U.S. patent application number 10/409559 was filed with the patent office on 2004-08-12 for metal alloy for medical devices and implants.
This patent application is currently assigned to W. C. Heraeus GmbH & Co. KG. Invention is credited to Trotzschel, Jens, Wachter, Jurgen.
Application Number | 20040158309 10/409559 |
Document ID | / |
Family ID | 32605362 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040158309 |
Kind Code |
A1 |
Wachter, Jurgen ; et
al. |
August 12, 2004 |
Metal alloy for medical devices and implants
Abstract
The present invention relates to a medical device or implant
made at least in part of a high strength, low modulus metal alloy
comprising Niobium, Tantalum, and at least one element selected
from the group consisting of Zirconium, Tungsten, and Molybdenum.
The medical devices according to the present invention provide
superior characteristics with regard to bio-compatibility,
radio-opacity and MRI compatibility.
Inventors: |
Wachter, Jurgen; (Rodermark,
DE) ; Trotzschel, Jens; (Bruchkobel, DE) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
W. C. Heraeus GmbH & Co.
KG
|
Family ID: |
32605362 |
Appl. No.: |
10/409559 |
Filed: |
April 8, 2003 |
Current U.S.
Class: |
623/1.13 ;
604/528; 623/1.15; 623/11.11; 623/2.24; 623/924 |
Current CPC
Class: |
A61L 31/18 20130101;
C22C 27/02 20130101; A61L 31/022 20130101; A61L 27/047 20130101;
C22C 30/00 20130101; C22C 27/00 20130101 |
Class at
Publication: |
623/001.13 ;
623/001.15; 623/002.24; 623/924; 623/011.11; 604/528 |
International
Class: |
A61F 002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 10, 2003 |
EP |
03 002 905.2 |
Claims
1. A medical implant or device fabricated from a metal alloy, said
medical implant or device comprising components at least partially
fabricated from a metal alloy comprising: (a) between about 0.1 and
70 weight percent Niobium; (b) between about 0.1 and 30 weight
percent in total of at least one element selected from the group
consisting of Tungsten, Zirconium and Molybdenum; (c) up to 5
weight percent in total of at least one element selected from the
group consisting of Hafnium, Rhenium and Lanthanides; (d) and a
balance of Tantalum, wherein the alloy provides for a uniform beta
structure, which is uniform and corrosion resistant, and has the
ability for conversion oxidation or nitridization surface hardening
of the medical implant or device.
2. A medical implant or device according to claim 1, wherein the
Lanthanide is cerium.
3. A medical implant or device according to claim 1, wherein the
alloy comprises between 0.1 and 15 weight percent Tungsten.
4. A medical implant or device according to claim 1, wherein the
alloy comprises between 0.1 and 10 weight percent Zirconium.
5. A medical implant or device according to claim 1, wherein the
alloy comprises between 0.1 and 20 weight percent Molybdenum.
6. A medical implant or device according to claim 1, wherein the
alloy comprises between 5 and 25 weight percent Niobium.
7. A medical implant or device according to claim 3, wherein the
alloy comprises about 10 weight percent Niobium and about 2.5
weight percent Tungsten.
8. A medical implant or device according to claim 3, wherein the
alloy comprises about 10 weight percent Niobium and about 7.5
weight percent Tungsten.
9. A medical implant or device according to claim 4, wherein the
alloy comprises about 10 weight percent Niobium and about 1 weight
percent Zirconium.
10. A medical implant or device according to claim 4, wherein the
alloy comprises about 10 weight percent Niobium and about 3 weight
percent Zirconium.
11. A medical implant or device according to claim 1, wherein the
medical device is a minimal-invasive device.
12. A medical implant according to claim 11, wherein the device is
one of a catheter and a guide wire.
13. A medical implant or device according to claim 1, wherein the
medical implant is an intra-cavernous implant.
14. A medical implant or device according to claim 13, wherein the
implant is an intravascular implant.
15. A medical implant according to claim 13, wherein the medical
implant is one of the group consisting of a stent, a stent graft, a
stent graft connector and a heart valve repair device.
16. A medical implant or device according to claim 1, wherein the
metal alloy has a surface that is passivated by oxidation or
nitridization.
17. A medical implant or device according to claim 1, wherein the
metal alloy has a surface that is one of electropolished,
mechanically polished, micro blasted, roughened and sintered.
18. A medical implant or device according to claim 1, wherein the
metal alloy has a surface coated with at least one of the group
consisting of a polymer, a blend of polymers, a metal, a blend of
metals, a ceramic and biomolecules.
19. A medical implant or device according to claim 18, wherein the
surface of the metal alloy is coated by at least one of the group
consisting of peptides, proteins, lipids, carbohydrates and nucleic
acides.
20. A medical implant or device according to claim 1, wherein the
metal alloy has a surface coated with at least one of stem cells
and bioactive substance.
21. A medical implant or device according to claim 20, wherein the
surface of the metal alloy is coated with at least one of the group
consisting of drugs, antibiotics, growth factors, anti-inflammatory
agents and anti-thrombogenic agents.
Description
[0001] The present invention relates to an improved metal alloy for
medical implants or devices for desired material properties.
BACKGROUND OF THE INVENTION
[0002] A medical implant or device must satisfy a number of
requirements. Factors affecting the choice of the medical implant
or device and the material thereof are mainly all mechanical
properties and biocompatibility. The material must not cause any
inflammatory reaction or allergic reaction. Commonly used materials
often include nickel, like medical grade 316L stainless steel,
which contains about 16% nickel. For patients with an allergic
reaction the implantation of such materials is contraindicated.
Another consideration in material selection is the need for the
implanting physician to be able to visualize the position of the
medical implant or device during procedure to the desired target
site in the body, and for purposes of examination from time to time
thereafter at the implant site, typically by X-ray fluoroscopy.
[0003] With the growing importance of magnetic resonance imaging
(MRI), MRI compatibility is desirable. The metal alloys commonly
used for implantation (like stainless steel 316) induce a local
disturbance of the magnetic field used in MRI, to the extent that
imaging of surrounding tissue is impeded. Although alloys like
Nitinol behave more favourably in MRI, their MRI compatibility is
not considered to be sufficiently good.
[0004] This invention relates to medical devices or implants in
general such as catheters, guide wires, stents, stent grafts and
heart valve repair devices.
[0005] Stents are generally thin walled tubular-shaped devices
composed of complex patterns of inter-connecting struts which
function to hold open a segment of a blood vessel or other body
lumen like oesophagus and urethra. Stent grafts are stents with a
circumferential covering or lining and are suitable for supporting
a dissected artery or intimal flap that can occlude a vessel lumen.
Stents and stent grafts are typically implanted by use of a
catheter. Initially they are maintained in a radially compressed
state to manoeuvre them through the lumen. Once in position, they
are deployed. The material from which the vascular prosthesis like
stents or stent grafts is constructed must allow the prosthesis to
undergo expansion, which typically requires substantial
deformation. Once expanded the stent must maintain its size and
shape and must be capable of withstanding the structural loads,
namely radial compressive forces, imposed on the stent as it
supports the walls of a vessel lumen. The wall of the prosthesis
must be sufficiently thick, depending on the stent material, not
only to withstand the vessel wall recoil but also allow the stent
to be seen on the fluoroscope. Finally, the prosthesis material
must be biocompatible so as not to trigger any adverse vascular
responses like restenosis or thrombus formation in the treated
vessel.
[0006] For medical devices such as all kind of catheters and guide
wires special mechanical properties are desired to have perfect
trackability and pushability during the intervention. Moreover,
good radio-opacity and MRI compatibility are essential in order to
survey medical procedures via x-ray and MRI. Finally also for these
medical devices biocompatibility is a must.
[0007] In the past years increased effort was undertaken to find
new materials for medical implants and devices bearing superior
characteristics over commonly used metals like stainless steel or
titanium. Numerous publications focus on titanium alloys aiming at
corrosion resistant, high strength and biocompatible alloys. As
described for example in U.S. Pat. No. 6,312,455, US 2001/0007953,
and WO 99/58184 many Titanium-alloys thereof are super-elastic or
shape memory alloys. A pseudo-elastic .beta.-titanium alloy
fabricated from Titanium, Molybdenum, Aluminium and optionally
Niobium, Chrome and Vanadium is described in U.S. Pat. No.
6,258,182. EP 0 788 802 provides a self-expanding stent consisting
of a titanium alloy including at least about 68 weight percent
titanium and optionally Niobium, Zirconium, and Molybdenum. U.S.
Pat. No. 6,238,491 and WO 00/68448 describe a
Niobium-Titanium-Zirconium-Molybdenum alloy for medical devices
providing a uniform .beta.-structure, which is corrosion resistant,
and can be processes to develop high-strength and low-modulus. The
alloy comprises 29 to 70 weight percent Niobium, 10 to 46 weight
percent Zirconium, 3 to 15 weight percent Molybdenum and a balance
of Titanium. In another approach Davidson (EP 0 601 804) employ an
alloy consisting essentially of Titanium, 10 to 20 or 25 to 50
weight percent Niobium and optionally up to 20 weight percent
Zirconium, the alloy having an elastic modulus less than 90 GPa.
Similar Titanium-alloys for medical implants also published by
Davidson comprise Titanium, 10 to 20 or 35 to 50 weight percent
Niobium and optionally up to 20 weight percent each Zirconium and
Tantalum (EP 0 437 079) or Titanium, 10 to 20 or 35 to 50 weight
percent each Niobium and Tantalum and optionally up to 20 weight
percent Zirconium (U.S. Pat. No. 5,690,670). EP 0 707 085 also
provides a low modulus, bio-compatible Titanium-base alloy for
medical devices consisting of 20 to 40 weight percent Niobium, 4,5
to 25 weight percent Tantalum, 2,5 to 13 weight percent Zirconium
and the balance Titanium. A further high strength, low modulus and
biocompatible Titanium-alloy is laid open in U.S. Pat. No.
4,857,269 and EP 0 359 446 consisting of Titanium and up to 25
weight percent Niobium, Zirconium, and Molybdenum. EP 1 046 722
describes a corrosion resistant Titanium-Zirconium-type alloy for
medical appliances consisting of 25 to 50 weight percent Titanium,
5 to 30 weight percent Niobium, 5 to 40 weight percent Tantalum and
25 to 60 weight percent Zirconium.
[0008] Further approaches to develop biocompatible, high strength
alloys which are also sufficiently radio-opaque and do not contain
Titanium are described in U.S. Pat. No. 6,478,815 and WO 02/43787.
Both documents reveal stents made from at least 90 weight percent
Niobium. Niobium is a relatively soft and ductile metal, which is
alloyed with traces of other elements, e.g. Zirconium, Tantalum or
Titanium for reinforcement of the alloy. However, Niobium surfaces
cannot be electropolished because of their tendency to smear (?).
Stents fabricated from binary Tantalum-Alloys, namely
Tantalum-Niobium and Tantalum-Tungsten, are disclosed in WO
02/05863.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Aim of the present invention is to provide an inventive
material for medical implants and devices, which comprises
favourable mechanical properties, excellent biocompatibility,
optimal radio-opacity while at the same time exhibiting minor image
artefact in MRI examination (MRI compatibility) and does therefore
overcome the drawbacks of recently available metals for medical
purposes.
[0010] The alloy fulfils all mechanical and structural requirements
according to its function in a medical implant or device. Moreover,
the device is sufficiently radio-opaque to allow for good imaging
of the device under x-ray without the addition of an extra layer or
portion of radio-opaque material. Also, the device is not overly
bright and therefore does not obscure the image of the surrounding
tissue, as would be the case with a device made from an extremely
dense material. In addition, the device is MRI safe and compatible,
preferably also visible under MRI.
[0011] Surprisingly, it has been found that the desired properties
can be given to a metal alloy comprising Tantalum, Niobium and at
least one element selected from the group consisting of Tungsten,
Zirconium and Molybdenum.
[0012] Tantalum is known as a very hard metal with a high melting
point, high strength, and good ductility and is almost completely
inert at body temperature. Tantalum has a high atomic number (73)
and a density of 16.6 g/cm.sup.3 resulting in a high radio-opacity.
Therefore, medical implants or devices made of pure tantalum have
the disadvantage that they are excessively radio-opaque, leading to
a completely black area on the x-ray image in the region where the
medical implant or device is located.
[0013] The radio-opacity of the inventive metal alloy is adjusted
by adding further elements possessing higher or lower atomic
numbers to the tantalum based alloy, which lowers the density of
the alloy. Niobium has an atomic mass of approximately half that of
Tantalum. Thus, tailoring the density of the inventive alloy by
variation of the Niobium portion allows achievement of appropriate
radio-opacity for each medical device or implant manufactured at
least in part of the inventive alloy. It is possible to fabricate
an alloy according to the present invention, which is sufficiently
radio-opaque to be readily visualized under x-ray during medical
procedures and yet is not so radio-opaque as to interfere with the
visualization of surrounding body tissue.
[0014] The alloys of the invention show excellent melting and
mixing properties with excellent uniformity since Niobium and
tantalum are arbitrarily miscible. Varying the amount of Tungsten,
Zirconium and Molybdenum, or optionally, the amount of Cerium,
Rhenium, or Hafnium, allows adjustment of the granular size of the
alloy.
[0015] Surprisingly, the alloy according to the present invention
is stronger than pure tantalum and in specific compositions even
stronger than stainless steel. In a preferred embodiment a stent is
manufactured from the alloy of the invention comprising a tailored
radio-opacity while having a reduced wall thickness. Such a stent
combines desired visibility under x-ray and excellent radial force
with minimised delivery profile and less turbulence when employed
in the vessel.
[0016] An additional advantage of the inventive alloy is the
formation of a passive oxide film primarily composed of
Tantalum-oxide (Ta.sub.2O.sub.5), which is generally more durable
and more corrosion resistant than for example the chromium-oxide
film formed during the passivation of stainless steel.
[0017] The inventive alloy can be easily cold-worked to increase
strength and reduce elastic modulus. It is possible to form a hard,
abrasion resistant surface on the inventive alloy through standard
oxidation and nitridizing methods known by those skilled in the
art. The presence of a hard, inert, abrasion resistant surface
layer presents an important option for medical implants and devices
in which it is desirable to have lower friction and wear,
electrical insulation and improved corrosion resistance.
[0018] To further improve the biocompatibility of the medical
implant or device fabricated at least in part from the inventive
alloy, at least a portion of the surface of the inventive alloy can
be conversion surface hardened and/or coated. Such coatings can
include, but are not limited to a polymer, a blend of polymers, a
metal, a blend of metals, a ceramic and/or biomolecules, in
particular peptides, proteins, lipids, carbohydrates and/or nucleic
acids (e.g. collagen, heparin, fibrin, phosphorylcholine,
cellulose, morphogenic proteins or peptides, growth factors).
Further-more the alloy surface or the coatings can comprise stem
cells and/or a bioactive substances, in particular drugs,
antibiotics, growth factors, anti-inflammatory agents and/or
anti-thrombogenic agents. Further, the surface can be modified by
electropolishing or mechanical polishing for formation of a
completely smooth surface, sintering to achieve a porous coating as
for example described in EP0601804, or by roughening procedures or
microblasting, in particular sand-blasting, to achieve a rough
surface.
[0019] The inventive alloy is useful in the manufacturing of a
variety of medical implants and devices. The manufacture of medical
devices from the invention alloy includes minimal-invasive devices,
in particular guide wires, catheters (balloon catheters, guiding
catheter, angiographic catheters, functional catheters, . . . ),
intra-cavernous implants, in particular intra-oesophagus,
intra-urethra, intra-tracheal implants and intra-vascular implants,
in particular stents, stent grafts, stent graft connector, heart
valve repair device or filters.
[0020] Preferred alloys contain the following elements:
[0021] (a) between about 0,1 and 70 weight percent Niobium,
[0022] (b) between about 0,1 and 30 weight percent in total of at
least one element selected from the group consisting of Tungsten,
Zirconium and Molybdenum,
[0023] (c) up to 5 weight percent in total of at least one element
selected from the group consisting of Hafnium, Rhenium and
Lanthanides, in particular Cerium,
[0024] (d) and a balance of Tantalum
[0025] The alloys preferably provide for a uniform beta structure,
which is uniform and corrosion resistant, and have the ability for
conversion oxidation or nitridization surface hardening of the
medical implant or device.
[0026] The tungsten content is preferably between 0,1 and 15 weight
percent.
[0027] The zirconium content is preferably between 0,1 and 10
weight percent.
[0028] The molybdenum content is preferably between 0,1 and 20
weight percent an more preferably between 0,1 and 10 weight
percent.
[0029] The niobium content is preferably between 5 and 25 weight
percent.
[0030] Especially preferred alloys contain about 10 weight percent
Niobium and about 2,5 weight percent Tungsten.
[0031] Also preferred are alloys which comprise about 10 weight
percent Niobium and about 7,5 weight percent Tungsten.
[0032] Also preferred are alloys which comprise about 10 weight
percent Niobium and about 1 weight percent Zirconium.
[0033] Also preferred are alloys which comprise about 10 weight
percent Niobium and about 3 weight percent Zirconium.
[0034] The invention also relates to medical implants or devices
fabricated from the above-mentioned alloys, e.g. minimal-invasive
devices, in particular catheters or guide wires, or intra-cavernous
implants, in particular intravascular implants, such as stents, a
stent grafts, stent graft connectors or heart valve repair
devices.
[0035] In the above implants and devices the surface of the metal
alloys may be passivated by oxidation or nitridization, or may be
electropolished, mechanically polished, micro blasted, roughened or
sintered, or may be coated with a polymer, a blend of polymers, a
metal, a blend of metals, a ceramic and/or biomolecules, in
particular peptides, proteins, lipids, carbohydrates and/or nucleic
acids; or may be coated with stem cells and/or a bioactive
substance, in particular drugs, antibiotics, growth factors,
anti-inflammatory agents and/or anti-thrombogenic agents.
EXAMPLE
[0036] The invention may be carried out with an alloy of the
following composition:
[0037] Ta: 71,5
[0038] Nb: 27,5
[0039] Zr: 1,0
[0040] Methods of producing the alloy are known to the person
skilled in the art.
* * * * *