traditional and novel metal alloys: advantagesalloys...
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Traditional and Novel Metal Alloys: AdvantagesAlloys: Advantages,
Disadvantages and Trendsg
Juan F. Granada, MD,Executive Director and Chief Scientific OfficerSkirball Center for Cardiovascular Research
Cardiovascular Research FoundationColumbia University Medical Center
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Common Metallic Materials Used in St t D l t & M f t iStent Development & Manufacturing
Key Element
Stainless Steel(316L)
CobaltChrome
(Elgiloy, MP35N,L-605)
Titanium(CP, Ti-6-4)
Nitinol( ) ( g y )
Iron 63% 1-15%
Titanium 90-100% 45%
Nickel 14% 15-35% 55%
Chromium 18% 20%
Cobalt 40 50%Cobalt 40-50%
Other Mo, Mn Mo, Mn, W Al, V
Slide courtesy (adapted) from Tom Duerig, Ph.D, NDC.
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Definition of Metal Strength“Ability of the material to withstand an applied stress without failure”
Material Strengthg
Stainless Steel Medium300/560 MPa
Cobalt-Chrome High600/1140 MPa
Titanium High880/950 MPa
Nitinol Highg500/1400 MPa
Slide courtesy (adapted) from Tom Duerig, Ph.D, NDC.
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Metal Stiffness: What is it?“Resistance of an elastic material to deformation by an applied force”
Material Stiffness
Stainless Steel High200 GPa
Cobalt-Chrome High200 GPa
Titanium ModerateTitanium Moderate90 GPa
Nitinol Very Low~25 GPa
Nitinol
Slide courtesy (adapted) from Tom Duerig, Ph.D, NDC.
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Conformability in Different Stent MaterialsA f th t i d t b d th t t t ifi tA measure of the torque required to bend the stent to a specific curvature,which is directly related to the flexibility of the stent. A lower required bending moment indicates increased flexibility. N=15 for each stent type.
Allocco et al. Trials 2010;11:1.
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Corrosion Resistance
Material Corrosion
Stainless Steel Good – Cr2O3(500 mV)
Cobalt-Chrome Good – Cr2O3(500 mV)
Titanium Excellent – TiO22(800 mV)
Nitinol Excellent – TiO2(800 mV)(800 mV)
66Slide courtesy (adapted) from Tom Duerig, Ph.D, NDC.
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Impact of Metal Properties on St t P f
Radial StrengthRadiopacity
Stent Performancegp y
Stent Recoil Crossing Profile
Menown et al. Adv Ther 2010;27:129-141
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Material +Structure + DesignStent Design PerformanceStent Design Performance
How Do you Increase Stent DeliverabilityHow Do you Increase Stent Deliverability Maintaining Visibility and Strength?
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Evolution of Stent TechnologyReduced Strut Thickness= Increase DeliverabilityReduced Strut Thickness= Increase Deliverability
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Platinum ChromiumElemental Composition
Platinum has over 2x the density of i b lt ( i di it )
Elemental Composition
iron or cobalt (superior radiopacity).Platinum is distributed evenly throughout the alloy to provide the
i t l l f i ibilitappropriate level of visibility.Platinum increases strength when alloyed with 316L stainless steel.Platinum chromium has the lowest nickel content (9%) compared to
316L Stainless Steel: 14% (TAXUS® Liberté Stent®)L605 Cobalt Chromium: 10%(XIENCE V® Stent)MP35N Cobalt Nickel: 35% (Endeavor® Stent)
Steiner R: ASM Handbook Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys. 10th ed. Materials Park, OH: ASM International; 1990. Bench test p , , g y , ;results may not necessarily be indicative of clinical performance. Data on file at BSC. MP35N is a trademark of SPS TECHNOLOGIES, LLC.
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Restenosis is the Result of the Interaction of Several Related Factors
EngineeringMaterials
MechanicalIntegrity
VascularResponse
Integrity
MechanicalScaffolding
DesignArtery
ScaffoldingBiology
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Strut Surface/Material and RestenosisImpact of Surface Material on RestenosisImpact of Surface Material on Restenosis
Inflow SteelInflow Gold NIR primoNIRoyal
38.149.7
40
50p=0.003 p=0.002
n=73137.540
50 p<0.001 p=ns
n=603
25.1
15.720
30%
23.620.6
17.520
30%
0
10
restenosis TVR0
10
restenosis TVR
Kastrati et al., Circulation. 2000;102(21):2593-8
restenosis TVR restenosis TVR
Reifart et al., Cathet Cardiov Interv. 2004;62(1):18-25
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Evolution of Early Stent TechnologyThe Evolution of Stent DesignsThe Evolution of Stent Designs
Wire Mesh StentWire Coil Stents
Cook GR II
Tubular Slotted Stents
Cook GR II
Modular StentsGuidant Multi-Link
Medtronic Wiktor
B t S i tifi NIRBoston Scientific NIR
Medtronic VascularJ&J Palmaz-Schatz
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Stent Design, Vessel Injury and RestenosisExperimental DataExperimental Data
injury adherent neointimal areaj yscore monocytes after 14 days
mm2%60 40 1.0
p < 0.001 p < 0.001 p < 0.0011.11
31.1
0.58
40
5030
22.50.31
0.69
20
30
40
20 0.5
10
2010
0 0 00 0 0
corrugated ring slotted tube
Rogers et al., Cir Res 1999
g g
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Randomized Trial With 5 Different Stents
InflowInflow Dynamics
n= 231
Inflow Dynamics
MULTI-LINKn= 227
ACS Guidant
NIRn= 2291147 Patients NIR
Boston Scientific
Palmaz-Schatz (PS)Johnson & Johnson
n= 233
PURA-ADevon Medical
n= 227
Devon Medical
Kastrati et al., Cathet Cardiovasc Interv 2000 Jul;50(3):290-7
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Randomized Trial With 5 Different Stents6 Month Results6-Month Results
Restenosis (≥50%) Restenosis (≥ 75%) TVR
353640p=0.145
( )
30 30
( )
p=0.012 p=0.04
2929
35
25
36
3018
2320
20
24
2120
% % %
25
20
18
14
11
201515 14
20
1010 10
0 0 0
Inflow NIR PS MULTI-LINKPURA-AInflow NIR PS MULTI LINKPURA A
Kastrati et al., Cathet Cardiovasc Interv 2000 Jul;50(3):290-7
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Stent Strut Design and Thickness in Currently FDA Approved Drug Eluting Stents
XIENCE V™ENDEAVOR™CYPHER® TAXUS® Express
FDA Approved Drug Eluting Stents
XIENCE VENDEAVORCYPHER TAXUS Express
Strut Thickness:Strut Thickness:Strut Thickness:Strut Thickness: Strut Thickness:
81 µmCoating
Strut Thickness:
91 µmCoating
Strut Thickness:
132 µmCoating
Strut Thickness:
140 µmCoating g
Thickness:7.8 µm
Thickness:4.8 µm
gThickness:19.6 µm
Thickness:12.6 µm
Photos taken by and on file at Abbott Vascular
Abluminal coating thickness represented, 3.0x18mm stent, 500X magnfication
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Optimization of Strut Thickness Leads to Reduction of Inflammation (14 Day Rabbit Iliac Arteries)( y )
Thick= 162 umThin= 82 um
3
Thi kThick
(%)
2ThickThin
Thin40
30
120
10
% Stenosis 0 Fibrin Score Inflammation Score0
Slide courtesy (adapted) of Renu Virmani
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Strut Thickness and RestenosisVascular Injury versus Rapid Endothelialization?Vascular Injury versus Rapid Endothelialization?
ISAR-STEREO-1
30 p=0.003 p=0 03
ISAR STEREO 1
25.820
p 0.003 p=0.03
MULTI-LINK
15.0 13.810
20
%MULTI-LINK
(50 µm)
8.6
13.810 MULTI LINKDuet (140 µm)
0restenosis TVR
Kastrati A. Circulation. 2001 Jun 12;103(23):2816-21.
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Strut Thickness and RestenosisVascular Injury versus Rapid Endothelialization?Vascular Injury versus Rapid Endothelialization?
ISAR-STEREO-2
n=611p=0.001 p=0.002
ISAR-STEREO-2
MULTI-LINK31.4
30
40%
BX Velocity
MULTI-LINK(50 µm)
17.9
12 3
21.920
BX Velocity(140 µm)
12.310
0restenosis TVR
Pache J. JACC. 2003 Apr 16;41(8):1283-8.
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Strut Thickness and Angiographic Restenosis in Small Coronary ArteriesRestenosis in Small Coronary Arteries
Retrospective Analysis of 941 PatientsThin Struts (<100 µm):Palmaz-SchatzACS MULTI-LINK %
0 001
Restenosis Rates
BiodivYsioBeStentJOSTENT FlexDi d (Ph ti )
36.630
40 p<0.001
Diamond (Phytis)V-Flex (Global Therapeutic)Sorin Carbostent
28.520
30
Thick Struts (≥100µm):NIRACS Duet
10
BX VelocityAVE-IICordis Crossflex LCB d XT
0
thick struts(n=436)
thin struts(n=505)Bard XT (n 436)(n 505)
Briguori C. JACC. 2002 Aug 7;40(3):403-9.
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Binary Restenosis Rate in the BMS Arms of Randomized Trials of DES
45.550
of Randomized Trials of DES
33 535.4
41.7
3
40
45
(%)
25.9
33.531.9
24.426.6
25
30
35
osis
Rat
e
20.217.9
15
20
25
ary
Res
ten
10.4
5
10
15
Bin
a
0
5
Ravel(118)
C-Sirius(50)
eSirius(177)
Sirius(159)
Taxus I(30)
Taxus II-S (136)
Taxus II-M (134)
Taxus IV(652)
Taxus V(579)
EndeavorII (599)
Spirit I(29)
Data Obtained from JACC, Aug 31,2010;Vol56, No10 (Suppl S)
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Conclusions• Stent material science is still evolving and aims to find
the perfect balance between acute device performance and clinical outcomesand clinical outcomes.
• New stent materials have permitted the development of thinner stent struts, but still maintaining similarthinner stent struts, but still maintaining similar mechanical properties compared to previous generation stents.Oth f t (i f h t i ti ) ll• Other factors (i.e., surface characteristics) may equally impact the overall long term performance of the device.
• Therefore the “ideal” stent design has to achieve aTherefore, the ideal stent design has to achieve a perfect balance between material selection, design and strut thickness.
• Still, despite the fact that BMS platforms have plateau in their restenosis rate, they have become superior delivery platforms for DES technologiesplatforms for DES technologies.