AU774984B2 - Bistable spring construction for a stent - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: JOMED GMBH Invention Title: BISTABLE SPRING CONSTRUCTION FOR A STENT The following statement is a full description of this invention, including the best method of performing it known to us: 2 -BISTABLE SPRING CONSTRUCTIONS FOR A STENT- Background Of the Invention There are several kinds of stents on the market with either balloon expDandable or self expanding function. Balloon exandable stents are generally madfrom a material that can easily be plastically deformed into two directions. Before insertion, the sr~enc is Placed around the balloon sectionat Z-the distal end of a catheter and pressed together -to reduce the outer dimensions.

As soon as the stent is brought into the body in the proper axial position it can be expanded and thereby plas-tically deformed by pumnping uip the balloon. In this final position, the stent is at its largest diameter and should function to smpport the surrounding tissue, preventing an undcsired shape change into a much =aller diameter, at least locally.

Therefore, the stent needs to have sufficienc rigidity in the radial direction.

but also somte flexibility in the axial direction when it is in the final position- Further, the amount of material should be as small as possiblc and in the inner surface of the stent :should not obstruct the flow through the channel for blood) or cause too much turbulec.

Problems that genierally occur with these stents are as follows: After compressing the stent to its Ismallest diameter around the balloon, the s-tent will alwayshave some elastic spring back to a slightly larger diameter, whbich can cause problems~ when the catheter is broug-ht into the patient's body. In addition, the axial frictionbetwe.en balloon and stent can become so small that the stent slips off the ca~heter.

Further, a larger size stent is typicallIy a disadvantage.

A further problem is the so called rccoil of these stents. This means that after expansion by ffic balloon pressure, the oucr diameter will always beeorne slightly Smaller as soon as thc be-Houn is dtflatcd. TFhis dcPrcc Of recoil can bec as much as which can cause-migration of the stent.

A different type of stcnt is"'made of a more or less elastically expanding 3 structure, which has to be held on the catheter by some external means. An example of this type is a stent that is held in its constrained state by a delivery sheath, that is removed at the moment that the stent should deploy to its natural form.

Some of these stents are made of shape memory material with either superelastic behaviour or temperature sensitive triggering of the expansion function.

A disadvantage of these self-expanding stents is the need for the delivery sheath, causing a larger insertion diameter. The removal of the sheath also requires a sheath retraction mechanism, which has to be activated at the proximal end.

Most stents of both types further have the :15 disadvantage of relatively large length change during exDansion and a poor hydrodynamic behavior because of the shape of the metal wires or struts.

Another disadvantage of some stents is the positive spring rate, which means that further expansion 20 can only be achieved by higher balloon pressure.

The construction of prior stents is typically made in such a way that the external forces, working on the stent in the radial direction, merely cause bending forces on the struts or wires of the structure.

25 For example, a unit cell of a Palmaz-Schatz7 stent, as produced by Johnson Johnson Interventional Systems or the ACT One Coronary stent, produced by Progressive Angioplasty Systems, Inc. has in its collapsed condition a flat, rectangular shape and in its expanded condition a more or less diamond-shaped form with almost straight struts (Palmaz-Schatz)or more curved struts (ACT- One).

The shape of the unit cell of such stents is typically symmetrical with four struts each having the same cross section. In addition, the loading of the cell in the axial direction will typically cause an elastic or plastic deformation of all of the struts, resulting.n an 4 elongate of the unit cell in the axial direction. These unit cells have a positive spring rate. In stents based upon these unit cells the stability against radial pressure is merely dependent on the bending strength of the struts and their connections.

SUMMARY OF THE INVENTION According to the present invention there is provided an expandable device comprising a plurality of cells defining a tubular surface, each cell having at least first and second stable states, each cell in the second state encompassing a larger area than in the first state, the cells characterized by a negative spring constant, the cells constructed and arranged so that the expandable device is characterized by at least first and second o stable states.

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o*oo \\melbfiles\hone$\shirleyp\specis\P44999 Divisional 11 May 2004.doc Brief Description of the Drawings Fig. 1 shows the principle of a bistable mechanism; Fig. 2 shows the force-displacement characteristic of the mechanism of Fig. 1; Fig. 3 shows another bistable mechanism with an asymmetric bistability; Fig. 4 shows the force-displacement characteristic of the mechanism of Fig. 3; Fig. 5a shows an inventive tubular stent in the stable, fully collapsed configuration; Fig 5b shows an inventive tubular stent in the stable fully expanded configuration.

15 Fig. 6 shows a part of a stent with one bistable unit cell, drawn in the stable expanded shape; Fig. 7 shows the part of the stent of Fig. 6 near its elastic bistable equilibrium position; Fig. 8 shows the part of the stent of Figs. 6 and 20 7 in its stable collapsed shape; and Fig. 9 shows a larger section of the stent of Figs. 6 and 8, showing some unit cells in the collapsed shape and some unit cells in the expanded shape.

Fig. 10 shows an inventive stent formed of a 25 plurality of smaller inventive stents joined together with flexible connectors.

Fig. 11 shows a partially expanded inventive stent having more than one type of bistable unit cell; Fig. 12 shows an inventive stent having a range of diameters along its length; Fig. 13 shows an inventive expansion ring in expanded state; -6- Fig. 14 shows the expansion ring. of Fig. 13 in contracted state, Fia. 15 shows an inventive stent j oini;ng two vessels together and secured with Mfvefltivc expanfsionl rings, the stent exterihor to the vessels; Fig. 16 shows a cross-sctional view of Fig. 15 along section line 16-16; Fig. 17 shows an inventive stcnt joining two vessels together, the stent interior to the vesscls; Fig. 18 shows two vessels joined together with an inventive cxpansion ring and a clampD Fig. 19 shows a bistable valve in the closed position; Fig. 20 shows the bistable valve of Fig. 19 in the open position; Fig. 21 a shows a multistable cell in the fully contracted state; Fig. 21lb shows the multistable cell of Fig. 21a in the fully expandcd state; Fig. 22a shows another rnultistable cell in the fully contrzcted state; Fig. 22b shows the nmltistabLe cell of Fig. 22a in the fully exoanded state; is Fifg. 23 shows several unit cells as shown in Figs. 21ab joined together and in the fully expanded state; and Fig. 24a shows several unit cells as shown in Figs. 22a~b joined together adin the contracted state; Fig. 24b shows the interconnected cells of Fig. 24a in fully expanded state; Fig. 24c shows the interconnected units cells of Fig. 24a in the process of expanding-, and 'Fig. 24d shows several strips of interconnected cells as in Figs. 24a,b joined together and in the process of expanding.

Oetilei escptin f the Dain Fig. 1 shows the principle on which Uric stcnt is based, Fig. la shows a rod I with u leng-dh L, which is compressed in its axial dircction unit;, it reaches its buck-ling, stress. Then the central cart Of tile rod will bend out in a sidewards direction, either to position 2 or-3 (dashed lines in Fig. lb). When the axial displacement L of the ends of~ the rod is held stable by Mxcrnnl clamps 4, it is possible to move the central section of 7thc rod between the two stable positions 2 and 3. This movement is in a direction XJ perpendicular to the original length axis A-A of the rod. Ail positions between the stable positions 2 and 3 are unstble. [n Fig. lb the centrn, part of the rod has to rotate over -7n angle P before the rod can be moved in direction X. Fig. 10 shows a second order curvature in rod 1, wltich occurs when the rotation over angle P3 is opposed by clamping the central part of rod I and maintaining thi s part p=rllel to the axis A-A.

Fig. 2 shows the force F as a function of displaccmencrt X, with X displayed in the horizonal direction.. The rod is moved from the upr 2 to the lower 3 stable position of Fig. 1. The force incrcasc-s rapidly from ze-ro to Fniax. At that moment the onset of either the first or second order cuirvature of Fg-.]b and Ic is reached. Futrther displacement in direction X costs lczs force, because this spring system has a negative spring rate. The force even becomes zero in the maid position and fulrther movement occurs automatically. It can be seen in Fig. 2 that the system is completely symmetrical a~nd the forcc needed to move back from the lower to the tipper position ha.s the same characteristic.

Fig. 3 shows rod 5, which will have an asymnmetrical force displacemcnt characteristic, because it already has a preset =uvature, even in the unloaded Position, where the length is already Ths can bencchicved by prior plastic dcformatrion, heat :trcatinent or the u~se of an asymrmetrical geometry of the cross section of the rod (not shown). The rod 5 in Fig. 3 can bc mounited between two clamps on a length.L and if it is elastically deformed in the same way as the rod in Figs lb and le, it will have a different stress distribution in the cross section in end position 2 and 3, compared tothe rod of Fig. 1. This means That the rod has become arerfcrcnrE unloaded stable position, shown in-.Fig. 3.

Fig., 4 shows the asymmet-ical. force -disp)lacemnent. characteristic of the precurved rod of Fig. 3 The initial displacement from the stable upp er position needs a starring, force F1 and if the rod is in its stable lower position' the starting force i the opposite diiection is only F2, being smaller than F1. Force F2 can be made as small as desired. even zero or negative, but needs to. have a positive value if stability of the lower position is required.

Figs. Sa and 5b show the general appearance of an inventive tubular stent in fully contracted and fully expanded configuration respectively. The stent, in its fully contracted&state shown generally at 50 and in its fully expanded state shown generally at is comprised of a plurality of interconnected bistable unit cells (shown in the expanded state at 64 in Fig. 5b). The bistable unit cells are formed from a first relatively rigid segment 52 (66 in Fig. 5b) and a second relatively flexible segment 54 (68 in Fig.

joined together at ends 70 and 72. Second relatively flexible segments 68 are interconnected with adjacent relatively rigid members 66. Adjacent cells in the longitudinal sense (the longitudinal axis is denoted by reference numeral 75) are joined at ends 70 and 72. By applying a uniform radially outward or inward force, the stent may be switched directly from a fully contracted to a fully expanded configuration or vice versa.

Fig. 6 (corresponding to inset 6 in Figure 5b) shows a small part of a stent such as that shown in Figs .5 which uses the bistable function of a unit cell, according to the present invention. The drawing shows a horizontal line A-A, which is parallel to the central axis of the stent. There are two series of sinusoidal segments with distinct size (see also Fig. 9 for an overview). The segments 7 and 9 have a relatively large cross section. Only segment 9 is shown entirely. The segments 9 and 10 have a relatively smaller cross section, and here only segment 8 is entirely shown. The segments are interconnected for example welded, at joints 11 and 12.

20 Because of the difference between the cross section of segment 8 and 9.

the deformation force of segment 8 is much lower than for segment 9. Therefore, segment 9 can be considered as a relatively rigid clamp, like the clamps 4 in Fig. Itopposing relative displacement between the joints 12 in the axial direction, parallel to axis A-A. Incontrast, segment 8 acts as a flexible rod, like rod 1, described in Fig. -or rod 5, described in Fig. 3. This combination of segments 7 and 8 or 9 and 10 defines a unit cell, acting as a bistable spring system with a force-displacement curve F-X like the described curves of Fig 2 and 4, depending on the unloaded condition and geometry of the, segments. Alternatively, instead of using segments or struts of different diameter, the segments can have the same diameters cross sectional area) and exhibit different strengths or rigidity and still accomplish the same effect. One way to obtain such differences in strength or rigidity would be to use different materials for the segments.

Another way would be to use the same material, lik.- a metal, for all -the segments butselectively strengthen by heat treating) thuse segirents that ueed to be rigid. It should be noted that heat treatmc'nt will not strengthen all materials. Nitinol, for exampi.b-ccomes more pliable as a result of heat treatment. This property of Nitinol can be exploited, however, to render one section of Nitinol more pliable relative to a second, non-heat-treted section of Nitinol.

Fig. 7 shows the same part of the stent (as depicted in Fig. 6) near the elastic equilibrium position. Segment 8 has been defformed into the direction X, caused by force F, but segment 9 ha.s alinost its original shape, because of its larger rigidity.

Fig. 9 shows the same unit cell of the stent of Figs. 6-7 after it has been .:pressed through the elastic equilibriumn ;osition. It automatically snaps into its stable position of Fig. 8. This snapping forc" can be strong enough to hold a deflated balloon *tight on the catheter shaft (not si own), d&,pending on the mechanical characteristics the strength) of the material(s) used to make the sepments. With the geometry shown in these figures, the segments 8 and 9 fit close together. taking up a minimum amount of spacc when the stent i-s in its smallest stable diameter.

Fig. 9 shows a section of the stent of Figs. 5, flatzcned for illustrative purposes, showing several flexibic segments in the cotlaoscd stable shape (segments 14, 18 and 20) and one segment element 16 in the expanided statble shape. Segm;nts 13, 17,-and 19 are relatively rigid segments and substantiaLly mainwain dheir original shapc.

The distance between two relatively rigid segmnents is shown us (hi) i the collapscd stable shape and (M4 in the expanded stable shape. The value of the displacement in the direction X depends on the height of an expanded unit cell or amplitude of thc se'ments -qnd the size of the connecting joints. The dcscrib-ed part of the stent is showin as a flat surface, but it may be clear that a cylindrical stent such as thu±t shown in Figs. is shaped if segments 13 and 20 are dirctiy connected to reach other with joints 21. In other words, the stent is shown separated along the joints 21 and in a flattened condition.

The range of stable diameters of the stent changes with the value c I ch time that a flexible segment snaps from the coliansed stable position to the expanded stable position. The result is a stent with an extremely rigid surfa-ce at aill diameters being able to withstand the externat forces better thanj with conventional stents.

In the length direction, the flexibility of the stent can be increased by disconnecting several unit cells from their neighbor unit cells, for example, by cutting the centerof one or more joints while maintaining the several joint pieces as joints.

Another method to increase flexibility is to change the geometry of several sections of the unit cells in the length direction from the relative flexible to the relative rigid shape several times along the total length of the stent. In other words, referring to Fig. 9 one or more or each of the segments 13 20 could be constructed with larger and smaller diameter (or otherwise flexible and rigid) sections which alternate after each joint 21.

Another possibility, as shown in Figure 10 is the use of a series of short multistable stents 100 aligned lengthwise end to end and connected with flexibility joints 104 having the same or a different geometry or configuration as the joints forming individual unit cells.

The scope of the invention should include all types of material. One of the most interesting materials is superelastic Nitinol, because of its large elastic strain, well defined stress values, caused by their plateau stresses and the possibility to define the desired curvature into the metal by means of a heat treatment. A stent of Nitinol can be made by forming slits or slots in a tube, while in its collapsed or smaller stable diameter. The slotted tube is then expanded by a separate shaping tool and heat treated 20 on this tool to define the expanded stable diameter as the unstrained shape.

In a more general sense, the present invention is directed to a device having a plurality of stable configurations. The device is comprised of a plurality of interconnected multistable cells. The cells include one or more relatively rigid sections and one or more relatively flexible sections interconnected so as to define a cell struture in the form of a multistable spring system having a plurality of stable configurations. In a preferred embodiment, the cells comprise a first arcuate member having first and second ends and a second arcuate member having first and second ends, the first end of the first member in communication with the first end of the second member, and the second end of the first member in communication with the second end of the second member. It should be noted, however that members need not be rigorously arcuate.

Other shaped members, including relatively straight members are contemplated'as well.

11- The invention, in particular, conteniplatcs bistabic cells, that is cellshaving two stable configurations. In one such cell, the distace between corresponding points on the first and second sections ii larger in the first stablc state of the cell than in the second. stable state of the cell. The cells themnselves are constructed arnd arraniged so that the device itself is at Least bistable and possibly multistable. One such device, cylindrical stent having two or More configurations with an initial diameter size and a final ]argcr diarnctcr size has been described above. However, multistablec stents aire also contemplated. Thus. for example, a stent may be constructed in which the cells are designed and arranged to provide a range of diameters in step-wise fashion. Ont such way this may be accomplished would be to employ severa.l different types of cells in the :stcnt, cach ty pe of cell h~aving~ a different spring constant so that depending on. the amnount of force used, the stent would assumne a different diameter- Such a stent in a partially e xpanded state is shown schew-atically in Fig- 11. A partially expanded szern is shown generally at 120. The Stent is com-prised-of relatively rigid segment 12.3, 127, 131 and 135 which substantially maintain their original shape, and relatively flexible segmnents 12 5, 12 9. and 13 3. The segments are interconnected, with joints 122. As depicted, -first flexiblc elcments 125, and 133 are in an expanded co-ntigurztion while second flexible cicinent 129 is in a contracted configuration. By applying a radially outward or tangential force.. flcxible elemnent 129 may be flipped to its fully expanded configuration resulting in a stent (not shown) with a larger diameter. As shown in Fig.

11. cells 138 are larger than cells 136 even in the contracted state. First tlexible elements 125 and 13 are charcterized by a different degree of flexibility than second flexible,, element 129.

Arnother form of stcnt, as shown genteral~l at 150 in schematic Fig. 12. has an first diameter at a first end 152, a second diameter at a second enid 154 and one (or more) intermediate diameters in a rep-ion 156 between FlrSL enid 152 and second end 154., the intermediate diameter differing from the first and second diarrctcrs. The interconnected cells in such a stent, as shown generaily at 150 in Fig. 12 may all have the sa.me fore- constant and hence be openable all ait once with the application of the ncccssary force or t.ere may be several different types of cells, each with their own force constant In order to achieve the multiplicity of diameiters, cells of differing sizes may be 12 used. In one embodiment of this type of stent, the first and second diameters are the same while in another embodiment, the first and second diameters differ.

A method of implanting an expandable stent having a plurality of stable configurations comprises the steps of applying the stent to an expanding means on a catheter, delivering the stent to a desired bodily location, expanding the expanding means so as to expand the stent from a first stable configuration to a desired second stable configuration, the second stable configuration having a larger diameter than the first stable configuration, and deploying the expanded stent at the ~desired bodily location. The expanding means may be a balloon, a mechanical device on or in the catheter, a heat 15 source where the cells can be induced to change states by heating or any other suitable expanding means. The stent may be applied to the balloon in the first stable configuration or may be applied in the second stable ~(expanded) configuration during the applying step. In the 20 latter case radially inward pressure may be applied to the .e stent so as to urge the stent into the first stable configuration to snap it onto the catheter. Where the S" stent has additional stable states, the stent may be Sapplied to the balloon in an intermediate stable state in which the diameter of the stent is intermediate between the diameter in the first state and the diameter in the second state. Again, the stent may be locked on the expanding means by further applying a radially inward pressure.

An embodiment of the invention is the use of a single bistable unit cell as an expander (expansion ring), that can be brought into a narrow place and then triggered to snap back into its expanded stable shape. As shown in.

H:\Shor.a1\Keep\Speci\P44999 Divisional 19/02/02 13 Fig. 13 an expansion ring shown generally in its expanded state at 250 consists of a first rigid member 254 having first 258 and second 262 ends and a second more flexible member 266 having first 270 and second member 274 ends.

First end 258 of first member 254 is connected to first end 270 of second member 266 and second end 262 of first member 254 is connected to second end 274 of second member 266. Fig. 14 depicts the expansion ring of Fig. 13 in its contracted state. Second member 266 is seen to be in a second stable position.

Another embodiment of the invention is the use of a single bistable loop (unit cell) as a clip, that can be used to clamp on an artery, fallopian tube or any other body part, to close or hold it for some time. For such a 15 clip it may be desirable to define the @9

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5 H:\Shonal\Keep\Speci\P44999 Divisional 19/02/02 14collapsed stable shape as the unstrained shape, because thc collapsed stable shape has f-o be the most stable one. In the collapsed state, the clip would resemblec the collapsed expansion ring of rig. 14. :JA triggering means would be used in conjunction wi'dh dt clamp to switch the bistable loop from one state to another. The'triggering means may be pneumatic, hydraulic, mechanical, thermal or electromechanical means. Examples of such triggering means include a human hand applying force to the bistalbie loop, and the application of heat to the loop. Other triggering means include pulling on the device.

pushing on the device, bending the rigid section of the device or releasing a restraint holding the flexible member- in place.

Another part of the present invention involves constructions between one or more ring-shapcd elements according to the present invcnition, combined with a tubular sleeve that is reinforced or held open wiith such elem-ents. An exampleis aso- 0 called graft sient made of a polymner with one or more expansion rings. The expansion rings may consist of the above-described bi-stable cells. The suinface of the stent 6009e0 0 0 15 compriscs, a skin mounted on the expansion rings. In mounting the skin, the skin may surround, be in or between the expansion rings. The skin may be human or animal skin, a polymeric mnaterial or any other suitable bio-compatibie mwerial. Such a stent may 0000 comprise one or more expansion rings, such as a first expansion ring at a first endl of the stent and a second expansion ring at a second e-nd of the stern. The stent may b-c of *006 *00000second diameter at the second end- 000:00The present invention is also directcd to a smter having an unexpanded 09 6:00600 longitudinal,_ wave-like first members characterized by a first wavel en gth, and having peaks and troughs and a plurality of generallv longitudinal wave-like second members characterized by a second wavelength, and having peaks and troughs. The wavclengths of the first, and Second longitudinal members are substantia~lv equaL 'lbec second members are capable of stably assuming two positions, a first position corresponding to th unexpanded configuration in which the first and second members are ini phase and a second position correspondinig to the expanded configuration, in which the first and second members are 1800 out of phase. the first members arc more rigid than the 15 second members. The first and second longitudinal members are disposed on the surface of the stent such that the longitudinal first and second members alternate. In the unexpanded state, each peak of each first member is connected to one adjacent peak of a second member in a region of attachment and each trough of each first member is attached to one adjacent trough of a second member in a region of attachment, as can be seen from Fig. 9. The regions of attachment are separated along the longitudinal direction by one wavelength. The so described s.ent can be snapped from the unexpanded configuration to the expanded configuration by applying a radially outward force and similarly can be snapped from the expanded to the unexpanded configuration by applying a radially inward force. While such stents may be used intenal to a bodily i. vessel, it may also be used external to vessels to join two vessels together.

The invention also contemplates a method of joining together two vessels comprising the steps of delivering an inventive stent in an unexpanded configuration in a first stable state to a bodily site, expanding the stnt to a second stable stare, the diameter ofthe stent in the second stable state exceeding that of the vessels to be joined and placing the stent over the vessels to be joined. The stent may then be contracted to a third stable state, the stent in the third stable state having a diameter intermediate between the diameters of the stent in the unexpanded state and in the second stable state.

The stent may further be secured to the vessel with the aid of one or more of the above- 20 described expansion rings (a bistable loop). One or more expansion rings, such as that depicted in Figs. 13 and 14 or small clamping stents (such as that formed from the strip shown in Fig. 23) may be delivered to each side of the stent in a contracted state and? deployed so as to clamp the vessels between the ring(s). Multiple rings may be used for additional-clamping. As shown generally at 300 in Fig. 15, a fist vessel'304 and a -4 second vessel 308 are joined together with inventive stent 312. Vessel 304 overlaps stent 312 in a first overlap region 316 while vessel 308 overlaps sten: 312 in a second overlap region 320. Vessel 304 is clamped between expansion ring 324 (shown in the expanded state) and stent 312 while vessel 308 is clamped between expansion ring 328 (shown in ihe unexpanded state for illustrative purposes only) and stent 312. the dotted lines associated with expansion ring 328 illustrate expansion ring 328 in its expanded state. It should be additionally noted that Fig. 15 provides a cut-away view of vessels showing 16the rings contained therein. Fig. 16 shows a cross-sectional view of Fig. 15 along section line 16-16.-Vessel 304 is shown sandwiched between stent 312 and expansion ring 324.

In another embodiment, as shown in Fig. 17, a first vessel 404 and a second vessel 408 are joined together by a stent 412. First end 416 of stent 412 rests in vessel 404 while second end 420 of stent 412 rests within vessel 408. Optional clamps (such as a small portion of a collapsible inventive stent shown later in strip form in Fig.

23) 424 and 428 residing on the outside of vessels 404 and 408 clamp the stent to the vessel. Additional clamps may be used as needed.

In another embodiment, a combination of the embodiments of Figs 15 and 17, the first end of the stent may protrude from one of the vessels and the second end of the stent may extend over the second vessel. Again, clamps and expansion rings may be used to further secure the stent to the vessels.

In another embodiment, as shown in Fig. 18, vessel 454 and vessel 458 are held together by an expansion ring 462 internal to the vessel and a clamp 466, consisting of, for example, a small section of collapsible stent, the stent chosen so that the diameter of the stent in a collapsed state affords a snug fit with vessels 454 and 458 'i and expansion ring 462. Either the expansion ring or the clamp, but not both, may be replaced by a suitable support such as a rigid collar.

The invention also contemplates a method of joining together two vessels 20 comprising the steps of delivering an inventive stent in an unexpanded configuration in a first stable state to a bodily site, placing two bodily vessels over the stent and expanding the stent to a second stable state, the diameter of the stent in the second stable state exceeding that of the vessels to be joined. The diameter of the stent in the second stable state is preferably chosen so that the vessels fit snugly over the stent. The delivery othe stent may be accomplished by delivering the stent in an unexpanded configuration through a bodily vessel and subsequently expanding the stent to rest snugly in the vessels to be joined (where a portion of the stent resides in a vessel), or by expanding the stent to its most expanded state, placing the stent over the vessel and then contracting the stent to an intermediate state over the vessel. The collars and expansion rings mentioned above may similarly be delivered. Alternatively, the stent, collars and expansion rings may be delivered by surgically exposing the vessel in question.

-17 The present invention is also directed to a bistable valve. Thc valve, as shown generailly al, 600 in 19 incluziesasnpcto.ioiinluitcishw generally at 604 located within a conduit 606. Snao-action bipositional unit cell 604 consists of a (substantially arcuate) llexible member 608 having a first end 612 and a se-cond end 616. First end 612 is in cornrnun.ication with a ftigg-cring me--ns 620 which is supported, in turn* by a support means 624 emierging frm the inner surface of conduit 606. Second end 616 of flexible member 608 is anchored to stop surface 628 which extends across conduit 606. Suipport mneans 624 and stop suirface 628 mus be sutfficiently rigid to hold flexible membe-r 608 in place and must be more rigid than flexible member 608. Stop surface 628 extends substantially obliquely across coinduitL 606 in. oblique regions 630 and hzas a onenirig 632 within in longitudinal region 634 to allow the flow thereibrough of a fluid. Alihouoli op::*ig 632 is or-iente:d along the longitudinal axis 636 of conduit 606, those of ordirnry skill in the art will recognize other possible orientations of the opening and stop surface. Valve closure member 640, actuated betwecen open and closed positions by flexible memnber 608, is constructed and arranged so as to block the flow of fluid through opening 632 when flexible member 608 is in the closed position. WVhen flexible menmber 608 is in the open position, as depicted in Fig. 210 valve closure member 640 no longer obstructs opening 632. therby allowing :the flow of fluid therethrough.

While triggering means 620 may any suitablt mechwnicai, hydraulic, pneumatic, or thermal based tigger -io'.vn in the art at present or in the future, in a preferred embodiment, triggering means5 620 is a piezoelectric element. In operation,* jf *the piezociemenrt shown in Fig. 19 at 620 is not activated, valve closure member 640 is closed. Activation of piezoelement 620, as shown in Fig. 20 causes a small shortenirign the longitudinal length (denoted by Y in Fig. 15) of piezoelemetnt 620 which in turn releases flexible member 608 froma its first position. With member 608 released, valve .closure member 640 is free to open under- the pressure transmitrted fr-om the fluid.

Member 608 assumes a second, inverted, position, as depicted in Fig. 20. Wiethe fluid pressure maintains MeMber 608 in its second positior, even in the ab.-ence of any fluid.

member 608 remains in its second position, as depicted in Fig. 20 if the-triggeringy is turned offeand piezoelerrcnit 620 assumnes~ its originial length. Valve closure Tnembcr.640 -18may be closed again, in the absence of fluid, by a subsequent triggering of piezoelemnt 620 allowing member 608 to transition to its second (closed) position which is the preferred position of member 608. Member 608 has been treated to receive a preferred position as shown in Fig. 3.

The valve depicted in Figs. 19 and 20 may be applied to medical and nonmedical devices. It is, in particular, an aim of the present invention to apply the inventive bistable valve to the control of urinary incontinence. In a patient with incontinence, the above described valve may be implanted in the urethra using any suitable means including the use of the above-described expansion rings to clamp the valve to the urethra. Although the valve in the default state is closed, the valve may be triggered when the bladder is full, to void the bladder. Upon voiding the bladder, the valve may be triggered again to close it. Another such application is to employ the inventive valve in conjunction with a shunt. The shunt may be activated by triggering the device and similarly may be closed by triggering the device.

Of course the valve may be used in other medical and non-medical applications as well.

In addition to the bistable unit cells disclosed above, bistable unit cells and more generally, multistable unit cells of other shapes are also contemplated by the present invention. Figs. 21a and 21b are schematic representations of another 20 embodiment of an inventive hinged multistable cell in its contracted and expanded states, respectively. The contracted cell, shown generally at 700, and the expanded cell, shown generally at 705, consist of four interconnected relatively rigid members. Two side members 709 are connected to opposite ends of top member 713 via hinges 715. Side members 709 are connected at their opposite ends to opposite ends of bottom member 717 via hinges 719. Preferably, the hinges are elastic or plastically deformable. The hinges may be fixedly attached to the side, top and bottom members or may be integral with these members. In the latter case, the hinges may be formed by removing material from, the cell in the region of the hinges so that the hinges are thinner or have a different geometry from the side, top and bottom members. In the process of transitioning from the expanded to the collapsed state, bottom member 717 opens slightly. The cell of Figs.

21a,b also has two additional intermediate states in which one or the other (but not both) -19of side members 709 and top member 713 are collapsed downward.

A hexagonal hinged multistable unit cell is shown schematically in Fig.

22a in the collapsed state and in Fig. 22b in the expanded state. The cell, shown generally at 750, consists of top member 754 and bottom member 758, and upper side members 762. Two upper side members 762 are connected to opposite ends of top member 754 via hinges 756. Upper side members 762 are connected to bottom member 758 via hinges 768. Bottom member 758 is shaped like a with the two uprights of the modified to lie at oblique angles with respect to the bottom part of the As with the previously discussed inventive cells, hinges 756 and 768 may be elastic or plastically deformable and may be fixedly attached to the members or integral with the members.

The hexagonal unit cell exhibits multiple stable states. In addition to the fully expanded and fully contracted states shown in Figs. 22a and 22b, the hexagonal cell can also achieve two intermediate stable configurations in which only one of the two upper side members 762 is collapsed inward along with top member 754.

The above described hinged multistable cells may be used in any of the above discussed applications e.g. to form stents, clamps, clips, expander rings, bistable valves.

In one such application a ring or stent is formed of the hinged cells of Figs. 21a and 21b. As shown in Fig. 23, a series of unit cells of the type depicted in Figs.

21 are joined together so that the top member of a cell forms a portion of the bottom member of an adjoining cell. As depicted, top member 814 of cell 810 forms a portion of bottom element 818 of cell 820. Similarly, top member 824 of cell 828 forms a portion of bottom element 832 of cell 836. Although the ring or stent in Fig. 23 has been-cut for illustrative purposes, the two ends 840 and 844 are normally joined together with a" portion of lower member 848 of cell 852 serving as an upper member for cell 856. The ring so formed has a range of stable stable states including a fully expanded state and a fully contracted state. Where the individual cells are made identically, only the fully expanded states may be accessed by the application of a uniform radially outward force to the stent in the fully contracted state. It may serve as a clamp or collar, an expansion ring or a stent. Larger stents may be formed by interconnecting a plurality of such rings.

Similar products may also be formed from other multistable units cells.

Figs. 24a and 24b illustrate one such possibility schemiatically in which hexagonal urii( cells such as those shown in Figs. 22a, b may be joined together to form- a Ting. The top member 884 of each cell 880 is joined with a the bottom portion 886 or modified 'U' shaped bottom member 890. Although shown in strip form in Figs. 24a and 24b, end 894 can be joined to end 898 to 1ormn a ring. The strip of Fig. 24a is shown in fully expandcd state in Fig. 24b. Adjacent cells 880 are seen. in their expanded state. For the sake of completeness, the hinges are designated 902. Fig. 24c shows one cell 920 in the process of expanding and one already expanded cell 924. The cells 920 and 924 are joined at bottom member 928 and top member 932. Hinges are shown at 936. Multiple strips may also be joined together so as to form a stent whose length is a multiple of the length of the hunit cell. In such a =ac, upper side memnbers of adjacent cells would be joincd together. This is illustrated in Fig. 24d which, like Fig. 24c shows cells 940 in the expanded state and cells 944 in the process of expanding. Upper side members 948 are 00:shown by dashed lines. Adjacent strips of interconnected cells 952 joined together by iS upper side members 948 as well as by oblique regions 956 of bottom membeirs 960.

it should be noted that the inventive devices of the present application may be used on a temporary basis or on a perm anent basis in the body. Thus, for example, permanent stents and clamps are contemplated, as are removable stenTs and clamps.

20 It should further be noted that in expanding some of the inventive rnultistable cells, there mnay be components of expansionlcontraction in a direction perpendicular to the direction of the fore: applicd to expand the cells.

Finally, for the purposes of this application, the term Thultistable' is intended to-include 'bistable'.

In the described drawings and text only some examples of different embodiments have been given. WhiWte the stents of the present invention can appear 3imilar to prior st=3t, the rnechnnical results are completely different due to the sp<:ciai combination of a rigid section and a. mome flexible section in the same unit cell. Of course there are, beside the illustrated sinusoidal shape many other possiblc basic shapes for the unit celwith simnilar characteristic behavior.

From the abovc disclosure of the general principles of the present 21 invention and the preceding detailed description, those skilled in this art will readily comprehend the various modifications to which the present invention is susceptible. It is intended for the coverage of the present application to include different geometries, different constructions and different combinations of one or more materials to obtain the same basic mechanical behaviour as exhibited by the above described examples.

For the purpose of this specification the words "comprising", "comprise" or "comprises" are understood to mean the inclusion of a feature but not exclusion of any other feature.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

*0 o o o \\melbfies\ho$e$\Sieona\Keep\Speci\15662 02.dac 10/05/04

Claims (14)

1. 2. The expandable device of claim 1 wherein the cells are bistable having first and second stable shapes.
2. 3. The expandable device of claim 2 wherein the cells are arranged and disposed such that the expandable device has a first stable state characterized by a first diameter and a second stable state characterized by a second diameter, the second diameter larger than the first 20 diameter. S4. The expandable device of claim 2 further having a third stable state, the third stable state having a third diameter different from the first and second diameters. The expandable device of claim 2 wherein the cells are formed from at least two different segments: a first segment which acts as a relatively rigid S•support for the cell, and 30 a second segment which is more pliable than the first segment, the second segment capable of existing in two distinct states, a first contracted state corresponding to the first stable state of the cell and a second expanded state corresponding to the second stable state of the cell, the first and second segments fixedly connected one to the other. \\melbfiles\hoce$\Simeona\Keep\Speci\15662 02.doc 10/05/04 23
3. 6. The expandable device of claim 5 wherein the cells are constructed and arranged so that the expandable device has two stable states, a contracted state having a first diameter and an expanded state having a second diameter larger than the first diameter.
4. 7. The expandable device of claim 5 wherein the first and second segments are formed of the same material, the first segment having a first cross-sectional area and the second segment having a second cross-sectional area larger than the first cross-sectional area.
5. 8. The expandable device of claim 5 wherein the first and second segments are made of different materials, the material of the first segment being more rigid than the material of the second segment. S. 9. The expandable device of cl.aim 5 wherein the first and second segments are made of the same material, 20 the first segments being strengthened by heat treating so as to increase the rigidity of the first segments. The expandable device of claim 5 having a uniform diameter and having three or more stable states, the *o 25 diameter of the expandable device differing in each stable state. o 11. The expandable device of claim 5 wherein the plurality of bistable cells comprises a plurality of 30 bistable cells of two or more types, the cell types requiring different amounts of force to expand.
6. 12. The expandable device of claim 1 wherein the plurality of cells comprise a plurality of multistable loops.
7. 13. The expandable device of claim 12 wherein each \\melb_files\hoeS\Simeona\Keep\Speci\15662 02.doc 10/05/04 24 one of the multistable loops comprises a first arcuate member having first and second ends and a second arcuate member having first and second ends, the first end of the first member coupled to the first end of the second member, and the second end of the first member coupled to the second end of the second member, wherein the second member is more pliablethan the first, the second member capable of assuming a first stable position and a second stable position.
8. 14. The expandable device of claim 13 wherein the first arcuate members define a plurality of generally longitudinal, first wave-like members characterized by a first wavelength, and having peaks and troughs and the second arcuate members define a plurality of generally longitudinal second wave-like members characterized by a second wavelength, and having peaks and troughs, the second wavelength substantially equal to the first wavelength, the second members capable of stably assuming 20 two positions, a first position corresponding to the unexpanded configuration in which the first and second members are in phase and a second position corresponding to the expanded configuration, in which the first and second members are 1800 out of phase, the first members more rigid than the second members. .15. A expandable device as in claim 1 wherein the cells are expandable from the first to the second stable state, the expansion having a tangential component and an 30 axial component.
9. 16. The expandable device of claim i, further comprising at least one unit cell includingat least four relatively rigid segments, each relatively rigid segment having a first end and a second end, each first end connected to a second end of an adjacent segment by a plastically or elastically deformable hinge and each \\melb_files\hoeS\Sinmeona\Keep\Speci\15662 02.doc 10/05/04 25 second end connected to a first end by a plastically or elastically deformable hinge so as to form a closed cell, whereby the unit cell can be switched between a first stable fully collapsed shape and a second stable fully expanded shape.
10. 17. The expandable device as in claim 16 wherein the fully collapsed configuration has a first area and the fully expanded configuration has a second area larger than the first area.
11. 18. The expandable device as in claim 16 wherein the unit cell has: a top segment; a bottom segment, the bottom segment including a portion that is substantially parallel to the top segment, the parallel segment having first and second ends, and two oblique portions that are disposed at oblique angles relative to the parallel portion, each oblique portion 20 situated at an end of the parallel portion; a first segment connecting the bottom and top segments and a second segment connecting the bottom and top segments, the first and second segments of substantially equal length, the cell symmetric about an axis that bisects the top and bottom segments. ro
12. 19. The expandable device as in claim 18 wherein the unit cell assumes a hexagonal shape in its expanded state. 30 20. The expandable device as in claim 16 wherein the unit cell has: a curved top segment; a bottom segment, the bottom segment substantially parallel to the top segment, a first segment connecting the bottom and top segments and a second segment connecting the bottom and \\melbfiles\homeS\Simeona\Keep\Speci\15662 02.doc 10105/04 26 top segments, the first and second segments of substantially equal length, the unit cell symmetric about an axis that bisects the top and bottom segments.
13. 21. An expandable device comprising a plurality of cells defining a tubular surface as defined in claim 1 and as substantially as herein described with reference to and as illustrated by the accompanying drawings.
14. 22. A stent of claim 5 wherein the first and second segments are made of the same material, the first segments being strengthened by heat treating so as to increase the rigidity of the first segments. Dated this 1 1 t h day of May 2004 JOMED GMBH o: By their Patent Attorneys 20 GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia e4 do LO..dA H\Simeona\Keep\Speci\15662 02.doc 11/05/04