Precoated polymeric prosthesis and process for making same

• US 20010011190A1
• Filed: 01/30/2001
• Published: 08/02/2001
• Est. Priority Date: 04/01/1999
• Status: Active Grant

• Current Assignee: Park, Joon B.
• Original Assignee: Park, Joon B.
• Inventors: Park, Joon B.
• Granted Patent: US 6,558,428 B2
• Time in Patent Office: Days
• US Class Current: 623/11.11
• CPC Class Codes: A61F 2/30767 Special external or bone-contacting surface, e.g. coating for improving bone ingrowth
• CPC Class Codes: A61F 2/3094 Designing or manufacturing processes
• CPC Class Codes: A61F 2/32 for the hip
• CPC Class Codes: A61F 2/34 Acetabular cups
• CPC Class Codes: A61F 2/36 Femoral heads ; Femoral endoprostheses
• CPC Class Codes: A61F 2/3662 Femoral shafts
• CPC Class Codes: A61F 2/38 for elbows or knees
• CPC Class Codes: A61F 2/3859 Femoral components
• CPC Class Codes: A61F 2/389 Tibial components A61F2/3868 takes precedence
• CPC Class Codes: A61F 2002/30014 differing in elasticity, stiffness or compressibility
• CPC Class Codes: A61F 2002/30153 rectangular
• CPC Class Codes: A61F 2002/30878 with non-sharp protrusions, for instance contacting the bone for anchoring, e.g. keels, pegs, pins, posts, shanks, stems, struts
• CPC Class Codes: A61F 2002/30929 having at least two superposed coatings
• CPC Class Codes: A61F 2002/30934 Special articulating surfaces
• CPC Class Codes: A61F 2002/30968 Sintering
• CPC Class Codes: A61F 2002/3611 Heads or epiphyseal parts of femur
• CPC Class Codes: A61F 2002/365 Connections of heads to necks
• CPC Class Codes: A61F 2002/4631 the prosthesis being specially adapted for being cemented
• CPC Class Codes: A61F 2230/0019 rectangular
• CPC Class Codes: A61F 2250/0018 differing in elasticity, stiffness or compressibility
• CPC Class Codes: A61F 2310/00011 : Metals or alloys
• CPC Class Codes: A61F 2310/00952 : Coating, pre-coating or prosthesis-covering structure made of bone cement, e.g. pre-applied PMMA cement mantle
• CPC Class Codes: A61L 2420/02 : Methods for coating medical devices
• CPC Class Codes: A61L 27/26 : Mixtures of macromolecular compounds
• CPC Class Codes: A61L 27/34 : Macromolecular materials
• CPC Class Codes: C08L 23/06 : Polyethene
• CPC Class Codes: C08L 2666/04 : Macromolecular compounds according to groups C08L7/00 - C08L49/00, or C08L55/00 - C08L57/00; Derivatives thereof
• CPC Class Codes: C08L 33/12 : Homopolymers or copolymers of methyl methacrylate
• CPC Class Codes: C09D 133/12 : Homopolymers or copolymers of methyl methacrylate
• CPC Class Codes: Y10S 623/923 : Bone

Abstract

The present invention is directed to a polymeric prosthesis precoated with a bone cement compatible polymer. The bone cement compatible polymer coating, is provided by an activated powder mixture of polymethyl methacrylate and ultra high molecular weight polyethylene which is bonded to the outer surface of the prosthesis by sintering. Once bonded to a polymeric prosthesis in accordance with the present invention, the precoat strengthens the interface between a bone cement and a prosthesis when the prosthesis is later implanted. The inner layer of the prosthesis may be provided of cross-linked UHMWPE powder sintered with virgin UHMWPE powder or fibers to provide a intermediate layer(s) of the coating present on the prosthesis. The precoat also decreases the likelihood that the prosthesis will loosen and break away from the cement over time. The polymeric implant product of the present invention is particularly well suited for use as an acetabular cup or a tibia plateau in replacing hip joints and knee joints respectively.

Claims

1. A process for coating a polymeric prosthesis prior to being implanted into the body, said process comprising the steps of:

providing a prosthesis having a shape configured to be implanted into a prepared area of the body, said prosthesis including a polymeric member, said polymeric member being adapted to be attached to an adjoining bone with a bone cement;

applying a coating of a bone cement compatible polymer to at least a portion of said polymeric member of said prosthesis; and

sintering said coating of said bone cement compatible polymer to said portion of said polymeric member.

2. A process as defined in

claim 1

, wherein said polymeric member comprises ultrahigh molecular weight polyethylene.

3. A process as defined in

claim 1

, wherein said coating of said bone cement compatible polymer comprises a plurality of sintered coatings, said plurality of coatings is up to about 2 millimeters thick.

4. A process as defined in

claim 1

, wherein said coating of said bone cement compatible polymer has a substantially pore free outer surface.

5. A process as defined in

claim 1

, wherein said bone cement compatible polymer comprises an acrylic polymer.

6. A process as defined in

claim 1

, wherein said bone cement compatible polymer comprises polymethyl methacrylate.

7. A process as defined in

claim 1

, wherein said prosthesis is made entirely of a polymer.

8. A process as defined in

claim 1

, wherein said coating of said bone cement compatible polymer is sintered upon said polymeric member of said prosthesis according to the following steps:

contacting said polymeric member with an activated mixture of PMMA and UHMWPE powder, thereby forming a surface layer of activated powder;

sintering said surface layer to said polymeric member, thereby providing a melted surface coating of UHMWPE and PMMA, said coating compatible with a bone cement.

9. A process as defined in

claim 8

, wherein said activated mixture is provided by a process of comprising:

combining UHMWPE powder with an excess of MMA liquid monomer;

removing said MMA monomer from said UHMEPE powder;

mixing said UHMWPE powder with an excess of a liquid MMA+PMMA stock solution;

drying said UHMWPE powder, thereby providing an activated powder of UHMWPE having a surface coated by PMMA.

10. A process for coating a polymeric prosthesis with a bone cement compatible polymer prior to implantation for improving the bond between said prosthesis and a bone cement, said process comprising the steps of:

providing a prosthesis made from a polymer;

contacting a portion of a surface of said prosthesis with an activated powder mixture of UHMWPE and PMMA; and

,

bonding said activated mixture to said portion of a surface of a prosthesis through a combination of heat and pressure, thereby providing a coating compatible with a bone cement.

11. A process as defined in

claim 10

, wherein said prosthesis is made from a polymer comprising polyethylene.

12. A process as defined in

claim 11

, wherein said activated powder is provided by a process comprising:

combining UHMWPE powder with an excess of MMA liquid monomer;

removing said MMA monomer from said UHMWPE powder;

mixing said UHMWPE powder with an excess of a liquid MMA+PMMA stock solution;

drying said UHMWPE powder, thereby providing an activated powder mixture of UHMWPE coated with PMMA.

13. A process as defined in

claim 12

, wherein said liquid MMA+PMMA stock solution is about a 9:

1 volume to weight ratio of MMA to PMMA.

14. A process as defined in

claim 10

, wherein said bonding step further comprises sintering at a temperature greater than 150 degrees C.

15. A process as defined in

claim 10

, wherein said bonding step further comprises supplying a pressure of about at least 20 MPa.

16. A process as defined in

claim 10

, further comprising the step of providing an interfacial layer between said surface of said prosthesis and said coating, said interfacial layer selected from the group of virgin polyethylene, cross-linked polyethylene, polyethylene fibers, and combinations thereof.

17. A process as defined in

claim 16

, further comprising the step of providing an interfacial layer comprising cross-linking polyethylene to the surface layer of a polyethylene prosthesis.

33. A process as defined in

claim 14

, wherein said sintering step further comprises sintering under an inert atmosphere.

18. An implant product for implantation into the body comprising:

a prosthetic member made from a polymer having a shape configured to be implanted into a prepared area of the body, said prosthetic member defining a surface adapted to be attached to an adjoining bone with a bone cement composition;

a coating covering said surface of said prosthetic member, said coating being made from a bone cement compatible polymer; and

an interfacial layer between said surface of said prosthetic member and said coating, said coating being bonded to said surface across said interfacial layer, said interfacial layer being made from a mixture of cross-linked polyethylene, virgin polyethylene, and polyethylene fibers.

19. An implant product as defined in

claim 18

, wherein said polymer used to make said prosthetic member comprises polyethylene.

20. An implant product as defined in

claim 19

, wherein said bone cement compatible polymer comprises a sintered mixture of UHMWPE and polymethyl methacrylate.

21. An implant product as defined in

claim 20

, wherein said polymethyl methacrylate coating is bonded to said polyethylene across said interfacial layer according to the following steps:

contacting said prosthetic member with an activated mixture comprising UHMWPE and PMMA; and

applying a combination of heat and pressure to said prosthetic member and said activated mixture, causing said activated mixture to melt, forming a surface coating suitable for bonding with an acrylate based bone.

22. An implant product as defined in

claim 18

, wherein said interfacial layer is at least 1 millimeter thick.

23. An implant product as defined in

claim 18

, wherein said coating of said bone cement compatible polymer is up to about 2 millimeters thick and has a substantially pore free outer surface.

24. An implant product as defined in

claim 18

, wherein said implant product comprises an acetabular cup or a tibia plateau.

25. A method of orthopedic implantation of a polymeric prosthesis with a bone cement composition comprising the steps of:

providing a polymeric prosthesis to be implanted;

contacting said prosthesis with an activated powder mixture of UHMWPE and PMMA;

sintering said activated powder mixture to said prosthesis, thereby providing a precoated prosthesis;

preparing an area within a patient to receive the precoated polymeric prosthesis;

inserting a quantity of a bone cement composition into the prepared area;

immediately positioning said precoated polymeric prosthesis in the prepared area; and

permitting said bone cement composition to cure for bonding said precoated polymeric prosthesis with said prepared area.

26. A process as defined in

claim 25

, wherein said polymeric prosthesis is made from a polymer comprising UHMWPE and said bone cement compatible polymer comprises a melted mixture of polymethyl methacrylate and UHMWPE.

27. A coating composition for a polymeric member comprising:

a sinterable mixture of an adhesive polymer and a structural polymer.

28. The coating composition according to

claim 27

wherein said adhesive polymer is PMMA.

29. The coating composition according to

claim 27

wherein said structural polymer is polyethylene.

30. The coating composition according to

claim 27

wherein said sinterable mixture comprises a bone cement compatible polymer of PMMA and a structural polymer of UHMWPE.

31. The coating composition according to

claim 27

wherein said sinterable mixture further comprises MMA.

32. The coating composition according to

claim 30

wherein said sinterable mixture further comprises MMA.

34. The coating composition according to

claim 32

wherein said MMA reacts under sintering conditions to form PMMA.