WO2001011097A1

WO2001011097A1 - Method for storing a shape memory alloy

Info

Publication number: WO2001011097A1
Application number: PCT/FR2000/002237
Authority: WO
Inventors: René SUIRE
Original assignee: Mat Inov Sarl
Priority date: 1999-08-04
Filing date: 2000-08-03
Publication date: 2001-02-15
Also published as: CN1183271C; CN1373816A; EP1204779A1; CA2381083A1; RU2262550C2; FR2797275B1; FR2797275A1

Abstract

The invention concerns a method for storing two geometric states of a product made of a shape memory alloy, said method being characterised in that it consists in: a) training said alloy for the first geometric state by stressing said product to bring it and maintain it in said state at a first temperature; then b) training the alloy for the second geometric state by stressing said product to bring it and maintain it in said second state at a second temperature. The invention also concerns applications of said method to products in the medical, dental, veterinary or other fields.

Description

METHOD FOR MEMORIZING A SHAPE MEMORY ALLOY

The present invention relates to a method for memorizing two geometric states of a product produced in a shape memory alloy. It relates to applications of this process to products intended to be fixed on another element then to be removed therefrom. It also relates to applications of this process to products in the medical, dental, veterinary or other fields.

We already know shape memory alloys also called AMF alloy.

Thanks to this memory effect, a material which has been deformed at a first temperature will resume its initial shape when it finds itself at a second temperature. This effect is due to a thermoelastic transformation between an austenitic solid phase and an equally solid martensitic phase.

Different known alloys can have such an effect.

The use of these alloys for this purpose in the medical field is also known, in particular for producing connecting pieces for elements bone or staples. Reference may be made in particular to French patent document FR-A-2 700 464 which describes the use of such a memory material.

Note that the application of the present invention to the medical field is given here by way of example. The use of shape memory alloys in the medical field is today limited to the fixing of a product on an element and does not allow a subsequent phase of extraction of said product from the element. For example, in the case of human implants, the use of memory alloys today facilitates their installation but does not contribute in any way to their extraction which is moreover not envisaged.

The aim of the present invention is to propose a method for processing a product with a memory effect so that this effect allows, on the one hand, the laying of the product concerned on an element, but also its extraction from said element. . The object of the present invention is therefore to propose a method for storing, not a geometric state as described in the state of the art, but two geometric states of a product produced in a shape memory alloy.

To do this, the method of the present invention therefore consists in: a) educating said alloy for the first geometric state by urging said product to bring it and leaving it in said first state at a first temperature, then b) educate said alloy for the second geometric state by soliciting said product to bring it and leave it in said second state at a second temperature. If the product under consideration is an implant intended to be placed in an organism, the placement of this implant is made by bringing it into one of the two geometric states by providing the necessary heat so that it acquires the temperature corresponding to this state. Its extraction is carried out by bringing it to the other geometrical state by supplying the necessary heat so that it acquires the temperature corresponding to this state.

It will be noted that the geometrical state of fitting corresponds to that for which said implant requests an element, such as another implant, another part or a part of the body so as to be fixed there. As for the geometrical state of extraction, it corresponds to that for which said implant returns to its initial state before placement or to a state close to it.

Thus, the fact that the implant is made of an alloy educated to present two distinct geometrical states allows its installation, in one of the states, and its extraction, in the other of the states.

The alloy used is for example an alloy of nickel and titanium, or a composite material reinforced by such an alloy.

For example, the highest temperature of the two considered temperatures is between + 37 ° C and + 55 ° C while the lowest temperature is between + 30 ° C and -30 ° C.

If the present invention finds application in the medical field, the highest temperature can be provided by a scalpel and the lowest temperature by a physiological saline, a cryode, etc. According to another characteristic of the invention, said method consists in finishing said product after education of said alloy for the first geometric state but before education of said alloy for the second geometric state. This finishing step can consist of polishing said product, for example by billing.

In order to prevent the nickel which said memory alloy may contain from being in contact with the human body, this finishing step can consist of the application of a thin protective layer, for example of the order of 1 to 5 microns.

This layer can be made from one of the following materials:

nickel carbide, aluminum oxide, molybdenum disulfide, titanium carbonitride, ternary nickel, titanium and aluminum material, chromium nitride, diamond carbon in the amorphous state, titanium carbide, titanium nitride, etc.

This protective layer is for example a layer obtained by nitriding at low temperature the surface of said product. It can be carried out by ion bombardment or by gas deposition.

It has been noted that this nitriding step at low temperature has the effect, in addition to protection for the human body, of amplifying the memories of the alloy, hot and cold.

In addition, it simplifies by shortening the polishing step of the raw product because it makes it possible to obtain a very good surface condition more quickly. It also makes it possible to produce friction and crushing parts.

The present invention can be applied to any field insofar as two geometrical states of a product are necessary. In particular, it relates to applications to products intended to be fixed by clamping on an element and to be extracted therefrom. In the following description, we will consider by way of example applications in the medical field, for example human implants.

Examples of application of the method of the invention are now described in relation to the accompanying drawings, among which: FIG. 1 is a view illustrating the method of the present invention in the case of a staple,

Figs. 2a to 2d are views illustrating the method of the present invention in the case of a nail,

Fig. 3 is a perspective view showing a cup to which the present invention can be applied,

Figs. 4a to 4c are views illustrating the method of the present invention in the case of an anchor pin, and

Fig. 5 is a view of a femoral stem system implementing the storage method of the present invention. To begin with, we will consider, in relation to FIG. 1, an application to human implants which are staples which may be of the orthopedic or trauma type and which are then used either to hold ligaments together, or to allow bone approximations (for example epiphyseal staples). It can also be staples used in the spine area to allow the maintenance of parts. They can also be staples for the medical or surgical field. The process for obtaining a staple according to the present invention is as follows. This clip is obtained from a wire 10, for example made of an alloy of nickel and titanium, advantageously in a stoichiometric ratio close to one, which is then mechanically shaped so as to have substantially the shape 11 of a " n "with two legs l ia and 11b linked together by a core 1 le. This is the so-called initial shape of the clip.

The legs 11a and 11b of the shaped clip are then respectively subjected to forces so that they approach each other. The first geometric state 12 is then obtained. This operation is carried out at a temperature T1, for example between 37 ° C and 55 ° C, for example still 40 ° C. This operation is for example carried out in a vice or using a matrix 20 of shape complementary to that which is desired. It will be said later that the clip was educated for its first state of memorization.

A finishing step can then be applied to the clip in its state 12. It can be a polishing, for example by billing, or the deposition at low temperature of a coating, for example, by phase deposition gas or nitriding. This step is marked N in FIG. 1.

After this finishing step, the legs of the clip are subjected to a force so that they end up in a second geometric state different from the first geometric state 12. Depending on the application envisaged, it may be the state 13 where the clip covers its initial shape 11 with its legs 11a and 11b parallel to each other or even in the state 13 'where the clip has its legs which are spaced from one another. This operation is carried out at a temperature T2, for example between -30 ° C and + 30 ° C, for example still 5 ° C. It is for example carried out using a pulley system or by placing in a matrix 21 or 21 'of suitable shape complementary to that which is desired as a second geometric state. In practice, in the case of a staple, state 13 will be preferred to state 13 'to allow its easy extraction.

The use of such a staple is as follows. During installation, the staple is put in place and a heat is communicated to it such that it reaches the temperature T1. This temperature being high, an electric scalpel is then used for example. It then acquires its geometrical state 12 where its legs are brought together. Then, the clip keeps this state. In this state, the clip clings to its support, for example a bone, and can no longer be disassembled without further intervention. For its extraction, heat is communicated to the clip considered so that it reaches a temperature close to the temperature T2 so that it then acquires its geometrical state 13 where its legs are again parallel to each other. The clip is then removed by pulling it parallel to these legs. This temperature being low, a physiological serum can be used. The shapes corresponding to the geometric states 12 and 13 or 13 ′ are determined at the time of their storage and can therefore be chosen so that they are suitable for the clip concerned.

It will be noted that, in the example of the clip given above and according to variants of the present invention, the temperature T1 could be the lowest, for example between -30 ° C and + 30 ° C and the temperature Highest T2, for example between + 37 ° C and 55 ° C.

Another application of the method of the present invention is described in relation to Figs. 2a to 2d and relates to a nail 30, one of the main uses of which is bone approximation. The nail 30 essentially consists of a tube open laterally by a longitudinal slot 31. Its lower end 32 is slightly frustoconical in order to facilitate its installation in a cavity pierced for this purpose.

There is shown in FIG. 2b the circular arc section of the nail 30 in its initial state 30 A before education. In Fig. 2c, the nail 30 is in its first geometric state 30B educated for the temperature T1. The circular arc which represents the section of the nail 30 is open relative to the initial state 30 A. In FIG. 2d, the nail 30 is in its second geometric state 30C educated for the temperature T2. The circular arc which represents the section of the nail 30 is slightly closed compared to the previous geometrical state 30B but open compared to the initial state 30 A.

The section in the form of a simple arc is given here as an example. It will be understood that it could have more sophisticated forms.

The last step previously described can be followed by another step in which the nail 30 is returned to its initial state. This step is performed mechanically at room temperature.

The use of such a nail 30 is done in the following manner. The surgeon makes a hole in the bone, for example using a bur, so as to accommodate the nail 30 in its initial state. The diameter of the hole is slightly greater than the outside diameter of the nail 30 so that it can be inserted therein.

Once introduced, the nail 30 is subjected to a heat such that it acquires the temperature T1. The nail 30 is then positioned in its first geometrical state 30B where it is wedged on the side wall of the hole made in the bone. It then keeps this shape during treatment and cannot be dismantled without further intervention.

The day of its extraction, it is subjected to a heat such that it acquires the temperature T2. It then contracts and finds itself in its second geometric state 30C. It will be noted that the fact that the degree of closure of its second geometric state 30C is slightly greater than that of its first geometric state 30B but less than that of its initial state 30A makes it possible not to damage the spongy tissue which has settled in inside the nail during processing.

Besides the fact that the method of the present invention allows the implanted nail 30 to be disassembled, the advantage which results from the use of a double memory material is here that it facilitates the installation of the nail in relation to the state of the technique where it was fixed by means of screws, the installation of which required the practitioner to work with an image intensifier from which he generally received harmful or even dangerous rays. In addition, installation and extraction operations are facilitated.

In the same way, that is to say in the form of a tube which is split longitudinally, it is also possible to produce rivets normally used for fixing plates, ligaments, etc. The use is substantially the same as that which has just been given concerning the nail 30 of FIG. 2a.

Always in the same way, we can also make femoral stems. Note that only part of the nail or rivet can be provided with a side slot, or even with several side slots.

In Fig. 3, there is shown a cup 40 which is normally intended to, on the one hand, receive the spherical head of a prosthesis, for example femoral and, on the other hand, to be fixed in the corresponding articular cavity. This acetabulum 40 consists of a substantially hemispherical hollow cap which is open laterally by a slot 41 whose width is zero. During manufacture, the width has an initial value eini. During the first education at the temperature Tl, the acetabulum is stressed so that it takes its first geometric state where the width e takes the value ei. For example, this value eι is greater than the value e _m i.

During the second education at temperature T2, the acetabulum is urged so that it takes its second geometric state where the width e takes the value e, which value can for example be slightly less than the initial value ei but greater at the value emi, and this for the same reason as that concerning the nail 30 described above.

The use of such a cup is as follows. As before, the acetabulum is placed in an articular cavity and is then subjected to a heat such that it acquires the temperature Tl. It then takes its first geometric state where the width of the slot 41 has the value ei, so that it is pressed against the walls of the articular cavity. If the temperature Tl is high, heat can be supplied by an electric knife.

Once in place, the cup keeps its place.

Upon extraction, it is subjected to heat such that it acquires temperature

T2 where it takes its second geometric state with a slot width 41 of e ₂ . This value of the width e is slightly less than the value ei of the first geometrical state which avoids, when removing the acetabulum from its location, from damaging the tissues which have formed. Such a cup in a material with two memories allows, in addition to the advantages resulting from the process of the invention, an easier and faster fitting than the cups of the prior art where it was necessary to use screws or cement. In addition, when screws were used, their friction with the polyethylene core of the acetabulum was a source of significant wear.

It will be noted that the acetabulum 40 could be provided with one or more slots such as the slot 41.

The present invention is also applicable to the mounting of implants of a metatarsophalangeal prosthesis. It is also applicable to the mounting of the lumbar cages then formed from a double memory material and educated to present two distinct geometrical states: one for placing the cage between two vertebrae and the other for extracting it from its laying position .

The present invention is also applicable to a dowel for anchoring a prosthesis, for example a knee, such as dowel 50 which is shown in

Figs. 4a to 4c. This pin 50 has a substantially cylindrical shape and is surmounted by a hemispherical cap 51 intended to receive the end of the prosthesis. It will be noted that this cap 51 could be equipped with a system for fixing to the prosthesis, for example a bayonet fixing or the like. In the cylindrical part of the plug 50, tabs are cut

52 which are then secured to the body 53 of the ankle by their bending bases

54. Thus, each of them can be flexed outward relative to its base 54.

There is shown in FIG. 4b, seen from above, a pin 50 whose tongues 52 are bent outward. This state of the ankle 50 is the first geometric state and corresponds to the state which will be given at the time of the installation of the ankle by applying heat so that it acquires a temperature close to the temperature T1.

In Fig. 4c, the ankle 50 has its tongues 52 which are retracted along the barrel of the ankle 50. This state of the ankle 50 is its second geometric state and corresponds to the state which will be given at the time of the extraction of the ankle by applying the heat necessary for it to acquire a temperature close to the temperature T2. Another application of the present invention is now described in connection with FIG. 5 which relates to a femoral stem system. This system is composed of a flat barrel 60, one end of which is provided with a centering cylinder 61 designed to receive, in a manner known per se, either directly or via a sleeve, a sphere intended to constitute the head of the femoral prosthesis. The system also includes a module 62 which is designed to adapt and cover the barrel 60. This module 62, in the example of embodiment shown, comprises two side walls 62a and 62b connected to each other by a core 62c. The module 62 is made of a memory effect material and undergoes a double education according to the method of the present invention. In the initial state, the walls 62a and 62b are parallel to each other and the distance d which separates them has a value d _m i slightly greater than the thickness of the barrel 60 so that said module 62 can be mounted in overlap of said barrel 60. In a first geometric state, the side walls 62a and 62b are slightly close to each other and the distance d is less than the value dmi and slightly less than the thickness of the barrel 60. This geometric state corresponds to the installation and fixing by simple tightening of the module 62 on the barrel 60, installation carried out at a temperature Tl. In a second geometric state, the side walls 62a and 62b are substantially parallel to each other and the distance d is consequently substantially equal to the initial value di _m and corresponds to the extraction of the module 62 from the barrel 60 which is carried out at temperature T2.

Claims

1) Method for memorizing two geometrical states of a product produced in a shape memory alloy, characterized in that it consists in: a) educating said alloy for the first geometrical state by soliciting said product to bring it and the leave in said first state at a first temperature, then at b) educate said alloy for the second geometric state by urging said product to bring it and leave it in said second state at a second temperature.

2) A storage method according to claim 1, characterized in that it consists in using as an alloy an alloy of nickel and titanium in a stoichiometric ratio close to 1, or a composite material reinforced with such an alloy.

3) A storage method according to claim 1 or 2, characterized in that the highest temperature of the two temperatures considered is between + 37 ° C and + 55 ° C while the lowest temperature is between + 30 ° C and -30 ° C.

4) Storage method according to one of the preceding claims, characterized in that said second geometric state is the initial state of said product before its first education.

5) A storage method according to one of the preceding claims, characterized in that it consists in finishing said product after education of said alloy for the first geometric state but before education of said alloy for the second geometric state.

6) A storage method according to claim 5, characterized in that said finishing step consists of polishing said product, for example by billing.

7) A storage method according to claim 5 or 6, characterized in that said finishing step consists of a low temperature deposition of a thin protective layer, made of one of the following materials: nickel carbide, carbide titanium, titanium nitride, aluminum oxide, molybdenum disulfide, titanium carbonitride, nickel ternary, titanium and aluminum, chromium nitride, diamond carbon in the amorphous state.

8) Application of the storage method according to one of claims 1 to 7 to products intended to be fixed by clamping on an element and to be extracted therefrom.

9) Application of the storage method according to claim 8, characterized in that said products are human implants.

10) Application of the storage method according to claim 9, characterized in that said human implants are staples comprising two legs connected together by a core, said two legs in said first geometric state being brought together and , in said second geometric state, being substantially parallel to one another.

11) Application of the storage method according to claim 9, characterized in that said implants consist of a tube open laterally by at least one longitudinal slot, said tube being more open in said first geometric state than in an initial state and is find, in said second geometric state, in a state close to said first geometric state also more open compared to its initial state.

12) Application of the storage method according to claim 9, characterized in that said implants are acetabular cups consisting of a hollow hemispherical cap provided with at least one slot, said slot being more open in said first geometric state than in the second geometric state.

13) Application of the storage method according to claim 9, characterized in that said implants are anchor pins essentially consisting of a cylinder whose side wall is provided with longitudinal tongues capable of bending outwardly relative to their base, said tabs being in their bent position in said first state geometric and lying along said cylinder in said second geometric state.

14) Application of the storage method according to claim 8, characterized in that said products are section modules in the shape of a "U" capable of being mounted on a flat barrel so as to form a femoral rod, the side walls of said module being close to each other in said first geometric state and being substantially parallel to each other in said second geometric state, said side walls clamping said flat barrel in said first geometric state so as to be fixed therein by clamping.