author(s):  
Dorota Lachowicz ◽  
Przemyslaw Mielczarek ◽  
Roma Wirecka ◽  
Katarzyna Berent ◽  
Anna Karewicz ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Self Assembly ◽  
Electrostatic Interactions ◽  
Dextran Sulfate ◽  
Force Microscopy ◽  
Grafting Reaction ◽  
Atomic Force ◽  
Transmission Electron ◽  
Efficient Delivery ◽  
Model Drug

A cationic derivative of pullulan was obtained by grafting reaction and used together with dextran sulfate to form polysaccharide-based nanohydrogel cross-linked via electrostatic interactions between polyions. Due to the polycation-polyanion interactions nanohydrogel particles were formed instantly and spontaneously in water. The nanoparticles were colloidally stable and their size and surface charge could be controlled by the polycation/polyanion ratio. The morphology of the obtained particles was visualized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The resulting structures were spherical, with hydrodynamic diameters in the range of 100–150 nm. The binding constant (Ka) of a model drug, piroxicam, to the cationic pullulan (C-PUL) was determined by spectrophotometric measurements. The value of Ka was calculated according to the Benesi—Hildebrand equation to be (3.6 ± 0.2) × 103 M−1. After binding to cationic pullulan, piroxicam was effectively entrapped inside the nanohydrogel particles and released in a controlled way. The obtained system was efficiently taken up by cells and was shown to be biocompatible.

Comparative Abrasive Wear Study of HVOF Coatings Obtained by Spraying WC-17Co Microcrystalline and Duplex Near-Nanocrystalline Cermet Powders

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
G. C. Saha ◽  
T. I. Khan
Keyword(s):  
Fracture Toughness ◽  
Wear Resistance ◽  
Abrasive Wear ◽  
Abrasive Wear Resistance ◽  
X Ray Diffraction ◽  
Nanocrystalline Coating ◽  
Force Microscopy ◽  
Coating Surface ◽  
Atomic Force

High velocity oxy-fuel spraying was used to develop a near-nanocrystalline coating from a duplex Co coated WC-17Co powder feedstock. A microstructural and mechanical property characterization of the coating with a similar microcrystalline coating of the same composition was made. X-ray diffraction analysis showed less decarburization of the nanocrystalline coating and a more homogeneous coating structure than the microcrystalline coating produced under the same spraying conditions. The mechanical assessment of the coatings was performed using microhardness and indentation fracture toughness measurements. The abrasive wear resistance was determined using the ASTM G65-04 dry-sand rubber wheel test. The results showed that the hardness of the near-nanocrystalline coating was 25% greater than that of the microcrystalline coating and a sixfold increase in the abrasive wear resistance was also recorded for the near-nanocrystalline coating. Examination of the worn surfaces using atomic force microscopy after abrasive testing showed a smoother surface roughness in the near-nanocrystalline coating than that of the microcrystalline coating surface. The increase in fracture toughness of the near-nanocrystalline coating prevented brittle fracture of the coating surface.

Analysis of the Polymer Coatings of Coronary Stents from the Aspect of Drug Absorbing and Eluting

2010 ◽  
Vol 659 ◽  
pp. 245-250 ◽  
Author(s):  
Beáta Robák ◽  
Péter Szabadíts ◽  
Eszter Bognár ◽  
Zsolt Puskás ◽  
Andrea Toldy
Keyword(s):  
Bare Metal Stents ◽  
Polymer Coatings ◽  
Bare Metal Stent ◽  
Steel Tube ◽  
Metal Stents ◽  
Stainless Steel Tube ◽  
Bare Metal ◽  
Force Microscopy ◽  
Atomic Force ◽  
Drug Eluting

The rate of restenosis can be decreased by the usage of drug eluting stents compared to bare metal stents. The aim of this work was the optimization of micro sprayed polymer coatings for medical applications and the examination of drug absorbing and releasing properties of these coatings. Control groups were bare metal stent models (316 LVM type austenitic stainless steel tube slices). Different types of medical grade polyurethane granules were applied onto the stent surface. Various methods were used for the examination of the surface and coating quality, such as optical microscopy, scanning electron microscopy and atomic force microscopy.

scholarly journals Carrier Fibers for the Safe Dosage of Nanoparticles in Nanocomposites: Nanomechanical and Thermomechanical Study on Polycarbonate/Boehmite Electrospun Fibers Embedded in Epoxy Resin

2021 ◽  
Author(s):  
Natalia Cano Murillo ◽  
Media Ghasem Zadeh Khorasani ◽  
Dorothee Silbernagl ◽  
Farnaz Emamverdi ◽  
Karen Cacua ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Epoxy Resin ◽  
Fiber Composite ◽  
Ambient Air ◽  
Mechanical Analysis ◽  
Thermomechanical Properties ◽  
Force Microscopy ◽  
Atomic Force ◽  
Fiber Reinforced Polymer Composites ◽  
Boehmite Nanoparticles

The reinforcing effect of boehmite nanoparticles (BNP) in epoxy resins for fiber composite lightweight construction is related to the formation of a soft but bound interphase between filler and polymer. The interphase is able to dissipate crack propagation energy and consequently increases the fracture toughness of the epoxy resin. Usually, the nanoparticles are dispersed in the resin and then mixed with the hardener to form an applicable mixture to impregnate the fibers. If one wishes to locally increase the fracture toughness at particularly stressed positions of the fiber-reinforced polymer composites (FRPC), this could be done by spraying nanoparticles from a suspension. However, this would entail high costs for removing the nanoparticles from the ambient air. We propose that a fiber fleece containing bound nanoparticles be inserted at exposed locations. For the present proof-of-concept study, an electrospun polycarbonate nonwoven and taurine modified BNP are proposed. After fabrication of suitable PC/EP/BNP composites, the thermomechanical properties were tested by dynamic mechanical analysis (DMTA). Comparatively, the local nano-mechanical properties such as stiffness and elastic modulus were determined by atomic force microscopy (AFM). An additional investigation of the distribution of the nanoparticles in the epoxy matrix, which is a prerequisite for an effective nanocomposite, is carried out by scanning electron microscopy in transmission mode (TSEM). From the results it can be concluded that the concept of carrier fibers for nanoparticles is viable.

scholarly journals Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

2016 ◽  
Vol 7 ◽  
pp. 554-571 ◽  
Author(s):  
Santiago D Solares
Keyword(s):  
Atomic Force Microscopy ◽  
Computational Study ◽  
Plane Surface ◽  
Material Behavior ◽  
Dynamic Mode ◽  
Viscoelastic Materials ◽  
Force Microscopy ◽  
Atomic Force ◽  
Standard Linear Solid ◽  
Standard Linear

Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip–sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young’s modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip–sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information.

scholarly journals Comparative Evaluation of Mechanical Properties of Dental Nanomaterials

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Cem Peskersoy ◽  
Osman Culha
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Modulus Of Elasticity ◽  
Dental Materials ◽  
Glass Ionomer ◽  
Force Microscopy ◽  
Atomic Force ◽  
Post Hoc ◽  
Dental Restorative ◽  
One Way Anova

This study examines the properties of nanobased dental restorative materials with nanoindentation method in a precise, repeatable, and comparable way. Microhybrid and nanohybrid composites, conventional glass ionomer materials, and light cured nanoionomer materials were utilised for the study. Specimen discs (r=10 mm,h=2 mm) were prepared to test the hardness, modulus of elasticity, yield strength, and fracture toughness values for each sample in a nanoindentation device with an atomic force microscopy add-on (n=25). Comparative analyses were performed by one-way ANOVA and post hoc Tukey tests. The hardness and modulus of elasticity values of nanocomposite were higher (2.58 GPa and 32.86 GPa, resp.) than those of other dental materials. Although glass ionomer exhibited a hardness that was similar to a nanoionomer (0.81 versus 0.87 GPa), glass ionomer had the lowest fracture toughness value (Kc=0.83 MPa/mm0.5). The mechanical properties of resin composites improve with additional nanoscale fillers, unlike the glass ionomer material.

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