Metal injection moulding for the production of medical implants

Abstract

An improved method for manufacturing medical implants, and particularly spinal implants, utilizing a metal injection moulding technique (MIM) is provided. The invention is generally directed to the manufacture of implants for complete insertion within the body of a patient. A special set of mechanical, physiological and legal requirements are associated with such medical implants. For example, in contrast with dental implants, such medical implants are not readily observable or removable meaning that they must be significantly more physically resilient. In addition, physiologically, such medical implants must be capable of full integration with the body. Finally, regulatory requirements provide for significantly stricter controls over such fully implanted medical devices.

1 . A method for forming a near-net shape medical implant for complete insertion into a patient, comprising the steps of: 
 mixing titanium powder and an organic binder to form an injection moulding compound;    plasticizing the injection moulding compound by kneading the compound to form an injection moulding feedstock;    moulding the injection moulding feedstock to form a medical implant body, the medical implant body having a weight of no more than 35 kg and a wall thickness of no more than 12 mm,    removing binder from the medical implant body by heating; and    sintering the medical implant body to produce a near-net medical implant wherein the density of the near-net medical implant is within 95% of the theoretical density of the original titanium material.    
   
   
       2 . The method according to  claim 1 , wherein the medical implant body undergoes a linear shrinkage of between 10 to 20% during sintering.  
   
   
       3 . The method according to  claim 1 , wherein the medical implant body is embossed with a surface finish during the moulding process, wherein the surface finish is designed to stimulate osseointegration.  
   
   
       4 . The method according to  claim 1 , wherein the step of sintering is conducted at a temperature near the melting temperature of the injection metal feedstock such that the medical implant body has a near uniform metal crystallinity.  
   
   
       5 . The method according to  claim 1 , wherein the step of sintering is conducted under a purge gas flow such that surface oxidation of the medical implant body is decreased.  
   
   
       6 . The method according to  claim 1 , wherein the titanium material is a titanium composite.  
   
   
       7 . The method according to  claim 6 , wherein the titanium composite further comprises silicon.  
   
   
       8 . The method according to  claim 1 , wherein the moulding step produces a near-net shape medical implant having a dimensional precision of plus or minus 0.5%.  
   
   
       9 . The method according to  claim 1 , wherein the moulding step produces a near-net shape medical implant having a dimensional precision of plus or minus 0.05%.  
   
   
       10 . The method according to  claim 1 , wherein the titanium powder has an average granule diameter of no more than 40 μm.  
   
   
       11 . The method according to  claim 1 , wherein the titanium powder has a carbon content of no mare than 0.3% of the powder by weight.  
   
   
       12 . The method according to  claim 1 , wherein the titanium powder has an oxygen content of no mare than 0.6% of the powder by weight.  
   
   
       13 . The method according to  claim 1 , wherein the medical implant has a weight of no more than 30 kg and a wall thickness of no more than 5 mm.  
   
   
       14 . The method according to  claim 1 , wherein the near-net shape medical implant is selected from the group consisting of: vertebral alignment screw components, intervertebral body cages, total hips, total knees, acetabular femoral tibial components, plates for prosthetic replacement of cranial deficiencies, implanted prosthetic devices, customized bony deficiency prosthesis, and related attachments.