GB2611690A

GB2611690A - Process for production of metal scaffolds and foams

Info

Publication number: GB2611690A
Application number: GB2300516.8A
Authority: GB
Inventors: Buhagiar Joseph; Tonna Christabelle; Nigel Manvers Tallowin Stephen; Grech Maurice; Curmi Albert; Pierre Schembri Wismayer
Original assignee: Universita ta Malta UM
Current assignee: Universita ta Malta UM
Priority date: 2020-06-18
Filing date: 2021-06-17
Publication date: 2023-04-12
Also published as: GB202009324D0; GB202300516D0; WO2021255195A1

Abstract

The present invention relates to a process for preparing a metal scaffold or foam, for instance a metallic scaffold suitable for use as a bone implant, and in particular a biodegradable metallic implant. The process comprises the steps of preparing a template, coating the template with a solid composition comprising metallic powder, and then material removal of the polymer template. The present invention also relates to a metallic scaffold or foam that is obtainable by said process. The present invention also relates to the use of a solid composition comprising metallic powder in a process of coating an additive- manufactured polymer template to produce a metal particle-coated polymer template.

Claims

1. A process for preparing a metallic scaffold or foam, the process comprising: (a) preparing a polymer template; (b) coating the polymer template by contacting the template with a solid composition comprising metallic powder to provide a metal particle-coated polymer template; and (c) effecting the material removal of the polymer template to provide the metallic scaffold or foam.

2. A process according to claim 1, wherein at least 90% of the metallic particles by number in the solid composition have a diameter of less than 20 pm, preferably wherein at least 90% of the metallic particles by number in the solid composition have a diameter of less than 10 pm, and more preferably wherein at least 90% of the metallic particles by number in the solid composition have a diameter of less than 5 pm.

3. A process according to claim 1 or claim 2, wherein the metallic powder comprises iron, magnesium, zinc, titanium or aluminium, and preferably comprises a mixture of any of the foregoing elements with one or more different elements selected from: Mn, Pd, Pt, Au, Ag, Cu, Al, Ti, Fe, Mg, Zn, Ca, Si, P, Cr, V, B, Zr, Ta, C, N, S, Mo and Ni.

4. A process according to claim 3, wherein the metallic powder comprises a mixture of iron with one or more of the following elements: Mn, Pd, Pt, Au, Ag, Cu, Al, Ti, Mg, Zn, Ca, Si, P, Cr, V, B, Zr, Ta, C, N, S, Mo and Ni; preferably wherein the metallic powder comprises an iron- manganese alloy and, optionally, one or more of the following elements: Pd, Pt, Au, Ag, Cu, Al, Ti, Mg, Zn, Ca, Si, P, Cr, V, B, Zr, Ta, C, N, S, Mo and Ni.

5. A process according to claim 3 or claim 4, wherein the metallic powder further comprises silver, and is preferably an iron-silver alloy, an iron-manganese-silver alloy, an iron-manganese- carbon-silver alloy, or an iron-manganese-carbon-silicon-silver alloy.

6. A process according to any one of claims 1 to 5, wherein step (b) comprises a dry-coating method for coating the polymer template, preferably wherein the dry-coating method is selected from: tumbling the polymer template in the presence of the solid composition, preferably in an enclosed container; spraying of the solid composition onto the polymer template; and use of a fluidised bed to contact the solid composition with the polymer template.

7. A process according to any one of claims 1 to 6, wherein step (b) is repeated at least once, and wherein the solid composition used when step (b) is repeated may comprise the same or a different metallic powder to that used when step (b) was first carried out.

8. A process according to any one of claims 1 to 7, wherein following step (b) but prior to step (c), the metal particle-coated polymer template is subjected to treatment with pressurised air such that excess metallic powder is separated from the template.

9. A process according to any one of claims 1 to 8, wherein following step (b) but prior to step (c), the metal particle-coated polymer template is subjected to curing with UV light and/or heating to a temperature of from 45 to 180 °C.

10. A process according to any one of claims 1 to 9, wherein following step (b) but prior to step (c), the metal particle-coated polymer template is further coated by application of a slurry comprising metallic powder, preferably wherein the slurry is a poly(vinyl alcohol)-based slurry or a polyethylene glycol)-based slurry.

11. A process according to claim 10, wherein following step (b) but prior to the metal particle- coated polymer template being further coated by application of a slurry, the metal particle- coated polymer template is heated to a temperature of from 150 to 250 °C, preferably from 175 to 200 °C.

12. A process according to any one of claims 1 to 11, wherein step (c) comprises heating the metal particle-coated polymer template.

13. A process according to claim 12, wherein: (A) step (c) comprises heating the metal particle-coated polymer template to a sintering temperature that is above the temperature at which the polymer template will undergo complete thermal degradation, but below the melting temperature of the metal; or (B) step (c) comprises the sub-stages of: (i) heating the metal particle-coated polymer template to a temperature which is below the temperature at which the polymer will undergo complete thermal degradation, and dwelling at that temperature for a time period of from 15 minutes to 6 hours, preferably from 1 to 3 hours; and (ii) subsequently heating the metal particle-coated template to a sintering temperature that is above the temperature at which the polymer template will undergo complete thermal degradation, but below the melting temperature of the metal.

14. A process according to claim 13, wherein the temperature of step (B)(i) is from 100 to 750°C, preferably from 150 to 250°C, and more preferably from 175 to 200°C.

15. A process according to claim 13 or claim 14, wherein the temperature of step (A) or step (B)(ii) is from 1050 to 1200°C.

16. A process according to any one of claims 13 to 15, wherein the time period for which the sintering temperature is maintained is from 1 to 5 hours.

17. A process according to any one of claims 13 to 16, wherein the metal particle-coated polymer template is heated in step (A), step (B)(i) and/or step (B)(ii) at a rate of from 60 to 600°C/hour, preferably from 250 to 350°C/hour.

18. A process according to claim 17, wherein the metal particle-coated polymer template is heated at the same rate in step (B)(i) as in step (B)(ii).

19. A process according to any one of claims 13 to 18, wherein the heating takes place under a reducing atmosphere.

20. A process according to claim 19, wherein the reducing atmosphere is obtained by applying a stream of reducing gas to the metal particle-coated polymer template, preferably wherein said reducing gas comprises nitrogen and hydrogen.

21. A process according to claim 20, wherein the flow rate of the stream of reducing gas is from 50 to 650 L/hr, preferably from 100 to 200 L/hr.

22. A process according to any one of claims 13 to 21, wherein the metal particle-coated polymer template is enclosed by a cover during the heating process, wherein said cover acts as a barrier to the flow of gas, preferably wherein said cover comprises metal or ceramic.

23. A process according to any one of claims 13 to 22, wherein after step (c), the surface of the metallic scaffold or foam is contacted with a chemical cleaning agent.

24. A process according to any one of claims 1 to 23, wherein the polymer template is prepared in step (a) by a method of additive manufacturing, preferably wherein the method of additive manufacturing is a VAT polymerisation method, a liquid base polymerisation additive manufacturing method (e.g. stereolithography), or a binder jetting method.

25. A process according to claim 24, wherein the polymer template: (i) comprises orthogonally arranged pores, and preferably has a square-section porous cubic structure; or (ii) has a triply periodic minimal surface (TPMS), preferably a Gyroid or Schwartz D structure.

26. A process according to any one of claims 1 to 25, wherein following step (a) but prior to step (b), the polymer template is subjected to: (i) cleaning with a solvent, preferably an alcohol or tripropylene glycol monomethyl ether; and/or (ii) cleaning with pressurised air; and/or (iii) curing with UV light and/or heating to a temperature of from 45 to 180°C.

27. A process according to claim 25 or claim 26, wherein following step (a) but prior to step (b), the polymer template is subjected to curing with UV light and the resultant polymer template is partially cured.

28. A process according to claim 26 or claim 27, wherein following step (a) but prior to step (b), the polymer template is subjected to both cleaning with a solvent, preferably an alcohol or tripropylene glycol monomethyl ether, and curing with UV light.

29. A process according to claim 25 or claim 26, wherein following step (a) but prior to step (b), the polymer template does not undergo curing with UV light.

30. A process according to any one of claims 25 to 29, wherein following step (a) but prior to step (b), the polymer template undergoes cleaning with a solvent, preferably an alcohol or tripropylene glycol monomethyl ether, with simultaneous ultrasonication.

31. A process according to any one of claims 25 to 30, wherein prior to step (b), at least 50% of the surface area of the polymer template is capable of being coated by the adhesion of said solid composition to the surface of the polymer template.

32. A process according to any one of claims 25 to 31, wherein following step (a) but prior to step (b), the polymer template is: (i) subjected to cleaning with a solvent for a period of from 30 seconds to 30 minutes, preferably under ultrasonication; and (ii) subsequently subjected to curing in the presence of UV light or both UV light and heat for a period of from 0 to 24 hours.

33. A process according to any one of claims 1 to 32, wherein the polymer template comprises a polymer to which particles of a metallic powder are capable of adhering.

34. A process according to claim 33, wherein the surface of the polymer template is sufficiently tacky such that a solid composition comprising metallic powder is capable of adhering to the template in the absence of any external binder or solvent, substantially coating the template.

35. A process according to claim 33 or claim 34, wherein the polymer is selected from poly(acrylates), poly(methacrylates), poly(urethanes) and wax-based resins.

36. A process according to any one of claims 1 to 35, wherein the polymer template comprises a strut thickness of at least 50 pm and a pore diameter of at least 100 pm, preferably a strut thickness of at least 280 pm and a pore diameter of at least 300 pm, preferably wherein the polymer template comprises a strut thickness of at least 420 pm and a pore diameter of at least 600 pm.

37. A metallic scaffold or foam obtainable by the process of any one of claims 1 to 36.

38. Use of a solid composition comprising metallic powder in a process of coating an additive- manufactured polymer template to produce a metal particle -coated polymer template.