U.S. patent application number 12/938746 was filed with the patent office on 2012-05-03 for modified polymeric materials and methods of modifying polymeric materials.
This patent application is currently assigned to ZIMMER, INC.. Invention is credited to Oludele Popoola, Brian Thomas, Michael Wallick, Donald Yakimicki.
Application Number | 20120109301 12/938746 |
Document ID | / |
Family ID | 45048205 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120109301 |
Kind Code |
A1 |
Thomas; Brian ; et
al. |
May 3, 2012 |
Modified Polymeric Materials And Methods Of Modifying Polymeric
Materials
Abstract
Methods of forming polymeric articles using plasma treated
polymer resins, and orthopedic implants comprising a polymeric
article wherein the polymeric article has reactive groups bonded to
polymer molecules in an interior region of the polymeric
article.
Inventors: |
Thomas; Brian; (Columbia
City, IN) ; Yakimicki; Donald; (Warsaw, IN) ;
Popoola; Oludele; (Granger, IN) ; Wallick;
Michael; (Warsaw, IN) |
Assignee: |
ZIMMER, INC.
Warsaw
IN
|
Family ID: |
45048205 |
Appl. No.: |
12/938746 |
Filed: |
November 3, 2010 |
Current U.S.
Class: |
623/16.11 ;
522/111; 522/112; 522/153; 522/161; 522/162 |
Current CPC
Class: |
A61L 27/50 20130101;
A61L 27/16 20130101; A61L 27/16 20130101; C08J 3/28 20130101; B29C
43/02 20130101; C08L 23/06 20130101 |
Class at
Publication: |
623/16.11 ;
522/161; 522/162; 522/153; 522/111; 522/112 |
International
Class: |
A61F 2/28 20060101
A61F002/28; C08J 3/28 20060101 C08J003/28 |
Claims
1. A method of forming a polymeric article suitable for use as an
orthopedic implant, the method comprising: providing particles of a
first polymer resin; exposing the particles of the first polymer
resin to a first plasma wherein the first plasma reacts with the
particles of the first polymer resin to bond one or more selected
reactive groups to the particles; and consolidating the first
polymer resin to form a polymeric article.
2. The method of claim 1 in which the plasma is formed from a gas
selected from the group consisting of nitric oxide, carbon dioxide,
ammonia, amine monomer, and combinations thereof.
3. The method of claim 1 in which the one or more selected reactive
groups are selected from the group consisting of amines, amides,
imides, carboxyl, carbonyl, hydroxyl, sulfonates, phosphates,
perfluoro and combinations thereof.
4. The method of claim 1 further including blending the particles
of the first polymer resin with an additive.
5. The method of claim 4 in which the additive is an antioxidant or
biological agent.
6. The method of claim 5 in which the blending occurs after
exposure of the particles to the first plasma.
7. The method of claim 1 further including exposing particles of a
second polymer resin to a second plasma wherein the second plasma
reacts with the particles of the second polymer resin to bond one
or more selected reactive groups to the particles of the second
resin; arranging the first and second resins relative to one
another; and consolidating the first and second resins to form a
polymeric article that includes different reactive groups located
in different regions of the polymeric article.
8. The method of claim 7 in which the arranging comprises mixing
the first and second resins.
9. The method of claim 7 in which the first polymer resin and the
second polymer resin comprise the same polymer.
10. The method of claim 1 in which consolidating comprises
compression molding the polymer resin.
11. The method of claim 1 in which the first polymer resin is
selected from the group consisting of as polyethylene, ultrahigh
molecular weight polyethylene, polyaryletherketones, polypropylene,
polyurethanes, acrylics, polyethylene-co-vinyl alcohol, nylon,
polysulfones, polycarbonates, and polyacrylamides or combinations
thereof.
12. The method of claim 1 wherein the particles of the first
polymer resin include polymer molecules, and the method further
comprises crosslinking the polymer molecules prior to or after
consolidation.
13. The method of claim 12 in which the crosslinking comprises
irradiating the polymeric article.
14. The method of claim 12 in which the reactive groups are
crosslinking agents and wherein the reactive groups crosslink the
polymer.
15. A method of forming a polymeric article suitable for use as a
medical implant, the method comprising: providing a plasma modified
polymer resin; and consolidating the polymer resin to form a
polymeric article.
16. The method of claim 15 in which the polymer resin is selected
from the group consisting of polyethylene, ultrahigh molecular
weight polyethylene, polyaryletherketones, polypropylene, and
combinations thereof.
17. An orthopedic implant, comprising: an article comprising a
polymer; said article having an outer surface and an interior
region; said polymer including a plurality of polymer molecules
having one or more reactive groups bonded thereto, wherein the
reactive groups provide one or more of selected properties from the
group consisting of crosslinks, lubricity, wettability,
hydrophobicity, hydrophilicity, selected biological response,
tissue attachment, protein binding and combinations thereof; and
the polymer molecules being located at least at the interior region
of the polymeric article.
18. The implant of claim 17 in which the reactive groups are
located substantially throughout the interior region and at
exterior surface of the article.
19. The implant of claim 17 in which reactive groups are located in
selective portions of the polymeric article.
20. The implant of claim 17 in which the properties are selected
from the group consisting of from the group consisting of
crosslinks, lubricity, wettability, hydrophobicity, hydrophilicity,
selected biological response, tissue attachment, protein binding
and combinations thereof.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates to modified polymeric
materials and methods of modifying materials. The modified
polymeric materials may be processed to produce bulk modified
constructs or polymeric articles that have modified polymeric
material located in inner portions of the constructs or throughout
the articles. In particular, the present disclosure relates to
plasma modified polymer powders or flakes that may be employed to
produce the bulk modified constructs, methods of making and using
plasma modified polymers powders and articles made from the plasma
modified polymer powders. The present disclosure also relates
methods of modifying porous polymers that may be processed to
produce bulk modified constructs having modified polymers located
at inner portions of the constructs. The present disclosure also
relates to methods of compression molding that employ ultrasonic
energy.
BACKGROUND
[0002] Numerous polymer-based implantable medical devices have been
developed for implantation or insertion into the body. Examples of
such medical devices include endoprosthetic joints, which typically
include a metal or ceramic component articulating on or bearing
against a polymeric article. On such endoprosthetic device is a
knee prosthesis that includes a femoral knee prosthesis which
articulates against a polymeric article. Such polymeric articles
are typically made from, for example, polyethylene, ultra high
molecular weight polyethylene (UHMWPE), polyaryletherketones,
polyurethanes, or combinations and blends of such polymers.
[0003] In an effort to enhance certain characteristics of the
polymeric article, such as hydrophilicity, wettability, lubricity,
and wear resistance, just to name a few, the exterior or outer
surfaces of the polymeric article may be modified to include or to
have bonded thereto selected functional groups. Surface
modification of a polymeric article is typically applied to an
already formed polymeric article, which has been formed by, for
example, compression molding, ram extrusion or deposition. After
the polymeric article has been formed, an exterior surface is
subjected to a modification process to introduce and bond
functional or reactive groups to the polymer molecules on or near
the exterior surface of the polymeric article. Exterior surface
modification of a polymeric article may be accomplished by, for
example, plasma treatment or wet or dry chemical treatments of the
polymeric article's exterior surface.
[0004] In the orthopedic field, due to the articulation and load
bearing functions of the polymeric article, over time, the exterior
surface is subjected to increased wear. As a result the functional
groups on the modified surface are worn off. When the original
modified exterior surface is worn off, the inner bulk unmodified
polymer material is exposed and, in effect, becomes the exterior
surface, which may also be the articulating and load-bearing
surface, of the polymeric article. Thus, when the modified exterior
surface is worn off, the beneficial properties or characteristics
provided by the functional groups and the modified surface
generally are diminished if not lost.
SUMMARY
[0005] In one aspect, the present disclosure is directed to a
method of forming a polymeric article suitable for use as an
orthopedic implant. The method includes providing particles of a
polymer resin. The particles of the polymer resin are exposed to a
plasma wherein the plasma reacts with the particles of the polymer
resin to bond one or more selected reactive groups to the
particles. The polymer resin is then consolidated to form a
polymeric article. The particles of polymer resin and the
consolidated polymer article may be further processed, by for
example, undergoing crosslinking, temperature treatments or
machining.
[0006] In another aspect, a method of forming a polymeric article
suitable for use as a medical implant includes providing a plasma
modified polymer resin and consolidating the polymer resin to form
a polymeric article. The particles of polymer resin and the
consolidated polymer article may be further processed, by for
example, undergoing crosslinking, temperature treatments or
machining.
[0007] In yet another aspect, an orthopedic implant includes an
article comprising a polymer. The article has an outer surface and
an interior region. The polymer includes a plurality of polymer
molecules that have one or more reactive groups bonded to the
molecules. The reactive groups provide one or more selected
properties, including but not limited to crosslinks, lubricity,
wettability, hydrophobicity, hydrophilicity, selected biological
response, tissue attachment, and protein binding. The polymer
molecules having the reactive groups bonded thereto are located at
least at the interior region of the polymeric article. In one
embodiment, the article includes reactive groups located
substantially throughout the interior region and at the exterior
surface of the polymeric article. In other embodiments, the
reactive groups are located in selective portions of the polymeric
article. In still other embodiments, the article is a multilayered
construction wherein one reactive group may be located in a first
portion of the article and another different reactive group may be
located in a second portion of the article.
[0008] In still another aspect, the present disclosure is directed
to a method of forming a polymer layer on a substrate wherein the
polymer layer has one or more reactive groups throughout. The
method includes forming a plasma stream. At least one polymer
powder and a modifier is introduced into the plasma stream, wherein
the modifier reacts with the polymer in the plasma stream to
produce a modified polymer powder that includes reactive groups
bonded thereto. The modified polymer is deposited onto a substrate
to form a polymer layer that includes reactive groups
throughout.
[0009] In a further aspect, the present disclosure is directed to a
method of forming an implantable polyaryletherketone substrate
having reactive groups within an interior region of the substrate.
The method includes providing a porous polyaryletherketone
substrate. The reactive groups are bonded to interior regions of
the substrate. The substrate is compressed to collapse pores in the
substrate.
[0010] In another aspect, the present disclosure is directed to a
method of forming a polymer article. The method includes providing
a polymer. The polymer is elevated to a selected temperature and
pressure. Ultrasonic energy is applied to the polymer while the
polymer is at the elevated temperature and pressure.
BRIEF DESCRIPTION OF THE FIGURES
[0011] In the course of this description, reference will be made to
the accompanying drawing(s), wherein:
[0012] FIG. 1 is an exploded perspective view showing the
components of a knee replacement system including one example of a
polymeric article;
[0013] FIGS. 2 and 3 are schematic drawings of pucks made from
consolidated polymer resin;
[0014] FIGS. 4 and 5 are graphs showing the ultimate tensile
strength of samples made from unmodified UHMWPE powder and samples
made from plasma modified UHMWPE powder;
[0015] FIGS. 6 and 7 are graphs showing the percent strain at auto
break of samples made from unmodified UHMWPE powder and samples
made from plasma modified UHMWPE powder;
[0016] FIGS. 8 and 9 are graphs showing the IZOD strength of
samples made from unmodified UHMWPE powder and samples made from
plasma modified UHMWPE powder;
[0017] FIG. 10 is a graph showing contact angles of samples made
from unmodified UHMWPE powder and samples made from plasma modified
UHMWPE powder;
[0018] FIG. 11 is a schematic drawing of the square waveform
utilized in wear testing;
[0019] FIG. 12 is a graph showing the accumulative wear rate at one
million cycles of samples made from unmodified UHMWPE powder and
samples made from plasma modified UHMWPE powder;
[0020] FIG. 13 is a schematic drawing of a plasma spray device;
and
[0021] FIG. 14 is a schematic illustration of a mold cavity fitted
with ultrasonic energy devices.
DETAILED DESCRIPTION
[0022] As required, detailed embodiments of the present invention
are disclosed herein; however, it will be understood that the
disclosed embodiments are merely exemplary of the invention, which
may be embodied in various forms. Therefore, specific details
disclosed herein are not to be interpreted as limiting, but merely
as a basis for the claims and as a representative basis for
teaching one skilled in the art to variously employ the present
invention in virtually any appropriate manner.
[0023] The polymeric materials and articles disclosed herein are
particularly useful in the manufacture of medical implants or
medical implant systems that are permanently or temporarily
implanted within a human or animal body. The polymer molecules of
the polymeric articles include functional or reactive groups and
that are located between or beneath the exterior surfaces or layers
of the polymeric article. The functional groups of the polymer
molecules may be selected to provide any number of characteristics
that add to, alter or otherwise affect the physical and chemical
properties of the polymeric article. For example, the functional
groups may provide or assist in providing one or more of
hydrophilicity, hydrophobicity, wettability, lubricity, wear
resistance, crosslinking, protein binding, tissue attachment, and
reduced or selected biological response. In one example, the
functional groups may provide a reduced biological response to wear
particles.
[0024] Further, the functional groups may be selected to bond with
certain proteins within an animal or human body. As wear debris
from the polymeric article is generated, the functional groups
bonded to the wear particles also bond to proteins and coagulate to
produce larger-sized wear debris. Larger wear particles have been
shown to illicit reduced biological reactions by the human or
animal body. Further, larger wear particles bonded to proteins by
the reactive groups may suppress the immune response typically
triggered by wear particles. Thus, reducing chronic inflammatory
response and the production of UHMWPE degrading enzymes and
destructive oxygen and nitrogen species.
[0025] In one embodiment, the polymer molecules having such
functional groups are distributed throughout the polymeric article.
As used herein, "throughout" refers to distribution of the
functional groups across substantially the entire article including
uniform or substantially uniform distribution and varied or
irregular distribution of functional groups in the polymeric
article. Alternatively, the polymer molecules having functional
groups may be selectively located, distributed or dispersed in
particular sections, portions or layers so that the polymeric
article only includes functional groups within the selected
portions, sections or layers of the polymeric article. For example,
the article may include a first section or layer that includes
functional groups and a second section or layer that does not have
any functional groups dispersed therein. Further, different
functional groups may be combined together in the same portion or
layer of the polymeric article. Alternatively, different portions
or layers of the polymeric article may have different functional
groups to form a composite or layered structure. The composite
structure may be layered so that as the exterior surface of the
polymer body is worn away, different functional groups are exposed
as the underlying portion or layer is exposed during the lifetime
of the structure. For example, the top or exterior layer may have a
first functional group and a second sub-layer or inner layer may
have a second functional group. As the exterior layer is worn away,
the sub-layer, having the second functional group, is exposed.
[0026] While the methods, devices and articles disclosed herein are
described in relation to medical devices and medical applications,
such methods and devices are not limited to such use. The methods,
devices and articles may have other uses and may be used in other
industries as well.
[0027] FIG. 1 illustrates one example of a prosthetic implant that
may include a polymeric article of the present disclosure. In
particular, FIG. 1 shows a prosthetic knee replacement system 10,
which includes a femoral implant 12, a tibial implant 14 and
polymeric article 16 between the femoral implant 12 and the tibial
implant 14. The femoral implant 12 includes a pair of condyle
members 18 that bear and articulate against the polymeric article
16. Although the polymeric article 16 in this example is shown as a
component of a prosthetic knee replacement system, the polymeric
articles described herein are not so limited. Polymeric articles
may be a component of an implant (as shown in FIG. 1), may be used
as an implant itself or may be used in other implant systems, such
as, but not limited to, artificial hips and knees, cups or liners
for artificial hips and knees, spinal replacement disks, artificial
shoulder, elbow, feet, ankle and finger joints, mandibles, and
bearings of artificial hearts, etc. The polymeric articles may also
be precursors of an article such as the consolidated bulk
construct, e.g. slabs, from which the article is made or
shaped.
[0028] As discussed above, polymeric article 16 includes polymer
molecules that have selected functional or reactive groups and are
located between the exterior surfaces or in middle portions,
sections or layers of polymeric article 16. The polymer molecules
may be located or present throughout polymeric article 16 so that
the polymeric article 16 has functional groups present
substantially across the entire body of the polymeric article.
Alternatively, the polymer molecules having functional groups may
be located or concentrated in particular sections, portions or
layers so that polymeric article 16 only includes functional groups
within selected portions, sections or layers. Further, the
polymeric article 16 may have different functional groups in
different layers of the body to form a multilayered construct.
[0029] As the condyle members 18 repeatedly and over time
articulate against the exterior surface of the polymeric article
16, the exterior surface experiences wear and eventually may be
worn away. In accordance with methods and systems disclosed herein,
by modifying the polymer molecules within middle portions, sections
or layers of polymeric article 16, as the exterior surface of the
polymeric article is worn away, the newly exposed portions or
layers of the polymeric article 16 include characteristics or
properties provided by these functional groups, which are now at
the "new" exterior surface of the polymeric article. Thus, the
polymeric article may be considered to have a renewable exterior
surface. Additionally, different layers or portions of the
polymeric article 16 can have different functional groups or
different characteristics and/or properties such that as the
polymeric article 16 undergoes wear and loses the properties
provided by the functional groups, new layers or section having
such characteristics and properties will be exposed over time.
[0030] The polymeric articles disclosed herein may be made from
polymer powders, such as polyethylene, polyaryletherketones,
polypropylene, polyurethanes, acrylics, polyethylene-co-vinyl
alcohol, nylon, polysulfones, polycarbonates, and polyacrylamides
or combinations thereof. One polymer powder that is commonly used
in medical implants is UHMWPE. UHMWPE is a semicrystalline, linear
homopolymer of ethylene, which may be produced by stereospecific
polymerization with a Ziegler-Natta catalyst at low pressure (6-8
bar) and low temperature (66-80 degrees Celsius). The synthesis of
nascent UHMWPE results in a fine granular powder. The molecular
weight and its distribution can be controlled by process parameters
such as temperature, time and pressure. UHMWPE generally has a
molecular weight of at least about 2,000,000 g/mol.
[0031] Suitable UHMWPE materials for use as raw materials to form
the polymeric articles of the present disclosure may be in the form
of a powder, resin or flake. The polymeric articles may be prepared
almost entirely from UHMWPE powder, or may be formed by combining
UHMWPE powder with other suitable polymer materials. For example,
the UHMWPE may be mixtures of UHMWPEs having different molecular
weights. Further, the combinations may be mixtures of UHMWPE with
lower molecular weight polyethylene powders, or UHMWPE with other
different polymer powders such as, but not limited to, any of the
other polymers listed above. In one embodiment the polymeric
article may include at least about 50 w/w % UHMWPE.
[0032] Examples of suitable UHMWPE powders include GUR 1020 and GUR
1050 available from Ticona, having North American headquarters
located in Florence, Ky. Suitable polymer materials for use in
combination with the UHMWPE materials may include disentangled
polyethylene, high pressure crystallized polyethylene, various
other "super tough" polyethylene derivatives or other polymers,
such as various copolymers with ethylene including
poly(ethylene-co-vinyl alcohol), poly(acrylic acid-co-ethylene),
and poly(ethylene-co-methacrylic acid) to name a few.
[0033] As discussed above, the functional groups, reactive groups
or moieties bonded to the polymer molecules may be selected to
provide or enhance any number of a variety of properties. For
example, the functional groups may be selected to provide or
enhance one or more of hydrophilicity, hydrophobicity, wettability,
lubricity, wear resistance, crosslinking, protein binding, tissue
attachment and biological response. Such functional groups may
include, for example, one or more of amines, amides, imine, imide,
hydroxyl, carbonyl, aldehyde, carboxylate, carboxyl, ether, ester,
sulfonic, epoxide, phosphate, perfluoro, etc.
Plasma Modification
[0034] Disclosed herein are polymeric articles made of polymer
groups that have been modified with selected functional groups to
enhance, improve or otherwise provide the polymeric articles with
selected characteristics or properties. The polymeric modified
molecules may be uniformly distributed throughout the article or in
selected regions or layers as desired or non-uniformly distributed,
i.e., with sections or portions of the article being more/less
concentrated with polymer modified by functional groups or having
no functional groups at all.
[0035] The polymeric article may be provided with the properties
described above in any number of ways. In one example, functional
groups may be introduced into the raw material of polymer from
which such articles are eventually made. One way of introducing the
functional groups into the raw material is by plasma modification
of polymer powder, such as polyethylene, polyaryletherketones,
polypropylene, polyurethanes, acrylics, polyethylene-co-vinyl
alcohol, nylon, polysulfones, polycarbonates, and polyacrylamides
or combinations thereof.
[0036] In one embodiment of plasma modification, reactive gas
plasmas may be used in a plasma treatment process to add functional
or reactive groups to the outer surfaces of the granules flakes or
particles that make up the polymer powders. The polymer powders may
then be consolidated, by for example, compression molding, ram
extrusion, hot isostatic pressing or any other suitable
consolidation process, to create polymeric articles or bodies that
may be used as or in orthopedic implants. Consolidation of the
modified powders results in a polymeric article that includes
functional or reactive groups in the interior regions or layers of
the body. The article may also include functional groups on the
exterior surface of the article. Additionally, the consolidation
process may be such that the body may have layers or portions that
include different functional groups.
[0037] The polymer powder may be plasma modified by any method
known in the art, such as by processes that use a plasma polymer
vacuum chamber or by an atmospheric plasma process that employs a
blanketed carrier gas. When a vacuum chamber is utilized, the
powder may be place in a rotating drum so that the powder is
uniformly exposed to the plasma as the drum is rotated.
[0038] In one method of using a vacuum chamber, the chamber is
evacuated to a selected pressure, and preferably a relatively low
pressure. The pressure may be any suitable pressure depending on
the desired application. One or more selected gases, such as, but
not limited to, nitric oxide, carbon dioxide, ammonia, amine
monomer (primary, secondary or tertiary) or a combination thereof,
are then pumped or flowed into the chamber. The gases within the
chamber are ionized by, for example, AC, DC or RF voltage, to form
a plasma within the chamber. The voltage and/or power level may be
such that a plasma is formed from the gases. The polymer powder is
treated with the plasma for a selected period of time to form or
bond one or more functional groups on the surfaces of the granules
of the powder.
[0039] In an alternative embodiment, the plasma system may be an
atmospheric plasma system. In this embodiment, the powder may be
placed into a fluidized bed. During the atmospheric plasma
treatment process the powder is passed through a reactive zone
containing the reactive gas and plasma. The powder is cycled
through the reactive zone a number of times to produce the desired
coverage of reactive groups.
[0040] It will be appreciated that the plasma modification process
is nonspecific in nature. The placement of the functional groups
created on the surface(s) or some selected distance below the
surface of the powder granules is non-specific. The plasma
modification of the polymer powders can at least partially be
controlled by varying several factors including, but not limited
to: (1) the type and shape of the plasma polymer chamber/reactor;
(2) the frequency of the discharge excitation voltage; (3) the
power of the discharge; (4) the flow rate of gases; (5) the gas
pressure within the chamber; (6) the powder temperature; (7) the
particle size and geometry; and (8) the duration of the treatment.
These factors may be varied to produce the desired modification for
a particular application.
[0041] As discussed above, the plasma modified polymer powder may
be processed to form an implantable polymeric article. Optionally,
the modified polymer powder may first be blended with additives,
such as antioxidants or biological agents. In another alternative
embodiment, the polymer powder may be blended with an additive then
plasma treated. Further, in other alternative embodiments, the
functional groups may be selected so as to bond with the
antioxidants or biological agents. The antioxidant may be, for
example, vitamin E, and the biological agent may be, for example,
an antibiotic, antimicrobial or anti-inflammatory.
[0042] The blended or unblended modified polymer powder may then be
consolidated and/or compressed into a suitable form for use as (or
as part of) a prosthetic device or other implant. Suitable
compression and/or consolidation techniques include, for example,
compression molding, direct compression molding, hot isostatic
pressing, ram extrusion, high pressure crystallization, injection
molding, sintering or other conventional methods of compressing
and/or consolidating polymer powders. If desired, the polymeric
article formed from the compressed/consolidated polymeric article
may be further processed or manufactured by crosslinking,
annealing, melting, heating, cooling, doping with antioxidant,
doping with biological agents, milling, machining, drilling,
cutting, assembling with other components, and/or other
manufacturing or pre-manufacturing steps conventionally employed to
manufacture implants from polymer. For example, the plasma modified
powder may be subject to any of the processes of forming an article
disclosed in U.S. Patent Application Publication No.
US2010/0029858, published Feb. 4, 2010, and US2009/0118390,
published May 7, 2009, which are incorporated herein by
reference.
[0043] A multilayered construct or article may be made during the
compression molding process. For instance, polymer powders having
different or no modifications may be selectively placed is
particular locations within the mold. For instance a first polymer
resin having a first type or types of functional groups may be
arranged relative to a second polymer having a second type or types
of functional groups. The arranging of the first and second resins
may including mixing the resins or may included selectively placing
portions of the first and second resins in a desired arrangement
relative to one another. For example, to make a layered construct,
a first polymer powder having a first type or types of functional
groups may be placed at the bottom of the mold to form a first
layer. A second polymer powder having different functional groups
or no functional groups (raw unmodified polymer powder) may be
placed on top of the first layer to create a second layer. In other
embodiments, several layers of polymer powders may be placed in the
mold. Further, placement of the polymer powders is not limited to
layers. The polymer powders, having different functional groups (or
no functional groups) may be selectively placed in different
regions or portions of the mold. Once the polymer powders have been
placed in the mold, the powder is compression molded to form an
article for use in or as a medical implant or a bulk material that
can be shaped into such an article.
[0044] Prior to and/or after processing the implant as discussed
above, the polymer may be crosslinked by any suitable crosslinking
process. For example, the polymer may be crosslinked by exposure to
radiation at a high radiation dose and/or a dose rate sufficient to
form a crosslinked polymer. The radiation may be, for example,
gamma or electron beam irradiation. In one embodiment, the
polymeric article may be exposed to electron beam irradiation at a
dose rate of between about 25 kGy/min and about 240 kGy/min for a
total dose of between about 90 kGy and about 200 kGy. In certain
embodiments, the desired radiation dose may be achieved in a single
exposure step at a high dose rate. In other embodiments, a series
of high dose rate irradiation steps may be employed to expose the
polymer to a desired dose of radiation. The crosslinking may be
conducted at any time from powder to implant and may be used in
conjunction with other manufacturing processes applied to the
polymeric article. Further, prior to irradiation, the polymer may
be preheated.
[0045] In certain embodiments, the radiation source is electron
beam radiation. Electron beam radiation exposure may be performed
using conventionally available electron beam accelerators. One
commercial source for such an accelerator is IBA Technologies
Group, Belgium. Suitable accelerators may produce an electron beam
energy between about 2 and about 50 MeV, more particularly about 10
MeV, and are generally capable of accomplishing one or more of the
radiation doses and/or dosage rates reported herein. Electron beam
exposure may be carried out in a generally inert atmosphere,
including for example, an argon, nitrogen, vacuum, or oxygen
scavenger atmosphere. Exposure may also be carried out in air under
ambient conditions according to one embodiment. Gamma and x-ray
radiation may also be suitable for use in alternate embodiments.
The processes described herein are not necessarily limited to a
specific type of source of radiation.
[0046] In another embodiment, the functional or reactive group
formed on the surface the polymer powder by plasma modification may
provide thermal crosslinking that can be activated with the
application of heat. Such functional groups may include amines,
phosphates, and sulfonates. The polymer powder may be modified to
include one or more functional groups. The functional group may
also serve a dual purpose, such as but not limited to, increasing
lubricity. In one embodiment, the crosslinking provided by the
functional group may be activated by the heat applied to the
polymer powder during consolidation. When the functional group
serves as a crosslinking agent, the polymeric article may or may
not also be subject to other crosslinking processes, such as
irradiation.
[0047] In one example, the UHMWPE powder may be modified so that
the surfaces of at least some of the granules include a sulfonic
acid crosslinking group bonded to the surface of the granules. Upon
application of heat, such as during consolidation, the crosslinking
groups undergo a dehydration reaction losing water and forming the
crosslinking bond, as shown below.
##STR00001##
[0048] Accordingly, the crosslinked polymer may be illustrated
as:
##STR00002##
[0049] During use, the surface of the polymeric article or implant
is worn exposing the underlying sulfonic anhydride groups. The
anhydride groups undergo a reaction with water in the body to
regenerate the sulfonic acid groups, and thereby imparting and
continually regenerating hydrophilicity in the surface of the
polymeric article, which increases lubricity. Thus, in this
example, the sulfonic groups provide or enhance crosslinking and
lubricity.
[0050] The polymeric article formed from consolidation of the
modified powder may also be subject to annealing. When annealing is
employed, the polymeric article may be annealed at a temperature of
between about 120.degree. C. and about 230.degree. C. for a time
period of between about 1 hour and about 60 hours. The annealing
may be used in conjunction with other manufacturing processes
applied to the polymeric article. Alternatively or additionally,
the crosslinked polymer may be subjected to the mechanical
annealing processes reported in U.S. Pat. No. 6,853,772 to
Muratoglu, which is incorporated herein by reference. In one
embodiment, however, no pre- or post-irradiation temperature and/or
annealing treatments are performed. In another embodiment, the
polymeric article may be subject to an irradiation process and then
annealed.
[0051] As part of the implant manufacturing process, additional
components may be combined with the polymer at any time during the
process reported herein. In one embodiment, tribological components
such as metal and/or ceramic articulating components and/or
preassembled bipolar components may be joined with the polymer. In
other embodiments, metal backing (e.g. plates or shields) may be
added. In further embodiments, surface components such a Trabecular
Metal.TM. material, fiber metal, beats, Sulmesh.RTM. coating,
meshes, cancellous titanium, and/or metal or polymer coatings may
be added to or joined with the polymer. Sulmesh and Trabecular
Metal are trademarks of Zimmer, Inc. of Warsaw, Ind. Still further,
radiomarkers or radiopacifiers such as tantalum, steel and/or
titanium balls, wires, bolts or pegs may be added. Further yet,
locking features such as rings, bolts, pegs, snaps and/or
cements/adhesives may be added. These additional components may be
used to form sandwich implant designs, radiomarked implants,
metal-backed implants to prevent direct bone contact, functional
growth surfaces, and/or implants with locking features.
[0052] After manufacturing of the implant has been completed, it
may be packaged and sterilized prior to distribution. Packaging is
generally carried out using either gas permeable packaging or
barrier packaging utilizing a reduced oxygen atmosphere.
[0053] A variety of implants, and in particular endoprosthetic
joint replacements, may be prepared by employing the methods
reported herein. Examples of such implants include artificial hips
and knees, cups or liners for artificial hips and knees, spinal
replacement disks, artificial shoulder, elbow, feet, ankle and
finger joints, mandibles, and bearings of artificial hearts.
EXAMPLES
[0054] The following non-limiting examples illustrate various
features and characteristics of the present invention, which is not
to be construed or limited thereto.
Example 1
[0055] In several of the various Samples below, UHMWPE powder
resins were used, which powders have been plasma modified with
various gases.
[0056] Table 1 sets forth the processing parameters for Samples
A-Z. Samples A, O, P and Y were control samples used for
comparative analysis. As set forth in Table 1, GUR 1050 brand
powder available from Ticona, having North American headquarters
located in Florence, Ky. was used in samples A-X and polyether
ether ketone available from Gharda, located in Newton, Pa., was
used in samples Y and Z.
[0057] For Samples B-N and Q-X GUR 1050 powder was plasma treated
by the gases and for the times listed in Table 1. For Samples J-N,
the Sample included a blend of two powders wherein each of the two
powders was treated with a different gas and then blended together
at a ratio of 50%/50% by weight For example, in Sample J, one batch
of GUR 1050 was treated with N.sub.2O and another batch of GUR 1050
was treated NH.sub.3. The powders of the two batches were then
blended together. The plasma treatment process was carried out by
PVA TePla America, Corona, Calif. In all of these samples, the
plasma treated powder was then consolidated by compression molding
to produce a puck or generally cylindrical polymeric article having
a diameter of 2.5 inches and a height of 1.5 inches. The GUR 1050
powder of control samples of A, O, P, and Y were not subjected to
plasma treatment. The untreated GUR 1050 powder of these control
samples were also consolidated by compression molding to produce a
puck or generally cylindrical polymeric article having a diameter
of 2.5 inches and a height of 1.5 inches.
[0058] Samples A-E, J-N, Y and Z received no further processing,
after consolidation. The additional processing of the other Samples
are as set forth below.
[0059] For Samples F-I, the compression molded pucks were then
annealed in a 49A-650D oven available from Precision Quincy,
located in Woodstock, Ill., at the time and temperature specified
in Table 1.
[0060] For Samples O, Q-T, the compression molded pucks were
irradiated at 10 MeV, at the dose rate listed in the Table 1 to a
total dose of 100 kGy at lotron Industries Canada Inc. located in
Port Coquitlam, B.C., Canada.
[0061] For Samples P, U-X, the compression molded pucks were
irradiated at 10 MeV, at the dose rate listed in Table 1 to a total
dose of 100 kGy at lotron Industries Canada Inc. located in Port
Coquitlam, B.C., Canada. These samples were then annealed in a
49A-650D oven available from Precision Quincy at the time and
temperature specified in Table 1.
TABLE-US-00001 TABLE 1 PREHEATING BEFORE RAW PLASMA IRRADIATION
IRRADIATION IRRADIATION SAMPLE MATERIAL TREATMENT .degree. C. DOSE
KGY DOSE RATE ANNEALING A GUR 1050 N/A N/A N/A N/A N/A B GUR 1050
N.sub.2O, 50 minutes N/A N/A N/A N/A C GUR 1050 CO.sub.2, 50
minutes N/A N/A N/A N/A D GUR 1050 NH.sub.3, 50 minutes N/A N/A N/A
N/A E GUR 1050 Allylamine, 50 N/A N/A N/A N/A minutes F GUR 1050
N.sub.2O, 50 minutes N/A N/A N/A 120 C., 40 hours G GUR 1050
CO.sub.2, 50 minutes N/A N/A N/A 120 C., 40 hours H GUR 1050
NH.sub.3, 50 minutes N/A N/A N/A 120 C., 40 hours I GUR 1050
Allylamine, 50 N/A N/A N/A 120 C., minutes 40 hours J GUR 1050
Blend of powder N/A N/A N/A N/A treated with N.sub.2O, 50 minutes
and powder treated with NH.sub.3, 50 minutes K GUR 1050 Blend of
powder N/A N/A N/A N/A treated with N.sub.2O, 50 minutes and powder
treated with CO.sub.2, 50 minutes L GUR 1050 Blend of powder N/A
N/A N/A N/A treated with N.sub.2O, 50 minutes and powder treated
with Allylamine, 50 minutes M GUR 1050 Blend of powder N/A N/A N/A
N/A treated with CO.sub.2, 50 minutes and powder treated with
NH.sub.3, 50 minutes N GUR 1050 Blend of powder N/A N/A N/A N/A
treated with Allylamine, 50 minutes and powder treated with
CO.sub.2, 50 minutes O GUR 1050 N/A 40 C. 100 kGy 30 kGy- N/A m/min
P GUR 1050 N/A 40 C. 100 kGy 30 kGy- 120 C., m/min 40 hours Q GUR
1050 N.sub.2O, 50 minutes 40 C. 100 kGy 30 kGy- N/A m/min R GUR
1050 CO.sub.2, 50 minutes 40 C. 100 kGy 30 kGy- N/A m/min S GUR
1050 NH.sub.3, 50 minutes 40 C. 100 kGy 30 kGy- N/A m/min T GUR
1050 Allylamine, 50 40 C. 100 kGy 30 kGy- N/A minutes m/min U GUR
1050 N.sub.2O, 50 minutes 40 C. 100 kGy 30 kGy- 120 C., m/min 40
hours V GUR 1050 CO.sub.2, 50 minutes 40 C. 100 kGy 30 kGy- 120 C.,
m/min 40 hours W GUR 1050 NH.sub.3, 50 minutes 40 C. 100 kGy 30
kGy- 120 C., m/min 40 hours X GUR 1050 Allylamine, 50 40 C. 100 kGy
30 kGy- 120 C., minutes m/min 40 hours Y PEEK N/A N/A N/A N/A N/A Z
PEEK N.sub.2O, 50 minutes N/A N/A N/A N/A
Results
[0062] Tests were preformed on the above samples to determine the
physical properties of the consolidated and processed polymer
materials of the above samples. In particular, tests were conducted
on sections of material taken from middle sections of the
above-described compression molded puck. FIGS. 2 and 3 illustrate
one example of a puck 100. A 0.75 inch portion 102 of the puck as
measured from an edge of the puck was removed. Referring to FIG. 2,
the puck 100 was then machined to create a plurality of flats 104
from the middle section of the puck. The flats 104 had a thickness
of about 0.125.+-.0.002 inches.
[0063] Tensile Test Results
[0064] The tensile properties of the samples were tested according
to ASTMD638-02a. Tensile bars test specimens were punched from
flats 104.
[0065] Tensile properties of each Sample were determined from the
average of 5 runs for samples E-I and 10 runs for all other
samples. An Instron Model 3345 Test System available from Instron,
Norwood, Mass., USA was used to test the tensile properties of each
sample. The results are listed in Table 2 with the standard
deviations in parenthesis.
TABLE-US-00002 TABLE 2 % STRAIN AT ULTIMATE TENSILE AUTOMATIC BREAK
ZERO SLOPE YIELD SAMPLE MATERIAL STRENGTH (MPA) (%) STRESS (MPA) A
GUR 1050 66.11 (4.25) 404.45 (19.10) 22.361 (0.27) B GUR 1050 N2O
44.54 (1.83) 332.52 (09.86) 21.264 (0.26) C GUR1050 CO2 39.32
(1.66) 301.74 (06.36) 21.585 (0.21) D GUR 1050 NH3 42.27 (1.94)
290.94 (09.65) 22.079 (0.37) E GUR1050 40.73 (2.41) 287.50 (12.91)
21.840 (0.46) Allylamine F GUR 1050 N2O 26.34 (2.45) 245.01 (29.78)
20.216 (0.31) Annealed G GUR1050 CO2 30.28 (2.08) 322.72 (17.27)
20.488 (0.95) Annealed H GUR 1050 NH3 30.57 (3.90) 324.37 (80.00)
20.720 (0.81) Annealed I GUR1050 27.00 (5.42) 247.51 (56.13) 20.540
(0.99) Allylamine Annealed J GUR 1050 41.68 (1.86) 310.75 (08.99)
21.235 (0.34) N2O/NH3 K GUR 1050 40.63 (0.45) 320.14 (07.87) 21.169
(0.25) N2O/CO2 L GUR 1050 41.08 (2.66) 309.05 (17.70) 21.083 (0.23)
N2O/Allylamine M GUR 1050 39.27 (1.58) 291.70 (10.48) 21.184 (0.33)
CO2/NH3 N GUR 1050 40.40 (2.76) 291.65 (16.29) 21.411 (0.37)
Allylamine/CO2 O GUR 1050 59.35 (4.19) 300.64 (14.13) 23.314 (0.50)
100 kGy P GUR 1050 44.71 (3.57) 239.29 (09.80) 21.053 (0.20) 100
kGy Annealed Q GUR 1050 N2O 45.30 (2.09) 252.95 (08.69) 22.625
(0.44) 100 kGy R GUR 1050 CO2 42.41 (1.19) 239.04 (06.26) 23.098
(0.22) 100 kGy S GUR 1050 NH3 38.19 (0.90) 208.10 (03.09) 22.558
(0.18) 100 kGy T GUR 1050 35.26 (1.86) 213.73 (07.29) 22.319 (0.23)
Allylamine 100 kGy U GUR 1050 N2O 25.94 (5.91) 197.45 (77.45)
21.062 (0.73) 100 kGy Annealed V GUR 1050 CO2 26.87 (1.29) 248.51
(11.99) 19.851 (0.23) 100 kGy Annealed W GUR 1050 NH3 26.70 (3.36)
217.22 (37.14) 19.710 (0.47) 100 kGy Annealed X GUR 1050 25.66
(2.77) 225.43 (14.47) 19.580 (0.70) Allylamine 100 kGy Annealed Y
PEEK 115.85 (06.14) 3.61 (1.05) 121.54 (1.91) Z PEEK Modified 94.86
(10.29) 2.62 (0.38) 94.042 (12.44)
[0066] FIGS. 4-7 are bar graphs illustrating the various tensile
strength properties of the samples. FIGS. 4 and 5 illustrate the
Ultimate Tensile Strength of samples A-X. FIGS. 6 and 7 illustrate
the Percent Strain At Automatic Break of Samples A-X.
[0067] IZOD Impact Test Results
[0068] IZOD impact testing conforming to ASTM F648-00 using double
notch IZOD specimens were performed on Samples A-E and O-T. The
above-described flats 104 were doubled notched and used in the IZOD
impact tests.
[0069] Properties of each Sample were determined from the average
of 5 runs. An IZOD Impact Tester from Tinius-Olsen was used to test
the tensile properties of each sample. The results are listed in
Table 3 with the standard deviation in parentheses.
TABLE-US-00003 TABLE 3 SAMPLE MATERIAL ENERGY PER AREA
(kJ/m{circumflex over ( )}2) A GUR 1050 111.982 (3.232) B GUR 1050
N2O 115.017 (1.717) C GUR1050 CO2 112.979 (3.181) D GUR 1050 NH3
116.109 (2.765) E GUR1050 Allylamine 108.574 (6.555) O GUR 1050
100kGy 75.718 (1.189) P GUR 1050 100kGy 59.432 (2.299) Annealed Q
GUR 1050 N2O 100kGy 67.888 (1.759) R GUR 1050 CO2 100kGy 70.948
(2.208) S GUR 1050 NH3 100kGy 70.734 (2.244) T GUR 1050 Allylamine
68.583 (3.622) 100kGy
[0070] FIGS. 8 and 9 are bar graphs illustrating the results of the
IZOD strength tests.
[0071] Contact Angle Test Results
[0072] Contact angle measurements, which measure the angle between
the surface of a liquid solvent (e.g. water, serum) and the surface
of the polymer substrate at the line of contact, were conducted on
samples A-E and Q-T in order to test the lubricity of the surface
layer of flats machined from the middle of the puck. In general,
the lower the contact angle, the more wettable the surface, which
indicates greater lubricity with the solvent. In the present case,
deionized water, phosphate buffered saline and bovine synovial
fluid were used as solvents. The bovine synovial fluid used is
available from Animal Technologies, Inc., located in Tyler, Tex.
Additionally, the contact angles were measured using a Kruss DSA
100 available from Kruss located in Matthews, N.C. The contact
angle test results are shown in Table 4 and illustrated in FIG.
10.
TABLE-US-00004 TABLE 4 Deionized Bovine SAMPLE MATERIAL H.sub.2O
PBS Synovial Fluid A GUR 1050 105.3 92.8 67.5 B GUR 1050 N2O 88.8
84.4 42.9 C GUR1050 CO2 89.5 90.4 62.0 D GUR 1050 NH3 92.8 92.2
50.1 E GUR1050 Allylamine 96.6 91.6 59.4 Q GUR 1050 N2O 100kGy 88.6
87.4 61.9 R GUR 1050 CO2 100kGy 84.0 83.5 30.1 S GUR 1050 NH3
100kGy 84.9 86.1 54.3 T GUR 1050 Allylamine 83.5 62.5 58.5
100kGy
Example 2
[0073] The Samples AA-JJ shown in Table 5 below were prepared in
the same manner as described above in Example 1, except that the
plasma modified and unmodified GUR 1050 powder was compression
molded into pucks having a diameter of 63.5 mm and a height of 52
mm. Table 5 shows the processing parameters for Samples AA-JJ.
TABLE-US-00005 TABLE 5 PREHEATING RAW BEFORE MATERIAL PLASMA
IRRADIATION IRRADIATION IRRADIATION SAMPLE GUR TREATMENT .degree.
C. DOSE KGY DOSE RATE ANNEALING AA GUR 1050 N/A N/A N/A N/A N/A BB
GUR 1050 N.sub.2O, 50 N/A N/A N/A N/A minutes CC GUR 1050 CO.sub.2,
50 N/A N/A N/A N/A minutes DD GUR 1050 NH.sub.3, 50 N/A N/A N/A N/A
minutes EE GUR 1050 Allylamine, 50 N/A N/A N/A N/A minutes FF GUR
1050 N/A 40 C. 100 kGy 30 kGy- N/A m/min GG GUR 1050 N.sub.2O, 50
40 C. 100 kGy 30 kGy- N/A minutes m/min HH GUR 1050 CO.sub.2, 50 40
C. 100 kGy 30 kGy- N/A minutes m/min II GUR 1050 NH.sub.3, 50 40 C.
100 kGy 30 kGy- N/A minutes m/min JJ GUR 1050 Allylamine, 50 40 C.
100 kGy 30 kGy- N/A minutes m/min
[0074] Wear Testing
[0075] Samples AA-JJ were subjected to wear testing, in terms of
weight loss, on a custom built pin-on-flat (POF) twelve-station
screening device located in the Tribology Testing Laboratory at
Zimmer, Inc. (Warsaw, Ind., USA). Briefly, the above described
compression molded pucks of Samples CC-LL were machined to produce
a test pin having a diameter of 9.07 mm and a length of 9.55
mm.
[0076] During testing, the pins were articulated against a CoCr
disk having an R.sub.a of <0.02 .mu.m to test wear properties in
terms of weight. The test was conducted at constant force of 445 N,
at 1.0 Hz for 75,000 cycles, and in undiluted bovine calf serum
including EDTA (disodium salt, 7.9 g/l) and Sodium Azide (3.0 g/l).
The CoCr disks were articulated against the pin surface in the 15
mm.times.15 mm square waveform as shown in FIG. 11. The pins were
removed from the device and cleaned, dried and weighed every 25,000
cycles. Additionally, the bovine serum was changed every 25,000
cycles. Three runs of each sample were used in this wear testing
and Table 6 shows the average weight loss of the three specimens
for each sample. FIG. 12 illustrates the accumulative wear rate at
one million cycles.
TABLE-US-00006 TABLE 6 AVERAGE AVERAGE AVERAGE PIN PIN PIN WEIGHT
WEIGHT WEIGHT LOSS LOSS LOSS AT 25K AT 50K AT 75K SAMPLE MATERIAL
CYCLES CYCLES CYCLES AA GUR 1050 1.99 mg 4.00 mg 6.25 mg BB GUR
1050 N.sub.2O 1.50 mg 3.25 mg 5.11 mg CC GUR 1050 1.81 mg 3.72 mg
5.66 mg CO.sub.2 DD GUR 1050 0.65 mg 1.49 mg 2.38 mg NH.sub.3 EE
GUR 1050 1.51 mg 3.36 mg 5.94 mg Amine FF GUR 1050 0.56 mg 1.37 mg
2.56 mg Irradiated II GUR 1050 NH.sub.3 1.54 mg 3.47 mg 5.76 mg
Irradiated JJ GUR 1050 0.98 mg 2.39 mg 3.71 mg Amine Irradiated
Plasma Spraying
[0077] The polymeric articles disclosed herein may also be
constructed by plasma spraying, thermal deposition corona spraying
or combinations thereof. In one embodiment, a plasma spraying
process is employed to modify polymer powder to include selected
functional groups.
[0078] Plasma spraying or thermal deposition are known coating
processes that are used to apply a coating or layer to a substrate
or work piece. In general, plasma spraying includes spraying of
molten or softened material onto a surface to provide a layer or
coating on the surface. In the context of polymer coatings, polymer
powders are injected into a very high temperature plasma flame,
where the polymer is heated and sprayed at high velocity onto a
substrate. The substrate may be, but is not limited to,
tribological components such as metal and/or ceramic substrates. In
other embodiments, metal backing (e.g. plates or shields) may be
used as the substrate. In further embodiments, the substrate may
include a trabecular metal or fiber metal.
[0079] FIG. 13 is a schematic illustration of a plasma spray 200
suitable for treating and modifying the substrates of orthopedic
implants. Plasma spray 200 includes an inner cathode 202 surrounded
by an outer anode 204 which is shaped to form a constricting nozzle
214. The anode 204 is typically made of cooper and the cathode 202
is typically made of tungsten. Gas is flowed between the cathode
202 and anode 204 as a direct current is maintained between the
cathode 202 and anode 204. A high voltage discharge causes
localized ionization and a path for an arc to form between the
cathode 202 and anode 204. The arc causes the gas to form a plasma.
The plasma exits the anode as a flame 206. In the embodiment shown,
the polymer powder 208 is feed into the flame by a feeding tube
212. However, the polymer powder 208 may be feed into the sprayer
at any suitable location and by any suitable method. The powder 208
injected is rapidly heated and accelerated to a high velocity. The
heated, high velocity powder impacts the substrate 210, where it
cools to create a coating or layer.
[0080] The gases used in the plasma spray modification methods
disclosed herein may be a mixture of inert gases with reactive
gases, may be a mixture of different reactive gases or may be only
a single reactive gas. Reactive gases are those that will produce a
reactive species when formed into plasma or when exposed to a
plasma. Such reactive gases include but are not limited to ammonia,
sulfur trioxide, carbon tetrafluoride and ethylene oxide. The
functional groups produced may include one or more amines, amides,
hydroxyl, carbonyl, aldehyde, carboxylate, carboxyl, ether, ester,
sulfonic, epoxide, phosphate, perfluoro, etc. When the reactive
gases are mixed with or exposed to a plasma created by an inert
gas, such inert gases may include argon, helium, hydrogen and
nitrogen.
[0081] The polymer powder may be any polymer powder suitable for
use in a plasma spray process. For example, the polymer powder may
be UHMWPE or polyaryletherketones (such as PEEK or PEKK). When the
polymer powder is feed into the plasma, the polymer and the
reactive species will react together in the plasma to modify the
polymer prior to the polymer being deposited onto a substrate. In
other words, the polymer will be modified to include functional
groups prior to deposition on the substrate, thereby resulting in a
polymer layer or coating that includes modification throughout the
layer.
[0082] Further, the type and amount of reactive gases employed in
the spraying process can be varied during the process to produce
polymeric articles having different functional groups or varying
amounts of functional groups throughout the body. In one
embodiment, the gases may be switched during the spraying process
to create a multilayered bulk construct. For example, one type of
reactive gas, such as PCl.sub.S, may be used to construct the
bottom of a polymeric article to may it osteoconductive and another
reactive gas, such as, SO.sub.2 may be employed to make the top of
the polymeric article cartilage friendly.
Compression Molding of Polymer Materials
[0083] Some polymers that have been functionalized or modified may
be difficult to melt process. Thus, materials and articles made of
such polymers are only surfaced modified or functionalized after
the desired shape is produced. As discussed above, as the surface
is worn away, so are the functional groups, thus reducing the
effectiveness of the surface modification over time.
[0084] Another embodiment of forming the polymer articles disclosed
herein includes a process of modification wherein a porous
polymeric article is subjected to functionalization treatments.
Such treatments may include sulfonation, plasma treatments,
ketone-to-ether reactions, etc. Sulfonation is a known process and
described in Sulfonation of Poly (Ether Ether Ketone) (PEEK):
Kinetic Study and Characterization, Huang et al., Journal of
Applied Polymer Science, Vol. 82 Issue 11, December 2001, pp.
2651-2660 and Synthesis and Characterization of Homogeneously
Sulfonated Poly (Ether Ether Ketone) Membranes: Effect of Casting
Solvent, Do et al., Journal of Applied Polymer Science, Vol. 110,
Issue 3, November 2009, pp. 1763-1770, which are incorporated by
reference herein.
[0085] The pores of the porous polymeric article allow the
treatments to penetrate into the polymeric article and bond and
introduce functional groups to the interior portions of the porous
polymeric article. After the porous body has been subjected to
modification treatments, it is compression molded to collapse the
pores resulting in a polymeric article that has functional or
reactive groups distributed substantially throughout the article.
The modified porous body may be compression molded into a final
implant shape or configuration or it may compression molded into a
shape that requires further processing.
[0086] In one embodiment, a PEEK or PEKK polymeric article having
functional groups throughout is formed. A porous PEEK or PEKK
polymeric article, which may be obtained for example from Porogen
located in Woburn, Mass., USA, is subjected to a modification
treatment to bond or otherwise attach functional groups to a
polymeric article. As discussed above, the pores of the porous PEEK
or PEKK polymeric article allow modification treatment of interior
regions to bond functional groups to the inner portions or layers
of the porous PEEK or PEKK body. The modification treatment may
include but is not limited to sulfonation, plasma treatment or
ketone-to-ether treatments. After the modification treatment, the
porous body is compression molded to collapse the pores and form a
PEEK or PEKK polymeric article having functional groups bonded to
inner portions of the polymeric article.
Ultrasonic Compression Molding of Polymer Materials
[0087] Another way by which a polymeric material or article may be
modified is by molding a polymer which employ applying ultrasonic
energy to the polymer during the molding process. These ultrasonic
molding methods may be used, for example, to consolidate
(compression mold or ram extrusion) UHMWPE.
[0088] Consolidation UHMWPE involves self-diffusion of polymer
chains in which the polymer chains of adjacent particles
intermingle and entangle on the molecular level. In order for
intermingling to occur, the particles must be in close proximity
and the polymer chains must have some mobility. Accordingly,
intermingling of adjacent particles is promoted by applying
elevated temperatures and pressure. The elevated pressure places
the grain boundaries or interfacing surfaces of adjacent particles
in close proximity, and elevating the temperature increases the
mobility of the polymer chains. Because consolidation involves
diffusion, the process requires maintaining the elevated
temperature and pressures for a sufficient time to allow the
polymer chains to migrate across the grain boundaries. Although the
polymer chains migrate and intermingle, the grain boundaries are
retained for the most part. The grain boundaries of a consolidated
polymeric UHMWPE body represent the weakest point in the
material.
[0089] In the methods disclosed herein, ultrasonic energy, such as
sound waves, may be applied to the UHMWPE during the consolidation
process to enhance or improve the intermingling of the polymer
chains of adjacent particles. In one embodiment, the ultrasonic
energy may be in the form of high energy or high frequency sound
waves. The application of ultrasonic energy can create localized
heating and provide energy that promotes polymer chain mobility and
entanglement.
[0090] The ultrasonic energy can be applied to the UHMWPE during
consolidation by any suitable method. For example, ultrasonic horns
may be fitted into a compression mold cavity. FIG. 14 illustrates
one example of an embodiment of a mold 300 that could be used in an
ultrasonic molding process. The mold 300 includes a top portion 302
and bottom portion 304, which open and close to form the mold. In
this embodiment, the bottom portion 304 includes two sections 306
and 308 which may separate to release the molded material. The mold
300 also includes ultrasonic energy generators 310 located in the
bottom portion 304 of the mold. However, the ultrasonic energy
generators 310 may be places in any suitable position. In one
embodiment, the ultrasonic energy generators 310 may be
specifically aimed direct ultrasonic energy to a particular portion
of the molded material.
[0091] In a compression molding process, UHMWPE is placed into the
mold and placed under elevated temperature and pressure, as done in
conventional compressing molding methods. When the polymer is in
the melt stage, ultrasonic energy is applied, for example through
activation of ultrasonic horns, to provide energy that promotes
greater diffusion of polymer chains of adjacent polymer particles.
Any suitable amount of ultrasonic energy may be applied during the
process. In one embodiment, the ultrasonic energy may be between
about 10 kHz and about 100 kHz, and more preferably about 20-40
kHz. The ultrasonic energy may also promote diffusion of polymer
chains from two distance boundary layers.
[0092] Using ultrasonic energy can provide several benefits,
including but not limited to, reduced cycle times, enhanced chain
entanglement and increased material strength. Further, because the
application of ultrasonic energy reduces air bubbles and voids, the
application of ultrasonic energy could be used to reduce the amount
of oxygen within the molded material, which would assist in
reducing oxidation of the material. This is believed to be
particularly useful when molding UHMWPE which has been blended with
an antioxidant, such as Vitamin E which is susceptible to
oxidation. Also, the ultrasonic energy could be employed to induce
crosslinking. The ultrasonic energy could be such that it results
in chain scission and cross-linking of the UHMWPE.
[0093] It will be understood that the embodiments described above
are illustrative of some of the applications of the principles of
the present subject matter. Numerous modifications may be made by
those skilled in the art without departing from the spirit and
scope of the claimed subject matter, including those combinations
of features that are individually disclosed or claimed herein. For
these reasons, the scope hereof is not limited to the above
description but is as set forth in the following claims, and it is
understood that claims may be directed to the features hereof,
including as combinations of features that are individually
disclosed or claimed herein.
* * * * *