U.S. patent application number 10/598080 was filed with the patent office on 2008-09-18 for graft fixation device.
This patent application is currently assigned to The Regents of the University of Colorado. Invention is credited to Reed Bartz, Kenneth Gall, Jeffrey Tyber, Chris Yakacki.
Application Number | 20080228186 10/598080 |
Document ID | / |
Family ID | 37074103 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080228186 |
Kind Code |
A1 |
Gall; Kenneth ; et
al. |
September 18, 2008 |
Graft Fixation Device
Abstract
In one aspect a device is disclosed for use as a bone implant
comprising, a body having a pre-implantation shape and a
post-implantation shape different from the pre-implantation shape.
The body is configured to change from the pre-implantation shape to
the post-implantation shape in response to the body being
activated. The body is configured to be inserted in a bone recess
while the body is in the pre-implantation shape. In another aspect
a method is disclosed comprising inserting a cable member into a
recess in a bone, inserting a retention device into the recess, the
retention device containing a shape memory material, and activating
the shape memory material.
Inventors: |
Gall; Kenneth; (Denver,
CO) ; Tyber; Jeffrey; (Castle Rock, CO) ;
Yakacki; Chris; (Boulder, CO) ; Bartz; Reed;
(Lafayette, CO) |
Correspondence
Address: |
GREENBERG TRAURIG, LLP
1200 SEVENTEENTH STREET, SUITE 2400
DENVER
CO
80202
US
|
Assignee: |
The Regents of the University of
Colorado
Boulder
CO
|
Family ID: |
37074103 |
Appl. No.: |
10/598080 |
Filed: |
April 3, 2006 |
PCT Filed: |
April 3, 2006 |
PCT NO: |
PCT/US2006/012934 |
371 Date: |
September 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60667876 |
Apr 1, 2005 |
|
|
|
Current U.S.
Class: |
606/63 ; 606/62;
606/76 |
Current CPC
Class: |
A61F 2002/0864 20130101;
A61B 17/0401 20130101; A61B 2017/0448 20130101; A61F 2002/0858
20130101; A61L 2400/16 20130101; A61B 2017/00871 20130101; A61F
2002/0888 20130101; A61F 2002/0882 20130101; A61L 27/16 20130101;
A61F 2/0811 20130101; A61L 2430/02 20130101; A61F 2210/0014
20130101; A61F 2002/0835 20130101; A61L 27/50 20130101 |
Class at
Publication: |
606/63 ; 606/62;
606/76 |
International
Class: |
A61B 17/56 20060101
A61B017/56 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The invention was sponsored by National Science Foundation
Grant No. NSF-DMI-0200495 and a National Institute of Health Grant
No. NIH-HL-067393 and the government has certain rights to this
invention.
Claims
1. A device for use as a bone implant comprising: a body having a
pre-implantation shape and a post-implantation shape different from
the pre-implantation shape; wherein the body is configured to
change from the pre-implantation shape to the post-implantation
shape in response to the body being activated; and wherein the body
is configured to be inserted in a bone recess while the body is in
the pre-implantation shape.
2. The device of claim 1, wherein the body further comprises a
shape memory material.
3. The device of claim 2, wherein the body is configured to change
from the pre-implantation shape to the post-implantation shape
largely due to the shape memory effect of the shape memory
material.
4. The device of claim 1, wherein the body is configured to couple
with the bone recess when the body is in the post-implantation
shape.
5. The device of claim 1, wherein the body comprises a material
that has no significant shape memory effects.
6. The device of claim 1, wherein the post-implantation shape is
selected from a substantially cylindrical shape, a dumbell type
shape, a cylindrical shape with ridges, and a threaded screw-like
shape.
7. The device of claim 2, wherein the shape memory material is
configured to fix a cable member to the body.
8. The device of claim 7, wherein the cable member is selected from
an animal tissue, a synthetic fiber, a natural fiber, a polymer, a
metallic wire, a bundle, and a composite.
9. The device of claim 8, wherein the animal tissue is human soft
tissue.
10. The device of claim 2, wherein the shape memory material is
selected from a shape memory polymer, a shape memory metal alloy of
nickel, a shape memory alloy of titanium, a shape memory foam, and
a shape memory ceramic.
11. The device of claim 1, wherein the body comprises a cavity.
12. The device of claim 11, further comprising a drug within the
cavity.
13. The device of claim 11, further comprising a shape memory
material, wherein the cavity is at least partially defined by a
shape memory material.
14. The device of claim 11, wherein the body in the
pre-implantation shape allows insertion of a cable member within
the cavity.
15. The device of claim 14, wherein the cavity is substantially
constricted while the body is in the post-implantation shape.
16. The device of claim 11, wherein the cavity is configured to
accept an activating element.
17. The device of claim 14, wherein the cavity is spaced from an
outer surface of the body to limit the amount of heat that is
transferred through the outer surface of the body when heat is
applied by an activating element.
18. The device of claim 11, wherein the cavity comprises an opening
on an outer surface of the body.
19. The device of claim 18, wherein the cavity comprises a recess,
the recess connected with an outer surface of the body.
20. The device of claim 19, further comprising a drug within the
recess.
21. The device of claim 1, further comprising a cable member.
22. The device of claim 21, wherein the cable member is attached to
the body.
23. The device of claim 21, wherein the cable member is selected
from an animal tissue, a synthetic fiber, a natural fiber, a
polymer, a metallic wire, a bundle, and a composite.
24. The device of claim 23, wherein the animal tissue is human soft
tissue.
25. The device of claim 1, wherein the body further comprises a
cable member.
26. The device of claim 25, wherein the cable member is selected
from an animal tissue, a synthetic fiber, a natural fiber, a
polymer, a metallic wire, a bundle, and a composite.
27. The device of claim 26, wherein the animal tissue is human soft
tissue.
28. The device of claim 1, wherein the body is selected from a soft
tissue graft fixation device, a tendon fixation device, a joint
capsule repair device, a tissue tack for labral, a tissue tack for
bicep repair, a suture anchor, an orthopedic screw, a fixation
screw for tenodesis, and a hard tissue spacer.
29. The device of claim 1, further comprising a packaging member,
the packaging member configured to surround the body and configured
to maintain the body in a sterile environment.
30. The device of claim 29, wherein the packaging member is
configured to constrain the body to the pre-implantation shape.
31. The device of claim 1, wherein the body is further configured
to create a load within the bone recess and normal to a surface
element of the bone recess in excess of 10 KPa.
32. The device of claim 31, wherein the load is less than 1
GPa.
33. The device of claim 11, wherein the cavity comprises a mold
configured to hold a monomer solution.
34. The device of claim 13, wherein the cavity comprises a mold
while the shape memory material is in the pre-implantation
shape.
35. The device of claim 1, wherein the body is configured to be
activated via receiving heat.
36. The device of claim 1, wherein the body is configured to be
activated via absorbing electromagnetic radiation.
37. The device of claim 1, wherein the body is configured to be
activated via the removing of constraints on the surface of the
body.
38. The device of claim 1, wherein the body further comprises an
elastomer.
39. The device of claim 38, wherein the body is configured to be
deformed into the pre-implantation shape by a force on the
body.
40. The device of claim 39, wherein the force on the body is
applied by a tube.
41. The device of claim 39, wherein the body is configured to
change from the pre-implantation shape to the post-implantation
shape largely due to the removal of the force on the body.
42. The device of claim 1, wherein the change from the
pre-implantation shape to the post-implantation shape comprises an
expansion.
43. The device of claim 1, wherein the change from the
pre-implantation shape to the post-implantation shape comprises a
contraction.
44. The device of claim 1, wherein the bone recess is a gap between
a first surface of a first bone and a second surface of a second
bone.
45. The device of claim 44, wherein the first surface and the
second surface are components of a joint.
46. A method comprising: inserting a cable member into a recess in
a bone; inserting a retention device into the recess, the retention
device containing a shape memory material; and activating the shape
memory material.
47. The method of claim 46, further comprising: fixing the cable
member to the recess.
48. The method of claim 46, further comprising: creating the recess
in the bone.
49. The method of claim 46, further comprising: dilating the recess
in the bone.
50. The method of claim 46, further comprising: compacting bone
tissue surrounding the recess in the bone.
51. The method of claim 46, wherein the cable member is selected
from an animal tissue, a synthetic fiber, a natural fiber, a
polymer, a metallic wire, a bundle, and a composite.
52. The method of claim 51, wherein the animal tissue is human soft
tissue.
53. The method of claim 46, further comprising: initiating a
polymerization of a monomer solution.
54. The method of claim 46, wherein activating comprises performing
an operation on the shape memory material, selected from heating,
exposing to radio frequency electromagnetic radiation, exposing to
infrared electromagnetic radiation, exposing to ultraviolet
electromagnetic radiation, and subjecting to a voltage
differential.
55. The method of claim 46, wherein the inserting the cable member
operation precedes the inserting the retention device
operation.
56. The method of claim 46, wherein the inserting the cable member
operation is performed simultaneously with the inserting the
retention device operation.
57. The method of claim 46, wherein after the activating operation
is performed, the retention devices contacts the recess in the bone
and contacts the cable member.
58. The method of claim 46, wherein after the activating operation
is performed, the cable member is held by the retention device and
the cable member does not substantially contact the recess in the
bone.
59. A kit comprising: a first bone implant, the first bone implant
having a first pre-implantation shape and a first post-implantation
shape different from the first pre-implantation shape; wherein the
first bone implant is configured to be inserted in a first bone
recess while the first bone implant is in the first
pre-implantation shape; wherein the first bone implant is
configured to fix a cable member to the first bone recess while the
first bone implant is in the first post-implantation shape; and a
second bone implant, the second bone implant having a second
pre-implantation shape and a second post-implantation shape
different from the second pre-implantation shape; wherein the
second bone implant is configured to be inserted in a second bone
recess while the second bone implant is in the second
pre-implantation shape; wherein the second bone implant is
configured to fix the cable member to the second bone recess while
the second bone implant is in the second post-implantation shape;
wherein the second post-implantation shape is different from the
first post-implantation shape.
60. The kit of claim 59, further including an insertion device
configured to aid the insertion of the first bone implant.
61. The kit of claim 60, wherein the insertion device comprises a
tube.
62. The kit of claim 60, wherein the insertion device comprises a
shaft.
63. The kit of claim 60, wherein the insertion device comprises a
guide wire.
64. The kit of claim 60, wherein the insertion device is configured
to separate into a first member and a second member.
65. The kit of claim 64, wherein the first member is configured to
be fixed in the first bone recess.
66. A method comprising: shaping a polymer material into a
post-implantation shape; deforming the polymer material into a
pre-implantation shape different from the post-implantation shape,
while maintaining the temperature of the polymer material above a
certain temperature; and cooling the polymer material to below the
certain temperature while holding the polymer material in the
pre-implantation shape.
67. The method of claim 66, wherein the pre-implantation shape is a
plug.
68. The method of claim 66, wherein the pre-implantation shape
comprises a cavity.
69. The method of claim 66, wherein the pre-implantation shape
comprises a channel and a recess.
70. The method of claim 69, further comprising: filling the recess
with a drug.
71. The method of claim 66, wherein the certain temperature is a
transition temperature of the polymer material.
72. The method of claim 66, further comprising: polymerizing a
material around a cable member.
73. A kit comprising: a first solution comprising a monomer, the
first solution contained in a first container; a second solution
comprising a cross-linker, the second solution contained in a
second container; wherein the second solution is configured to form
a third solution if the second solution is mixed with the first
solution; wherein the third solution is capable of forming a shape
memory polymer upon polymerization; and a cable member configured
to function as a soft tissue replacement in a human body.
74. The kit of claim 73, further comprising a polymerizing device,
the polymerizing device configured to polymerize the third solution
into a shape memory polymer.
75. The kit of claim 74, wherein the polymerizing device is
selected from a radiation source, an ultraviolet light source, a
heating source, and a source of electrical current.
76. The kit of claim 73, wherein the third solution is configured
to be polymerized via receiving heat from a human body.
77. The kit of claim 73, wherein the cable member is further
configured to be partially encapsulated in the shape memory
polymer.
78. The kit of claim 73, further comprising a mold configured to
hold the third solution.
79. The kit of claim 78, wherein the mold is further configured to
allow the third solution to be polymerized by the polymerizing
device.
80. The kit of claim 73, further comprising a mixing member.
81. The kit of claim 73, further comprising a first metering
device.
82. The kit of claim 81, wherein the first metering device is
integrated with the first container.
83. The kit of claim 81, wherein the first metering device is
integrated with the second container.
84. The kit of claim 73, further comprising a mixing vessel.
85. The kit of claim 84, wherein the mixing vessel is integrated
with a first metering device and the first metering device
comprises markings.
86. The kit of claim 84, wherein the mixing vessel is capable of
functioning as a mold to define a shape of the third solution while
it is polymerized.
87. The kit of claim 73, further comprising a support configured to
hold the cable member partially enveloped by the third solution
while the third solution is polymerized by polymerizing device.
88. The kit of claim 73, wherein the cable member is selected from
an animal tissue, a synthetic fiber, a natural fiber, a polymer, a
metallic wire, a bundle, and a composite.
89. The kit of claim 88, wherein the animal tissue is human soft
tissue.
90. The kit of claim 73, wherein the monomer is tert-butyl
acrylate.
91. The kit of claim 73, wherein the cross-linker is polyethylene
glycol dimethacrylate.
92. The kit of claim 73, further comprising a photo-initiator.
93. The kit of claim 92, wherein the photo-initiator is
2,2-dimethoxy-2-phenylacetophenone.
94. A polymerized composition comprising: a linear chain comprising
an acrylate; and a first cross-linker comprising a multi-functional
acrylate; wherein the polymerized composition exhibits a transition
at a temperature between about -50 degrees Celsius and about 150
degrees Celsius; wherein the polymerized composition exhibits shape
memory effects.
95. The polymerized composition of claim 94, wherein the
polymerized composition comprises polyethylene glycol and methyl
methacrylate.
96. The polymerized composition of claim 95, wherein the
polymerized composition is polyethylene glycol-methyl
methacrylate.
97. The polymerized composition of claim 94, wherein the linear
chain is selected from tert-butyl methacrylate, methyl
methacrylate, and 2-hydroxyethyl methacrylate.
98. The polymerized composition of claim 94, wherein the first
cross-linker is selected from polyethylene glycol dimethacrylate,
diethylene glycol dimethacrylate, triethylene glycol dimethacrylate
and ethylene dimethacrylate.
99. The polymerized composition of claim 94, comprising a second
cross-linker, different from the first cross-linker.
100. The polymerized composition of claim 99, wherein the second
cross-linker differs from the first cross-linker in
composition.
101. The polymerized composition of claim 99, wherein the second
cross-linker differs from the first cross-linker in molecular
weight.
102. The polymerized composition of claim 94, containing more than
about 10% of the weight of the polymerized composition as the first
cross-linker.
103. The polymerized composition of claim 94, wherein the
multi-functional acrylate is di-functional.
104. The polymerized composition of claim 94, wherein the
transition is a glass transition.
105. The polymerized composition of claim 94, wherein the
transition is a melting point.
106. The polymerized composition of claim 94, wherein the
polymerized composition exhibits a transition at about 37 degrees
Celsius.
107. The polymerized composition of claim 94, wherein the
polymerized composition exhibits a transition at a temperature
between about 34 degrees Celsius and about 50 degrees Celsius.
108. A polymerized composition comprising: a first percentage by
weight of a linear chain; and a second percentage by weight of a
first cross-linker; wherein the polymerized composition exhibits
shape memory effects.
109. The polymerized composition of claim 108, wherein the linear
chain is selected from tert-butyl methacrylate, methyl
methacrylate, and 2-hydroxyethyl methacrylate.
110. The polymerized composition of claim 109, wherein the first
cross-linker is selected from polyethylene glycol dimethacrylate,
diethylene glycol dimethacrylate, triethylene glycol dimethacrylate
and ethylene dimethacrylate.
111. The polymerized composition of claim 108, wherein the second
percentage is greater than about 10 percent.
112. The polymerized composition of claim 108, further comprising a
third percentage by weight of a second cross-linker, different from
the first cross-linker.
113. The polymerized composition of claim 110, wherein the second
cross-linker differs from the first cross-linker in
composition.
114. The polymerized composition of claim 110, wherein the second
cross-linker differs from the first cross-linker in molecular
weight.
115. The polymerized composition of claim 108, wherein the
polymerized composition exhibits shape memory effects.
116. The polymerized composition of claim 108, wherein the first
cross-linker comprises polyethylene glycol dimethacrylate.
117. A surgical method comprising: creating a recess in a bone of a
patient, the bone having a bone temperature; inserting a cable
member into the bone; and inserting an implant into the bone, the
implant containing a shape memory material at an insertion
temperature different than the bone temperature.
118. The surgical method of claim 117, wherein inserting the
implant thereby causes transfer of heat from the bone to the shape
memory material.
119. The surgical method of claim 118, wherein the transfer of heat
to the shape memory material thereby heats the shape memory
material to near a transition temperature of the shape memory
material.
120. The surgical method of claim 118, wherein the transfer of heat
to the shape memory material thereby heats the shape memory
material to the transition temperature of the shape memory
material.
121. The surgical method of claim 118, wherein the transfer of heat
to the shape memory material thereby heats the shape memory
material to above the transition temperature of the shape memory
material.
122. The surgical method of claim 117, wherein the inserting the
implant is performed along an insertion axis.
123. The surgical method of claim 122, wherein inserting the
implant thereby causes the expansion of the shape memory material
along a transverse axis which is at an angle to the insertion
axis.
124. The surgical method of claim 123, wherein the angle is greater
than 45 degrees.
125. The surgical method of claim 117, wherein inserting the
implant thereby puts the implant and the cable member into
contact.
126. The surgical method of claim 117, wherein inserting the
implant thereby applies a pressure between the implant and a
portion of the bone.
127. The surgical method of claim 126, wherein the pressure is
transmitted between the implant and the bone by the cable
member.
128. The surgical method of claim 117, wherein the implant has a
first configuration with a first diameter during insertion and a
second configuration with a second diameter following insertion,
the second configuration different than the first configuration and
the second diameter being larger than the first diameter.
129. The surgical method of claim 128, wherein the first
configuration has a first generally solid tubular shape having a
first length and the second configuration has a second generally
solid tubular shape having a second length shorter than the first
length.
130. The surgical method of claim 117, wherein the shape memory
material is a shape memory polymer.
131. The surgical method of claim 130, wherein the shape memory
polymer comprises poly-ethylene glycol and poly-methyl
methacrylate.
132. The surgical method of claim 130, wherein the cable is a
tendon.
133. The surgical method of claim 132, wherein the bone is a head
of a femur.
134. The surgical method of claim 117, further comprising:
contacting the implant with a fluid having a temperature different
than the insertion temperature.
135. The surgical method of claim 117, wherein the recess is a bone
tunnel comprising a side wall and an end wall and the implant
contacts at least a portion of the side wall when the implant is in
the second configuration.
136. A surgical method for anterior cruciate ligament
reconstruction comprising: creating a bone tunnel in a head of a
femur of a patient, the bone having a bone temperature; inserting a
connective tissue into the bone tunnel; and inserting a shape
memory polymer plug into the bone tunnel wherein the plug has a
first configuration for insertion and a second configuration for
affixation, the second configuration comprising a radially expanded
dimension that presses the connective tissue against a side wall of
the bone tunnel such that the connective tissue becomes affixed in
the bone tunnel and wherein the plug changes from the first
configuration to the second configuration based on an activation
temperature equal to or greater than the bone temperature.
137. The surgical method of claim 136, wherein the bone tunnel
temperature is an average temperature of the human body.
138. The surgical method of claim 137, wherein the tissue is a part
of a hamstring tendon of the patient.
139. The method of claim 54, wherein the activating is heating, and
wherein the heating comprises a transfer of heat from the bone to
the shape memory material.
140. The method of claim 54, wherein the activating is heating, and
wherein the heating comprises flooding the retention device with a
liquid bath.
141. The method of claim 54, wherein the activating is heating, and
wherein the heating comprises a transfer of heat from the bone to
the shape memory material, and flooding the retention device with a
liquid bath.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/667,876 filed Apr. 1, 2005, which application is
hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] Ligaments are strong fibrous soft tissue connecting the
articular ends of bones to bind them together and to facilitate or
limit motion. Injuries to ligaments are common, and patients who
are physically active are generally more susceptible to such
ligament injuries. The anterior cruciate ligament (ACL) of the knee
joint is a ligament frequently injured by such patients. ACL
injuries cause instability in the knee joint which, when left
untreated, may lead to degenerative arthritis. Because of this
condition, ACL reconstruction may be required. Generally during ACL
reconstruction, a substitute soft tissue ligament or graft is
attached to the femur (femoral fixation) and/or to the tibia
(tibial fixation) to facilitate regrowth and permanent
attachment.
[0004] There are several known methods for performing ACL
reconstruction, and there are also several tibial or femoral
fixation devices that may be used with these methods.
[0005] In surgery it is generally known to use soft tissue tendon
grafts (e.g. hamstring tendon, taken from the thigh of the patient)
to replace the severely damaged ACL. In a typical surgical
procedure one end of a soft tissue graft is fixed into a drill hole
made from the knee joint into the distal femur and another end of
the graft is fixed into a drill hole made into the proximal tibia.
The ends of the graft are fixed into the drill holes with fixation
screws and in most cases with so-called interference screws. An
interference screw may be a screw that has a larger diameter
(including any grafts or tendons) than the cavity, thus generating
a force that holds the tendon. A screw is installed into the space
between the drill hole and the soft tissue grafts to lock the
grafts into the drill hole. The tendon then acts as a new ACL.
[0006] There are several known methods for performing ACL
reconstruction, and there are also several tibial or femoral
fixation devices that may be used with these methods. The fixation
screws, like interference screws, are normally made of metal like
stainless steel or titanium, or of a bio-absorbable polymer like
polylactide. An interference screw may be considered as metallic
and/or bio-absorbable polymeric materials and composites, which are
suitable for manufacturing of tendon graft fixation screws, are
well known in the art, for example as described in the
literature.
[0007] Conventional extra-articular hamstring graft fixation
techniques have complications, such as suture stretch, graft tunnel
motion and so-called windshield wiper effect where the size of the
intra-articular drill hole end will increase due to graft movement
in the drill-hole. Also the use of screws as fixation implants for
soft tissue grafts in anterior crucial ligament procedures is
complicated due to: 1) the threads of the screw cutting the grafts
during screw installation if the screw is too big in relation to
the tendon and/or if the space between the drill hole and tendon
grafts is too small; 2) the threads of the screw damaging the
tendon during screw installation; 3) the tendon rotating with the
screw during screw installation so that the optimal position of the
grafts is lost and/or the grafts are damaged; 4) divergence of the
grafts and/or screw occurring; and 5) the bio-absorbable screw
breaking during insertion.
SUMMARY OF THE INVENTION
[0008] In one embodiment, the invention provides a fixation device,
which may fix a soft tissue graft, like a tendon or ligament graft,
to a bone with little risk of damaging the soft tissue graft during
insertion.
[0009] One aspect is a device for use as a bone implant comprising,
a body having a pre-implantation shape and a post-implantation
shape different from the pre-implantation shape. The body is
configured to change from the pre-implantation shape to the
post-implantation shape in response to the body being activated.
The body is configured to be inserted in a bone recess while the
body is in the pre-implantation shape.
[0010] Another aspect is a method comprising inserting a cable
member into a recess in a bone, inserting a retention device into
the recess, the retention device containing a shape memory
material, and activating the shape memory material.
[0011] Another aspect is a kit comprising a first bone implant. The
first bone implant has a first pre-implantation shape and a first
post-implantation shape different from the first pre-implantation
shape. The first bone implant is configured to be inserted in a
first bone recess while the first bone implant is in the first
pre-implantation shape. The first bone implant is configured to fix
a cable member to the first bone recess while the first bone
implant is in the first post-implantation shape. The kit also
comprises a second bone implant. The second bone implant has a
second pre-implantation shape and a second post-implantation shape
different from the second pre-implantation shape. The second bone
implant is configured to be inserted in a second bone recess while
the second bone implant is in the second pre-implantation shape.
The second bone implant is configured to fix the cable member to
the second bone recess while the second bone implant is in the
second post-implantation shape. The second post-implantation shape
is different from the first post-implantation shape.
[0012] Another aspect is a method comprising shaping a polymer
material into a post-implantation shape and deforming the polymer
material into a pre-implantation shape different from the
post-implantation shape, while maintaining the temperature of the
polymer material above a certain temperature. The method also
comprises cooling the polymer material to below the certain
temperature while holding the polymer material in the
pre-implantation shape.
[0013] Another aspect is a kit comprising a first solution
comprising a monomer, the first solution contained in a first
container, a second solution comprising a cross-linker, the second
solution contained in a second container. The kit also includes a
cable member configured to function as a soft tissue replacement in
a human body. The second solution is configured to form a third
solution if the second solution is mixed with the first solution,
wherein the third solution is capable of forming a shape memory
polymer upon polymerization.
[0014] Another aspect is a polymerized composition comprising, a
linear chain comprising an acrylate, a first cross-linker
comprising a dimethacrylate, wherein the polymerized composition
exhibits a glass transition at a temperature between about -50
degrees Celsius and about 150 degrees Celsius and wherein the
polymerized composition exhibits shape memory effects.
[0015] Another aspect is a polymerized composition comprising, a
first percentage by weight of a linear chain, and a second
percentage by weight of a first cross-linker, wherein the
polymerized composition exhibits shape memory effects.
A BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a cross-section of an embodiment of an anterior
cruciate ligament repair site;
[0017] FIG. 2 shows a cross-section of a device installed and in a
post-implantation shape with a cable member in a bone recess;
[0018] FIG. 3 shows a cross-section of another embodiment of a
device installed and in a post-implantation shape with a cable
member in a bone recess;
[0019] FIG. 4 shows a cross-section of another embodiment of a
device installed and in a post-implantation shape with a cable
member in a bone recess;
[0020] FIG. 5 shows flow-chart of a method for performing
surgery;
[0021] FIG. 6 shows a flow-chart of a method of manufacturing
devices;
[0022] FIGS. 7a-7h shows multiple forms of possible unconstrained
shapes of devices;
[0023] FIG. 8 shows a polymer extrusion unit;
[0024] FIG. 9a shows an embodiment of a pre-deformed or
unconstrained shape;
[0025] FIG. 9b shows and embodiment of a deformed shape or
pre-implantation shape;
[0026] FIG. 10 shows different tip geometries of devices;
[0027] FIG. 11 shows experimental results of stresses of several
polymer compositions;
[0028] FIG. 12 shows the free strain recovery time of devices
strained and then stored in the strained state before recovery was
initiated;
[0029] FIG. 13 shows experimental results of constrained recovery
time as a function of crosslinking.
[0030] FIG. 14 shows a custom force measuring fixture;
[0031] FIG. 15 shows experimental results of the recovery load of a
shape memory polymer plug;
[0032] FIG. 16 shows experimental results of the load of a prior
art interference screw;
[0033] FIG. 17 shows a test setup for an in-vitro maximum failure
strength and cyclic strength of a fixation device as installed;
[0034] FIG. 18 shows experimental results comparing SMP fixation
devices and a Delta Interference Screw;
[0035] FIG. 19 shows experimental results comparing tensile
strengths and displacement ratios of the cyclic response (e.g.,
response to multiple cycles) of a ShapeLoc fixation device;
[0036] FIG. 20a shows mean and standard deviations of tensile
strengths of various fixation devices;
[0037] FIG. 20b shows mean and standard deviations of stiffnesses
of various fixation options;
[0038] FIG. 20c shows mean and standard deviations of slip rates of
various fixation options;
[0039] FIG. 21 shows a tissue encapsulation setup;
[0040] FIG. 22a shows a device in a pre-implantation shape;
[0041] FIG. 22b shows a device in a mid-deployment shape;
[0042] FIG. 22c shows a device in an unconstrained shape;
[0043] FIG. 23 shows a device with a polymerized solution around
the device;
[0044] FIG. 24 shows a schematic of the three-point flexure
thermomechanical setup and the results of a Dynamic Mechanical
Analysis (DMA) test showing storage modulus and tan-delta as a
function of temperature for the PEGDMA copolymer and PLA.
DETAILED DESCRIPTION OF THE INVENTION
[0045] The following description of various embodiments is merely
exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0046] An example of a joint repair surgery in which the following
polymers, devices, methods and kits may be used is the repair of an
ACL in a human knee. A ruptured ACL may be repaired through, in
part, attaching a cable member the native posterior ACL attachment
site (e.g., an opening of the tunnel at the site). For example, a
cable member may be attached to the site via creating a bone recess
and fixing the cable member to the bone recess. A bone recess may
be used to increase the surface area of bone to which the cable
member may be fixed.
[0047] A technique in the prior art for fixation of an ACL soft
tissue graft includes drilling a properly sized tunnel from the
anteromedial tibial metaphysis into the native posterior ACL
attachment site, feeding a soft tissue graft into the tunnel, and
fixing the soft tissue graft to the tunnel via an interference
screw driven into the tunnel against the soft tissue graft.
[0048] Another technique in the prior art includes drilling a
tunnel in a tibia and placing an anchor with an attached suture
into the tunnel thus anchoring the suture in the bone. The suture
is then attached to the soft tissue graft.
[0049] FIG. 1 shows a cross-section of an embodiment of an anterior
cruciate ligament (ACL) repair site 100. The ACL repair site 100
comprises a patella 110, a femur 112, and a tibia 114. A tibia
recess 116 has been created in the tibia 114, and a femur recess
120 has been created in the femur 112. A cable member 102 is
partially inside both the tibia recess 116 and the femur recess
120. Devices 104 are inside each of the tibia recess 116 and the
femur recess 120.
[0050] A surgeon or other practitioner may insert devices 104 into
either or both of the tibia recess 116 and the femur recess 120
using an insertion device 106. In one embodiment, the insertion
device 106 is a guide wire that may aid in the insertion of a
device 104. For example, a device 104 may be threaded onto a guide
wire (e.g., the guide wire enters the device through one opening in
the device and exits through another opening in the device), and
the device may be pushed into an installed position along the guide
wire. In another embodiment, the insertion device 106 is a shaft
that may be used to push the device 104 into place. For example, a
cavity in the device 104 may accept the insertion device 106,
allowing the insertion device (e.g., shaft) to couple with the
device, guide the device and move the device into an installed
position. As another example, the device 104 may be attached to the
insertion device 106 and the device 104 and insertion device 106
may be separated (e.g., when the device is in an installed
position).
[0051] In the embodiment shown in FIG. 1, the devices 104 are
substantially smooth and have narrow tips in the pre-implantation
shape (shown). In another embodiment, the devices 104 have a
shorter, wider shape in the post-implantation shape (not
shown).
[0052] The devices 104 shown in FIG. 1 represent one embodiment of
a device which may be used to repair an ACL in this manner.
Numerous other embodiments of devices and modifications to devices
similar to the devices 104 shown in FIG. 1 are described herein.
For example, any of the embodiments described herein of devices,
methods and polymers may be used to repair an ACL.
[0053] The descriptions of devices, methods and polymers herein
should not be understood to be limited only to the Figures or to
any specific Figure. Therefore, the devices shown in FIG. 1 may be
used as shown in other Figures or may otherwise be used, and the
devices shown in other Figures or otherwise described may be used
in FIG. 1 or may otherwise be used.
[0054] In the embodiment shown, the cable member 102 is used to
replace a torn or failed ACL. The cable member is held by the
devices 104 at points (e.g., artificial attachment sites) in the
tibia 114 and the femur 112. The cable member 102 may comprise any
suitable material, as described further herein.
[0055] An ACL repair in a knee is discussed here as an example of a
surgery site where a device and/or method of the present invention
may be employed. Other sites, joints and parts of anatomy may have
surgery performed on them using a polymer, device or method of the
present invention. For example, the devices and methods described
herein can be used for rotator cuff reconstruction, for
acromioclavicular (AC) reconstruction, for ACL reconstruction and
for fastening tendons, grafts, or sutures to other tissue, such as
bone or other soft tissue.
[0056] Common weaknesses with the ACL replacement methods practiced
in sports medicine industry are caused by the fixation device and
how it is used. For example, the fixation device may be the source
of failure for the surgery by allowing a cable member (e.g.,
tendon) to slip. The fixation device may also cause a cable member
to break. For example, an interference screw may cut into or
entirely through the cable member during the process of insertion
into the bone tunnel.
[0057] A cable member as used herein may be a tendon, ligament,
artificial soft tissue replacement, a metal wire, a composite
structure, synthetic fiber or any member that may be used to create
a substitute for an animal soft tissue (e.g., tendon, ligament,
fascia, vessel).
[0058] FIG. 2 shows a cross-section of a device 200 installed and
in a post-implantation shape with a cable member 202 in a bone
recess 204. The device 200 comprises a cavity 206. The device 200
presses the cable member 202 against a wall of the bone recess 204
thereby using friction (e.g., friction between the wall and the
cable member, friction between the device and the cable member,
friction between the device and the wall) to fix the cable member
to a bone 212.
[0059] The device 200 may be inserted into the bone recess 204 in a
pre-implantation shape that is different from the post-implantation
shape. In one embodiment, the device 200 comprises a shape memory
material. The shape memory material allows the device 200 to change
from the pre-implantation shape to the post-implantation shape. For
example, after the device is placed within a bone recess, the shape
memory material may be activated into a post-implantation shape. In
another embodiment, the device 200 comprises an elastomer. The
elastomer allows the device 200 to change from the pre-implantation
shape to the post-implantation shape. For example, the device 200
may be placed within a bone recess 204 while the is elastomer
constrained by a constraining member. The removal (e.g.,
separating, dissolving) of the constraining member may allow the
elastomer to change into a post-implantation shape. In yet another
embodiment, another material may be used to allow the device 200 to
change from a pre-implantation shape to a post-implantation
shape.
[0060] The discussion herein of shape memory materials and devices
that use shape memory materials may be understood as an example of
how a device may be used with a pre-implantation shape and a
post-implantation shape to fix a cable member as part of a surgical
procedure. The use of shape memory materials is not meant to
exclude the analogous use of elastomer materials or other
appropriate materials.
[0061] The post-implantation shape may be a function of the bone
recess 204 and the cable member 202 as installed with the device. A
device may also have an unconstrained shape that the device would
embody if it were activated with little or no constraints on the
device's shape (e.g., the device resting on a table, the device in
a water bath, the device resting on a heating plate). The
post-implantation shape may be a function of the device's
unconstrained shape. For example, the device may exert a force
(e.g. stress) on a cable member and/or a bone recess based on the
difference between the post-implantation shape of the device and
the unconstrained shape of the device (e.g., the difference may
represent the strain on the device caused by the deformation still
present in the device, as installed, after activation).
[0062] A device may have different post-implantation shapes based
on particular installation. To the extent that the stress (e.g.
forces transmitted from the bone recess 204 and the cable member
202) induce strain on the device, the device's post-implantation
shape may be determined by the particular installation and
installation procedure of the cable member and determined by the
particular bone recess. In one embodiment, the pre-implantation
shape is substantially different from the device's
post-implantation shape. In another embodiment, some elements of
the device do not change significantly between the device's
pre-implantation shape and the post-implantation shape.
[0063] As used herein the term "bone recess" may comprise any
volume at least partially defined by a bone wall. For example, a
bone recess may be a hole in a bone, a pre-existing configuration
of a bone, a configuration between two bones, or a configuration
between two boney structures. In one embodiment, a bone recess 204
is a tunnel drilled into a bone 212. In another embodiment, a bone
recess comprises a space between two bones in a joint (not shown).
For example, a bone recess within a joint may accept a device in a
pre-implantation shape and the bone recess within the joint may be
spread by the activation of the device into a post-implantation
shape. In yet another embodiment, a bone recess is an irregular
cavity in a bone (not shown). For example, a bone recess may be a
fracture in a bone or a milled shelf in a bone.
[0064] Shape memory materials may recover a predetermined shape
after mechanical deformation, exhibiting a shape memory effect. A
shape memory effect is often initiated by a change in temperature
and has been observed in metals, ceramics, and polymers. However, a
shape memory effect may be initiated by another cause. From a
macroscopic point of view, the shape memory effect in polymers may
differ from ceramics and metals due to the lower stresses and
larger recoverable strains sometimes achieved in polymers.
[0065] For example, a polymer is a shape memory polymer (SMP) if
the original shape (e.g., an unconstrained shape) of the polymer
body may be recovered by heating the body without substantial
constraints above a shape recovery temperature, a glass transition
temperature, or deformation temperature (T.sub.d), even if the
original shape of the polymer has been destroyed mechanically at a
lower temperature than T.sub.d, or if the memorized shape (e.g.,
the unconstrained shape) is recoverable by application of another
stimulus. Any polymer that can recover an original shape from a
temporary shape (e.g., a pre-implantation shape) by application of
a stimulus such as temperature may be considered a SMP. The
original shape is set by manufacture and the temporary shape is set
by thermo-mechanical deformation.
[0066] A SMP may have the ability to recover large deformation upon
heating. In one embodiment, a device with a memorized shape (e.g.,
original shape) is made from a SMP, which can subsequently be
crushed or deformed and inserted into a bone recess, used to hold a
graft, and the device is deployed (e.g., expanded, contracted) by
increasing the temperature of the device. In one embodiment, the
device's deployment may be controlled by controlling the
temperature of the device.
[0067] However, the shape memory effect of a shape memory material
is different from, and usually greater in terms of absolute effect,
than the thermal expansion of a material. Those with skill in the
art will understand the differences and similarities between shape
memory effects and thermal expansion effects.
[0068] The thermomechanical response of shape memory polymers may
be defined by four critical temperatures. The glass transition
temperature, T.sub.g, is typically represented by a transition in
modulus-temperature space and can be used as a reference point to
normalize temperature. Shape memory polymers offer the ability to
vary T.sub.g over a temperature range of several hundred degrees by
control of chemistry or structure. The pre-deformation temperature,
T.sub.d, is the temperature at which the polymer is deformed into
its temporary shape. Depending on the required stress level and
strain level, the initial deformation at T.sub.d can occur above or
below T.sub.g. The storage temperature, T.sub.s, represents the
temperature in which no shape recovery occurs. T.sub.s is often
equal to or below T.sub.d. At the recovery temperature, T.sub.r,
the shape memory effect is activated, which causes the material to
recover its original shape, and is typically in the vicinity of
T.sub.g or above. Therefore, T.sub.s is often below T.sub.g because
shape recovery begins at T.sub.r. In an embodiment, recovery may be
accomplished isothermally by heating to a fixed T.sub.r and then
holding, or by continued heating up to and past T.sub.r.
[0069] Generally, a transition temperature may be a characteristic
of a material (e.g., SMP, thermoplastic, thermoset) and may be
defined in a number of ways. For example, a transition temperature
may be defined by a temperature of a material at the onset of a
transition, the midpoint of a transition, or the completion of a
transition. As another example, a transition temperature may be
defined by a temperature of a material at which an inflection point
of the modulus of a material (e.g., peak tan-delta).
[0070] A transition temperature may be represented by a glass
transition temperature, a melting point, or another temperature
related to a change in a process in a material or a characteristic
of a material.
[0071] A transition temperature may be related to a number of
processes or characteristics. For example, a transition temperature
may relate to a transition from a stiff (e.g., glassy) behavior to
a rubbery behavior of a material. As another example, a transition
temperature may relate to a melting of soft segments of a
material.
[0072] The processes and characteristics relating to a transition
temperature may be microscopic or macroscopic. For example, a
transition temperature may relate to molecule mobility or
microscopic material structure. As another example, a transition
temperature may relate to the strength of molecular bonds As yet
another example, a transition temperature may relate to a modulus
of the material.
[0073] In addition, the microscopic processes, including those
processes around a transition temperature, may be related to the
macroscopic properties of the material. Indeed, one method of
determining whether a microscopic process is occurring (or has
occurred) is to monitor macroscopic processes or characteristics.
Microscopic characteristics are commonly related to macroscopic
characteristics, and macroscopic characteristics are commonly
monitored as a substitute for monitoring microscopic
characteristics.
[0074] From a macroscopic viewpoint, a polymer often has a shape
memory effect if it possesses a glass transition, a
modulus-temperature plateau in the rubbery state, and a difference
between the maximum achievable strain, .epsilon..sub.max, during
deformation and permanent plastic strain after recovery,
.epsilon..sub.p. The difference .epsilon..sub.max-.epsilon..sub.p
is defined as the recoverable strain, .epsilon..sub.recover, while
the recovery ratio is defined as
.epsilon..sub.recover/.epsilon..sub.max.
[0075] The microscopic mechanism responsible for shape memory in
polymers depends on both chemistry and structure. A cause of shape
recovery in polymers is the low conformational entropy state
created and subsequently frozen during the thermomechanical cycle.
If the polymer is deformed into its temporary shape at a
temperature below T.sub.g, or at a temperature where some of the
hard polymer regions are below T.sub.g, then internal energy
restoring forces will also contribute to shape recovery. In either
case, to achieve shape memory properties, the polymer often has
some degree of chemical crosslinking to form a "memorable" network
or may contain a finite fraction of hard regions serving as
physical crosslinks.
[0076] Polymers may be selected based on the desired glass
transition temperature(s) (e.g., at least one segment is amorphous)
or the melting point(s) (e.g., at least one segment is
crystalline), which in turn is based on the desired applications,
taking into consideration the environment of use. Shape memory
polymers may be designed for use in medical devices. Design
decisions may depend on the targeted body system and other device
design constraints such as required in-vivo mechanical
properties.
[0077] For example, a SMP may be designed so that the polymer
transition temperature is near a standard human body temperature
(e.g., T.sub.r.about.T.sub.g.about.37.degree. C.) thereby using a
body's thermal energy to activate the SMP. The mechanical
properties (e.g. stiffness) of the SMP material often depend on
T.sub.g. Those with skill in the art will recognize that designing
a stiff SMP device when the polymer T.sub.g is close to a standard
human body temperature may be difficult due to the compliant nature
of the polymer.
[0078] In an embodiment, the required storage temperature, T.sub.s,
of a shape memory polymer with T.sub.g.about.37.degree. C. will
possibly be below room temperature requiring "cold" storage prior
to deployment. A shape memory polymer may also be designed so that
the recovery temperature is higher than a standard human body
temperature T.sub.r.about.T.sub.g>37.degree. C. In one
embodiment, the glass transition temperature of the SMP is about
48.degree. C. Those with skill in the art will recognize that the
storage temperature may be equal to room temperature thereby
facilitating storage of the device and reducing unwanted
deployments. A higher recovery temperature than .about.37.degree.
C. may require localized heating of the SMP to induce recovery of
the SMP. Damage to some cells in the human body may occur at
temperatures about 5 degrees Celsius above the body temperature
through a variety of mechanisms including apoptosis and protein
denaturing. Local heating "bursts" may be used to minimize exposure
of human cells to elevated temperatures and to circumvent cell
damage through over-heating.
[0079] SMPs may have biocompatibility with different areas of the
body. For example, FDA approved dental materials may not be
biocompatible in a cardiovascular environment. Polyethyleneglycol
(PEG), a form of which is also known as polyethylene oxide (PEO),
has been studied for its protein and cell resistance, which renders
a non-fouling surface. Polylactic acid (PLA) as well as
polyglycolic acid (PLGA) have already been FDA approved in devices
such as interference screws and suture materials. However, there
may be some concerns about PLA being hydrolytically broken down
into lactic acid, which could potentially cause an inflammatory
response in surrounding cells. Nonetheless, PEG copolymerized with
PLA (PEG-co-PLA) may form a cross-linked hydrogel. These hydrogels
may be modified with methacrylate groups to achieve a wide range of
properties. PEG modified with methacrylates have shown
biocompatibility with tissue engineering. Other biodegradable
polymers are polypropylene-fumarate-co-ethyleneglycol,
polycaprolactone, polyanhydrides, and polyphosphazenes.
[0080] SMP polymer segments may be natural or synthetic. The
polymer segments may be biodegradable or non-biodegradable.
Biodegradable materials may degrade by hydrolysis, by exposure to
water or enzymes under physiological conditions, by surface
erosion, by bulk erosion, or a combination thereof.
Non-biodegradable polymers used for medical applications may not
include aromatic groups other than those present in naturally
occurring amino acids.
[0081] The polymer may be in the form of a hydrogel (typically
absorbing up to about 90% by weight of water). The polymer may also
be ionically crosslinked with multivalent ions or polymers. Ionic
crosslinking between soft segments can be used to hold a structure,
which, when deformed, can be reformed by breaking the ionic
crosslinks between the soft segments. The polymer may also be in
the form of a gel in solvents other than water or aqueous
solutions. In these polymers, a temporary shape can be fixed by
hydrophilic interactions between soft segments.
[0082] Representative natural polymer blocks or polymers include
proteins such as zein, modified zein, casein, gelatin, gluten,
serum albumin, and collagen, and polysaccharides such as alginate,
celluloses, dextrans, pullulane, and polyhyaluronic acid, as well
as chitin, poly(3-hydroxyalkanoate)s, especially
poly(.beta.-hydroxybutyrate), poly(3-hydroxyoctanoate) and
poly(3-hydroxyfatty acids). Representative natural biodegradable
polymer blocks or polymers include polysaccharides such as
alginate, dextran, cellulose, collagen, and chemical derivatives
thereof (substitutions, additions of chemical groups, for example,
alkyl, alkylene, hydroxylations, oxidations, and other
modifications routinely made by those skilled in the art), and
proteins such as albumin, zein and copolymers and blends thereof,
alone or in combination with synthetic polymers.
[0083] Representative synthetic polymer blocks or polymers include
polyphosphazenes, poly(vinyl alcohols), polyamides, polyester
amides, poly(amino acid)s, synthetic poly(amino acids),
polyanhydrides, polycarbdnates, polyacrylates, polyalkylenes,
polyacrylamides, polyalkylene glycols, polyalkylene oxides,
polyalkylene terephthalates, polyortho esters, polyvinyl ethers,
polyvinyl esters, polyvinyl halides, polyvinylpyrrolidone,
polyesters, polylactides, polyglycolides, polysiloxanes,
polyurethanes and copolymers thereof. Examples of suitable
polyacrylates include poly(methyl methacrylate), poly(ethyl
methacrylate), poly(butyl methacrylate), poly(isobutyl
methacrylate), poly(hexyl methacrylate), poly(isodecyl
methacrylate), poly(lauryl methacrylate), poly(phenyl
methacrylate), poly(methyl acrylate), poly(isopropyl acrylate),
poly(isobutyl acrylate) and poly(octadecyl acrylate).
[0084] Synthetically modified natural polymers include cellulose
derivatives such as alkyl celluloses, hydroxyalkyl celluloses,
cellulose ethers, cellulose esters, nitrocelluloses, and chitosan.
Examples of cellulose derivatives include methyl cellulose, ethyl
cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose,
hydroxybutyl methyl cellulose, cellulose acetate, cellulose
propionate, cellulose acetate butyrate, cellulose acetate
phthalate, carboxymethyl cellulose, cellulose triacetate and
cellulose sulfate sodium salt. These are collectively referred to
herein as "celluloses".
[0085] Representative synthetic degradable polymer segments include
polyhydroxy acids, such as polylactides, polyglycolides and
copolymers thereof; poly(ethylene terephthalate); polyanhydrides,
poly(hydroxybutyric acid); poly(hydroxyvaleric acid);
poly[lactide-co-(.epsilon.-caprolactone)];
poly[glycolide-co-(.epsilon.-caprolactone)]; polycarbonates,
poly(pseudo amino acids); poly(amino acids);
poly(hydroxyalkanoateis; polyanhydrides; polyortho esters; and
blends and copolymers thereof. Polymers containing labile bonds,
such as polyanhydrides and polyesters, are well known for their
hydrolytic reactivity. Hydrolytic degradation rates of these
polymers may be altered by simple changes in the polymer backbone
and the polymer's sequence structure.
[0086] Examples of non-biodegradable synthetic polymer segments
include ethylene vinyl acetate, poly(meth)acrylic acid, polyamides,
polyethylene, polypropylene, polystyrene, polyvinyl chloride,
polyvinylphenol, and copolymers and mixtures thereof.
[0087] Hydrogels can be formed from polyethylene glycol,
polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone,
polyacrylates, poly (ethylene terephthalate), poly(vinyl acetate),
and copolymers and blends thereof. Several polymeric blocks, for
example, acrylic acid, are elastomeric only when the polymer is
hydrated and hydrogels are formed. Other polymeric blocks, for
example, methacrylic acid, are crystalline and capable of melting
even when the polymers are not hydrated.
[0088] Either type of polymeric block can be used, depending on the
desired application and conditions of use. For example, shape
memory is observed for acrylic acid copolymers largely in the
hydrogel state, because the acrylic acid units are substantially
hydrated and behave like a soft elastomer with a very low glass
transition temperature. The dry polymers do not exhibit significant
shape memory effects. When dry, the acrylic acid units behave as a
hard plastic even above the glass transition temperature and show
little change in mechanical properties on heating. In another
example, copolymers including methyl acrylate polymeric blocks as
the soft segments show shape memory properties even when dry.
[0089] The polymers can be obtained from commercial sources such as
Sigma Chemical Co., St. Louis, Mo.; Polysciences, Warrenton, Pa.;
Aldrich Chemical Co., Milwaukee, Wis.; Fluka, Ronkonkoma, N.Y.; and
BioRad, Richmond, Calif. Alternately, the polymers can be
synthesized from monomers obtained from commercial sources.
[0090] In an embodiment, SMPs may be photopolymerized from
tert-butyl acrylate (tBA) di-functional monomer with polyethylene
glycol dimethacrylate (PEGDMA) tetra-functional monomer acting as a
crosslinker. A di-functional monomer may be any compound having a
discrete chemical formula further comprising an acrylate functional
group that will form linear chains. A tetra-functional monomer may
be any compound comprising two acrylate, or two methacrylate
groups. A crosslinker may be any compound comprising two or more
functional groups (e.g., acrylate, methacrylate). Also,
ethyleneglycol, diethyleneglycol, and triethyleneglycol based
acrylates are forms of polyethyleneglycol based acrylates with one,
two, or three repeat units.
[0091] A functional group may refer to any reactive group. For
example, a functional group may be an acrylate group. A
mono-functional molecule refers to a molecule having one functional
group (e.g., an acrylate group, a methacrylate group). A
multi-functional molecule may have two or more functional
groups.
[0092] In one embodiment, the SMP material is a photo-initiated
network comprising of tert-butyl acrylate (tBA), polyethyleneglycol
dimethacrylate (PEGDMA), and 2,2-dimethoxy-2-phenylacetephenone as
a photo-initiator. The glass transition temperature (T.sub.g) may
be tailored to a T.sub.g.about.48.degree. C. through controlling
the amount of cross-linking PEGDMA. A T.sub.g of roughly 48.degree.
C. is a useful T.sub.g or shape recovery within a human body
temperature.
[0093] Those with skill in the art will recognize that other
polymerization techniques, such as thermal radical initiation, can
be used for polymer fabrication.
[0094] Shape memory properties of a class of polymers with a high
degree of biocompatibility may be investigated using a three-point
flexure testing apparatus (as shown in FIG. 24) to investigate the
thermomechanics of the shape memory effect under various
conditions. The experimental results below form a foundation for
understanding the effects of pre-deformation temperature,
constraint level, and recovery temperature/time on the shape memory
effect in a biocompatible polymer system. The examples and
embodiments described herein are meant to illustrate, not to limit,
the present invention.
[0095] Other potential applications of biocompatible shape memory
polymers, which capitalize on some of the observed thermomechanical
behaviors include rotator cuff reconstruction, for
acromioclavicular (AC) reconstruction, for anterior cruciate
ligament reconstruction (ACL) and generally for fastening tendons,
grafts, or sutures to tissue, including soft tissue and bone.
[0096] In an alternate embodiment (not shown) the device has a
substantially cylindrical cross-section with ridges. The ridges are
just an example of shapes and shape features that may be used to
aid in fixing the device to the bone recess and/or the cable
member. For example, baffles, flaps, screw-like threads and/or
bumps may be used to aid the fixation of the device to the bone
recess and/or the cable member. The below description of ridges,
therefore, should be understood to apply to all types of shapes and
shape features of a device.
[0097] Ridges may be part of the device's shape in order to
increase the device's contact surface area, for example, between
the device (e.g., 200) and the cable member (e.g., 202) or between
the device and the bone recess. In one embodiment, ridges may be
configured to conform to the bone recess, providing a more solid
fixation force between the bone recess and the device.
[0098] In one embodiment, the ridges may be part of the device's
pre-implantation shape, In another embodiment, the ridges may be
part of the device's post-implantation shape. In yet another
embodiment, the ridges may be part of both the device's
pre-implantation shape and the device's post-implantation
shape.
[0099] In one embodiment, the cable member may conform to the
ridges, providing increased contact surface area between the device
and the cable member. In another embodiment, the device may conform
to the cable member or the bone recess. In yet another embodiment,
the device and the cable member (and/or the bone recess) may
conform, to some extent, to each other.
[0100] The device 200 may also have surface features (not shown),
such as textures or porosity. For example, surface features may be
provided for physical purposes, such as increasing the fixing
forces provided by the device. In one embodiment, the surface
features are on the shape memory material. In another embodiment,
the surface features are on a part of the device that is not a
shape memory material. In one embodiment, the surface features may
increase friction between a cable member and the device. In another
embodiment, the surface features may increase friction between a
part of the bone recess and the device.
[0101] Surface features may also be provided for physiological
purposes. For example, surface features may be provided to
encourage bone in-growth. In one embodiment, surface features are
configured in a manner that encourages bone deposits and the
surface features may hold bone-growth stimulants. In another
embodiment, surface features are configured in a manner that
encourages bio-compatability. In yet another embodiment, surface
features are configured in a manner that encourages soft tissue
growth.
[0102] The device 200 may have a curved or otherwise shaped tip to
ease insertion into the bone recess with a cable member. In one
embodiment, the device has a curved tip in the device's
pre-implantation shape. In another embodiment, the device has a
curved tip in the device's pre-implantation shape and a differently
curved tip in the device's post-implantation shape.
[0103] In one embodiment, the device 200 has a cavity 206. In one
embodiment, the cavity 206 is configured to accept a heating
element (not shown) to aid in the application of heat to a shape
memory material contained in the device. For example, the cavity
206 may be spaced from the outer surfaces of the device 200 that
contact cells that surround the device (e.g., living cells, human
cells) that may be damaged by heating. Spacing of the cavity from
outer surfaces of the device may allow activation of a shape memory
material in manners that limit the amount of heat transferred to
surrounding cells. Inner walls of the cavity 206 may be contacted
using a heating element (not shown) to supply heat to the inner
walls of the cavity. Certain methods may be used to reduce the heat
transferred to surrounding cells. For example, a method of using
heating "bursts" may be employed to limit heat transfer to
surrounding cells.
[0104] In another embodiment, the cavity 206 is configured to
accept a drug, a bone cement, suture material, or another material.
For example, a material may be inserted into the device 200 after
the device has been inserted into the bone recess 204. Delivery of
material inserted into the device may be achieved through
absorption by the device, or through channels as described further
below. In yet another embodiment, the cavity 206 is configured to
accept a heating element and is configured to accept material after
the shape memory material has been activated. For example, a shape
memory material may not have significant channels before being
activated (e.g., in the material's pre-implantation shape), and the
shape memory material may have channels after being activated
(e.g., in the material's post-implantation shape).
[0105] In another embodiment, the cavity 206 is configured to hold
a guide wire to aid insertion of the device 200. For example, the
guide wire may be used as is shown in FIG. 1. In one embodiment,
the cavity 206 has one opening on each of two ends of the device
200 while the device is in its pre-implantation shape, allowing a
guide wire to be threaded through the device. In another
embodiment, the cavity 206 has one opening on each of two ends of
the device 200 while the device is in its pre-implantation shape,
and the cavity 206 has only one opening on one end of the device
while the device is in its post-implantation shape. In yet another
embodiment, the cavity 206 has another opening that does not change
shape during the device's change from the device's pre-implantation
shape to the device's post-implantation shape.
[0106] The device 200 may come in a kit that also includes a
packaging (not shown) that is removed before being inserted. The
packaging may maintain a sterile environment around the device 200.
For example, the packaging may surround the device. In one
embodiment, the packaging is a form-fitting packaging such as a
shrink-wrap packaging. For example, the packaging may provide a
force resisting deployment of the device from its pre-implantation
shape to its post-implantation shape (e.g., through shape memory
effect, through an elastomeric response) before an appropriate time
(e.g., installation). In another embodiment, the packaging encloses
the device 200 with another material. For example, the packaging
may enclose the device in a sterile fluid or gas (e.g. a
pressurized compressible gas).
[0107] FIG. 3 shows a cross-section of another embodiment of a
device 300 installed and in a post-implantation shape with a cable
member 302 in a bone recess 304 in a bone 314. The device 300 fixes
the cable member 302 to the device 300 inside a cavity 306 within
the device. The cavity 306 within the device 300 is at least
partially defined by a fixation element 310.
[0108] The device 300 may incorporate any of the properties or
elements of other devices described herein.
[0109] The device 300 is configured to interface with a bone recess
304 and fix the cable member 302 to the bone thereby. In one
embodiment, the device 300 is configured to fix a cable member to
the device before interfacing (e.g., through insertion) with the
bone recess. In another embodiment, the device is configured to
interface with a bone recess and be fixed to the bone recess before
accepting and fixing a cable member in the cavity 306. In yet
another embodiment, the device is configured so that either the
cable member may be fixed to the device first or the device may be
fixed to the bone recess first.
[0110] The fixation element 310 may be constructed in many manners.
In one embodiment, the fixation element comprises by a solid body.
In another embodiment, the fixation element comprises a liquid that
is transformed (e.g., polymerized, cured) into a solid body to hold
a cable member after the cable member is inserted. In this case,
the device 300 may also be the mold in which the liquid is
transformed.
[0111] Such a transformable liquid may be provided in a kit with
the device 300 in separate containers that must be mixed to create
the transformable liquid. The kit allows a surgeon to create the
device at the time of surgery in order to form the device into the
shape necessary to fix the cable member in the bone recess 304.
[0112] For example, one or more monomers and cross-linkers may be
provided in separate containers in a kit that when mixed may be
polymerized or may automatically polymerize. In an embodiment, the
polymer created may be a shape memory polymer. Such a kit may also
include a cable member configured to function as a soft tissue
replacement in a human body and the cable member may be further
configured to be partially encapsulated in the shape memory
polymer. As discussed in greater detail herein, the cable may be
made from one or more of an animal tissue, a synthetic fiber, a
natural fiber, a polymer, a metallic wire, a bundle, or a
composite.
[0113] Such a kit may also include a polymerizing device to
initiate the polymerization reaction, such as for example, a
radiation source, an ultraviolet light source, a heating source,
and a source of electrical current. Alternatively, the
polymerization may be automatic or caused by a heat generated by
the ambient environment or the patient. Other devices may also be
included in the kit to assist the surgeon, such as a mixing element
like a spatula, one or more metering devices for metering precise
amounts of monomer and crosslinking solutions, mixing vessels or
plates which may also server dual purposes such as a mold or a heat
conductor or insulator, and a support configured to hold the cable
member.
[0114] In yet another embodiment, the fixation element comprises a
body (e.g., a spring member) that folds or collapses upon itself in
response to a force (not shown) to hold the cable member, thereby
allowing the cable member to be inserted but not removed.
[0115] The fixation element 310 may adapt to accommodate a cable
member 302 when it is inserted. For example, the fixation element
310 may be deformed (e.g., strained) by the cable member 302 as the
cable member is inserted into the cavity within the device and the
stress between the cable member and the fixation element may help
fix the cable member to the device. The cable member may also be
deformed (e.g., strained) by the fixation element 310 as the cable
member is inserted into the cavity within the device and the
resulting stress between the cable member and the fixation element
may help fix the cable member to the device.
[0116] The fixation element 310 may comprise a shape memory
material (e.g., a SMP). A shape memory material may be used in the
fixation element to provide a source of strain and/or stress after
insertion of the cable member. For example, a cable member may be
inserted into the cavity and a stress/strain relationship between
the cable member and the fixation element may be established as
described herein. The shape memory material contained in the
fixation device may then be activated to produce a different
stress/strain relationship between the cable member and the
fixation device. The activation of shape memory materials and the
stresses and strains produced as a result of activation are
discussed further herein.
[0117] Shape memory materials may be used in other parts of the
device as well. For example, shape memory materials may be used to
aid in fixing the device to the bone recess as described in greater
detail herein.
[0118] FIG. 4 shows a cross-section of another embodiment of a
device 400 installed with a cable member 402 in a bone recess 404
in a bone 414. The device 400 includes an external cavity 406, a
channel 410, and an internal recess 412. The external cavity 406 is
connected to the channel 410. The external cavity is connected to
the internal recess 412. The device may have more than one external
cavity 406. The discussion of the external cavity 406 below may be
applied to all shapes and shape features of a device, such as the
ridges discussed above with respect to FIG. 2 (those ridges may
also form at least one external cavity on a device).
[0119] The device 400 may incorporate any of the properties or
elements of other devices described herein.
[0120] An external cavity 406 may be used to interact with the
cable member 402 in a manner that aids the fixation of the device
to the cable member and/or the fixation of the cable member to the
bone recess. In one embodiment, the cavity 406 may buckle the cable
member. In another embodiment, the cavity 406 may provide the cable
member with an area of decreased stress, and potentially, decreased
strain. The stress/strain interaction of a device, a cable member
and a bone recess is described further herein.
[0121] An external cavity may hold a material (e.g., a monomer
solution, a bone cement, a drug) that is useful to have held
against a cable member, a bone recess or both. For example, a
device 400 may allow for insertion (e.g., injection) of the
material into the external cavity after the device has been
installed with a cable member. In one embodiment, the device 400
allows for polymerization of a monomer liquid after the device has
been installed with a cable member. In another embodiment, a device
allows for insertion of a drug (e.g., a bone-growth stimulant) into
the external cavity 406 after installation (e.g., for dispensing
the drug over time to the bone recess and tendon).
[0122] In another embodiment, the cable member 402 may be attached
to the device 400 or integrated with the device. In one embodiment,
the cable member 402 may be held by a shape memory polymer of the
device 400 while the device is in the post-implantation shape. For
example, a cable member may contact a part of the device 400 (e.g.,
internal to the device, on an external wall) and the device may
fixedly grip the cable member 402 while the device is in the
post-implantation shape. In another embodiment, the cable member
402 may be attached via a polymerization of a solution that is in
contact with the device. For example, a solution containing a
linear chain and a crosslinker may be polymerized while contacting
both the cable member and the device. In one embodiment, the
solution contacts an external surface of the device 400. In another
embodiment, the solution contacts an internal surface of the device
400. The cable member 402 also may be attached to the device 400 as
described further herein.
[0123] A channel 410 may connect with an external cavity 406. For
example, a channel 410 and an external recess 406 may define a
contiguous volume. In one embodiment, the channel 410 is
substantially cylindrical in shape, defining a shape such as a tube
or pipe. In another embodiment, the channel 410 is an irregular
shape. The channel 410 may connect with an internal recess 412.
[0124] The channel 410 may provide a passage for transferring a
material (e.g., matter such as solids, liquids, gases) from an
internal recess 412 and an external cavity 406. The channel 410 may
store the material. The internal recess 412 may contain a drug or a
bone cement agent. The internal recess 412 may also contain a
polymerizing agent or an activation agent. The channel 410 may also
contain any of these drugs or agents.
[0125] Those with skill in the art will recognize that there need
not be a definite demarcation between an internal recess 406, a
channel 410, and an external cavity 412, nor do those elements need
to be identifiably distinct. For example, an internal recess 412
may be connected with an external cavity 406 by an orifice that
defines a boundary of both the internal recess and the external
cavity. In another embodiment, an orifice defines a boundary of the
channel 410 and the external cavity.
[0126] An orifice may have a seal or flap restricting the transfer
of matter (e.g., solids, liquids, gases) between the internal
recess and the external cavity. For example, the seal (e.g., flap,
orifice) may block transfers from the internal recess to the
external cavity.
[0127] The seal or flap may comprise a shape memory material. In
one embodiment, the seal blocks transfers of matter before the
shape memory material is activated and the seal allows transfers of
matter after the shape memory material is activated. In another
embodiment, the seal allows transfers of matter differently before
the shape memory material is activated than after the shape memory
material is activated.
[0128] Activation of a shape memory material in the device may
cause the internal recess to change. For example, the internal
recess may be defined by a shape memory material, the activation of
which changes the internal recess. In one embodiment, the
activation of a shape memory material lessens the volume of an
internal recess (e.g., constricts the recess). For example, the
constriction of the internal recess (e.g., lessening of the volume
of the recess) may deliver a drug contained in the recess to the
external cavity. In another embodiment, the activation of a shape
memory material expands an internal recess (e.g., increases the
volume of an internal recess). For example, the expansion of the
internal recess may create a low-pressure region (e.g., a partial
vacuum) within the external cavity and the low-pressure region may
aid in fixing the device to the cable member and/or the bone recess
(e.g., through a partial vacuum in an external cavity).
[0129] In an embodiment, a selection of multiple bone implant
devices having different shapes and sizes may be packaged and sold
as a kit. The selection may include implants of different
diameters, shapes or implants exhibiting different properties. The
components within the kit may be pre-sterilized so that the kit may
be opened and used during surgery without an additional
sterilization step. The kit may include one or more insertion
devices for inserting the implants into the bony recess as
described above. Such an insertion device may include a simple
metal tube shaped to engage with the one or more of the implants.
Alternatively, the insertion device may be a sold shaft, a guide
wire or some other component adapted facilitate insertion by the
surgeon. For example, an insertion device may include a threaded
rod that engages in interior threads provided by a threaded bore
within the implant, which may be provided by a separate element
such as a nut contained within the implant. After insertion, the
rod may be unscrewed from the implant and discarded. Such an
insertion device may also be used in the activation of the
activation implant. For example, a stainless steel insertion rod
may be heated in order to heat the implant. The kit may further
include instructions for selecting the appropriate implant.
[0130] FIG. 5 shows flow-chart of a method 500 for performing
surgery. The method 500 may be embodied as a surgical procedure for
repairing a joint, ligament, tendon or other anatomical part. The
method 500 includes inserting a cable member 510 into a bone
recess, inserting a retention device 512 into the bone recess,
activating a shape memory material 514.
[0131] The method 500 may include fixing the cable member to the
bone recess (not shown). In one embodiment, the method 500 performs
the fixing the cable member to the bone recess operation via fixing
the cable member to the retention device. In another embodiment,
the method 500 performs the fixing the cable member to the bone
recess operation via pinning the cable member between the retention
device and a wall of the bone recess.
[0132] The method 500 includes creating a bone recess 502. Creating
a bone recess 502 may be performed using techniques now known in
the art (e.g., drilling), or using techniques that are yet to
become known. In one embodiment, the creating a bone recess
operation 502 may be adapted to create a larger surface area of
bone with which a retention device may contact the bone. In another
embodiment, the creating a bone recess operation 502 may be adapted
to provide access to a bone site used for connecting a cable member
(e.g., through the use of a retention device).
[0133] The method 500 includes dilating the recess in the bone 504.
In one embodiment, the dilating the recess in the bone operation
504 is at least partially performed via compacting bone tissue
surrounding the recess in the bone (e.g. 506). In another
embodiment, the dilating the recess in the bone operation 504 is
performed by shaving bone tissue from the walls of the bone
recess.
[0134] The method 500 includes compacting bone tissue surrounding
the recess in the bone 506. The compacting bone tissue operation
506 may be performed by many techniques. For example, a shape
memory material in a retention device may produce sufficient
pressure to compact the bone tissue surrounding a bone recess.
[0135] In one embodiment, the inserting a cable member operation
510 is performed before the inserting a retention device operation
512. For example, the cable member may be inserted 510 against a
wall of the bone recess and the retention device may be inserted
against the cable member and another wall (or another part of the
same wall) of the bone recess. In another embodiment, the inserting
of a retention device operation 512 is performed before the
inserting a cable member operation 510. For example, the retention
device may be inserted 512 against a wall of the bone recess (e.g.,
it may contact two walls, opposite sides of the same cylindrical
wall, or may fill the bone recess, contacting substantially all the
walls of the recess), and the cable member may be inserted 510 into
the retention device. It should be noted that when the cable member
is inserted 510 into the retention device, it is necessarily being
inserted into the bone recess, if the retention device itself is in
the bone recess.
[0136] In yet another embodiment, the inserting a cable member
operation 510 and the inserting a retention device operation 512
are performed simultaneously. For example, a part of a cable member
may be connected or coupled with a retention device and the
combined cable member and retention device structure may be
inserted into the bone recess. In one embodiment, the cable member
may only be partially inserted into a bone recess. In another
embodiment, the retention device may be fully inserted into a bone
recess.
[0137] The method 500 may also include initiating a polymerization
of a monomer solution (not shown). In one embodiment, a monomer
solution is inserted into a cavity within the retention device, a
cable member is inserted into the cavity, and a polymerization of
the monomer solution is initiated (e.g., through heating the
solution or irradiating the solution). In another embodiment, such
a cavity configured for holding a monomer solution exists in the
post-implantation shape of the retention device.
[0138] After the inserting a cable member operation 510 and the
inserting a retention device operation 512 have been performed, the
cable member and the retention device may be positioned within the
bone recess in a number of configurations. Any of the
configurations described herein may define the relative positions
of a cable member and a retention device. For example, any of the
devices in the herein description may be used as a retention
device. In one embodiment, a cable member may be fixed within a
cavity of the retention device. In another embodiment, a cable
member may be fixed between a wall of the bone recess and an outer
surface of the retention device.
[0139] In one embodiment, the inserting a retention device
operation 512 may be performed by inserting one of the devices
described herein comprising a shape memory material. In another
embodiment, the inserting a retention device operation 512 may be
performed by inserting a device separate from a shape memory
material and the activating a shape memory material operation 510
may be performed on a shape memory material member separate from
the device that is inserted into the bone recess.
[0140] The method 500 includes activating a shape memory material
514. The activating a shape memory material operation 510 may be
performed in the manners further described herein. In one
embodiment, the activating a shape memory material operation 514
may be performed by providing heat to the shape memory material. In
another embodiment, the activating a shape memory material
operation 514 may be performed by irradiating the shape memory
material with electromagnetic radiation. The activating a shape
memory material operation 514 may also be performed in manners yet
to become known.
[0141] The method 500 may also include attaching sutures to the
retention device and/or the cable member. In one embodiment, a
suture may be attached to a part of the retention device and
threaded through a part of the cable member. In another embodiment,
a suture may be attached from one part of a cable member to another
part of the cable member.
[0142] FIG. 6 shows a flow-chart of a method 600 of manufacturing
devices. The method 600 includes shaping a polymer material 602
into a post-implantation shape, deforming the polymer material 604
into a pre-implantation shape, and cooling the polymer material 606
to below a certain temperature.
[0143] The method 600 includes cooling the polymer material 606 to
below a certain temperature. The certain temperature may be the
glass transition temperature of the polymer material. In one
embodiment, the cooling the polymer material operation 606 is
performed after the deforming the polymer material operation 604.
For example, the polymer material may be above the glass transition
temperature while the deforming the polymer material operation 604
is performed. In another embodiment, the cooling the polymer
material operation 606 is performed before the deforming the
polymer material operation 604.
[0144] The shaping the polymer material operation 602 may be
performed in many manners. In one embodiment, the polymer material
may be polymerized from a solution into a solid body while in a
mold. For example, the mold may define a post-implantation shape or
a pre-implantation shape. In another embodiment, the polymer
material may be shaped via cutting; milling, turning (e.g., using a
lathe), or other techniques used for shaping materials. As another
example, the mold may hold a solution and a cable member while the
solution is polymerized around an end of the cable member.
[0145] The shaping the polymer material operation 602 and the
deforming the polymer material operation 604 may result in
pre-implantation shapes and post-implantation shapes such as those
described herein.
[0146] In another embodiment, the process 600 may include
polymerizing a solution (not shown) around a cable member (e.g.,
while an end of a cable member is inserted in the solution). The
polymerizing a solution operation may be performed to provide a
strong interface between a cable member and a polymer solution. The
polymerizing a solution operation may also be performed to create a
device that has a cable member incorporated in the device (e.g.,
attached to the device, part of the device). For example, a device
with an incorporated cable member may be used to facilitate surgery
or to verify attachment between the device and cable member before
a surgical procedure is begun. The incorporation of a cable member
in a device is further described herein in relation to other
devices and methods.
[0147] Polyethylene glycol dimethacrylate-poly methyl methacrylate
(PEGDMA-PMMA) compositions and polyethylene glycol-poly methyl
methacrylate (PEG-PMMA) are described herein as examples of SMPs
that may be used for devices. PEGDMA-PMMA and PEG-PMMA are
described herein partially because of the biocompatability of the
substances and the high forces the substances are often able to
generate. PEGDMA may be referred to as PEG for short, although PEG
may mean other functionalized forms of polyethylene glycol.
[0148] By combining PEG with a functional group (e.g, DMA) into
novel SMP compositions, a range of glass transition temperatures
and installment forces (e.g., post-implantation forces creating
pressures on bone recesses) may be selected. In some instances, the
glass transition temperature of a SMP composition will vary with
(or otherwise be related to) the installment force achievable by
the SMP. By utilizing two or more different cross-linkers, the
relationship between the glass transition temperature of a SMP and
the installment force achievable by the SMP may be varied or even
non-associated (e.g., the Tg and installment force may be varied
independently).
[0149] The percentage (as a function of total weight of the
polymer, or by weight) of cross-linker in the polymer composition
may also be varied. The amount of cross-linker in a polymer
composition may be varied to change the polymer compositions
characteristics (e.g., strength, force, glass-transition
temperature, response time, elasticity). In one embodiment, a
cross-linker may comprise about 5% or less of a polymer
composition. In another embodiment, a cross-linker may comprise
more than about 10% of a polymer composition. In yet another
embodiment, a cross-linker may comprise about 80% of a polymer
composition.
[0150] The following examples describe some of the experimental
results achieved with respect to creating SMPs with various glass
transition temperatures and installment forces.
EXAMPLES
[0151] Experimental work on SMP systems used in graft fixation
devices was performed to demonstrate the feasibility and advantages
of these devices over currently used ACL fixation devices.
[0152] The following examples are presented to demonstrate a SMP
polymerization process, fabrication, characterization and testing
of materials in accordance with the present invention. These
examples are not intended to limit the scope of the invention in
any way. All starting materials are commercially available.
Thermomechanical characterization was performed by dynamic
mechanical analysis (DMA) on a Perkin Elmer Dynamic Mechanical
Analyzer DMA-7.
Example 1
SMP Fabrication
[0153] Tert-butyl acrylate (tBA) monomer (Aldrich), poly
(ethyleneglycol) dimethacrylate (PEGDMA) cross-linker (Aldrich),
and the photoinitiator 2,2-dimethoxy-2-phenylacetophen one
(Aldrich) were used in their as-received condition without further
purification. A polymer solution was formulated by combining 10 wt
% PEGDMA, 0.1 wt % initiator, with the balance tBA. Other
crosslinker/momomer ratios can be considered and can range from 1
wt %-99 wt % cross-linker. Other photoinitiators include
acetophenone, anisoin, anthraquinone, benzene chromium tricarbonyl,
benzil, benzoin, benzoin ethyl ether, berizoin isobutyl ether,
benzoin methyl ether, benzophenone, 4-benzoylbiphenyl,
2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone,
4,4'-bis(diethylamino)-4' benzophenone,
4,4'-bis(dimethylamino)-4'benzophenone, camphorquinone,
2-chlorothioxanthen-9-one, dibenzosuberenone,
2,2-diethoxyacetophenone, 4,4'-dihydroxybenzophenone,
4-(dimethylamino)benzophenone, 4,4'-dimethylbenzil,
2,4(5)'-dimethylbenzophenone, 3,4-dimethylbenzophenone,
4'-ethoxyacetophenone, 2-ethylanthraquinone, ferrocene,
3(4)'-hydroxyacetophenone, 3(4)'-hydroxybenzophenone,
1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone,
2(3)-methylbenzophenone, methyl benzoylformate,
2-methyl-4'-(methylthio)-2-morpholinopropiophenone,
phenanthrenequinone, 4'phenoxyacetophenone, thioxanthen-9-one,
triarylsulfonium hexafluoroantimonate salts, and triarylsulfonium
hexafluorophosphate salts.
[0154] Glass slides, approximately 1''.times.3''.times.1 mm, were
precoated with a hydrophobic polymer glass treatment solution RainX
glass treatment sold by SOPUS Products, Houston, Tex.), which acted
as a non-reactive releasing agent. The glass slides were separated
with 1 mm spacers. The above solution was mixed manually in a glass
vial and then injected between two glass slides using a pipette.
Photo-polymerization was then achieved by placing the solutions
under a UV lamp (Model B100AP, UVP Blak-Ray) at an intensity of
.about.10 mW/cm.sup.2 for 10 minutes. Samples for thermomechanical
testing were laser cut from the polymer to dimensions of 20
mm.times.5 mm.times.1 mm. The edges of the samples were polished
using 600-grit silicon carbide sandpaper to remove any edge effects
caused by the laser cutting. The material was stored in a
refrigerator with no light contact.
[0155] SMP's may be photopolymerized in a semi-LV transparent mold.
This includes polymerization through glass molds, such as test
tubes or custom shaped glassware, silicone molds, or any degradable
mold, such as water-soluble molds. Thermal initiation can be used
in place of phoyopolymerization. With thermal initiation, the
initiator reacts to heat instead of UV light. Benzoyl-peroxide and
other thermal initiators can be used. In this case, any removable
mold may be used in molding SMP devices. Other methods of machining
include CNC machining for complex geometries and lathing for
cylindrical specimens.
[0156] Storage and stability of the polymer were tested in two
ways. First, a packaged plug was stored in a freezer for .about.1
year under no constraint. The plug was then heated in a body
temperature bath and the plug recovered to its original shape
(e.g., unconstrained shape, pre-deformed shape). Second, samples
were placed in a body temperature saline bath (pH=7.4) for 6
months. Weight measurements (to determine if any hydrolytic
degradation had occurred) were taken every 2-4 weeks. The polymer
showed no signs of weight loss or degradation after 6 months.
Example 2
SMP Thermomechanical Characterization
[0157] The polymer samples were tested using a Perkin Elmer Dynamic
Mechanical Analyzer (DMA-7). A three-point flexural configuration
was used for glass transition (T.sub.g), strain recovery, and
stress recovery tests (FIG. 24 inset). The three-point flexure
loading allowed reasonable stress/strain levels in the sample for
the temperature range spanning the glassy to the rubbery state. In
particular, this configuration allowed 30% maximum bending strain
over a 5 mm span during the stress and strain recovery tests. FIG.
24 shows a comparison between the PEGDMA copolymer and PLA, which
is a biodegradable polymer used in tibial devices. The drop in
storage modulus as temperature increases indicates the material is
transforming from a glassy or stiff state to a rubbery state. Also,
T.sub.g may be defined in relation to the peak of the tan delta
curve.
[0158] The glassy storage modulus is an indication of the
material's stiffness. A SMP plug will have a stiffness close to PLA
after installation. Furthermore, PLA will show some minor shape
memory effect around its glass transition. It may then be possible
to engineer the PLA system to exhibit a large shape memory effect.
The material selected for this study is not the only choice. It may
be possible, with the correct polymer engineering, to match the
necessary material characteristic to current FDA approved polymer
devices.
[0159] The test results shown in FIG. 24 may offer insight into the
thermomechanics of shape-storage deformation and shape recovery of
SMPs. A three-point flexural configuration (shown in FIG. 24) may
be used for glass transition, free strain recovery, and stress
recovery tests. In all tests, heating and cooling is typically
performed at a constant rate of 5.degree. C./min with data
collection every 2 seconds. For example, in Tg tests, samples were
cycled at a frequency of 1 Hz between minimum and maximum bending
forces of 10 mN and 90 mN. The glass transition temperature (Tg) of
the polymers was tested over a range of 100.degree. C. and depended
on the molecular weight and concentration of the crosslinker. The
polymers showed a 100% strain recovery up to maximum strains of
approximately 80% at low and high deformation temperatures (Td).
Free strain recovery depended on the temperature during
deformation. For example, lower deformation temperatures (Td<Tg)
decreased the temperature required for free strain recovery.
Constrained stress recovery shows a complex evolution as a function
of temperature and also depends on Td. In an embodiment, using
variations of crosslinking density, nano reinforcement, fiber
reinforcement, the amount of deformation (e.g., the ratio of
compression, the ratio of expansion), or layering, a SMP may
withstand a range from 0.5 MPa to 20 MPa stress levels. Tendon
slippage is unlikely to occur with installed fixation loads above
about 0.25 MPa.
Example 3
Plug Manufacturing
[0160] The test plug material was machined from a 45 wt % PEGDMA
ratio to 55% PMMA (poly methyl methacrylate) with a 0.1% photo
initiator and mixed in a 14 mm diameter glass test tube. The open
end of the test tube was blocked off with a rubber stopper and the
test tube plus solution was placed in a 0.degree. C. water bath
under a UV lamp for 10 minutes. The glass test tube was then
removed leaving a 14 mm PEGPMMA cylinder with a glass transition
temperature (T.sub.g) of 40.degree. C. The plugs were machined from
the cylinder stock using coconut oil as lubricant and spinal speeds
of 450 RPM to be approximately 11.5 mm in diameter and 25.4 mm in
length. The edges of the device were filleted to 0.5 mm radii to
ensure the device would not shear a soft tissue (tendon) on
contact.
[0161] In addition, various unconstrained (or un-deformed) shapes
were created to demonstrate multiple forms of possible
unconstrained shapes, shown in FIG. 7. Unconstrained shapes and
their differences from post-implantation shapes are described
further herein.
[0162] The plugs were then coated with lubricant (e.g., spray
Teflon) and prepared for insertion in an extrusion apparatus. The
extrusion apparatus deforms plugs into a deformed shape, for
example, into a pre-implantation shape. FIG. 8 shows the three
extrusion stages that the SMP undergoes in the current setup. The
extrusion unit 800 operates by placing the un-deformed plug in an
entry zone 802 in the extrusion unit 800 and applying a pressure
using a hardened pressure bar 810 to push the plug into the
reduction zone 804. An additional plug (or dummy plug) may be
inserted to transmit a force onto the plug in the reduction zone
804 and further deform the plug to conform with the final zone 806
(e.g., the plug being then in a pre-implantation shape). After the
polymer has been fully extruded into the final dimension zone, the
extrusion unit is placed in a controlled temperature environment
below the polymers glass transition, to allow the polymer to set in
its temporarily deformed stored shape. The polymer may then be
released at room temperature or below (depending on the Tg of the
polymer). FIGS. 9a and 9b, show the pre-deformed shape (the
original shape or unconstrained shape) and the deformed shape
(pre-implantation shape). Storing the deformed plug at a
temperature below its glass transition temperature can reduce
incidence of premature deployment (e.g., expansion to
post-implantation shape or unconstrained shape depending on
constraints present during deployment).
[0163] The geometry and material mechanics were varied during
experimentation. FIG. 10 shows different tip geometries of devices
used during the installation process to analyze the effect of
device insertion force as a function of geometry. The experimental
results indicated devices with the more tapered or "aerodynamic"
appearing configurations provided the easiest insertion into bone
recesses.
[0164] Several different polymers compositions were used to vary
the recovery force of the SMP, for example the 20 wt % PEG to tBa
system shows a lower recovery force than the 40, 45, 50 wt % PEG to
PMMA compositions, FIG. 11. This allows for the recovery force of
the polymer to be varied with regards to linear chain material and
percent crosslinking. The variation in percent crosslinker also
affected the glass transition and allowed the polymer to recover at
different temperatures. FIG. 12 shows the free strain recovery time
after devices (e.g., SMP plugs) were strained (e.g., deformed)
between about 25% and about 30% then stored in the strained state
before recovery was initiated. The T.sub.recovery (e.g., recovery
temperature) indicated in the figure references the transition
temperature of the device. FIG. 13 shows constrained recovery time
as a function of crosslinking.
[0165] After performing the above experiments, plugs were created
to have a 45 wt % PEG PMMA composition with the crosslinker having
a molecular weight of 875. This allowed for the optimal deployment
temperature to be body temperature. The deployment temperature can
be raised or lowered by changing the material composition. Changing
material composition will also influence the deployment time and
force after activation.
Example 4
Recovery Force
[0166] Two forms of testing have been designed to compare the
utility of the current interference screw to utility of a SMP
fixation device (e.g., a SMP plug). The first test analyzed the
force caused from the recovery of a 20 wt % PEG tBa SMP plug when
confined in a 10 mm tunnel with tendon. To simulate the boney
tunnel, the custom fixture (FIG. 14) was manufactured from aluminum
and mounted inside a thermally controlled chamber. The plug (2) in
its deformed position was placed between aluminum constraints (1)
and the extension fixed. The temperature was increased gradually
over time and the SMP plug recovered gradually resulting in a
compressive loading being applied to the aluminum fixture (FIG.
14). It should be noted that the SMP plug recovered via contracting
some of the plug's dimensions and expanding some of the plug's
dimensions. The results, FIG. 15, show the recovery load of an 11
mm diameter SMP plug is approximately 600N. This force is arbitrary
and can be increased or decreased by, for example, changing the
dimensions of the SMP plug (e.g., in the unconstrained shape or
original shape) or changing the composition of the SMP (e.g.,
changing the type or percentage of cross-linker). This is because
the recovery force is dependant on the geometry and composition of
the plug, which can be changed during the manufacturing
process.
[0167] The second test, FIG. 16, measured the forces for the prior
art interference screw during insertion and after insertion. This
was achieved by recording the force exerted on a 10 mm constrained
tunnel (e.g., through the fixture in FIG. 14) during insertion of a
10 mm interference screw. FIG. 16 shows the immediate increase and
relaxation in the force levels (e.g., loads) during the
installation of the interference screw and a gradual relaxation of
the device and tendon construct post-installation. The spiking and
relaxation of the loads in the interference screw are directly
related to an application of a variable torque to the device used
to install the screws.
Example 5
Failure Strength
[0168] FIG. 17 shows the test setup for the in-vitro maximum
failure strength and cyclic strength of the ACL tendon construct.
Three hundred bovine knees were harvested and cleaned of soft
tissue. 100 bovine extensor tendons were also harvested. The bone
mineral density of the specimens ranged from 0.78 g/cm.sup.3 to
0.84 g/cm.sup.3, thus closely approximating the bone mineral
density of young human tibia.
[0169] The bone was mounted into a custom made fixture (FIG. 17),
which provided access to the distal opening of the tibial tunnel. A
10-mm diameter tibial tunnel was drilled from the anteromedial
proximal metaphysis to the mid-articular surface of the proximal
tibia with the aid of a standard ACL tibial guide set to fifty-five
degrees. A four-stranded, non-weaved cable member (e.g., graft) was
prepared by passing tendons (10 mm sized) over doubled number 1
absorbable sutures. Each end of the four-stranded graft was secured
with a running, interlocking, whip stitch using #1 fiberwire in
order to apply tension to each limb of the graft during fixation.
Unfortunately, due to the in-vitro deployment simulation
requirements of the SMP plug, this initial pretension force was
lost. After the soft tissue graft was passed retrograde through the
10 mm tibial tunnel, a 4 mm stainless steel rod was passed through
the looped end of the graft and attached to the upper cross head of
a screw driven uniaxial testing machine, representing the femoral
fixation site. The SMP plug was then inserted in its deformed
position to the approximate center of the tendon construct as shown
in FIG. 17. The entire specimen was removed and placed in body
temperature saline for 30 minutes to initiate shape memory
recovery. The specimen was then placed back into the custom
fixture. Using extension control the crosshead was run at 0.25
mm/sec until a displacement of 30 mm had been reached.
[0170] The shape memory polymer material selected for these plugs
was 45 wt % PEGDMA to PMMA and manufactured to have an initial
deployed diameter of 11.5 mm and a length of 25.4 mm. The plugs
were then deformed using a extrusion unit (e.g., extrusion device
described in example 3) to a final diameter of 8 mm. The deformed
plugs were stored at 0.degree. C. in a glass vial until 5 min prior
to installation. The glass plugs were then inserted using a 10 mm
diameter, 3 inch long cylindrical shaped push rod used to insert
the plug into position.
[0171] FIG. 18 shows experimental results comparing SMP fixation
devices (ShapeLoc devices by MedShape Solutions, Inc., Castle Rock,
Colo.) and a Delta Interference Screw (by Arthrex, Inc., Naples,
Fla.). FIG. 19 shows experimental results comparing tensile
strengths and displacement ratios of the cyclic response (e.g.,
response to multiple cycles) of a ShapeLoc fixation device. FIG.
20a shows mean and standard deviations of tensile strengths of
various fixation devices. FIG. 20b shows mean and standard
deviations of sniffinesses of various fixation options. FIG. 20c
shows mean and standard deviations of slip rates of various
fixation options.
Example 6
Tissue Incorporation
[0172] A photo-polymerization process allows for a cable member
(e.g., a synthetic graft, a living tissue) to be encapsulated
within a polymer material. In one embodiment, the encapsulation
provides a more complete interface, thus reducing the incidence of
a cable member (e.g., a tendon) slipping or tendon-device damage.
In another embodiment, the encapsulation provides an interface that
may be tested before installation in a surgery site.
[0173] The use of the PEGDMA-PMMA system allows for strong adhesion
between the tendon and the device. This allows the graft to be
directly attached (e.g., polymerized) to the fixation device.
[0174] The shape memory polymer system used for this example was
the 45 wt % PEG to PMMA and prepared similar to example 1. FIG. 21,
shows a tissue encapsulation setup and is described below. The
tendon was sized to be inserted into a 10 mm tunnel. The tendon was
carefully wrapped in a cold saline soaked cloth leaving only a 25
mm portion of the tendons distal end exposed. A 12 mm glass test
tube was then coated with a hydrophobic polymer glass treatment
solution (RainX glass treatment sold by SOPUS Products, Houston,
Tex.) and the SMP solution was poured into the base of the tube.
The tendon, leading with the uncovered end was lowered into the
polymer solution until the upper looped portion was restricted with
a crosspin. The distal tendon ends were pressed against a wall of
the test tube. The setup, shown in FIG. 21, was then placed under
the direct contact from a UV lamp and was slowly rotated over a
course of 10 minutes until full polymerization had occurred. The
combined tendon and polymer device was then removed from the glass
tube and stored in a household freezer.
[0175] This example represents the idea of incorporating the tendon
directly to the device prior to surgical installation. Example 7
will illustrate the use of the device to provide a barrier to allow
the tendon and SMP plug to be installed within the bone tunnel,
followed by a monomer solution being polymerized inside the
tunnel.
Example 7
Tissue Incorporation
[0176] In this experiment a SMN device was machined (e.g., lathed)
from 45 wt % PEG to PMMA to resemble a "dog bone" type shape. The
two ends were deformed at 60.degree. C., as shown in FIG. 22a, and
stored at 0.degree. C. The deformed SMP plug was inserted with a 10
mm sized tendon into a 10 mm foam bone tunnel (used to model human
bone). The foam, tendon and deformed device (e.g., device in its
pre-implantation shape) was then placed in body temperature saline
and heated for 10 minutes. FIGS. 22a-c show the device during the
device's change from a pre-implantation shape (FIG. 22a) through a
mid-deployment shape (FIG. 22b), toward the device's unconstrained
shape (FIG. 22c). After the device showed near full change to the
post-implantation shape (as installed) an 18 G syringe was used to
deposit a mixture of 45 wt % PEG to PMMA solution with 0.1%
photo-initiator. Next an ultraviolet light source was located at
the open end of the tunnel and initiated the free radical
polymerization through the SMP device of the solution (45 wt % PEG
to PMMA solution with 0.1% photo-initiator) distributed around the
device (FIG. 23).
[0177] There are two reasons for using a SMP device in this
example. The first reason is to ensure the maximum amount of the
soft tissue comes into the contact with the bone tunnel wall. This
will aid the healing and tendon regeneration process. The second
reason is to allow a barrier to restrict the use of the PEG-PMMA
mixture to only the boney tunnel. An additional method is the use
of a thermal initiator with an activation temperature at body
temperature. This would allow the initial SMP plug to hold the
tendon in place while the remaining PEG-PMMA solution (or even a
homomonomer of PMMA) polymerizes over time due to the heat energy
generated from body temperature.
[0178] While various embodiments have been described for purposes
of this specification, various changes and modifications may be
made which will readily suggest themselves to those skilled in the
art and which are encompassed in the spirit of the invention both
disclosed herein and as defined in the appended claims.
[0179] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as molecular weight,
reaction conditions, and so forth used in the specification and
claims are to be understood as being modified in all instances by
the term "about." Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the present
invention. At the very least, and not as an attempt to limit the
application of the doctrine of equivalents to the scope of the
claims, each numerical parameter should at least be construed in
light of the number of reported significant digits and by applying
ordinary rounding techniques.
[0180] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard deviation found in their respective testing
measurements.
* * * * *