Method for producing undercut micro recesses in a surface, a surgical implant made thereby, and method for fixing an implant to bone

Abstract

Method for producing a multiplicity of undercut micro recesses in a surface of an article, such that the article exhibits a greater fractal area at a level below the surface than is exhibited at the surface. The method comprises applying a maskant layer to a selected surface of the article, removing the maskant layer in selected loci to expose underlying portions of the article surface in a selected pattern, applying an etchant to the exposed underlying surface portions for a time sufficient to etch the exposed portions of the article and to enable the etchant to etch beneath portions of the remaining maskant layer, and removing the remaining maskant layer to provide the surface in exposed condition with the multiplicity of undercut recesses, to provide an engineered pattern of the recesses.

What is claimed is:  
     
         1 . A method for producing a multiplicity of undercut micro recesses in a surface of an article, the article thereby exhibiting a greater fractal area at a level below the surface than is exhibited at the surface, the method comprising: 
 applying a maskant layer to substantially an entirety of the surface of the article;    removing portions of the maskant layer in selected loci to expose underlying portions of the article surface in a selected pattern;    applying an etchant to the exposed underlying surface portions for a time sufficient to etch the exposed surface portions and to enable the etchant to etch beneath remaining portions of the maskant layer and produce a multiplicity of undercut recesses; and    removing the remaining maskant layer portions to provide the article surface in exposed condition with the multiplicity of recesses undercut and comprising interconnected recesses, to provide an engineered pattern of the recesses.    
     
     
         2 . The method in accordance with  claim 1 , wherein the article comprises a material selected from a group consisting of metal, ceramic, plastics, and glass materials, and composites thereof.  
     
     
         3 . The method in accordance with  claim 2 , wherein the metal article comprises a metal selected from a group consisting of ferrous metal, non-ferrous metal, and alloys thereof.  
     
     
         4 . The method in accordance with  claim 2 , wherein the metal article comprises a metal selected from a group consisting of titanium, zirconium, stainless steel, tantalum, refractory metals, metal carbides, and cobalt/chromium alloys.  
     
     
         5 . The method in accordance with  claim 1 , wherein the maskant comprises a material selected from a group consisting of an acrylic, an epoxy, and a polyester.  
     
     
         6 . The method in accordance with  claim 5 , wherein the maskant further comprises a selected one of a dye and a pigment.  
     
     
         7 . The method in accordance with  claim 6  wherein the pigment comprises carbon black.  
     
     
         8 . The method in accordance with  claim 1  wherein the maskant comprises a polymer resist.  
     
     
         9 . The method in accordance with  claim 1  wherein the maskant layer is about 0.001-0.010 inch thick.  
     
     
         10 . The method in accordance with  claim 9  and further comprising baking the maskant layer at 200° F. (±10° F.) for about 15-17 minutes.  
     
     
         11 . The method in accordance with  claim 6  and further comprising dispersing the pigment in the maskant in a high shear mixer, and mixing the maskant and pigment therein until a temperature rise of 15°-20° C. is realized by the mixture.  
     
     
         12 . The method in accordance with  claim 1  wherein applying the maskant layer to the surface of the article comprises a selected one of dipping, spraying, spinning, brushing, and electrostatically depositing the maskant onto the article.  
     
     
         13 . The method in accordance with  claim 1  wherein removal of the maskant is effected by laser ablation.  
     
     
         14 . The method in accordance with  claim 13  wherein the laser ablation is computer controlled.  
     
     
         15 . The method in accordance with  claim 14  wherein the pattern is formed by selectively removing the maskant by an active laser projection pattern.  
     
     
         16 . The method in accordance with  claim 1  wherein the application of etchant to exposed surface portions of the article is effected by a spray etcher.  
     
     
         17 . The method in accordance with  claim 16  wherein the spray etcher is operated at 100° F. spray temperature and 10 lbs/in 2  spray pressure in a nitric-hydrofluoric acid solution for about 20 minutes.  
     
     
         18 . The method in accordance with  claim 1  wherein the remaining maskant layer portions are removed by immersion of the surface in a NU/Phase  23  Stripper bath at 180° F. for about ten minutes.  
     
     
         19 . The method in accordance with  claim 14  wherein the controlling computer operates in conjunction with a CAD system having facility for storing patterns in digital format or transferring said data into a photo tool.  
     
     
         20 . The method in accordance with  claim 13  wherein the laser ablation is. effected by a selected one of a YAG laser, a CO 2  laser, and a green laser, and other laser providing a wavelength appropriate for absorption of the maskant.  
     
     
         21 . The method in accordance with  claim 1  wherein the undercut recesses are of a non-spherical configuration.  
     
     
         22 . The method in accordance with  claim 21  wherein the configuration is substantially ovoid.  
     
     
         23 . A method for producing a multiplicity of undercut micro recesses in a surface of an article in a selected pattern which can be repeated in any selected number of surfaces, the method comprising: 
 applying a maskant layer to substantially an entirety of a selected surface of the article;    removing portions of the maskant layer by computer-directed laser ablation in programmed loci to expose underlying portions of the surface of the article in a programmed pattern;    applying an etchant to the exposed underlying surface portions for a time sufficient to etch the exposed surface portions and to enable the etchant to etch beneath remaining portions of the maskant layer and produce the multiplicity of undercut recesses; and    removing the remaining maskant layer portions to provide the selected surface in exposed condition with the multiplicity of undercut recesses therein.    
     
     
         24 . The method in accordance with  claim 23  wherein the laser ablation is performed by a neodymium-doped YAG laser with a wavelength of about 1.06 microns.  
     
     
         25 . The method in accordance with  claim 23  wherein the laser ablation is performed by a selected one of a CO 2  laser, a diode pump laser, and a green laser.  
     
     
         26 . The method in accordance with  claim 23  wherein the programmed pattern is stored in a selected one of a Tagged Image File Format and a Plot Graphic File.  
     
     
         27 . The method in accordance with  claim 23  wherein the undercut recesses are of a non-spherical configuration.  
     
     
         28 . The method in accordance with  claim 27  wherein the configuration is substantially ovoid.  
     
     
         29 . A method for producing a surgical implant having facility for stimulating ingrowth of bone upon attachment of the implant to a bone, the method comprising: 
 providing a rigid article;    applying a maskant layer to substantially an entirety of a datum surface of the article;    removing portions of the maskant layer in selected loci to expose underlying portions of the datum surface of the article;    applying an etchant to the exposed underlying datum surface portions for a time sufficient to enable the etchant to undercut remaining portions of the maskant layer and produce a multiplicity of undercut recesses having sharp edges at their intersections with the datum surface; and    removing the remaining portions of the maskant layer to provide the datum surface in exposed condition with the sharp edges for shaving particulate matter from the bone, and with the recesses for receiving and retaining the bone particulate matter for stimulating ingrowth of bone.    
     
     
         30 . A method for producing a textured surface in a surgical implant, the method comprising: 
 applying a maskant layer to substantially an entirety of a datum surface of the implant;    removing portions of the maskant layer in selected loci to expose underlying portions of the datum surface of the implant;    applying an etchant to the exposed underlying datum surface portions for a time sufficient to etch the exposed surface portions and to enable the etchant to etch beneath remaining portions of the maskant layer and produce a multiplicity of undercut recesses having sharp edges at their intersections with the datum surface; and    removing the remaining portions of the maskant layer to provide the datum surface in exposed condition with the sharp edges for shaving particulate matter from the bone, and with the recesses for receiving and retaining the bone particulate matter for stimulating ingrowth of bone.    
     
     
         31 . A method for attaching a surgical implant to a bone, the method comprising: 
 providing a surgical implant having a datum surface and a multiplicity of undercut micro recesses in the datum surface, such that the implant exhibits a greater fractal area at a level below the datum surface than is exhibited at the datum surface, intersections of the datum surface and the recesses defining sharp edges;    pressing the datum surface against a surface of the bone;    and    urging the implant along the bone surface, to cause the sharp edges to shave particulate bone matter from the bone;    wherein the recesses receive and retain the particulate bone matter which stimulates ingrowth of the bone.    
     
     
         32 . A method for attaching a surgical implant to a bone, the method comprising: 
 providing a surgical implant having a datum surface, a multiplicity of micro recesses in the datum surface, and bone milling structure on the datum surface;    pressing the datum surface against a surface of the bone; and    urging the implant along the bone surface to mill particulate bone matter from the bone;    wherein the recesses are adapted to receive and retain the particulate bone matter which stimulates ingrowth of the bone.    
     
     
         33 . The method in accordance with  claim 32  wherein the undercut recesses are of a non-spherical configuration.  
     
     
         34 . The method in accordance with  claim 33  wherein the configuration is substantially ovoid.  
     
     
         35 . A method for bone harvesting and seeding of a surgical implant with particulate bone matter during attachment of the implant to the bone, the method comprising: 
 providing a surgical implant having a surface for engagement with a bone surface, the implant having a multiplicity of undercut micro recesses and bone milling structure, in the surface thereof; and    moving the implant along the bone, such that the milling structure dislocates particulate bone matter from the bone, the bone matter falling into the micro recesses and retained thereby to stimulate ingrowth of the bone into the undercut recesses.    
     
     
         36 . The method in accordance with  claim 35  wherein the undercut recesses are of a non-spherical configuration.  
     
     
         37 . The method in accordance with  claim 36  wherein the configuration is substantially ovoid.  
     
     
         38 . A method for making a surgical implant having generally opposed datum surfaces spaced from each other by a predetermined distance, each of the datum surfaces being adapted to interlock with a bone surface, the method comprising the steps of: 
 providing an article having first and second datum surface portions adapted to respectively engage first and second bone surfaces, the datum surface portions being spaced from each other by the predetermined distance which is substantially equal to a distance between the first and second bone surfaces;    applying a maskant layer to substantially an entirety of each of the datum surfaces;    removing the maskant layers in selected loci to expose underlying portions of the datum surfaces in selected patterns;    applying an etchant to the exposed underlying datum surface portions for a time sufficient to etch the exposed portions of the datum surfaces and to enable the etchant to etch beneath the remaining maskant layers and produce undercut recesses; and    removing the remaining maskant to provide the opposed datum surfaces in exposed condition with the multiplicity of undercut recesses;    wherein the datum surfaces are devoid of structure protruding therefrom.    
     
     
         39 . A surgical implant comprising: 
 an article having a datum surface for abutting engagement with a bone;    a multiplicity of undercut micro recesses in the datum surface, such that said article exhibits a greater fractal area at a level below the surface than is exhibited at the datum surface;    intersections of said recesses and the datum surface defining sharp edges adapted to cut the bone and produce bone particulates;    said recesses being adapted to receive and retain the bone particulates cut from the bone by the edges, to stimulate ingrowth of the bone into said recesses.    
     
     
         40 . The surgical implant in accordance with  claim 39 , wherein said article is of a material selected from a group consisting of metal, ceramic, plastics, and glass materials, and composites thereof.  
     
     
         41 . The surgical implant in accordance with  claim 40 , wherein the metal article is of a metal selected from a group consisting of ferrous metal, non-ferrous metal, and alloys thereof.  
     
     
         42 . The surgical implant in accordance with  claim 40  wherein the metal article is of a metal selected from a group consisting of titanium, zirconium, stainless steel, tantalum, refractory metals, metal carbides, and cobalt/chromium alloys.  
     
     
         43 . The surgical implant in accordance with  claim 39  wherein the undercut recesses are of a non-spherical configuration.  
     
     
         44 . The surgical implant in accordance with  claim 43  wherein the configuration is substantially ovoid.  
     
     
         45 . The method in accordance with  claim 1  wherein the etchant is applied to the exposed surface at an angle selected from (i) normal to the exposed surface, and (ii) acute relative to the exposed surface.  
     
     
         46 . The surgical implant in accordance with  claim 39  wherein the micro recesses each have a central axis at a selected one of (i) normal to the datum surface, and (ii) at an acute angle to the datum surface.