U.S. patent application number 17/374104 was filed with the patent office on 2021-11-04 for controlled randomized porous structures and methods for making same.
The applicant listed for this patent is Smith & Nephew, Inc.. Invention is credited to Aashiish Agnihotri, Laura J. Gilmour, Ryan L. Landon, Jeffrey Sharp, Randy C. Winebarger.
Application Number | 20210338902 17/374104 |
Document ID | / |
Family ID | 1000005712809 |
Filed Date | 2021-11-04 |
United States Patent
Application |
20210338902 |
Kind Code |
A1 |
Landon; Ryan L. ; et
al. |
November 4, 2021 |
CONTROLLED RANDOMIZED POROUS STRUCTURES AND METHODS FOR MAKING
SAME
Abstract
Improved randomized porous structures and methods of
manufacturing such porous structures are disclosed. The scaffold of
the porous structures are formed from by dividing the space between
a plurality of spatial coordinates of a defined volume, where the
plurality of spatial coordinates have been moved in a random
direction and a random finite distance according to a predetermined
randomization limit.
Inventors: |
Landon; Ryan L.; (Memphis,
TN) ; Agnihotri; Aashiish; (Memphis, TN) ;
Gilmour; Laura J.; (Memphis, TN) ; Sharp;
Jeffrey; (Memphis, TN) ; Winebarger; Randy C.;
(Memphis, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Smith & Nephew, Inc. |
Memphis |
TN |
US |
|
|
Family ID: |
1000005712809 |
Appl. No.: |
17/374104 |
Filed: |
July 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16728668 |
Dec 27, 2019 |
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17374104 |
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16153207 |
Oct 5, 2018 |
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16728668 |
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13509585 |
Aug 7, 2012 |
10166316 |
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PCT/US2010/056602 |
Nov 12, 2010 |
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16153207 |
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61260811 |
Nov 12, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 27/56 20130101;
A61L 2430/02 20130101; Y10T 428/249953 20150401; B33Y 80/00
20141201 |
International
Class: |
A61L 27/56 20060101
A61L027/56 |
Claims
1. A model of scaffold for a porous structure comprising: a tiled
plurality of base volumes, each base volume comprising a plurality
of randomized struts, each strut having an elongated body and a
node at each end thereof, each strut being connected to one or more
other struts at a node; wherein the plurality of base volumes are
normalized such that struts intersecting an outer face of any base
volume are co-localized with corresponding struts in adjacent base
volumes when the base volumes are tiled to create the scaffold.
2. The model of claim 1, wherein each base volume is a
hexahedron.
3. A process for creating each base volume of claim 2, comprising:
defining a plurality of evenly-spaced outer seed points on a
boundary of the base volume comprising: a plurality of inbound
outer seed points evenly disposed on each face of the hexahedron; a
plurality of edge outer seed points evenly disposed on the edges of
the hexahedron; and a corner outer seed points disposed on each
corner of the hexahedron.
4. The process of claim 3, further comprising: for each inbound
outer seed point, identifying a corresponding inbound outer seed
point on an opposite face of the hexahedron such that both
corresponding inbound seed points have identical locations on the
opposite faces; and perturbing locations of both of the
corresponding inbound outer seed points in a random direction and a
random distance.
5. The process of claim 4, further comprising: for each edge outer
seed point, identifying corresponding edge outer seed points on all
parallel edges of the hexahedron such that the corresponding edge
seed points have identical locations on parallel edges; and
perturbing locations of the corresponding edge outer seed points in
a random direction and a random distance.
6. The process of claim 5, wherein locations of all edge outer seed
points on parallel edges of the hexahedron are perturbed as
group.
7. The process of claim 5, further comprising: perturbing locations
of all corner outer seed points in a random direction and a random
distance.
8. The process of claim 7, further comprising: defining a plurality
of evenly-spaced inner seed points interior to the base volume; and
perturbing locations of each of the inner seed points in random
directions and random distances.
9. The process of claim 8, wherein a distance between nearest
neighboring seed points after perturbation of the inner and outer
seed points is limited by a randomization limit.
10. The process of claim 9, wherein the randomization limit is
different for inner seed points and outer seed points.
11. The process of claim 8, wherein the scaffold is created by:
creating a plurality of base volumes having normalized outer seed
points; tiling a sufficient number of the base volumes having
normalized outer seed points to form the scaffold with desired
dimensions; dividing the space between all of the randomized seed
points generated by the copying and tiling of the base volumes; and
removing the seed points to form a three dimensional model of the
randomized scaffold.
12. The process of claim 11, wherein the dividing the space further
comprises: applying a tessellation using to the tiled based volumes
to create a plurality of three-dimensional cells in the tiled based
volumes, wherein edges of the cells define locations of the
elongated strut bodies and further wherein locations of the end
nodes of the struts are locations being equidistant from three or
more seed points.
13. The process of claim 12, wherein each base volume has
differently randomized inner seed points but identically randomized
outer seed points.
14. The process of claim 8, wherein the scaffold is created by:
creating a single base volume having perturbed seed points;
dividing the space between the randomized seed points of the single
base volume; removing the seed points such that the single base
volume defines randomized struts; and tiling a sufficient number of
identical copies of the single base volume to form the scaffold
with desired dimensions.
15. The process of claim 14, wherein dividing the space further
comprises: applying a Voronoi tessellation to the single base
volume to create a plurality of three-dimensional cells in the
single base volume having the seed points as centroids of each
three-dimensional cell; wherein the edges of each three-dimensional
cell created by the tessellation define locations of the struts for
the single base volume.
16. The model of claim 1, wherein the model further specifies a
cross-sectional shape and thickness for each strut.
17. The model of claim 16, wherein the cross-sectional shape and
thickness for each strut may differ from strut-to-strut.
18. The model of claim 17, wherein the model further specifies a
taper angle for each strut.
19. A process for fabricating the porous structure specified by the
model of claim 1 using a computer-aided apparatus, comprising:
providing the model of the porous structure to the computer-aided
apparatus; controlling the computer-aided apparatus to iteratively
deposit successive layers of a material, each successive layer of
material creating a cross-section of the porous structure in
accordance with the model; and controlling the computer-aided
apparatus to fuse, melt, re-melt or sinter each successive layer of
deposited material by application of energy from an energy
source.
20. The model of claim 1, wherein the porous structure is an
orthopedic implant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of pending
U.S. patent application Ser. No. 16/728,668, filed Dec. 27, 2019,
entitled "Controlled Randomized Porous Structures and Methods for
Making Same", which is a continuation application of pending U.S.
patent application Ser. No. 16/153,207, filed Oct. 5, 2018,
entitled "Controlled Randomized Porous Structures and Methods for
Making Same", which is a divisional application of U.S. patent
application Ser. No. 13/509,585, filed Aug. 7, 2012, now U.S. Pat.
No. 10,166,316, entitled "Controlled Randomized Porous Structures
and Methods for Making Same", which application is the national
phase application under 35 U.S.C. 371 of International Application
No. PCT/US2010/56602, filed Nov. 12, 2010, entitled "Controlled
Randomized Porous Structures and Methods for Making Same", which
claims priority to, and the benefit, of U.S. Provisional Patent
Application No. 61/260,811, filed Nov. 12, 2009 and entitled
"Controlled Randomization of Porous Structures for Medical
Implants," the disclosures of which are incorporated by reference
herein in their entirety.
FIELD OF THE DISCLOSURE
[0002] 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 OF THE DISCLOSURE
[0003] Certain medical implants and orthopedic implants require
strength for weight bearing purposes and 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. For
example, metal foam structures are porous, three-dimensional
structures that have been used in medical implants, particularly
orthopedic implants, because they have the requisite strength for
weight bearing purposes as well as the requisite porosity.
[0004] Metal foam structures and other porous 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.
[0005] Another similar conventional method includes 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.
[0006] While metal foams formed by such conventional methods
provide good porosity, they may not provide the desired 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.
[0007] 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.
[0008] 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.
[0009] While DMF can be used to provide dense structures strong
enough to serve as weight bearing structures in medical implants,
the porous structures conventionally used employ arrangements with
uniform, non-random, and regular features that create weak areas
where the struts of the three-dimensional porous structure
intersect. That is, the conventional structure configurations lack
directional strength and compensate for the weakness by making
struts thicker, thereby decreasing the porosity, and conversely, a
conventional structure with the desired porosity often lacks the
desired strength because of the thinner struts. That is, the
desired strength can be achieved in the prior art at the expense of
porosity, or vice versa. There are no methods and/or products
currently available that provide both the improved strength,
improved porosity, and improved connectivity.
[0010] Further, trabecular bone structures are non-uniform and
random in appearance on a micro-scale. It is also known that
effective medical implants must be physiologically compatible with
their surroundings in addition to providing the requisite strength,
porosity and connectivity. Yet the conventional porous structures
with uniform, non-random, and regular features that do not resemble
trabecular bone structures. For example, U.S. Publication Nos.
2006/0147332 and 2010/0010638 show examples of these prior art
configurations employed to form porous structures that exhibit the
disadvantages discussed above, e.g., weak areas at the strut
intersections, improved strength at the expense of porosity, and no
trabecular features.
[0011] One way to enhance the effectiveness of an orthopedic
implant may be to randomize the porous structure of an implant so
it better simulates trabecular structures in which it is implanted.
Therefore, in addition to strength, porosity and connectivity
properties, it is believed that the performance of an implant with
a porous structure could be improved if the porous structure could
be randomized porous thereby providing a randomized scaffold
structure as opposed to a uniform open cell structure. Methods
known in the art to create randomized structures typically involve
randomizing an existing uniform structure. These methods, however,
are limited because they typically require manual manipulation of
the struts, i.e., solid space, of one unit to match up with another
unit to build a scaffold of desired dimensions. If the struts of
the units do not match up, the integrity of the structure may be
compromised if it has too many loose struts. Similarly, a
randomized structure with poorly oriented struts may have poor
distribution of residual stresses due to the manufacturing method
resulting in warped or inaccurate parts. Accordingly, the structure
of the initial units of the prior art, either identical or not, is
usually simple to keep the stacking or building process manageable.
Otherwise, building a scaffold from complex randomized initial
units would be too time consuming and costly, particularly in
computation expenses. Further, an additional drawback to
randomizing an existing uniform structure is potentially making the
structure weaker due to the unanticipated changes in the properties
of the structure resulting from changes in the modulus and
direction during the randomization process. Consequently, an
original randomized structure, as opposed to a randomized existing
structure, provides for improved strength along with improved
porosity and enhanced complexity--e.g., trabecular features. As
mentioned above, in the prior art, software applications typically
produce porous structures that are predominantly uniform and
regular. For efficiency, they repeat a small unit tile in the
coordinate directions to fill a volume without gaps between the
tiles. However, relatively few and simple shapes are employed
within the unit tile due to the complexity of matching these tiles
together.
[0012] Further, 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.
[0013] In light of the above, there is still a need for efficient
methods to manufacture three dimensional porous structures, and the
structures themselves, with randomized scaffold structures that
provide for improved porosity without sacrificing the strength,
improved strength including seamless junctions between units, and
improved connectivity and having trabecular features.
SUMMARY OF THE DISCLOSURE
[0014] One objective of the invention is to provide porous
biocompatible structures suitable for use as medical implants that
have improved strength for weight bearing purposes and porosity for
tissue in-growth structures.
[0015] Another objective of the invention is to provide porous
biocompatible structures suitable for use as medical implants that
have improved connectivity to resemble trabecular bone
features.
[0016] Another objective of the invention is to provide porous
biocompatible structures that promote bone tissue and soft tissue
in-growth.
[0017] Another objective of the invention is to provide porous
biocompatible structures suitable for use as medical implants
having a controlled, yet random arrangement of struts and nodes for
improved performance characteristics.
[0018] Yet another objective of the invention is to provide methods
for fabricating such improved porous biocompatible structures.
[0019] Another objective of the invention is to provide efficient
methods for fabricating randomized porous structures by
manipulating the space between the struts.
[0020] Yet another objective of the invention is to provide methods
for providing a seamless fit between structures that are joined
together, regardless of whether the structures are identical or
not.
[0021] Another objective of the invention is to provide methods to
fabricate a randomized porous structure that can be customized to
specific needs, e.g., a particular patient or application, having
the appropriate distribution, pore size, porosity, and
strength.
[0022] Another objective of the invention is to provide methods for
controlling the randomization of a scaffold for a structure.
[0023] To meet the above objectives, there is provided, in
accordance with one aspect of the invention, a method for
fabricating a porous structure comprising the steps of: creating a
model of a porous structure, the creating step includes defining a
three dimensional space having an outer boundary and an inner
volume, placing a plurality of outer spatial coordinates along the
boundary, placing a plurality of inner spatial coordinates in the
inner volume, moving one or more inner spatial coordinates a finite
distance in a random direction, moving one or more outer spatial
coordinates a finite distance in a random direction. The step of
creating a model of a porous structure further includes dividing
the volume of the three dimensional space evenly among the
randomized outer and inner spatial coordinates, defining the
boundary of one or more divided volume with one or more struts and
one or more nodes, where each strut has a first end, a second end,
and a continuous elongated body between the first and second ends
for each strut, and each node is an intersection of at least two
struts, and selecting a thickness and a shape for one or more
struts. The method further includes the step of fabricating the
porous structure according to the model by exposing fusible
material to an energy source.
[0024] In accordance with another aspect of the invention, the
method also includes a step of providing a second three dimensional
space that is a duplicate of the first three dimensional space
where the inner and outer coordinates have already been
randomized.
[0025] In one embodiment, the moving of the inner spatial
coordinates a finite distance in a random direction is performed
within a preselected or predetermined randomization limit that
avoids any overlap of the inner spatial coordinates. In another
embodiment, the moving of the outer spatial coordinates a finite
distance in a random direction is performed within a predetermined
randomization limit so that the randomized outer spatial
coordinates of one three dimensional space match or correspond to
their respective outer spatial coordinates on a second
substantially identical three dimensional space. Alternatively, the
second three dimensional space is not substantially identical to
the first three dimensional space.
[0026] In one embodiment, a Voronoi tessellation is applied to the
randomized spatial coordinates and struts to remove redundant
struts. In another embodiment, the method includes the step of
fabricating the porous structure that comprises two or more
substantially identical three dimensional spaces having randomized
spatial coordinates and corresponding struts. In some embodiments
where the overlap of inner and outer spatial coordinates after
randomization or perturbation is not problematic, randomization
limits may be avoided altogether or used sparingly.
[0027] In some embodiments, only selected inner and/or outer
spatial coordinates are perturbed or randomized. In other
embodiments all or substantially all inner and/or outer spatial
coordinates are randomized or perturbed.
[0028] The perturbations or randomizations may be carried out for
each inner and each outer spatial coordinate, or for some of the
outer spatial coordinates and some of the inner spatial
coordinates, or for some of the outer spatial coordinates and none
of the inner spatial coordinates, or a little as one region of the
outer spatial coordinates. A complete randomization of all spatial
coordinates is not required.
[0029] In some embodiments, the predetermined randomization is
configured to avoid at least one inner spatial coordinate from
overlapping with at least one other inner spatial coordinate. In
other embodiments, the method further includes selecting a
predetermined randomization limit for at least one inner spatial
coordinate, the selecting comprising the steps of: defining a
volume around the at least one inner spatial coordinate, the volume
is based at least on the proximity of one other surrounding inner
spatial coordinate; and limiting the randomized movement of the at
least one inner spatial coordinate to be within the defined
volume.
[0030] Yet in other embodiments, the defined volume comprises a
geometric shape selected from the group consisting of spheres,
Archimedean shapes, Platonic shapes, polyhedrons, prisms,
anti-prisms and combinations thereof. In some embodiments, at least
one dimension of said defined volume has a radius of less than 50%
the distance between said at least one inner spatial coordinate and
other surrounding inner spatial coordinate.
[0031] In other embodiments, the matching is accomplished by moving
at least two corresponding outer spatial coordinates the same
finite distance and the same direction. In some embodiments, the
three dimensional space comprises a geometric shape selected from a
group consisting of space filling polyhedra, space-filling convex
polyhedra with regular faces, and space-filling convex polyhedra
with irregular faces.
[0032] Yet in other embodiments, the shape selected for the struts
comprises a polygon. In some refinements, the shape selected for
one strut differs from the shape of another strut, where the
selected shape is configured to promote tissue ingrowth.
[0033] In some embodiments, 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.
In other embodiments, the method 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.
[0034] According to another aspect of the invention, there is
provided 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 of at least two struts, where the
plurality of struts and nodes formed from a model created by
dividing the space between a plurality of spatial coordinates of a
defined volume, said plurality of spatial coordinates having been
moved in a random direction and a random finite distance according
to a predetermined randomization limit.
[0035] In some embodiments, the predetermined randomization is
configured to avoid at least one inner spatial coordinate from
overlapping with at least one other inner spatial coordinate. In
other embodiments, the dimension of said defined space surrounding
said one or more spatial coordinates is based at least on the
proximity of one other surrounding spatial coordinate. In some
refinements, the other spatial coordinate is a nearest neighbor to
the one or more spatial coordinates.
[0036] Yet in other embodiments, the defined space comprises a
geometric shape selected from the group consisting of spheres,
Archimedean shapes, Platonic shapes, polyhedrons, prisms,
anti-prisms and combinations thereof. In other refinements, at
least one dimension of said defined volume has a radius of less
than 50% the distance between said one or more spatial coordinates
and said one other surrounding spatial coordinate.
[0037] In some refinements, the three dimensional space comprises a
geometric shape selected from a group consisting of space filling
polyhedra, space-filling convex polyhedra with regular faces, and
space-filling convex polyhedra with irregular faces.
[0038] In other embodiments, a Voronoi tessellation is applied to
the randomized plurality of spatial coordinates to divide the space
between all spatial coordinates. In some refinements, the shape for
the cross sectional of said struts comprises a polygon. In some
refinements, the shape selected for one strut differs from the
shape of another strut, where the shape selected is configured to
promote tissue ingrowth.
[0039] In some embodiments, the porous structure further includes a
material selected from the group consisting of metal, ceramic,
metal-ceramic (cermet), glass, glass-ceramic, polymer, composite
and combinations thereof. In other refinements, 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.
[0040] According to yet another aspect of the present invention,
there is provided, a method for providing a seamless union between
at least two scaffolds comprising the steps of: providing at least
two three-dimensional spaces, each space having an outer boundary
and an inner volume, providing a total volume having said at least
two spaces; placing a plurality of spatial coordinates along the
outer boundary of each of said three-dimensional space, placing a
plurality of inner spatial coordinates in the inner volume, of each
of said three-dimensional space; forming said scaffold by dividing
the volume of the three dimensional space among the outer and inner
spatial coordinates and defining the boundary of a portion of said
divided volume with one or more struts, where each strut has a
first end, a second end, and a continuous elongated body between
the first and second ends for each strut, selecting at least one
thickness and at least one shape for one or more struts; and
fabricating a porous structure according to the scaffold with said
one or more struts having at least one thickness and at least one
shape by exposing fusible material to an energy source. In some
embodiments, the method further includes moving at least one
spatial coordinate from one of said plurality of outer spatial
coordinates and said plurality of inner spatial coordinates; said
movement configured to provide a scaffold having a seamless union
between said at least two spaces.
[0041] According to yet another aspect of the invention, there is
provided, a porous structure having 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 of at least two struts, where the
plurality of struts and nodes formed from a model created by
dividing the space between a plurality of spatial coordinates of
two or more defined volumes. In some embodiments, a Voronoi
tessellation is applied to the spatial coordinates to divide the
space.
[0042] 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
[0043] For a more complete understanding of the disclosed methods
and apparatuses, reference should be made to the embodiments
illustrated in greater detail in the accompanying drawings,
wherein:
[0044] FIG. 1 is a perspective view of the initial cube volume
illustrating a portion of the outer seed points or outer spatial
coordinates according to one aspect of the present invention;
[0045] FIG. 2 is a perspective view of the initial cube volume of
FIG. 1 with inner seed points according to one aspect of the
present invention;
[0046] FIG. 3 is a perspective view illustrating a randomization of
the inner seed points or spatial coordinates according to one
aspect of the present invention;
[0047] FIG. 4 is a perspective view illustrating one embodiment to
confirm compatibility of the inner seed points according to one
aspect of the present invention;
[0048] FIGS. 5A-5B are perspective views illustrating one
embodiment to randomize certain outer seed points according to one
aspect of the present invention;
[0049] FIGS. 6A-6B are perspective views illustrating one
embodiment to randomize other outer seed points according to one
aspect of the present invention;
[0050] FIGS. 7A-7B are perspective views illustrating one
embodiment to randomize yet other outer seed points according to
one aspect of the present invention;
[0051] FIG. 8 illustrates one embodiment of a seed point cloud
volume defined by randomized inner seed points and randomized outer
seed points according to one aspect of the present invention;
[0052] FIG. 9 illustrates one embodiment of an array of seven of
the seed point cloud tiles illustrated in FIG. 8 according to one
aspect of the present invention;
[0053] FIG. 10 illustrates one embodiment of a web or scaffold of
randomized struts produced according to one embodiment of the
present invention;
[0054] FIG. 11 illustrates the web or scaffold of randomized struts
of FIG. 10 placed as the center tile in an array according to one
aspect of the present invention;
[0055] FIG. 12 illustrates the various lines of a convex hull
according to one aspect of the present invention;
[0056] FIG. 13 illustrates one embodiment to remove certain
redundant lines from the convex hull of FIG. 12 according to one
aspect of the present invention;
[0057] FIGS. 14-15 illustrate the seamless joining of two identical
volumes of randomized struts disposed side-by-side according to one
aspect of the present invention;
[0058] FIG. 16 illustrates one refinement to apply certain shapes
and thicknesses to the struts of the volume of randomized struts in
FIG. 11;
[0059] FIG. 17 illustrates one embodiment of a porous structure
with four (4) volumes of randomized struts having a 10%
randomization limit according to one aspect of the present
invention;
[0060] FIG. 18 illustrates one embodiment of a porous structure
with four (4) volumes of randomized struts having a 20%
randomization limit according to one aspect of the present
invention;
[0061] FIG. 19 illustrates one embodiment of a porous structure
with four (4) volumes of randomized struts having a 30%
randomization limit according to one aspect of the present
invention;
[0062] FIG. 20 is a partial view of the porous structure of FIG. 19
illustrating one embodiment of a porous structure having a seamless
interface between two or more volumes of randomized struts
according to one aspect of the present invention;
[0063] FIG. 21 is a scanning electron microscope (SEM) image of a
stainless steel random porous structure made in accordance with one
aspect the present invention (image taken at 50x);
[0064] FIG. 22 is another SEM image of a stainless steel random
porous structure made in accordance with one aspect the present
invention (image taken at 50x);
[0065] FIGS. 23-25 are photographs of structures fabricated on an
EOS.TM. metal laser sintering machine, employing a 30%
randomization limit in accordance with one aspect of the present
invention;
[0066] FIGS. 26A-26C illustrates one embodiment of a porous coating
being formed from volumes of randomized struts according to one
aspect of the present invention;
[0067] FIG. 27 illustrates one embodiment of a Boolean intersect
volume according to one aspect of the present invention.
[0068] FIGS. 28A-28B illustrate a porous structure according to one
aspect of the present invention with two different randomized tiles
seamlessly joined together.
[0069] 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.
It should be understood, of course, that this disclosure is not
limited to the particular embodiments illustrated herein.
DETAILED DESCRIPTION
[0070] The present disclosure provides for methods to fabricate
porous structures with improved strength, porosity, and
connectivity. 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). Typically, in RMT or free-form
fabrication, a model, or calculations defining the desired
structure, or a computer readable file of the desired structure is
provided to 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 provided
model.
[0071] 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.
[0072] 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 sintering technologies have enabled
the direct manufacture of solid or 3-D structures of high
resolution and dimensional accuracy from a variety of
materials.
[0073] 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.
[0074] In another embodiment, the disclosed fabrication methods may
form a complete orthopedic implant structure, or the disclosed
techniques may be applied to a substrate or work piece which forms
part of an implant. The fabrication methods disclosed herein
produce porous structures the desired porosity, pore size, strength
and connectivity by controlling the randomization of the scaffold
of a porous structure. Cell attachment, bone in-growth and initial
fixation may be improved with the randomized scaffold structures
produced by the disclosed methods because the scaffold structures
better simulate natural trabecular structures. As an added benefit,
the implants are more aesthetically pleasing to the physician and
patient, since they better resemble natural trabecular
structures.
[0075] Preferably, the randomized scaffold can be created by
dividing a defined volume evenly between a series of seed points
that have been randomized at the boundary and within the volume.
The seed points have been randomized according to a predetermined
randomization limit that is preferably designed to avoid any
overlap of the seed points within the volume. If more than one
identical volume is used to create the randomized scaffold, the
predetermined randomization limit can be used to ensure the seed
points at the boundary of the volume ("outer seed points") match up
with the outer seed points of other identical volumes. As
described, the volume has been divided into random portions because
the seed points have been randomly placed, but the random division
is controlled because there was a limit on the random placement of
the seed points. The border of the divided portions serve as the
struts of the randomized scaffold, and the randomized scaffold can
be built into a porous structure once a strut thickness and shape
are selected.
[0076] The following paragraphs provide more detailed descriptions
and various embodiments and refinements of the present invention.
Referring to FIGS. 1 and 2, an initial geometry in the form of a
cube 100 may be chosen, which defines a volume. The cube 100 has an
outer boundary 102 and an inner or interior volume 104. For
demonstration purposes, FIG. 2 represents inner volume 104 as a
cube within cube 100. This is not meant to limit the scope of the
present disclosure where inner volume 104 can be any space within
the outer boundary 102. In other embodiments, it is envisioned that
other space-filling polyhedra can be used to define the disclosed
volume. As illustrated, a plurality of outer seed points 106, 108,
and 110 are placed at the outer boundary 102 of cube 100. While
FIG. 1 shows only the top face of cube 100 containing these outer
seed points, it is envisioned that in other embodiments, all or
most of the faces of the cube or other space-filling polyhedra may
contain these outer seed points. In FIG. 1, there are three types
of outer seed points. The first type is the corner outer seed
points 106, the second type is the edge outer seed points 108, and
the third is the inbound outer seed points 110. In FIG. 1, These
outer seed points are evenly distributed at the boundary of cube
100. Referring to FIG. 2, in addition to these outer seed points, a
plurality of inner seed points 112 are placed in the inner volume
104. The number of seed points and their initial positions
illustrated in these FIGS. is intended for illustration purposes
only, and the actual number of inner and outer seed points depends
on the initial spatial geometry and desired randomness. Also, in
the preferred embodiment, the inner seed points are indexed and
randomized independently of the indexing and randomization of the
"outer" seed points. In other refinements, the randomization of the
inner and outer seed points are not independent. For more complex
inner seed point tiles or volumes, the copying or arraying process
illustrated in FIG. 4 may need to be expanded beyond the seven-tile
array shown in FIG. 4. Also, in some embodiments, the inner and
outer seed points may be defined based at least upon the particular
seed point's level of influence on the boundary between volumes.
For instance, seed points that do not have any or have minimal
influence on the boundary between volumes would be defined as inner
seed points. On the other hand, seed points that have substantial
influence on the boundary would be defined as outer seed points.
Further, in these embodiments, it may not be necessary to array the
inner seed point tiles or volumes as the inner seed points, as
defined, should not have any influence or minimally influence the
boundary.
[0077] After the inner seed points 112 are placed or created, their
positions are randomized in three-dimensional space as illustrated
in FIG. 3. Each seed point or spatial coordinate 112 is moved or
"perturbed" in random directions by random magnitudes using a
random number generator algorithm. That is, each seed point or
spatial coordinate 112 is moved a finite distance in a random
direction within cube 100, where the finite distance each seed
point has been moved is also random. The perturbation or moving of
the seed points 112 is not completely random, however, because a
preselected or predetermined randomization limit is imposed on the
random movement of each seed point 112.
[0078] In one embodiment, the predetermined randomization limit is
based upon the position of the closest neighboring seed point 112,
which can be determined by, for instance, the nearest neighbor
algorithm or other similar algorithms. The limit ensures that the
random movements of the inner seed points 112 do not cause one
inner seed point to overlap with another inner seed point 112. One
seed point can overlap another seed point by partially or fully
lying on top of the other seed point, or there can also be overlap
when one seed point enters the defined volume surrounding another
seed point. Typically, overlapping occurs more or most frequently
when two dissimilar tiles are joined together because the more
dissimilar the tiles, the more difficult it is to distinguish inner
and outer seed points. Conversely, overlapping occurs less
frequently when substantially similar tiles are combined. One way
of ensuring no overlap is to limit the movement of any inner seed
point 112 to be within a volume determined by the proximity of
surrounding inner seed points 112. In one embodiment, such a volume
may be defined as a hexahedron or a sphere with at least one of its
dimensions having a radius of less than 50% or half the distance to
the closest neighboring seed point. For example, referring to FIG.
2, using the inner seed point 112a located at the lower left corner
of the inner volume 104 as an example, the closest neighboring seed
points to inner seed point 112a are inner seed points 112b and
112c. If the randomization of the inner seed point 112a is limited
in magnitude or distance to within the volume of the sphere 114
surrounding point 112a, then the random placement of inner seed
point 112a can only occur within that volume 114 and any random
movements of point 112a cannot result in an overlap of point 112a
with the other two seed points 112b and 112c.
[0079] In other embodiments, more abstract and complex volumes may
be defined to delineate the bounds of perturbation for a given seed
point. In yet other embodiments, different volume sizes can be used
to limit the randomization. For instance, a 10% randomization limit
placed on the movements of the inner seed points 112 means that
each seed point 112 can be moved randomly within a sphere (or other
shapes) having a radius of 10% of the distance between that
particular seed point and its closest neighboring seed point prior
to the perturbation. A 30% randomization limit means that each seed
point can be moved randomly within a sphere having a radius of 30%
of the distance between the seed point and its closest neighbor
prior to perturbation. Accordingly, by limiting the random
magnitude and direction of the perturbation of each inner seed
point 112 to within a sphere or other defined three dimensional
space 114 with a radius of less than half the distance to a
neighboring seed point, the two seed points 112a and 112c cannot
not overlap or engage each other even if the randomization results
in these seed points moving directly toward each other. In some
embodiments, greater limits of randomization may be established in
order to allow seed point overlaps and seed point crossings during
perturbation steps. However, by preventing seed points from
overlapping and/or crossing, a higher level of porosity control and
strength may be achieved. Accordingly, the randomization limit can
be any number between 0% to 100% of the distance between a
particular seed point and its closest neighbor, e.g., 5%, 10%, 15%,
20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%,
85%, 90%, 95%, or 100%. In other embodiments, the range can exceed
100% the distance between a particular seed point and its closest
neighbor. For instance, the range of the randomization limit can be
100% to 200% or 0% to 200%. Although the specification has
discussed defining the predetermined randomization limit with
respect to inner spatial coordinates, it should be understood that
the steps discussed above can apply equally to randomizing outer
spatial coordinates. In further embodiments, inner and outer seed
points may be randomized using different methods and degrees of
randomization.
[0080] In the preferred embodiment, the model or randomized
scaffold of the porous structure is created by arraying or stacking
identical cloud volumes or tiles of perturbed seed points. When the
duplicated cloud volumes or tiles are arrayed or stacked, it is
preferred that the randomized inner seed points 112 do not
intercept or create conflicts with the outer seed points 106, 108,
and 110. One way of ensuring compatibility between the inner and
outer seed points is to array identical versions of cube 100 with
perturbed inner seed points 112 in three-dimensional space as
illustrated in FIG. 4 where one of the six identical versions of
cube 100 of FIG. 3 is placed adjacent to each face of cube 100 of
FIG. 3.
[0081] In a refinement, inner seed points 112 are randomized before
the outer seed points 106, 108, and 110. Turning to FIGS. 5A-7A,
the outer seed points 106, 108, and 110 are shown prior to
perturbation. That is, FIG. 5A shows inbound outer seed points 110
evenly distributed on the top face, front face, and right side face
of cube 100. FIG. 6A shows the edge outer seed points 108 evenly
distributed around the edges of the top face, front face, and right
side face of cube 100. FIG. 7A shows the corner outer seed points
106 evenly placed at the corners of the top face, front face, and
right side face of cube 100. For simplification purposes, the outer
seed points 106, 108, and 110 are shown only for the top face,
front face, and right side face of cube 100. In other embodiments,
more or less faces of the initial cube or other space-filling
polyhedra can include these outer seed points. In the preferred
embodiment, instead of randomizing the outer seed points 106, 108,
and 110 together or as a group like the inner seed points 112, the
outer seed points 106, 108, and 110 are randomized essentially in
pairs due to the six-sided cubical geometry of cube 100. That is,
each outer seed point and its counterpart outer seed points are
identified and randomized in the same direction and magnitude.
[0082] Turning to FIGS. 5A and 5B, the outer seed points 110a of a
front face region 118 are first identified and indexed. All the
front outer seed points 110a may be randomized at the same time
using the random number generator algorithm to generate the random
finite distance and direction for each front outer seed point 110a,
while the predetermined randomization limit (e.g., a sphere at 30%
limit). Because the initial geometry 100 is a regular hexahedron, a
corresponding set of outer seed points (not shown) on a back face
region 120 are also identified, indexed, and randomized. Each back
outer seed point (not shown) is randomized in the same direction
and magnitude (distance) as its corresponding front outer seed
point 110a. In other words, each front outer seed points 110a has
identical x- and z-coordinates as its and its corresponding back
outer seed point, but both have different y-coordinates. Each of
the back outer seed points may be randomized individually or all
the back outer seed points may be randomized as a group, so long as
the randomization used for each back outer seed point is of the
same magnitude and direction as its corresponding front outer seed
point 110a. This process results in the front region 118 and the
back face region 120 with identical randomized inbound outer seed
points. The result is shown in FIG. 8, where the inbound outer seed
points 110a of face 122 are identical in the x-direction and
z-direction as the inbound outer seed points 110b of face 124. To
confirm compatibility, the point clouds shown in FIG. 5B may be
copied in three-dimensional space upwards, downwards and to all
four sides in a similar manner as shown in FIG. 4.
[0083] For purposes of keeping FIGS. 5A and 5B simplified, the
inbound outer seed points 110 on the top and side faces of cube 100
are not perturbed. Also, referring to FIG. 8, the faces, other than
faces 122 and 124, of cube 100 are intentionally left blank. This,
however, is only for demonstration purposes and does not limit the
scope of either the claims or the present disclosure. That is, it
is understood that the side outer seed points 110c can also be
identified, indexed, and randomized as described for front face 118
and back face 120. That is the right side outer seed points 110c
can be perturbed first according to a random number generator
algorithm and a predetermined randomization limit, as described
above. A corresponding set of left side outer seed points (not
shown) are then randomized individually or as a group, where the
magnitude and direction of each perturbation of the right outer
seed points are identified and applied to each corresponding left
outer seed points (not shown). Accordingly, the right and left
outer seed points will have identical y- and z-coordinates, and
different x-coordinates, after perturbation. To confirm
compatibility, the resulting point clouds can be copied in
three-dimensional space upwards, downwards and to all four sides in
a similar manner as shown in FIG. 4. The same process can be
performed for the top outer seed points 110d and corresponding
bottom outer seed points. That is, after the top 110d and
corresponding bottom outer seed points are identified, the
corresponding pair of outer seed points are randomized using the
same directions and magnitude to provide top and bottom outer seed
points with identical x- and y-coordinates but different
z-coordinates. The result is that the opposing top and bottom faces
with identically randomized seed point clouds. To confirm
compatibility, the resulting point clouds shown are copied in 3D
space upwards, downwards and to all four sides in a similar manner
as shown in FIG. 4.
[0084] In summary, inbound outer seed points disposed on, adjacent
to, or defining a face region like seed points 110a, c, d in FIG.
5A, may be randomized as a group similar to the inner seed points
112; however, inbound outer seed points disposed along an opposite
face region need to be moved in an identical fashion to their
counterparts as shown and described above. In the embodiment shown
in 5B, at least two of the six face regions will have matching
inbound outer seed point patterns in space. In some embodiments, at
least some seed points may be randomized, while other seed points
remain unperturbed. For instance, some refinements may exist, where
perturbations only occur at every Nth seed point in a region. Other
refinements may include cubes or tiles or volumes of perturbed seed
points, e.g., cube 800 of FIG. 8, where the one or more inner seed
points 112 are perturbed while one or more outer seed points 106,
108, and 110 remain unperturbed and arranged in an ordered fashion
to ensure compatibility between either randomized or non-randomized
cubes or tiles or volumes.
[0085] It may be preferable to provide a gradient of randomness
while still maintaining a controlled porosity and/or pore size. The
gradient of randomness can be achieved by many means. One way is to
gradually or abruptly increase the randomization limit (e.g.,
increasing from 10% to 30% limit) in one or more directions within
a given cube or tile or volume. Another way is to gradually or
abruptly increase the number of perturbed seed point in one or more
directions within a cube or tile or volume. In yet other
embodiments, only one or more outer seed point regions may be
perturbed, and inner seed points 65 remain unperturbed to form a
sandwich of non-random seed points between random seed points. More
alternatively, some refinements may exist where seed points are
only perturbed at predetermined regions within an overall seed
point cloud cube or tile or volume, e.g., cube 800 of FIG. 8.
Various combinations of the aforementioned embodiments are can be
employed.
[0086] Turning to FIGS. 6A and 6B, a similar randomization process
is employed for the edge outer seed points 108 disposed along the
edge regions of cube 100. With embodiments employing regular
hexahedron geometry (cube) as illustrated, seed points edge outer
seed points 108 may be randomized in groups according to the
following disclosure. FIG. 6A illustrates an even distribution of
the edge outer seed points 108, which are disposed along the edge
regions parallel with the x-axis, y-axis, and z-axis. In the
preferred embodiment, all the edge outer seed points 108 are
identified and randomized together as a group or individually.
Regardless of individual or group randomization, the edge outer
seed points 108 are perturbed with identical directions and
magnitudes as shown in FIG. 6B. For purposes of keeping FIGS. 6A
and 6B simplified, the edge outer seed points 108 of the back,
bottom, and left faces of cube 100 are not shown, and only selected
edge outer seed points 108 are perturbed. This, however, is only
for demonstration purposes and does not limit the scope of either
the claims or the present disclosure. To confirm compatibility, the
point clouds shown in FIG. 6B can be copied in 3-D space upwards,
downwards and to all four sides in a similar manner as shown in
FIG. 4. In confirming compatibility, it is preferred that
duplicated seed points are removed. In other embodiments, however,
duplicated seed points may not be removed. In another embodiment,
compatible seed point clouds may be reduced prior to any copying
and/or arraying to prevent duplicate seed points during the
multiplication process.
[0087] The perturbation process can be similarly repeated for other
edge outer seed points 108. That is, other edge outer seed points
108 can also be identified, indexed, and randomized according to a
random number generator algorithm and a predetermined randomization
limit, as described above. A corresponding set of edge outer seed
points (not shown) located at the opposite face of the cube is then
randomized individually or as a group, where the magnitude and
direction of each perturbation of the corresponding set of points
are identical to the previously randomized set. Thus, for edge
outer seed points 108 disposed along an edge region that is
parallel to an axis, the seed points that share a common coordinate
value for that axis can be randomized independently within the
group or together, as long as their counter parts are randomized
identically to ensure compatible edge regions. Here, unlike FIGS.
5A and 5B, perturbation of one edge outer seed point 108a results
in the perturbation of three other corresponding edge outer seed
points 108b (the third edge outer seed point is not shown). This is
because two adjacent sides share one edge outer seed point 108.
FIG. 8 demonstrates the identical randomization of corresponding
sets of edge outer seed points 108 on faces 122 and 124. The other
faces are left intentionally blank to keep FIG. 8 simplified. This,
however, is not intended to limit the scope of the claims or
present disclosure. It is envisioned that other edge seed points
can be perturbed in the same manner and included in cube 800.
[0088] Turning to FIGS. 7A and 7B, for regular hexahedron geometry,
the corner outer seed points 106 are identified and may be
randomized together as a group but in an identical fashion as shown
in FIG. 7B. In other words, each corner seed point 106 is moved in
the same direction and by the same magnitude to ensure that all
eight corner regions are compatible as illustrated in FIG. 7B. To
confirm compatibility, the corner point clouds shown in FIG. 8A are
copied in 3D space upwards, downwards and to all four sides in a
similar manner as shown in FIG. 4.
[0089] FIG. 8 demonstrates a resulting overall seed point cloud
cube or volume 800 having an inner seed point cloud volume 104, and
identical outer seed point clouds at face region 122 and face
region 124, including identical edge, inbound, and corner outer
points 106, 108, and 110. As mentioned above, only two faces of
cube 800 are shown, but that is only for demonstration purposes and
is not intended to limit the scope of the claims or the present
disclosure. As already discussed, to ensure compatibility between
the cubes, the seed point cloud volume 800 may be copied in
three-dimensional space to the front, back, top, bottom and both
sides to produce array 900 as illustrated in FIG. 9. To keep FIG. 9
simplified, inner seed point cloud volume 104 has been omitted.
This, however, is not intended to limit the scope of the claims or
the present disclosure.
[0090] In summary, after or during perturbation of the inner and
outer seed points, to ensure that no unexpected aberrations occur
at the boundaries or faces between the seed point cloud cubes or
tiles or volumes, the randomized seed point cloud cube or tile or
volume may be arrayed with identical seed point cloud tiles to make
sure that: (1) the front and back face regions have matching seed
point spatial patterns; (2) the right and left or side face regions
have matching seed point spatial patterns; (3) the top and bottom
face regions have matching seed point spatial patterns; (4) the
edge regions disposed along and parallel to the x-axis have
matching seed point spatial patterns; (5) the edge regions disposed
along and parallel to the y-axis have matching seed point spatial
patterns; (6) edge regions along and parallel to the z-axis have
matching seed point spatial patterns; and (7) all corner regions
have matching seed point spatial patterns. In one embodiment, an
array of seed point cloud volume may be used for further processing
to create the randomized scaffold of the porous structure. It
should be noted that edge regions may not be parallel to a
particular axis, especially for more complex shapes used for the
initial geometry.
[0091] In a refinement, the randomization of the inner seed points
112 and the outer seed points 106,108, and 110 of the base cube or
tile or volume is performed using a numerical computing environment
algorithm. For example, the numerical computing environment
algorithm may be a MATLAB.TM. algorithm. Other non-limiting
examples of numerical computing environment programs SCILAB.TM.,
OCTAVE.TM., FREEMAT.TM., JMATHLIB.TM., MATHNIUM.TM., TELA.TM.,
ALGAE.TM., LUSH.TM., YORICK.TM., RLAB.TM., MAXIMA.TM., SAGE.TM.,
EULER.TM., S-LANG LIBRARY.TM., PYTHON.TM., NUMPY.TM., SCIPY.TM.,
THE R PROJECT', LUA.TM., any similar programs that provide the same
or similar computing environments as the listed programs, and
combinations, sub-combinations and variations thereof. Other
programs will be apparent to those skilled in the art and future
programs either under current development or future development
will also be apparent to those skilled in the art. This disclosure
is not limited to the particular software used to generate the
randomized base tile and the software used to create
three-dimensional structures from the multiplied randomized base
cube or tile or volume. The volume of the initial geometry and
number of seed points distributed within the volume and at the
boundary can be chosen at the user's discretion. In the preferred
embodiment, the volume and number of seed points depend on the
information provided by clinical studies and literature regarding
the preferred or optimal openings and pore size per volume.
[0092] While the figures illustrate the disclosed methods using a
cubical space or cubical spatial coordinates, it will be noted here
that this disclosure is not limited to six-sided base structures or
six-sided outer geometries. Instead, as mentioned previously, the
disclosed methods apply to any space filling polyhedra (sometimes
referred to as plesiohedra), space-filling convex polyhedra with
regular faces including the triangular prism, hexagonal prism,
cube, truncated octahedron and gyrobifastigium, space-filling
convex polyhedra with irregular faces including the rhombic
dodecahedron, elongated dodecahedron, and squashed dodecahedron,
and any non-self-intersecting quadrilateral prism. Other
possibilities are too numerous to mention here. In lieu of
Cartesian coordinates, spherical, cylindrical and other coordinates
may also be used that would require the tiles to be appropriately
scaled as they are positioned further away from the origin base
tile. In a refinement, a gradient density algorithm can be
incorporated into the data for the base tile to aid in matching up
the borders between tiles. Thus, use of the terms "tile," "volume,"
and "initial geometry" herein covers multiple types of
three-dimensional shapes.
[0093] In the preferred embodiment, the base volume of randomized
seed points may then be multiplied and tiled together with other
identical base volumes to form a three dimensional scaffold for a
porous structure, where the scaffold has a controlled randomness.
However, in other refinements, a single base volume of randomized
seed points can serve as the scaffold for the porous structure.
That is, if the initial volume selected is sufficiently large, then
it can serve as the scaffold of a porous structure after seed
points are planted and randomized in a controlled manner as
described above. In this refinement, it may not be necessary to
confirm compatibility with other identical volumes since only one
volume is necessary to form the scaffold. The methods of the
present disclosure are applicable to fabricate a variety of
implants, including but not limited to, implants of the hip,
including compression hip screws, knee, ankle, dental, shoulder,
foot/hand, flanges, spine, skull plates, fracture plates,
intramedullary rods, augments, staples, bone screws, cardiovascular
implants, such as heart valves and artificial heart and ventricular
assist devices, ligament and muscle fasteners, other small joint
implants, and other implants. Also, while the base volume of
randomized seed points is preferably used to build three
dimensional scaffold structures for porous implants, it may apply
to other applications as well, such as manufactured items that
require resistance to vibrations, irregular loads, twisting of the
structure, such as filters, heat sinks, cushions, wound dressings,
cartilage or fat pad substitute, instrument weight reduction
material, rasp, tissue sampling structure, debridement burr.
[0094] The disclosed techniques for fabricating porous structures
of controlled randomness substantially reduce memory requirements
of the RMT. For instance, the calculation for an initial tile or
volume can be duplicated and reused to build an implant or many
implants.
[0095] In embodiments using a plurality of identical volumes of
randomized seed points produced by the process described above, it
is also desirable to define an initial volume that is as large as
possible so that the final scaffold has a minimal number of seams
between tiles or volumes. If a spherical, cylindrical, etc.
coordinate system is chosen, the tiles are scaled as they are
positioned further and further away from the origin of the
coordinate system or center of an array of seed points such as the
one shown in FIG. 9. In that case, a gradient density within unit
tiles may be used to aid in matching up the borders between tiles.
The techniques for reducing memory and use of various software
algorithms would still apply. The data can be exported to a RMT
machine directly or exported to a machine or computer that controls
the RMT machine.
[0096] Also in refinements of scaffolds using a plurality of
identical volumes of randomized seed points, struts are then
created for the scaffold by dividing the space between the
randomized seed points with lines after compatibility between the
identical cubes or tiles or volumes is confirmed. The division of
the volume can be achieved in several ways. Preferably, it is done
by applying any higher-order Voronoi tessellation algorithm, such
as a QHull algorithm, Ken Clarkson's "Hull" algorithm, cdd, or
Mac-Queen's k-means algorithm, to the randomized seed points.
However, any method/algorithm of calculating the three-dimensional
Voronoi tessellation, other than a QHull algorithm, may produce
acceptable results. Because the compatibility between the identical
cubes or tiles or volumes of randomized seed points has been
confirmed, the Voronoi tessellation algorithm can be applied before
or after the multiplication of the base volume of randomized seed
points. That is, one way the scaffold can be built is by (1)
creating a base volume of randomized seed points according to the
disclosed methods, (2) multiplying and tiling a sufficient number
of identical base volume of randomized seed points to form a
scaffold with the desired dimensions, (3) dividing the space
between all the randomized seed points generated by the copying and
tiling of the base volumes, e.g., applying a higher order Voronoi
tessellation algorithm, to form the struts of the scaffold, and (4)
removing the seed points to form a three dimensional model of the
randomized scaffold. A second way it can be done is by (1) creating
a base volume of randomized seed points according to the disclosed
methods, (2) dividing the space between the randomized seed points
of just that single base volume of randomized seed points, e.g.,
applying a Voronoi tessellation algorithm, to form the struts for
that base volume, (3) removing the seed points to form a base
volume with randomized struts, and (4) multiplying the base volume
with randomized struts and tiling a sufficient number of identical
base volumes with randomized struts to form a scaffold with the
desired dimensions. Both of these ways of dividing the space
between the randomized seed points result in the same division and
randomized struts structures for the scaffold. Also, before the
space between the randomized seed points is divided, it is
contemplated that certain seed points may be eliminated or
additional seed points may be added to achieve the irregularity
and/or porosity as desired or required by certain applications.
[0097] In one embodiment, a user can code the software program used
to divide the space between the seed points to eliminate any
redundant lines. FIG. 10 illustrates a base volume with randomized
struts produced according to the present disclosure. That is, an
initial geometry and volume were selected, inner and outer seed
points were distributed according to the desired openings and pore
size per volume, all or certain seed points were identified and
randomized according to a predetermined randomization limit, the
volume between the randomized seed points was divided according to
an algorithm, e.g., Voronoi tessellation, and the seed points were
removed to form tile or volume 1000 of FIG. 10. Volume 1000 of
randomized struts can be tiled or stacked to form a scaffold for a
porous structure of desired dimensions. After the size and
thickness of the struts are selected, the scaffold model can be
sent directly to the RMT machine to fabricate the porous
structure.
[0098] In other embodiments, however, the step of dividing the
space between the randomized seed points and eliminating any
redundant lines may be separated. Referring to FIG. 11, the
triangulated base volume or volume of randomized struts 1100 was
produced by a different division of the space between the seed
points where the division yielded various redundant lines or
struts. FIG. also illustrates the spatial arrangement of the center
tile to its coordinate neighbor tiles. The creation of redundant
lines is typical of many Voronoi tessellations and/or QHull
algorithms. If not eliminated, these redundant lines would result
in unnecessary struts and nodes, which could consume unnecessary
amounts of material and/or create various structural problems
related to strength, porosity, connectivity, in the pore structure
or incompatibilities between neighboring volumes with randomized
struts.
[0099] One way of removing the excess redundant lines is
illustrated in FIGS. 12-13. In FIG. 12, a convex hull 1202 is
illustrated, where the convex hull 1202 is one of many that is part
of the base volume 1100 of FIG. 11 before the redundant lines are
removed. In FIG. 12, the structural lines 1204 of the convex hull
1202 are shown as thinner lines and the redundant lines 1206 of the
convex hull 1202 are shown as thicker lines. FIG. 13 illustrates
the treatment of one area 1300 of the convex hull 1202 to remove
redundant lines 1206. Referring to FIG. 13, to eliminate or at
least reduce the number of redundant lines 1206, a determination is
made as to the extent which an alleged redundant line 1206 and/or a
facet 1210 created by one or two redundant lines 1206 is co-planar
with the surrounding structural face. Specifically, referring to
FIG. 13, facets 1210 which may have redundant lines 1206 are
identified. If an angle, between a line normal to a facet 1210,
e.g., N.sub.4, and a line normal to neighboring facet 1210, e.g.,
N.sub.3, is sufficiently small or below a threshold angle .theta.,
then the shared redundant line or redundant lines 1206 between
facets could be eliminated. Similarly, if a line normal to the
polygon face and a line normal to a facet 1210 is sufficiently
small or below a threshold angle .theta., then the interior
redundant line or redundant lines 1206 may be eliminated. Other
algorithms to eliminate redundant lines 1206 may be used. For
instance, angles between lines can be compared with a threshold
angle, and eliminated if they are less than the threshold angle.
Alternatively, a shape recognition algorithm using polygon shape
templates or polyhedral shape templates may be used to identify
lines within the triangulated tile 1100 that collectively
approximate the shape of the template. Structural lines 1204 not
forming a portion of or falling within a tolerance of a shape
template may be considered redundant lines 1206 and be removed.
[0100] The threshold angle .theta. is typically 10.degree. or less,
e.g., 1.degree., 2.degree., 3.degree., 4.degree., 5.degree.,
6.degree., 7.degree., 8.degree., or 9.degree.. If, after choosing a
threshold angle .theta. that may be too low and some of the
openings in a convex hull 1202 are still obscured by a number of
redundant lines 1206, the threshold angle .theta. may be increased
and the algorithm re-run. However, choosing a high threshold angle
.theta., e.g., greater than 10.degree., may risk of removing some
of the desirable edges of a base volume with randomized struts.
This is generally not desirable, but may advantageously be used to
increase pore size without significantly affecting the strength. In
another refinement, the threshold angle range may be less than
6.degree., and more preferably, the threshold angle range may be
less than 4.degree..
[0101] The above-described threshold angle .theta. limitation
technique can also yield a base volume with randomized struts
similar to base volume 1100 of FIG. 11. The base volume 1100 can be
produced from the convex hull 1202 of FIG. 12 using a threshold
angle .theta. of less than 10.degree.. As shown in FIGS. 14-15, the
resulting base volumes 1100 (whether produced by a one step Voronoi
tessellation and redundant line removal or a two-step algorithms)
fit together seamlessly with compatible faces 1502 and 1504. This
is possible because the spatial coordinates (locating the voids) in
close proximity to the compatible faces on each tile were placed in
a compatible arrangement before the web or scaffold of struts for
each tile was created. While the preferred embodiment provides for
a porous structure where the redundant lines are removed to
eliminate all loose struts, it is envisioned that other embodiments
may have loose struts and are still in accordance with the present
disclosure.
[0102] After a scaffold comprising one or more base volumes of
randomized struts is created, the line data of that scaffold may be
exported a modeling program or algorithm, or directly to rapid
manufacturing equipment (e.g., by first converting line data to a
*.stl file and downloading to a rapid prototyping machine). When
the scaffold is sent directly to the machine, it must have a means
of determining which portion of the scaffold should be built and
which should be ignored because it is outside of the solid part. In
one example, the lines defining the struts of base volume 1100 may
be assigned a coordinate system, which can be used to transform
individual STL shells representing an idealized strut of
appropriate shape and thickness to the location of the lines. Then
the resulting collection of STL shells is written to an STL file to
define a porous three-dimensional tile. In another example, the
lines defining the struts of base volume 1100 may be converted to a
text file (*.exp extension) that corresponded to UNIGRAPHICS.TM.
"expressions" that could be imported into such a modeling program.
The solid-modeling program serves the purpose of taking a scaffold
structure with infinitely thin lines, such as the base volume 1100
of FIG. 11 and provides the struts with appropriate shapes and
thicknesses T. FIG. 16 demonstrates examples of the different
geometric shapes 1602 and thicknesses T available for the struts
1204, e.g., circle, triangle, pentagon. The identified shapes are
for demonstration purposes and are not intended to limit the scope
of the claims or present invention. For example, other geometric
shapes can include a square, rectangle, hexagon, octagon, heptagon,
etc. In some embodiments, the strut thickness can be proportional
to the length of the strut or the pore size. For instance, if the
pores are bigger, they can accommodate larger struts and still
maintain a desired pore opening size. Also, in instances where the
struts are longer than a predetermined or selected length, they can
be thickened to create more uniform strength characteristics with
struts that are shorter as long struts are more flexible and/or
weaker than shorter struts having the same thickness.
[0103] In other refinements, the three dimensional scaffold model
may be converted to line data readable by a CAD program or directly
to data readable by a solid modeling program if not already in a
format directly readable by rapid manufacturing equipment. Other
sold-modeling programs may be used or algorithms may be used to
apply one or more predetermined thicknesses to the line data of the
three dimensional scaffold model, so the model can be exported to
the machine for fabricating a corresponding porous structure.
[0104] In one embodiment, during the modeling process, the strut
lines 1204 (e.g., FIG. 11, 14, or 15) may be recorded in a part
file, and then when reading in the lines 1204 using a modeling
program and applying the desired thicknesses T, the struts 1204 may
be oriented to match an adjacent tile or volume. The locations of
each endpoint of each strut 1204 may be read as an ordered pair.
The modeling program may also allow the diameter/thickness of strut
1204 and any other relevant information to be inputted, such as the
general width, length, and height of the tile or volume 1100 (e.g.,
FIG. 11). Randomization algorithms similar to those described
herein for perturbing seed points may also be used to randomly
assign cross-sectional shapes or randomly assign strut thicknesses
to one or more lines 1204 in any portion of the base volume of
randomized struts 1100 of FIG. 11. Asymmetries or non-uniform
profiles may be defined in a part file and then associated with one
or more lines 1204 to form one or more struts within a tile or
volume, e.g., volume 1100 of FIG. 11, that are non-uniform. Such
associations may be random, selectively predetermined, or may be
applied to every line within a base volume of randomized struts.
Struts 1204 may also be randomly or non-randomly assigned a taper
angle or a varying cross-sectional shape from one endpoint to
another endpoint. Providing different shapes and/or dimensions to
each strut as described may provide better strength, biologic
fixation, and trabecular appearance, while maintaining full control
of overall porosity.
[0105] In at least the refinements where the volume of randomized
seed points are first multiplied and tiled to form a generally
shaped scaffold of desired dimensions before the total volume of
that scaffold is divided between the randomized seed points, an
algorithm to unite the different volumes may not be necessary as
process produces a seamlessly divided overall scaffold. In other
refinements, however, a Boolean unite algorithm may be used to
create a more unified scaffold if necessary. Referring to FIGS.
17-19, after one of the tiles 1702, 1802, 1902 is created, the data
for the lines 1204 of the volume 1100 (e.g. FIG. 11) are no longer
needed and may be deleted to keep the file size to a minimum. In
one variation, the file may be save as a *.prt, or part file, which
is the native file format for UNIGRAPHICS.TM.. A para-solid format
may also be employed.
[0106] In FIG. 17, individual tiles 1702 have struts that have been
randomized at a 10% randomization limit. Porous structure 1700 is
made up of four identical tiles 1702. Similarly, in FIGS. 18 and
19, tiles 1802 have struts randomized at a 20% randomization limit
and tiles 1902 at a 30% randomization limit. While FIGS. 17-19 show
porous structures 1700, 1800, and 1900 comprising identical tile
volumes, these serve as examples and do not limit the scope of the
invention. For instance, in one embodiment, a porous structure can
comprise of a combination of tiles that were randomized at limits
of 0%, 10%, 20%, 30%, etc. In other refinements, a porous structure
can comprise of tiles that have different shapes, and the tiles may
or may not have the same randomization limits.
[0107] The tiles 1702, 1802, and 1902 may be arranged row by row
and stacked with only the outermost struts 1204 overlapping to
create any size or shape as illustrated in FIGS. 17-19. The tiles
or volumes 1702, 1802, and 1902 may be assembled to create a bulk
structure for use at a later time. A Boolean unite algorithm may be
used to create the seamless body from two tiles 2002 and 2004 as
shown in FIG. 20. As seen, tiles 2002 and 2004 can be substantially
identical or tiles 2002 and 2004 can be different shapes and
randomization. For example, FIGS. 28A and 28B illustrate an example
of a porous structure having two tiles with different maximum pore
size. Regardless of the shape or randomization of the tiles, the
disclosed methods provide for a seamless interface between the
porous tiles. Individual tiles can be exported as a file that can
be tiled within a rapid manufacturing machine or software used by
such machines. Individual tiles can be interpreted by the machine
and then mapped to individual 3-D tiled positions to minimize file
size. As will be apparent to those skilled in the art, the 3-D
tiles do not have to be laid in a side-by-side fashion as
illustrated in FIGS. 17-19. As discussed above, machines may
include metal `selective` laser sintering machines (SLS), electron
beam melting machines (EBM), or laser engineered net shaping
(LENS.TM.) machines.
[0108] Also, many software applications will work to perform the
tiling/forming operation. The tiling can be performed in a
solid-modeling program like UNIGRAPHICS.TM., in a program used for
advanced NURBS.TM. and triangulation manipulation such as
GEOMAGIC.TM., in a program dedicated to triangulated file formats
like NetFabb, or manually in the *.stl file itself *.stl files are
simply a representation of triangulated solids which can be
translated and mirrored with any number of bodies. Once the solid
has been tiled and manipulated as desired, an *.stl file or the
like can be used in rapid-prototype machines. Once the desired
structure is defined, it can be exported to a format readable by
rapid prototype machines such as *.stl (stereolithography) format.
While the specific tiles 1802, 1902, and 2002 disclosed FIGS. 18-20
are rectangular and arrayed accordingly, the disclosed methods
apply to a multitude of tiling patterns in three dimensions, such
as spherical and cylindrical coordinate tilings. The disclosed
methods would be applicable to acetabular cups and stems for
example.
[0109] Scanning Electron Microscopy (SEM) photographs of a portion
of tiles 1702, 1802, 1902 disclosed FIGS. 17-19 are shown in FIGS.
21-22, and conventional enlarged photographs of tiles 1702, 1802,
1902 disclosed FIGS. 18-20 are shown in FIGS. 23-25. FIG. 24 is a
photograph of a curved portion of a metaphyseal cone fabricated on
an EOS.TM. metal laser sintering machine, employing random struts
and a 30% randomization limit. FIG. 23 is a photograph of a top
portion of the metaphyseal cone shown in FIG. 23. FIG. 25 is a
photograph of a cone section of a metaphyseal cone shown in FIGS.
23-24.
[0110] Preferred embodiments of porous structures may include
60-85% porosity as known to those skilled in the art. In some
embodiments, the average diameter of the pores of the present
invention is in the range of 0.01 to 2000 microns. More preferably,
the average diameter of the pores is in the range of 50 to 1000
microns. Most preferably, the average diameter of the pores is in
the range of 400 to 850 microns. FIG. 21 illustrates one exemplary
way the average pore diameter may be measured. The average pore
diameter typically is measured by the average diameter of the
larger openings captured by an SEM image. In other embodiments, the
average diameter 2102 may be measured horizontally or at any
desired diagonally position. The average diameter of smaller
openings or windows may also be measured.
[0111] In a refinement, the average strut thickness for a tile
ranges from about 100 .mu.m to about 400 .mu.M. More preferably,
the range is from about 180 .mu.m to about 300 .mu.m. In another
refinement, the average pore size (MVIL) or fenestration opening
diameter ranges from about 200 .mu.m to about 1970 .mu.m, more
preferably from 100 .mu.m to 700 .mu.M, and most preferably from
200 .mu.m to 450 .mu.m. Also, the strut thicknesses may be
randomized and/or the pore sizes may be randomized.
[0112] MVIL refers to Mean Void Intercept Length, which is another
way of characterizing the average pore size, particularly in
structures where the pore shapes and sizes are not uniform. One
generally known definition of MVIL is "measurement grid lines are
oriented parallel to the substrate interface. The number of times
the lines intercept voids is used with the volume percent void to
calculate the mean void intercept length."
[0113] Boolean-intersect and Boolean unite functions may be
employed with base volume of randomized struts 1100 (e.g., FIG. 11)
or tile structures like those shown at 1702, 1802, and 1902
disclosed FIGS. 17-19 to apply a coating 2602 on a surface 2604 of
an implant or substrate 2606 as illustrated in FIGS. 26A-26C, and
the data can be exported to the fabrication machine either with the
substrate 2606 data or separately. In FIGS. 26A-26C, the substrate
2606 is a tibial tray that is coated with a plurality of tiles 2702
shown in FIG. 27 to form a porous coating. The desired thickness of
the Boolean intersect volume of the coating 2602 is shown at 2704
in FIG. 27. The volume and shape 2610 of the porous material shown
in FIG. 26A is used in a Boolean intersect algorithm to convert the
larger tile 2702 shown in FIG. 27 to a smaller portion 2612 shown
in FIG. 26B for filling the Boolean intersect volume 2610 of FIG.
26A. Thus, using the Boolean intersect algorithm, less than the
entire tile 2702 of FIG. 27 may be used to form the portion 2612 of
the desired coating geometry or Boolean intersect volume 2610 to
create a desired shape. As shown in FIG. 26C, a Boolean unite
function may be used to unite the portion 2612 of porous material
with surrounding material as the actual coating 2602 is being
constructed. Alternately, all of the tiles 1100 (e.g., FIG. 11) or
tile structures could be joined together using a Boolean unite and
then intersect the joined tiles all at once with the portion 2612
in sub-sections or as a whole. It should be noted that while not
shown in the drawings, a base volume of randomized struts, e.g.,
1100, may be used to create the portion to be joined 2612, instead
of a tile 2702. This may be done such that Boolean intersect volume
2610 is filled with portions of united or un-united portions 2612
of base volume 1100. Strut thicknesses T may be assigned to one or
more of the lines 1204 of the tile portions 2612 before or after
uniting them. Alternatively, strut thicknesses T may be assigned to
one or more of the lines 1204 after the tile portions 2612 are
individually or collectively intersected with substrate 2606. In
alternative embodiments, Boolean difference or trim operations
using planes or sheets can also be used to create the desired
shapes, such as volume 2610. In another refinement, before strut
thicknesses T may be assigned, a Boolean trim may be performed on
the lines 1204 to eliminate certain portions of the lines 1204. As
discussed, alternate methods of partitioning the porous volume into
its final shape may encompass combinations of intersecting and
shaping the solid or precursor lines using trimming sheets.
Alternately, this shaping or partitioning by trimming sheets may be
performed after slicing or interpreting the solid and porous
material into a format readable by a rapid-manufacturing
machine.
[0114] As mentioned above, FIG. 28A illustrates porous structure
2800 having two tiles 2802 and 2804 joined together seamlessly
according to the present disclosure. FIG. 28B is a blown up partial
view of the seamless interface between tile 2802 and tile 2804. As
demonstrated by FIGS. 28A-28B, the tiles 2802 and 2804 have been
designed with a periphery that matches seamlessly on all sides.
That is, any permutation of arranging a plurality tiles 2802 and
2804 would result in a porous structure that does not have any
discernable seams between the tiles. For example, the interfaces
would be seamless between an arrangement having all tiles 2802, or
all tiles 2804, or any combination thereof. Yet the inner struts of
tile 2802 differ from the struts of tile 2804. For example, tile
2802 has fewer, and therefore, larger pores than tile 2804. The
seamless interface was created without the need to manually
manipulate the struts to match up or to perform any node matching
algorithm.
[0115] As demonstrated, the present disclosure provides for the
seamless interface between two different scaffold unit tiles
without the need to manually manipulate the struts of the two tiles
to match up to one another. Instead, in some embodiments, the
seamless interface was created by manipulating the negative space,
i.e., the space between the struts. The negative space manipulation
can be achieved by ensuring that the seed points at the interface
between the two tiles, whether substantially identical in shape and
randomization or substantially different, correspond to one
another. For instance, preferably, there should be only one shared
subset of outer seed points at the interface of two tiles. This can
be achieved at least by randomizing the outer seed points separate
from the inner seed points, limiting the randomization of certain
inner seed points, or adding or removing inner seed points. After
the negative space is divided to form a scaffold, then the struts
can be given a shape and a size to create a seamless porous
structure that is made up of different tiles. Preferably, two seed
point clouds, whether dissimilar or not, that share a boundary
before the scaffold is created will share struts after the scaffold
is created.
[0116] In view of the above, the present disclosure provides for
methods to fabricate a randomized porous structure by manipulating
the negative space, i.e., the space between the struts, rather than
manipulating the struts themselves for randomization. Accordingly,
the methods of the present disclosure allows for time- and
cost-effective fabrications of complex porous structure. The
present disclosure provides for methods to fabricate original
randomized structures, as opposed to a randomized existing
structure, that have seamless unions between any connecting units.
Consequently, the porous structure created according to the aspects
of the present disclosure provide improved strength without
requiring the struts to be thicker, as other uniform porous
structures may. Further, the randomized structure provides enhanced
stress or vibration resistance due to the randomized placement of
the struts and their intersections, thereby eliminating planes of
fractures that exist in uniform structures where the structures are
exposed to shear stress. Additionally, the improved complexity of
the porous structures of the present disclosure provides for
resemblance of trabecular features and improved porosity. Moreover,
the methods of the present disclosure allow for simple and
efficient customization of a porous structures with the desired
strength, pore distribution, average pore sizes, porosity, etc.
[0117] Also, the present disclosure may be used to create and
combine a plurality of tiles without randomizing the seed points.
The tiles can have substantially identical or substantially
different shapes and/or sizes, ranging from simple to complex
structure, as long as the tiles have the same or corresponding
outer seed points, a seamless interface can be formed when the
space is divided. In some embodiments, creating a seamless union
between one tile of one shape or size can have a regular
distribution of seed points and another tile of another shape
and/or size can be done by ensuring the same placement in both
tiles of the seed points that most influences the boundary between
the tiles, i.e., the outer seed points. For example, it is
difficult to create a Weaire-Phelan structure as a tile that is
stackable to form a seamless porous structure. The methods
described in the present disclosure, however, provide for simple
techniques to achieve such tasks and allow for automation of such
process via programming of software.
[0118] 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.
* * * * *