US20120215310A1 - Porous implant structures - Google Patents

Abstract

Porous biocompatible structures suitable for use as medical implants and methods for fabricating such structures are disclosed. The disclosed structures may be fabricated using rapid manufacturing techniques. The disclosed porous structures has a plurality of struts and nodes where no more than two struts intersect one another to form a node. Further, the nodes can be straight, curved, portions that are curved and/or straight. The struts and nodes can form cells which can be fused or sintered to at least one other cell to form a continuous reticulated structure for improved strength while providing the porosity needed for tissue and cell in-growth.

Description

• The present application claims the benefit of U.S. Provisional Patent Application No. 61/235,269, filed Aug. 19, 2009 and entitled “Porous Implant Structures,” the disclosure of which is incorporated by reference herein in its entirety.
FIELD OF INVENTION
• The present invention generally relates to porous structures suitable for medical implants, and more particularly to porous structures suitable for medical implants that have improved combinations of strength, porosity and connectivity and methods for fabricating such improved porous structures.
BACKGROUND
• Metal foam structures are porous, three-dimensional structures with a variety of uses, including medical implants. Metal foam structures are suitable for medical implants, particularly orthopedic implants, because they have the requisite strength for weight bearing purposes as well as the porosity to encourage bone/tissue in-growth. For example, many orthopedic implants include porous sections that provide a scaffold structure to encourage bone in-growth during healing and a weight bearing section intended to render the patient ambulatory more quickly.
• Metal foam structures can be fabricated by a variety of methods. For example, one such method is mixing a powdered metal with a pore-forming agent (PFA) and then pressing the mixture into the desired shape. The PFA is removed using heat in a “burn out” process. The remaining metal skeleton may then be sintered to form a porous metal foam structure.
• Another similar conventional method include applying a binder to polyurethane foam, applying metal powder to the binder, burning out the polyurethane foam and sintering the metal powder together to form a “green” part. Binder and metal powder are re-applied to the green part and the green part is re-sintered until the green part has the desired strut thickness and porosity. The green part is then machined to the final shape and re-sintered.
• While metal foams formed by such conventional methods provide good porosity, they may not provide sufficient strength to serve as weight bearing structures in many medical implants. Further, the processes used to form metal foams may lead to the formation of undesirable metal compounds in the metal foams by the reaction between the metal and the PFA. Conventional metal foam fabrication processes also consume substantial amounts of energy and may produce noxious fumes.
• Rapid manufacturing technologies (RMT) such as direct metal fabrication (DMF) and solid free-form fabrication (SFF) have recently been used to produce metal foam used in medical implants or portions of medical implants. In general, RMT methods allow for structures to be built from 3-D CAD models. For example, DMF techniques produce three-dimensional structures one layer at a time from a powder which is solidified by irradiating a layer of the powder with an energy source such as a laser or an electron beam. The powder is fused, melted or sintered, by the application of the energy source, which is directed in raster-scan fashion to selected portions of the powder layer. After fusing a pattern in one power layer, an additional layer of powder is dispensed, and the process is repeated with fusion taking place between the layers, until the desired structure is complete.
• Examples of metal powders reportedly used in such direct fabrication techniques include two-phase metal powders of the copper-tin, copper-solder and bronze-nickel systems. The metal structures formed by DMF may be relatively dense, for example, having densities of 70% to 80% of a corresponding molded metal structure, or conversely, may be relatively porous, with porosities approaching 80% or more.
• While DMF can be used to provide dense structures strong enough to serve as weight bearing structures in medical implants, such structures do not have enough porosity to promote tissue and bone in-growth. Conversely, DMF can be used to provide porous structures having enough porosity to promote tissue and bone in-growth, but such porous structures lack the strength needed to serve as weight bearing structures. Other laser RMT techniques are similarly deficient for orthopedic implants requiring strength, porosity and connectivity.
• As a result of the deficiencies of metal foam implants and implants fabricated using conventional DMF methods, some medical implants require multiple structures, each designed for one or more different purposes. For example, because some medical implants require both a porous structure to promote bone and tissue in-growth and a weight bearing structure, a porous plug may be placed in a recess of a solid structure and the two structures may then be joined by sintering. Obviously, using a single structure would be preferable to using two distinct structures and sintering them together.
• In light of the above, there is still a need for porous implant structures that provide both the required strength and desired porosity, particularly for various orthopedic applications. This disclosure provides improved porous structures that have both the strength suitable for weight bearing structures and the porosity suitable for tissue in-growth structures and a method for fabricating such improved porous structures.
SUMMARY OF THE INVENTION
• One objective of the invention is to provide porous biocompatible structures suitable for use as medical implants that have improved strength and porosity.
• Another objective of the invention is to provide methods to fabricate porous biocompatible structures suitable for use as medical implants that have improved strength and porosity.
• To meet the above objectives, there is provided, in accordance with one aspect of the invention, there is a porous structure comprising: a plurality of struts, each strut comprises a first end, a second end; and a continuous elongated body between the first and second ends, where the body has a thickness and a length; and a plurality of nodes, each node comprises an intersection between one end of a first strut and the body of a second strut.
• In a preferred embodiment, the first and second ends of one or more struts extend between the body of two other struts. In another preferred embodiment, the body of one or more struts comprise a plurality of nodes.
• In accordance with another aspect of the invention, there is a porous structure comprising a plurality of struts, wherein one or more struts comprise a curved portion having a length and thickness; a plurality of junctions where two of said curved portions intersect tangentially; and a plurality of modified nodes, each modified node comprises an opening formed by three or more of said junctions.
• In a preferred embodiment, the porous structure includes at least one strut comprising a straight portion having a length and a thickness. In another preferred embodiment, the porous structure includes at least one strut having a first end, a second end; and a continuous elongated body between the first and second ends, where the body has a thickness and a length; and at least one closed node comprising an intersection between one end of a first strut and the body of a second strut, wherein the strut can comprise of a straight portion, a curved portion, or both.
• In accordance with another aspect of the invention, there are methods for fabricating a porous structure. One such method comprises the steps of: creating a model of the porous structure, the creation step comprises defining a plurality of struts and a plurality of nodes to form the porous structure and fabricating the porous structure according to the model by exposing metallic powder to an energy source. The defining step comprises the steps of providing a first end, a second end; and a continuous elongated body between the first and second ends for each strut, selecting a thickness a length for the body; and providing an intersection between one end of a first strut and the body of a second strut for each node.
• In a preferred embodiment, the method includes defining the first and second ends of one or more struts extend between the body of two other struts. In another preferred embodiment, defining the body of one or more struts to comprise a plurality of nodes.
• In accordance with another aspect of the invention, a second method for fabricating a porous structure comprises the steps of: creating a model of the porous structure; the creation step comprises selecting at least one frame shape and size for one or more cells of the porous structure, where the frame shape comprises a geometric shape selected from the group consisting of Archimedean shapes, Platonic shapes, strictly convex polyhedrons, prisms, anti-prisms and combinations thereof; adding one or more struts to the frame where the struts comprises a curved portion, said adding step is performed by inscribing or circumscribing the curved portion of the one or more struts within or around one or more faces of the selected shape; selecting a thickness for the frame and the one or more struts; and fabricating the porous structure according to the model by exposing metallic powder to an energy source.
• In a preferred embodiment, the creation step includes the step of removing a portion of the frame from one or more cells of the model. In another preferred embodiment, the fabrication step includes defining N_{(1, x)}layer-by-layer patterns for the porous structure based on the selected dimensions, at least one cell shape and at least one cell size, where N ranges from 1 for the first layer at a bottom of the porous structure to x for the top layer at a top of the porous structure; depositing an N^thlayer of powdered biocompatible material; fusing or sintering the N^thpattern in the deposited N^thlayer of powdered biocompatible material; and repeating the depositing and fusing or sintering steps for N=1 through N=x.
• In a refinement, the method may further comprise creating a model of the porous structure wherein, for at least some nodes, no more than two struts intersect at the same location.
• In another refinement, the method may comprise creating a model of the porous structure wherein at least one strut or strut portion is curved.
• The disclosed porous structures may be fabricated using a rapid manufacturing technologies such as direct metal fabrication process. The struts can be sintered, melted, welded, bonded, fused, or otherwise connected to another strut. The struts and nodes can define a plurality of fenestrations. Further, the struts and nodes can be fused, melted, welded, bonded, sintered, or otherwise connected to one another to form a cell, which can be fused, melted, welded, bonded, sintered, or otherwise connected to other cells to form a continuous reticulated structure.
• In some refinements, at least one, some, or all struts of a cell may have a uniform strut diameter. In some refinements, one, some, or all of the struts of a cell may have a non-uniform strut diameter. In some refinements, a cell may have combinations of struts having uniform and non-uniform strut diameters. In some refinements, at least one, some, or all of the uniform diameter struts of a cell may or may not share similar, different, or identical strut diameters, longitudinal shapes, cross-sectional shapes, sizes, shape profiles, strut thicknesses, material characteristics, strength profiles, or other properties. In some refinements, one, some, or all struts within a cell may grow or shrink in diameter at similar, different, or identical rates along a predetermined strut length.
• In some refinements, struts within a cell may extend between two nodes. In a further refinement of this concept, struts may have varying cross-sectional diameters along a strut length, including a minimum diameter at a middle portion disposed between the two nodes. In further refinement of this concept, struts may have two opposing ends, with each end connected to a node and a middle portion disposed between the two ends. Struts may flare or taper outwardly as they extend from the middle portion towards each node so that a diameter of the middle portion is generally smaller than a diameter of either or both of the two opposing ends. In some instances, the struts may flare in a parabolic fluted shape or may taper frusto-conically.
• In other refinements, at least one, some, or all struts within a cell are curved. In further refinement of this concept, one, some, or all of the cells within a porous structure comprise at least one curved strut. In further refinement of this concept, all of the struts that make up a porous structure are curved. In further refinement of this concept, curved struts may form complete rings or ring segments. The rings or ring segments may be inter-connected to form open sides or fenestrations of multiple-sided cells. In some instances, a single ring may form a shared wall portion which connects two adjacent multiple-sided cells. In some instances, one or more ring segments alone or in combination with straight strut portions may form a shared wall portion which connects two adjacent multiple-sided cells. In still a further refinement, the number of sides of each cell may range from about 4 to about 24. More preferably, the number of sides of each cell may range from about 4 to about 16. One geometry that has been found to be particularly effective is a dodecahedron or 12 sided cell. However, as explained and illustrated below, the geometries of the individual cells or the cells of the porous structure may vary widely and in the geometries may vary randomly from cell to cell of a porous structure.
• In another refinement, the configurations of the cells, struts, nodes and/or junctions may vary randomly throughout the porous structure to more closely simulate natural bone tissue.
• In another refinement, each cell may be multiple-sided and having an overall shape that may fit within a geometric shape selected from the group consisting of tetrahedrons, truncated tetrahedrons, cuboctahedrons, truncated hexahedrons, truncated octahedrons, rhombicuboctahedrons, truncated cuboctahedrons, snub hexahedrons, snub cuboctahedrons, icosidodecahedrons, truncated dodecahedrons, truncated icosahedrons, rhombicosidodecahedrons, truncated icosidodecahedrons, snub dodecahedrons, snub icosidodecahedrons, cubes, octahedrons, dodecahedrons, icosahedrons, prisms, prismatoids, antiprisms, uniform prisms, right prisms, parallelpipeds, cuboids, polytopes, honeycombs, square pyramids, pentagonal pyramids, triangular cupolas, square cupolas, pentagonal cupolas, pentagonal rotundas, elongated triangular pyramids, elongated square pyramids, elongated pentagonal pyramids, gyroelongated square pyramids, gyroelongated pentagonal pyramids, triangular dipyramids, pentagonal dipyramids, elongated triangular dipyramids, elongated square dipyramids, elongated pentagonal dipyramids, gyroelongated square dipyramids, elongated triangular cupolas, elongated square cupolas, elongated pentagonal cupolas, elongated pentagonal rotundas, gyroelongated triangular cupolas, gyroelongated square cupolas, gyroelongated pentagonal cupolas, gyroelongated pentagonal rotundas, gyrobifastigium, triangular orthobicupolas, square orthobicupolas, square gyrobicupolas, pentagonal orthobicupolas, pentagonal gyrobicupolas, pentagonal orthocupolarotundas, pentagonal gyrocupolarotundas, pentagonal orthobirotundas, elongated triangular orthobicupolas, elongated triangular gyrobicupolas, elongated square gyrobicupolas, elongated pentagonal orthobicupolas, elongated pentagonal gyrobicupolas, elongated pentagonal orthocupolarotundas, elongated pentagonal gyrocupolarotundas, elongated pentagonal orthobirotundas, elongated pentagonal gyrobirotundas, gyroelongated triangular bicupolas, gyroelongated square bicupolas, gyroelongated pentagonal bicupolas, gyroelongated pentagonal cupolarotundas, gyroelongated pentagonal birotundas, augmented triangular prisms, biaugmented triangular prisms, triaugmented triangular prisms, augmented pentagonal prisms, biaugmented pentagonal prisms, augmented hexagonal prisms, parabiaugmented hexagonal prisms, metabiaugmented hexagonal prisms, triaugmented hexagonal prisms, augmented dodecahedrons, parabiaugmented dodecahedrons, metabiaugmented dodecahedrons, triaugmented dodecahedrons, metabidimini shed icosahedrons, tridiminished icosahedrons, augmented tridiminished icosahedrons, augmented truncated tetrahedrons, augmented truncated cubes, biaugmented truncated cubes, augmented truncated dodecahedrons, parabiaugmented truncated dodecahedrons, metabiaugmented truncated dodecahedrons, triaugmented truncated dodecahedrons, gyrate rhombicosidodecahedrons, parabigyrate rhombicosidodecahedrons, metabigyrate rhombicosidodecahedrons, trigyrate rhombicosidodecahedrons, diminished rhombicosidodecahedrons, paragyrate diminished rhombicosidodecahedrons, metagyrate diminished rhombicosidodecahedrons, bigyrate diminished rhombicosidodecahedrons, parabidiminished rhombicosidodecahedrons, metabidiminished rhombicosidodecahedrons, gyrate bidiminished rhombicosidodecahedrons, and tridimini shed rhombicosidodecahedrons, snub disphenoids, snub square antiprisms, sphenocorons, augmented sphenocoronas, sphenomegacorona, hebesphenomegacorona, disphenocingulum, bilunabirotundas, triangular hebesphenorotundas, and combinations thereof.
• In another refinement, the powder is selected from the group consisting of metal, ceramic, metal-ceramic (cermet), glass, glass-ceramic, polymer, composite and combinations thereof.
• In another refinement, the metallic material is selected from the group consisting of titanium, titanium alloy, zirconium, zirconium alloy, niobium, niobium alloy, tantalum, tantalum alloy, nickel-chromium (e.g., stainless steel), cobalt-chromium alloy and combinations thereof.
• In another refinement, the porous structure forms at least a portion of a medical implant, such as an orthopedic implant, dental implant or vascular implant.
• Porous orthopedic implant structures for cell and tissue in-growth and weight bearing strength are also disclosed that may be fabricated using a near-net shape manufacturing process such as a direct metal fabrication (DMF) process for use with metallic biomaterials or a stereo-lithography manufacturing process for use with polymeric biomaterials. In instances where a DMF process is utilized, a powdered biocompatible material is provided in layers and individual particles of one layer of powdered biocompatible material are fused or sintered together one layer at a time. Exemplary porous structures comprise a plurality of three-dimensional cells. Each cell comprises a plurality of struts. Each strut may be sintered or fused to one other strut at a node. Each node may comprise a junction of not more than two struts. The struts and nodes of each cell define a plurality of fenestrations. Each cell comprises from about 4 to about 24 fenestrations. At least one strut of at least some of the cells are curved. Each cell may be fused or sintered to at least one other cell to form a continuous reticulated structure.
• Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
• FIGS. 1A-1B illustrate 3-D representations of an example of the struts at a node in a porous structure of the prior art where the struts ofFIG. 1A have like diameters and the struts ofFIG. 1B have different diameters.
• FIG. 2 is a SEM (Scanning Electron Microscope) microphotograph of an example of fractured struts of the prior art.
• FIGS. 3-5 illustrate 3-D representations of one embodiment of the struts and nodes of the present invention.
• FIGS. 6-8 illustrate 3-D representations of another embodiment of the struts and nodes of the present invention where at least some of the struts comprises a smaller cross-sectional diameter at the body portion of the strut as compared to the cross-sectional diameter at the node.
• FIGS. 9A and 9B illustrate plan views of the embodiments inFIGS. 6-8.
• FIGS. 10A-10F illustrate 2-D representations of various configurations of the frame of struts and nodes in a porous structure of the prior art.
• FIGS. 11A-11F illustrate 2-D representations of the corresponding configurations of the frame of struts and nodes of the prior art inFIGS. 10A-10F modified by one embodiment of the present invention.
• FIGS. 12A-12D illustrate 3-D representations of exemplary embodiments of the porous structure of the present invention comprising one or more frame configurations inFIGS. 11A-11F.
• FIGS. 13A-13M illustrate 2-D representations of various exemplary configurations of the frame of the two struts of the present invention forming a node, including frames for struts that are straight, curved, or a combination of both.
• FIG. 14 illustrates a 2-D representation of an exemplary embodiment of the porous structure of the present invention comprising one or more frame configurations inFIGS. 13A-13M.
• FIGS. 15A-15C illustrate 2-D representations of exemplary configurations of various curved frames and corresponding struts of the present invention intersecting to form a node.
• FIG. 16 illustrates a 3-D representation of an exemplary embodiment of the porous structure of the present invention comprising one or more frame configurations inFIGS. 13A-13M, including frames for struts that are straight, curved, or a combination of both.
• FIG. 17 illustrates a 3-D representation of an exemplary frame for a generally cubical cell of the porous structure of the present invention.
• FIG. 18 illustrates a 3-D representation of an exemplary arrangement of frames for cubical cells inFIG. 17.
• FIG. 19 illustrates a 3-D representation of an arrangement of cubical cells of the porous structure of the prior art.
• FIG. 20 illustrates a 3-D representation of an exemplary arrangement of cubical cells of the porous structure of the present invention.
• FIG. 21 illustrates a blown up view of the arrangement inFIG. 20.
• FIG. 22 illustrates a 3-D representation of an exemplary frame for a tetrahedron-shaped cell of the porous structure of the present invention.
• FIG. 23 illustrates a 3-D representation of an exemplary frame for square-based pyramid cell of the porous structure of the present invention.
• FIGS. 24A and 24B illustrate various views of 3-D representations of a conventional cell of the porous structure of the prior art based on a dodecahedral shape.
• FIGS. 25A and 25B illustrate various views of 3-D representations of one embodiment of a cell of the porous structure of the present invention also based on a dodecahedral shape.
• FIGS. 26-28 illustrate 3-D representations of a frame of the convention cell inFIGS. 24A and 24B modified by one embodiment of the present invention.
• FIGS. 29A and 29B illustrate 3-D representations of a cell of the present invention formed fromFIGS. 26-28, whereFIG. 29B is a partial view of a 3-D representation of the frame of the cell.
• FIG. 30 illustrates the frame ofFIG. 27 unfolded into a 2-D representation.
• FIG. 31 illustrates a frame of a truncated tetrahedral cell unfolded into a 2-D representation.
• FIG. 32 illustrates the frame ofFIG. 31 formed with curved struts according to one embodiment of the present invention.
• FIG. 33 illustrates the frame of a truncated octahedral cell unfolded into a 2-D representation.
• FIG. 34 illustrates the frame ofFIG. 33 formed with curved struts according to one embodiment of the present invention.
• FIGS. 35A-35E illustrate 2-D representations of examples of a circle or an ellipse inscribed within various geometric shapes according to one embodiment of the present invention.
• FIG. 36 illustrates the frame of a truncated tetrahedral cell unfolded into a 2-D representation with circles circumscribed around each face of the cell according to one embodiment of the present invention.
• FIGS. 37A and 37B illustrate various views of 3-D representations of another embodiment of a cell of the present invention based on a dodecahedral shape.
• FIG. 38 illustrates a 3-D representation of yet another embodiment of a cell of the present invention based on a dodecahedral shape.
• FIGS. 39A-38C illustrate various views of 3-D representations of yet another embodiment of a cell of the present invention based on a dodecahedral shape.
• FIG. 40 illustrates a 3-D representation of an exemplary arrangement of the cells ofFIGS. 24 and 25.
• FIGS. 41A and 41B illustrate various views of 3-D representations of an exemplary arrangement of the cells ofFIGS. 24,25, and37
• FIG. 42 illustrates a 3-D representation of an exemplary arrangement of the cells based on a truncated tetrahedral shape having one or more curved struts.
• FIG. 43 illustrates a 3-D representation of an exemplary arrangement of the present invention of cells based on truncated octahedra.
• FIG. 44 illustrates a 3-D representation of an exemplary arrangement of the present invention of cells based on cubes (light grey), truncated cuboctahedra (black), and truncated octahedra (dark grey).
• FIG. 45 illustrates a 3-D representation of an exemplary arrangement of the present invention of cells based on cuboctahedra (black), truncated octahedra (dark grey) and truncated tetrahedra (light grey).
• FIG. 46 illustrates a frame view of the arrangement ofFIG. 42.
• FIG. 47 illustrates a frame view of the arrangement ofFIG. 43.
• FIGS. 48-50 illustrate 3-D reprsentations of a frame based an octahedron modified by one embodiment of the present invention.
• FIGS. 51A and 51B illustrate various views of 3-D representations of a cell of the present invention formed from the frames ofFIGS. 48-50.
• FIG. 52 illustrates a 3-D representation of a frame based a truncated tetrahedron.
• FIGS. 53A-53D illustrate various views of 3-D representations of a cell formed from the frame ofFIG. 52 that was modified by one embodiment of the present invention.
• FIGS. 54A-54E illustrate various views of 3-D representations of an exemplary arrangement of the cells ofFIG. 53.
• FIGS. 55A-55E illustrate 3-D representations of a cell formed from a frame based on a hexagonal prism that was modified by one embodiment of the present invention.
• FIGS. 56A-56B and57A-57B illustrate 3-D representations of an exemplary arrangement of the cells ofFIG. 55.
• FIGS. 58-61 illustrate 3-D representations of frames based on a dodecahedron modified by various embodiments of the present invention.
• It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. Also, for simplification purposes, there may be only one exemplary instance, rather than all, is labeled. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.
DETAILED DESCRIPTION OF INVENTION
• As discussed above, Rapid Manufacturing Techniques (RMT) such as Direct Metal Fabrication (DMF) can be used to produce porous structures for medical implants. However, using DMF or other RMT to fabricate porous structures can create weak areas between fenestrations of the three-dimensional porous structure. This is mostly due to the shapes and configurations of the cells that have been used in the prior art to form these porous structures. In particular, fractures typically occur at areas where struts are connected together at a node. The fractures occur in porous structures of the prior art because the cross-sectional area of a strut where it connects to the node is typically less than the cross-sectional area of the resulting node. The areas where the struts connect to their node, typically referred to as stress risers, are common points of structural failure. The pattern of failure at the stress risers can also occur when the molten phase of particles does not completely melt and fuse together or when the surrounding substrate surfaces is too cold, which causes the hot powdered material to bead up during the DMF process. Regardless of the exact causes of strut fractures and the resulting poor performance of porous structures of the prior art, improved porous structures that can be fabricated using RMT, including DMF, and other free-form fabrication and near net-shape processes (e.g., selective laser sintering, electron beam melting, and stereo-lithography) are desired.
• FIGS. 1A and 1B provide an illustration of where fractures may occur.FIGS. 1A-1B illustrate an example of a porous structure with three or four struts, respectively, connected at a single node, where the struts ofFIG. 1A have the same diameters and the struts ofFIG. 1B have different diameters. Specifically, inFIG. 1A, threestruts102 of generally equal diameters are connected together atnode104. Threestress risers106 are created at the connections between the three struts102. Because the cross-sectional diameters ofstruts102 at thestress risers106 are less than the cross-sectional diameter of thenode104, thestress risers106 are locations for a typical strut failure. InFIG. 1B, threesmaller struts108 are connected to alarger strut110 at anode112. Three of the four resulting stress risers are shown at114, which have substantially smaller cross-sectional diameters than thenode112.FIG. 2 is a SEM (Scanning Electron Microscope) microphotograph of astructure200 fabricated using RMT, and it shows an example of strut fracture surfaces202. InFIG. 2, the sample shown is occluded withbuild powder204 in the areas around the strut fracture surfaces202.
• Referring toFIGS. 3-5, various embodiments of the present invention are shown. InFIGS. 3-5, struts302,402, and502 are connected together at theirrespective nodes304,404, and504 in various combinations. Each ofnodes304,404, and504 is a connection between only two struts. For example, inFIG. 5,node504acomprises a connection betweenstruts502aand502b; node504bcomprises a connection betweenstruts502band502c; andnode504ccomprises a connection betweenstruts502band502d. By reducing the number ofstruts302,402, and502 that meet or are connected at theirrespective nodes304,404, and504, the diameter or cross-sectional area where thestruts302,402, and502 are connected is substantially equal to the cross-sectional area at therespective nodes304,404, and504. Therefore, the effect of the stress risers (not shown) on the strength of the structure is lessened in the structures illustrated inFIGS. 3-5. Consequently, the resulting structures are substantially stronger than the structures of the prior art illustrated inFIGS. 1A-1B.
• FIGS. 6-8 illustrate alternative embodiments of the porous structures of the present invention comprising strut and node combinations where at least some of the struts are characterized by a smaller cross-sectional diameter at the body of the strut than at the stress riser. Thestruts602,702, and802 are characterized by a fluted or conical shape where each ofstruts602,702, and802 flares to a wider cross-sectional diameter as the strut approaches and connects at therespective nodes604,704, and804. The designs ofFIGS. 6-8 illustrate incorporatefluted struts602,702, and802 andnon-fluted struts606,706, and806, where both types of struts are connected at therespective nodes604,704, and804.
• Thus, each of the connections between thefluted struts602,702, and802 and thenon-fluted struts606,706, and806 has a cross-sectional diameter that is essentially equivalent to the maximum cross-sectional diameter offluted struts602,702, and802. Accordingly, the effect of the stress risers (not shown) of the structures are thereby reduced. Referring toFIG. 9A, it is a plan view of thestruts802 andnodes804 inFIG. 8.FIG. 9B is a plan view of an individual node inFIGS. 6-8, which is labeled asstruts602 andnode604 for demonstrative purposes. Referring toFIGS. 9A-9B, the fluted struts602,802 have a larger or maximum cross-sectional diameter at theends606,806 that meet at thenodes804,604, and a smaller or minimum cross-sectional diameter at the middle portions. Thus, the effect of stress risers (not shown) at the junctions between the struts flutedstruts602,702, and802 and thenon-fluted struts606,706, and806 are reduced. Preferably, only two struts, e.g.,602 and606, meet any given node, e.g.604, for added strength.
• FIGS. 10A-10F illustrate 2-D representations of various configurations of the frame of the struts and nodes in a porous structure of the prior art. For simplification purposes, the struts are not represented in 3-D but rather each strut is represented by a different line, e.g., its frame, that is either solid, bolded solid, or dashed lines. This representation is simply exemplary and not meant to be limiting. In the prior art, it is typical for a porous structure to have more than two struts meeting at anode1002, regardless whether the strut may be straight, curved or irregular. WhileFIG. 10A may show two struts meeting at a node, the stress risers of this configuration has the effect of the stress risers at a node with four struts connecting or intersecting one another. For example, U.S. Publication Nos. 2006/0147332 and 2010/0010638 show examples of these prior art configurations employed to form porous structures.
• In contrast, to the prior art configurations ofFIGS. 10A-10F, the present invention reduces the effect of the stress risers at the nodes by ensuring that no more than two struts intersect at a node. Consequently, some embodiments result in the diameter or cross-sectional area where the struts intersect being substantially equal to the cross-sectional area at each node, thereby reducing the effect of the stress risers on the strength of the structure.FIGS. 11A-11F illustrate exemplary embodiments of the present invention for modifying the corresponding configurations of the prior art to ensure that no more than two struts intersect at a node. As seen inFIGS. 11A-11F, each ofnodes1102 has only two struts intersecting. For simplification purposes, only one of the numerous nodes in11A-11F is labeled with thenumber1102. In particular, theFIGS. 11A-11F show atnodes1102, the end of one strut intersect the body of another strut. Further, the modification of the prior art configurations according to one embodiment of the present invention forms a modifiedpore1104 that is open in each configuration that provides additional porosity with added strength, which is a great improvement over the prior art.FIGS. 12A-12D illustrate 3-D representations of exemplary embodiments of the porous structure of the present invention formed with one or more configurations inFIGS. 11A-11F, where the frames, e.g., lines, have been given a thickness to form struts. InFIGS. 12A-12D, the porous structures havestruts1202 that intersect one another atnodes1204 where no more than two nodes intersect at a node.
• As demonstrated byFIGS. 11A-11F, theconventional nodes1002 ofFIGS. 10A-10F are effectively being “opened” up to ensure that no more than two struts meet at a node. In addition to reducing the effect of stress risers at the node, this “opening” up of theconventional nodes1002 ofFIGS. 10A-10F intonodes1102 ofFIGS. 11A-11F has the added benefit of reducing heat variations during the fabrication process. As with any other thermal processes, being able to control the heat variations, e.g., cooling, of the material is important to obtain the desired material properties.
• Referring toFIGS. 13A-13M, the present invention also provides for embodiments that reduce the effect of stress risers by incorporating curved struts into the porous structures.FIGS. 13A-13M illustrate 2-D representations of these various exemplary configurations of the frame of the two struts of the present invention forming a node, including frames for struts that are straight, curved, or a combination of both. As shown, only two struts intersect each other at thenode1302. At least inFIGS. 13A-13C, the struts intersect one another tangentially at thenode1302, providing increased mechanical strength and bonding.FIG. 14 illustrates 2-D representation of an exemplary embodiment of the porous structure of the present invention comprising one or more frame configurations inFIGS. 13A-13M, including frames for struts that are straight, curved, or a combination of both. As shown byFIG. 14, no more than two struts, whether curved or straight, meet at each node.FIGS. 15A-15C illustrate 2-D representations of exemplary configurations of the present invention of various curved frames and corresponding struts intersecting to form a node1502. InFIGS. 15A-15C, the dashed lines represent theframes1504 and the solid lines represent the correspondingstruts1506. As shown,node1502ais formed where the circular strut with its center at1508 tangentially intersect or meet the circular strut with its center at1510. Thenode1502bis formed where the circular strut with its center at1508 tangentially intersect or meet the circular strut with its center at1512. Similarly,FIG. 15B shows the circular strut with its center at1514 tangentially intersecting the circular strut with its center at1516 to formnode1502c. Likewise,FIG. 15C shows the circular strut with its center at1518 tangentially intersecting the circular strut with its center at1520 to form node1502d.FIG. 16 illustrates a 3-D representation of an exemplary embodiment of the porous structure of the present invention comprising one or more frame configurations inFIGS. 13A-13M, including frames for struts that are straight, curved, or a combination of both.
• FIG. 17 illustrates a 3-D representation of an exemplary frame for a generallycubical cell1700 formed by twelvestruts1702 and sixteennodes1704. Again, for simplification purposes, only some of the struts and nodes are labeled. By using sixteennodes1704 that form connections between only twostruts1702 as opposed to eight nodes that form connections between three struts as in a conventional cube design (not shown), thecell1700 providesstronger nodes1704, and stronger connections between thestruts1702 andnodes1704. As a result, this novel configuration of one embodiment of the present invention avoids variations in cross-sectional diameters betweenstruts1702 andnodes1704. As a result, the negative effects of stress risers like those shown atstress risers106 and114 inFIGS. 1A-1B on the strength of the structure are lessened.FIG. 18 illustrates aporous structure1800 formed from a plurality of connected cells1802, which are similar to those shown inFIG. 17. Similarly,FIGS. 19-20 show another comparison between the arrangement of cells of the prior art inFIG. 19 and one embodiment of the arrangement of cells of the present invention inFIG. 20. As previously discussed, by having more than two struts intersect at a node, the porous structure of the prior art is weak due to the increased effect of the stress risers. On the other hand, the arrangement inFIG. 20 of the present invention provides the requisite porosity with an improved strength because no more than two struts intersect at a node. In addition, the arrangement ofFIG. 20 has the added benefit of having more trabecular features, resembling the characteristics of cancellous bone, unlike the regular prior art configuration. Moreover, the advantage of looking trabecular while being formed in a calculated manner provides another benefit to the porous structures formed in accordance with the invention: a decreased need for expansive randomization of the porous structure. Consequently, the arrangement ofFIG. 20 resembles the characteristics of bones more so than the prior art configuration ofFIG. 19.FIG. 21 is a blown up view of the arrangement inFIG. 20 where the dashedlines2102 represent the frames of the struts to better show where the struts meet to form a node.
• Similarly,FIG. 22 illustrates another embodiment of a cell of the present invention.Cell2200 is based on a tetrahedron-shaped cell, or a triangular pyramid, where it is formed using only sixstruts2202 and eightnodes2204. Eachnode2204 connects only twostruts2202 together.FIG. 23 illustrates asimilar cell2300, which is a square-based pyramid. Referring toFIG. 23, eightstruts2302 and elevennodes2304 are used to form thecell2300. Other geometrical shapes for cells, such as dodecahedrons, icosahedrons, octagonal prisms, pentagonal prisms, cuboids and various random patterns are discussed below. In addition,FIGS. 17,18,22 and23 illustrate frames of struts that can be built from these frames where the thickness of each strut can be selected. As such, the thickness for each strut can be uniform or vary from one strut to another strut. Further, the struts can incorporate the fluted struts ofFIGS. 6-8. In addition, the struts do not have to be cylindrical in shape. As further discussed below, the cross-section of the struts can be rectangular or square or any other shape, e.g., geometric shape or irregular shapes, that would be suitable for the application.
• As discussed above with respect toFIGS. 17,18,22, and23, various cell designs of various shapes can be created using various techniques discussed above, e.g., DMF. Generally speaking, almost any three-dimensional multiple-sided design may be employed. For example, cells with an overall geometric shape such as Archimedean shapes, Platonic shapes, strictly convex polyhedrons, prisms, anti-prisms and various combinations thereof are within the contemplation of the present invention. In other embodiments, the number of sides of each cell may range from about 4 to about 24. More preferably, the number of sides of each cell may range from about 4 to about 16. One geometry that has been found to be particularly effective is a dodecahedron or 12 sided cell. However, as explained and illustrated below, the geometries of the individual cells or the cells of the porous structure may vary widely and in the geometries may vary randomly from cell to cell of a porous structure.
• For example,FIGS. 24A and 24B illustrate a conventionally designeddodecahedral cell2400 from a prior art porous structure with eachnode2404 being a connection between threestruts2402. Again, U.S. Publication Nos. 2006/0147332 and 2010/0010638 disclose examples of porous structures formed from these conventional cells. A porous structure with a given porosity and having a desired volume can be formed using a plurality ofcells2400 by attaching onecell2400 to anothercell2400 until the desired volume is achieved. Further, the structures using the prior art cell configuration may be disadvantageous because they do not resemble the randomness of native cancellous structures. That is, they do not adequately resemble the features of trabecular bone. More importantly, referring toFIGS. 24A and 24B, higher stresses are placed at eachnode2404 because thestruts2402 intersect one another at 120° angles, thereby increasing stress concentration factors due to the formation of notches or grooves on the face of thenodes2404 and the connection between more than twostruts2402 at eachnode2404.
• FIGS. 25A and 25B illustrate one embodiment of the present invention that provides a solution to these problems of the prior art. As shown byFIGS. 25A and 25B,cell2500 eliminated theconventional nodes2404 inFIGS. 24A and 24B by usingcurved struts2502 that form a ring or hoop, thereby eliminating the stress concentration factors caused by these nodes. In addition,cells2500 replaceconventional nodes2404 inFIGS. 24A and 24B with modifiednodes2504 that can be open or porous to provide additional porosity, which is an added benefit for many applications, such as enhancing tissue/bone ingrowth for orthopeadic implants. Accordingly,cell2500 provides additional strength with increased porosity while theconventional cell2400 is weaker and less porous.
• FIGS. 26-28 illustrate one embodiment to forming the cell inFIGS. 25A and 25B.FIG. 26 illustrates adodecahedral frame2600 for prior art cells as discussed with respect toFIGS. 24A and 24B.FIG. 27 illustratesframe2700 which comprisesframe2800 ofFIG. 28 superimposed over thedodecahedral frame2600 ofFIG. 26.FIG. 29A illustrates a cell similar to that ofFIGS. 25A and 25B formed by selecting a thickness forframe2800. InFIG. 29A, thecell2900 is constructed from twelvecurved struts2902 that, in this embodiment, may form a ring, a loop, an annulus, or a hoop. Thecurved struts2902 are joined together at triangular modifiednodes2904 that are more easily seen inFIG. 29B. Referring toFIG. 29B, the thicker circles represent four of thecurved struts2902 of thecell2900 while the thinner circles highlight the modifiednodes2904 formed bystruts2902. Each modifiednode2904 includes three fused connections orsintering junctions2906 between two differentcurved struts2902. That is,curved struts2902 tangentially intersect one another at therespective junction2906. Depending on the thickness of eachstrut2902, modifiednode2904 may also be porous withopenings2908 disposed between the threejunctions2906 or occluded with no openings disposed between the threejunctions2906. Preferably, modifiednode2904 hasopenings2908 disposed between the threejunctions2906 to provide additional porosity in conjunction with the porosity provided by thefenestrations2910 of thecurved struts2902. Referring toFIG. 29B, while thestruts2906 tangentially intersect one another, e.g., their frame tangentially meet, the struts' thickness may render theindividual junctions2906 relatively long as indicated by thedistance2912. These long, generallytangential sintering junctions2906 provide increased mechanical strength and bonding.
• Referring toFIG. 30, it depicts an unfolded or flattened two-dimensional representation ofFIG. 27, withconventional frame3008 and theframe3010 ofcell2900. As shown byFIG. 30, the location and number ofindividual junctions3006, as compared toconventional nodes3004 of theconventional configuration3008, is different when usingcurved struts3002 provided by the invention. For example,junctions3006 are generally located around the center of the body ofcurved struts3002, whileconventional nodes3002 is located at the end of the conventional struts. In addition, in this particular embodiment, the number ofjunctions3006 where thecurved struts3002 meet is three times the number ofconventional nodes3004 where straight struts meet forframe3008. Accordingly, the increased number of junctions provide increased mechanical strength.
• FIGS. 31-34 illustrate how frames for cells based on a typical polyhedron can be modified with curved struts to form a cell similar tocell2900 ofFIG. 29. Specifically,FIG. 31 illustrates aframe3100 of a truncated tetrahedral cell unfolded into a 2-D representation. InFIG. 32,frame3202 representsframe3100 ofFIG. 31 as modified by one embodiment the present invention to be formed withcurved struts3202. Similarly,FIG. 33 illustrates theframe3300 of a truncated octahedral cell unfolded into a 2-D representation, andframe3402 ofFIG. 34 representsframe3300 ofFIG. 31 as modified by one embodiment the present invention to be formed withcurved struts3402. As discussed above, e.g., with respect toFIG. 30, the cells formed withframes3200 and3400 have increased mechanical strength and porosity overframes3100 and3300, respectively.
• FIGS. 35A-35E illustrate one way of modifying a typical polyhedron frame with curved struts. According to one embodiment of the invention, the polyhedron can be modified by inscribing, within the polyhedron, a circle or other shapes that contain curved features, such as an ellipse or oblong. Specifically,FIG. 35A is a circle inscribed within a square,FIG. 35B is a circle inscribed within a hexagon,FIG. 35C is a circle inscribed within a triangle,FIG. 35D is a circle inscribed within an octagon, andFIG. 35E is an oval inscribed within a parallelogram.FIGS. 35A-35E are merely demonstrative of the different configurations available and are not intended to limit the scope of the invention.
• FIG. 36 illustrates another way of modifying a typical polyhedron frame with curved struts. According to another embodiment of the invention, the polyhedron can be modified by circumscribing the polyhedron with a circle or other shapes that contain curved features, such as an ellipse or oblong.FIG. 36 illustrates aframe3600 of a truncated tetrahedral cell withcircles3602 circumscribed around each face of the cell. Some or all portions offrame3600 may be removed to form a new cell frame that can be used to fabricate a porous structure according to the present invention.
• FIGS. 37-39 illustrate embodiments of the present invention that incorporate both straight and curved struts. Specifically,FIGS. 37A and 37B illustratecell3700 formed fromframe2700 ofFIG. 27, which is a combination of thedodecahedral frame2600 ofFIG. 26 withframe2800 ofFIG. 28.Cell3700 has increased strength due to the addition of the curved struts, which result in a blending of the stress risers. As shown,cell3700 has modifiednode3704 comprising a conventional node formed withstraight struts3702band a node formed by three junctions of thecurved struts3702a.FIG. 38 illustratescell3800 formed by keeping one or more conventional nodes3804 formed bystraight struts3802 while modifying the other struts of the cells withcurved struts3806 to formjunctions3808 and modifiednodes3810. InFIG. 38 some struts are selectively thicker than other struts, depending on applications.
• Referring toFIG. 38, thecell3800 has at least onecurved strut3802, and preferably a plurality ofcurved struts3802 that form modified node3804awhen joined with two othercurved struts3802. In other embodiments, the modified nodes can be formed by joining together curved struts, curved strut sections, straight struts, or straight strut sections, or combinations thereof. An example of a node formed by joining together straight and curved struts is shown inFIGS. 39A-39C as modifiednode3904b. Modified nodes3804aare preferably triangular formed by threejunctions3806.Cell3800 may contain someconvention nodes3808 that joinstraight struts3810 or straight strut sections that may comprise notches formed by intersecting angles practiced in the prior art. The modified node3804amay be porous as discussed previously and indicated by3804aor occluded as indicated at3804b. The occluded modifiednodes3804band the porous modified nodes3804amay be formed by tangent sintering three ormore junctions3806 between curved or “ring-like” struts together. Any combination ofoccluded nodes3804b, porous modified nodes3804a,conventional nodes3808,straight struts3810, curvedstruts3802, and portions or segments thereof may be used in different predetermined or random ways in order to create stronger, more cancellous-appearing cell structure. Referring toFIGS. 39A-39C,cell3900 is an example of such combination.Cell3900 hascurved struts3902athat are “ring-like” and struts3902b. It also hasstraight struts3906 andconventional nodes3908. The combination of struts forms porous modifiednodes3904aand occluded modifiednodes3904b.
• Thus, while thecells3800 within a porous structure may be homogeneous, they may be arranged in a random and/or predetermined fashion with respect to each other to more closely resemble the appearance of cancellous bone. In some instances, it may be desirable to utilize one or more heterogeneous cell configurations which may be arranged systematically in predetermined patterns and/or arranged in random fashion to create a porous structure. Various arrangements can be designed using computer aided design (CAD) software or other equivalent software as will be apparent to those skilled in the art.
• FIGS. 40 and 41 show exemplary configurations of how thecells2400,2900, and3700 fromFIGS. 24,29, and37, respectively, can be combined, e.g., attached, joined, tiled, stacked, or repeated. Specifically,FIG. 40 illustratesarrangement4000 comprisingcell2400 andcell2900 fromFIGS. 24 and 29, respectively. Inarrangement4000, at the face wherecell2400 attaches tocell2900,conventional nodes2404 is placed partially within modifiednodes2904. Accordingly, by using various combinations ofcells2400 andcells2900, or other cells formed according to the present invention, a number of modifiednodes2504 can be selectively occluded completely or partially by matching conventional nodes with modified nodes.FIGS. 41A and 41B illustratearrangement4100 comprisingcells2400,2900, and3700. Again,FIGS. 40 and 41 are illustrative and do not limit the combination that can be made with these cells or other cells formed according to the embodiments of the present invention.
• FIG. 42 illustrates aporous structure4200 formed by joining a plurality ofcells4202 together, where the shape ofcells4202 is based on a truncated tetrahedron. One or morecurved struts4204 which may or may not form complete rings are inscribed within, or circumscribed around, each face of the selected polyhedral shape, which is a truncated tetrahedron inFIG. 42. Alternatively, the truncated tetrahedron shape or other selected polyhedral shape may be formed using a large number of short straight struts to closely approximate truly curved ring struts, such as the ring struts ofcell2900 inFIG. 29.
• FIGS. 43-45 illustrate 3-D representations of exemplary arrangements cells formed in accordance with the embodiments of the present invention. Specifically,FIG. 43 illustrates one way cells based on truncated octahedra can be stacked to form bitruncatedcubic honeycomb structure4300, which is by space-filling tessellation. The cells ofstructure4300 in both shades of gray are truncated octahedra. For simplification purposes, each cell is not modified with a curved strut but rather the dashed circle serves to illustrate that one or more faces of one or more truncated octahedra can be modified according to the embodiments of the present invention, e.g., curved struts to form porous structures with increased strength and porosity. Similarly,FIG. 44 illustrates one way, e.g., space-filling tessellation, cells based on a combination of cubes (light grey), truncated cuboctahedra (black), and truncated octahedra (dark grey) can be stacked to form cantitruncatedcubic honeycomb structure4400. Again, it is understood that the dashed circles represent how one or more polyhedron ofporous structure4400 can be modified according to the embodiments of the present invention, e.g., curved struts to form porous structures with increased strength and porosity. Likewise,FIG. 45 illustrates one way, e.g., space-filling tessellation, cells based on a combination of cuboctahedra (black), truncated octahedra (dark grey) and truncated tetrahedra (light grey) can be stacked to form truncated alternatedcubic honeycomb structure4500. Again, it is understood that the dashed circles represent how one or more polyhedron ofstructure4500 can be modified according to the embodiments of the present invention, e.g., curved struts to form porous structures with increased strength and porosity.
• FIG. 46 illustrates a frame view of the bitruncatedcubic honeycomb structure4300 ofFIG. 43.FIG. 47 illustrates a frame view cantitruncatedcubic honeycomb structure4500 ofFIG. 45. As shown byFIGS. 46 and 47, porous structures formed with polyhedral are not random, and thus, are not as suitable for implantation purposes, particularly for bones, because they do not adequately resemble the features of trabecular bone. On the other hand, as it can be envisioned that modifying certain or all cells of the frames inFIGS. 46 and 47 would result in porous structures resembling trabecular bone.
• When curved struts are employed, at least one curved strut portion may generally form a portion of a ring which at least partially inscribes or circumscribes a side of a polyhedron. Such a polyhedral shape may be any one of isogonal or vertex-transitive, isotoxal or edge-transitive, isohedral or face-transitive, regular, quasi-regular, semi-regular, uniform, or noble. Disclosed curved strut portions may also be at least partially inscribed within or circumscribed around one or more sides of one or more of the following Archimedean shapes: truncated tetrahedrons, cuboctahedrons, truncated cubes (i.e., truncated hexahedrons), truncated octahedrons, rhombicuboctahedrons (i.e., small rhombicuboctahedrons), truncated cuboctahedrons (i.e., great rhombicuboctahedrons), snub cubes (i.e., snub hexahedrons, snub cuboctahedrons either or both chiral forms), icosidodecahedrons, truncated dodecahedrons, truncated icosahedrons (i.e., buckyball or soccer ball-shaped), rhombicosidodecahedrons (i.e., small rhombicosidodecahedrons), truncated icosidodecahedrons (i.e., great rhombicosidodecahedrons), snub dodecahedron or snub icosidodecahedrons (either or both chiral forms). Since Archimedean shapes are highly symmetric, semi-regular convex polyhedrons composed of two or more types of regular polygons meeting in identical vertices, they may generally be categorized as being easily stackable and arrangeable for use in repeating patterns to fill up a volumetric space.
• In some embodiments, curved strut portions according to the invention are provided to form a porous structure, the curved strut portions generally forming a ring strut portion at least partially inscribing within or circumscribing around one or more polygonal sides of one or more Platonic shapes (e.g., tetrahedrons, cubes, octahedrons, dodecahedrons, and icosahedrons), uniform polyhedrons (e.g., prisms, prismatoids such as antiprisms, uniform prisms, right prisms, parallelpipeds, and cuboids), polytopes, polygons, polyhedrons, polyforms, and/or honeycombs. Examples of antiprisms include, but are not limited to square antiprisms, octagonal antiprisms, pentagonal antiprisms, decagonal antiprisms, hexagonal antiprsims, and dodecagonal antiprisms.
• In yet other embodiments, a porous structure may be formed from cells comprising the shape of a strictly convex polyhedron, (e.g., a Johnson shape), wherein curved strut portions generally form a ring strut portion at least partially inscribed within or circumscribed around one or more face of the strictly convex polyhedron, wherein each face of the strictly convex polyhedron is a regular polygon, and wherein the strictly convex polyhedron is not uniform (i.e., it is not a Platonic shape, Archimedean shape, prism, or antiprism). In such embodiments, there is no requirement that each face of the strictly convex polyhedron must be the same polygon, or that the same polygons join around each vertex. In some examples, pyramids, cupolas, and rotunda such as square pyramids, pentagonal pyramids, triangular cupolas, square cupolas, pentagonal cupolas, and pentagonal rotunda are contemplated. Moreover, modified pyramids and dipyramids such as elongated triangular pyramids (or elongated tetrahedrons), elongated square pyramids (or augmented cubes), elongated pentagonal pyramids, gyroelongated square pyramids, gyroelongated pentagonal pyramids (or diminished icosahedrons), triangular dipyramids, pentagonal dipyramids, elongated triangular dipyramids, elongated square dipyramids (or biaugmented cubes), elongated pentagonal dipyramids, gyroelongated square dipyramids may be employed. Modified cupolas and rotunda shapes such as elongated triangular cupolas, elongated square cupolas (diminished rhombicuboctahedrons), elongated pentagonal cupolas, elongated pentagonal rotunda, gyroelongated triangular cupolas, gyroelongated square cupolas, gyroelongated pentagonal cupolas, gyroelongated pentagonal rotunda, gyrobifastigium, triangular orthobicupolas (gyrate cuboctahedrons), square orthobicupolas, square gyrobicupolas, pentagonal orthobicupolas, pentagonal gyrobicupolas, pentagonal orthocupolarotunda, pentagonal gyrocupolarotunda, pentagonal orthobirotunda (gyrate icosidodecahedron), elongated triangular orthobicupolas, elongated triangular gyrobicupolas, elongated square gyrobicupolas (gyrate rhombicuboctahedrons), elongated pentagonal orthobicupolas, elongated pentagonal gyrobicupolas, elongated pentagonal orthocupolarotunda, elongated pentagonal gyrocupolarotunda, elongated pentagonal orthobirotunda, elongated pentagonal gyrobirotunda, gyroelongated triangular bicupolas (either or both chiral forms), gyroelongated square bicupolas (either or both chiral forms), gyroelongated pentagonal bicupolas (either or both chiral forms), gyroelongated pentagonal cupolarotunda (either or both chiral forms), and gyroelongated pentagonal birotunda (either or both chiral forms) may be utilised. Augmented prisms such as augmented triangular prisms, biaugmented triangular prisms, triaugmented triangular prisms, augmented pentagonal prisms, biaugmented pentagonal prisms, augmented hexagonal prisms, parabiaugmented hexagonal prisms, metabiaugmented hexagonal prisms, and triaugmented hexagonal prisms may also be practiced with the invention. Modified Platonic shapes such as augmented dodecahedrons, parabiaugmented dodecahedrons, metabiaugmented dodecahedrons, triaugmented dodecahedrons, metabidiminished icosahedrons, tridiminished icosahedrons, and augmented tridiminished icosahedrons may be employed. Moreover, modified Archimedian shapes such as augmented truncated tetrahedrons, augmented truncated cubes, biaugmented truncated cubes, augmented truncated dodecahedrons, parabiaugmented truncated dodecahedrons, metabiaugmented truncated dodecahedrons, triaugmented truncated dodecahedrons, gyrate rhombicosidodecahedrons, parabigyrate rhombicosidodecahedrons, metabigyrate rhombicosidodecahedrons, trigyrate rhombicosidodecahedrons, diminished rhombicosidodecahedrons, paragyrate diminished rhombicosidodecahedrons, metagyrate diminished rhombicosidodecahedrons, bigyrate diminished rhombicosidodecahedrons, parabidiminished rhombicosidodecahedrons, metabidiminished rhombicosidodecahedrons, gyrate bidiminished rhombicosidodecahedrons, and tridimini shed rhombicosidodecahedrons are envisaged. Snub disphenoids (Siamese dodecahedrons), snub square antiprisms, sphenocorona, augmented sphenocorona, sphenomegacorona, hebesphenomegacorona, disphenocingulum, bilunabirotunda, and triangular hebesphenorotunda and other miscellaneous non-uniform convex polyhedron shapes are contemplated.
• In some embodiments, the average cross section of the cell fenestrations of the present invention is in the range of 0.01 to 2000 microns. More preferably, the average cross section of the cell fenestrations is in the range of 50 to 1000 microns. Most preferably, the average cross section of the cell fenestrations is in the range of 100 to 500 microns. Cell fenestrations can include, but are not limited to, (1) any openings created by the struts such as the open modified pores, e.g.,3804aofFIG. 38 or1104 ofFIGS. 11A-11F, created by the junctions, e.g.,3806 ofFIG. 38 ornodes1102 ofFIGS. 11A-11F, or (2) any openings inscribed by the struts themselves, e.g.,2910 ofFIG. 29B. For example, in embodiments where the cell fenestrations are generally circular, the average cross section of a fenestration may be the average diameter of that particular fenestration, and in embodiments where the cell fenestrations are generally rectangular or square, the average cross section of a fenestration may be the average distance going from one side to the opposite side.
• Applying the above principles to other embodiments,FIGS. 51A and 51B illustrate acell5100 formed from an octahedron frame shown inFIG. 48 modified according to one embodiment of the present invention, shown inFIGS. 49-50. InFIG. 49,frame4900 is formed by inscribing circles within the faces offrame4800 inFIG. 48. InFIG. 50,frame5000 is formed by removingframe4800 fromframe4900 ofFIG. 49. As shown inFIG. 49, theframe5000 generally fits within theoctahedron frame4800.FIGS. 51A and 51B illustrate the completedcell5100, which is formed by selecting a shape and thickness forframe5000 inFIG. 50. Referring toFIGS. 51A and 51B,cell5100 generally comprises eightcurved struts5102 that may be provided in the form of rings. The eightcurved struts5102 are connected to one another at twelvedifferent junctions5106. Six porous modifiednodes5104, each modified node having a generally rectangular shape are formed by the fourdifferent junctions5106 and the correspondingstruts5102. As shown byFIGS. 51A and 51B, unlike the curved struts ofcell2500 ofFIGS. 25A and 25B,curved struts5102 have a rectangular or square cross-section rather than a circular cross-section of cells similar tocells2500 inFIGS. 25A and 25B. Cells with a rectangular or square cross-section provide the porous structure with a roughness different than that of the cells with a circular cross-section. It is envisioned that struts of other embodiments can have different shapes for a cross-section. Accordingly, the struts of a cell can have the same cross-section, the shape of the cross-section of the struts can be randomly chosen, or the cross-section shape can be selectively picked to achieve the strength, porosity, and/or roughness desired.
• As another alternative,FIGS. 53A-53D illustrate yet anothercell5300 based on a truncated tetrahedron frame shown inFIG. 52 as modified by one embodiment of the present invention. Referring toFIGS. 53A-53D, thecell5300 is formed in a similar manner tocell5100 ofFIGS. 51A and 51B. That is,frame5200 is inscribed with circles to form a second frame comprising circular struts, andframe5200 is removed leaving behind the circular frame.Cell5300 is completed by selecting a thickness and shape of the cross-sectional area for theframe5300. As discussed above, the thickness and shape of the cross-section of the struts can be uniform or it can vary randomly or in a predetermined manner, including struts with a uniform cross-section or struts that are fluted.Cell5300 includes four largercurved struts5302athat correspond with the four large hexagonal sides of the truncatedtetrahedral frame5200 and four smaller curved struts5202bthat correspond with the four smaller triangular sides of the truncatedtetrahedral frame5200. Alternative, a cell can be formed by circumscribing a circle about the large sides5202 and small sides5204 of the truncatedtetrahedral frame5200. A 2-D representation of this alternative embodiment is shown inFIG. 36. While not expressly shown in the drawings, it is also contemplated that in some embodiments, combinations of inscribed and circumscribed curved struts may be employed. As illustrated inFIGS. 53A-53D, porous triangular modifiednodes5304 are formed between threejunctions5306 that connect the struts5202aand5202btogether, but those skilled in the art will recognize that occluded modifiednodes3804bas shown inFIG. 38 may also be employed. Also, as shown inFIGS. 53A-53D, largercurved struts5302ahave a circular cross-section while smallercurved struts5302bhave a rectangular cross-section.FIGS. 54A-54E illustrate various angles of a porous structure formed by stackingcells5300 ofFIG. 53 in one exemplary manner. It is envisioned that that in some embodiments,cells5300 ofFIG. 53 can be stacked in different manners as known be a person skilled in the art.
• FIGS. 55A-55E illustrate yet another embodiment where acell5500 is based on a hexagonal prism (Prismatic) frame with upper and lower hexagons and that includes six vertical sides. The six smallercurved struts5502aare used for the six sides and larger upper and lowercurved struts5502bare used for the top and bottom. In thecell5500 illustrated inFIGS. 55A-55E, the eightcurved struts5302a,5302bare connected by occluded modifiednodes5504 but, it will be apparent to those skilled in the art that porous modified nodes such as those shown inFIG. 25 may also be employed. In the particular embodiment shown inFIGS. 55A-55E, the six smallercurved struts5502aused for the six sides have a slightly smaller cross-sectional area than the two larger upper and lowercurved struts5302b. However, it would be apparent to those skilled in the art that the struts with uniform or substantially uniform cross-sectional areas can also be employed without departing from the scope of this disclosure.FIGS. 56A-56B illustrate various angles of a porous structure formed by stackingcells5500 ofFIGS. 55A-55E in one exemplary manner. InFIGS. 56A and 56B,cells5500 are placed adjacent to one another to form alayer5602 and the layers are placed on top of one another either in a predetermined or random manner.FIGS. 57A and 57B similarly show a greater number ofcells5500 stacked in the same manner as shown inFIGS. 56A and 56B. As seen,cells5500 are stacked bylayers5702. It is envisioned that in some embodiments,cells5500 ofFIG. 55 can be stacked in different manners as known to a person skilled in the art.
• FIGS. 58-61 illustratedodecahedral frames5800,5900,6000, and6100 modified according to another embodiment of the invention. Instead of using curved struts or struts with curved portions to eliminate or reduceconventional nodes5802,5902,6002, and6102, the particular embodiments ofFIGS. 58-61 adjust the conventional nodes by ensuring at least one of the conventional nodes have no more than two nodes intersecting at a node as shown by at leastFIGS. 11A-11F. As shown byFIGS. 58-61, frames5800,5900,6000, and6100 have at least one modifiednode5804,5904,6004, and6104.
• In some embodiment, the configurations of the cells, struts, nodes and/or junctions may vary randomly throughout the porous structure to more closely simulate natural bone tissue. Particularly, the cells formed according to the present invention, such as the cells illustrated inFIGS. 25A-25B,29A,37A-37B,38,39A-39C,42,51A-51B,53A-53D, or55A-55B, can be stacked or repeated according to the methods outlined in U.S. Application No. 61/260,811, the disclosure of which are incorporated by reference herein in its entirety. In addition, the methods of U.S. Application No. 61/260,811 can also be employed to modify conventional nodes such that no more than two struts intersect at a node. In yet another embodiment, the porous structure formed according to the invention can be used in medical implants, such as an orthopedic implant, dental implant or vascular implant.
• As further discussed in the following paragraphs, the present disclosure also provides for a method to fabricate the porous structures described above. Preferably, the improved porous structures of the present invention is formed by using a free-from fabrication method, including rapid manufacturing techniques (RMT) such as direct metal fabrication (DMF). Generally, in free-form fabrication techniques, the desired structures can be formed directly from computer controlled databases, which greatly reduces the time and expense required to fabricate various articles and structures. Typically in RMT or free-form fabrication employs a computer-aided machine or apparatus that has an energy source such as a laser beam to melt or sinter powder to build the structure one layer at a time according to the model selected in the database of the computer component of the machine.
• For example, RMT is an additive fabrication technique for manufacturing objects by sequential delivering energy and/or material to specified points in space to produce that part. Particularly, the objects can be produced in a layer-wise fashion from laser-fusible powders that are dispensed one layer at a time. The powder is fused, melted, remelted, or sintered, by application of the laser energy that is directed in raster-scan fashion to portions of the powder layer corresponding to a cross section of the object. After fusing the powder on one particular layer, an additional layer of powder is dispensed, and the process is repeated until the object is completed.
• Detailed descriptions of selective laser sintering technology may be found in U.S. Pat. Nos. 4,863,538; 5,017,753; 5,076,869; and 4,944,817, the disclosures of which are incorporated by reference herein in their entirety. Current practice is to control the manufacturing process by computer using a mathematical model created with the aid of a computer. Consequently, RMT such as selective laser re-melting and sinering technologies have enabled the direct manufacture of solid or 3-D structures of high resolution and dimensional accuracy from a variety of materials.
• In one embodiment of the present invention, the porous structure is formed from powder that is selected from the group consisting of metal, ceramic, metal-ceramic (cermet), glass, glass-ceramic, polymer, composite and combinations thereof. In another embodiment, metallic powder is used and is selected from the group consisting of titanium, titanium alloy, zirconium, zirconium alloy, niobium, niobium alloy, tantalum, tantalum alloy, nickel-chromium (e.g., stainless steel), cobalt-chromium alloy and combinations thereof.
• As known by those skilled in the art, creating models of cells or structures according to the disclosure of the present invention can be done with computer aided design (CAD) software or other similar software. In one embodiment, the model is built by starting with a prior art configuration and modifying the struts and nodes of the prior art configuration by either (1) adjusting the number struts that intersect at a node, such as the configurations inFIGS. 3-8,11A-11F,12A-12D,17-20, or22-23, or (2) introduce curved portions to the struts such as the configurations inFIGS. 13A-13M,14,15A-15C,16, or58-61. In another embodiment, curved “ring-like” struts can be added to form cells illustrated inFIGS. 25A-25B,29A,37A-37B,38,39A-39C,42,51A-51B,53A-53D, or55A-55B. Referring toFIG. 26, in one embodiment, these cells can be formed by starting with aframe2600 based on a polyhedron, such as a dodecahedron. Referring toFIG. 27, the next step is to inscribe circles within each face of theframe2600 to formframe2700, which isframe2800 superimposed onframe2600. Subsequently,frame2600 can be removed fromframe2700, leaving onlyframe2800. The thickness and shape of the cross-section offrame2800 can be selected to form a completed cell, such ascell2900 inFIG. 29A. As discussed above, a portion of the faces offrame2600 can be inscribed with circles and/or a portion offrame2600 can be removed to form, orframe2600 is not removed at all. The cells formed by such combinations are illustrated inFIGS. 37A-37B,38, and39A-39C. As shown byFIGS. 48-53 and55, the same steps can be applied to any type of frames based on a polyhedron. Also with the aid of computer software, stacking, tiling or repeating algorithm can be applied to create a model of a porous structure with the desired dimensions formed from unit cells or struts and nodes of the present invention. One such stacking algorithm is space filling tessellation shown byFIGS. 43-45. As mentioned above, the methods disclosed in U.S. Application No. 61/260,811, which is incorporated by reference herein in its entirety, can be applied to stack the cells of the present invention or to form the struts according to the disclosures of the present invention by controlled randomization.
• Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims (26)

1. A porous structure comprising:

a plurality of struts, each strut comprises:

a first end;

a second end; and

a continuous elongated body between said first and second ends, said body having a thickness and a length; and

a plurality of nodes, each node comprises an intersection between one end of a first strut and the body of a second strut;

wherein said porous structure is produced at least by a rapid manufacturing technologies process.

2. The porous structure ofclaim 1 wherein the first and second ends of one or more struts extend between the body of two other struts.

3. The porous structure ofclaim 1, wherein the body of one or more struts comprise a plurality of nodes.

4. The porous structure ofclaim 1, wherein the cross-section of at least one end of one or more struts is larger than the cross-section of a portion of the body of said one or more struts.

5. The porous structure ofclaim 1 wherein at least a portion of the body of one or more struts is curved.

6. The porous structure ofclaim 1 wherein the plurality of struts can be sintered, melted, welded, bonded, fused, or otherwise connected to one another.

7. The porous structure ofclaim 1 wherein a plurality of the struts and nodes define at least one fenestration.

8. The porous structure ofclaim 1 further comprising material selected from the group consisting of metal, ceramic, metal-ceramic (cermet), glass, glass-ceramic, polymer, composite and combinations thereof.

9. The porous structure ofclaim 8 wherein the metallic material is selected from the group consisting of titanium, titanium alloy, zirconium, zirconium alloy, niobium, niobium alloy, tantalum, tantalum alloy, nickel-chromium (e.g., stainless steel), cobalt-chromium alloy and combinations thereof.

10. The porous structure ofclaim 1 wherein the cross section of one or more struts comprises a polygon.

11. The porous structure ofclaim 1 wherein at least a portion of the circumference of the cross-section is curved.

12. A method for fabricating a porous structure comprising the steps of:

creating a model of a porous structure at least in a computer generated environment, wherein the creation step comprises:

defining one or more struts with a first end, a second end, and a continuous elongated body between the first and second ends for each strut, selecting a thickness and length for the body; and

defining at least one node with an intersection between one end of a first strut and the body of a second strut for each node; and

fabricating the porous structure according to the model by exposing fusible material to an energy source.

13. The method ofclaim 12, further comprises the step of defining the first and second ends of one or more struts to extend between the body of two other struts.

14. The method ofclaim 12 further comprises the step of defining the body of one or more struts to comprise a plurality of nodes.

15. The method ofclaim 12 further comprises the step of defining the cross-section of at least one end of one or more struts to be larger than the cross-section of a portion of the body of said one or more struts.

16. The method ofclaim 12 further comprises the step of defining at least a portion of the body of one or more struts to be curved.

17. The method ofclaim 12 further comprises the step of sintering, melting, welding, bonding, or fusing a plurality of struts to one another.

18. The method ofclaim 12 further comprises the step of defining at least one fenestration in the porous structure using a plurality of the struts and nodes.

19. The method ofclaim 12 wherein the fabricating step further comprises selecting a material for fabricating the one or more struts from the group consisting of metal, ceramic, metal-ceramic (cermet), glass, glass-ceramic, polymer, composite and combinations thereof.

20. The method ofclaim 19 further comprises selecting a metallic material from the group consisting of titanium, titanium alloy, zirconium, zirconium alloy, niobium, niobium alloy, tantalum, tantalum alloy, nickel-chromium (e.g., stainless steel), cobalt-chromium alloy and combinations thereof.

21. The method ofclaim 12 further comprises the step of defining the cross section of one or more struts with a polygon.

22. The method ofclaim 12 further comprises the step of defining at least a portion the circumference of the cross-section with a curved portion.

23. A porous structure comprising:

at least one cell comprising:

a plurality of sides, each side comprising a polygon, wherein each leg of the polygon comprises a strut; wherein the strut comprises:

a first end;

a second end; and

a continuous elongated body between said first and second ends, said body having a thickness and a length; and

a plurality of nodes, each node comprises an intersection between one end of a first strut and the body of a second strut.

24. The porous structure ofclaim 23 further comprising:

a plurality of cells coupled to one another in a stacked pattern wherein at least two cells share one side.

25. The porous structure ofclaim 24 wherein said cell comprises a hollow interior.

26. The porous structure ofclaim 23 wherein said porous structure is manufactured with rapid manufacturing technologies.

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