U.S. patent application number 13/872163 was filed with the patent office on 2013-09-12 for shape memory polymer medical device.
This patent application is currently assigned to MedShape, Inc.. The applicant listed for this patent is MEDSHAPE, INC.. Invention is credited to Kenneth A. Gall.
Application Number | 20130237632 13/872163 |
Document ID | / |
Family ID | 43379386 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130237632 |
Kind Code |
A1 |
Gall; Kenneth A. |
September 12, 2013 |
SHAPE MEMORY POLYMER MEDICAL DEVICE
Abstract
Methods and apparatus described herein may utilize activation of
an SMP material to install medical devices with respect to a
surgical site. Activation of the SMP material may be performed with
the use of a triggering force and/or a constraint applied to the
SMP material. Activation using a triggering force and/or a
constraint may be used to create varied activation rates in an SMP
material and varying speeds and times of activation to occur in
shape memory polymers in devices. The disclosure also describes
devices using wedge elements for activation of shape memory
response in the SMP material.
Inventors: |
Gall; Kenneth A.; (Atlanta,
GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDSHAPE, INC. |
Atlanta |
GA |
US |
|
|
Assignee: |
MedShape, Inc.
Atlanta
GA
|
Family ID: |
43379386 |
Appl. No.: |
13/872163 |
Filed: |
April 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12870697 |
Aug 27, 2010 |
8430933 |
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13872163 |
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PCT/US2008/071066 |
Jul 24, 2008 |
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12870697 |
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Current U.S.
Class: |
523/115 |
Current CPC
Class: |
A61K 31/74 20130101;
A61B 2017/042 20130101; A61B 17/0401 20130101; A61B 2017/00871
20130101 |
Class at
Publication: |
523/115 |
International
Class: |
A61K 31/74 20060101
A61K031/74 |
Claims
1. A medical device comprising: a shape memory polymer portion that
has been set with a stored strain between a temporary shape and a
memorized shape, wherein the stored strain is adapted to be stored
in the shape memory polymer portion by the shape memory polymer
portion being at a temperature below an activation temperature of
the shape memory polymer portion; and an activation triggering
element adapted to apply a physical force to the shape memory
polymer portion in an opposing direction to the stored strain while
the shape memory polymer portion is below the activation
temperature; wherein the activation triggering element is further
adapted to complete recovery of the stored strain in the shape
memory portion via applying the physical force to the shape memory
polymer portion while the shape memory polymer portion is below the
activation temperature.
2. The medical device of claim 1, wherein the activation triggering
element is further adapted to vary a magnitude of the physical
force applied to the shape memory polymer portion during recovery
of the stored strain.
3. The medical device of claim 1, wherein the activation triggering
element is further adapted to vary a direction of the physical
force applied to the shape memory polymer portion during recovery
of the stored strain.
4. The medical device of claim 1, further comprising: a
recovery-control mechanism adapted to apply a plurality of discreet
levels of physical constraint via the activation triggering element
during recovery of the stored strain below the activation
temperature.
5. The medical device of claim 1, further comprising: a
recovery-control mechanism adapted to apply a continuously-variable
level of physical constraint via the activation triggering element
during recovery of the stored strain below the activation
temperature.
6. The medical device of claim 1, wherein the activation triggering
element is connected to the shape memory polymer portion via a
connection that is adapted to be broken during insertion into a
surgical site, thereby dislodging the activation triggering element
from the shape memory polymer portion.
Description
RELATED APPLICATIONS
[0001] This Application is a continuation under 35 U.S.C. .sctn.120
of U.S. application Ser. No. 12/870,697, filed Aug. 27, 2010, and
entitled "Method and Apparatus for Deploying A Shape Memory
Polymer," issuing on Apr. 30, 2013 as U.S. Pat. No. 8,430,933,
which is a continuation under 35 U.S.C. .sctn.120 of International
Application No. PCT/US2008/071066, filed Jul. 24, 2008, and
entitled "Method and Apparatus for Deploying A Shape Memory
Polymer," the disclosures of which are incorporated herein by
reference in their entirety.
BACKGROUND
[0002] Medical personnel use a variety of implantable medical
devices in a patient to position, fix, hold, and otherwise
manipulate a patient's body. The installation procedures for such
implantable medical devices may be advantageously designed to allow
medical personnel to install the medical device quickly,
effectively, and consistently. The design of the medical device may
actually facilitate and/or simplify the installation procedure.
Furthermore, the design of a medical device may facilitate a
particular installation procedure. Active elements of a medical
device, including shape memory polymer portions, may be
incorporated in medical devices. A shape memory polymer (SMP) may
be activated to induce shape change and/or to generate forces
against constraints surrounding the SMP. Medical devices comprising
SMP portions may utilize activation of the SMP portion to change
the configuration of the medical device to an installed
configuration with respect to a surgical site and/or to generate
forces against the surgical site.
SUMMARY
[0003] Methods and apparatus described herein may utilize
activation of an SMP material to install medical devices with
respect to a surgical site. Activation of the SMP material may be
performed with the use of a triggering force and/or a constraint
applied to the SMP material. Activation using a triggering force
and/or a constraint may be used to create varied activation rates
in an SMP material and varying speeds and times of activation to
occur in shape memory polymers in devices. The disclosure also
describes devices using wedge elements for activation of shape
memory response in the SMP material.
[0004] The disclosure describes an exemplary medical device
comprising a shape memory polymer portion that has been set with a
stored strain between a temporary shape and a memorized shape,
wherein the stored strain is adapted to be stored in the shape
memory polymer portion by the shape memory polymer portion being at
a temperature below an activation temperature of the shape memory
polymer portion. The exemplary medical device includes an
activation triggering element adapted to apply a physical force to
the shape memory polymer portion in an opposing direction to the
stored strain while the shape memory polymer portion is below the
activation temperature. The activation triggering element is
further adapted to complete recovery of the stored strain in the
shape memory portion via applying the physical force to the shape
memory polymer portion while the shape memory polymer portion is
below the activation temperature. In some embodiments, the
activation triggering element is further adapted to vary a
magnitude of the physical force applied to the shape memory polymer
portion during recovery of the stored strain. In some embodiments,
the activation triggering element is further adapted to vary a
direction of the physical force applied to the shape memory polymer
portion during recovery of the stored strain. In some embodiments,
the medical device includes a recovery-control mechanism adapted to
apply a plurality of discreet levels of physical constraint via the
activation triggering element during recovery of the stored strain
below the activation temperature. In some embodiments, the medical
device includes a recovery-control mechanism adapted to apply a
continuously-variable level of physical constraint via the
activation triggering element during recovery of the stored strain
below the activation temperature. In some embodiments, the
activation triggering element is connected to the shape memory
polymer portion via a connection that is adapted to be broken
during insertion into a surgical site, thereby dislodging the
activation triggering element from the shape memory polymer
portion.
[0005] The disclosure also describes an exemplary method that
includes inserting into a surgical site a medical device including
a shape memory polymer portion having a stored strain. The method
also includes raising the temperature of the shape memory polymer
portion to a first activation temperature, thereby activating the
shape memory polymer portion at a first activation rate. The method
also includes applying a trigger force to the shape memory polymer
portion, thereby changing the activation rate of the shape memory
polymer portion from the first activation rate to a second
activation rate. The disclosure also describes an exemplary method
that includes straining a shape memory polymer that forms at least
a portion of a medical device with a deforming force from an
unconstrained shape to a pre-implantation shape. The method also
includes inserting the medical device into a surgical site while
the shape memory polymer is in the pre-implantation shape. The
method also includes applying a trigger force to the shape memory
polymer, thereby activating the shape memory polymer, and reducing
the trigger force after the shape memory polymer has achieved a
post-implantation shape different from the pre-implantation
shape.
[0006] The disclosure also describes an exemplary medical device
that includes a body having a shape memory polymer portion, with
the shape memory polymer portion in a storage shape having a stored
strain. The stored strain corresponds to a first difference in
length between a first unconstrained length of the shape memory
polymer portion in an unconstrained shape and a first storage
length of the shape memory polymer portion in the storage shape,
with each first length being measured along a first measured
direction of the shape memory polymer portion. The medical device
also includes a trigger element adapted to be coupled with the
body, the trigger element being further adapted to activate the
shape memory polymer portion while the shape memory polymer portion
is in the storage shape. The trigger element is adapted to activate
the shape memory polymer portion through application of a trigger
force to the shape memory polymer portion.
[0007] The disclosure also describes an exemplary medical device
including an elongated body having a shape memory polymer portion
having a stored strain. The medical device also includes a trigger
element oriented with respect to the elongated body such that a
displacement of the trigger element transfers an installation
strain to the shape memory polymer portion.
A BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a graph of force versus displacement applied to
exemplary shape memory polymer bodies with different degrees of
stored strain.
[0009] FIG. 2 is a flow chart of an exemplary method for installing
a medical device having an SMP portion into a patient's body during
surgery.
[0010] FIG. 3 is a flow chart of another exemplary method for
installing a medical device having an SMP portion into a patient's
body during surgery.
[0011] FIGS. 4A-4C are cross-sectional representations of an
exemplary suture anchor as it is being installed in a patient's
bone through three exemplary stages during installation and
configuration change through activation of an SMP portion of the
suture anchor.
[0012] FIGS. 5A-5B are cross-sectional representations of an
exemplary cylindrical medical device with a wedge element through
two exemplary stages of installation through activation of an SMP
portion while in a surgical site in a patient's bone.
[0013] FIGS. 6A-6B are representations of an exemplary cylindrical
medical device with a wedge element through two exemplary stages of
activation of an SMP portion while in an unconstrained environment
(substantially free of constraints).
[0014] FIG. 7 is a schematic of an exemplary medical device with a
compressive trigger element partially disposed within the medical
device.
[0015] FIG. 8 is a schematic of another exemplary medical device
with a compressive trigger element entirely disposed outside of the
medical device.
DETAILED DESCRIPTION
[0016] The following description of various embodiments is merely
exemplary in nature. While various embodiments have been described
for purposes of this specification, various changes and
modifications may be made to the embodiments disclosed herein.
[0017] A polymer having a shape memory property, which may be
termed a "shape memory polymer" (SMP), may be characterized by an
ability to retain a "memory" of a shape in as much as the SMP may
change shape and return to the memorized shape under a certain set
of conditions through a process of activation, described further
herein. As used herein, "SMP" may refer to a body or a portion of a
body that has an SMP property.
[0018] The memorized shape is also referred to herein as an
unconstrained shape of the SMP because the SMP may achieve the
memorized shape in the absence of constraints and after all stored
strain in the SMP is recovered. The term "stored strain" as used
herein is the strain defined by the difference between the
unconstrained shape and a storage shape, also referred to herein as
a temporary shape. In other words, a material may have an
inhomogeneous stored strain comprising multiple regions with
strains that differ from one another.
[0019] As used herein, the term "strain" (when used without a
qualifier) is used to refer to an engineering strain in the form of
a linear/normal strain, a shear strain, and/or any combination
thereof in a material. Linear strain (or normal strain) is the
difference in length (e.g., distortion) of a material along a
measured direction divided by the original length of that material
along the measured direction. The "measured direction" of the
linear strain may referred to herein simply as the direction of the
linear strain. The difference in length is measured by the new
length subtracted by the original length. Therefore, negative
strains indicate compression along the measured direction and
positive strains indicate expansion along the measured direction.
Shear strain is the differential angular change in a line through a
body between a reference point and a point that moves based on
deformation. Strains are associated with measured directions and/or
lines through the material and are dimensionless. Complex
distortions and shape changes in a material (e.g., SMP) may include
multiple types and directions of strain such as one or more linear
strains and/or shear strains. For example, a bend in a material may
comprise one or more concurrent linear strains (e.g., areas of
compression and/or expansion) along one or more measured
directions. As another example, a twist in a material may comprise
one or more shear strains (e.g., angular distortions).
[0020] An SMP may be caused to take on a temporary shape different
from the memorized shape through straining the SMP from the
memorized (unconstrained) shape to the storage (temporary) shape.
This process of straining the SMP from a memorized to a storage
shape may also be referred to herein as "deforming" the SMP or
"setting a temporary shape". The strain imparted to an SMP that is
necessary to set the temporary shape in the SMP may be
incrementally different from the stored strain eventually held by
the SMP in the temporary shape. For example, during the setting of
the temporary shape, if a force is reduced/removed from the SMP,
the SMP may recoil from the imparted strain into the stored strain
embodied in the temporary shape.
[0021] Under conditions where an SMP is not activated, the SMP will
maintain a temporary shape and the molecules of the SMP will
maintain a lower entropy state (e.g., configuration of the
molecules) than the state of the molecules while the SMP is in the
unconstrained shape. When an SMP is activated, the molecules of the
SMP are allowed to seek a higher entropy state and when the SMP is
not activated, the molecules of the SMP are limited from seeking a
higher entropy state. The term "activation," as used herein, refers
to enabling recovery in an SMP through providing activation stimuli
to the SMP, and thereby inducing the molecules to seek a higher
entropy configuration. Depending on the constraints applied to the
SMP material, recovery caused by activation can include shape
change and/or generation of forces against a constraint. For
example, even though activation may enable a change in molecular
configuration (and thereby a shape change), that shape change may
be inhibited by the application of external constraints.
[0022] In accordance with the present disclosure, methods and
apparatus have been developed whereby mechanical stimuli may be
used as activating stimuli for an SMP. Mechanical stimuli may be
referred to as a force and/or a constraint applied to the SMP
material. For different activation stimuli, such as temperature
and/or trigger forces, as described further herein, different
"activation rates" are may be achieved. Different activation rates
may be measured through the externally-observable properties of an
SMP, including shape change and generation of force, as described
further herein.
[0023] The term "constraint" as used herein refers to a structural
confinement (limitation in one or more directions) on a body. A
constraint may or may not have forces generated against it by the
body. A constraint applied to an SMP may be used as an externally
measureable indication of a trigger force applied to the SMP. For
example, a trigger force may not be easily measureable, so the
application of a constraint or a series of constraints may be used
to control the activation of an SMP. As described further herein,
the application of a constraint on an SMP may cause a varying force
on the SMP as the SMP responds to the applied constraint, through
the SMP responding elastically and/or the SMP responding with
conformational motion. For example, the application of a constraint
may cause a sufficient force to be applied to the SMP such that a
yield point is crossed and conformational motion of the SMP
molecules occurs, thereby conforming the SMP to the constraint and
lowering the force applied by the constraint. As described further
herein, the application of a series of constraints may raise and
lower through multiple cycles the forces applied on the SMP by the
series of constraints.
[0024] An activation temperature of an SMP is a temperature above
which the SMP is significantly activated (e.g., which causes
significant recovery in the SMP) absent other activation stimuli.
Activation temperatures and other transition temperatures for SMPs
may be defined by changes in macroscopic material properties, such
as changes in the modulus of the SMP (e.g., an inflection point in
a modulus curve, a midpoint of a transition in a modulus curve).
The modulus of an SMP may be measured using standard techniques
known to those with skill in the art, such as through using a
dynamic modulus analysis setup. An SMP need not reach or exceed its
so-called "transition temperature" for activation to occur. For
example, activation of an SMP may occur in a temperature range
below the transition temperature of the SMP.
[0025] In an SMP material with a high cross-linking density, the
activation temperature may be about 30-20 degrees Celsius below the
transition temperature and the SMP material may be designated as
having a broad transition (e.g., a broad range of temperatures in
which recovery significantly occurs). In an SMP material with a
moderate cross-linking density, the activation temperature may be
about 20-10 degrees Celsius below the transition temperature and
the SMP material may be designated as having a moderate transition.
In an SMP material with a low cross-linking density, the activation
temperature may be about ten to three degrees Celsius below the
transition temperature and the SMP material may be designated as
having a narrow transition. In an SMP material with a very low
cross-linking density, the activation temperature may be about 3 or
fewer degrees Celsius below the transition temperature and the SMP
material may be designated as having a very narrow transition.
[0026] An unconstrained shape refers to a shape of an SMP portion
with no strain that has been imparted or stored. An unconstrained
shape may be achieved through full activation (e.g., release of all
stored strain) such as through sufficient activation in an
unconstrained environment. An unconstrained environment may be any
environment with little or no constraints imposed on the SMP
material, such as the SMP material submerged in a fluid bath or
resting on a table.
[0027] Activation rates may be tested or benchmarked in an
unconstrained environment given predetermined activating stimuli as
described further herein (e.g., temperature, trigger force) applied
to a test sample of the SMP material. For example, a test
activation rate may be determined through applying a predetermined
temperature (e.g., temperature controlled fluid bath) to the sample
of SMP material (with a stored strain) in an unconstrained
environment and measuring the strain recovery (shape change) that
occurs over time. For example, a first exemplary test or benchmark
activation rate may be determined to be five percent strain
recovery in 30 minutes. A second exemplary test or benchmark
activation rate may be five percent strain recovery in 15 minutes.
A third exemplary test or benchmark activation rate may be five
percent strain recovery in ten minutes. A fourth exemplary test or
benchmark activation rate may be five percent strain recovery in
five minutes. A fifth exemplary test or benchmark activation rate
may be 20 percent strain recovery in 15 minutes. A sixth exemplary
test or benchmark activation rate may be 20 percent strain recovery
in ten minutes. Other test or benchmark rates as selected based on
an appropriate rate for the surgical procedure. The activation
rates as measured by percentage recovery over a certain period of
time may be extrapolated to larger or smaller strain recoveries,
and actual activations and recoveries are not limited to the
specific percentages or time periods described herein. For example,
recoveries of less than one percent strain to greater than 100
percent strain (e.g., in the case of tensile strain) may be
recovered by shape memory polymers.
[0028] As described further herein, different activation rates may
be achieved through application of trigger forces. Activation rates
may also be controlled/changed through the modification of
temperature and/or trigger forces or combinations thereof during
surgical procedures using the devices described herein.
[0029] The discussion herein of activation rates should be
understood as including long-term (e.g., average) activation rates,
as well as instantaneous activation rates. The activation rates
described herein may be changed through changes in stimuli (e.g.,
forces, temperature) causing the activation. For example, an
activation rate may vary considerably within a large range during
activation during a surgical procedure. The activation rate of the
SMP may therefore be equal to each of the values in that range for
a period of time, however short.
[0030] Stored strains and triggering forces may be compressive,
expansive, bending, torsional and/or any combination of those
forces/strains. In order for a force or a constraint to trigger
activation of an SMP material, the force or constraint may have at
least a component that bears a certain relation(s) to the stored
strain in the SMP. Some embodiments of trigger forces or
constraints may have components perpendicular to the stored strain.
Some embodiments of triggering forces/constraints may have
components in an opposite and parallel direction to the stored
strain. The term "parallel" is used herein to describe a
relationship such that two vectors (e.g., relating to two forces,
relating to two strains) share the same direction, and may or may
not be translated (e.g., have a different initial point). For
example, two forces or vectors directly opposing each other are
parallel.
[0031] The term "trigger force" is used herein to denote a force
exerted on the SMP body that causes activation of the SMP (e.g., an
increase in activation rate), as described further herein. The
trigger force may be transmitted through other parts of a medical
device to an SMP portion. As an example, the medical device may be
constructed entirely from SMP material or may include other
materials that are not SMP materials. In one embodiment, the SMP
subjected to the trigger force may receive the trigger force
through these other materials. In another embodiment, the SMP
subjected to the trigger force may receive the trigger force
through a portion of SMP that does not activate due to the
application of the trigger force. As examples, the SMP that does
not activate may not have any stored strain or may not have a
stored strain that is activated by the particular direction of the
trigger force being applied.
[0032] A "trigger element" may be adapted, as described further
herein, to apply trigger force(s) and/or constraint(s) on an SMP
material in order to activate the SMP material. For example, an
element may be adapted to apply compressive force(s) and
constraint(s) in a perpendicular direction to a stored compressive
strain (e.g., negative strain along a measured direction) in the
SMP material. As another example, a trigger element may be adapted
to apply expansive forces and/or constraints in a parallel
direction to a stored compressive strain in the SMP material. As a
further example, a trigger element may be adapted to apply a
trigger force or constraint in a rotational or bending direction
that is opposite a rotational or bending direction of a stored
strain (e.g., a strain with a shear component).
[0033] Implantable medical devices described herein use various
shapes SMP portions and transitions between those shapes to achieve
advantageous configurations. The medical device configurations may
be advantageously applied with respect to bone, soft tissue, and
other elements in a surgical site. The medical device
configurations may interact with these elements in the surgical
site through various equilibria reached between the medical device
and these elements and the respective strains embodied in these
elements.
[0034] The term "surgical site" as used herein may include any
portion of a patient to which operating personnel (e.g., surgeon,
nurse) may have access during surgery. The term "patient" as used
herein should not be limited to human patients, but may include
other patients as well.
[0035] Unless otherwise indicated, all numbers expressing
quantities, temperatures, strains, 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.
[0036] 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.
[0037] FIG. 1 shows a graph of force versus displacement applied to
an embodiment of a shape memory polymer. Force-displacement curve
110 tracks an embodiment of a force-displacement relationship of an
SMP being deformed from an unconstrained shape into a temporary
shape (e.g., imparting a stored strain) along one measured
direction (in millimeters) denoted on the displacement axis. The
test elements of SMP that were used were roughly the same starting
length in the measured direction, and one skilled in the art may
convert the change in length along this measured direction into a
strain value. The test elements shared the same cross-sectional
area as measured along a plane normal to the force applied, thereby
allowing equal forces to be equated to equal stresses on the test
elements.
[0038] The force-displacement curve 110 begins with an initial
elastic portion 110a, through a yield region 110b, continuing with
a conformational motion portion 110c. After a sufficient or desired
strain is imparted to the SMP through the conformational motion
portion 110c, the conditions, forces and/or constraints that are
imparting the strain on the SMP may be removed.
[0039] When the SMP is in a temporary shape and is not activated,
the constituent molecules of the SMP are in a lower entropy
configuration than when the SMP is in the unconstrained shape. The
process of lowering the entropy of the configuration of molecules
of the SMP occurs through a mechanism of "conformational motion" of
the molecules of the SMP. An embodiment of driving the conformation
motion of molecules of an SMP may be seen in the conformational
motion portion 110c of the force-displacement curve 110. During the
conformational motion portion 110c, a portion of the work performed
on the SMP is converted into the lower entropy configuration of the
molecules of the SMP.
[0040] The force-displacement curve 120 shown in FIG. 1 reflects an
SMP that already has a stored strain while in initial shape with
initial length 118. The force-displacement curve 120 begins with an
initial elastic portion 120a. In the embodiment shown, the initial
elastic portion 120a is shorter than the initial elastic portion of
the force-displacement curve 110 for an SMP without a stored
strain. The force-displacement curve 120 has a yield region 120b
that occurs at a lower force than the yield region 110b for the SMP
without stored strain. The explanation for this lowered force is
that, in this embodiment, the force is applied in such a manner as
to activate the SMP into releasing the stored strain.
[0041] In the embodiment shown, a conformational motion portion
120c of the force-displacement curve 120 occurs while the force is
continued to be applied and as further activation occurs. The term
"conformational motion" may be used to describe the process by
which the configuration of the molecules changes. Conformational
motion may result in raising the entropy in the molecular
configuration (e.g., activation) of an SMP, shown through the
conformational motion portion 120c, or may result in lowering the
entropy of the molecular configuration (e.g., storing of strain,
creating a temporary shape, deforming) of an SMP, shown through
conformational motion portion 110c. As described further herein,
conformational motion (e.g., activation, storing strain) may occur
at one rate due to the temperature of the SMP, at a different rate
based on mechanical forces applied to the SMP, at a different rate
based on stored strain in the SMP, and at still different rates
based on combinations of temperature, force, and stored strain.
[0042] During activation of an SMP portion, an activating force
(e.g., a trigger force) may be a constant force and/or a varying
force. In one embodiment, a constant or near-constant activating
force may be applied to achieve a constant or near-constant
activation rate. In another embodiment, a varying activation rate
may be achieved through imposing a constraint on the SMP portion,
either directly or through applying a constraint to a medical
device containing the SMP portion.
[0043] For example, a constraint may be applied on the SMP portion
that exerts a varying force on the SMP portion. In one embodiment,
a ratchet mechanism may be applied to the SMP portion that imposes
a predetermined constraint on the SMP portion whereby an
incremental increase in the constraint (e.g., one notch on the
ratchet mechanism) increases the force applied to the SMP portion.
As the SMP portion responds to the applied constraint through
conformational motion, the force applied by the ratchet mechanism
decreases from a maximum magnitude force because the constraint
imposed on the SMP portion remains constant while conformational
motion of the SMP molecules allows the SMP to conform to the
constraint. With another incremental increase in the constraint,
the force applied to the SMP portion will again increase to a
maximum magnitude and then decrease. Imposing constraints may be
referred to herein as imposing a predetermined strain (e.g.,
determined by the difference between an original length and the
length imposed by a stop-point in the ratchet mechanism).
[0044] While a ratchet mechanism or other mechanisms may apply
discreet levels of constraint on an SMP portion, other mechanisms
may be used to apply continuously variable constraints to an SMP
portion. For example, there is a wide array of continuously
variable mechanisms, including wedges, levers, and clamps. A
continuously variable constraint may be applied to an SMP portion
in order to create a constant force on the SMP portion while
conformational motion is occurring. For example, a constant force
may be used to activate an SMP portion at a constant or near
constant rate, as described further herein. A continuously variable
mechanism (e.g., wedge) may be combined with a discreet mechanism
(e.g., ratchet) or discreet operation such that the continuously
variable mechanism is operated in a discreet manner. For example, a
wedge may be operated by a ratchet mechanism or may be operated
through discreet operations (e.g., repeated impactions, hammering)
such that the wedge moves in a generally discreet or incremental
manner.
[0045] FIG. 2 shows a flow chart of an embodiment of a method 200
for performing surgery. The method includes inserting 202 a medical
device containing an SMP portion into a surgical site. In the
embodiment shown, the SMP portion of the medical device initially
has a stored strain before insertion. The SMP portion with the
stored strain may be referred to as being in a "temporary shape" or
a "pre-implantation shape" because the shape of the SMP portion for
use in the medical device is adapted for the implantation process
and the SMP portion may change shape thereafter. The stored strain
may be imparted by known processes for setting a temporary shape in
an SMP.
[0046] In optional operation 204, further strain may be imparted
204 after or through the act of inserting the SMP portion 202,
thereby straining the SMP portion into an alternate shape. The
further strain may be imparted 20-4, as described further herein,
through the act of inserting the SMP portion 202, such as through
interaction with a surgical site, and/or through a separate
application of mechanical force, such as by using a clamp or
hammer. In one embodiment, the further strain may be cumulative to,
or added to, the stored strain, and may contain a component in the
same direction as the stored strain.
[0047] The temperature of the SMP portion is raised 206 to a
temperature that causes the SMP portion to activate at a heated
activation rate. The temperature of the SMP portion may be raised
206 through heat received from the surgical site (e.g., a patient's
body heat). For example, the SMP portion initially have been at a
temperature that is below the temperature of the surgical site
(e.g., a normal temperature for an exposed portion of the human
body during surgery), thus inducing a heat transfer from the
surgical site to the SMP portion (e.g., through thermal
conduction). The temperature of the SMP portion may alternatively
be raised through heat received from another transfer mechanism,
including conduction from another material, radiation (e.g.,
electromagnetic) or other transfer mechanism.
[0048] The heated activation rate may be a rate that is significant
or insignificant with respect to the surgery and/or installation of
the medical device in the surgical site. The temperature to which
the SMP portion is raised 206 may be considered an activation
temperature for the SMP portion (e.g., causing a threshold amount
of shape change to a test sample of the SMP composition while the
test sample is largely free of constraints). Because non-zero
activation rates occur at temperatures below an activation
temperature, even absent constraints, the heated activation rate
may occur below what may be considered activation temperature or
transition temperature for the SMP material.
[0049] The operation 208, a trigger force is applied 208 to the SMP
portion. In one embodiment, applying a trigger force 208 follows
raising the temperature 206 of the SMP portion. For example,
applying the trigger force 208 may increase the activation rate of
the SMP portion from the heated activation rate (caused by
operation 206) to a faster activation rate.
[0050] In another embodiment, the operations 206 and 208 may be
reversed in sequence, i.e., applying a trigger force 208 may
proceed raising the temperature 206 of the SMP. For example,
applying the trigger force 208 may activate the SMP at a mechanical
activation rate and raising the temperature 206 of the SMP may
increase the activation rate of the SMP from the mechanical
activation rate to a faster rate.
[0051] The temperature of the SMP and trigger forces applied to the
SMP may be modified, as described further herein, and the
activation rates of the SMP may thereby also be modified. In
optional operation 210, the temperature of the SMP may be changed
210 (e.g., through thermal conduction) during the process of
installing a medical device comprising the SMP portion. In optional
operation 212, the trigger force may be changed 212 (e.g., through
using a ratchet mechanism) during the process of installing a
medical device comprising the SMP.
[0052] Through activation of the SMP (e.g., through raising the
temperature, through mechanical activation), as described in
operations 206 through 212 (and further herein), a portion of the
stored strain in the SMP may be recovered. A determination may be
made 214 whether the portion of stored strain has been recovered by
the SMP. For example, the portion of stored strain may be a desired
portion of strain recovered, thereby transitioning a medical device
comprising the SMP portion from a pre-installed configuration to an
installed configuration with respect to the surgical site. As
another example, the portion of stored strain may be a portion that
puts the medical device in a configuration with respect to the
surgical site such that the medical device remains in fixed
relation to the surgical site while activation from another
stimulus (e.g., heat) completes the medical device's transition to
the installed configuration.
[0053] The stored strain may be determined 214 to have been
recovered through observation of the medical device, through
instrumentation and/or tools in contact with the medical device,
and/or through other means. The SMP portion itself may also be
directly tested/observed to make the determination, including
through observation/testing of the properties of the SMP portion
(e.g., rubbery modulus, stress exerted).
[0054] After a portion of the stored strain in the SMP is
determined 214 to have been recovered by the SMP, the trigger force
may be reduced 216 on the SMP. Reducing the trigger force 216 may
comprise an incremental removal of force. Reducing the trigger
force 216 may comprise modifying, reducing, and/or ceasing
operation of a triggering device applied to the medical device. For
example, a clamp may be operated on the medical device to impose a
compressive force on the medical device. As another example, a
wedge may be operated on or within the implanted medical device to
impart or impose an expansive force on the medical device.
Triggering elements (e.g., wedge, clamp) and operations thereof are
described further herein.
[0055] FIG. 3 shows a flow chart of another embodiment of a method
300 for performing surgery. The method 300 may include the optional
operation 302 of straining an SMP portion 302 of a medical device.
The straining of an SMP portion 302 and storage of the strain
(e.g., a temporary shape of the SMP, a pre-implantation shape) is
described further herein. The method 300 includes inserting the
medical device 304 into a surgical site, as described further
herein.
[0056] In some embodiments, applying a trigger force 306 may be
performed with, and/or through inserting the medical device 304
into the surgical site. For example, a medical device may interact
with the surgical site such that the process of inserting the
medical device 304 causes a trigger force to be applied 306. As
another example, a trigger force may be applied 306 to an SMP
portion of the medical device during the installing of the medical
device 304. Examples of devices are described herein (e.g., trigger
elements) that may use installation processes whereby trigger
forces may be applied 306 during the installation process.
[0057] The trigger force applied 306 may include any force on the
SMP portion, including compressive, expansive, rotating, shear,
tangential, twisting, and/or bending forces. As described further
herein, the trigger force applied to the SMP portion does not need
to be the same force applied to the medical device. For example,
the force applied to the medical device may be a compressive force
and the configuration of the medical device may cause an expansive
trigger force to be applied 306 to the SMP portion. As another
example, the force applied to the medical device may be a torsional
or bending force and the configuration of the medical device and/or
triggering device may cause expansive trigger forces to one SMP
portion and/or compressive trigger forces to another SMP portion.
Examples of medical devices that transmit and translate forces
applied to the medical device into trigger forces are described
further herein.
[0058] The trigger force may be applied 306 until it is determined
308, as described further herein, that the SMP has achieved a
post-installation shape. The term "post-installation shape" may
refer to the shape of the SMP that puts the medical device in an
installed configuration with respect to the surgical site. The
post-installation shape of the SMP does not need to resemble the
installed configuration of the medical device, as other portions of
the medical device (e.g., other SMP portions that are
non-activated, portions of non-SMP materials) may be configured to
translate the change in shape of the SMP to a change in
configuration of the medical device as a whole. For example, an
expansion of an SMP portion of the medical device may cause other
portions of the medical device to flare, tear, extend, and/or
rotate.
[0059] As described further herein, there may be multiple
acceptable installed configurations of the medical device with the
surgical site (e.g., multiple different configurations of forces
holding a tendon against a bone surface) that may be achieved based
on different activation processes. For example, activation of the
SMP may continue (e.g., due to thermal activation) after
reducing/removing triggering forces from the SMP, thereby
potentially transforming the medical device from one installed
configuration to another installed configuration. In one
embodiment, if the medical device operates to hold a cable member
(e.g., tendon, animal soft tissue, cord comprising artificial
material) against a bone surface, an installed configuration of the
medical device may include a configuration that holds the cable
member against a bone surface with a desired level of force. In
another embodiment, an installed configuration of a suture anchor
achieves a sufficient pull out strength (e.g., minimum force to
pull the suture anchor from a bone via an attached suture).
[0060] The systems and devices described herein may implement
methods described herein. In addition, methods described herein,
when implemented in any appropriate medium, including SMPs and
other materials, may form systems and devices described herein.
Therefore, the descriptions of the methods and systems herein
supplement each other and will be understood by those with skill in
the art to form a cumulative disclosure.
[0061] The methods described herein may be performed by any part of
an element of a system described herein. In addition, the methods
described herein may be performed iteratively, repeatedly, and/or
in parts. In addition, some of the methods or parts of the methods
described herein may be performed simultaneously.
[0062] FIGS. 4A-4C are cross-sectional representations of an
exemplary suture anchor 400 as it is being installed in a patient's
bone 408 through three exemplary stages during installation and
configuration change through activation of an SMP portion of the
suture anchor. As shown in FIGS. 4A-4C, the installation process of
the suture anchor 400 includes a transformation of the
configuration of the suture anchor inside the bone 408. The
transformation may include an activation of an SMP portion that has
complex stored strains, such as stored compressive (negative),
expansive (positive), bending, rotating, and twisting strains. The
activation of the portion of the SMP may therefore include recovery
of these stored strains. In various embodiments, the activation may
be performed, as described further herein, through heating the SMP
portion, through trigger forces applied to the SMP portion, and/or
a combination thereof
[0063] FIG. 4A shows the exemplary suture anchor 400 with an
opening 406 that is configured to apply a trigger force to an SMP
portion of the suture anchor through insertion of the suture anchor
into a bone 408 of a patient. The suture anchor 400 may be made
entirely of a single SMP material, although other embodiments may
substitute other materials for portions of the suture anchor. As an
example, the suture anchor 400 uses an SMP portion that is in a
temporary shape before insertion into a patient and is thereafter
activated into a different shape, as shown in FIGS. 4B-4C and
described further herein. The suture anchor 400 uses an
installation process and concomitant interaction with a surgical
site to apply a trigger force to the SMP portion.
[0064] The elongated body 402 of the suture anchor 400 includes at
least a portion made from an SMP material. The embodiment of the
suture anchor 400 is made of SMP material and has two elongated
bodies 402 substantially aligned while at least one SMP portion is
in its temporary shape. The elongated bodies 402 are attached at an
attachment portion 404. In one embodiment, the attachment portion
404 is made of SMP material, but the attachment portion does not
have stored strain before or after an installation process. In
other words, some SMP portions of medical devices need not have the
same stored strains as other SMP portions of the medical devices
and the interactions of some SMP portions with a surgical site may
differ from the interactions of other SMP portions.
[0065] In one embodiment, the elongated bodies 402 form an opening
406 that is configured to receive trigger forces when the suture
anchor is inserted into the bone 408. The opening 406 may be
adapted to receive trigger forces through interfacing directly with
the bone 408 and/or may receive trigger forces in another manner,
such as through interfacing with another element. Therefore, the
opening 406, another element (e.g., wedge element 407), and/or a
combination of the opening and another element may be considered a
trigger element for the medical device.
[0066] In one embodiment, the opening 406 may be configured to
engage the bone 408 and receive trigger forces directly from the
bone when the ends of the elongated bodies 402 (forming the
opening) are inserted in the bone. For example, the opening 406 may
be adapted to provide an interface with the bone 408 of a patient
whereby the bone presses (e.g., imparts a force) into the opening
406 so as to separate (e.g., strain) the elongated bodies 402.
[0067] In another embodiment, a wedge element 407 may be adapted to
impart trigger forces to the opening 406 and/or to the elongated
bodies 402, and thereby the wedge element 407 may form at least
part of a trigger element during several phases of installation of
the suture anchor 400 as shown in FIGS. 4A-4C. In one embodiment,
the wedge element 407 may be adapted to interact with the suture
anchor 400 through translating forces from the bone into forces on
the elongated bodies 402 of the suture anchor. In another
embodiment, the wedge element 407 may be adapted to be operated
through use of a pull cord, as described further herein.
[0068] The wedge element 407 may be inserted along with the suture
anchor 400 into the bone 408. For example, the wedge element 407
may be attached to the opening 406 of the suture anchor 400, such
as through being adhered to the opening, or being formed as part of
the same body of material as one or both of the elongated bodies
402. As another example, the wedge element 407 may be adapted to be
attached to, adhered to, placed on, or inserted in the bone 408
separately from the opening 406. For example, the wedge element 407
may be adapted to be placed into a pilot hole in the bone 408
before the suture anchor is inserted in the bone.
[0069] The wedge element 407 may take another shape than the
triangular shape shown in FIGS. 4A-4C. For example, the wedge
element 407 may be another shape that aides in translating forces
from the bone 408 into trigger forces exerted against portions of
the suture anchor 400.
[0070] The wedge element 407 may be formed from a portion of the
suture anchor 400, and may be adapted to deform during the process
of the suture anchor being inserted into the bone 408. For example,
the wedge element 407 may be formed as a part of the suture anchor
400 that is adapted to be dislodged from the suture anchor as the
suture anchor is inserted into the bone.
[0071] FIG. 4B shows the exemplary suture anchor 400 partially
inserted into the bone 408 of a patient. As the suture anchor 400
is initially inserted into the bone 408, the opening 406 comes in
contact with the patient's bone 408. As the suture anchor continues
to be inserted into the bone 408, the bone exerts forces, some of
which are shown by arrows 410. The arrows 410 represent some of the
normal forces acting on the suture anchor 400 by the bone 408,
although there may be other forces acting on the suture anchor
while the suture anchor is installed, such as tangential forces
(e.g., frictional forces) acting along the surface of the suture
anchor.
[0072] FIG. 4C shows the exemplary suture anchor 400 inserted into
an installed configuration within the bone 408 of a patient. The
forces shown by the arrows 410 may be translated into trigger
forces applied to at least a SMP portion of the suture anchor 400
containing a stored strain, as described further herein. As shown
in FIG. 4C, the trigger forces in the suture anchor 400 may
include, in various embodiments, bending moments 412, expansive
forces 414, and compressive forces 416. As described further
herein, a trigger force is applied to a portion of an SMP with a
stored strain such that the SMP is activated to recover that stored
strain. For example, an SMP portion with stored strain comprising a
shear strain (e.g., twist) may be activated to a trigger force with
an opposing bending moment 412. Other interactions between stored
strains in SMP portions and their activation via trigger forces are
described further herein.
[0073] An SMP with complex stored strains, which is described
further herein, may be activated by complex trigger forces.
Therefore, some or all of the trigger forces shown in FIG. 4C,
including bending moments 412, expansive forces 414, and
compressive forces 416 may be applied to an SMP portion of the
suture anchor 400. In other embodiments, other trigger forces may
be applied to the suture anchor 400 to activate other stored
strains in the suture anchor.
[0074] FIGS. 5A-5B are cross-sectional representations of an
exemplary cylindrical medical device 500 with a wedge element 504
through two exemplary stages of installation through activation of
an SMP portion while the medical device is in a surgical site in a
patient's bone. The medical device 500 may be installed within a
surgical site such as a bone cavity 507 defined in bone 508 to
press a cable member 506 such as a tendon or artificial tendon
replacement against the bone cavity. In the installed
configuration, the medical device 500 is expanded against the walls
of the bone cavity 508 and forces between and among the medical
device, cable member 506, and the bone 508 to hold them in spatial
relation to one another. In some embodiments, the cable member 506
may be used as a replacement tendon attached to a bone 508 of a
patient. For example, in an anterior cruciate ligament repair
surgery, a cable member may be attached to the distal end of a
patient's femur and attached to the proximal end of the patient's
tibia inside the patient's knee.
[0075] FIG. 5A shows the medical device 500 with the wedge element
504 pressing against the end of the body 502 of the medical device.
In one embodiment, there is an SMP portion of the body 502 with a
stored strain, such as a stored compressive circumferential strain
510. The wedge element 504 is adapted to impart expansive trigger
forces (indicated by the expansive arrows 512) to activate the
stored strain (indicated by the compressive arrows 510) in the SMP
portion. The wedge element may be operated through a pull cord 518,
through direct operation (e.g., hammering, driving), or through
other means. Wedge element 504 may be formed in many shapes,
including spherical (as shown), ellipsoid, angled, pyramid.
[0076] A pull cord 518 may be designed to respond to an anticipated
stress (e.g., pulling on a long axis of the pull cord) through
straining to an anticipated amount of strain. The strain in the
pull cord 518 may be adapted to be used to apply forces and/or to
recover that strain through a process that beneficial to the
installation of the medical device (e.g., application of forces to
the wedge element 504). For example, the pull cord 518 may be fixed
against a part of the medical device 500 (e.g., through the use of
a ratchet mechanism), such as an end of the medical device, after
applying a force to the pull cord (e.g., operation of the wedge
element via applying the force to the pull cord), and the pull cord
may thereafter apply a force to the wedge element 504 through
recovery of strain in the pull cord. A pull cord 518 may also
recover strain while the pull cord is being used to operate the
wedge element (e.g., during reductions in stress on the pull
cord).
[0077] A pull cord 518 may be designed to be significantly strained
(e.g., stretched) along its long axis under the stress anticipated
to be used in operating the wedge element 504 in the medical
device. A pull cord 518 may be designed such that the pull cord
will respond elastically under the stress anticipated to be used in
operating the wedge element 504. A pull cord 518 may be made of a
material (e.g., elastic material, shape memory alloy) such that
significant strain may be stored in the pull cord without plastic
deformation and such that the pull cord may apply forces to the
wedge element based on the stored strain in the pull cord. For
example, in one embodiment, the pull cord 518 may be made of a
stainless steel wire that is designed (e.g., sufficiently thick) as
to avoid the pull cord from being plastically deformed. In another
embodiment, the pull cord 518 may be designed as a structure other
than a solid longitudinal cord (e.g., a spring) in order to tailor
the force-displacement response of the pull cord.
[0078] In one embodiment, a pull cord 518 may be made of a shape
memory alloy and designed to undergo a phase transformation from an
austenitic to a martensitic phase in at least part of the shape
memory alloy under the stress anticipated to be used in operating
the wedge element 504. For example, a pull cord 518 made at least
in part of shape memory alloy may be designed to be strained by the
stress anticipated in operating the wedge element 504, and the pull
cord may apply forces to the wedge element through the recovery of
that strain. The shape memory alloy in the pull cord 518 may
exhibit "super-elastic" or "pseudo-elastic" properties based on a
martensitic phase present in the shape memory alloy, and the forces
applied by the pull cord 518 through the recovery of the strain in
the martensitic phase may be relatively constant, as compared to
elastic recovery of strain by the same material in its austenitic
phase.
[0079] FIG. 5B shows the medical device 500 with the wedge element
504 partially translated through the body 502. The configuration of
the medical device 500 is shown in FIG. 5B in one of potentially
multiple installed configurations of the medical device, as
described further herein. In the installed configuration shown, a
part 514 of the medical device body 502 containing an SMP portion
in an installed shape holds the combination of the medical device
500, the cable member 506, and the bone 508 in spatial relation to
one another. Activation may continue, as described further herein,
through, for example, continued thermal activation (e.g.,
interaction with the surgical site), and/or continued constraint
provided by the wedge element 504. The wedge element 504 may be
adapted to continue to provide constraint(s) and/or trigger
force(s) due to its continued presence within the body 502 after
ceasing operation of the wedge element (e.g., through pull cord
518, through hammering the wedge element directly).
[0080] FIGS. 6A-6B are representations of an exemplary cylindrical
medical device 600 with a wedge element 604 through two exemplary
stages of activation of an SMP portion while in an unconstrained
environment (substantially free of constraints).
[0081] FIG. 6A shows the exemplary medical device 600 in a position
with stored strain in the device 606 and a wedge element 604
adapted to be coupled the body 602 of the device. The configuration
of the medical device 600 shown in FIG. 6A may be an exemplary
storage configuration of the device, such as a configuration in
which the device may be shipped or stored prior to use in
surgery.
[0082] FIG. 6B shows the exemplary medical device 600 in a position
with a partially activated part 608 of the medical device that has
recovered some or all of the stored strain 610, as described
further herein. The exemplary medical device 600 shown in FIG. 6B
may have been activated through both the operation of the wedge
element 604 and through another activation stimulus (e.g.,
temperature), thereby allowing the top portion of the medical
device to recover strain beyond the strain recovered through
activation caused by operation of the wedge element 604 alone.
[0083] The medical device 600 has been activated in an
unconstrained environment and allowed to change shape while
reaching force equilibria (e.g., substantially zero force,
gravitational force) with its environment that are different
equilibria than reached by a medical device that is activated
inside a surgical site. During activation in a constrained
environment, as described further herein and with respect to FIGS.
5A-5B, strains may remain in portions of the medical device due to
force equilibria met between the medical device and its environment
(e.g., cable member, bone) despite sufficient time for activation
to allow strain recovery to occur through the respective activation
rates of the portions of the medical device. During activation of
the medical device 600, different portions of the medical device
may have different respective activation rates, as described
further herein. In the configuration shown in FIG. 6B, stored
strains 610 may remain in portions apart from the top portion and
be recovered due to the different activation rates.
[0084] FIG. 7 shows an embodiment of a medical device 700 with a
compressive trigger element 704. The compressive trigger element
704 includes two end plates 706 situated on opposite ends of the
body 702 of the medical device 700. The end plates 706 are attached
through a pull cord 708 which is actuated by ratchet mechanism 710.
The ratchet mechanism 710 presses an end plate 706 against an end
of the body 702, while holding the pull cord 708 in relation to the
both end plates 706. The ratchet mechanism 710 may be used to
apply, as described further herein, a series of discreet
compressive constraints on the body 702 of the medical device 700
through pulling the pull cord 708. The ratchet mechanism 710 may be
used to apply leverage to the pull cord 708 and/or to latch the
pull cord, thereby aiding operation of the pull cord.
[0085] An SMP portion of the medical device 700 may be strained,
activated, and otherwise operated as described further herein. In
one embodiment, the medical device 700 may be inserted into a
surgical site with a stored strain that is adapted to be activated
by a trigger force as described further herein from the trigger
element 704.
[0086] In one embodiment, the medical device 700 may be used in a
surgery fixing a bone cavity and a cable member, as described
further herein. Portions of the trigger element 704 may be
configured to remain within the patient. For example, the pull cord
708 and/or either or both the end plates 706 may remain within the
patient with the medical device 700 in the surgical site. Other
portions of the medical device 700 and/or elements related to the
trigger element 704 (e.g., the ratchet mechanism 710) may be
configured to be removed from the surgical site during the surgical
procedure.
[0087] FIG. 8 shows another embodiment of a medical device 800 with
a compressive trigger element 804. The compressive trigger element
804 contains two end plates 806 situated on opposite ends of the
body 802 of the medical device 800. The end plates 806 are attached
to each other through a clamp mechanism 808 situated around the
body 802. The clamp mechanism 808 may actuate the end plates 806 to
apply a compressive constraint to the body 802 of the medical
device 800. The clamp mechanism 808 may be configured to apply
constraints to the body 802 continuously, discreetly, and/or a
combination thereof.
[0088] The medical device 800 may be used in a surgery fixing the
medical device and a cable member in relation to a bone cavity, as
described further herein. In one embodiment, the clamp mechanism
808 may be integrated with the medical device 800 and/or may remain
within the patient after the surgical procedure is complete. In
another embodiment, the clamp mechanism 808 may be removed from the
patient before the surgical procedure is complete. For example, the
clamp mechanism 808 may be configured to access the medical device
800 through two ends of a bone cavity, such as at either end of a
bone tunnel through the distal end of a patient's femur.
[0089] Other embodiments of devices may include devices that
utilize a stored twisting, bending, expansive and/or compressive
strain in an SMP portion, as described further herein. A trigger
force that activates the stored strain may allow the strain to
recover into a different (e.g., post-installation) shape, thereby
causing transformation of an associated medical device into an
installed configuration, as described further herein. The specific
devices described herein are examples of the broad range of
potential configurations of devices described herein through, for
example, the description of the operations of the materials of the
devices. Therefore, the description herein of devices and methods
should serve as illustrative examples from which teachings may be
drawn for further useful devices.
* * * * *