Pulsed current sintering for surfaces of medical implants

Abstract

A porous medical implant and a method of making same is described. The medical implant comprises a porous surface formed by application of pulsed electrical energy ins such a way as to cause a localized heating in the surface of the material comprising portions of the implant. The method comprises a pulsed current sintering technique.

1 . A method of making a medical implant having a porous surface and a solid substrate, comprising the steps of: 
 placing a finite number of individual bodies in continuous contact with one another, said finite number of individual bodies comprising a first material;    sintering said first material by applying pulsed electrical energy across at least a portion of the aggregate mass of said individual bodies, thereby creating a cohesive porous structure; and,    attaching said first material to a second material, said second material comprising said solid substrate.    
   
   
       2 . The method of  claim 1 , wherein said step of attaching said first material to a second material comprises sintering said first material to said second material by applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and the second material while the first material and the second material are in physical contact with one another.  
   
   
       3 . The method of  claim 1 , wherein said steps of sintering and attaching are performed simultaneously by applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and the second material while the first material and the second material are in physical contact with one another.  
   
   
       4 . The method of  claim 1 , wherein said steps of sintering and attaching are performed sequentially by first applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and thereafter applying pulsed electrical energy across at least a portion of the aggregate mass of the first material and the second material while the first material and the second material are in physical contact with one another.  
   
   
       5 . The method of  claim 1 , wherein said step of attaching said first material to a second material comprises a step selected from the group consisting of welding, soldering, diffusion bonding, brazing, adhering using an adhesive or grouting material or both, and any combination thereof.  
   
   
       6 . The method of  claim 1 , wherein said step of placing a finite number of individual bodies in continuous contact with one another comprises placing a finite number of individual bodies of at least two materials in continuous contact with one another.  
   
   
       7 . The method of  claim 6 , further comprising the step of removing at least a portion of at least one of said at least two materials either during or after said step of sintering, thereby creating a cohesive porous structure where said material was removed.  
   
   
       8 . The method of  claim 1 , further comprising the step of applying a mechanical load to at least a portion of said first material or to at least a portion of said second material or to at least a portion of both said first material and said second material.  
   
   
       9 . The method of  claim 8 , wherein said step of applying a mechanical load is performed during said step of sintering.  
   
   
       10 . The method of  claim 1 , wherein said step of sintering is performed at an elevated temperature.  
   
   
       11 . The method of  claim 1 , wherein said step of sintering comprises applying pulsed electrical energy at high frequencies.  
   
   
       12 . The method of  claim 1 , wherein said first material and said second material are selected from the group consisting of metal, ceramic, polymer, composite materials, and any combination thereof.  
   
   
       13 . The method of  claim 1 , wherein the composition of said first material and said second material are different.  
   
   
       14 . The method of  claim 1 , wherein the first material and the second material are refractory materials.  
   
   
       15 . The method of  claim 1 , wherein one or both of the first material and the second material are non-refractory materials.  
   
   
       16 . The method of  claim 1 , wherein a portion of said individual bodies of said first material are of different composition from another portion of said individual bodies of said first material.  
   
   
       17 . The method of  claim 1 , wherein a portion of said individual bodies of said first material comprises a refractory material and another portion of said individual bodies of said first material comprises a non-refractory material.  
   
   
       18 . The method of  claim 1 , wherein one of said first material and said second material is refractory and the other is non-refractory.  
   
   
       19 . The method of  claim 1 , wherein said first material has a form selected from the group consisting of symmetric particles, asymmetric particles, single fibers, multiple fibers, flat porous sheets, deformed porous sheets, reticulated open-celled structures, and any combination thereof.  
   
   
       20 . The method of  claim 19 , wherein said first material has a symmetric particle form and is a spherical particle.  
   
   
       21 . The method of  claim 1 , wherein said step of sintering is performed in a controlled environment.  
   
   
       22 . The method of  claim 21 , wherein said controlled environment is a pressure less than atmospheric pressure.  
   
   
       23 . The method of  claim 21 , wherein said controlled environment comprises an atmosphere of an inert gas.  
   
   
       24 . The method of  claim 21 , wherein said controlled environment comprises an atmosphere of a reactive gas.  
   
   
       25 . The method of  claim 21 , wherein said controlled environment is varied during said step of sintering.  
   
   
       26 . The method of  claim 1 , wherein said step of placing comprises using a binder.  
   
   
       27 . The method of  claim 1 , further comprising the step of infusing at least a portion of the porous region with a material.  
   
   
       28 . The method of  claim 27 , wherein said step of infusing comprises infusing with a method selected from the group consisting of direct compression molding, injection, solution deposition, vapor deposition, and any combination thereof.  
   
   
       29 . The method of  claim 27 , wherein said material to be infused is a polymer.  
   
   
       30 . The method of  claim 27 , wherein said material to be infused comprises a growth factor or antibiotic.  
   
   
       31 . The method of  claim 27 , wherein said material to be infused is selected from the group consisting of hydroxyapatite, fluoroapatite, chloroapatite, bromoapatite, iodoapatite, calcium sulfate, calcium phosphate, calcium carbonate, calcium tartarate, bioactive glass, and any combination thereof.  
   
   
       32 . A method of making a medical implant having a porous surface comprising the steps of: 
 placing a finite number of non-spherical individual bodies in continuous contact with one another; and,    sintering said individual bodies by applying pulsed electrical energy across at least a portion of the aggregate mass of said individual bodies, thereby creating a cohesive porous structure.    
   
   
       33 . The method of  claim 32 , wherein said step of placing a finite number of non-spherical individual bodies in continuous contact with one another further comprises placing said individual bodies in contact with at least one other material.  
   
   
       34 . The method of  claim 33 , further comprising the step of removing at least a portion of said at least one other material either during or after said step of sintering, thereby creating a cohesive porous structure where said material was removed.  
   
   
       35 . The method of  claim 32 , further comprising the step of applying a mechanical load to at least a portion of said individual bodies.  
   
   
       36 . The method of  claim 35 , wherein said step of applying a mechanical load is performed during said step of sintering.  
   
   
       37 . The method of  claim 32 , wherein said step of sintering is performed at an elevated temperature.  
   
   
       38 . The method of  claim 32 , wherein said step of sintering comprises applying pulsed electrical energy at high frequencies.  
   
   
       39 . The method of  claim 32 , wherein said individual bodies are selected from the group consisting of metal, ceramic, polymer, composite materials, and any combination thereof.  
   
   
       40 . The method of  claim 32 , wherein the composition of a portion of said individual bodies is different from the composition of another portion of said individual bodies.  
   
   
       41 . The method of  claim 32 , wherein at least a portion of said individual bodies comprise a refractory material.  
   
   
       42 . The method of  claim 32 , wherein said individual bodies have a form selected from the group consisting of symmetric particles, asymmetric particles, single fibers, multiple fibers, flat porous sheets, deformed porous sheets, reticulated open-celled structures, and any combination thereof.  
   
   
       43 . The method of  claim 32 , wherein said step of sintering is performed in a controlled environment.  
   
   
       44 . The method of  claim 43 , wherein said controlled environment is a pressure less than atmospheric pressure.  
   
   
       45 . The method of  claim 43 , wherein said controlled environment comprises an atmosphere of an inert gas.  
   
   
       46 . The method of  claim 43 , wherein said controlled environment comprises an atmosphere of a reactive gas.  
   
   
       47 . The method of  claim 43 , wherein said controlled environment is varied during said step of sintering.  
   
   
       48 . The method of  claim 32 , wherein said step of placing comprises using a binder.  
   
   
       49 . The method of  claim 32 , further comprising the step of infusing at least a portion of the porous structure with a material.  
   
   
       50 . The method of  claim 49 , wherein said step of infusing comprises infusing with a method selected from the group consisting of direct compression molding, injection, solution deposition, vapor deposition, and any combination thereof.  
   
   
       51 . The method of  claim 49 , wherein said material to be infused is a polymer.  
   
   
       52 . The method of  claim 49 , wherein said material to be infused comprises a growth factor or antibiotic.  
   
   
       53 . The method of  claim 49 , wherein said material to be infused is selected from the group consisting of hydroxyapatite, fluoroapatite, chloroapatite, bromoapatite, iodoapatite, calcium sulfate, calcium phosphate, calcium carbonate, calcium tartarate, bioactive glass, and any combination thereof.  
   
   
       54 . A medical implant comprising a solid substrate and a porous sintered surface, wherein said solid substrate possesses substantially the same bulk mechanical and tribological properties after sintering which existed prior to sintering.  
   
   
       55 . The medical implant of  claim 54 , wherein said material possesses substantially the same microstructure after sintering which existed prior to sintering.  
   
   
       56 . A medical implant having a porous surface produced by the process comprising the steps of: 
 placing a finite number of non-spherical individual bodies in continuous contact with one another; and,    sintering said individual bodies by applying pulsed electrical energy across at least a portion of the aggregate mass of said individual bodies, thereby creating a cohesive porous structure.    
   
   
       57 . A medical implant having a porous surface produced by the process comprising the steps of: 
 placing a finite number of individual bodies in continuous contact with one another, said finite number of individual bodies comprising a first material;    sintering said first material by applying pulsed electrical energy across at least a portion of the aggregate mass of said individual bodies, thereby creating a cohesive porous structure; and,    attaching said first material to a second material, said second material comprising said solid substrate.