U.S. patent application number 13/088844 was filed with the patent office on 2011-11-10 for implant with antimicrobial coating.
This patent application is currently assigned to DERU GMBH. Invention is credited to Roger Thull, Ulrike Thull.
Application Number | 20110272276 13/088844 |
Document ID | / |
Family ID | 42557549 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110272276 |
Kind Code |
A1 |
Thull; Roger ; et
al. |
November 10, 2011 |
IMPLANT WITH ANTIMICROBIAL COATING
Abstract
In a coated implant that releases silver ions in the human body
and thereby has an antimicrobial effect, a first surface component
of the coating is formed by an anode material. A second surface
component of the coating is formed by a cathode material. The
cathode material is higher in the electrochemical voltage sequence
than the anode material. The cathode and the anode are connected
with one another in an electrically conducting manner. Together
with the body electrolyte in the vicinity of the implant the anode
and the cathode material form a plurality of local galvanic
elements.
Inventors: |
Thull; Roger; (Wurzburg,
DE) ; Thull; Ulrike; (Bassersdorf, CH) |
Assignee: |
DERU GMBH
Norderstedt
DE
|
Family ID: |
42557549 |
Appl. No.: |
13/088844 |
Filed: |
April 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61424270 |
Dec 17, 2010 |
|
|
|
Current U.S.
Class: |
204/242 |
Current CPC
Class: |
A61L 2300/404 20130101;
A61L 2300/104 20130101; A61L 27/54 20130101; A61L 31/16
20130101 |
Class at
Publication: |
204/242 |
International
Class: |
A61L 27/54 20060101
A61L027/54; A61K 9/00 20060101 A61K009/00; A61F 2/02 20060101
A61F002/02; C25B 9/06 20060101 C25B009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2010 |
EP |
10004140.9 |
Claims
1. An implant that releases silver ions in the human body and
provides an antimicrobial effect, comprising: an implant component
including a first coating portion forming an anode comprising
silver and a second coating portion forming a cathode, wherein the
first coating portion and the second coating portions are spatially
separated, wherein the cathode comprises a material having an
electrochemical voltage sequence higher than silver, and wherein
the cathode and the anode are coupled in an electrically conducting
manner.
2. The coated implant of claim 1, wherein the anode comprises pure
silver.
3. The coated implant of claim 1, wherein the anode comprises
silver having a purity level of 90%, 91%, 92%, 93%, 94%, 95%, 96%,
97%, 98%, 99%, 99.5%, or 99.9%.
3. The coated implant of claim 1, wherein a standard electrode
potential for release of silver ions of the anode is less than
about +0.8 V.
4. The coated implant of claim 1, wherein a standard electrode
potential of the cathode is greater than about +0.8 V.
5. The coated implant of claim 4, wherein the cathode material is
gold.
6. The coated implant of claim 1, wherein a standard electrode
potential of the cathode is greater than the standard electrode
potential of the anode by at least about 0.3 V, about 0.5 V, or
about 0.7 V.
7. The coated implant of claim 1, wherein the cathode material is
embedded in the anode in an island-shaped manner.
8. The coated implant of claim 1, wherein the first surface
component that is occupied by the anode occupies greater than about
50%, about 70%, or about 80% of the surface area of the
coating.
9. The coated implant of claim 1, wherein the first surface
component that is occupied by the anode occupies greater than about
50%, about 70%, or about 80% of the coating.
10. The coated implant of claim 1, wherein the anode and the
cathode abut against one another in flush manner.
11. The coated implant of claim 1, wherein the cathode protrudes
relative to the anode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of EP Application
No. 10004140.9 filed 19 Apr. 2010; and U.S. Provisional Application
Ser. No. 61/424,270 filed 17 Dec. 2010; which are incorporated
herein by reference in their entireties.
FIELD OF THE INVENTION
[0002] The invention relates to an implant with a coating that
releases silver ions in the human body and results in an
antimicrobial effect
BACKGROUND
[0003] When implants are inserted into the human body, there is a
risk of infections. Triggers for infections can be microorganisms
that are brought into the human body or that are located on the
surface of the implant. It is known that the risk of infections can
be diminished by providing the implant with a coating that releases
silver ions into their vicinity. The silver ions have a known
antimicrobial effect. In addition they have the advantage that--if
they do not encounter a microorganisms and act against it--they
combine with the chloride of the body electrolyte to AgCl and can
be excreted from the body in this form. In contrast to other
antimicrobially effective materials the silver ions do therefore
not accumulate in the body.
[0004] The known silver coatings release silver ions only to a
limited extent The released silver ions in addition move only
incidentally in the vicinity of the implant. There is therefore a
high probability that the silver ions combine in the body
electrolyte to form AgCl and thereby lose their antimicrobial
effectiveness before they encounter a microorganism.
SUMMARY
[0005] The present disclosure provides an implant whose coating
features an improved antimicrobial effectiveness. Advantageous
embodiments are described herein.
[0006] According to one embodiment a first surface component of the
coating is formed by a silver-containing anode material that is
provided for the release of silver ions. For a second surface
component a cathode material is provided. The cathode material is
higher in the electrochemical voltage sequence than the anode
material. The cathode material and the anode material are connected
with one another in an electrically conducting manner.
[0007] Initially a few terms are explained. The term implant
encompasses all types of objects that are inserted into the body.
These include, for example, endoprotheses for bones or joints, but
also implants that are inserted into other parts of body tissue,
such as, for example, stents in the heart circulatory system.
Encompassed also are implants that are only partially inserted into
the human body and protrude in part, such as tooth implants or
external fixators that represent an indirect osteosynthesis
external to the body that is partially stabilized with a tensioning
device.
[0008] The terms first surface component and second surface
component express that the cathode material in the coating is
spatially separated from the anode material. Not meant by this is a
coating in which several materials are evenly mixed with one
another. It is possible but not strictly required that the second
surface component is covered comprehensively with the cathode
material.
[0009] In the electrochemical voltage sequence the materials are
sorted according to their standard electrode potential. The higher
the position of a material in the electrochemical voltage sequence
the lower is its release pressure, meaning its tendency to release
ions into the water present in the vicinity. A metal that is
positioned higher in the electrochemical voltage sequence is
labeled as precious; a metal that is positioned lower in the
electrochemical voltage sequence, is labeled as base. For most
materials the position in the electrochemical voltage sequence is
known, the respective value can be obtained from the relevant
tables. If the position of a material in the electrochemical
voltage sequence is not known, it can be determined by means of
building a galvanic element with a known material and measuring the
generated potential difference. Based on the potential difference
the position in the voltage sequence can be determined. The terms
anode material and cathode material serve the purpose of
representing the relative position of the utilized materials
relative to one another in the electrochemical voltage sequence.
The cathode material and the anode material are electrically
conducting materials.
[0010] When the implant is inserted into the body, the anode
material and the cathode material of the coating form with the body
electrolyte in the vicinity of the implant a local galvanic
element. The tendency of the anode material to release silver ions
into the vicinity is thereby amplified. The electrons that remain
behind after the release of the silver ions in the anode material
can move into the cathode material because of the electric
connection. Because of the potential difference the silver ions are
attracted in the direction of the cathode material.
[0011] The effect of the coating according to the invention is
therefore doubled. First, the anode material has, because of the
local galvanic element an increased tendency to releast silver ions
into the surrounding body electrolyte. Compared with a coating that
consists only of the respective anode material, a larger number of
silver ions is therefore released, with the result that the
antimicrobial efficacy is increased. Furthermore the movement of
the released silver ions is no longer in any arbitrary direction,
but the silver ions are moved in the direction of the potential
difference between the two materials, meaning in the direction of
the cathode material. The probability is increased that the silver
ions will in fact become effective against the microorganisms that
are situated on the surface of the implant instead of combining in
the body electrolyte to AgCl and losing thereby the antimicrobial
efficacy. The effect of the coating according to the invention is
therefore concentrated on the surface of the implant. The coating
is particularly suited for fighting the dangerous biofilm that can
form on the surface of implants.
[0012] The coating can cover the entire surface of the implant.
This will be desirable in the context of many implants that are
entirely inserted into the body. In particular in the case of joint
prostheses it can also be provided that only one part of the
surface is coated. The coating can be deposited on the part of the
surface with which the prosthesis, in the implanted state, is in
contact with bodily tissue, while another part of the surface,
which for example is intended for the interaction with another
prosthesis components or, as in the case of the fixator, is located
external to the body, is free of the coating.
[0013] The anode material can be made of pure silver, or any
percentage thereof, including, for example, 90%, 91%, 92%, 93%,
94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9%. With a standard
electrode potential of about +0.8 V, silver is a relatively
precious metal that belongs in the upper range of the
electrochemical voltage sequence. A reference size for the voltage
specifications of the standard electrode potential is the normal
hydrogen electrode.
[0014] The cathode material that acts together with the pure silver
has to have a standard electrode potential of more than +0.8 V. If
the cathode material is a metal, it is therefore more precious than
silver. A cathode material suitable for the interaction with pure
silver is for example gold, which features a standard electrode
potential on the order of +1.5 V. Even if not pure silver but an
alloy of silver and another material is utilized as anode material,
the standard electrode potential of the cathode material should be
larger than about +0.8 V. Preferably the standard electrode
potential of the cathode material is greater by at least about 0.3
V, by at least about 0.5 V, or by at least about 0.7 V than the
standard electrode potential of the anode material.
[0015] The larger the difference between the standard electrode
potential of the anode material and the standard electrode
potential of the cathode material, the stronger the effect of the
local galvanic element. In an advantageous embodiment form a
silver-containing material is therefore utilized as the anode
material since its standard electrode potential is smaller than
+0.8 V. The anode material in that case comprises, in addition to
the silver components, other components that can be released from
the anode. The standard electrode potential indicated for the anode
material refers to the release pressure for silver ions. Preferably
a material is selected for the anode from which no other materials
besides the silver ions are released to the body electrolyte. If in
addition to the silver ions, other materials are released, the risk
exists that the additional materials could have undesirable effects
in the body. Therefore, for the anode as well as also for the
cathode a material should be chosen that is biocompatible.
[0016] The antimicrobial effect of the coating according to the
invention depends on the silver ions that are released from the
cathode material. As the number of released silver ions increases
the greater the surface component of the coating occupied by the
anode material. The surface component of the coating that is
occupied by the anode material is, therefore, preferably larger
than about 50%, larger than about 70%, or larger than about 80% of
the total surface area. Comparatively, the area component occupied
by the cathode material is of lesser importance. However, the area
component of the cathode material must not be too small if a good
efficacy of the galvanic elements is be achieved. Preferably the
portion of the surface of the coating occupied by the cathode
element is larger than about 0.1%, larger than about 1%, or larger
than about 5%.
[0017] It is desired that the silver ions, after they have exited
the anode material, will cover a certain distance before impinging
on the cathode material. During this movement the silver ions can
act in a antimicrobial manner. The surface components of the
coating occupied by the anode material and the cathode material
should for this reason be separated from one another in such a
manner that the silver ions do not necessarily impinge on the
cathode material immediately. The coating encompasses for this
reason a plurality of circular surface areas with a diameter
preferably of more than about 1 .mu.m, more than about 5 .mu.m,
more than about 15 .mu.m, or more than about 50 .mu.m that are
formed exclusively from anode material and are free of cathode
material. On the other hand, it is not advantageous for the
efficacy of the coating if the open path distance over which the
silver ions must travel is too long. The diameter of the circular
surface areas should for that reason be smaller than about 5 mmm,
preferably smaller than about 1 mm, or smaller than about 0.5 mm.
Preferably more than about 30%, or more than about 50% of the
surface of the coating is occupied by such surface components.
[0018] Silver ions exiting in the center of such an area have to
cover a certain distance before they impinge on cathode material.
While silver ions cover the distance they can act in an
antimicrobial manner. The open distance that the silver ions cover
can be dimensioned with the diameter of the bacteria in mind, which
is also in the pm range. One can assume that the silver ions move
along an arch-shaped path and that the largest distance to the
surface that the silver ions have along their path is of the same
order of magnitude as the distance that is covered parallel to the
surface. Therefore, if the covered open path distance corresponds
approximately to the diameter of the bacteria, it is accomplished
that the silver ions can act against bacteria that are located on
the surface during their entire path of travel.
[0019] The coating can be designed such that the cathode material
is embedded island-shaped in the anode material or is island-shaped
deposited on the anode material. The cathode material can itself be
deposited in the form of linked surface areas with a diameter of,
for example, a few pm. Another possibility is the possibility that
the cathode material is deposited on a second surface component in
the form of individual particles, without the anode material in
this area providing comprehensive coverage.
[0020] In many cases the surface of the implant is to be smooth.
This can be achieved if the anode material and the cathode material
are flush against one another. In an alternative embodiment the
cathode material can protrude relative to the anode material. The
silver ions then move a small distance to the surface of the
coating so that a good effect against microorganisms in the direct
vicinity of the coating is achieved. It is desirable to initially
deposit the anode material in an even coating thickness and to
subsequently deposit cathode material in selected areas on the
coating
[0021] The coating thickness of the anode materials can be between
about 100 nm and about 10,000 nm, preferably between about 200 nm
and about 400 nm. This range is particularly valid when the anode
material is pure silver. The coating thickness of the cathode
material that is deposited on the anode materials can likewise be
between about 100 nm and about 10,000 nm, preferably between about
200 nm and about 400 nm.
[0022] It is also possible to initially deposit a coating of the
cathode material comprehensively. On the cathode material a coating
of anode material can be placed that features openings so that the
cathode material is accessible through the anode material from the
outside. If the anode material is deposited with a plasma coating
method, then the openings can be generated due to the fact that
during the deposition of the coating larger fragments with a
diameter of, for example, 20 .mu.m are aimed at the surface that
knock out a piece from the coating that is forming, see WO
2009/036846. With this approach the thickness of the coatings is
preferably between about 100 nm and about 10,000 nm, or preferably
between about 200 nm and about 400 nm.
[0023] One embodiment provides an implant that releases silver ions
in the human body and provides an antimicrobial effect, comprising
an implant component including a first coating portion forming an
anode comprising silver and a second coating portion forming a
cathode, wherein the cathode comprises a material having an
electrochemical voltage sequence higher than silver, and wherein
the cathode and the anode are coupled in an electrically conducting
manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The invention is described by example in what follows in
reference to the enclosed drawings using the advantageous
embodiment forms. The drawings show:
[0025] FIG. 1 shows a first embodiment of an implant;
[0026] FIG. 2 shows a component of the implant from FIG. 1;
[0027] FIG. 3 shows a second embodiment of an implant;
[0028] FIG. 4 shows a section from the body of an implant with
coating;
[0029] FIG. 5 shows the coating from FIG. 4 in a plan view;
[0030] FIG. 6 shows the view from FIG. 4 in the case of a different
embodiment;
[0031] FIG. 7 shows the view from FIG. 5 in the case of the
embodiment according to FIG. 6;
[0032] FIG. 8 shows the view from FIG. 4 in the case of a further
embodiment; and
[0033] FIG. 9 shows the view from FIG. 5 in the case of a further
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0034] An implant shown in FIG. 1 is intended to replace a part of
the human skeleton that extends from the hip to below the knee. A
sphere-shaped joint head 10 forms a joint surface that is designed
to interact with an acetabulum. The joint head 10 is connected with
a head piece 11 of the implant by means of a screw connection. The
part of the implant that is replacing the center shaft of the femur
encompasses three implant components 12, 13, 14. The implant
components 12, 13, 14 are also connected among each other and with
the head piece 11 by means of screw connections. A knee piece 15
forms an articulated connection with the shaft 16 that is intended
to connect the implant with the tibia. The implant components 12,
13, 14 are available in different lengths so that the implant can
be adapted to femurs of different length.
[0035] FIG. 2 presents an implant component 17 that corresponds to
the implant components 12, 13, 14 in an enlarged representation.
The implant component 17 encompasses a threaded bolt 18 as well as
a threaded bore 19 that is indicated in dashed lines. By means of
the threaded bolt 18 and the threaded bore 19 the implant component
17 can be connected at its two ends with other implant
components.
[0036] The threaded bolt 18, the threaded bore 19 as well as the
adjacent front faces 20 and 21, therefore, do not abut, in the
implanted state of the implant component 17, against the bodily
tissue of the patient, but instead abut against other implant
components. The surface area 22 of the implant component 17, on the
other hand, is designed for the purpose of being in contact with
human tissue in the implanted state. The surface area 22 is
provided with an antimicrobial coating 23 that is indicated by
means of speckles. The remaining surface of the implant component
is free of the coating 23.
[0037] The coating 23 is represented in FIGS. 4 and 5 in an
enlarged manner. The coating 23 comprises, to a large part, pure
silver that coats the surface area comprehensively. Gold in the
form of several rectangular islands of cathode material 26 is
introduced into the silver coating, as FIG. 5 illustrates. The gold
material is embedded in the silver coating so that the two
materials abut against each other in a flush manner and a smooth
surface is obtained. A smooth surface is desired to minimize
irritation of the surrounding bodily tissue as a result of
friction. The coating 23 includes a first surface component 28 that
is formed by means of the silver material and a second surface
component 29 that is formed by means of the gold material. The
surface component 28 that is formed by the silver material occupies
more than 80% of the surface area formed by the coating 23. Between
the islands there remain, as indicated in FIG. 5 in a dashed line,
circular surface areas 27 in which the entire surface area formed
by the coating 23 comprises silver material and is not interrupted
by gold material. The surface area 27 features a diameter of more
than 0.1 mm.
[0038] The silver and the gold are connected with one another in
the coating in an electrically conducting manner. Silver is a less
precious metal than gold and is situated lower in the
electrochemical voltage sequence than gold. In the sense of the
function of the coating according to the invention silver is
therefore an anode material 25 and gold is the cathode material
26.
[0039] After the implantation, the coating 23 is surrounded with
body electrolyte. The silver material has a tendency to release
positively charged silver ions into the body electrolyte. This
tendency is referred to as release pressure. When silver ions are
released out of the coating, excess electrons remain behind in the
coating and an excess of negatively charged carriers forms in the
coating. Since the silver material and the gold material are
connected with one another in an electrically conducting manner,
the excess electrons can move freely in the direction of the gold
material. The gold material is likewise subject to a certain
release pressure to release ions into the body electrolyte. Since
gold is a more precious metal than silver and is situated higher in
the electrochemical voltage sequence, the release pressure is lower
than the release pressure of the silver. The silver ions that are
released in larger concentration move toward the gold material. By
these means the body electrolyte forms, together with the silver as
anode material 25 and with the gold as cathode material 26, local
galvanic elements. The silver ions emerge from the anode material
25 and move, parallel to the coating 23, in the direction of the
cathode material 26. On this path the silver ions can develop an
antimicrobial effect relative to microorganisms that are situated
on the surface of the coating 23.
[0040] The tooth implant that is shown in FIG. 3 is an alternative
embodiment. An implant body 30 is screwed into the jaw bone 31 with
its lower end. The upper end of the implant body 30 protrudes from
the jaw bone 31 and the gum 32 that surrounds the jaw bone 31 in an
upward direction. An abutment post 34 that is covered with an
artificial tooth crown 33 is screwed into the open end of the
implant body 30. The tooth implant replaces a natural tooth by
these means. The implant body 30 in turn is provided with a coating
23 that is indicated by means of speckles.
[0041] The coating 23 is represented in FIGS. 6 and 7 in an
enlarged manner. On the surface of the implant 30 initially a
silver coating is deposited that features an even thickness of
about 400 nm. On the surface of the silver coating gold material is
deposited in a grid-shaped disposition with a coating thickness of
likewise about 400 nm. The areas that are enclosed in the grid, in
which the surface of the coating 23 is formed by the silver
material, form in their entirety the first surface component 28 of
the coating 23. The grid-shaped disposition of the gold material
forms the second surface component 29 of the coating. The
grid-shape of the gold material is dimensioned in such a manner
that circular surface areas 27 with a diameter of more than 50 pm
remain free of the gold material.
[0042] In the case of the coating shown in FIG. 8 the implant
component 17 is initially covered comprehensively with a coating of
gold as a cathode material 26. A silver coating deposited there
upon as anode material 25 features a plurality of interruptions.
The interruptions form in their sum a second surface component 29
in which the anode material 25 is accessible from the outside
through the cathode material 26.
[0043] In the embodiment shown in FIG. 9 the anode material 26 is
deposited on the second surface component 29 not in a comprehensive
manner but as a plurality of individual particles. This does not
change anything in the effectiveness according to the invention of
the coating.
[0044] As explained above, the silver is an anode material 25 for
the purposes of the invention and the gold is a cathode material
26. Together with the body electrolyte in the vicinity of the
implant body 30 the coating 23 forms a plurality of local galvanic
elements. Since the gold as cathode material 26 protrudes relative
to the anode material 25, the silver ions can move at a small
distance to the silver coating also in the direction of the cathode
material 26.
[0045] In the case of the tooth implant the antimicrobial coating
23 has the particular function to act against microorganisms at the
transition between the implant body 30 and the gum 32 or the jaw
bone 31. In the vicinity of the mouth it is generally known that
there is a plurality of microorganisms and the risk of an infection
in the surroundings of the implant body 30 is high. If by means of
the antimicrobial coating 23 the intrusion of microorganisms
between the implant body 30 and the gum 32 can be eliminated,
unpleasant infections for the patient can be prevented.
* * * * *