U.S. patent application number 17/678743 was filed with the patent office on 2022-06-09 for method for producing biocorrodible magnesium alloy implant.
The applicant listed for this patent is BIOTRONIK AG. Invention is credited to Bodo Gerold, Hermann Kalb, Alexander Rzany.
Application Number | 20220175513 17/678743 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-09 |
United States Patent
Application |
20220175513 |
Kind Code |
A1 |
Kalb; Hermann ; et
al. |
June 9, 2022 |
METHOD FOR PRODUCING BIOCORRODIBLE MAGNESIUM ALLOY IMPLANT
Abstract
A method forms an implant with a base body made of a
biocorrodible magnesium alloy. The methods make magnesium alloy
that contains a plurality of statistically distributed particles,
with one or more of the elements Y, Zr, Mn, Sc, Fe, Ni, Co, W, Pt
and noble earths with the atomic numbers 57 to 71, or the particles
comprise alloys or compounds containing one or more of the elements
mentioned. The mean distance of the particles from each other is
smaller than the hundredfold mean particle diameter.
Inventors: |
Kalb; Hermann; (Schnaittach,
DE) ; Rzany; Alexander; (Nuernberg, DE) ;
Gerold; Bodo; (Karlstadt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BIOTRONIK AG |
Buelach |
|
CH |
|
|
Appl. No.: |
17/678743 |
Filed: |
February 23, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16038446 |
Jul 18, 2018 |
11284988 |
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17678743 |
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13977323 |
Jun 28, 2013 |
10052188 |
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PCT/EP2012/051669 |
Feb 1, 2012 |
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16038446 |
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61446051 |
Feb 24, 2011 |
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International
Class: |
A61F 2/06 20060101
A61F002/06; A61L 27/04 20060101 A61L027/04; A61L 27/30 20060101
A61L027/30; A61L 27/58 20060101 A61L027/58; A61L 31/02 20060101
A61L031/02; A61L 31/08 20060101 A61L031/08; A61L 31/14 20060101
A61L031/14 |
Claims
1. A method for producing an implant having a base body comprising
a biocorrodible magnesium alloy, wherein the method comprises the
following steps: (i) providing a blank made of the biocorrodible
magnesium alloy; (ii) applying particles having the above-mentioned
composition to the blank, the particles comprising one or more of
the elements Y, Zr, Mn, Sc, Fe, Ni, Co, W, Pt, and noble earths
with the atomic numbers from 57 to 71, or alloys, or compounds
containing one or more of these elements; and (iii) melting the
magnesium alloy in the near-surface region of the blank to result
in the magnesium alloy containing a plurality of statistically
distributed particles, wherein the mean distance of the particles
from each other is smaller than the hundredfold mean particle
diameter, and the particles are incorporated into a surface or into
a near-surface region of the base body.
2. A method according to claim 1, wherein the particles consist of
one or more of the elements Y, Zr, Mn, Sc, Fe, Ni, Co, W, Pt, and
noble earths with the numbers 57 to 71, or alloys, or compounds
consisting one or more of these elements.
3. A method according to claim 1, wherein the step of applying the
particles comprises applying an adhesion enhancing polymer to a
surface of the bland, applying the particles in powder form to the
surface, and shaking the surface to achieve a homogenous
distribution of the particles.
4. A method according to claim 1, and further including the step of
providing the particles in a quantity to result in the number of
the particles in the volume of the base body to range between
1.times.10.sup.3 and 1.times.10.sup.9 per mm.sup.3, and wherein the
particles have a mean diameter of 1 nm to 10 .mu.m.
5. A method according to claim 1, and further comprising the step
of providing the particles in a quantity and are distributed to
result in a mean distance between the particles being between 200
nm and 100 .mu.m.
Description
CROSS REFERENCE
[0001] The present application claims priority from and is a 35
U.S.C. .sctn..sctn. 120 and 121 divisional of U.S. application Ser.
No. 16/038,446, which was filed on Jul. 18, 2018, which application
was a divisional of U.S. application Ser. No. 13/977,323, now U.S.
Pat. No. 10,052,188, which application was a 35 U.S.C. .sctn. 371
National Stage application which claims priority to International
Application No. PCT/EP2012/051669 filed on Feb. 1, 2012, which
application claims priority to U.S. provisional patent application
Ser. No. 61/446,051 filed on Feb. 24, 2011 under 35 U.S.C. .sctn.
119(e); all of which applications are incorporated herein by
reference.
TECHNICAL FIELD
[0002] One aspect of the invention relates to an implant comprising
a base body made of a biocorrodible magnesium alloy.
BACKGROUND
[0003] Implants are being employed in a wide variety of forms in
modern medical technology. They are used, for example, to support
vessels, hollow organs and vein systems (endovascular implants,
such as stents), for fastening and the temporary fixation of tissue
implants and tissue transplantations, but also for orthopedic
purposes, such as nails, plates or screws. A particularly
frequently used form of an implant is the stent. Implant materials
comprise polymers, metallic materials, and ceramic materials (as
coatings, for example). Biocompatible metals and metal alloys for
permanent implants comprise, for example, stainless steels (such as
316L), cobalt-based alloys (such as CoCrMo cast alloys, CoCrMo
forge alloys, CoCrWNi forge alloys and CoCrNiMo forge alloys),
technical pure titanium and titanium alloys (such as cp titanium,
TiAl6V4 or TiAl6Nb7) and gold alloys. In the field of biocorrodible
stents, the use of magnesium or technical pure iron as well as
biocorrodible base alloys of the elements magnesium, iron, zinc,
molybdenum, and tungsten are proposed. Aspects of the present
invention relate to biocorrodible magnesium base alloys.
[0004] The implantation of stents has become established as one of
the most effective therapeutic measures for the treatment of
vascular diseases. Stents have the purpose of performing a
stabilizing function in hollow organs of a patient. For this
purpose, stents featuring conventional designs have a filigree
supporting structure comprising metal braces, which is initially
present in compressed form for introduction into the body and is
expanded at the site of the application. One of the main
application areas of such stents is to permanently or temporarily
dilate and hold open vascular constrictions, particularly
constrictions (stenoses) of the coronary blood vessels. In
addition, aneurysm stents are also known, which are used primarily
to seal the aneurysm. The support function is additionally
provided.
[0005] Stents comprise a peripheral wall with sufficient
load-bearing capacity to hold the constricted vessel open to the
desired extent and a tubular base body through which the blood
continues to flow without impairment. The peripheral wall is
generally formed by a lattice-like supporting structure, which
allows the stent to be introduced in a compressed state, in which
it has a small outside diameter, all the way to the stenosis of the
particular vessel to be treated and to be expanded there, for
example by way of a balloon catheter, so that the vessel has the
desired, enlarged inside diameter. As an alternative, shape memory
materials such as nitinol have the ability to self-expand when a
restoring force is eliminated that keeps the implant at a small
diameter. The restoring force is generally applied to the material
by a protective tube.
[0006] The implant, notably the stent, has a base body made of an
implant material. An implant material is a non-living material,
which is used for applications in medicine and interacts with
biological systems. A basic prerequisite for the use of a material
as implant material, which is in contact with the body environment
when used as intended, is the body friendliness thereof
(biocompatibility). Biocompatibility shall be understood as the
ability of a material to evoke an appropriate tissue response in a
specific application. This includes an adaptation of the chemical,
physical, biological, and morphological surface properties of an
implant to the recipient's tissue with the aim of a clinically
desired interaction. The biocompatibility of the implant material
is also dependent on the temporal course of the response of the
biosystem in which it is implanted. For example, irritations and
inflammations occur in a relatively short time, which can lead to
tissue changes. Depending on the properties of the implant
material, biological systems thus react in different ways.
According to the response of the biosystem, the implant materials
can be divided into bioactive, bioinert and degradable or
resorbable materials.
[0007] Implant materials comprise polymers, metallic materials, and
ceramic materials (as coatings, for example). Biocompatible metals
and metal alloys for permanent implants comprise, for example,
stainless steels (such as 316L), cobalt-based alloys (such as
CoCrMo cast alloys, CoCrMo forge alloys, CoCrWNi forge alloys and
CoCrNiMo forge alloys), technical pure titanium and titanium alloys
(such as cp titanium, TiAl6V4 or TiAl6Nb7) and gold alloys. In the
field of biocorrodible stents, the use of magnesium or technical
pure iron as well as biocorrodible base alloys of the elements
magnesium, iron, zinc, molybdenum, and tungsten are proposed.
Aspects of the present invention relate to biocorrodible magnesium
base alloys.
[0008] The use of biocorrodible magnesium alloys for temporary
implants having filigree structures is made difficult in particular
in that the degradation of the implant progresses very quickly in
vivo. So as to reduce the corrosion rate, this being the
degradation speed, different approaches are being discussed. For
one, it is attempted to slow the degradation on the part of the
implant material by developing appropriate alloys. In addition,
coatings are to bring about a temporary inhibition of the
degradation. While the existing approaches are promising, none of
them has so far been implemented in a commercially available
product. Regardless of the efforts made so far, there is rather a
continuing need for solutions that make it possible to at least
temporarily reduce the in vivo corrosion of magnesium alloys.
SUMMARY
[0009] One or more of the disadvantages of the prior art mentioned
above are solved, or at least mitigated, by the implant according
to the invention. One embodiment of the implant according to the
invention comprises a base body made of a biocorrodible magnesium
alloy. The magnesium alloy contains a plurality of statistically
distributed particles, comprising one or more of the elements Y,
Zr, Mn, Sc, Fe, Ni, Co, W, Pt and noble earths with the atomic
numbers 57 to 71, or alloys, or compounds containing one or more of
these elements. The mean distance of the particles from each other
is smaller than the hundredfold mean particle diameter. Put another
way, the statistical mean distance between the particles is less
than 100.times.(average particle diameter). In some embodiments,
the statistical mean distance between particles is less than
50.times.(average particle diameter).
[0010] A method for producing an implant having a base body of a
biocorrodible magnesium alloy includes providing a blank made of
the biocorrodible magnesium alloy. A non-aqueous suspension of
particles to is applied to the blank. The particles include one or
more of the elements Y, Zr, Mn, Sc, Fe, Ni, Co, W, Pt, and noble
earths with the atomic numbers from 57 to 71, or alloys, or
compounds containing one or more of these elements. The particles
are rolled into the surface or into the near-surface region of the
blank to thereby result in the magnesium alloy containing a
plurality of statistically distributed particles, wherein the mean
distance of the particles from each other is smaller than the
hundredfold mean particle diameter, and the particles are
incorporated into a surface or into a near-surface region of the
base body.
[0011] A method for producing an implant having a base body of a
biocorrodible magnesium alloy, includes providing a blank made of
the biocorrodible magnesium alloy. Particles are applied to the
blank. The particles include one or more of the elements Y, Zr, Mn,
Sc, Fe, Ni, Co, W, Pt, and noble earths with the atomic numbers
from 57 to 71, or alloys, or compounds containing one or more of
these elements. The magnesium alloy is melted in the near-surface
region of the blank to result in the magnesium alloy containing a
plurality of statistically distributed particles, wherein the mean
distance of the particles from each other is smaller than the
hundredfold mean particle diameter, and the particles are
incorporated into a surface or into a near-surface region of the
base body.
[0012] In the development of magnesium materials so far, the
corrosion resistance has always been improved by increasing the
purity of the magnesium material. Iron, nickel, chromium, and
cobalt are considered to be critical elements in this context.
Particles comprising intermetallic compounds, particles of a
different chemical nature (oxides, hydrides) or segregations
(Al12Mg17) in magnesium materials result in microgalvanic corrosion
due to the different electrochemical potential. This results in
local corrosive processes, which massively accelerate the corrosion
rate of the material. For this reason, previously attempts have
been made to minimize the concentration of the particles to the
extent possible.
[0013] The solution according to the invention, however, exploits
the surprising discovery that an effective solution can be achieved
by taking exactly the opposite approach of the prior art. In
magnesium materials, in general, the corrosion that is observed
attacks the material locally very inhomogeneously. In the process,
it has been discovered that cathodic processes occur, which are
accompanied by the release of hydroxide ions and the development of
hydrogen, more specifically at defined centers, namely the
above-mentioned particles. The anodic dissolution process of the
magnesium material takes place in the surroundings of the cathodic
center. The process can be divided into the following partial
reactions:
Anodic: Mg->Mg.sup.2++2e.sup.-
Cathodic: 2H.sub.2O+2e.sup.-->2 OH.sup.-+H.sub.2
[0014] It has been discovered that the anodic process is highly
dependent on the pH value. For example, the Mg corrosion is
massively accelerated at pH<5, while it is massively decelerated
at pH>10 and basically completely disrupted. Given this
behavior, the release of hydroxide ions on the cathodic center
leads to the protection of the direct surroundings.
[0015] The invention is based on the discovery that the corrosion
of implants made of biocorrodible magnesium alloys can be delayed
by adding a plurality of homogenously distributed particles to the
material volume, a near-surface region, or the surface. It has been
discovered that the particles act as cathodic centers within the
above-mentioned meaning, which is to say, the hydrogen overvoltage
is sufficiently low and the reaction can take place at a high rate.
The particles comprise one or more of the elements Y, Zr, Mn, Sc,
Fe, Ni, Co, W, Pt and nobles earths with the atomic numbers 57 to
71, or alloys, or compounds containing one or more of these
elements. In the present invention, the term `alloy` shall cover
metallic compositions of the elements, and also compositions in
which covalent bonds exist between the elements. The alloys
preferably contain magnesium. Compounds comprise in particular
hydrides and carbides of the above-mentioned elements.
[0016] Preferably, the particles consist of one or more of the
elements Y, Zr, Mn, Sc, Fe, Ni, Co, W, Pt and nobles earths with
the atomic numbers 57 to 71, or alloys, or compounds consisting of
one or more of these elements.
DETAILED DESCRIPTION
[0017] With the above summary now presented, detailed description
of invention embodiments can now be presented. It will be
appreciated that the present invention may be embodied in an
implant or in a method for making an implant. Accordingly, it will
further be appreciated that when describing an implant embodiment,
description of a method for making that implant may also be made,
and vice versa. Before discussing particular embodiments, some
general definitions are offered for clarity.
[0018] Biocorrodible as defined by the invention denotes alloys in
the physiological environment of which degradation or remodeling
takes place, so that the part of the implant made of the material
is no longer present in its entirety, or at least
predominantly.
[0019] A magnesium alloy in the present case shall be understood as
a metal structure, the main constituent of which is magnesium. The
main constituent is the alloying constituent having the highest
weight proportion in the alloy. The proportion of the main
constituent is preferably more than 50% by weight, particularly
more than 70% by weight. The alloy is to be selected in the
composition thereof such that it is biocorrodible. A possible test
medium for testing the corrosion behavior of a potential alloy is
synthetic plasma, as that which is required according to EN ISO
10993-15:2000 for biocorrosion analyses (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).
For this purpose, a sample of the alloy to be analyzed is stored in
a closed sample container with a defined quantity of the test
medium at 37.degree. C. and pH 7.38. The samples are removed at
intervals--which are adapted to the anticipated corrosion
behavior--ranging from a few hours to several months and analyzed
for traces of corrosion in the known manner. The synthetic plasma
according to EN ISO 10993-15:2000 corresponds to a blood-like
medium and thus is a possible medium to reproducibly simulate a
physiological environment as defined by the invention.
[0020] The term corrosion refers in the present example to the
reaction of a metallic material with the environment thereof,
wherein a measurable change of the material is caused, which--when
using the material in a component--results in an impairment of the
function of the component. The corrosion process can be quantified
by the provision of a corrosion rate. Swift degradation is
associated with a high corrosion rate, and vice versa. Relative to
the degradation of the entire base body, an implant that is
modified as defined by the invention will result in a decrease of
the corrosion rate as compared to the same implant if not modified
by the invention.
[0021] The particles preferably have a mean diameter of 1 nanometer
to 10 micrometers, particularly preferred 500 nanometers to 3
micrometers, and more particularly 1 to 2 micrometers. Other
diameters may also prove useful, including those smaller than 1
nanometer and those larger than 10 micrometers.
[0022] In the surroundings of the cathodic center, protected
regions develop as a result of the release of hydroxide ions. The
majority of the protected region around an individual cathodic
center depends on the size and composition of the particles and the
surrounding matrix of the magnesium material. The size of the
protected area per particle should be at least 1 square micrometer,
preferably up to 100 square micrometers, with up to 10000 square
micrometers being particularly preferred.
[0023] Within the material, the area of the protected regions has a
size distribution that is determined by the distribution of the
particles. The protective effect on the total surface of the
magnesium material is dependent on the number and size distribution
of the protected regions. The number of particles on the surface of
the base body is preferably 1.times.10.sup.2 to 1.times.10.sup.6
particles per mm.sup.2, or the number of particles in the volume of
the base body is 1.times.10.sup.3 to 1.times.10.sup.9 particles per
mm.sup.3. A ratio of the mean particle diameter to the mean
distance of the particles from each other preferably ranges between
1:2 and 1:100, and more particularly between 1:2 and 1:10. Other
ratios may be employed.
[0024] The corrosion rate is quantitatively influenced by the
cathodic centers as follows: [0025] a) The protected total area
A_protect is obtained by assuming non-overlapping protected regions
from the sum over the distribution of the areas A_cathodic_center
protected by the individual cathodic centers:
[0025] A protect = i = 1 .times. .times. .times. .times. N .times.
A cathodic .times. .times. center ##EQU00001## [0026] where N is
the number of particles. [0027] b) The corrosion rate R_corr is
directly proportional to the corrosion of the accessible sample
area A_corr, wherein A_total denotes the total area of the
material:
[0027] R corr .varies. A corr .varies. A total - A protect .varies.
A total .function. ( 1 - A protect A total ) ##EQU00002##
[0028] As a result, assuming the same abrasion depth, the corrosion
rate decreases as the percentage of area of the protected region
decreases. The percentages of area mentioned can be determined
experimentally.
[0029] A particularly high protective effect is achieved precisely
when a sufficiently large number of cathodic centers is uniformly
distributed in the material, and the overlap between the protected
regions is as small as possible. This requires determining an
optimal balance between too many and too few particles. It has been
discovered that the optimal mean distance d mean between cathodic
centers without overlap can be estimated from a statistical
analysis of the distribution:
d m .times. e .times. a .times. n = 2 A p .times. r .times. o
.times. t .times. e .times. c .times. t N .pi. ##EQU00003##
[0030] The protective effect can be increased both by a large
number of small protected regions and by a small number of large
protected regions. In many embodiments, the mean distance between
the particles preferably ranges between 200 nm and 100 .mu.m. The
mean distance in some embodiments is in particular smaller than 20
.mu.m.
[0031] The protected area per cathodic center is dependent on the
chemical nature of the cathodic center and the material matrix.
[0032] The claimed modification of the material can be applied not
only to the entire material volume, but optionally can also be
limited to the surface or the near-surface region of an implant. In
this way, it is possible to deliberately introduce cathodic centers
into the surface of a workpiece by means of rolling. Those
knowledgeable in the art understand the meaning of rolling, and the
general process this refers to. A detailed discussion of rolling is
not necessary for this reason and will be avoided for the
additional sake of brevity. In general, rolling is a process in
which heated metal stock is shaped as desired by passing between
two opposing wheels that "roll" the stock into a piece of a desired
thickness. Hot rolling generally refers to rolling performed at
temperatures above the metal's recrystalization temperature, and
cold rolling to rolling performed at temperatures below the
recrystalization temperature. It has been discovered that rolling
within the scope of the invention as described above creates an
initial corrosion barrier, and the degradation rate increases over
time. The particles are preferably incorporated in the surface or
the near-surface region of the base body. A relatively low
corrosion rate then occurs at the beginning of the onsetting
corrosive processes, said rate increasing over the course of time.
This behavior is referred to as temporarily reducing the corrosion
rate. In the case of coronary stents, the mechanical integrity of
the structure should be maintained for a period of three to six
months after implantation.
[0033] Implants as defined by the invention are devices introduced
into the body by a surgical procedure and comprise fastening
elements for bones, such as screws, plates or nails, surgical
suture material, intestinal clamps, vessel clips, prostheses in the
area of hard and soft tissues, and anchoring elements for
electrodes, particularly for pacemakers or defibrillators. The
implant is made entirely or partially of the biocorrodible
material. If only a part of the implant is made of the
biocorrodible material, this part is to be modified accordingly.
The implant is preferably a stent.
[0034] A further concept of the invention is to provide two methods
for producing an implant comprising a main body made of a
biocorrodible magnesium alloy, wherein the magnesium alloy contains
a plurality of statistically distributed particles having the
above-mentioned composition, and the mean distance of the particles
from each other is smaller than the hundredfold mean particle
diameter, and the particles are incorporated in the surface or in a
near-surface region of the base body.
[0035] According to a first embodiment, a method of the invention
comprises the following steps: [0036] (i) providing a blank made of
the biocorrodible magnesium alloy; [0037] (ii) applying a
non-aqueous suspension of particles having the above-mentioned
composition to the blank; and [0038] (iii) rolling the particles
into the surface or into the near-surface region of the blank.
[0039] Accordingly, an oily suspension containing the particles to
incorporated is applied to the blank, from which the base body is
to be shaped, and incorporated by rolling. This suspension can be
used as a lubricant both during cold rolling and during hot
rolling. By optimizing the volume flow of the suspension,
temperature, contact pressure and speed, the incorporation of the
particles in the surface of the rolled magnesium material can be
optimized. The variant is suited in particular for magnesium alloys
based on WE43.
[0040] According to a second embodiment, a method comprises the
following steps: [0041] (i) providing a blank made of the
biocorrodible magnesium alloy; [0042] (ii) applying particles
having the above-mentioned composition to the blank; and [0043]
(iii) melting the magnesium alloy onto the near-surface region of
the blank.
[0044] According to this variant, the particles to be incorporated
are applied directly onto the blank, which later forms the base
body. After that, the magnesium alloy is locally melted on the
surface, for example by laser treatment. After cooling, the
particles are then embedded in the near-surface region of the
blank.
[0045] According to the two methods for producing an implant, the
particles preferably consist of preferably, the particles consist
of one or more of the elements Y, Zr, Mn, Sc, Fe, Ni, Co, W, Pt and
nobles earths with the atomic numbers 57 to 71, or alloys, or
compounds consisting of one or more of these elements.
[0046] The invention will be explained in more detail hereinafter
based on some example embodiments.
Embodiment 1
[0047] An iron particle-containing (chemicals for the production
are available from Sigma-Aldrich, particle diameter smaller than
100 nm) suspension is applied, for example by spraying or
immersion, onto a plate-shaped blank made of the magnesium alloy
AZ31 so as to generate a film having a statistically homogeneous
distribution of iron particles. The carrier fluid for the
suspension may be selected form any of a number of suitable
alternatives.
[0048] This suspension can be used as a lubricant both during cold
rolling and during hot rolling. The particles are incorporated in
the surface of the blank by the rolling process. The particles not
only increase the corrosion protection, but also the wear
resistance by increasing the hardness. The blank is subsequently
processed into the base body of the implant.
Embodiment 2
[0049] Tungsten particles (available from Sigma-Aldrich; particle
diameter approximately 150 nm, other useful diameters ranges
including, for example, 100 nm-200 nm) are applied in the form of a
powder onto a plate-shaped blank made of the magnesium alloy AZ31
and homogeneously distributed by shaking. When using complicated
three-dimensional structures, it is also advantageous to use an
adhesion-promoting polymer to coat the surface before the laser
alloying process. Many suitable polymers will be apparent to those
knowledgeable in the art. By varying the polymer to tungsten
particle ratio, it is possible to directly adjust the mean distance
between tungsten particles.
[0050] The tungsten particles are incorporated into the magnesium
alloy by laser alloying. To this end, the workpiece is locally
melted using a high-performance laser diode under argon inert gas.
The laser output is between 1.2 and 1.6 kW, and the feed rate of
the laser is 0.5 to 1.0 m/min. The use of the argon prevents an
oxidation of the magnesium material and of the tungsten during
processing.
[0051] Using the laser alloying technology, it is possible in
particular to locally protect a workpiece made of a magnesium
alloy. In connection with stents, for example, sequential fragment
of the implant can be achieved by locally influencing the
degradation rate, for example by providing the surfaces of the
segment rings of a stent structure, but not the longitudinal
connecting struts of the segment rings, with cathodic centers
according to the invention, whereby the struts degrade more quickly
than the segment rings. Because the connecting struts dissolve more
quickly, high longitudinal flexibility is achieved quickly, wherein
the load-bearing capacity of the segment rings is still
maintained.
[0052] The particles provide not only corrosion protection, but
also increase the wear resistance against abrasion by increasing
the hardness. In addition, by suitably selecting the particles and
the composition thereof, polymeric substances can be effectively
bonded to the surface. These polymeric substances can have a
corrosion-inhibiting effect on the one hand, and on the other hand,
they may contain one or more pharmacological active ingredients, or
exhibit a pharmacological effect themselves.
[0053] The additional coating with a polymer can be technically
implemented, for example, as follows. PLLA L214S (Boehringer
Ingelheim) is dissolved in a concentration of 1.6% (w/v) in
chloroform and rapamycin is added as the active substance. The
active ingredient content preferably ranges between 15% and 20%, in
relation to the solid matter content. The implant made of the
modified magnesium alloy is immersed for 1 second into the solution
using an underwater robot, pulled out, and air containing nitrogen
is blown on so as to evaporate the solvent. This process is
repeated until a sufficient layer thickness of approximately 5
.mu.m has been reached.
[0054] The embodiments also apply analogously to other
biocorrodible magnesium alloys and particle compositions.
[0055] 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. Other alternate embodiments may include some or
all of the features disclosed herein. Therefore, it is the intent
to cover all such modifications and alternate embodiments as may
come within the true scope of this invention.
* * * * *