U.S. patent application number 12/777644 was filed with the patent office on 2010-12-23 for stent having improved stent design.
This patent application is currently assigned to BIOTRONIK VI PATENT AG. Invention is credited to Frank Bakczewitz, Steffen Mews.
Application Number | 20100324659 12/777644 |
Document ID | / |
Family ID | 42670461 |
Filed Date | 2010-12-23 |
United States Patent
Application |
20100324659 |
Kind Code |
A1 |
Mews; Steffen ; et
al. |
December 23, 2010 |
STENT HAVING IMPROVED STENT DESIGN
Abstract
A stent is provided having a base body circumscribing a
cylindrical shape and radially expandable from a contracted
starting position into a dilated support position, including a
plurality of meander-shaped struts disposed in the circumferential
direction and arrayed on one another in the axial direction, each
strut being meander-shaped in its coarse structure and made of a
flexible material, and at least one axial connector in the axial
direction, connecting the meander-shaped struts of two axially
adjacent meandering curves, wherein the at least one axial
connector connects the inside radius of a zenith point of a first
meandering curve with a second meandering curve, characterized in
that the at least one axial connector at the inside radius of the
zenith point of the first meandering curve has an at least
double-arm structure.
Inventors: |
Mews; Steffen; (Rostock,
DE) ; Bakczewitz; Frank; (Rostock, DE) |
Correspondence
Address: |
BIOTECH BEACH LAW GROUP , PC
5677 OBERLIN DRIVE, SUITE 204
SAN DIEGO
CA
92121
US
|
Assignee: |
BIOTRONIK VI PATENT AG
Baar
CH
|
Family ID: |
42670461 |
Appl. No.: |
12/777644 |
Filed: |
May 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61218999 |
Jun 22, 2009 |
|
|
|
Current U.S.
Class: |
623/1.16 |
Current CPC
Class: |
A61F 2002/91575
20130101; A61F 2002/91541 20130101; A61F 2002/91583 20130101; A61F
2/915 20130101; A61F 2002/91566 20130101; A61F 2002/91558
20130101 |
Class at
Publication: |
623/1.16 |
International
Class: |
A61F 2/82 20060101
A61F002/82 |
Claims
1. A stent having a base body circumscribing a cylindrical shape
and radially expandable from a contracted starting position into a
dilated support position, comprising: a) a plurality of
meander-shaped struts disposed in the circumferential direction and
arrayed on one another in the axial direction, each strut being
meander-shaped in its coarse structure and made of a flexible
material; b) at least one axial connector in the axial direction,
connecting the meander-shaped to struts of two axially adjacent
meandering curves; wherein the at least one axial connector
connects the inside radius of a zenith point of a first meandering
curve with a second meandering curve; wherein the at least one
axial connector at the inside radius of the zenith point of the
first meandering curve has an at least double-arm structure.
2. The stent according to claim 1, wherein the at least double-arm
structure has two arms enclosing in the dilated support position an
angle in the range of 30.degree. to 180.degree., optionally in the
range of 60.degree. to 180.degree., optionally in the range of
90.degree. to 180.degree..
3. The stent according to claim 1, wherein the at least double-arm
structure has three arms, wherein one arm, optionally the middle
one, runs parallel to the axial direction.
4. The stent according to claim 1, wherein the flexible material is
a material selected from the group consisting of metals, metal
alloys and polymers.
5. The stent according to claim 1, wherein the flexible material is
a biodegradable material.
6. The stent according to claim 5, wherein the biodegradable
material is a material selected from the group consisting of
magnesium, iron, zinc, tungsten and a metal alloy of any
combination thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This invention claims benefit of priority to U.S.
provisional patent application Ser. No. 61/218,999, filed on Jun.
22, 2009; the contents of which is herein incorporated by reference
in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates to a stent having improved stent
design.
BACKGROUND OF THE INVENTION
[0003] Implantation of stents has become established as one of the
most effective therapeutic measures for treatment of vascular
diseases. Stents assume a supporting function in the hollow organs
of a patient. Stents of conventional construction have a base body
with a plurality of circumferential support structures. For
example, metallic struts have a base body which is initially in a
compressed form for insertion into the body and then is dilated at
the site of use. One of the main areas for use of such stents is
for permanently or temporarily widening and keeping open of
vascular obstructions, in particular constrictions (stenoses) of
the coronary vessels. In addition, aneurysm stents are known that
serve to support damaged vascular walls or seal off intracerebral
vascular bulges.
[0004] Conventional stents for the treatment of stenoses have a
cylindrical base body of sufficient load-bearing capacity that
opens the constricted vessel and keeps it open to the desired
degree to restore unobstructed blood flow. The circumferential wall
of the base body is typically formed by a lattice-like bearing
structure, allowing for the stent to be inserted in a compressed
(crimped) state with a small outside diameter up to the point of
constriction of the vessel to be treated, and to be sufficiently
widened, e.g., by means of a dilatation balloon catheter until the
vessel has the desired increased inside diameter. The steps of
placing and expanding the stents during this procedure and their
final positioning in the tissue upon completion of the procedure
must be monitored by the cardiologist. This may be accomplished by
means of imaging methods such as x-ray examinations.
[0005] The stent has a basic body made of an implant material. An
implant material is a nonviable material that is used in medicine
and interacts with biological systems. The basic prerequisite for
the use of a material as implant material that is in contact with
the physical body environment during its intended use is its
physical compatibility (biocompatibility). Biocompatibility refers
to the ability of a material to induce an appropriate tissue
reaction in a specific application. This includes adaptation of the
chemical, physical, biological and morphological surface properties
of an implant to the recipient tissue with the goal of clinically
desirable interaction. The biocompatibility of the implant material
further depends on the chronological course of reaction of the
biosystem in which it is implanted. Irritations and inflammations
may occur at relatively short notice and cause tissue changes.
Biological systems thus react in different ways, depending on the
properties of the implant material. According to the reaction of
the biosystem, implant materials may be categorized as bioactive,
bioinert and biodegradable/resorbable materials.
[0006] Stents have a cylindrical base body including a lumen along
the axial direction. The base body has a plurality of
meander-shaped struts, forming the circumferential support
structures, e.g. circumferential cylindrical meandering rings or
helices, arranged one after the other along the axial direction.
The support structures are connected in the axial direction by
means of connecting elements, so-called axial connectors or
connectors. At least in vascular support stents these axial
connectors must on the one hand be arranged in such a manner that
sufficient bending flexibility of the stent is guaranteed, and on
the other hand they should not obstruct the crimping and/or
dilatation processes.
[0007] U.S. Pat. No. 6,464,720 proposes a stent design in which the
stent base body has apertures. These apertures serve to accommodate
radiopaque markers made of a material that does not allow the
passage of x-rays. While the apertures in this stent design only
minimally affect crimpability, they hinder homogenous plastic
deformation of the support elements and thus have a significant
negative impact on the mechanical properties of the stent.
[0008] A cause for increased vascular inflammatory reactions upon
stent implantation is the targeted use of stent overdilatation,
which is necessitated by a certain spring-back of the stent shortly
after implantation, so-called recoil. Such recoil, whose degree
depends on the respective design and, particularly, the material
used, is shown by any material composition used for implants. To
achieve a minimum lumen size that is physiologically reasonable for
the treated vessel after implantation, overdilatation of the stent
is necessary to offset recoil. This overdilatation causes the
vessel to be overstretched so that vessel damage occurs, causing
the body to respond with an inflammatory reaction and subsequent
increased formation of new tissue (neointimal proliferation). Both
reactions need to be to minimized in the context of stent
implantations.
[0009] Especially when using magnesium or a magnesium alloy as a
degradable stent material, it is particularly important, due to
their not very favorable mechanical material properties, to
minimize the effects on the distribution of forces, combined with
an effective utilization of crimp space, which calls for optimal
design of the axial connectors.
SUMMARY OF THE INVENTION
[0010] The present invention is targeted at solving the above
mentioned problems. In particular, a stent design is to be provided
that allows for minimum impact on the distribution of forces in the
supporting struts while effectively utilizing the space available
for crimping and at the same time allowing for homogeneous plastic
deformation, particularly during dilatation of the stent base body
at the treatment site. In particular, recoil of the stent body
following implantation is to be kept at a minimum.
[0011] This problem is solved by providing a stent having a base
body circumscribing a cylindrical shape and being radially
expandable from a contracted starting position into a dilated
support position, including a plurality of meander-shaped struts
disposed in the circumferential direction and arrayed on one
another in the axial direction, each strut being meander-shaped in
its coarse structure and made of a flexible material, and at least
one axial connector in the axial direction, connecting the
meander-shaped struts of two axially adjacent meandering curves,
wherein the at least one axial connector connects the inside radius
of a zenith point of a first meandering curve with a second
meandering curve, wherein the at least one axial connector, at the
inside radius of the zenith point of the first meandering curve,
has an at least double-arm structure.
[0012] The solution according to the invention is characterized in
that the at least one axial connector connecting the meander-shaped
struts joins with the inside radius of the zenith point in an at
least double-arm structure. Due to this at least double-arm
structure of the connection between the meander-shaped strut and
the axial connector, homogeneous distribution of strains and
stresses in the curved elements of the stent remains unaffected.
Homogeneous plastic deformability of the stent of the invention is
thus ensured. Due to the at least double-arm structure, additional
plastic deformation areas are created in the stent system as a
whole, which adds to reinforcing the system.
[0013] Due to joining the at least double-arm structure of the
axial connector to the inside radius of the zenith point, the joint
only takes up little space so that enough space is available to
ensure sufficient crimpability and bending flexibility of the stent
of the invention.
[0014] Due to the joining sites of the at least double-arm
structure of the axial connector being distributed over the entire
inside radius of the zenith point, the stent according to the
invention provides an optimal distribution of forces from one
support structure to the next, as well as the required stability.
Alignment of the axial connectors substantially along the axial
direction of the stent results in optimal utilization of space in
the crimped state of the stent of the invention.
[0015] Due to the at least double-arm structure of the axial
connectors of the stent according to the invention, the axial
connectors support the stent in its standard and radial forces. The
radial force is the force that is perpendicular to the axial
direction and radially pointing outward, imparting to the stent the
support properties to keep the lumen of the blood vessel open. Due
to the connection by means of the at least double-arm structure,
apertures are formed between the arms of the at least double-arm
structure and the inner radius of the joined zenith point. These
apertures constitute closed cells in the stent structure,
increasing stent stiffness and thus contributing to reinforcing the
whole system. Due to the stiffening of the entire system, recoil of
the system as a whole is minimized. Therefore, by means of the at
least double-arm structure, the axial connectors contribute to
increasing the radial force, and thus the supporting force of the
stent, and keep undesired recoil at a minimum.
[0016] In a preferred embodiment, the at least double-arm structure
includes two arms. In the dilated support position of the stent
upon implantation, the two arms of the at least double-arm
structure enclose an angle in the range of 30.degree. to
180.degree., preferably in the range of 60.degree. to 180.degree.,
and particularly preferred in the range of 90.degree. to
180.degree..
[0017] In another preferred embodiment, the at least double-arm
structure includes three arms. The middle one of the three arms
runs parallel to the axial direction of the stent. The overall
arrangement of the arms is in symmetry relative to the axial
direction. Asymmetrical arrangements, however, are also possible
and feasible.
[0018] The base body of the stent according to the invention may be
made of any implantation material suitable for the production of
implants, particularly stents. Implant materials for stents include
polymers, metallic materials and ceramic materials. Biocompatible
metals and metal alloys for permanent implants include, for
example, stainless steels (such as 316L), cobalt base alloys (such
as CoCrMo casting alloys, CoCrMo forge alloys, CoCrWNi forge
alloys, and CoCrNiMo forge alloys), pure titanium and titanium
alloys (such as cp titanium, TiAl.sub.6V.sub.4 or
TiAl.sub.6Nb.sub.7), and gold alloys. Preferably, the base body
includes a metallic implant material.
[0019] Particularly preferred, the stent according to the invention
has a base body including a biodegradable implant material. In the
field of biodegradable stents, magnesium or pure iron as well as
biodegradable base alloys of the elements magnesium, iron, zinc,
molybdenum, and tungsten are used. In particular, the base body of
a stent according to the invention may include a biodegradable
magnesium alloy.
[0020] For the purposes of the present invention, "alloy" is meant
to designate a metallic lattice whose main component is magnesium,
iron, zinc or tungsten. The main component is the alloy component
having the highest percentage by weight of the alloy. Preferably, a
main component percentage is more than 50% by weight, in particular
more than 70% by weight.
[0021] It is not imperative that both the base body and the at
least one axial connector be made of the same material. In fact,
any combination of materials--metals and polymers--is possible.
When using biodegradable stents care is to be taken that all the
materials used are biodegradable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention is described based on the attached
drawings.
[0023] FIG. 1a schematically shows a section of a base body of the
stent according to the invention, wherein the at least double-arm
structure consists of exactly two arms, and the axial connector in
each case connects the inside radius of the zenith point of the
first meandering curve with the outside radius of the zenith point
of the second meandering curve.
[0024] FIGS. 1b and 1e schematically show sections of a base body
of a stent according to the invention, wherein the at least
double-arm structure consists of exactly two arms, and the axial
connector in each case connects the inside radius of a zenith point
of a first meandering curve with the inside radius of the zenith
point of a second meandering curve.
[0025] FIGS. 1d and 1e schematically show sections of a base body
of a stent according to the invention, wherein the at least
double-arm structure consists of exactly two arms, and the axial
connector in each case connects the inside radius of a zenith point
of a first meandering curve with the straight segment of a second
meandering curve.
[0026] FIGS. 2a and 2b schematically show sections of a base body
of a stent according to the invention, wherein the at least
double-arm structure consists of exactly three arms.
[0027] FIG. 3 schematically shows a section of a base body of a
stent according to the invention, wherein the at least double-arm
structure consists of a ramification of the axial connector having
five arms.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The invention will subsequently be explained in greater
detail on the basis of the exemplary embodiments in conjunction
with the figures.
[0029] A stent has a base body circumscribing a cylindrical shape
and enclosing a lumen along an axial direction. Upon implantation
of the stent into a blood vessel, the blood flow can be effected
through this lumen. The base body includes a plurality of
meander-shaped struts disposed in the circumferential direction and
arrayed on one another in the axial direction, each strut being
meander-shaped in its coarse structure and made of a flexible
material. The meander-shaped struts are substantially responsible
for the support function of the stent. The necessary expansion of
the stent base body upon stent implantation is ensured by the
meandering shape of the struts.
[0030] The meandering shape has zenith points alternating their
direction of curving in the course of the meander-shaped strut. A
right curve is followed by a left curve, with a short straight
segment of the meander-shaped strut in between. This system
continues along the axial direction in an alternating manner such
that a ring-shaped circumferential structure is formed, enclosing a
lumen. The zenith points have an inside radius and an outside
radius. The inside radius of the zenith point is the zone lying
inside the circle, if the zenith point is conceived as part of a
circular shape. Correspondingly, the outside radius is the outside
boundary of the imagined circular shape of the zenith point.
[0031] Besides having a plurality of support structures, the base
body includes one or more axial connectors, thus enabling two
successive circumferential support structures to be connected with
each other by at least one axial connector. The axial connectors of
the stent according to the invention are designed to allow for
connecting a plurality of support structures to form one base body
that is suitable for use in an expandable stent. For this purpose,
one axial connector in each case connects a zenith point of a first
meandering curve of a meander-shaped strut with a second meandering
curve of an axially adjacent meander-shaped strut. The zenith
points of the first and second meandering curves lie in the
axial-parallel direction, or in opposite directions to each other,
or in an offset pattern, respectively, so that the axial connector
runs along the length of the cylindrical area of the base body. Two
successive meander-shaped struts may also be connected with each
other by more than one axial connector. Preferably, the axial
connectors are just long enough to provide sufficient flexibility
of the two neighboring meander-shaped struts, but not so long that
the stent of the invention will become torsion-soft. One or more or
all of the axial connectors of a stent according to the invention
may have a curved shape. The axial connectors are aligned in a
substantially axial direction between the two circumferential
meander-shaped struts to be connected, but the axial connectors are
not necessarily arranged in exactly parallel alignment to the axial
direction.
[0032] The stent according to the invention includes axial
connectors having an elongated shape. The axial connector is
composed of a main stem and the at least double-arm structure. The
main stem of the axial connector passes directly and immediately
into the at least double-arm structure. The at least double-arm
structure connects the axial connector with the inside radius of
the zenith point of the meander-shaped strut. The at least
double-arm structure of the axial connector consists of at least
two arms. The at least two arms of the axial connector constitute
the joining of the main stem with the inside radius of the zenith
point of the meander-shaped strut.
[0033] The main stem of the axial connector has a web width
d.sub.1, and the arms of the at least double-arm structure have a
web width d.sub.2, with d.sub.1 being greater than d.sub.2. The
diameters of the arms, however, may also have different sizes.
[0034] At both of its ends the axial connector has joints with the
meander-shaped strut. At the joints of the at least double-arm
structure the at least two arms pass into the inside radius of the
zenith point of the meander-shaped structure. The joining site of
the arms, however, may also be located in the straight segment of
the meandering curve.
[0035] Joining the at least one axial connector with the second
meandering curve is accomplished either by means of joining with an
outside radius of the zenith point of the second meandering curve,
an inside radius of the zenith point of the second meandering
curve, or a point on the straight connection between the inside
radius and the outside radius of the second meandering curve
("strut"). The joining of the at least one axial connector with the
second meandering curve may also be effected by a multiple-arm
structure.
[0036] The web width of the at least two arms of the double-arm
structure and the web width of the main stem at the joint
immediately before the transition to the meander-shaped to
structure are larger than the respective web widths d.sub.1 and
d.sub.2, respectively. The web width of the joints tapers
continuously towards the axial connectors. This tapering may be
homogeneous, but it may also be uneven.
[0037] FIG. 1a shows a section of a base body of a stent according
to the invention. What is shown are sections of two meander-shaped
struts 2 and 2' disposed in the circumferential direction U and
arrayed on one another in the axial direction A, which are
connected with each other by means of axial connectors 4. The
meander-shaped struts 2 and 2' have meandering curves 3 and 3'. The
meandering curves 3 and 3' show zenith points 5 and 5', having an
inside radius 6, 6' and an outside radius 7, 7'. The axial
connectors 4 connect the inside radius 6 of the zenith point 5 with
the outside radius 7' of the zenith point 5' of the meander-shaped
strut 2' adjacent in the axial direction A. The at least double-arm
structure is accomplished in FIG. 1a by two arms 11 and 11',
respectively.
[0038] The axial connector 4 is composed of a main stem 8 and the
double-arm structure 10. The main stem 8 of the axial connector
passes directly and immediately into the double-arm structure 10.
The main stem 8 of the axial connector has a web width d.sub.1, and
the two arms 11 and 11', respectively, of the double-arm structure
10 have a web width d.sub.2, with d.sub.1 being greater than
d.sub.2.
[0039] In the embodiment having a double-arm structure, the two
arms together with the inside radius of the zenith point of the
meandering curve define an aperture having a ladle-like shape.
[0040] FIGS. 1b and 1c show sections of a base body of a stent
according to the invention. What is shown are sections of two
meander-shaped struts 2 and 2' disposed in the circumferential
direction U and arrayed on one another in the axial direction A,
which are connected with each other through axial connectors 4. The
meander-shaped struts 2 and 2' have meandering curves 3 and 3'. The
meandering curves 3 and 3' show zenith points 5 and 5', having an
inside radius 6 and an outside radius 7. What is shown are two
different variants of a so-called valley-to-valley connection; this
means that the axial connectors 4 connect the inside radius 6 of
the zenith point 5 with the inside radius 6' of the zenith point 5'
of the meander-shaped strut 2' adjacent in the axial direction A.
The at least double-arm structure is accomplished in FIGS. 1b and
1c by two arms 11 and two arms 11'.
[0041] FIGS. 1d and 1e show sections of a base body of a stent
according to the invention. What is shown are sections of two
meander-shaped struts 2 and 2' disposed in the circumferential
direction U and arrayed on one another in the axial direction A,
which are connected with each other through axial connectors 4. The
meander-shaped struts 2 and 2' have meandering curves 3 and 3'. The
meandering curves 3 and 3' show zenith points 5 and 5', having an
inside radius 6 and an outside radius 7. What is shown are two
different variants of a so-called valley-to-strut connection; this
means that the axial connectors 4 connect the inside radius 6 of
the zenith point 5 with the straight segment of the meander-shaped
strut 2' adjacent in the axial direction A. The at least double-arm
structure in FIGS. 1d and 1e is accomplished by means of two arms
11 and two arms 11'.
[0042] FIGS. 2a and 2b show sections of a base body of a stent
according to the invention. What is shown are sections of two
meander-shaped struts 2 and 2' disposed in the circumferential
direction U and arrayed on one another in the axial direction A,
which are connected with each other through axial connectors 4. The
meander-shaped struts 2 and 2' have meandering curves 3 and 3'. The
meandering curves 3 and 3' show zenith points 5 and 5', having an
inside radius 6 and an outside radius 7. The axial connectors 4
connect the inside radius 6 of the zenith point 5 with the outside
radius 7 of the zenith point 5' of the meander-shaped strut 2'
adjacent in the axial direction A. The at least double-arm
structure is accomplished in FIGS. 2a and 2b by means of three arms
12 and 12', respectively, so that a three-armed structure is
created. The axial connector 4 is composed of a main stem 8 and the
three-armed structure 10. The main stem 8 of the axial connector
passes directly and immediately into the three-armed structure 10.
This is a joining design having ladle-shaped apertures 20 (FIG. 2a)
and a design wherein the apertures enclosed by arms 12 and 12',
respectively, together with the meander-shaped struts 2 and 2',
respectively, have a chandelier-like shape 21 (FIG. 2b).
[0043] FIG. 3 is a section of a base body of a stent according to
the invention. What is shown are sections of two meander-shaped
struts 2 and 2' disposed in the circumferential direction U and
arrayed on one another in the axial direction A, which are
connected with each other through axial connectors 4. The
meander-shaped struts 2 and 2' have meandering curves 3 and 3'. The
meandering curves 3 and 3' show zenith points 5 and 5', having an
inside radius 6 and an outside radius 7, 7'. The axial connectors 4
connect the inside radius 6 of the zenith point 5 with the outside
radius 7' of the zenith point 5' of the meander-shaped is strut 2'
adjacent in the axial direction A. The at least double-arm
structure in FIG. 3 is accomplished by means of five arms 13 and
13'. The axial connector 4 is composed of a main stem 8 and the
ramification of the at least double-arm structure 10. The main stem
8 of the axial connector passes directly and immediately into the
five arms 13 and 13', respectively, of the at least double-arm
structure 10.
[0044] In the embodiment including a five-armed structure, the five
arms 13 and 13', respectively, together with the inside radius 6
and 6', respectively, of the zenith point of the meandering curve,
define an aperture having a chandelier-like shape.
[0045] Besides non-degradable metallic alloys, degradable metals
and their alloys may also be used for implementing the invention.
The alloys of the elements magnesium, iron, zinc or tungsten are
selected such in a composition as to be biodegradable. For the
purposes of this invention, "biodegradable" is used to denote such
alloys that undergo degradation in a physiological environment,
eventually resulting in loss of mechanical integrity of the entire
implant or the part of the implant made of said material. For
testing the degradation behavior of an alloy in question,
artificial plasma is used as a test medium, as prescribed under EN
ISO 10993-15:2000 for biodegradation testing (composition NaCl 6.8
g/l, CaCl.sub.2 0.2 g/l, KCl 0.4 g/l, MgSO.sub.4 0.1 g/l,
NaHCO.sub.3 2.2 g/l, Na.sub.2HPO.sub.4 0.126 g/l, NaH.sub.2PO.sub.4
0.026 g/l). A sample of the alloy to be tested is stored in a
closed test container with a defined amount of test medium at
37.degree. C. At time intervals from between a few hours to several
months, adjusted to the degradation behavior to be expected,
samples are taken and examined in a known fashion for traces of
degradation. The artificial plasma according to EN ISO
10993-15:2000 corresponds to a blood-like medium, and thus provides
a chance to reproduceably imitate a physiological environment for
the purposes of the invention.
[0046] The term "degradation" presently refers to the reaction of a
metallic material with its environment, wherein a measurable change
of the material is caused, resulting, if the material is used in a
component, in an impaired function of the component. A degradation
system presently consists of the degrading metallic material as
well as a liquid degradation medium, which in its composition
imitates the conditions in a physiological environment or is in
itself a physiological medium, in particular blood. Factors
influencing degradation as far as the material is concerned are,
e.g., the composition and pre-treatment of the alloy, micro- and
submicroscopical inhomogeneities, fringe properties, temperature
and stress conditions, and in particular the composition of a
surface coating layer. As for the medium, the degradation process
is influenced by conductibility, temperature, temperature
gradients, acidity, volume-to-surface ratio, differences in
concentration, and flow rate.
[0047] DE 197 31 021 A1 discloses suitable biodegradable metallic
implant materials whose main component is an element from the group
of alkali metals, earth alkali metals, iron, zinc, and aluminum.
Alloys on the basis of magnesium, iron and zinc are described as
being particularly suitable. Secondary components of the alloys may
be manganese, cobalt, nickel, chromium, copper, cadmium, lead, tin,
thorium, zirconium, silver, gold, palladium, platinum, silicon,
calcium, lithium, aluminum, zinc, and iron. From DE 102 53 634 A1
it is further known to use a biodegradable magnesium alloy with a
content of magnesium >90%, yttrium 3.7-5.5%, rare earth metals
1.5-4.4%, and the rest <1%, which is particularly suited for the
production of an endoprosthesis, e.g. in the form of a
self-expanding or balloon-expandable stent.
[0048] It will be apparent to those skilled in the art that
numerous modifications and variations of the described examples and
embodiments are possible in light of the above teaching. The
disclosed examples and embodiments are presented for purposes of
illustration only. Therefore, it is the intent to cover all such
modifications and alternate embodiments as may come within the true
scope of this invention.
LIST OF REFERENCE NUMBERS
[0049] A axial direction [0050] U circumferential direction [0051]
2 meander-shaped strut [0052] 3, 3' meandering curves [0053] 4
axial connector [0054] 5, 5' zenith point [0055] 6, 6' inside
radius of the zenith point [0056] 7, 7' outside radius of the
zenith point [0057] 8 main stem of the axial connector 4 [0058] 10
at least double-arm structure [0059] 11, 11' arms of the at least
double-arm structure 10 [0060] 12, 12' arms of the at least
double-arm structure 10 in the case of three arms [0061] 13 arms of
the at least double-arm structure 10 in the case of five arms
[0062] 20 ladle-shaped aperture [0063] 21 chandelier-shaped
aperture
* * * * *