U.S. patent application number 15/299347 was filed with the patent office on 2017-09-14 for 3d printed osteogenesis scaffold.
The applicant listed for this patent is Thomas Afzal. Invention is credited to Thomas Afzal.
Application Number | 20170258606 15/299347 |
Document ID | / |
Family ID | 59788275 |
Filed Date | 2017-09-14 |
United States Patent
Application |
20170258606 |
Kind Code |
A1 |
Afzal; Thomas |
September 14, 2017 |
3D PRINTED OSTEOGENESIS SCAFFOLD
Abstract
Osteogenesis scaffold such as for spinal fusion or an
intermedullary nail includes a number of arcuate struts. The
scaffold may have a functional modulus of elasticity that is a
result of the modulus of the material of the struts together with
the architecture of the struts, and may be within the range of 5
GPa and 75 GPa. An anisotropy of a physical property such as
stiffness, compressive strength or elastic modulus corresponds to
the same physical property of native bone in the vicinity of the
intended implantation site.
Inventors: |
Afzal; Thomas; (Menlo Park,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Afzal; Thomas |
Menlo Park |
CA |
US |
|
|
Family ID: |
59788275 |
Appl. No.: |
15/299347 |
Filed: |
October 20, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62244374 |
Oct 21, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2002/30069
20130101; A61F 2002/3008 20130101; A61F 2002/30593 20130101; A61F
2/4465 20130101; A61F 2002/30985 20130101; A61F 2/4455 20130101;
A61F 2002/4495 20130101; A61F 2002/30062 20130101; A61B 17/72
20130101; A61F 2002/30571 20130101; A61B 2017/00862 20130101; A61F
2002/30187 20130101 |
International
Class: |
A61F 2/44 20060101
A61F002/44; A61B 17/72 20060101 A61B017/72 |
Claims
1. An osteogenesis scaffold configured for spinal fusion,
comprising: a superior support surface; an inferior support
surface; a plurality of arcuate struts separating the superior and
inferior support surfaces, the struts comprising a material having
a strut modulus; the scaffold having a functional modulus which is
different than the strut modulus and is the result of the strut
modulus and the architecture of the implant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit under 35 U.S.C.
.sctn.119 (e) of U.S. Provisional Application No. 62/244,374, filed
Oct. 21, 2015, the entirety of which is hereby incorporated by
reference herein.
BACKGROUND OF THE INVENTION
[0002] Spondylosyndesis, or spinal fusion, is a surgical technique
used to combine two or more vertebrae into a single, rigid working
unit. This is typically achieved by introducing a supplementary
bone tissue, such as an autograft or allograft, into the
intervertebral space between two target vertebrae, at the location
that is typically occupied by an intervertebral disc. The
supplementary bone tissue is then used in conjunction with the
patient's natural osteoblastic processes in order to grow bone or
osseous tissue between the two or more target vertebrae, which acts
to fuse them together into the desired rigid unit. This procedure
is used primarily to eliminate pain that is caused by abnormal
motion of one or both of the target vertebrae; pain relief occurs
by immobilizing the vertebrae themselves and preventing the
abnormal motion. Alternatively, surgically implantable synthetic
intervertebral fusion cages or devices may be used to perform
spinal fusion procedures.
[0003] Surgically implantable intervertebral fusion cages are well
known in the art and have been actively used to perform spinal
fusion procedures for many years. Their use became popularized
during the mid 1990's with the introduction of the BAK Device from
the Zimmer Inc. The BAK system is a fenestrated, threaded,
cylindrical, titanium alloy device that is capable of being
implanted into a patient as described above through an anterior or
posterior approach, and is indicated for cervical and lumbar spinal
surgery. Most common spinal fusion systems today are made from
metals, such as titanium or cobalt chrome alloys, or from a polymer
such as polyetheretherketone (PEEK) which is commonly used in
biomedical implants. Unfortunately, these implant materials have a
modulus which is much higher than that of bone and there is
clinical evidence of implant subsidence and movement which is
believed to be attributable to mechanical incompatibility between
natural bone and the implant material. Also bone pressure necrosis
does occur as a result of the presence of these metal implants.
[0004] Implants based on bone material from a donor (allograft) or
from the patient itself (autograft) do have an inconsistent
mechanical strength and show subsidence over time. The inconsistent
properties of these implants make them generally unpredictable,
challenging to reliably machine and especially prone to migration
and explusion due to the difficulty of consistently machining teeth
into the upper and lower implant contact surfaces.
[0005] Although titanium alloy cages give good fusion rates, their
modulus is significantly dissimilar to human bone. The stress
transfer between an implant device and a bone is not homogeneous
when Young's moduli of the implant device and the bone are
different. This results in stress shielding. In such conditions,
bone atrophy occurs and leads to the loosening of at the implant
bone interface and eventually lead to failure. Therefore, the
stiffness (Young's modulus) of the implant is preferably not too
high compared to that of bone. Implant devices made from metallic
biomaterials such as stainless steels, Co--Cr alloys, and titanium
(Ti) and its alloys have a Young's modus generally much greater
than that of the bone. Young's moduli of the most widely used
stainless steel for implant devices, SUS316L stainless steel and
Co--Cr alloys, are around 180 GPa and 210 GPa, respectively.
Young's moduli of Ti (pure titanium) and its alloys are generally
smaller than those of stainless steels and Co--Cr alloys. For
example, Ti and its alloy, Ti-6A1-4V ELI, which are widely used for
constructing implant devices, have a Young's modulus of around 110
GPa. However, this value is still higher than that of the bone,
which is on the order of 10-30 GPa.
[0006] The foregoing shortcomings in the spinal fusion cage arts
apply to other orthopedic implants as well, such as intermedullary
nails for long bones such as the femur.
[0007] Therefore, there remains a need for a biostable implant such
as for use as an orthopedic implant or plate which has a tensile
modulus comparable to that of bone, which does not subside and
provides a good stability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a side elevational perspective view of an implant
in accordance with the present invention, in the form of a spinal
fusion cage.
[0009] FIG. 2 is a top plan view of the spinal fusion cage shown in
FIG. 1.
[0010] FIG. 3 is a perspective elevational cross section through
the spinal cage of FIG. 2.
[0011] FIG. 4 is an elevational cross section through the cage of
FIG. 2, taken along an axis perpendicular to the cross-section of
FIG. 3.
[0012] FIG. 5 is a side elevational view of the cage of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] The present invention addresses the problem by providing
implants such as intermedullary nails or spinal fusion cages that
have a functional modulus of elasticity that is substantially the
same as the modulus of elasticity of the native bone at the implant
site. For example, implants can be provided having a functional
modulus of elasticity of between about 5 GPa and about 75 GPa,
typically between about 10 GPa and about 50 GPa and in some
implementations between about 10 and about 30 GPa. Functional
modulus means the effective modulus of the final implant, which
will be the result of both the modulus of the material of the
implant as well as the result of the arcuate strut architecture of
the implant, as will be described below.
[0014] In addition, human or animal tissue is generally not
structurally isotropic. For example, cancellous bone includes
trabeculae, also referred to as spicules, defining a plurality of
open spaces. The trabeculae and open spaces are generally oriented
in a direction of principle stress (e.g., axially along a long bone
such as a femur). The trabeculae form a porous or spongy-type
tissue that is generally stiffer in a particular direction. For
example, cancellous bone in the femur is generally stiffer axially
than radially to accommodate an axial direction of the primary
stress on the bone.
[0015] A prosthetic orthopedic implant such as a fusion cage should
therefore be designed to avoid producing load concentrations which
can lead to stress shielding of nearby bone. Bone can remodel to
adapt to the load applied to it. If a particular location within a
bone experiences increased load, the body will increase bone growth
at that location. The reverse is also true. In response to a
reduced load at a particular location, the body will tend to resorb
bone from that location. Therefore, concentrating stresses within a
prosthetic implant providing structural support can lead to
weakening and resorption of the surrounding bone.
[0016] An isotropic implant together with the anisotropy of nearby
bone, can lead to stress shielding, such as if the isotropic
implant is stiffer in one direction (e.g., in a radial direction,
for a long bone such as a femur) than the nearby native bone. An
anisotropic porous scaffold support structure can help reduce or
avoid such stress shielding, such as by providing anisotropy in a
similar direction to the anisotropy of the nearby native bone.
[0017] For example, the osteogenesis scaffold can be configured so
that an anisotropy of a physical property, such as stiffness,
compressive strength, elastic modulus, and the like, is the same or
substantially the same as an anisotropy of the same physical
property in the native bone in the vicinity of the intended
implantation. In an example, the porous scaffold can be configured
to be stiffer in a first direction (e.g., axially) compared to a
second direction (e.g., laterally), such as to mimic anisotropic
stiffness of nearby native bone in the first direction and second
direction. The porous scaffold can be configured so that the
physical property, such as stiffness, is the same or substantially
the same as the same physical property in the nearby native bone in
both the first direction and the second direction. In an example,
"substantially the same," when referring to the matching of a
physical property between the porous scaffold and the nearby native
bone can refer to the value of the physical property of the porous
scaffold in the first direction being within about 10% or
preferably within about 5% of the value of the physical property of
the nearby native bone in the first direction, such as within 3%,
1%, or less. Similarly, the physical property in the second
direction can be considered to be substantially the same if the
value of the physical property of the porous scaffold in the second
direction is within about 10% or preferably within about 5%, or
within 3%, 1%, or less of the value of the physical property of the
nearby native bone in the second direction.
[0018] Referring to FIG. 1, there is illustrated a perspective view
of an osteogenesis scaffold 10. The scaffold 10 can take any of a
variety of configurations depending upon the intended anatomical
environment, and is illustrated in FIG. 1 in the form of a spinal
fusion cage 12.
[0019] Fusion cage 12 comprises a superior support surface 14, and
an inferior support surface 16 spaced apart by a body portion 18.
Measured in an axial direction, the anterior side 20 typically has
a greater height then a posterior side 22.
[0020] The osteogenesis cage 12 comprises a plurality of arcuate
struts, configured to produce an implant having a functional
modulus which is a composite of the modulus of the material of
construction, taken together with the physical properties
attributable to the architecture of the implant. In the illustrated
embodiment, the cage 12 comprises a plurality of arcuate struts
configure to permit a degree of compression and expansion in the
axial (superior inferior) direction, in response to cyclic
physiologic load. Each arcuate strut is configured to function as a
leaf spring, within the constraints imposed by the material and
geometry of the struts.
[0021] In the illustrated embodiment, the superior support surface
14 comprises a plurality of struts as will be discussed.
Alternatively, the superior support surface 14 and or inferior
support service 16 may comprise a unitary apertured or porous plate
or other construct for engaging the adjacent bony end plate.
[0022] In the illustrated embodiment, the superior support surface
14 comprises a plurality of interior surface struts 24 extending
radially outwardly from a centerpoint 26 along the superior support
surface 14. At least about two or four or six or eight or more
interior surface struts 24 may be provided. In the illustrated
embodiment, four long struts intersect at the centerpoint 26 to
provide eight interior surface struts 24.
[0023] The surface struts 24 described above may be reproduced on
the inferior support surface 16 in a symmetrical arrangement. The
surface struts 24 may reside in a plane. Preferably, however, the
surface struts 24 define an arcuate surface which is slightly
convex in a direction away from the body 18, to complement the
surface of the bony end plate of the adjacent vertebral body.
[0024] The superior support service 14 is spaced apart from the
inferior support surface 16 by, among other things, a plurality of
peripheral axial struts 28. In the illustrated embodiment, each of
the radially outwardly facing ends of the surface struts 24 is
connected to an axial strut 28. Thus, in the illustrated
embodiment, eight axial struts 28 are positioned about the
periphery of the body 18. However, any of a variety of numbers such
as at least about four, six, eight, 10, 12 or more axial struts 28
maybe provided depending upon the overall desired scaffold design.
Axial struts 28 maybe linear, or, preferably, each axial strut 28
may define an arc. In the illustrated embodiment, each of the axial
struts 28 is concave in the direction of the central axis of the
body 18. This may allow a slight axial compression of the body 18
under anatomical loads.
[0025] The intersections of the axial struts 28 and surface struts
24 are connected by a superior peripheral frame 30. In the
illustrated embodiment, the peripheral frame 30 comprises a
continuous annular strut, defining the outer periphery of the
superior support surface 14. The inferior support surface 16 is
provided with a symmetrical peripheral frame 32, defining the outer
periphery of the inferior support surface 16.
[0026] Referring to FIG. 2, there is illustrated a top plan view of
the superior support surface 14. A plurality of diagonal surface
struts 34 join radial ends of alternating radial surface struts 24.
Diagonal surface struts 34 may be nonlinear, and, in the
illustrated embodiment, are arcuate with a concavity pointing in
the direction of the periphery of the body 18. At least two or four
or more diagonal surface struts 34 may be provided in each plane
such as the superior support surface 14. In the illustrated
embodiment, four diagonal service struts 34 are provided,
intersecting the peripheral frame 30 at approximately 90.degree.
spacing.
[0027] The strut geometry residing in the plane of the superior
support surface 14 may be symmetrically reproduced for the inferior
support surface 16. That strut geometry may be further reproduced
within one or two or more intermediate planes, residing in between
the superior support surface 14 and inferior support surface
16.
[0028] Referring to FIG. 3, there is illustrated a vertical
cross-section through a central surface strut 24. Within the body
18, a plurality of struts are provided. At least about 50%,
preferably least about 80%, and typically at least about 90 or 95%
of the struts are curved.
[0029] The first concave upward strut 40 extends from the
peripheral frame 30 on the superior support surface 14, to the
inferior support surface 16, and back to a second end of the
peripheral frame 30 on superior support surface 14. A second
concave upward strut 42 extends from the inferior frame 32 to the
centerpoint 26 on the superior support surface 14. Each of the
first second and third concave upward struts have an arcuate
configuration with an upward facing concavity.
[0030] Referring to FIGS. 4 and 5, the peripheral surface of the
body 18 is provided with a dock 60, for releasable engagement with
an insertion tool. The dock 60 may be provided with an aperture,
projection, or other surface structure (not illustrated) which is
complementary to a distal portion of an insertion tool. For
example, the dock 60 may be provided with a threaded aperture for
threadable engagement with a threaded distal end of an insertion
tool. The dock 60 is preferably provided on a peripheral surface of
the implant, and maybe on the posterior, anterior, lateral or
posterior lateral sides, depending upon the desired route of
implantation.
[0031] In general, the implant 10 is formed as a cage having a
unitary body, with openings provided through the top and bottom
surfaces to form cavities or passageways throughout, wherein
openings from the top surface are in communication with openings
from the bottom surface and are configured and dimensioned to
receive graft material, such as bone particles or chips,
demineralized bone matrix (DBM), paste, bone morphogenetic protein
(BMP) substrates or any other bond graft expanders, or other
substances designed to encourage bone ingrowth into the cavities to
facilitate the fusion. Additionally the implant 10 may be provided
with side openings as shown that are also in communication with the
interior cavities.
[0032] The implant 10 may be made from any of a variety of
materials well known in the orthopedic implant arts. For example,
implants may be made from PEEK (polyetheretherketone) such as by
being machined therefrom, but alternatively, may be manufactured by
injection molding or three-dimensional lithographic printing, for
example. When manufactured by three-dimensional lithographic
printing, implant 10 may be made of polymers, such as PEEK or other
polymer and/or absorbable materials such as tri-calcium phosphate
(TCP), hydroxyapatite (HA) or the like. When made of metal, implant
10 may be machined or made by metal powder deposition, for example.
Alternatively, implant 10 may be made of PEKK
(poly(oxy-p-phenyleneisophthaloyl-phenylene/oxy-p-phenylenetere-phthaloyl-
-p-phenylene) or carbon-filled PEEK. Manufacturing the implant from
any of these materials make it radiolucent, so that radiographic
visualization can be used to view through the implant 10 to track
the post-procedural results and progress of the fusion over time.
Alternatively, implant 10 could be made of titanium or other
biocompatible, radiopaque metal. However, this is less preferred as
this type of implant would obscure post-procedural radiographic
monitoring.
[0033] Preferably, the implant comprises a metal such as titanium
or a titanium alloy, manufactured using a 3D printing technology.
Such technologies are known in several variations, sometimes
referred to as Additive manufacturing, rapid prototyping, solid
free form technology, powder bed fusion, in which a bed of powdered
metal is selectively fused (through sintering or melting) by a
laser or electric arc. Also, electron beam melting of metal powder
(EBM) may be used.
[0034] The three-dimensional lattice configuration of the present
invention, including configurations constructed from a plurality of
arcuate struts may be adapted for use in a variety of orthopedic
applications outside of the spine. For example, intramedullary
nails for use in long bones such as the femur, tibia, fibula,
radius or ulna may be constructed using the arcuate struts of the
present invention, to provide an anisotropic characteristic such as
modulus, to match that of the native surrounding environment. Extra
medullary implants, such as plates, screws, spacers, rods,
sacroiliac joint fusion implants or others may also be constructed
utilizing the 3D printed arcuate strut or lattice configurations
disclosed here in.
[0035] The implants disclosed herein may be provided with a porous
or textured surface, such as to facilitate osteogenesis or in the
case of porous surfaces, to elute drugs such as antibiotics,
anticoagulants, bone growth factors or others known in the art.
[0036] Implants produce in accordance with the present invention
may alternatively comprise hybrid constructs, with a first
component made from 3-D printed lattice and a second component
molded, machined or otherwise formed from a conventional implant
material such as titanium, various metal alloys, PEEK, PEBAX or
others well known in the art.
* * * * *