U.S. patent application number 15/430788 was filed with the patent office on 2017-06-29 for collapsible, shape memory alloy structures and folding fixtures with associated method for collapsing same.
The applicant listed for this patent is Medplate LifeSciences Corporation. Invention is credited to Michael D Black, Richard Thomas Briganti, Mike Y Chen, Rob K Rao.
Application Number | 20170182225 15/430788 |
Document ID | / |
Family ID | 49624277 |
Filed Date | 2017-06-29 |
United States Patent
Application |
20170182225 |
Kind Code |
A1 |
Rao; Rob K ; et al. |
June 29, 2017 |
COLLAPSIBLE, SHAPE MEMORY ALLOY STRUCTURES AND FOLDING FIXTURES
WITH ASSOCIATED METHOD FOR COLLAPSING SAME
Abstract
A shape memory alloy structure comprises at least one tubular
member formed of shape memory material, each tubular member
including a plurality of panels having side edges, wherein each
tubular member is moveable between a radially contracted position
and a radially extended position, and wherein the coupled side
edges of adjacent panels of each tubular member form hinges for
moving the structure between the contracted position and the
extended position. Multiple layer tubular structures, methods for
forming and fixtures for collapsing same are also disclosed.
Inventors: |
Rao; Rob K; (Moraga, CA)
; Briganti; Richard Thomas; (Philadelphia, PA) ;
Black; Michael D; (Palo Alto, CA) ; Chen; Mike Y;
(San Marino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Medplate LifeSciences Corporation |
Bridgeville |
PA |
US |
|
|
Family ID: |
49624277 |
Appl. No.: |
15/430788 |
Filed: |
February 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14550636 |
Nov 21, 2014 |
9622885 |
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15430788 |
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PCT/US13/41943 |
May 21, 2013 |
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14550636 |
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61649431 |
May 21, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 35/0222 20130101;
B32B 7/05 20190101; A61F 2230/0069 20130101; A61L 27/04 20130101;
C22C 19/03 20130101; B32B 2307/718 20130101; C22C 19/058 20130101;
A61F 2210/0014 20130101; B32B 1/08 20130101; A61L 2400/16 20130101;
A61L 31/022 20130101; B23K 35/0255 20130101; A61F 2/2418 20130101;
A61F 2/82 20130101; C22C 27/02 20130101; B23K 35/32 20130101; B32B
15/01 20130101; A61F 2/07 20130101; A61F 2/2412 20130101; A61L
31/14 20130101; B32B 2535/00 20130101 |
International
Class: |
A61L 31/02 20060101
A61L031/02; A61F 2/24 20060101 A61F002/24; B32B 1/08 20060101
B32B001/08; A61L 31/14 20060101 A61L031/14; B32B 15/01 20060101
B32B015/01; B23K 35/02 20060101 B23K035/02; B23K 35/32 20060101
B23K035/32; A61F 2/82 20060101 A61F002/82; B32B 7/04 20060101
B32B007/04 |
Claims
1. An shape memory alloy structure extending along a longitudinal
axis and having a radially retracted state and a deployed state,
said structure comprising a tubular member including a plurality of
substantially solid, concave outer surface panels forming the
tubular member circumference, each panel coupled to two adjacent
panels on opposed sides at peak portions at radially outermost
portions of the tubular member in the deployed state, and wherein
each panel extends substantially parallel to the prosthesis's
longitudinal axis, and wherein the retracted state has the panels
and the peak portions of the tubular member positioned radially
inwardly of their respective positions in the deployed state and
the retracted state has each panel bending about an axis parallel
to the longitudinal axis forming generally greater outer surface
concavity than in the deployed state, whereby a substantially tight
serpentine structure is formed by the panels and peaks in the
retracted state.
2. The shape memory alloy structure according to claim 1 wherein
the shape memory alloy is a nitinol structure and wherein the
effective outer diameter of the structure in the radially retracted
state is less than about 6 mm.
3. A shape memory alloy structure comprising at least one tubular
members formed of shape memory alloy and formed of a plurality of
substantially solid scalloped panels separated by peaks, wherein
the structure is moveable between a radially contracted position
and a radially extended position, wherein the effective outer
diameter of the structure in the radially extended position is at
least 3.5 times the effective outer diameter of the structure in
the radially contracted position.
4. The shape memory alloy structure according to claim 3 wherein
the effective outer diameter of the structure in the radially
contracted position is less than about 6 mm.
5. The shape memory alloy structure according to claim 3 wherein
the shape memory alloy is a nitinol structure.
6. The shape memory alloy structure according to claim 3 wherein
the structure is a prosthetic cardiovascular stent.
7. A method of compacting a collapsible shape memory alloy
structure comprising the steps of (a) providing a folding fixture
with a body member having an inlet opening of a first diameter at
one end thereof and a smaller diameter outlet at an opposite end
thereof and a converging surface extending between the inlet
opening and the outlet opening; and (b) passing the collapsible
shape memory alloy structure entirely through the inlet opening and
the outlet opening of the folding fixture.
8. The method of compacting a collapsible shape memory alloy
structure according to claim 7 wherein the passing of the
collapsible shape memory alloy structure through the entirely
through the inlet opening and the outlet opening of the folding
fixture is manual.
9. The method of compacting a collapsible shape memory alloy
structure according to claim 8 including the step of (c) providing
a second folding fixture with a body member having an inlet opening
of a first diameter at one end thereof and a smaller diameter
outlet at an opposite end thereof and a converging surface
extending between the inlet opening and the outlet opening, wherein
the second folding fixture is received within the first folding
fixture.
10. The method of compacting a collapsible shape memory alloy
structure according to claim 9 wherein the second folding fixture
is received within the outlet opening of the first folding fixture,
and wherein the passing of the collapsible shape memory alloy
structure entirely through the inlet opening and the outlet opening
of the first folding fixture will pass the collapsible shape memory
alloy structure entirely through the inlet opening and the outlet
opening of the second folding fixture.
11. The method of compacting a collapsible shape memory alloy
structure according to claim 7 further including a holding fixture
wherein the folding fixture is received within the holding fixture
during the passing of the collapsible shape memory alloy structure
entirely through the inlet opening and the outlet opening of the
folding fixture.
12. The method of compacting a collapsible shape memory alloy
structure according to claim 11 wherein the holding fixture
includes a holding pin configured to support the collapsible shape
memory alloy structure.
13. The method of compacting a collapsible shape memory alloy
structure according to claim 12 further including a slot within the
folding fixture configured to receive the holding pin during the
passing of the collapsible shape memory alloy structure entirely
through the inlet opening and the outlet opening of the folding
fixture.
14. The method of compacting a collapsible shape memory alloy
structure according to claim 7 wherein the shape memory alloy
structure includes at least one tubular member formed of shape
memory alloy, each tubular member formed of a plurality of concave
panels wherein circumferentially adjacent panels are coupled at
substantial tangential portions of each circumferentially adjacent
panels, and wherein these coupled edges form hinges for movement of
the shape memory alloy structure between a contracted position and
a radially extended position.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of patent application
Ser. No. 14/550,636 filed Nov. 21, 2014 and published as
publication number 2015/0148886 on May 28, 2015, which publication
is incorporated herein by reference. Patent application Ser. No.
14/550,636 is a continuation of international patent application
serial number PCT/US2013/041943 filed May 21, 2013 which is
incorporated herein by reference and which designated the United
States and is entitled "Collapsible, Shape Memory Alloy Structures
and Folding Fixtures for Collapsing Same." International patent
application serial number PCT/US2013/041943 claims priority to
United States provisional patent application Ser. No. 61/649,431
filed May 21, 2012, entitled "Collapsible, Shape Memory Alloy
Structures and Method for Forming Same" which prior applications
are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to collapsible shape memory
alloy structures, and more particularly to lightweight or low
profile, collapsible, shape memory alloy structures and method for
forming same. Such collapsible, shape memory alloy structures may
be formed as cardiovascular stents, cardiovascular valves, filters,
closure devices, drug delivery devices, pumps or stents for any
lumen or tissue in or outside of the body, or even an electronic
component.
[0004] 2. BACKGROUND INFORMATION
[0005] Materials combining ultra-low density with the desirable
characteristics of metals have been under technical development for
decades, and a variety of metals and alloys are commercially
available in various cellular forms. Cellular structures made from
shape-memory alloys (SMAs), most commonly nitinol, are particularly
intriguing for their potential to deliver shape memory and/or
superelasticity in a lightweight material. Shape memory refers to
the ability of SMA to undergo deformation at one temperature, then
recover its original, un-deformed shape upon heating above its
"transformation temperature." Superelasticity occurs at a narrow
temperature range just above its transformation temperature; in
this case, no heating is necessary to cause the undeformed shape to
recover, and the material exhibits enormous elasticity, some 10-30
times that of ordinary metal.
[0006] Over 20 years ago a survey focused on predicting the then
future technology, market, and applications of SMA's. The companies
predicted the following uses of nitinol in a decreasing order of
importance: (1) Couplings, (2) Biomedical and medical, (3) Toys,
demonstration, novelty items, (4) Actuators, (5) Heat Engines, (6)
Sensors, (7) Cryogenically activated die and bubble memory sockets,
and finally (8) lifting devices. Many of these applications have
come to pass. One significant application of nitinol in medicine is
in stents because a collapsed stent can be inserted into a vein and
return to its original expanded shape helping to improve blood
flow. The biocompatibility of nitinol has made it essentially a
material of choice in biomedical device developments. Nitinol is
known in a variety of other common applications such as extremely
resilient glasses frames, some mechanical watch springs,
retractable cell phone antennas, microphone booms, due to its
highly flexible & mechanical memory nature.
[0007] Some methods of forming SMA structures are described in U.S.
Pat. No. 7,896,222 which is incorporated herein by reference and
relates to a transient-liquid reactive brazing method that allows
the fabrication of low density metal alloy structures, such as
cellular or honeycomb structures, wire/tube space-frames, or other
sparse built-up structures using nitinol (near-equiatomic
titanium-nickel alloy) or related shape-memory and superelastic
alloys, or high temperature SMAs, such as NiTi X alloys, wherein X
is Hf or Zr substituted for Ti and/or X is Cu, Pd, Pt and/or Au
substituted for Ni, e.g., NiTiCu or TiNiPd. More particularly,
shape memory alloys (SMAs), in forms such as corrugated sheets,
discrete tubes, wires, or other SMA shapes are joined together
using a transient-liquid reactive metal joining technique, wherein
a brazing metal contacts an SMA, like nitinol, at an elevated
temperature. The brazing metal, preferably niobium, liquefies at a
temperature below the melting point of both the brazing metal and
the SMA, and readily flows into capillary spaces between the
elements to be joined, thus forming a strong joint. In this method,
no flux is required and the joined structures are biocompatible.
See also U.S. Pat. Nos. 8,273,194 and 8,465,847 which are
incorporated herein by reference and which disclose methods of
manufacture of shape-memory alloy cellular materials and structures
by transient-liquid reactive joining.
[0008] U.S. Publication 2009-0149941, which is incorporated herein
by reference, is directed to a compressed tubular tissue support
structure that can easily be introduced into vessels requiring
support. This reference notes that in medical fields the
"Introduction of a stent into a hollow organ is difficult When the
stent is introduced into the hollow organ there is a risk that the
surrounding tissue will be injured by abrasion in the process,
because the stent is too large and has sharp edges. The
shape-memory effect is therefore also used again to reduce the
diameter of the stent when the stent is in turn to be removed.
Examples of removable stents composed of metals with shape-memory
properties are known, for example, in: U.S. Pat. Nos. 6,413,273;
6,348,067; 5,037,427; and 5,197,978"; and these patents are
incorporated herein by reference. U.S. Pat. Nos. 5,716,410,
5,964,744, 6,245,103 and 6,475,234 and WIPO documents WO
2002/041929, WO 2003/099165, WO 2004/010901, and WO 2005/044330 are
also discussed as relevant disclosure of SMA stent designs and
these patents and documents are incorporated herein by
reference.
[0009] There remains a need to expand the available lightweight,
collapsible, shape memory alloy structures for applications in
numerous fields.
SUMMARY OF THE INVENTION
[0010] One aspect of the present invention provides a shape memory
alloy structure that may include at least two layers formed of
shape memory material. Each layer is formed with a plurality of
panels having side edges, wherein at least some of the adjacent
layers are coupled together at selected edges of adjacent panels.
The structure is moveable between a contracted position and an
extended position and wherein the coupled edges may form hinges for
moving the structure between the contracted position and the
extended position. The edges of the panels are referenced as hinges
in that, as described below, the panels move to a contracted
position effectively relative to edges that comprise the relatively
unbendable part of the structure, similar to a hinge pin. In the
present design, as described below these edges are essentially the
stiff joints and the "bearing" surfaces for crimping and later
outer diameter support of whatever may encloses it the
structure.
[0011] The invention provides a shape memory alloy structure
including at least one tubular member formed of shape memory
material. Each tubular member includes a plurality of panels having
side edges, wherein each tubular member is moveable between a
radially contracted position and a radially extended position. The
coupled side edges of adjacent panels of each tubular member form
hinges for moving the structure between the contracted position and
the extended position.
[0012] The invention also provides a shape memory alloy structure
comprising at least one tubular member formed of shape memory
alloy, each tubular member formed of a plurality of concave panels
wherein circumferentially adjacent panels are coupled at
substantial tangential portions of each circumferentially adjacent
panels, and wherein each tubular member is formed for movement of
the shape memory alloy structure between a contracted position and
a radially extended position.
[0013] The invention also provides a shape memory alloy structure
comprising at least two substantially concentric tubular members
formed of shape memory alloy. Each tubular member is formed of a
plurality of scalloped panels separated by peaks. At least some of
the peaks of at least one concentrically inner of the tubular
members are aligned with adjacent peaks of the immediately
outwardly adjacent tubular member.
[0014] The invention provides a shape memory alloy structure
including at least one tubular member formed of shape memory alloy
and formed of a plurality of substantially solid scalloped panels
separated by peaks. The structure is moveable between a radially
contracted position and a radially extended position, wherein the
effective outer diameter of the structure in the radially extended
position is at least 3.5 times the effective outer diameter of the
structure in the radially contracted position.
[0015] The invention provides a method of compacting a collapsible
shape memory alloy structure comprising the steps of (a) providing
a folding fixture with a body member having an inlet opening of a
first diameter at one end thereof and a smaller diameter outlet at
an opposite end thereof and a converging surface extending between
the inlet opening and the outlet opening; and (b) passing the
collapsible shape memory alloy structure entirely through the inlet
opening and the outlet opening of the folding fixture.
[0016] The invention provides a method of manually compacting a
collapsible shape memory alloy structure comprising the steps of
(a) providing a folding fixture with a strap; (b) looping the strap
about the perimeter of the collapsible shape memory alloy
structure; manually tightening the strap about the perimeter of the
collapsible shape memory alloy structure.
[0017] The invention provides a method of compacting a collapsible
shape memory alloy structure, comprising the steps of (a) providing
a shape memory alloy structure which includes at least one tubular
member formed of shape memory alloy, each tubular member formed of
a plurality of concave panels wherein circumferentially adjacent
panels are coupled at hinges for movement of the shape memory alloy
structure between a contracted position and a radially extended
position; (b) providing a folding fixture having a plurality of
radially moveable pins; (c) engaging the pins with the panels of
the shape memory alloy structure; (d) moving the pins radially
inwardly while in contact with the panels of the shape memory alloy
structure to compact the shape memory alloy structure.
[0018] The invention provides a shape memory alloy structure
extending along a longitudinal axis and having a retracted state
and a deployed state. The structure includes a tubular member
including a plurality of substantially solid, concave outer surface
panels forming the tubular member circumference. Each panel is
coupled to two adjacent panels on opposed sides at peak portions at
radially outermost portions of the tubular member in the deployed
state. Each panel extends substantially parallel to the
prosthesis's longitudinal axis, and wherein the retracted state has
the panels and the peak portions of the tubular member positioned
radially inwardly of their respective positions in the deployed
state and the retracted state has each panel bending about an axis
parallel to the longitudinal axis forming generally greater outer
surface concavity than in the deployed state, whereby a
substantially tight serpentine structure is formed by the panels
and peaks in the retracted state.
[0019] The invention provides a shape memory alloy structure
extending along a longitudinal axis and having a retracted state
and a deployed state, said structure comprising: an outer tubular
member including a plurality of substantially solid, concave outer
surface panels forming the tubular member circumference, each panel
coupled to two adjacent panels on opposed sides at peak portions at
radially outermost portions of the tubular member in the deployed
state, and wherein each panel extends substantially parallel to the
prosthesis's longitudinal axis; and an inner tubular member
including a plurality of substantially solid convex inner surface
panels forming the circumference of the inner tubular member, each
panel coupled to two adjacent panels on opposed sides at peak
portions at radially outermost portions of the tubular member in
the deployed state, and wherein each panel extends substantially
parallel to the prosthesis's longitudinal axis; and wherein the
inner tubular member peaks are coupled to the outer tubular member
peaks, and wherein central portions of the inner tubular member
panels are spaced from the central portions of the outer tubular
member panels.
[0020] It is noted that, as used in this specification and the
appended claims, the singular forms "a," "an," and "the" include
plural referents unless expressly and unequivocally limited to one
referent. The features that characterize the present invention are
pointed out with particularity in the claims which are part of this
disclosure. These and other features of the invention, its
operating advantages and the specific objects obtained by its use
will be more fully understood from the following detailed
description and the operating examples. These and other advantages
of the present invention will be clarified in the brief description
of the preferred embodiment taken together with the drawings in
which like reference numerals represent like elements
throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1A and 1B are perspective views of a lightweight,
collapsible, shape memory alloy structure in the form of a
collapsible lumen in accordance with one embodiment of the present
invention;
[0022] FIG. 2 is a graphical schematic representation of the
collapse and expanded states of the lightweight, collapsible, shape
memory alloy structure of FIGS. 1A and 1B;
[0023] FIG. 3A is a perspective view of one layer of the
lightweight, collapsible, shape memory alloy structure of FIGS. 1A
and 1B;
[0024] FIG. 3B is a schematic side elevation view of the layer of
FIG. 3A;
[0025] FIG. 3C is a schematic end view of the layer of FIG. 3A;
[0026] FIG. 3D is an enlarged schematic end view of
circumferentially adjacent scalloped panels of the layer of FIG.
3A;
[0027] FIG. 3E is an enlarged schematic end view of coupling of
ends of the layer of FIG. 3A to form the collapsible lumen;
[0028] FIG. 4A is a perspective view of the second layer of the
lightweight, collapsible, shape memory alloy structure of FIGS. 1A
and 1B;
[0029] FIG. 4B is a schematic side elevation view of the layer of
FIG. 4A;
[0030] FIG. 4C is a schematic end view of the layer of FIG. 4A;
[0031] FIG. 4D is an enlarged schematic end view of
circumferentially adjacent scalloped panels of the layer of FIG.
4A;
[0032] FIG. 4E is an enlarged schematic end view of coupling of
ends of the layer of FIG. 4A to form the lumen;
[0033] FIG. 5 is a plan view of a shape memory alloy sheet used to
form each of the layers of the lightweight, collapsible, shape
memory alloy structure of FIGS. 1A and 1B;
[0034] FIG. 6A is an exploded view of a formation fixture for
forming each layer of the lightweight, collapsible, shape memory
alloy structure of FIGS. 1A and 1B;
[0035] FIG. 6B is a sectional schematic view of the formation
fixture of FIG. 6A for forming each layer of the lightweight,
collapsible, shape memory alloy structure of FIGS. 1A and 1B;
[0036] FIG. 6C is a perspective schematic view of an alternative
formation fixture for forming each layer of the lightweight,
collapsible, shape memory alloy structure of FIGS. 1A and 1B, and
FIG. 6D is a sectional schematic view of a brazing fixture for
completing the brazing attachment of the layers of the lightweight,
collapsible, shape memory alloy structure of FIGS. 1A and 1B;
[0037] FIG. 7A is a perspective view of an alternative lightweight,
collapsible, shape memory alloy structure in accordance with
another embodiment of the invention;
[0038] FIG. 7B is a schematic end view of the lightweight,
collapsible, shape memory alloy structure of FIG. 7A;
[0039] FIG. 7C is a schematic side elevation view of the
lightweight, collapsible, shape memory alloy structure of FIG.
7A;
[0040] FIG. 7D is an enlarged schematic end view of
circumferentially adjacent scalloped panels of the lightweight,
collapsible, shape memory alloy structure of FIG. 7A;
[0041] FIG. 8 is a perspective view of a heart valve formed with
the lightweight, collapsible, shape memory alloy structure
according to the present invention;
[0042] FIGS. 9A and 9B are partial section views of a folding
fixture for collapsing a lightweight, collapsible, shape memory
alloy structure according to the present invention;
[0043] FIGS. 10A-D are partial section views of a further folding
fixture for collapsing a lightweight, collapsible, shape memory
alloy structure according to the present invention;
[0044] FIGS. 11A and 11B are partial section views of a further
folding fixture for collapsing a lightweight, collapsible, shape
memory alloy structure according to the present invention;
[0045] FIGS. 12A-12E are partial section views of a further folding
fixture for collapsing a lightweight, collapsible, shape memory
alloy structure according to the present invention;
[0046] FIGS. 13A and 13B are perspective views of further folding
fixtures for collapsing a lightweight, collapsible, shape memory
alloy structure according to the present invention; and
[0047] FIG. 14 is a response curve illustrating the pressure
exerted over a range of outer diameter sized for a lightweight,
collapsible, shape memory alloy structure formed according to the
present invention.
DESCRIPTION OF THE PREFFERED EMBODIMENTS
[0048] The present invention provides a shape memory alloy
structure 10 that may include at least two layers 20 and 30 formed
of shape memory material, such as NiTI-based alloys including
nitinol. As described in further detail herein the structure 10 can
have numerous applications. FIGS. 1A and 1B perspective views of a
lightweight, collapsible, shape memory alloy structure 10 in the
form of a collapsible lumen that can form for example a medical
stent in accordance with one embodiment of the present invention.
Other configurations and applications are possible without
departing from the scope of the present invention and only a few
representative examples will be discussed herein.
[0049] The collapsible lumen of structure 10 of FIGS. 1A and B is
helpful to illustrate the particulars of the present invention. The
phrase collapsible is used herein to reference a change in shape of
the alloy structure 10 typically to accommodate the application or
deployment of the structure 10 to its operative location. It is
anticipated that the operative condition of the structure 10 may in
some applications actually be the retracted position, such as for
example where the alloy structure 10 is a lumen designed to
approximate valve leaflets towards a closed position, thus the term
collapsible is not intended to define the operative condition of
the structure 10. As described in detail below one advantageous
property of the lumen or tubular shaped structure 10 is that it
moved between the retracted or collapsed stated and the expanded
state without changing length. This feature increases the ability
of the users to precisely place the structure 10, such as when
formed as a stent or valve in medical application or a filter
support in remote placement applications, into its operational
position as will become more apparent in the following
description.
[0050] As noted the structure 10 of FIGS. 1A and B includes two
layers 20 and 30, an inner layer 30 and an outer layer 20. Each
layer 20 and 30 is formed with the structure in the expanded
position as shown in FIGS. 1A and B as including a plurality of
concave or scalloped panels 22 and 32 each having side edges
forming peaks 24 and 34. The phrase "side edges" is not intended to
set forth a sharp "edge" but merely the lateral ends of the panel
22 or 32 on either side thereof, as in practice there is a blending
of the radii as the surface moves from the panel 22 or 32 to the
relatively sharp radii of "convex" peaks 24 and 34.
[0051] The present invention provides that at least some, if there
are more than two layers 20 and 30 in structure 10, of the adjacent
layers 20 and 30 are coupled together via a filler material such as
a niobium (Nb) metal, at selected edges of adjacent panels. The
filler material may be a niobium braze material such as disclosed
in U.S. Pat. No. 7,896,222, which is incorporated herein by
reference. As further detailed in the '222 patent niobium based
braze material may be implemented as a liquid reactive braze
material, for fabrication of "cellular" or "honeycomb structures",
wire space-frames or other "sparse" built up structures or discrete
articles using Nitinol and related shape-memory and super-elastic
alloys. The braze process is properly summarized as a reactive
eutectic brazing process using Nb as a melting point depressant for
nitinol. The Niobium brazing material when brought into contact
with Nitinol at elevated temperature, liquefies at temperatures
below the melting point and flows readily into capillary spaces
between the elements to be joined, thus forming a strong joint.
This Niobium based brazing material, such as pure niobium and
niobium alloys, and the associated coupling techniques are well
suited for coupling the layers 20 and 30 of the structure 10 at
adjacent peaks 34 and 24.
[0052] Regarding the Niobium containing brazing material and
associated brazing methods see also U.S. Patent publication numbers
2011/0009979, 2011/0008643, and 2008/0290141 which are incorporated
herein by reference. Regarding general background for similar
couplings see also "Transient Liquid Phase Bonding", MacDonald et
al., 1992, Annu. Rev. Mater. Sci. 22:23-46; "Transient Liquid Phase
(TLP) Diffusion Bonding of a Copper Shape Memory Alloy Using Silver
as Interlayer", DeSalazar et al., Scripta Materialia, vol. 37, No.
6, pp. 861-867, 1997. It is noted, however, that the title of these
articles may be somewhat misleading as to the present process
described in U.S. Patent publication numbers 2011/0009979,
2011/0008643, and 2008/0290141, wherein the braze process is
properly summarized as a reactive eutectic brazing process using Nb
as a melting point depressant for nitinol, and not a "transient
liquid" bonding process as the term "transient liquid" is sometimes
used.
[0053] The joining technique using niobium based filler for
coupling peaks 24 and 34 may be a "spot-welding" technique for the
shape-memory alloy layers 20 and 30 using conventional
resistance-welding techniques. For example, a thin foil of pure
niobium is placed between the peaks 24 and 34 to be joined.
Thereafter, under appropriate clamping pressure, an electrical
current pulse is passed through the coupled peaks 24 and 34 with
sufficient intensity to cause transient melting. The spot welding
technique can be used to hold complex structures together prior to
the full brazing process described herein to avoid the necessity to
use elaborate fixtures or jigs. A schematic brazing fixture is
discussed in connection with FIG. 6D which can assist in the
process allowing all couplings to be made at once.
[0054] The adhering process using niobium based filler can include
metal-inert gas (MIG) welding of shape-memory alloys of the peaks
24 and 34 wherein, for example, a pure niobium welding wire is fed
into the welding arc which is shielded by an appropriate flow of
inert gas. The same principles of flux-less processing, eutectic
liquid formation, and the formation of ductile, biocompatible
solidification products associated with the Niobium brazing process
applies to this MIG method of joining layers 20 and 30.
[0055] For small scale structures 10, such as used for medical
stents and valves, the filler metal, such as niobium and niobium
alloys, may sputtered onto at least some of the edges or peaks 24
and 34 to allow for thin film application associated with these
applications. It will likely be applied to only one of the two
surfaces to be joined, whichever presents the easier application
surface. Sputtering is a preferred method for placing niobium when
the amount needed is less than can be provided by a wrought niobium
foil. The method of forming the shape memory alloy structure 10 may
further provide that the sputtering step of applying niobium to the
selected edges or peaks 24 and 34 of the layers 20 and 30 includes
the use of mask members to control the application of the niobium
filler material to only the designated desired area. In essence
such masks will cover those areas of the layer 20 or 30 not to be
sputtered with the filler material. Other methods of filler
material application include vacuum evaporation, plasma deposition
or kinetic spray techniques, some of which may prove to be
particularly efficient and cost effective.
[0056] The filler material as discussed above may be referenced as
a brazing material a welding material or even a soldering material.
Preferably the filler material is pure niobium or niobium alloyed
with any metal capable of forming an alloy with niobium. Niobium
composite structures are also possible with multilayer foils.
[0057] Returning to the FIG. 1A and B, the structure 10 is moveable
between a contracted position shown schematically in FIG. 2 and an
extended position shown in FIG. 1A and B wherein the coupled edges
or peaks 34 and 24 essentially form hinges as shown for moving the
structure 10 between the contracted position and the extended
position. As noted FIG. 2 is a graphical schematic representation
of the collapse and expanded states of the structure 10 of FIGS. 1A
and 1B. The scalloped panels 22 and 32 and the peaks 24 and 34
allow for the unique compaction demonstrated in FIG. 2. This
collapsing design as shown allows for a wide variety of
expanding/contracting structures to be designed, including wherein
the structure 10 is moveable between a radially contracted position
and a radially extended position, wherein the effective outer
diameter of the structure in the radially extended position is at
least twice, at least three times, at least three and one half
times or even 3.8 times in the example shown, of the effective
outer diameter of the structure in the radially contracted
position. Thus for example the effective outer diameter of the
structure 10 in the radially contracted position as shown is less
than about 6 mm, allowing for the structure to effectively form
medical devices such as inner lumen delivered stents and valves in
medical applications.
[0058] Turning to FIGS. 3A-E, FIG. 3A is a perspective view of one
layer 30, the inner layer 30, of the lightweight, collapsible,
shape memory alloy structure 10 of FIGS. 1A and 1B. As noted above
more than two layers 20 or 30 can be used to form the structure 10.
FIG. 3B is a schematic side elevation view of the layer 30 of FIG.
3A; while FIG. 3C is a schematic end view of the layer 30 of FIG.
3A showing the undulating scalloped pattern of panels 32 and peaks
34. FIG. 30 is an enlarged schematic end view of circumferentially
adjacent scalloped panels 32 of the layer 30 with intermediate
peaks 34. The layer 30 is formed of a shape memory alloy as noted
such as a sheet 40 of nitinol shown in FIG. 5. FIG. 5 is a plan or
top view of a shape memory alloy sheet 40, such as a NiTi-alloy
sheet used to form each of the layers 20 and 30 of the lightweight,
collapsible, shape memory alloy structure 10 of FIGS. 1A and
1B.
[0059] When formed into the undulating shape with scalloped panels
32 and peaks 34 the ends 36 of the sheet 40 will overlap at some
section and the overlapping ends 36 can be coupled together in the
same fashion as the adjacent aligned peaks 34 and 24 discussed
above. FIG. 3E is an enlarged schematic end view of coupling of
overlapped ends 36 of the layer 30 of FIG. 3A to form the lumen
layer 30 for the structure 10. As discussed above, a niobium filler
material such as in a braze material can couple ends 36. The length
of overlap of ends 36 may be minimized, or may alternatively be
positioned on a panel 32. However the peak 34 placement of the
overlapped ends 36 may assist in securing the ends 36 together
throughout operation of the structure 10. An alternative
configuration is to align the ends 36 next to each other and butt
weld (with Niobium based welding material, for example) the edges
of these ends 36 to avoid a double thickness portion, but the
overlapped ends 36 as shown is generally believed to be more easily
manufactured.
[0060] Turning to FIGS. 4A-E, which are analogous to FIGS. 3A-E,
FIG. 4A is a perspective view of one layer 20, the outer layer 20,
of the lightweight, collapsible, shape memory alloy structure 10 of
FIGS. 1A and 1B. More than two layers 20 or 30 can be used to form
the structure 10, and in an alternative configuration only a single
layer 20 or 30 may form the structure. FIG. 4B is a schematic side
elevation view of the layer 20 of FIG. 4A; while FIG. 4C is a
schematic end view of the layer 20 of FIG. 4A showing the
undulating scalloped pattern of panels 22 and peaks 24. FIG. 40 is
an enlarged schematic end view of circumferentially adjacent
scalloped panels 22 of the layer 20 with intermediate peaks 24. The
layer 20 is formed of a shape memory alloy as noted such as the
sheet 40 of nitinol shown in FIG. 5. When formed into the
undulating shape with scalloped panels 22 and peaks 24 the ends 26
of the sheet 40 will overlap as shown in FIG. 4E at some section
and the overlapping ends 26 can be coupled together in the same
fashion as ends 36 discussed above.
[0061] FIG. 6A is an exploded view of a formation fixture for
forming each layer 20 or 30 of the lightweight, collapsible, shape
memory alloy structure 10 of FIGS. 1A and 1B from the individual
NiTi sheets 40 of FIG. 5. FIG. 6B is a sectional schematic view of
the formation fixture of FIG. 6A. As shown a simple formation
fixture can include an annular base 52 receiving a plurality of
outer dies or molds or bending forms 54 that have an inner surface
matching the desired shape of the panels 32 or 22 and peaks 24 or
34 of layers 20 or 30. The forms 54 surround a core 56 having an
outer surface matching the desired shape of the panels 32 or 22 and
peaks 24 or 34 of layers 20 or 30. The forms 54 includes alignment
holes 59 therein that will align with holes 57 in core for receipt
of aligning pins or bolts 58. The threading of holes 57 allows the
bolts 58 to be tightened to clamp down on an intervening sheet 40.
Placing sheet 40 into the fixture of FIGS. 6A and 6B allows the
sheet 40 to be formed in the desired configuration shown for layers
20 and 30. Heat treating of the sheet in fixture 40 may be used to
set the shape of the shape memory alloy as known to those of
ordinary skill in the art.
[0062] FIG. 6C is perspective view of a formation fixture for
forming each layer 20 or 30 of the lightweight, collapsible, shape
memory alloy structure 10 of FIGS. 1A and 1B from the individual
NiTi sheets 40 of FIG. 5. The concept is somewhat similar to the
formation fixture of FIGS. 6A and B. As shown a simple formation
fixture can include a plurality of outer dies or molds or bending
forms 54 that have an inner surface matching the desired shape of
the panels 32 or 22 and peaks 24 or 34 of layers 20 or 30. The
forms 54 surround a core 56 having an outer surface matching the
desired shape of the panels 32 or 22 and peaks 24 or 34 of layers
20 or 30. The forms 54 includes alignment holes (analogous to holes
59 above) generally on opposed sides of the sheets 40 in the
fixture, and the holes in forms 54 will align with holes (analogous
to holes 57 above) in core 56 for receipt of aligning pins or bolts
58. The threading of holes in core 56 allows the bolts 58 to be
tightened to clamp down on an intervening sheet 40. Placing sheet
40 into the fixture of FIG. 6C, like FIGS. 6A and 6B, allows the
sheet 40 to be formed in the desired configuration shown for layers
20 and 30. Heat treating of the sheet in fixture 40 may be used to
set the shape of the shape memory alloy as known to those of
ordinary skill in the art.
[0063] FIG. 6D is section schematic view of a brazing furnace
fixture for forming the lightweight, collapsible, shape memory
alloy structure 10 of FIGS. 1A and 1B from the individual NiTi
layers 30 and 20. The furnace fixture concept of FIG. 6D is
somewhat similar to the formation fixture of FIG. 6C. As shown a
brazing fixture can include a plurality of outer clamping member
forms 154 that have an inner surface matching the desired shape
peaks 24 and 34 of layers 20 and 30, with open recesses 153 aligned
with panels 22 and 32 of layers 20 and 30. The forms 154 surround a
core 156 having an outer surface matching the desired shape peaks
24 and 34 of layers 20 and 30, with open recesses 157 aligned with
panels 22 and 32 of layers 20 and 30. The forms 154 and core 156
may be bolted together in the same manner as the fixtures of FIGS.
6A-C.
[0064] Placing layers 20 and 30 into the fixture of FIG. 6D with
the brazing material located at the peaks 24 and 34 and placing the
fixture into an associated furnace allows the brazing to be
completed to form the structure 10. The furnace fixture as shown
would be made out of material appropriate for withstanding furnace
application for completing the brazing. In short the furnace
fixture of FIG. 6D will clamp the peaks 24 and 34 together for the
brazing operation while the recesses 153 and 157 accommodate and
are spaced from the panels 32 and 22. It may be desirable to have
the fixture fabricated primarily from Tungsten, Molybdenum,
Inconel, or possibly Nitinol itself. Additionally portions that are
non-contact elements may be made from stainless steel. As shown the
clamping fixture effectively limits contact to that along the
single braze lines at the peaks 22 and 34 and may further be
longitudinally limited to only the last 10% or so on each side
(i.e. ends of the fixture). The "furnace fixture" of FIG. 6D could
also possibly serve as an electrical spot welding fixture with the
inclusion onto the surfaces of the forms 154 and core 156 of
electrical couplings or leads 158 that, because of the recesses 153
and 157 will contact only the layers 20 and 30 and only at the
desired brazing lines at the peaks 24 and 34.
[0065] Placing layers 20 and 30 into the spot welding fixture with
the brazing material located at the peaks 24 and 34 allows the
brazing to be completed to form the structure 10, whereby, under
appropriate clamping pressure, an electrical current pulse is
passed through the coupled peaks 24 and 34 with sufficient
intensity to cause desired melting.
[0066] The radii at peaks 24 and 34 and the other radii forming
panels 22 and 32 are blended to form a continuous curvature. The
peaks 24 and 34 are generally formed with minimal radii as
reasonable while the various radii of the panels 32 and 22 depend
upon the desired number of panels 22 and 32, the desired size of
the inner lumen formed by panel 32 and the desired size of the
channels formed between the panels 22 and 32 and the diameter of
the contracted position with a given size for the nitinol forming
each layer 20 or 30. The response characteristics desired can also
be used in the design for selecting particular radii. The
illustrated structures 10 are intended to be representative and not
restrictive or limiting of the relative shapes of the panels and
peaks of layers 20 and 30.
[0067] FIGS. 7A-D illustrates an alternative lightweight,
collapsible, shape memory alloy structure 10 in accordance with
another embodiment of the invention. FIG. 7A is a schematic
perspective view of the lightweight, collapsible, shape memory
alloy structure 10; FIG. 7B is a schematic end view of the
structure 10; FIG. 7C is a schematic side elevation view the
structure 10 and FIG. 70 is an enlarged schematic end view of
circumferentially adjacent scalloped panels 22 and 32 of the
lightweight, collapsible, shape memory alloy structure 10 of FIG.
7A. The difference in these figures from earlier described
embodiments is the elimination of the filler material, such as the
niobium braze, coupling the layers 30 and 20. In this embodiment
the peaks 24 includes openings 28 that receive corresponding leaves
38 of aligned peak 34 that can receive an interlocking pin 39 to
couple the adjacent layers 20 and 30 at peaks 24 and 34. This
embodiment is to illustrate alternative "braze-less" coupling
techniques for layers 20 and 30. Alternative mechanical couplings
can be implemented.
[0068] The tubular multilayer structure 10 shown in FIGS. 1A-B can
be used in a variety of applications. For example structure 10 is
effective, essentially as shown, as a biomedical stent. In the
medical field a stent is an artificial `tube` inserted into a
natural lumen or passage or conduit in the body to prevent, or
counteract, a localized flow constriction. The term can also refer
to a tube used to temporarily hold such a natural lumen open or to
create a lumen or passage to allow access for surgery, in other
words to act as a tubular retractor or conduit for medical
procedures (and similar devices are used in non-medical
procedures).
[0069] The structure 10 of the present invention has exceptional
response curve shown in FIG. 14, namely a "flatter" response over
radial constriction that can allow a single size structure to be
utilized over a wider range of applicable lumen sizes than prior
art stent designs. In other words a more constant radial force is
exhibited over a wider deformation than can be found in prior art
stent designs. This advantageous result is believed to also be
present to a lesser degree with only a single layer 20 or 30. The
multi-layer structure as shown increases this advantageous
characteristic.
[0070] FIG. 14 is a graph of a response curve illustrating the
pressure exerted by a structure 10 over a range of outer diameter
sized for a lightweight, collapsible, shape memory alloy structure
10 formed according to the present invention as a 23 mm outer
diameter structure 10 formed as the device shown in FIG. 1A. The
graph illustrates a fully expanded size of 23 mm and a preferred
operating range for constant pressure. A simple increase in the
diameter of the structure 10, which may be a stent, would shift the
black recoverable curve to the right, allowing, for example, the
intersection points of the 18 mm and 22 mm lines to be essentially
in the plateau of the black curve. This characteristic of the
structure 10 when applied to a stent would make the applied force
of the structure within the designated range of operation
relatively constant throughout multiple size vessels irrespective
of the age of the patient. This gives the structure 10 the ability
to effectively stay in contact with a continuously changing
diameter of the associated lumen within which the structure 10 is
placed (such as in a stent application and the diameter change
being due to pulsatility found in the human body). Because of the
constant outward force over a wide range of diameters in the
preferred operating range, the structure 10 of the present
invention will stay in contact with a vessel that is changing
sizes.
[0071] As noted, the static axial length of the structure 10, as a
stent in particular, offers a distinct operational advantage in
that there is a much higher degree of certainty in the device 10
placement due to the static axial length between radially different
positions. Further when implemented as a stent the device 10 of the
invention differs from conventional "self-expanding stents" that
generally consist of a single layer of NiTi and are commonly
laser-cut from tubes which is associated with an unfavorable
crystallographic texture in the circumferential direction. Further
unlike device 10, conventional stents typically rely on ligaments
that bend within the cylindrical surface of a virtual tube (having
surface normal in the radial direction) wherein, by contrast, the
device 10 described herein allows the possibility of
metallurgically-bonded corrugations and/or honeycombs, so-called
thin-walled "cellular" structures. It should be evident from the
description that this cellular structure is not to be confused with
"porous" SMAs which do not have regular, periodic structures and
are not thin-walled). In contrast with conventional stent designs
the structure 10 allows construction of the device from wrought
NiTi elements that have improved mechanical properties and
transformation strain (with a more favorable texture), and can
employ bending within the "tube" cross-section (with normal in the
axial, z-direction). These advantages extend beyond the stent
field, but the stent field allows for easy comparison of the
present structure 10 to conventional construction.
[0072] The "stent" concept is not limited to medical applications
but can be used for opening and holding-open other restricted
lumens, or creating a lumen or passageway in industrial
applications, e.g., a crimped fuel line can be internally
reinforced with the structure 10 allowing reinforcement without
taking the system off line and disassembling the device, which may
be particularly advantageous for complex machinery; or a flexible
vent tube of a machine may be held in an expanded state for access
of an inspection scope. Another representative application is using
the structure 10 as a base for an internal filter structure such as
to contain emboli in medical applications or unwanted particulate
matter in general applications. A filter sack or filtering material
would be extended across the inner surface of the outer layer 20
such as at the down-stream end to contain the emboli within the
structure 10. The structure 10 could be later removed, such as in
distal protection filters used in angioplasty and stent placement.
In industrial applications, it could be used in a fuel or hydraulic
fluid line downstream of a filtering assembly that is being
replaced or otherwise serviced. Another representative application
is using a shortened version of structure 10 as an expanding
membrane that can used to occlude a defect.
[0073] The shape of the multi-layer structure 10 as shown has other
advantages, as illustrated the adjacent panels 32 and 22 of
adjacent layers 20 and 30 form channels between the layers 20 and
30. These channels can be used in medical applications for onsite
drug delivery purposes. Specifically one or more medicaments may be
placed within selected channels to be delivered in situ. For
example an anticoagulant or anti thrombotic medicament may be
included in channels of a stent formed from the structure 10. The
types of medicaments are not limited and there can be as many
distinct types as channels. Additionally, for medical applications
the surfaces of the layers 20 and 30 may be surface treated or
coated to provide medicaments or desired biomolecule, such as
heparin coated on the inner surface of inner layer 30 for a stent
application. The outer surface of outer layer 20 may have a
distinct bio-coating or surface treatment particular to its
application, and the inside of the channels may have a third
surface treatment or coating. The coatings or surface treatments
may be in addition to the packing or filling of the channels with
medicaments as discussed above. The filling of the channels with
material to be dispensed when the structure is positioned is only
limited in that the channel must not be filled too much so as to
interfere with moving from a retracted state to the deployed state.
The channels could also serve as effective location for other
elements, such as the positioning of nanotechnology or
nanomachines, such as for example the NANOPUMP.TM. brand of
Debiotech's miniaturized drug delivery pumps.
[0074] As noted the shape memory alloy structure 10 according to
the present invention may have an outer facing surface of an
outermost of the layer with a distinct surface treatment or coating
from an inner facing surface of an innermost of the layers. This
concept of different structuring can include different surface
finishes on the inner and outer layers 20 and 30. For example, the
shape memory alloy structure 10 according to the invention may have
one of the outer facing surface of the outermost of the layers 20
and the inner facing surface of the innermost of the layers 30 be
substantially uniformly perforated and the other be substantially
solid. In an alternative arrangement one surface may have a
textured surface for attachment wherein the other surface is
intentionally smooth. Alternatively, different alloys (having
different transformation temperatures) for the inner and outer
sheets 20 and 30 may be utilized, to provide, for example, an
increase in the temperature range of functionality, or to control
the plateau characteristics of the stress-strain behavior of the
resulting structure 10 discussed in connection with FIG. 14. In a
further alternative, the two layers 20 and 30 could also be of
different thickness to provide the desired operating
characteristics of the structure 10. The multi-layer construction
of structure 10 allows these differing constructions to be more
easily accommodated than other nitinol structures such as existing
medical stent designs.
[0075] The multi-layer construction of structure 10 according to
the present invention is applicable for many biologic applications
in humans and animals with medical stents and filters as discussed
above being two easily understood implementations. A heart valve 60
as shown in FIG. 8 represents another important implementation of
the present invention. FIG. 8 is a perspective view of a heart
valve 60 formed with the lightweight, collapsible, shape memory
alloy structure 10 according to the present invention. Leaflet
valve members are coupled to the inner layer 30 panels 32 forming
the valve. The structure 10 can include a number of preformed
suture openings 62 for securing the valve 60 in place. The
construction of the leaflets is known in the art and not discussed
further herein as this is merely to illustrate another
implementation of the present structure 10. The valve structure 60
may be a more general medical valve, such as various body
sphincters--gastric, urinary, or rectal as examples. The collapsing
and expanding characteristic of the structure 10 makes it
particularly beneficial for medical valve applications; however the
valve as shown need not be used in a medical application.
[0076] Other representative medical applications that the structure
10 of the present invention may be useful in forming include atrial
septal defect prosthesis, orthopedic pins, rods, plates, anchors
and screws, auditory implants (such as portions of a cochlear
implant), nasal implants, urinary tract implants, tear duct
implants, and esophageal implants. This is not an exhaustive list,
merely intending to show the wider application of the structure
10.
[0077] In many medical implant procedures for implanting a device,
such as valve 60, the device must be collapsed to its retracted
position on site and not pre-loaded. Pre-loading is referencing a
collapsing of the device at the manufacturer and shipping it to
users in the retracted condition within a deployment vehicle. In
many applications it is desired to maintain the structure 10 in the
expanded condition till immediately prior to deployment and then,
on site, collapse the structure and load it into a delivery
vehicle, such as a catheter. For these applications there is a need
for simple collapsing or folding fixtures to allow for easy
"loading" of the device on site. Existing folding fixtures for
nitinol medical devices have been overly complex.
[0078] The structure 10 of the present invention allows for a
greater simplicity in suitable on site folding fixtures than many
other existing nitinol folding fixtures. FIGS. 9A and 9B are
partial section schematic views of a folding fixture 70 for
collapsing a lightweight, collapsible, shape memory alloy structure
10 according to the present invention. The fixture 70 is formed of
a body member 72 with an inlet opening 74 of a first diameter at
one end thereof configured to receive the expanded structure 10
therein and a smaller diameter outlet 78 at an opposite end thereof
of a diameter associated with the desired loading diameter for the
structure 10. A converging surface 76 extends between the inlet
opening 74 and the outlet opening 78. The operator merely manually
passes the collapsible shape memory alloy structure 10 entirely
through the inlet opening 74 and the outlet opening 78 of the
folding fixture 70 and loads the structure 10 into the delivery
device (not shown) such as a suitably sized delivery catheter.
[0079] The construction of the structure 10 described above allows
the structure to collapse as it advances through the fixture 70.
The openings 74 and 78 and intervening surface 76 can be configured
to match the peripheral shape of the structure 10. The folding
fixture 10 of FIGS. 9a and b is merely illustrative of the concept
and FIGS. 10A-D are partial section views of a further folding
fixture 10 for collapsing the lightweight, collapsible, shape
memory alloy structure 10 according to the present invention. In
these figures a second folding fixture with a body member 82 is
provided. Body 82 is analogous to body 72 in that it contains an
inlet opening 84 of a first diameter at one end thereof, a smaller
diameter outlet 88 at an opposite end thereof and a converging
surface 86 extending between the inlet opening 84 and the outlet
opening 88. The second folding fixture is configured to have body
82 be received within the first folding fixture body 72, namely the
second folding fixture body 82 is received within the outlet
opening 78 of the first folding fixture body 72 with the inlet 82
receiving the structure 10 from the outlet 78 of the body 72. As
shown in the figures this staged fixture construction allows for
the passing of the collapsible shape memory alloy structure 10
entirely through the inlet opening 74 and the outlet opening 78 of
the first folding fixture body 72 and concurrent passing of the
collapsible shape memory alloy structure 10 entirely through the
inlet opening 84 and the outlet opening 88 of the second folding
fixture body 82. This staged folding fixture allows a gradual
collapsing to occur over a limited total or effective fixture
length due to the nesting of the bodies 72 and 82.
[0080] FIGS. 11A and 11B are partial section views of a further
folding fixture for collapsing a lightweight, collapsible, shape
memory alloy structure 10 according to the present invention in
which a holding fixture 90 is provided for receiving and supporting
the structure 10 during folding. In the illustrated embodiment a
pin 92 supports the structure 10 and the folding fixture body 72 is
received within the holding fixture 90 during the passing of the
collapsible shape memory alloy structure 10 entirely through the
inlet opening 72 and the outlet opening 78 of the folding fixture
body 72. A slot 94 is in the body 72 to allow for receipt of the
pin 92 during advancement of the body 72 relative to the holding
fixture 90. It should be apparent that the staged folding fixture
of FIGS. 10a-d could be used with a holding fixture as shown in
FIGS. 11a-b.
[0081] FIGS. 12A-12E are partial section views of a further folding
fixture 70 for collapsing a lightweight, collapsible, shape memory
alloy structure 10 according to the present invention. In this
embodiment the fixture 70 includes outer control discs 102 and
inner guide discs 102. The outer control discs 102 are rotatable to
a certain extent relative to the inner guide discs 102. The inner
discs include spacers 104 to space the one guide disc 102 from the
opposed guide disc 102. A plurality of pins 106 are provided that
are received and moved within grooves 108 in the opposed guide
discs 102 and are also received within and moveable along helical
control grooves (not shown) within control discs 100 with the
associated control grooves configured to have the control discs 100
rotate opposite to each other for operation. Rotation of the
control discs 100 opposite to each other will cause the pins 106 to
slide along the radial slots or grooves 108. In operation one pair
of discs 102 and 104 is removed to allow for insertion of the
structure 10 in the position shown in FIGS. 12B and C with the pins
106 aligned with panels 32 and 22. The discs 102 and 104 are
reattached to have the pins 106 engaged on both ends as shown in
FIG. 12A. Rotating the discs 100 opposite to each other in one
direction will cause the pins 106 to move along grooves 108 and
collapse the structure 10 to the position shown in FIGS. 120 and E.
The one pair of discs 102 and 104 is removed to allow for removal
and loading of the collapsed structure 10 in the position shown in
FIGS. 120 and E.
[0082] FIGS. 13A and 13B are perspective views of a further folding
fixture 70 for collapsing a lightweight, collapsible, shape memory
alloy structure 10 according to the present invention. In this
design the folding fixture is formed of a conventional band
clamping member for ease of use and operation.
[0083] The illustrated embodiments of structure 10 have shown
generally circular or concentric tubular lumen shapes, however
alternative geometries are possible. Conical and frusta-conical
structures 10 are easily designed. Further structures 10 which are
non-symmetrical about a center axis may be applicable for certain
implementations as would be combinations of symmetrical and
asymmetrical shapes, Further, non-tubular, generally "flat panels"
which are folded, for example, in an accordion fashion are
possible.
[0084] Another application of the structure 10 may be as a
component in an electrical circuit. Structure 10 may act as a
resistor that does not change in length even with heating. [0085]
The preferred embodiments described above are illustrative of the
present invention and not restrictive hereof. It will be obvious
that various changes may be made to the present invention without
departing from the spirit and scope of the invention. The precise
scope of the present invention is defined by the appended claims
and equivalents thereto.
* * * * *