Method of Forming a Polymer Component

• US 20110153025A1
• Filed: 06/21/2010
• Published: 06/23/2011
• Est. Priority Date: 12/21/2009
• Status: Active Grant

• Current Assignee: Jointmedica Ltd.
• Original Assignee: Derek J. Mcminn
• Inventors: McMinn, Derek J.
• Granted Patent: US 9,017,416 B2
• Time in Patent Office: Days
• US Class Current: 623/20.32
• CPC Class Codes: A61F 2/30771 applied in original prostheses, e.g. holes or grooves
• CPC Class Codes: A61F 2/3094 Designing or manufacturing processes
• CPC Class Codes: A61F 2/34 Acetabular cups
• CPC Class Codes: A61F 2/38 for elbows or knees
• CPC Class Codes: A61F 2/4609 of acetabular cups
• CPC Class Codes: A61F 2002/30026 differing in wear resistance
• CPC Class Codes: A61F 2002/30112 Rounded shapes, e.g. with rounded corners
• CPC Class Codes: A61F 2002/30143 hexagonal
• CPC Class Codes: A61F 2002/30205 conical
• CPC Class Codes: A61F 2002/30207 Double convex cones, i.e. element having two convex cones, one at each of its opposite ends
• CPC Class Codes: A61F 2002/30324 differing in thickness
• CPC Class Codes: A61F 2002/30331 made by longitudinally pushing a protrusion into a complementarily-shaped recess, e.g. held by friction fit
• CPC Class Codes: A61F 2002/30352 Protrusion and recess of D-shaped cross-section
• CPC Class Codes: A61F 2002/30378 Spherically-shaped protrusion and recess
• CPC Class Codes: A61F 2002/30448 using adhesives
• CPC Class Codes: A61F 2002/30462 retained or tied with a rope, string, thread, wire or cable
• CPC Class Codes: A61F 2002/3052 unrestrained in only one direction, e.g. moving unidirectionally
• CPC Class Codes: A61F 2002/30561 breakable or frangible
• CPC Class Codes: A61F 2002/30685 Means for reducing or preventing the generation of wear particulates
• CPC Class Codes: A61F 2002/30841 Sharp anchoring protrusions for impaction into the bone, e.g. sharp pins, spikes
• 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 2002/30889 : Arcuate pegs
• CPC Class Codes: A61F 2002/30904 : serrated profile, i.e. saw-toothed
• CPC Class Codes: A61F 2002/30971 : Laminates, i.e. layered products
• CPC Class Codes: A61F 2002/344 : the inner shell having an inner hip femoral head-receiving cavity offset from its centre line
• CPC Class Codes: A61F 2002/4681 : by applying mechanical shocks, e.g. by hammering
• CPC Class Codes: A61F 2220/0025 : Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
• CPC Class Codes: A61F 2220/0033 : made by longitudinally pushing a protrusion into a complementary-shaped recess, e.g. held by friction fit
• CPC Class Codes: A61F 2220/005 : using adhesives
• CPC Class Codes: A61F 2220/0075 : sutured, ligatured or stitched, retained or tied with a rope, string, thread, wire or cable
• CPC Class Codes: A61F 2230/0004 : Rounded shapes, e.g. with rounded corners
• CPC Class Codes: A61F 2230/0017 : Angular shapes
• CPC Class Codes: A61L 27/14 : Macromolecular materials
• CPC Class Codes: A61L 27/50 : Materials characterised by their function or physical properties , e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
• CPC Class Codes: A61L 27/505 : Stabilizers
• CPC Class Codes: B29C 2043/147 : by compressing after the laying of further material
• CPC Class Codes: B29C 2043/148 : using different moulds
• CPC Class Codes: B29C 43/003 : characterised by the choice of material
• CPC Class Codes: B29C 43/146 : for making multilayered articles
• CPC Class Codes: B29K 2023/06 : PE, i.e. polyethylene
• CPC Class Codes: B29K 2105/0044 : Stabilisers, e.g. against oxydation, light or heat
• CPC Class Codes: B29L 2031/7532 : Artificial members, protheses
• CPC Class Codes: B32B 1/00 : Layered products having a non-planar shape
• CPC Class Codes: B32B 15/08 : of synthetic resin
• CPC Class Codes: B32B 2535/00 : Medical equipment, e.g. bandage, prostheses, catheter medical patches B32B2556/00
• CPC Class Codes: B32B 3/00 : Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
• CPC Class Codes: B32B 7/12 : using interposed adhesives or interposed materials with bonding properties
• CPC Class Codes: B33Y 80/00 : Products made by additive manufacturing
• CPC Class Codes: C08J 2300/00 : Characterised by the use of unspecified polymers
• CPC Class Codes: C08J 2323/06 : Polyethene
• CPC Class Codes: C08J 3/00 : Processes of treating or compounding macromolecular substances
• CPC Class Codes: C08J 3/24 : Crosslinking, e.g. vulcanising, of macromolecules mechanical aspects B29C35/00; crosslinking agents C08K
• CPC Class Codes: C08J 3/28 : Treatment by wave energy or particle radiation
• CPC Class Codes: C08K 2201/012 : Additives improving oxygen scavenging properties
• CPC Class Codes: C08K 5/1545 : Six-membered rings

Abstract

This invention relates to a method of forming a polymer component and comprises blending polymer particles with antioxidant to form a mixture in which the antioxidant coats the polymer particles, irradiating the mixture to cross-link the polymer particles therein and forming the irradiated mixture into a consolidated component. The invention also relates to a method of forming an articular surface for a prosthesis and a prosthesis having a polymer articular bearing surface wherein at least one pre-determined portion of the bearing surface is provided with cross-linked polymer bonds.

Claims

1. A method of forming a polymer component comprising:

blending polymer particles with antioxidant to form a mixture in which the antioxidant coats the polymer particles;

irradiating the mixture to cross-link molecules therein; and

forming the irradiated mixture into a consolidated component.

2. The method according to claim 1 wherein the antioxidant comprises vitamin E constituting 0.1%, 0.5%, 1%, 2%, or 3% of the weight of the mixture.

3. The method according to claim 1 wherein the step of forming the irradiated mixture into a consolidated component comprises the use of heat and/or pressure.

4. The method according to claim 1 wherein the polymer particles are provided in the form of a resin or a hydrogel.

5. The method according to claim 1 wherein the antioxidant is provided in the form of a liquid, powder, solution or suspension.

6. The method according to claim 1 further comprising the step of processing the consolidated component using high pressure and/or high temperature crystallization.

7. The method according to claim 1 wherein the consolidated component forms a product, a part of a product, or bar stock from which a product or a part of a product can be made.

8. The method according to claim 1 wherein the product is constituted by a bearing component, a medical device, or a prosthesis.

9. The method according to claim 8 wherein the prosthesis is configured for use in the hip, knee, spine, neck, ankle, toe, shoulder, elbow, wrist, finger or thumb.

10. The method according to claim 7 wherein the part constitutes the whole or a part of at least one surface of a product.

11. The method according to claim 10 wherein the part constitutes the whole or a part of an articular surface for an acetabular cup prosthesis and, optionally, the prosthesis includes one or more further cross-linked surface and/or one or more further cross-linked portion of a surface.

12. A method of forming an articular surface for a prosthesis comprising:

forming a first layer comprising a first polymer;

forming a second layer comprising a second polymer, wherein the second layer constitutes the whole or a part of an articular surface layer;

joining the first and second layers together to form an articular surface component;

irradiating the second polymer to cross-link the molecules therein; and

facilitating the consumption of free radicals in the second layer to thereby minimise the risk of oxidation of the second layer.

13. The method according to claim 12 wherein the first and second polymers are the same prior to the step of irradiation.

14. The method according to claim 12 wherein the first layer further comprises an antioxidant.

15. The method according to claim 14 wherein the antioxidant comprises vitamin E.

16. The method according to claim 12 wherein the step of facilitating the consumption of free radicals in the second layer is performed by ensuring that the second layer has a concentration of an antioxidant that is low enough to allow polymer cross-linking with radiation but high enough to consume the free radicals generated as a result of the radiation.

17. The method according to claim 14 wherein the step of facilitating the consumption of free radicals comprises heating the component to encourage the antioxidant in the first layer to diffuse into the second layer to consume the free radicals therein.

18. The method according to claim 17 wherein in the step of facilitating the consumption of free radicals, the component is heated to below its melting point.

19. The method according to claim 12 wherein the step of joining the first and second layers together comprises hot compression moulding.

20. The method according to claim 12 wherein the second polymer is irradiated before or after it is formed into the second layer.

21. The method according to claim 12 wherein the second polymer is irradiated after the second layer has been joined to the first layer.

22. The method according to claim 12 wherein the steps of forming the first and/or second layers may comprise moulding.

23. The method according to claim 22 wherein the moulding comprises hot or cold compression moulding.

24. The method according to claim 22 wherein the first layer is moulded from a first powder comprising the first polymer.

25. The method according to claim 22 wherein the second layer is moulded from a second powder comprising the second polymer.

26. The method according to claim 12 wherein the steps of forming the first and/or second layers may comprise machining.

27. The method according to claim 26 wherein the first layer is machined from a first bar stock comprising the first polymer.

28. The method according to claim 26 wherein the second layer is machined from a second bar stock comprising the second polymer.

29. The method according to claim 24 wherein the step of forming the first layer comprises compression moulding the first layer by placing the first powder including an antioxidant into a mould and compression stamping the powder into the desired shape of the first layer.

30. The method according to claim 29 wherein the desired shape includes multiple protrusions in the intended wear zone to diffuse the interface between the first and second layers.

31. The method according to claim 25 wherein the step of forming the second layer comprises compression moulding by placing the second powder over the whole or part of the formed first layer and applying a second mould to compression stamp the desired shape of the second layer.

32. The method according to claim 12 wherein the first layer is compression moulded by applying a first piston through a syringe-like shroud.

33. The method according to claim 32 wherein the first piston is then removed from the shroud and the second polymer passed down the shroud before a second piston is applied through the shroud to compression mould the second layer onto the first layer.

34. The method according to claim 12 wherein the step of forming the second layer comprises compression moulding by placing the second polymer into a second mould and hot or cold compression stamping the second polymer into the desired shape of the second layer.

35. The method according to claim 12 wherein the articular surface component is configured for use in an acetabular cup prosthesis and, optionally, the prosthesis includes one or more further cross-linked surface and/or one or more further cross-linked portion of a surface.

36. A method of forming an articular surface for a prosthesis comprises:

forming a polymer component comprising an antioxidant;

selectively removing the antioxidant, wholly or in part, from a portion of an articular surface layer;

irradiating the component to cross-link the molecules in said portion; and

facilitating the consumption of free radicals in said portion to thereby minimise the risk of oxidation of said portion.

37. The method according to claim 36 wherein the step of removing the antioxidant from the portion of the articular surface layer comprises leaching out the antioxidant using a surfactant.

39. The method according to claim 36 or 38 wherein the antioxidant comprises vitamin E.

40. The method according to claim 36 or 38 wherein the step of forming the polymer component comprises moulding and/or machining.

41. The method according to claim 36 or 38 wherein the step of facilitating the consumption of free radicals is performed by ensuring that the portion/articular surface layer has a concentration of antioxidant that is low enough to allow polymer cross-linking with radiation but high enough to consume the free radicals generated as a result of the radiation.

42. The method according to claim 36 or 38 wherein the step of facilitating the consumption of free radicals comprises heating the component to encourage the antioxidant in the remainder of the polymer component to diffuse into said portion/articular surface layer to consume the free radicals therein.

43. The method according to claim 36 or 38 wherein the articular surface is configured for use in an acetabular cup prosthesis and, optionally, the prosthesis includes one or more further cross-linked surface and/or one or more further cross-linked portion of a surface.

38. A method of forming an articular surface for a prosthesis comprises:

forming a polymer component comprising an antioxidant;

selectively inactivating the antioxidant, wholly or in part, from the whole or a portion of an articular surface layer;

irradiating the component to cross-link the molecules in said articular surface layer; and

facilitating the consumption of free radicals in said articular surface layer to thereby minimise the risk of oxidation of said articular surface layer.

44. A prosthesis having a polymer articular bearing surface wherein at least one pre-determined portion of said bearing surface is provided with cross-linked polymer bonds.

45. The prosthesis according to claim 44 wherein the pre-determined portion corresponds to a pre-determined wear zone.

46. The prosthesis according to claim 44 wherein the polymer is relatively thick in the region of the pre-determined portion.

47. The prosthesis according to claim 44 wherein multiple protrusions are provided at the interface between the cross-linked polymer portion and the remainder of the polymer.

48. The prosthesis according to claim 47 wherein the protrusions are in the form of ridges or fingers.

49. The prosthesis according to claim 47 wherein the protrusions are provided by introducing roughness at the interface between the two types of polymer.

50. The prosthesis according to claim 44 wherein the prosthesis is configured as an acetabular cup.

51. The prosthesis according to claim 50 wherein the acetabular cup comprises a metal outer shell and a polymer inner liner, the inner surface of which constitutes the articular bearing surface having said pre-determined portion provided with cross-linked polymer bonds.

52. The prosthesis according to claim 44 wherein the prosthesis is configured as a femoral component or a tibial component for use in total knee replacement techniques.

53. The prosthesis according to claim 52 wherein the articular bearing surface is constituted by the condylar bearing surfaces provided on the tibial component.

54. The prosthesis according to claim 52 wherein the articular bearing surface is constituted by one or both mating surfaces of a cam and peg follower, one of which is provided on the femoral component and the other of which is provided on the tibial component.