Bone cement containing coated radiopaque particles and its preparation

• US 20040157952A1
• Filed: 10/20/2003
• Published: 08/12/2004
• Est. Priority Date: 05/30/2001
• Status: Active Grant

• Current Assignee: Tecres S.P.A.
• Original Assignee: Tecres S.P.A.
• Inventors: Robotti, Pierfrancesco, Soffiati, Renzo
• Granted Patent: US 7,186,761 B2
• Time in Patent Office: Days
• US Class Current: 523/115
• CPC Class Codes: A61L 24/001 Use of materials characterised by their function or physical properties
• CPC Class Codes: A61L 24/0089 containing inorganic fillers not covered by groups A61L24/0078 or A61L24/0084
• CPC Class Codes: A61L 2430/02 for reconstruction of bones; weight-bearing implants
• CPC Class Codes: A61L 27/16 obtained by reactions only involving carbon-to-carbon unsaturated bonds
• CPC Class Codes: A61L 27/44 having a macromolecular matrix
• 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: C08L 33/12 Homopolymers or copolymers of methyl methacrylate

Abstract

An acrylic radiopaque bone cement for orthopedic use comprises a solid phase composed of a mixture of at least one poly(methyl acrylate)-based polymer, one free-radical polymerization initiator and one or more substances opaque to X-rays, and a liquid phase substantially composed of a mixture of at least one monomer, one accelerator and one stabilizer. The radiopaque substances comprise metallic tungsten and tantalum particles, compounds or mixtures thereof, covered with a polymer coating compatible with said bone cement. The coating layer of the particles of radiopaque substances is an acrylic polymer based on poly(methyl methacrylate). The amount of radiopacifying element is between 1% and 20% by weight, relative to the solid phase, preferably between 2% and 5% by weight, relative to the solid phase. The solid phase may additionally comprise one or more pharmacologically active substances. The method for its preparation consists in preparing the radiopacifying material by coating the metal particles with a layer of a polymer which is compatible with the matrix and exhibits oxygen barrier properties such that said layer does not dissolve completely in the liquid phase so as to keep its oxygen barrier properties at least partly unchanged.

Claims

1. Radiopaque acrylic bone cement for orthopaedic use, comprising a solid phase essentially composed of a powder of at least one poly(methyl acrylate)-based polymer, one free-radical polymerization initiator and one radiopacifying material, and a liquid phase substantially composed of a mixture of at least one monomer, one accelerator and one stabilizer, said solid phase being capable of hardening upon mixing thereof with said liquid phase so as to give a bone cement matrix, wherein said radiopacifying material comprises particles of metals having molecular weight equal to or higher than 130 Dalton, mixtures, alloys or compounds thereof, which particles are covered with a coating layer of a polymer which is compatible with said matrix, characterised in that said metal particles comprise tantalum and/or tungsten particles, said polymer coating layer covering each of said metal particles to protect them from exposure to oxygen, said coating layer being so sized that it does not completely dissolve in said liquid phase during polymerisation of said bone cement so as to keep its oxygen barrier properties.

2. Acrylic bone cement according to claim 1, characterized in that said metals of high molecular weight are selected in such a way as to have an oxygen content of less than 300 ppm by weight.

3. Acrylic bone cement according to claim 1, characterized in that said coating layer of said metal particles is a poly(methyl methacrylate)-based polymer.

4. Acrylic bone cement according to claim 1, characterized in that each single uncoated metal particle has an average diameter of between 1 μ

m and 100 μ

m.

5. Acrylic bone cement according to claim 1, characterized in that each single coated metal particle has an average diameter of between 1 μ

m and 150 μ

m.

6. Acrylic bone cement according to claim 1, characterized in that said polymer coating layer covers an aggregate of previously synthesized nanometre-sized metal particles.

7. Acrylic bone cement according to claim 6, characterized in that said metal particles of said aggregate have an average diameter of between 25 nm and 1000 nm.

8. Acrylic bone cement according to claim 1, characterized in that the molecular weight of the coating polymer of said particles which is compatible with said bone cement is between 20,000 and 800,000 Dalton.

9. Acrylic bone cement according to claim 1, characterized in that the molecular weight of the coating polymer of said particles which is compatible with said bone cement is between 300,000 and 800,000 Dalton.

10. Acrylic bone cement according to claim 1, characterized in that the weight ratio between the metal contained in said particles and their coating polymer is between 95:

5 and 70;

30.

11. Acrylic bone cement according to any of the preceding claims, characterized in that the amount of the radiopacifying material is between 1 and 20% by weight, relative to said solid phase.

12. Acrylic bone cement according to claim 11, characterized in that the amount of radiopacifying material is preferably between 2% and 5% by weight, relative to said solid phase.

13. Acrylic bone cement according to any one of the preceding claims, characterized in that said solid phase further comprises one or more pharmacologically active substances.

14. Acrylic bone cement according to any one of the preceding claims, characterized in that said solid phase and said coated radiopaque particles are contained in the same package.

15. Acrylic bone cement according to any one of the preceding claims, characterized in that said solid phase and said coated radiopaque particles are contained in separate packages.

16. Acrylic bone cement according to any one of the preceding claims, characterized in that said solid phase comprises poly(methyl methacrylate), poly(methyl methacrylate/styrene), poly(butyl methacrylate) and copolymers thereof.

17. Method for preparing a radiopaque acrylic bone cement for orthopaedic use, comprising the steps of:

preparing a solid phase essentially composed of a powder of at least one poly(methyl methacrylate)-based polymer, one free-radical polymerization initiator and one radiopacifying material;

preparing a liquid phase composed of a mixture of at least one monomer, one accelerator and one stabilizer,

mixing said solid phase with said liquid phase so as to perform polymerization in such a way that a bone cement matrix is obtained,

in which the radiopacifying material is obtained by preparing a powder of metal particles of molecular weight equal or higher than 130 Dalton, mixtures, alloys or compounds thereof, said metal particles comprising tantalum and/or tungsten particles, and coating said particles with a layer of a polymer which is compatible with said matrix, said polymer coating layer being so selected to protect said metal particles from exposure to oxygen, said polymer coating layer being so sized that it does not completely dissolve in said liquid phase so as to keep its oxygen barrier properties.

19. Method according to claim 17, characterized in that said metal particles, before being coated, are subjected to a step of removal of their surface layer.

20. Method according to claim 17, characterized in that said coating layer of said metal particles is obtained by adding said polymer, dissolved in water-miscible organic solvents, to an aqueous dispersion of said radiopaque metal particles, followed by evaporation and drying of said solvents.