U.S. patent application number 11/131831 was filed with the patent office on 2005-09-22 for encapsulated intervertebral disc prosthesis and methods of manufacture.
Invention is credited to Kavanaugh, Sean, Lambrecht, Gregory, Stonebrook, Scott.
Application Number | 20050206039 11/131831 |
Document ID | / |
Family ID | 46280850 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050206039 |
Kind Code |
A1 |
Lambrecht, Gregory ; et
al. |
September 22, 2005 |
Encapsulated intervertebral disc prosthesis and methods of
manufacture
Abstract
The present invention relates generally to intervertebral disc
repair devices and methods of manufacture. A method of
manufacturing a dynamically responsive encapsulated intervertebral
disc repair device that prevents the flow of disc material out of
the disc, provides support to the anulus fibrosus, and shields the
nerves of the anulus and spinal cord, is provided.
Inventors: |
Lambrecht, Gregory; (Natick,
MA) ; Kavanaugh, Sean; (Eastham, MA) ;
Stonebrook, Scott; (Phoenix, AZ) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
46280850 |
Appl. No.: |
11/131831 |
Filed: |
May 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11131831 |
May 18, 2005 |
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10194428 |
Jul 10, 2002 |
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11131831 |
May 18, 2005 |
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09696636 |
Oct 25, 2000 |
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6508839 |
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09696636 |
Oct 25, 2000 |
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09642450 |
Aug 18, 2000 |
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6482235 |
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09642450 |
Aug 18, 2000 |
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09608797 |
Jun 30, 2000 |
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6425919 |
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60311559 |
Aug 10, 2001 |
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60304545 |
Jul 10, 2001 |
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60149490 |
Aug 18, 1999 |
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60161085 |
Oct 25, 1999 |
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60172996 |
Dec 21, 1999 |
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Current U.S.
Class: |
264/320 ;
623/17.16; 623/901 |
Current CPC
Class: |
A61F 2/4611 20130101;
A61F 2002/30062 20130101; A61F 2002/30261 20130101; A61F 2210/0004
20130101; A61F 2230/0069 20130101; A61F 2230/0091 20130101; A61F
2002/30777 20130101; A61F 2002/4635 20130101; A61F 2310/00161
20130101; A61F 2002/30172 20130101; A61F 2002/30224 20130101; A61F
2310/00293 20130101; A61F 2002/30601 20130101; A61F 2002/448
20130101; A61F 2220/0075 20130101; A61F 2002/30131 20130101; A61F
2002/2817 20130101; A61F 2002/30177 20130101; A61F 2250/0018
20130101; A61F 2310/00976 20130101; A61F 2230/0052 20130101; A61F
2230/0082 20130101; A61B 2090/062 20160201; A61B 17/320708
20130101; A61F 2310/00029 20130101; A61B 2017/00261 20130101; A61B
2090/061 20160201; A61F 2/30723 20130101; A61F 2002/4435 20130101;
A61F 2210/0061 20130101; A61F 2230/0034 20130101; A61F 2002/30228
20130101; A61F 2/441 20130101; A61F 2002/30566 20130101; A61F
2230/0028 20130101; A61F 2002/4662 20130101; A61B 5/4514 20130101;
A61F 2002/30166 20130101; A61F 2/30907 20130101; A61F 2210/0085
20130101; A61F 2002/30136 20130101; A61F 2002/30092 20130101; A61B
5/1076 20130101; A61F 2310/00023 20130101; A61F 2002/302 20130101;
A61F 2002/30785 20130101; A61F 2002/4661 20130101; A61F 2002/30014
20130101; A61B 2017/22077 20130101; A61F 2230/0056 20130101; A61F
2/4601 20130101; A61F 2230/0004 20130101; A61F 2230/0013 20130101;
A61F 2002/30909 20130101; A61F 2/2846 20130101; A61F 2002/4627
20130101; A61F 2002/30583 20130101; A61F 2002/30971 20130101; A61F
2/442 20130101; A61F 2002/30677 20130101; A61F 2002/444 20130101;
A61F 2002/4658 20130101; A61F 2230/0065 20130101; A61F 2002/30187
20130101; A61F 2/4657 20130101; A61F 2002/30462 20130101; A61F
2002/30571 20130101; A61F 2002/30075 20130101; A61B 2017/3445
20130101; A61F 2002/30291 20130101; A61B 2017/320044 20130101; A61F
2002/30576 20130101; A61F 2210/0014 20130101; A61F 2310/00365
20130101; A61F 2310/0097 20130101; A61F 2002/30289 20130101; A61F
2002/30589 20130101; A61F 2310/00017 20130101 |
Class at
Publication: |
264/320 ;
623/017.16; 623/901 |
International
Class: |
B29C 031/00 |
Claims
What is claimed is:
1. A method of making an intervertebral disc implant comprising:
providing a barrier frame having first and second sides;
positioning a first membrane adjacent the first side and a second
membrane adjacent the second side; applying force such that the
first membrane contacts the second membrane at one or more points;
and heating the first and second membrane to form bonds at the one
or more points.
2. The method of claim 1, wherein said first membrane is attached
to said second membrane.
3. The method of claim 1, wherein said first membrane and said
second membrane are opposing sides of an envelope.
4. The method of claim 1, wherein said positioning step comprises
positioning at least a portion of the membrane beyond the
frame.
5. The method of claim 1, wherein said one or more points are
positioned beyond the periphery of the frame.
6. The method of claim 1, wherein said positioning step comprises
positioning an ePTFE membrane.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/194,428 filed Jul. 10, 2002, which claims benefit to U.S.
Provisional Application No. 60/311,559 filed Aug. 10, 2001 and U.S.
Provisional Application No. 60/304,545 filed Jul. 10, 2001, and
which is a continuation-in-part of co-pending U.S. application Ser.
No. 09/696,636 filed Oct. 25, 2001, which is a continuation-in-part
of co-pending U.S. application Ser. No. 09/642,450 filed Aug. 18,
2000, which is a continuation-in-part of co-pending U.S.
application Ser. No. 09/608,797 filed Jun. 30, 2000, which claims
benefit to U.S. Provisional Application No. 60/149,490 filed Aug.
18, 1999, U.S. Provisional Application No. 60/161,085 filed Oct.
25, 1999 and U.S. Provisional Application No. 60/172,996 filed Dec.
21, 1999, the entire teachings of these applications being
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to intervertebral
disc devices suitable for delivery into a body to treat injured
discs or to improve the function of non-injured discs.
[0004] 2. Background
[0005] Methods of encapsulating a new intervertebral prosthesis are
not known in the art. The most relevant prior art can be found in
references concerning the encapsulation of stents and grafts in
flexible biocompatible materials. However, these references are
limited to teaching the coating of certain cylindrical structures
with a single or double-sided coating of expanded
polytetrafluoroethylene. These teachings do not address some or all
of the requirements of a new intervertebral disc device which may
be semicircular in cross-section, collapsible, fatigue resistant,
biocompatible, and suitable for the dynamic disc environment.
[0006] Fluoropolymer tubings and other extruded or expanded polymer
products are well known in the art and can provide an excellent
material for encapsulation. Expanded polytetrafluoroethylene
(ePTFE) is made by expanding polytetrafluoroethylene (PTFE) tubing
or sheet material under controlled conditions during the
manufacturing process. This process alters the physical properties
of the material by creating microscopic pores in the structure of
the material. The resulting material is imparted with unique
physical properties that make it ideal for use in medical devices,
electronic insulators, high performance filters, and a host of
other applications. Material made from ePTFE differs from regular
PTFE in that the material is microporous, soft, very flexible, has
a lower dielectric constant, increased linear strength, and
improved biocompatibility.
[0007] The structure of ePTFE is unique in that the material is
made up of a number of solid nodes inter-connected by a matrix of
thin fibrils. The gaps, or pores, between the fibrils are what
allows the material to excel in applications requiring cellular
ingrowth. ePTFE is also utilized for its endothelization and
thrombogenic properties. Both ePTFE and PTFE resin have long been
utilized for implantable medical devices due to their inertness and
biocompatibility. The amount of expansion in ePTFE is usually
referred to as internodal distance (IND). IND is a measure of the
average distance between the material's nodes. ePTFE is commonly
available from manufacturers in IND sizes ranging from 5.mu. to
over 200.mu.. IND plays a role in the softness, flexibility, and
degree of potential ingrowth that the material exhibits. Some
commercial suppliers of ePTFE sinter the outside of the material
after the expansion process in order to make it more durable and
smooth.
[0008] Other useful PTFE based materials known in the art are PTFE
resin aqueous dispersions or "aqueous PTFE" and heat shrinkable
PTFE. Aqueous PTFE is commonly comprised of milky white dispersions
of PTFE particles in water stabilized by wetting agents. Its
composition is usually 30 to 60 percent PTFE particles and the
remainder is comprised of water and a nonionic surfactant. Objects
can be dip-coated with repeated passes into aqueous PTFE until the
final desired thickness is obtained. The water can then be removed
and the other ingredients deactivated. The melting temperature of
these resins are around 325.degree. Celsius. The dried resin
particles can be coalesced by heat into a continuous coating or the
substrate can remain coated, or impregnated, with unmelted
particles. Both glass fabric and synthetic substrates can be
processed.
[0009] Heat shrinkable PTFE tubing is well known in the art and
provides a method for the application of a tight, protective
covering to items that will be subjected to the extremes of heat,
corrosion, shock, moisture, and other critical environmental
conditions. Shrinkable PTFE tubing requires around 340.degree.
Celsius to recover. Upon reaching approximately 330.degree. the
PTFE goes into the "gel" state (amorphous from crystalline). PTFE
begins to shrink at 340.degree. and completes its recovery during
the cooling cycle.
[0010] This disclosure utilizes particular orthopedic references,
nomenclature, and conventions. Accordingly, several background
figures and descriptions are included to aid in the understanding
of the environment under which specific embodiments of the
invention may be used. FIGS. 1A and 1B show the general anatomy of
a functional spine unit 345. In this description and the following
claims, the terms `anterior` and `posterior`, `superior` and
`inferior` are defined by their standard usage in anatomy, i.e.,
anterior is a direction toward the front (ventral) side of the body
or organ, posterior is a direction toward the back (dorsal) side of
the body or organ; superior is upward (toward the head) and
inferior is lower (toward the feet).
SUMMARY OF THE INVENTION
[0011] The invention relates generally to methods of manufacture of
intervertebral disc devices suitable for delivery into a body to
treat injured or poorly functioning discs or to reinforce healthily
discs.
[0012] In one or more of the several embodiments, the present
invention provides for an intervertebral disc prosthesis that is
biocompatible, collapsible, concave shaped, and sized to fit within
the area defined by the superior and inferior end plates and
outermost lamella of the anulus fibrosus of a functional spinal
unit.
[0013] It is further objective of one or more of several
embodiments of this invention to provide a device useful in
shielding the nerves of the anulus and spinal cord from pressure
and or chemicals within the disc.
[0014] It is a further objective of one or more of various
embodiments to provide a device that provides support to a weakened
or healthy anulus in an intervertebral disc.
[0015] It is a further object in one or more of the several
embodiments to provide a method for the manufacture of one or more
of the several embodiments of the invention.
[0016] It is a further object to provide in one or more of the
several embodiments an encapsulating covering that is permanently
retained on an intervertebral barrier device and substantially
isolates it from bodily tissue.
[0017] It is a further objective of one or more of various
embodiments to provide a method of encapsulating an intervertebral
prosthesis in a biocompatible material that does not interfere with
the deformation and flexibility of the barrier frame.
[0018] It is another object of several embodiments of the invention
to provide a method of making an intervertebral disc implant by
providing a barrier frame having first and second sides,
positioning a first membrane adjacent the first side and a second
membrane adjacent the second side, applying force so that the first
membrane contacts the second membrane at one or more points and
heating the first and second membrane to form bonds at one or more
of those points. The first membrane may be attached to the second
membrane. In one embodiment, the first membrane and second membrane
may be opposing sides of an envelope. In a preferred embodiment,
the first and/or second membrane is an ePTFE membrane. In another
embodiment, a portion of the membrane is positioned beyond the
frame or its periphery.
[0019] It is yet another object of the current invention to provide
a method for making an intervertebral prosthesis by placing a first
encapsulating material over a mandrel, placing a device frame on
the first encapsulating material, placing a second encapsulating
material on top of the device frame, placing a mandrel cover on top
of the second encapsulating material and applying force so that the
edges of the first and second encapsulating material form contact
points with each other around the device frame and heating the
mandrel and/or cover until the first and second encapsulating
material bond to each other at the contact points, thereby
encapsulating the frame.
[0020] It is yet another object of the current invention to provide
a method for making an intervertebral prosthesis by placing a first
biocompatible encapsulating material over a heatable mold with a
curved face, the material being sized to extend from about 0.1 mm
to about 0.5 mm beyond the edges of a barrier frame. The barrier
frame, which is dimensioned to span beyond the distance defined by
the maximun distance between an inferior and superior endplate of a
normal intervertebral disc and to extend circumferentially along
the lateral and posterior surfaces of an anulus, the barrier having
a semi-circular cross-section and comprised of nickel titanium
alloy, is placed on the first encapsulating material. A second
encapsulating material, designed to extend from about 0.1 mm to
about 5 mm beyond the edges of the barrier frame, is placed on top
of the device frame. A mold cover with a concave interior
corresponding to face of the mold on top of the second
encapsulating material is placed on top of the device frame. Force
is then applied such that the edges of the first and second
encapsulating material form one or more contact points with each
other around the barrier frame. The base and/or the cover and/or
the frame sandwiched between the first and the second encapsulating
material is heated until the first and second encapsulating
material bond to each other at said one or more contact points.
[0021] It is a further object of various embodiments of the present
invention to provide a method for making an intervertebral
prosthesis by placing a first biocompatible encapsulating material
over a heatable mold with a curved face, where the curved face has
a first axis and a second axis which are perpendicular to one
another. The first axis is a longitudinal axis which has a first
radius of curvature and the second axis is a transverse axis which
has a second radius of curvature. The first radius of curvature has
a range of about 0.1 cm to about 4 cm and the second radius of
curvature has a range of about 2.0 cm to about 7.0 cm.
Alternatively, the device can be `U` shaped in the transverse
orientation and preferably has lateral legs in the range of about
0.1 cm to about 2.0 cm that protrude perpendicularly through a
gradual curve with an inner diameter in the range of about 0.2 cm
to about 1.5 cm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0023] FIGS. 1A and 1B show the general anatomy of a functional
spinal unit. FIG. 1A is a view of a transverse section, and FIG. 1B
is a view of a sagittal section. FIGS. 1C and 1D show a functional
spine unit with a defect in the anulus. FIG. 1C is a view of a
transverse section of the functional spine unit and shows a defect
in the anulus which could have been created iatrogenically as in
the performance of an anulotomy or naturally occurring. FIG. 1D is
a view of a transverse section of the spine unit with a defect in
the anulus that does not extend completely through the anulus.
[0024] FIGS. 2A and 2B are side and front views of the device of
the present invention.
[0025] FIGS. 3A-3C show the device frame. FIG. 3A shows a front
view of the frame.
[0026] FIGS. 3B, 3C and 3D show embodiments of the frame with
different frame heights and curvatures.
[0027] FIG. 4 shows a front view of the device with an encapsulated
frame.
[0028] FIGS. 5A and 5B illustrate perspective views of the barrier
frame mounted within an intervertebral disc.
[0029] FIGS. 6A and 6B illustrate perspective views of the device
mounted within an intervertebral disc.
[0030] FIG. 7 shows a cross sectional view of the mandrel, the
sandwich-like arrangement of a first encapsulating membrane, the
barrier frame, and a second encapsulating membrane, and a mandrel
cover. The arrangement depicted can also be formed by a frame
disposed within a tubular encapsulating membrane.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] The environment in which various embodiments of the present
invention find greatest utility is within a human intervertebral
disc that has a weakened or compromised anulus. FIG. 1A is an axial
view along the transverse axis M of a vertebral body with the
intervertebral disc 315 superior to the vertebral body. Axis M
shows the anterior (A) and posterior (P) orientation of the
functional spine unit within the anatomy. The intervertebral disc
315 contains the anulus fibrosus 310, which surrounds a central
nucleus pulposus 320. Also shown in this figure are the left 370
and right 370' transverse spinous processes and the posterior
spinous process 380.
[0032] FIG. 1B is a sagittal section along sagittal axis N through
the midline of two adjacent vertebral bodies 350 (superior) and
350' (inferior). Intervertebral disc space 355 is formed between
the two vertebral bodies and contains intervertebral disc 315,
which supports and cushions the vertebral bodies and permits
movement of the two vertebral bodies with respect to each other and
other adjacent functional spine units.
[0033] Intervertebral disc 315 is comprised of the outer anulus 310
which normally surrounds and constrains the nucleus 320 to be
wholly within the borders of the intervertebral disc space. Axis M
extends between the anterior (A) and posterior (P) of the
functional spine unit. The vertebrae also include facet joints 360
and the superior 390 and inferior 390' pedicle that form the neural
foramen 395.
[0034] FIG. 1C is an axial view of the anulus 310 and nucleus 320
wherein the anulus has a partial defect that does not completely
perforate the anulus 310. FIG. 1C shows a spine unit with a
iatrogenic or naturally occurring hole 300 in the anulus 311. This
condition can cause pain and diminishes the function of the disc
because of a loss of intervertebral pressure and disc height. FIG.
1D shows a cross sectional view of a spine unit with a defect 121
in the posterior anulus 310 in which the perforation of the tissue
is partial. In this condition, the anulus 310 is weakened and may
protrude when loaded but does not permit the egress of nucleus 320
tissue outside of the disc.
[0035] In several of embodiments herein, the present invention
provides a device for sealing or reinforcing defects in tissue
walls separating two anatomic regions of the body and to methods of
making such device. Alternatively, one or more of the several
embodiments of the device may be used to provide support to tissue
walls that do not exhibit holes but are nonetheless weakened and
can benefit from an implanted support structure. Also, prosthetic
devices and method of their manufacture are disclosed which provide
the closure or support of a defect in the anulus of the human
intervertebral disc, preventing the egress of material from within
the disc and/or distributing pressure within the disc space across
an inner wall surface of the disc.
[0036] Closure of the defect and/or support of the weakened sector
comprising the defect can be achieved by placing a membrane or
barrier device on an interior aspect of the defect. In the case of
the intervertebral disc, the device 120 is positioned either on the
interior aspect of the anulus proximate to the nucleus or between
layers of the AF. The device 120 may be inserted in the desired
location after dissecting a space between the anulus and nucleus.
Alternatively, a portion of the nucleus and/or anulus may be
resected to create adequate space. Ideally, the device 120 is
inserted through a defect in the anular surface or through a
minimally invasive iatrogenic hole 300. Such a hole is shown in
FIG. 1D.
[0037] FIGS. 2A and 2B depict an intervertebral disc device 120
comprising an encapsulating or covering membrane or material 51 and
a dynamic support frame 53. The concave portion of the device
preferably faces the nucleus 20 while the convex surface faces the
defect 16 and the inner aspect of the anulus 10. This embodiment
exploits pressure within the disc to compress device 120 against
neighboring vertebral bodies 50 and 50' to aid in sealing. The `C`
shape cross-section as shown in FIG. 2A is the preferred shape of
the device 120 wherein the convex portion of the barrier or patch
rests against the interior aspect of the anulus while the concave
portion faces the nucleus. To improve the sealing ability of such a
device 120, the upper and lower portions of this `C` shaped device
are positioned against the vertebral endplates or overlying
cartilage. As the pressure within the nucleus increases, these
portions of the patch are pressurized toward the endplates with an
equivalent pressure, preventing the passage of materials around the
device. Dissecting a matching cavity prior to, or during device
placement, can expedite the implantation of such a `C` shaped
patch.
[0038] The geometries of the support frame 53 shown in FIGS. 3, 4
and 5 can preferably be formed from a relatively thin sheet of
material. The material may be a polymer, metal, or gel, however,
the superelastic properties of nickel titanium alloy (NITINOL)
makes this metal particularly advantageous in this application.
Sheet thickness can generally be in a range of about 0.002 inches
to about 0.080 inches and for certain embodiments has been found to
be optimal if between about 0.003 inches to about 0.015 inches, for
the thickness to provide adequate expansion force to maintain
contact between the covering material 51 and surrounding vertebral
endplates. The pattern may be Wire Electro-Discharge Machined
(EDM), cut by laser, chemically etched, or formed by other suitable
means.
[0039] FIG. 3A shows an embodiment of a frame 53 having a superior
edge 166 and an inferior edge 168. The frame 53 can form a frame of
device 120. This embodiment comprises dissecting surfaces or ends
160, radial elements or fingers 162 and a central strut 164. The
circular shape of the dissecting ends 160 aids in dissecting
through the nucleus pulposus 20 and/or along or between an inner
surface of the anulus fibrosus 10. Alternatively, the ends 160 may
be blunt and fully encapsulated in the covering material 51. The
distance between the left-most and right-most points on the
dissecting ends is the frame length 170. This length 170 preferably
lies along the inner perimeter of the posterior anulus following
implantation. The frame length 170 can be as short as 3 mm and as
long as the entire interior perimeter of the anulus fibrosus. The
superior-inferior height of these dissecting ends 160 is preferably
similar to or larger than the posterior disc height.
[0040] This embodiment employs a multitude of fingers 162 to aid in
holding the membrane against the superior and inferior vertebral
endplates. The distance between the superior-most point of the
superior finger and the inferior-most point on the inferior finger
is the frame height 172. This height 172 is preferably greater than
the disc height at the inner surface of the posterior anulus. The
greater height 172 of the frame 53 allows the fingers 162 to
deflect along the superior and inferior vertebral endplates,
enhancing the seal of the device 120 against egress of material
from within the disc 15.
[0041] The spacing between the fingers 162 along the frame length
170 can be tailored to provide a desired stiffness of the frame 53.
Greater spacing between any two neighboring fingers 162 can further
be employed to insure that the fingers 162 do not touch if the
frame 53 is required to take a bend along its length. The central
strut 164 can connect the fingers and dissecting ends and
preferably lies along the inner surface of the anulus 10 when
seated within the disc 15. Various embodiments may employ struts
164 of greater or lesser heights and thicknesses to vary the
stiffness of the overall frame 53 along its length 170 and height
172.
[0042] FIGS. 3B, 3C and 3D show a cross sectional view of the
device frame 53 with different frame heights 172 and curvatures to
accommodate different anatomical applications. In a preferred
embodiment, the curved face has a first axis and a second axis
which are perpendicular to one another. The first axis is a
longitudinal axis which has a first radius of curvature and the
second axis is a transverse axis which has a second radius of
curvature. Preferably, the two radii are not equal to one another.
The first radius of curvature has a range of about 0.1 cm to about
4 cm, preferably from about 0.2 cm to about 2.5 cm, more preferably
about 0.97 cm. The second radius of curvature has a range of about
2.0 cm to about 7.0 cm, preferably from about 3.0 cm to about 5.0
cm.
[0043] In an alternative embodiment, the device can be `U` shaped
in the transverse orientation and preferably has lateral legs in
the range of about 0.1 cm to about 2.0 cm, preferably in the range
of about 0.5 cm to about 1.3 cm, that protrude perpendicularly
through a gradual curve with an inner diameter in the range of
about 0.2 cm to about 1.5 cm.
[0044] FIG. 4 shows another embodiment of the barrier frame 53
encapsulated in the membrane or encapsulating material 51 to form
the device 120.
[0045] FIGS. 5A and B show the barrier frame 53 within a disc.
FIGS. 6A and B show the barrier frame 53 and encapsulating material
51 of the device 120 within a disc situated in front of the
posterior anulus.
[0046] The encapsulating membrane or material 51 of the device 120
may be a relatively soft, smooth, and flexible biocompatible
material so that the device 120 does not injure the intra anular
walls or superior and inferior endplates. Bio-compatality and
inertness are also important so that there is minimal physiological
reaction to the device 120. The material(s) comprising the
encapsulating material 51 can be impermeable to liquid transfer
such that its surface does not permit travel of disc tissue through
its surface and outside the disc. Accordingly, the preferred
embodiment is made of ePTFE, which exhibits these properties. ePTFE
is also strong and resilient enough to withstand the high pressure
and dynamic environment found in the intervertebral disc and aids
in the devices ability to seal defects and shield nerves in the
anulus. Preferably, the internodal distance of the ePTFE, i.e., the
average distance between the material's nodes, ranges from 0..mu.
to over 200.mu.. As will be further discussed, the encapsulating
membrane 51 can fully or partially encapsulate the frame 53 or
merely form a portion of a single side of the frame 53.
[0047] Though the preferred embodiment of the device 120 utilizes
ePTFE for the encapsulating material 51 other suitable
biocompatible materials may be used. For example, the membrane may
alternatively comprise biologic materials such as keratin,
collagen, bio-engineered anulus fibrosus, protein polymers or the
like. Other suitable synthetic materials include polyamides,
polyimides, silicones, polyurethane, natural rubber, latex and
other fluoropolymers such as perfluoroalkoxy (PFAs) and fluorinated
ethylene-propylene (FEP). These materials can be affixed to the
barrier frame through compression molding, solvent bonding,
injection molding, or through in situ polymerization.
[0048] In one embodiment of the invention, the encapsulating
material or membrane 51 can be fixed to the frame 53 by sutures.
The frame 53 may simply be encapsulated in ePTFE material by
suturing two pieces of material around the periphery of the frame
53. Also, to minimize the amount of stitches, a single folded piece
of material or a tube may be used. This method provides a very
durable attachment between the two pieces of material and yet
permits the device to flex evenly. Suturing the encapsulating
material 51 to the frame 53 can also permit the frame 53 to move or
flex relatively unimpeded by the encapsulating material 51.
Suturing is also advantageous because it is strong, reliable,
finely detailed, and will not harm the disc. In addition to
suturing along the periphery of the frame 53, the fingers 162 and
internal geometry of the frame may be secured to the encapsulating
material by suturing.
[0049] Ultrasonic welding may also be used as above to bond the
edges of the ePTFE to each other around the periphery of the
barrier frame 53. Because of the intense heat delivered by this
method, the mechanical properties of the ePTFE may be different at
the weld. This can be reduced by selectively welding the
encapsulating material at measured points spanning the periphery of
the barrier frame including between the fingers 162 and between
other voids in the geometry.
[0050] In a preferred method of manufacturing the device 120, the
frame 53 is encapsulated in ePTFE by first making a sandwich-like
arrangement 300 of the frame 53 and a first 54 and second
encapsulating material 55. Each of the encapsulating material 54
and 55 is comprised of a thin sheet of ePTFE that is patterned to
extend around from about 0.004 inches to about 0.25 inches beyond
the periphery of the frame. The thickness of the ePTFE may be
between about 0.001 inches to about 0.25 inches and preferably in
the range of about 0.005 inches to about 0.025 inches. The IND of
each encapsulating material may be in the range of about 5.mu. to
about 200.mu. with the higher value being more suited to
encouraging tissue ingrowth but exhibiting less strength. The IND
of each encapsulating material may be different to effect different
mechanical properties on either side of the device, mechanical
bonding, and fixation. The ePTFE material should preferably be of
an unprocessed extrudate variety that has not been subjected to
further surface treatments such as sintering and exhibits uniform
physical and chemical properties throughout.
[0051] Besides exhibiting superior elasticity, strength, and
biocompatibility, the material chosen for the barrier frame 53 will
preferably be able to withstand the temperatures and exposure times
required to monolithically encapsultate it in the encapsulating
material 51. In this preferred embodiment, a nickel titanium alloy
is chosen.
[0052] FIG. 7 shows a method of encapsulating the frame 53 within
the encapsulating material 51. The encapsulating material 51 can be
further comprised of either 2 sheets, i.e. a first encapsulating
material 54 and a second encapsulating material 55, formed as a
tube, or as a larger sheet capable of folding over the frame 53.
Referring back to the FIG. 7, a sandwich-like arrangement 300 of
the barrier frame 53 disposed between a first 54 and second
encapsulating material 55, is placed on the hemi circular or curved
face of a mandrel 310. A cover 320 is placed on top of the
sandwich-like arrangement 300 and force is applied sufficient to
cause the edges of the encapsulating material 51 to contact each
other. The contact may be continuous around the periphery of the
barrier frame 53 and may even form contacts through the holes in
the complex geometry of the barrier frame 53. Also, the surface of
the mandrel face 310 or cover 320 may contain recesses which serve
to not provide pressure or force at locations where bonding is not
desired to further permit the barrier frame 53 to move within
encapsulating first and second encapsulating material 51. In order
to create bonds at the contact points, the arrangement 300, mandrel
310, and cover 320 are heated to a temperature around the
crystalline melting point of ePTFE, 327.degree. Celsius. Also, it
may be preferable to utilize a range of temperatures from 325 to
375.degree. Celsius to control the rate of bonding. Also, the
barrier can be preheated by subjecting it to 300.degree. Celsius
for around one minute to decrease the time that the arrangement
300, mandrel 310, and cover 320 must be heated. The exact time
required for the desired bonding is quite variable and dependant on
several factors including the mass and consistency of the mandrel
and geometry of the barrier frame 53. Accordingly, one of ordinary
skill could easily determine the proper time for a particular
set-up taking care not overheat the ePTFE and cause it to degrade
or adversely affect the heat treatment of the frame 53.
[0053] This method can alternatively be practiced using a tube or
folded sheet of ePTFE so that fewer edges need form a bond to
effectively encapsulate the frame 53. Using a folded sheet
encapsulating material 51 can also be used to create a partially
covered frame 53. Alternatively, using a tube is particularly
advantageous in forming the arrangement 300 since the step of
applying the second encapsulating material 55 is not necessary. The
frame 53 is simply inserted in the hollow encapsulating material 51
and then heated in the covered mandrel.
[0054] Another method of making the device 120 comprises the
adhesion of the first encapsulating material 54 to the second
encapsulating material 55 using aqueous PTFE. Here a sandwich of
first encapsulating material/aqueous PTFE/barrier frame/aqueous
PTFE/second encapsulating material is made and then heated to the
melting point of the aqueous PTFE, around 325.degree., which is
less than the sintering temperature of the encapsulating material.
In this way, the water and wetting agents are burned off and the
PTFE particles melt and mechanically bond to the surfaces of the
first and second encapsulating material 51.
[0055] Aqueous PTFE or other adhesion material may be used to
encapsulate the frame 53 within a tube, folded single sheet, or
between two sheets of the encapsulating material 51. Also, selected
portions of the encapsulating material 51 can be coated with the
adhesion material depending on the degree and location of the
bonding one desires. For example, a single sheet encapsulating
material 51 on a either side of the frame 53 may be attached with
the aqueous PTFE by depositing it along either or both sides of the
frame 53 allowing it to contact the encapsulating material through
and around the frame 53 and heating it until mechanical bonds form.
Other adhesion material may also be used to bond, either chemically
or mechanically, the encapsulating material 51 to itself or the
frame 53. Examples of adhesion material include, but are not
limited to, common medical adhesives like cyanoacrylate, light
curing adhesives, urethane, epoxy, and silicone. Further examples
include polyamides, polyimides, silicones, polyurethane, natural
rubber, latex and other fluoropolymers such PFAs and FEPs.
[0056] Heat shrinking PTFE wrap or tubing around the barrier frame
53 is yet another way to provide a biocompatible and resilient
encapsulation. PTFE begins to shrink around 340.degree. Celsius and
completes its recovery during the cooling cycle. In one method, the
barrier frame 53 can be preheated to around 340.degree. Celsius and
a slightly larger tube may be placed over it whereupon the tube
shrinks in place upon contact and when cooled provides a smooth
coverage leaving only two small uncovered spots at the tails of the
barrier 53. These uncovered spots do not affect the devices ability
to retain intervertebral disc material, pressure, or height. Using
the methods described above, these ends may also be sutured or
welded. Alternatively, an assembly of the barrier frame 53 placed
within a slightly larger tube may be positioned on a mandrel 310
with a hemi circular face and covered with a mandrel cover 320 and
then heated to around 340.degree. Celsius until the PTFE shrink
fits around barrier frame 53.
[0057] As disclosed above, partial encapsulation or covering of the
frame 53 may be accomplished with these methods. For example, an
encapsulating material 51 comprised of ePTFE disposed around the
fingers 162 and face of the device 120 but leaving the center of
the frame 53 exposed may be advantageous for delivery and placement
of the device. By leaving a portion of the frame 53 uncovered, a
solid contact point is provided that can be used to couple the
device 120 to a delivery instrument. Alternatively, the
encapsulating material 51 can be designed to have a channel within
itself or covering a channel in the frame 53 that accepts a guide
or probe from the delivery instrument.
[0058] An alternative method is comprised of applying an extremely
thin, highly expanded PTFE film around the frame 53. By wrapping
the film transversely around the long axis of the frame radial
strength can be added to the underlying longitudinal strength of
the PTFE tube. The radially wrapped tube can then be placed on the
mandrel face 310 and compressed and heated to 350-390.degree.
Celsius in conjunction with the mandrel cover. The heating process
will allow the film to shrink and bond to the underlying PTFE
substrate and encapsulating the frame 53. The additional film will
provide radial strength and minimize any potential for protrusion
of the frame through the PTFE. In addition, while the film wrapping
is being performed a template can be placed on the convex side of
the PTFE tube. Over-wrapping of this tube will allow for creation
of a pocket on the convex side of the frame 53. This pocket in
conjunction with the windows left in the tube covering would allow
for attachment of a delivery instrument to the convex side of the
frame. An important manufacturing consideration of this application
method is the need for such high temperatures for sufficient
bonding of the PTFE film and its deleterious effects on the
underlying metallic substrate. Using an FEP/PTFE laminated film
with corresponding lower bonding temperatures of 300-320.degree.
Celsius can reduce this effect.
[0059] Subsequent to the application of pressure to the first
encapsulating material and/or semicircular frame and/or second
encapsulating material assembly and sintering the same to
mechanically bond the ePTFE, the mandrel cover is removed and the
device is removed from the mandrel. In this state the device is now
ready for implantation into an intervertebral disc. In use, the
encapsulated barrier is folded or crimped via stress-induced
martinsite or heat induced martinsite into a delivery cannula so
that it may be inserted through a naturally occurring or minimally
invasive iatrogenic hole. The unique structure and composition of
the device allows it to endure a ninety-degree bend and be
delivered parallel to the anular lamellae and in front of the
anular defect.
[0060] While references are made to a semi-circular frame and
matching mandrels, alternative cross sectional shapes of the frame
of the present invention may be employed to achieve various
stiffness or pressure response characteristics of the overall
device. As an example, compound curves may be desirable to create
multiple convexities and concavities in the frame. Alternatively, a
single concavity with varying radii of curvature may be employed
rather than the single radius of a semi-circle. Appropriately
shaped mandrels may be used with any of these shapes to achieve the
encapsulation methods described above.
[0061] Accordingly, utilizing the methods described herein will
provide a biocompatible and durable implant. In a preferred
embodiment, the implant is folded or crimped into a delivery
cannula so that it may be inserted through a naturally occurring or
minimally invasive iatrogenic hole. Among other features, the
unique structure and composition of the device allows it to endure
a ninety-degree bend and to be delivered parallel to the anular
lamellae and in front of the anular defect.
[0062] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *