Coating processes – Medical or dental purpose product; parts; subcombinations;... – Implantable permanent prosthesis
Reexamination Certificate
2001-03-12
2003-04-15
Beck, Shrive P. (Department: 1762)
Coating processes
Medical or dental purpose product; parts; subcombinations;...
Implantable permanent prosthesis
C427S002240, C427S002280, C427S240000, C427S241000, C427S242000, C427S248100, C427S250000, C427S252000, C427S255120, C427S255290, C427S255500, C427S457000, C427S472000, C427S295000
Reexamination Certificate
active
06548104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention relates to a method and apparatus for coating prosthetic components to achieve a uniform shiny smooth coating that will exhibit exceptional wear when placed in articular or sliding bearing engagement with another prosthetic component.
2. Description of the Related Art
Orthopedic prosthetic joints are used to replace at least portions of a diseased or damaged natural joint between at least two bones of a patient. A total joint replacement typically involves accessing the diseased or damaged joint and resecting opposed ends of the bone that form the joint. Metallic components then are affixed to the resected ends of the bones.
Metal on metal sliding or articular contact is known to produce molecular or chemical reactions that generate wear debris and degrade the performance of the prosthetic joint. As a result, the typical prior art prosthetic joint is designed to have metallic components of the prior art prosthetic joint articulate or slide against a non-metallic component. For example, plastic bearings may be incorporated into a joint for sliding and/or articular bearing engagement with the metallic components of the joint. The plastic bearing should be hard, wear resistant and chemically inert in the presence of the biological fluids. Many prior art prosthetic joints employ bearings made of an ultra high molecular weight polyethylene (UHMWPe). The UHMWPe bearing will not cause the chemical reactions that occur when metallic components slide against one another. However, UHMWPe bearings can wear if the metallic part that slides against the bearing is rough. In view of the above, it is important to provide very smooth surfaces for articulation or sliding against a UHMWPe bearing.
Many prosthetic joints employ metallic components formed from alloys of titanium or cobalt-chromium. Cobalt chromium alloys are very hard and strong and exhibit appropriate flexure. However, cobalt chromium also is very expensive and many patients exhibit sensitivity to cobalt-chromium alloys. Titanium alloys, such as titanium aluminum vanadium alloys also exhibit appropriate strength and flexure. Additionally, patients are less likely to exhibit sensitivity to titanium alloys, and titanium alloys are less expensive than cobalt-chromium alloys. However, titanium alloys generally are not as hard as cobalt chromium alloys. As a result, articulating surfaces of prosthetic components formed from titanium alloys typically are provided with a thin ceramic coating. For example, the articular surfaces of a titanium alloy prosthetic component may be provided with a titanium nitride (TiN) coating.
Ceramic coatings typically have been applied to metallic alloy substrates by known physical vapor deposition processes. This technology is widely used, for example, in the machine tool art to enhance the life of cutting tools. Prior art physical vapor deposition technology-typically applies the coating to a substrate in a vacuum coating chamber. A charge is applied to the substrate to be coated in the chamber, while an opposite charge is applied to the material to be coated onto the substrate. An arc is struck in the chamber, and the substrate to be coated is subjected to high energy ion bombardment. A gas then is introduced into the chamber. The gas reacts with the ions of the cathode and produces an ionic deposition of a highly-adherent ceramic coating onto the substrate.
FIG. 1
hereto schematically illustrates the prior art vacuum coating chamber for applying a TiN coating to a titanium alloy prosthetic component. In particular,
FIG. 1
shows a vacuum chamber
10
having a plurality of surface-mountable femoral components
12
for replacement hips. Each femoral component
12
includes a mounting stem
14
that will be mounted in a mounting aperture formed in the resected proximal end of the femur. The femoral component
12
further includes a head
16
having a convex bearing surface
18
and an opposed concave surface (not shown) for nesting tightly over the resected proximal end of the femur. The convex bearing surface
18
of the femoral component
12
will be in articular bearing engagement with a plastic bearing liner of the acetabular component of the hip prosthesis. The plastic bearing liner typically will be formed from UHMWPe. The prior art vacuum chamber
10
is employed to impart a TiN coating to the convex articular bearing surface
18
of the prior art femoral component
12
. As noted above, the coating must be hard to prevent wear of the coating and must be smooth to prevent wear of the UHMWPe bearing against which the femoral component
12
will articulate.
In an effort to achieve uniform coating, the prior art chamber includes a fixture
20
that extends into the prior art chamber
10
. The prior art fixture
20
is in a substantially central position within the prior art chamber
10
and is constructed to permit the femoral components
12
to be mounted thereon such that the convex articular bearing surfaces
18
of the femoral components
12
face outwardly and away from fixture
20
. The prior art fixture
20
is mounted to a power supply
22
disposed externally of the prior art chamber
10
. The power supply
22
imparts a charge to the fixture and to the femoral components
12
in the prior art chamber
10
. The power supply
22
further functions to rotate the prior art fixture
20
within the prior art chamber
10
in an effort to achieve uniform coating on the convex bearing surfaces
18
of the prosthetic components
12
.
The prior art chamber
10
further includes titanium evaporator
24
mounted in the walls of the chamber
10
and facing the prosthetic components
12
. A charge is applied to the evaporators
24
that is opposite to the charge applied to the fixture
20
. An arc then is struck in the chamber
10
and the convex articular bearing surfaces
18
of the prosthetic components
12
are subject to an ionic bombardment. Nitrogen gas is introduced into the chamber
10
. The gas reacts with the ions and produces an ionic deposition of a highly-adherent ceramic TiN coating onto the articular bearing surfaces
18
of the prosthetic components
12
.
Conventional wisdom, as practiced in the prior art, is to employ the prior art fixture
20
with the articular bearing surfaces
18
of the prosthetic components
12
facing the evaporators
24
in an effort to achieve optimum coating.
It recently was observed by the applicant herein that parts produced by the above-described prior art chamber
10
were slightly dull at certain locations and shinier in other locations. Analysis was conducted to determine the reason for the different appearances at different locations on the bearing surfaces
18
of the prosthetic components
12
. It was determined that the improperly coated prosthetic components were not properly rotated in the prior art chamber
10
, and thus one side was not directly exposed to the ion bombardment. Dull regions on the improperly coated prosthetic components
12
were determined to be attributable to very small droplets formed on the prosthetic components
12
. The droplets form an asperity on the bearing surface
18
which would increase wear against UHMWPe bearings.
Accordingly, it is an object of the subject invention to provide a coating apparatus and process that will limit asperity and thereby provide a bearing surface with excellent wear characteristics.
SUMMARY OF THE INVENTION
The above-described malfunctioning apparatus demonstrated that one side of the prosthetic component in the prior art chamber with the malfunctioning fixture had a high quality coating, while the opposed side had an inferior coating. In an effort to determine which sides of the prosthetic components achieved the better coating, a chamber was developed which fixtured the prosthetic components so that the surface that required a smooth hard coating would define the “dark side” of the chamber. Thus, the fixtures were arranged so that the convex articular bearing surfaces of the prosthetic components faced away from t
Beck Shrive P.
Casella Anthony J.
Hespos Gerald E.
Kolb Michener Jennifer
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