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Different coronary stent design
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DIFFERENT CORONARY STENT DESIGN
DR AWADHESH KUMAR SHARMA DEPARTMENT OF CARDIOLOGY PGIMER & DR RML HOSPITAL,NEW DELHI
BACKGROUND
The introduction of angioplasty led to the development of a completely new approach to treat CAD.
Until 1994, the percutaneous transluminal coronary angioplasty (PTCA) was the alone treatment for coronary artery disease.
However, the incidence of restenosis of coronary arteries was an important problem, necessitating repeated interventional procedures in 30% of patients treated with PTCA alone.
NEJM 1994;331:489-95
Coronary artery stents were developed to provide a
metal scaffolding for the angio-plastied vessel, in an
attempt to limit negative re-modelling.
Sigwart et al first reported the efficacy of stents in
reducing restenosis rates in 1987.
By 1994, the Food and Drug Administration (FDA)
had approved two stents (Gianturco-Roubin stent
and the Palmaz- SchatzTM stent).
Journal of Invasiv Cardiology.2001;13:634-639
GIANTURCO-ROUBIN II
Flat wire coil attached to a single longitudinal strut
316 L stainless steel The first coronary stent
approved by the FDA in June 1993.
J. clinical pathology.2005,aug;58(8):795-804
PALMAZ-SCHATZ
Balloon expandable; slotted tube
316 L stainless steel
J. clinical pathology.2005,aug;58(8):795-804
The wide acceptance of coronary stenting was based on
the results of the BElgian NEtherlands STENT
(BENESTENT) and the STent REStenosis Study
(STRESS) trials, which showed the superiority of
stenting over balloon angioplasty.
After the wide acceptance of coronary stents the primary
concern of stent development is the need to reduce
device profiles and to increase flexibility to facilitate safe
delivery. N Engl J Med,1994;331:489-95.
STENT SELECTION
STENT SELECTION-PERFORMANCE & EASE OF USE
STENT SELECTION-GOOD ACUTE ANGIOGRAPHIC RESULTS
JACC 2003;41:1283-1288
TYPES OF STENTS Mechanism of expansion (self-expanding or balloon-
expandable)
Materials (stainless steel, cobalt-based alloy, tantalum,
nitinol, Pt,Ir,Cr, inert coating, biodegradable)
Forms (sheet, wire or tube)
Manufacturing methods (laser cut, water-jet cutting, photo-
etching)
Geometrical configurations/design (mesh structure, coil, slotted
tube, ring, multi-design)
Addition to stent (grafts, radio-opaque markers, coatings)Min Invas Ther & Allied Technol 2002;11:137-47.
STENT GEOMETRIC DESIGN
MECHANISM OF EXPANSION
Balloon-expandable stents
The stent is pre-mounted on a balloon and the inflation
of the balloon plastically expands the stent with respect
to the balloon diameter.
Self-expanding stents- The smart material auto expands
to a calculated size. Journal of invasive cardiology 1995;7:127-134
MATERIALS
Corrosion resistance
Biocompatibility
Adequately radio-opaque
Create minimal artifacts during MRI
STENT PLATFORMSSTENT MATERIALS- NON DEGRADABLE MATERIAL
316L stainless steel-
Excellent mechanical properties and corrosion
resistance
Ferromagnetic nature and low density make it a non-
MRI compatible
Poorly visible fluoroscopic material
First generation DESs, Cypher (sirolimus-eluting
stent, Cordis, Warren, NJ) and Taxus (paclitaxel-
eluting stent, Boston Scientific, Natick, MA)JACC 1996;27:53
CO-CR
Superior radial strength and improved radiopacity
Thinner stent struts
The second generation DES, Xience V (everolimus-
eluting stent, Abott Vascular, CA) and Endeavor
(zotarolimus-eluting stent,Medtronic Vascular,
Santa Rosa, CA).
JACC 1996;27:53
TA- TANTALUM
Excellent corrosion resistant material
Coated on 316L SS to improve corrosion properties
and biocompatibility
High density and non-ferromagnetic properties
Fluoroscopically visible and MRI compatible
Higher rates of recoil- poor mechanical properties
JACC 1996;27:53
TI
Excellent biocompatibility and corrosion resistance
Low tensile strength and ductility
Ti alloys in combination with Ni-Ti
Ti-nitride oxide coating on 316L SS
JACC 1996;27:53
NI-TI
Good biocompatibility, radial force and shape
memory
Coated by some materials such as polyurethane, Ti
nitride and polycrystalline oxides to improve the
corrosion resistance
Inadequate visibility under fluoroscopy
American J of cardiology.2008;86:1073-1079
PT-IR
Pt-Ir alloy of 90% platinum and 10% iridium
Excellent radiopacity and a reduction in both
thrombosis and neointimal proliferation with less
inflammatory reactions
Recoiling percentage was much higher (16%) than
the 316L SS stents
Journal of invasive cardiology 1995;7:127-134
BIODEGRADABLE METALLIC MATERIALS
Pure Fe
Oxidation of Fe into ferrous and ferric irons
Mg alloys
There are two Mg alloys, AE2153 and WE4357,
used for making stents
Radiolucent
Biomaterials.2006;27:1728-1734
RATIONAL FOR BIODEGRADABLE STENTS
Metal stent drawbacks Cause permanent physical
irritation Risk of long term endothelial
dysfunction and chronic inflammation
Metal have thrombogenic properties
Inability for the vessel to restore its a normal physiology
Biodegradable stent advantages May eliminate early and late
complications of bare-metal stents
Restore the vasoreactivity Allow a gradual transfer of the
mechanical load to the vessel Higher capacity for drug
incorporation and complex release kinetics
The need for a permanent prosthesis decreases dramatically 6 months post-implantation
STENT DESIGN
On the basis of design, stents can be divided into
three groups: coil, tubular mesh, and slotted tube.
Coil stents are characterised by metallic wires or
strips formed into a circular coil shape
Tubular mesh stents consist of wires wound
together in a meshwork, forming a tube.
Slotted tube stents are made from tubes of metal
from which a stent design is laser cut.Eur Heart J 1997;18:1536–47
COIL VS. TUBE
Coil design had greater strut width with gaps and
fewer or no connections between struts
The strut width is greater; there are gap between
struts, and no connections between struts which
give it more flexibility.
However, the design lack radial strength, and the
wide gap allow tissues to dangle.
Singapore Medical Journal, 2004.
COIL VS TUBE
As a result, coil design has become obsolete and
replace by the more superior in radial strength, the
tube design.
In tubular, there are two type of specification, a
slotted tube and modular tube.
Singapore Medical Journal, 2004.
SLOTTED TUBE VS. MODULAR (TUBULAR)
MODULAR DESIGN
SLOTTED TUBE VS. MODULAR (TUBULAR)
Slotted tube stents resisted restenosis more than
the modular stents (22.1% vs 25.2%)
Slotted tube- Closed cell design, and open cell
design
CLOSED CELL
Sequential ring construction
All Internal inflection points of the structural
members are connected by bridging elements.
Regular peak-to-peak connections.
Optimal scaffolding and a uniform surface,
regardless of the degree of bending.
Less flexible than a similar open-cell design.
Ann Ist Super Sanita 2007;43,no1:89-100
CYPHER STENT BY CORDIS
OPEN CELL
Some or all the internal inflection points of the
structural members are not connected by bridging
elements.
Periodic peak-to-peak connections, peak-to-valley
connections, and mid-strut to mid strut connections
The unconnected structural elements contribute to
longitudinal flexibility.
Ann Ist Super Sanita 2007;43,no1:89-100
OPEN CELL DESIGN
STENT DESIGN IMPACTS DRUG DELIEVERY
LENGTH & DIAMETER OF STENT
Long vs. Short
Stent length is associated with restenosis rate and
clinical events (mainly target lesion revascularization)
Short stent has lower cases of restenosis than long
stent.
Wide vs. Narrow
The wide diameter stent is more favorable than the
narrow oneEuropean Heart Journal 2001;22:1585-1593
NUMBER OF STRUTS
More struts vs. less
Less struts induce less chance of restenosis
compare to more struts.
THIN STRUT VS THICK STRUT
STRUT THICKNESS
Although the immediate stent performance may be
improved by increasing strut thickness (which increases
radiovisibility, radial strength and arterial wall support)
excessive strut thickness, on the other hand, may impart
more vascular injury, trigger more intimal hyperplasia, and
engender a higher risk for restenosis than thinner struts.
Strut thickness was observed to be an independent
predictor of in-stent restenosis
ISAR STEREO study(Circulation 2001;103:2816-21)
ISAR-STEREO-2 trial(J Am Coll Cardiol 2003;41:1283-8.)
In an effort to further reduce strut thickness while
maintaining adequate radiovisibility and radial
strength, novel metallic materials such as cobalt-
chromium alloy are being used for the production of
stent.
THICK VS. THIN STRUTS
The stents with thinner struts is preferred for the
design of new stents as they can reduce
angiographic and clinical restenosis more than
those with thicker struts
ISAR-STEREO and ISAR-STEREO 2 trials
SQUARE VS. ROUND STRUT CROSS-SECTION
The round strut cross-section without corners or
sharp edges is popular at present
Round strut cross-section area is ideal for
smoothness design.
Square strut cross-section area in not recommend
because it interferes with blood flow due to their
sharp edge which can slice blood cells.
Kluwer Academic Publishers 2012
SQUARE VS. ROUND STRUT CROSS-SECTION
ROUGH VS. SMOOTH SURFACE
Smoothness of a stent can affect the performance and
biocompatibily of the stent.
Smooth surface can reduce thrombus adhesion and
neointimal growth.
To obtain smoothness, the stent need to be treated with acid-
pickling and then electrochemical polishing.
The process removes slag which includes depositions and
burrs, formed on the surface of stents due to the laser cutting
production process.Seminars in interventional cardiology1998;3:139-144
ELEMENT OF STENT DESIGN- BALLOON OVERHANG
DRUG DELIVERY VEHICLES – COATING POLYMER- DRUG CARRIERS IN DESS
Nonbiodegradable and biodegradable polymers
Non biodegradable polymers
First and the second generation of DESs
The first generation of DES
Cypher - polyethylene-co-vinyl acetate (PEVA)/poly-n-butyl
methacrylate (PBMA)
Taxus - polystyrene-b-isobutylene-b-styrene (SIBS)
The second generation of DES
Xience V – fluoropolymer
Endeavor - phosphorylcholine (PC) Eurointervention,2005;1:266-272
Biodegradable polymers
Polylactic acid (PLA)
Polyglycolic acid (PGA)
Polylactic-co-glycolic acid (PLGA)
NON POLYMER
Titanium–nitric oxide alloy
Microporous stainless steel stent (Yukon, Translumina, Germany)
A nanoporous hydroxyapetite (a biocompatible crystalline derivative of
calcium phosphate) coating
Magnetic nanoparticles (MNPs) Eurointervention,2005;1:266-272
YUKON Choice DES system: Translumina modified stent surface containing micropores to enable the adsorption of different organic substances.
Abizaid A , and Costa J R Circ Cardiovasc Interv 2010;3:384-393
Copyright © American Heart Association
THERAPEUTIC AGENTS
Sirolimus (Rapamycin)
A macrocyclic lactone
Inhibits the migration and proliferation of SMCs
Zotarolimus
The sirolimus analogues
Developed by Abbott laboratories
Extremely lipophilic property and low water solubility
Everolimus
Sirolimus analogue
Immunosuppressive agent
Absorbs to local tissue more rapidly and has a longer celluar residence time and activity
Biolimus
PACLITAXEL AND ITS ANALOGUES
Paclitaxel
Promoting tubulin polymerization and cell cycle arrest
Inhibiting the migration and proliferation of SMCs
Coroxane
Nanoparticle albumin bound paclitaxel (nab-paclitaxel)
To improve the solubility
Docetaxel
Semi-synthetic analogue
Better anti-proliferative properties
OTHERS
Tacrolimus
Pimecrolimus
Curcumin
Resveratrol
CD 34 antibody
Anti-VEGF
RADIO-OPACITY ENHANCEMENTS
Stainless steel or nitinol - hard to see
fluoroscopically
To improve X-ray visibility, markers are often
attached to the stents.
These additions are typically made from gold,
platinum or tantalum
Electroplating (with gold) is also being used to
enhance X-ray visibility
COATINGS
To increase biocompatibility
Heparin was one of the first. Its mode of action is to
reduce the coagulation cascade (and thus possibly the
thrombogenic risk) after the deployment of a stent.
Phosphorylcoline and silicon-carbide have been used in
order to reduce platelet activation and interaction, thus
possibly controlling their adhesion to the stent struts
during the acute phase of stent re-endothelization.
Passive coverage has been also shown to be
useful.
Indeed, covered stents have been created, in which
a PTFE layer was put between two stents (Jostent
graft, Jomed) or one stent was covered by a inner
and an outer layer of PTFE (Symbiot, Boston
Scientific)
COMMONLY USED CORONARY STENTS IN CLINICAL PRACTICE
XIENCE FAMILY OF STENTS
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
XIENCE Xpedition
Abott vascularFDA Approved
Everolimus100μg/cm2
L-605 CoCr Hybrid cellMultilink0.0032" strut thickness,laser cut
PBMANon erodible
SV-2.25MV-2.5,2.75,3.0,3.25,3.5,4.0LL2.5,2.75,3.0,3.25,3.5,4.0
8,12,15,18,23,28
33,38
XIENCE V Abott vascularFDA Approved
Everolimus100μg/cm2Multi-layer Coating
MULTI-LINK VISION CoCr stent
Hybrid cellMultilink0.0032" strut thickness,laser cut,
PBMANon erodible
2.25,2.5,2.75,3.0,3.5,4.0
8,12,15,18,23,28
XINCE PRIME
Abott vascularFDA Approved
Everolimus100μg/cm2
Cobalt Chromium
Hybrid cellMultilink0.0032" strut thickness,laser cut,
biocompatible fluorinated copolymer
SV-2.25MV2.5,2.75,3.0,3.5,4.0LL-2.5,2.75,3.0,3.5,4.0
8,12,15,18,23,28Same33,38
THE XIENCE XPEDITION EVEROLIMUS ELUTING CORONARY STENT SYSTEM(ABOTT VASCULAR) FDA, CE MARK
The drug-coated stent and the balloon expandable delivery system
22% less force used to deliever than prime. Ultra low distal seal technology for outstanding
crossability. Unique 3.25mm diameter for more accurate vessel
sizing. More flexible multilayered balloon with flatter
compliance.
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
Promus element Plus
Boston scientific Everolimus Platinum Chromium
Tubular open cell,thin strut,high radial strength,good delieverality & trackability
Thin, fluorinated copolymer matrix for controlled drug release (100% drug elution in 120 days)
2.25,2.5,2.75,3.0,3.5,4.0
8,12,16,20,24,28,32,38
Endeavor Sprint Medtronic Zotarolimus-Eluting10μg/mm
cobalt-based alloy (cobalt, nickel, chromium, and molybdenum)
Modular design,Sinusoidal form wire,helical wrap,laser fused
Phosphorylcholine polymer
2.25,2.5,2.75,3.0,3.5,4.0
8,12,14,18,22,26,30,34,38
Resolut Integrity Medtronic Zotarolimus eluting
cobalt-based alloy (cobalt, nickel, chromium, and molybdenum)
Modular design,Sinusoidal form wire,helical wrap,laser fused
BioLinx biocompatible polymer
2.25,2.5,2.75,3.0,3.5,4.0
8,12,14,18,22,26,30,34,38
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
Taxus Liberte Boston Scientific Paclitaxel 1 μg/mm2 paclitaxel in a slow release (SR)*
316L surgical grade stainless steel
Sinusoidal ring modules linked via curved link elements
SIBS[poly(styrene-b-isobutylene-b-styrene)], a tri-block copolymer(trade name: Translute)
2.50, 2.75, 3.00, 3.50, 4.00
8, 12, 16, 20, 24, 28, 32
TAXUS Express Boston Scientific Paclitaxel1μg/mm2 paclitaxel in a slow release (SR)
316L surgical grade stainless steel
modular ring strut pattern consists of two separate module designs: short, narrow sinusoidal Micro elements linked via straight articulations to long, wide sinusoidal Macro elements
SIBS[poly(styrene-b-isobutylene-b-styrene)], a tri-block copolymer(trade name: Translute)
2.50, 2.75, 3.00, 3.50
8, 12, 16, 20, 24, 28, 32
Taxus Element Boston Scientific Paclitaxel1.0 μg/mm2
Platinum Chromium
Sinusoidal ring modules consisting of alternating long and short crowns linked via “Z” shaped elementsthin-strut coronary stent
SIBS[poly(styrene-b-isobutylene-b-styrene)], a tri-block copolymer(trade name: Translute)
2.25,2.50,2.75,3.0,3.5,4.0,4.5
8,12,16,20,24,28,32,38
Stent Manufacturer
Drug Base Form/Design Polymer Diameter Length
Coracto Alvimedica Rapamycin Stainless steel
Tubular,open cell design
Ultrathin polymer layer absobes 100% in 10-12 week
2.5,2.75,2.90,3.00,3.5,4.0
9,13,17,21,26,28,32
Coroflex please
B.Braun Paclitaxel1μg/cumm
Stainless steel
Multicellular ring design,HybridSuperb radioopacity
P matrix-polysulfone coating
2.5,2.75,3.0,3.5,4.0
8,13,16,19,25,28,32
Cypher cordis Sirolimus100% drug release with in 1 month
Stainless steel
Tubular,laser cut,sinusoidal pattern,closed cell
two non-erodiblepolymers: polyethylene-co-vinyl acetate (PEVA) and poly n-butyl methacrylate (PBMA)
2.50, 2.75, 3.00, 3.50
8, 13, 18, 23, 28, 33
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
YUKON Choice 4DES
Translumina, GermanCE mark
Sirolimus Medical Stainless Steel, 316 LVM, Surface containing micro-pores1million pores/sqcmBalloon marker material Platinum / Iridium
microporous PEARL SurfaceStrut thickness 0,0034” / 87 μmHybrid design
NonpolymericShellac resin biocompatible resin6 to 8 weeks release
2.0,2.25,2.50,2.75,3.0,3.5,4.0
8,12,16,18,21,24,28,32,40
GEN X Sync MIV therapeutics India pvt ltd
Sirolimus Co Cr Open cell,alternate S link,uniform sinusoidal strut design
Bio resorb PLLA-poly L lactic acidpolymerUltrathin coating(3μm)Drug sudden release f/b release upto 40-50 days.
2.0,2.25,2.50,2.75,3.00,3.50,4.0,4.5
8,13,16,19,24,29,32,37
Supralimus Sahajanand Medical Technologies Pvt Ltd, India
Sirolimus Sainless steel Hybrid biodegradable drug-carrier ,50% drug release in 7 days next 50% in 41days
2.5,2.75,3.0,3.5
8,12,16,20,24,2832,36,40
Supralimus-Core
Sahajanand Medical Technologies Pvt Ltd, India
Sirolimus cobalt-chromium
Hybrid biodegradable drug-carrier ,50% drug release in 7 days next 50% in 41days
same same
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
YUKON Choice PC
Translumina, GermanCE mark
Rapamycin (Sirolimus)Release of sirolimus up to 4 weeks
Medical Stainless Steel, 316 LVM, Surface containing micro-pores1million pores/sqcmFavours better endothelialisationBalloon marker material Platinum / Iridium
microporous PEARL SurfaceStrut thickness 0,0034” / 87 μmHybrid design
The biodegradable components polylactide and shellac
2.0,2.50,2.75,3.0,3.5,4.0
8,12,16,18,21,24,28,32,40
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
BioMatrix Biosensors Inc, Newport Beach, CalifCE mark
biolimus A9highly lipophilic, semisynthetic sirolimus analogue(≈15.6 μg/mm of stent length)
S-Stent (316 L) stainless steel stent with a strut thickness of 0.0054 inches (137 μm)
laser-cut, tubular stent S-Stent platformOpen cell,quadrature link
Biodegradable,Polylactic acid (PLA) applied to the abluminal surface
2.25,2.50,2.75,3.0,3.5,4.0
8,11,14,18,24,28,33,36
Pronova Vascular concepts,UK
Sirolimus Co Cr HybridS shaped articulations
Biocompatible,biostable polymer,drug release upto 30 days
2.25,2.50,2.75,3.0,3.25,3.50,4.0
13,18,23,28,33,38
Biomime Meril Life Sciences, India
Sirolimus1.25μgm/sqmm of stent surface,30 day elution kinetics
Co Cr Hybrid cell design65μm strut thickness
Biodegradable polymer
2.5,2.75,3.0,3.5,4.0,4.5
8,13,16,19,24,29,32,37,40
Stent Manufacturer
Drug Base Form/Design
Polymer Diameter Length
ACTIVE& ACTVE small
IHT Paclitaxel Stainless steel Open cell,tubular
P5 - Biocompatible polymer
2.0,2.25,2.5,2.75,3.0,3.5,4.0,4.5
9,14,18,19,23,28,36
EVERLITE Unimark remedies
EverolimusLow drug dose 1.2μg/sqmm
Co Cr Open cell,Sinosoidal strut design,alternative S link,ultrathin strut 65μm
Biodegradable 2.25,2.5,2.75,3.0,3.5,4.0,4.5
8,13,16,19,24,29,32,37,40
Flexy Rap Lancer medical technology
Rapamycin 1μg/sqmm
Co Cr Open cell, Radial star segments combined with flexible links,Strut 65μm,
Biodegradable polymer
2.25,2.5,2.75,3.0,3.5,4.0
7,10,13,15,17,20,24,28,33,38,42
INDOLIMUSCe mark
Sahajanand medical
sirolimus Co Cr Open cell,laser cut,seamless tube,60 micm strut thickness
Biodegradable polymer matrix
2.5,2.75,3.0,3.5 8,12,16,20,24,28,32,36,40
THANKS