Method for fabricating artificial bone implant green parts

• US 5,639,402 A
• Filed: 08/08/1994
• Issued: 06/17/1997
• Est. Priority Date: 08/08/1994
• Status: Expired due to Term

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Marcus, Harris L., Lee, Goonhee, Lagow, Richard J., Beaman, Joseph J., Barlow, Joel W., Crawford, Richard H.
• Primary Examiner(s): Fiorilla, Christopher A.
• Application Number:
  US08/288,120
• Time in Patent Office: 1,044 Days
• Field of Search: 264/16, 264/60, 264/56, 264/63, 264/497, 264/430, 264/482, 264/6, 264/434
• US Class Current: 264/6
• CPC Class Codes: A61F 2/28 Bones joints A61F2/30
• CPC Class Codes: A61F 2/2875 Skull or cranium A61F2/2803 and A61F2/3099 take precedence
• CPC Class Codes: A61F 2/3094 Designing or manufacturing processes
• CPC Class Codes: A61F 2/30942 for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques
• CPC Class Codes: A61F 2002/30199 Three-dimensional shapes
• CPC Class Codes: A61F 2002/30929 having at least two superposed coatings
• CPC Class Codes: A61F 2002/30952 using CAD-CAM techniques or NC-techniques
• CPC Class Codes: A61F 2002/30968 Sintering
• CPC Class Codes: A61F 2230/0063 Three-dimensional shapes
• CPC Class Codes: A61F 2310/00293 containing a phosphorus-containing compound, e.g. apatite
• CPC Class Codes: A61L 27/46 with phosphorus-containing inorganic fillers
• CPC Class Codes: B29C 64/153 using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• CPC Class Codes: B29C 64/165 using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
• CPC Class Codes: B29L 2031/7532 Artificial members, protheses
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 70/00 Materials specially adapted for additive manufacturing
• CPC Class Codes: B33Y 80/00 Products made by additive manufacturing
• CPC Class Codes: C04B 2235/3201 Alkali metal oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3212 Calcium phosphates, e.g. hydroxyapatite
• CPC Class Codes: C04B 2235/36 Glass starting materials for making ceramics, e.g. silica glass
• CPC Class Codes: C04B 2235/5409 : expressed by specific surface values
• CPC Class Codes: C04B 2235/5436 : micrometer sized, i.e. from 1 to 100 micron
• CPC Class Codes: C04B 2235/6026 : Computer aided shaping, e.g. rapid prototyping
• CPC Class Codes: C04B 2235/608 : Green bodies or pre-forms with well-defined density
• CPC Class Codes: C04B 2235/61 : Mechanical properties, e.g. fracture toughness, hardness, Young's modulus or strength
• CPC Class Codes: C04B 2235/616 : Liquid infiltration of green bodies or pre-forms
• CPC Class Codes: C04B 2235/6584 : at an oxygen percentage below that of air
• CPC Class Codes: C04B 2235/665 : Local sintering, e.g. laser sintering
• CPC Class Codes: C04B 2235/77 : Density
• CPC Class Codes: C04B 2235/80 : Phases present in the sintered or melt-cast ceramic products other than the main phase
• CPC Class Codes: C04B 2235/96 : Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 2235/9615 : Linear firing shrinkage
• CPC Class Codes: C04B 35/447 : based on phosphates , e.g. hydroxyapatite
• CPC Class Codes: C04B 35/628 : Coating the powders or the macroscopic reinforcing agents
• CPC Class Codes: C04B 35/63424 : Polyacrylates; Polymethacrylates

Abstract

Bone implants are made from calcium phosphate powders by selectively fusing layers of calcium powders that have been coated or mixed with polymer binders. The calcium powder mixture may be formed into layers and the polymer fused with a laser. Complex three-dimensional geometrical shapes can be automatically replicated or modified using this approach.

Claims

1. A method for making an implant green part, comprising the steps of:

(a) forming a mixture of a calcium phosphate composition and a polymer binder, wherein the calcium phosphate composition is calcium metaphosphate, calcium pyrophosphate, or mixtures thereof; and

(b) selectively fusing the polymer binder with a laser beam to form the implant green part.

2. The method of claim 1, wherein the mixture comprises a plurality of agglomerated polymer-coated calcium phosphate particles.

3. The method of claim 2, wherein the polymer-coated particles are formed by spray drying an aqueous mixture of the calcium phosphate and the polymer binder.

4. The method of claim 1, further comprising the steps of infiltrating and thermally sintering the implant green part.

5. The method of claim 4, wherein the implant green part is infiltrated with a calcium phosphate solution.

6. The method of claim 1, further comprising the step of thermally sintering the implant green part.

7. The method of claim 6, further comprising the steps of infiltrating and again thermally sintering the implant green part.

8. The method of claim 7, wherein the implant green part is infiltrated with a calcium phosphate solution.

9. The method of claim 1, wherein the polymer binder is selectively fused to replicate a desired geometrical shape.

10. The method of claim 1, wherein the polymer binder is selectively fused to form a desired geometrical shape.

11. The method of claim 9 or claim 10, wherein the desired geometrical shape is communicated to the laser beam by a computer.

12. The method of claim 11, wherein the desired geometrical shape is obtained from computed tomographic data.

13. The method of claim 11, wherein the desired geometrical shape is obtained from computer aided design software data.

14. The method of claim 1, wherein the calcium phosphate composition is prepared by reacting aqueous solutions of hydroxyapatite and phosphoric acid.

15. The method of claim 1, wherein the calcium phosphate composition contains:

from about 25 to about 45 percent by weight calcium oxide, or from about 0.5 to about 2 percent by weight sodium oxide.

16. The method of claim 1, wherein the calcium phosphate comprises calcium metaphosphate.

17. The method of claim 1, wherein the calcium phosphate has a mean particle size of from about 5 to about 100 microns.

18. The method of claim 1, wherein the calcium phosphate has a mean particle size of from about 30 to about 50 microns.

19. The method of claim 1, wherein the polymer binder has the following properties:

(a) a T_g of between about 40°

C. and about 100°

C.; and

(b) a melt flow index of between about 1 and about 50 g/10 minutes at 200°

C. and 75 psi extrusion pressure.

20. The method of claim 19, wherein the polymer binder comprises a homopolymer, copolymer, or terpolymer of methyl methacrylate.

21. The method of claim 20, wherein the polymer binder comprises a poly(methyl methacrylate-co-n-butyl methacrylate) copolymer.

22. A method for making an implant green part, comprising the steps of:

(a) forming a mixture of a calcium phosphate composition and a polymer binder, wherein the calcium phosphate composition is calcium metaphosphate, calcium pyrophosphate, or mixtures thereof;

(b) forming a layer of the mixture;

(c) selectively fusing the polymer binder with a laser beam; and

(d) repeating steps (b) and (c) a desired number of times to form a plurality of layers, wherein each layer is fused to adjacent layers to form the implant green part.

23. The method of claim 22, wherein the thickness of each layer is from about 3 to about 12 thousandths of an inch.

24. The method of claim 22, wherein the implant green part has a mean pore size of from about 100 to about 300 microns.

25. The method of claim 22, wherein the implant green part has a relative density of from about 50 to about 80%.