Intervertebral Cage with Porosity Gradient

Abstract

An intervertebral cage with an outer frame, an open inner core region and a porosity gradient within the outer frame is provided. The outer frame includes a posterior wall, an anterior wall, a pair of side walls extending between the posterior wall and the anterior wall and the porosity gradient may comprise at least one of: a decreasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; an increasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; a decreasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls; and an increasing average pore diameter in a direction from an upper surface to a lower surface of at least one of the side walls.

1 . An intervertebral cage comprising:
 an outer frame with an outer surface and an open inner core region defining an inner core surface, the outer frame further comprising superior and inferior surfaces and proximal and distal ends; and   a porosity gradient within the outer frame with at least a portion of both the outer surface and inner core surface being porous;   wherein the outer frame comprises a predefined pattern of apertures that form the porosity gradient within the outer frame;   wherein the intervertebral cage is shaped to facilitate placement of the intervertebral cage between two vertebrae in an intervertebral disc space; and   wherein the superior and inferior surfaces are each configured to maintain the intervertebral cage in the intervertebral disc space once inserted therein.   
     
     
         2 . The intervertebral cage of  claim 1 , wherein the outer frame comprises a plurality of layers with a predefined and regular pattern of apertures bonded to each other such that the predefined and regular pattern of apertures in each of the plurality of layers forms the porosity gradient within the outer frame. 
     
     
         3 . The intervertebral cage of  claim 1 , wherein the outer frame comprises a plurality of bonded layers, each layer having a predefined pattern of apertures prior to bonding such that altogether the predefined pattern of apertures in each layer of the plurality of layers forms the porosity gradient within the outer frame. 
     
     
         4 . The intervertebral cage of  claim 1 , wherein the porosity gradient extends through the superior and inferior surfaces. 
     
     
         5 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises an increasing average pore diameter in a direction from an outer surface to an inner surface. 
     
     
         6 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises an increasing average pore diameter in a direction from both the superior surface and the inferior surface into the outer frame. 
     
     
         7 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises a decreasing average pore diameter in a direction toward both the superior and inferior surfaces. 
     
     
         8 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises an increasing average pore diameter in a direction toward the inner core surface. 
     
     
         9 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises an increasing average pore diameter in a direction from at least one of the proximal end and distal end of the outer frame. 
     
     
         10 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises at least one of: an increasing average pore diameter in a direction from the superior surface into the outer frame, and a decreasing average pore diameter in a direction from within the outer frame toward the inferior surface. 
     
     
         11 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises at least one of: an increasing average pore diameter in a direction from the inferior surface into the outer frame, and a decreasing average pore diameter in a direction from within the outer frame toward the superior surface. 
     
     
         12 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises a first portion with a porosity within a range of about 5% by volume to about 30% by volume and a second portion within a range of about 30% by volume to about 90% by volume. 
     
     
         13 . The intervertebral cage of  claim 1 , wherein the porosity gradient comprises a first portion with a porosity with an average diameter between about 5 μm and about 100μ and a second portion with a porosity with an average diameter between about 100 μm and 1000 μm. 
     
     
         14 . An intervertebral cage comprising: an outer frame comprising:
 a superior surface, an inferior surface, a posterior wall, an anterior wall and a pair of side walls extending between the anterior wall and the posterior wall;   an open inner core region between the posterior wall, the anterior wall, and the pair of side walls; and   a porosity gradient within at least one of the posterior wall, the anterior wall, and the pair of side walls;   wherein the porosity gradient promotes bone ingrowth and fusion between adjacent vertebrae;   wherein the outer frame comprises a predefined pattern of apertures that forms the porosity gradient within the outer frame;   wherein the superior and inferior surfaces are each configured to maintain the intervertebral cage in an intervertebral disc space between two vertebral bodies once inserted therein;   wherein at least one of the anterior wall and posterior wall is not the same length as the pair of side walls.   
     
     
         15 . The intervertebral cage of  claim 14 , wherein the porosity gradient comprises a first portion with a porosity within a range of about 5% by volume to about 30% by volume and a second portion within a range of about 30% by volume to about 90% by volume. 
     
     
         16 . The intervertebral cage of  claim 14 , wherein the porosity gradient comprises a first portion with a porosity with an average diameter between about 5 μm and about 100μ and a second portion with a porosity with an average diameter between about 100 μm and 1000 μm. 
     
     
         17 . The intervertebral cage of  claim 14 , wherein the porosity gradient is selected from at least of: a decreasing average pore diameter in a direction from an inner surface to an outer surface of at least one of the pair of side walls; an increasing average pore diameter in a direction from an outer surface to an inner surface of at least one of the pair of side walls; an increasing average pore diameter in a direction from an upper surface toward a lower surface of at least one of the side walls; and an increasing average pore diameter in a direction from a lower surface toward an upper surface of at least one of the side walls. 
     
     
         18 . The intervertebral cage of  claim 14 , wherein at least a portion of the outer frame is formed using at least one of the following: 3D printing, electric discharge machining, mechanical machining, etching, chemical etching, and layer-by-layer processes. 
     
     
         19 . The intervertebral cage of  claim 14 , further comprising at least one aperture between the open inner core region and an exterior surface of the intervertebral cage. 
     
     
         20 . The intervertebral cage of  claim 14 , wherein the superior and inferior surfaces include features intended to increase the friction between the features and an adjacent boney structure.