NL7907231A - COMPOSITE MATERIAL FOR PROSTHESIS. - Google Patents

Description

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Composite material for prostheses.

The invention relates to a composite material, consisting of a porous coating of metal wires on a metal substrate, and also a method for the production thereof. Such a composite material can find use in implantation prostheses, wherein the porous coating comes in direct contact with the surrounding bone tissue and allows the bone tissue to grow into the porous coating so that a firm anchoring of the prostheses can be achieved.

As is known, prostheses are used to partially or completely replace joints or bone segments in the skeleton of humans and animals. Usually these prostheses are intended for implantation in the remaining part of the skeleton. Various problems can arise here, both in the field of excessive wear and a corresponding short life, as well as in the field of durable attachment to the remaining hard bone parts. With regard to this durable fixation, various methods are currently in use, such as punching a prosthetic rod into the medullary cavity of the bone; a mechanical fastening 20 by means of screws; and an attachment by means of an in situ polyraerizing bone cement. Especially the latter method, with methyl methacrylate as cement, is widely used. The problem with these and other methods, however, is that failing adhesion often involves destruction or resorption of the surrounding bone tissue.

Recently, other methods of durable attachment have been proposed that utilize the ability of the surrounding bone tissue to effect binding and bonding. Examples of these methods are: using notches, ribs or rough spots on the surface of the prostheses to allow bone tissue to grow thereon; the use of biologically active materials that can react with the bone tissue to form a tight bond; and the use of porous layers or elements in which the bone tissue can penetrate and grow 7307231 • dt -2- to create stable anchoring.

The invention is mainly concerned with the latter method.

Various embodiments have already been proposed for prostheses with a porous layer or element 5. It has been found that the use of a porous coating on a substrate is preferable to a completely porous object, because of the mechanical requirements such as tensile strength and fatigue strength, which the prosthesis must meet. Furthermore, the material of the porous layer has been set. of considerably stressed ferments than ceramics or polymers, due to their better mechanical properties such as tensile strength and ductility. Furthermore, a porous metal wire coating is more satisfactory than a porous metal powder coating, since metal wires provide an open-pore structure with a larger average pore size and considerably better strength and ductility at the same porosity.

U.S. Pat. No. 3,906,550 to Rostoker and Galante discloses an implant-type prosthesis 20 which, in one embodiment, consists of a metal rod as a load-bearing element surrounded by a porous layer of sintered thin metal wires. The porous layer has an open pore structure and is intended to grow bone tissue in the pores in the above manner in order to obtain an anchoring.

In this known prosthesis, the porous layer is made by pleating, cutting into pieces, ultra-thin wires of stainless steel or a similar metal, compressing the pieces in a die with punches into a three-dimensional network of mechanically interlocking fibers and this network sintering in order to metallurgically bond the fibers at the contact sites.

The resulting porous layer can be attached to the metal rod 35 of the prosthesis by sintering or otherwise.

As a result of the manufacturing method used, the metal wires in the porous layer of the known prosthesis are oriented quite randomly. The result is a 7907231 t ·. Open pore structure, but the shape and dimensions of the pores, as well as the degree of porosity, can vary widely from place to place. In addition, the pores cannot be too large, since the mechanical strength of the material then deteriorates too much. Also, the porous layer has a relatively large specific surface area relative to the volume of the prosthesis, which greatly increases the release of metal ions in yivo. Finally, the adhesion of the porous layer to the metal rod, which must be provided in an additional processing step, is a greeting problem.

It is an object of the invention to obviate said drawbacks and to provide a composite material with a porous coating and a metal substrate, which meets high requirements and which can be used excellently for prostheses of the type already outlined. Moreover, it aims to provide a manufacturing method for such a material which is simpler than the known method and which enables large-scale manufacturing.

The invention provides a composite material, consisting of a porous layer of metal wires on a metal substrate, which material is characterized in that the porous layer is composed of at least one layer of metal wire mesh, in which the wires at the contact points are metallurgically connected to each other and to the substrate are attached.

It also provides a method of manufacturing such a material, which is characterized by laying at least one layer of metal wire mesh on a metal substrate and connecting the wires of the mesh on their contact plates metallurgically and to the substrate.

In this way, the stated objectives can be properly achieved. Thanks to the use of a metal wire mesh, an even and easily controllable pore size as well as an even porosity can be obtained. It also becomes possible to set any desired pore size and porosity, and in particular to make large sized pores without detriment to the mechanical strength or integrity of the porous layer. In addition, a smaller ratio 790 7 2 3 t materiaal -4- of specific surface area to volume of the material to be implanted is provided, thereby reducing the release of metal ions in vivo. An advantage of the production method according to the invention is moreover that the formation of the porous layer, the bonding of the metal wires and the bonding of the metal wires to the substrate can now be carried out in almost a single operation, which entails a considerable simplification and a Enables manufacturing on a larger scale. For a good understanding of the invention, reference is made to the drawing, which shows a composite material according to the invention in perspective and by way of example. This material consists of a metal substrate 1 with a layer of metal wire mesh 2 thereon. The mesh 2 is a fabric with a flat bond, consisting of warp threads 3 and weft threads 4. It can be clearly seen that the wires 3 and 4 are metallurgically connected at their contact points. and bonded to the substrate 1 to provide a tight bond. Pores 5,6 remain between the various wires 3 and 4, which, thanks to the fabric used, are uniform in shape and dimensions. Although only one layer of wire mesh is drawn, it will be apparent that more layers of wire mesh may also be present on top of each other, the wires then being metallurgically joined together and on the. wires from a previous layer will be attached.

The invention will now be described in more detail.

The substrate 1 may consist of any metal which is compatible with living tissues, such as, for example, rust-titanium, titanium alloys, Co-Cr alloys, tantalum, 30 or zirconium. A metal is preferred over other materials, such as ceramics or polymers, since the substrate will generally form the load-bearing member when used in prostheses, and therefore must have good mechanical strength and good ductility. The substrate can further have any suitable shape, for example the shape of a flat plate, a round rod or the like.

It is not absolutely necessary that the substrate already has the desired shape for a prosthesis since it can also be brought into the desired shape later on.

The wires of the wire mesh 2 used may also consist of any metal which is compatible with living tissues. In principle, the same metals as 5 for the substrate can be used for this. Although the wire mesh porous layer is not intended directly as a load-bearing element, it should ensure a firm bond with the bone tissue, which however should not be stronger than the internal saraenhahg of the composite material, therefore metals are preferred here above 10 other materials. .

The wire mesh 2 provides a porous layer with almost uniform mechanical properties, in which pores 5 of uniform size occur. This mesh can optionally be woven or knotted, although a woven mesh is preferred. It is also important that the wires of the mesh cross in many places, thus creating the important pores 6 which are of concern for ingrowth of bone tissue and thus for entanglement of porous surface and bone.

The diameter of the threads and the number of threads per unit length in the mesh can vary inner limits depending on the desired pore size and porosity. For example, metal wires with a diameter between 0.025 and 1.25 mm can be used, while the number of wires per inch in any desired direction can be between 400 and 6. Taking these limits into account, it is ensured that the mesh size or pore size in the mesh is always larger than the desired minimum size for ingrowth of bone tissue into the pores.

Here, too, it is not necessary that the wire mesh already has the desired shape and dimensions for a prosthesis 30. Whey should be slightly adapted in shape and size to that of the substrate used.

Optionally, one or more layers of wire mesh can be used, depending on the desired thickness of the porous layer on the substrate. In the case of multiple layers, these are usually staggered relative to each other to promote better adhesion of the different layers to each other, but the possibility of a number of straight layers of equal mesh size becomes 790 7 2 3 f> r Ν -6- not excluded.

In the manufacture of the composite material according to the invention, one or more layers of wire mesh are placed on the metal substrate, after which the wires of the mesh are metallurgically connected to each other and to the substrate at their contact points.

The metallurgical bond is preferably effected by sintering / and even more preferably by pressure sintering. Although such a bond could in principle also be obtained by spot welding, this possibility is not preferred, if in practice it proves practically impossible, especially with curved substrate surfaces, a large number of metal wires are joined by spot welding at their contact points simultaneously and weld to a substrate. By sintering, and especially pressure sintering, a good bond between the various metal wires and a good bond between the wires and the substrate can be obtained, so that this method is by far preferred.

A first advantage of pressure sintering over normal sintering is that the wires of the wire mesh are pressed against the substrate during sintering, so that good contact is obtained for causing sinter neck formation. In addition, pressure sintering has the advantage that the sintering temperature can be lowered.

The metals which are preferably used for the wire mesh 25 are normally sintered at temperatures above 1100 ° C. However, when such high temperatures are used, the mechanical properties (tensile strength, ductility, fatigue strength) of the substrate deteriorate sharply, which is a problem. However, by now sintering under pressure, the sintering temperatures can be chosen to be about 200-500 ° C lower, thereby overcoming or at least greatly reducing this problem.

It is noted that the use of printing inserts to obtain a porous structure layer, as in the present invention, is in sharp contrast to the prior art. Pressure sintering is usually used to obtain sintered compact objects of the highest possible density. Often 790 7 2 3 t • 'S, k? -7- approximated the theoretical density of the material. The use of pressure sintering on a mass of randomly oriented metal wires would also lead to a strong compaction of the material. On the other hand, in the present invention, thanks to the use of wire mesh, it is possible to use a pressure sintering which does not lead to such compaction (and to a loss of porosity).

The pressure sintering operation can be carried out with the equipment available for this purpose, which on the one hand can provide the required discharge pressure and on the other hand the required temperature and atmosphere.

The temperature and the duration of the sintering, as well as the pressure applied thereto, strongly depend on the type of metal used. Moreover, these factors are interdependent, because an increase in sintering pressure or sintering duration automatically implies a decrease in the required sintering temperature. In general, it can be stated that the pressure sintering proceeds well at temperatures of 600 ° C ° C, pressures of 1-150 MPa and times of 5 minutes to 8 hours.

20 Within these general limits, however, further specifications are possible on the basis of the material type used. For example, stainless steel can be sintered well under pressure at 850-950 ° C, while this temperature for titanium is at 650-750 ° C and for titanium alloys at 85 ° -950 ° C. The associated pressures and durations can easily be determined experimentally.

The effect of the pressure sintering can be further improved if the wire mesh is pressed against the substrate 30 in a separate processing step prior to sintering. A contact surface, instead of a contact point or contact line, is then already present at the start of sintering, and this can be of great advantage for obtaining a good metallurgical bond.

For this pre-compacting pressures of from 10 to 00 MPa can be used, depending on the metal of wire mesh and substrate and on the mechanical properties and recruitment characteristics of the mesh.

When using more than one layer of wire mesh, no change in operations occurs. The various layers are placed on top of each other and on the substrate in the desired position, after which the product as a whole is subjected to a pressure sintering, possibly preceded by a pre-compaction. Although the phenomena appearing are more complicated, it is now necessary to establish metallurgical bonds between the intersecting wires of each layer, between the intersecting wires of two successive layers and also between the wires of the bottom layer and the substrate, all these phenomena can still be realized in a single sintering operation and at the same time.

Thanks to this simple method, an economical manufacture of the product and even mass production is possible.

The product according to the invention, as obtained by the method outlined, is a composite material consisting of a dense metal substrate with a porous coating of sintered wire mesh on top. Due to the use of relatively low sintering temperatures, the substrate has optimal mechanical properties. Thanks to the pressure sintering 20 in one operation, it is well bonded. wire mesh on the substrate and of all intersecting wires in the wire mesh are mutually present. The porous layer has uniformly sized pores that are evenly distributed over the layer.

Any desired size of the pores and in particular also a relatively high pore size can be realized.

The composite material of the invention is particularly suitable for use in implantation prostheses, since the porous layer on the substrate is an excellent means to promote ingrowth of bone tissue and thereby achieve a durable fixation of the prosthesis to the bone. The material can be used for many orthopedic prostheses, such as hip, knee and other joint prostheses. In addition, it is possible to encapsulate non-metallic parts of these prostheses in the metal substrate bearing the porous coating. Furthermore, the composite material can be used in dental prostheses, for example a defect bridging prosthesis in the jaw. Excellent performance can be obtained in all these applications, 790 7 2 3 1 -9-

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vessel concerns the ingress of bone tissue into the porous layer and a durable attachment of the prosthesis to the skeleton.

Some non-limiting exemplary embodiments will now follow. of the method according to the invention.

Example I

A layer of wire mesh of the same material was placed on a flat metal substrate of stainless steel AISI 316 L.

The wire mesh was a plain weave fabric 10 containing 20 threads per inch in each direction with a thread diameter of 0.375 mm.

At room temperature, the wire mesh was pressed against the substrate with a pre-pressure of 150 MPa. The wires were then adhered to each other and to the substrate by pressure sintering with a conventional pressure sintering press. A sintering temperature of 375 ° C was maintained for 1 hour under a pressure of 10 MPa. A composite was obtained, consisting of a porous metal mesh coating on a metal substrate, in which the coating is well adhered to the substrate, and also exhibited uniform porosity and pore size.

Example II

The method of Example I was repeated, except that the sintering now took 2 hours at a temperature of 900 ° C and a pressure of 10 MPa. A composite material with similar properties as in Example 1 was obtained.

790 7 23 1

Claims (16)

Composite material consisting of a porous layer of metal wires on a metal substrate, characterized in that the porous layer is composed of at least a layer of metal wire mesh, in which the wires at the contact points are metallurgically connected to each other and to the substrate are attached. 2. Material according to claim 1, characterized in that the metal wires of the wire mesh consist of stainless steel, titanium, titanium alloys, cobalt alloys, tantalum / tantalum bearings or zirconium. Material according to claim 1, characterized in that the wire mesh is a fabric. Material according to claim 1, characterized in that the wire mesh has a wire diameter of 0.025-1.25 mm and contains 400 to 6 wires per inch in each direction. Material according to claim 1, characterized in that more than 1 layer of wire mesh is present on the substrate. 6. Method for making a composite material consisting of a porous layer of metal wires on a metal substrate, characterized in that at least one layer of metal wire mesh is laid on a metal substrate, and the wires of the mesh are metallurgically contacted at their contact points with to each other and to the substrate. A method according to claim 6, characterized in that the wires of the wire mesh consist of stainless steel, titanium, a titanium alloy, a cobalt alloy, tantalum, a tantalum alloy or zirconium. 8. Method according to claim 6, characterized in that the wire gauze is a fabric. A method according to claim 6, characterized in that the wire mesh has a wire diameter of 0.025-1.25 mm and contains 400 to 6 wires per inch in each direction. 10. A method according to claim 6, characterized in that more than one layer of metal wire mesh is placed on the substrate and bonded thereto. Method according to claim 6, characterized in that the metallurgical compound is effected by pressure sintering. 79 0 7 2 3 f -11- β, A method according to claim 7, characterized in that the sintering temperature is between 600 and 1000 ° C, the sintering pressure is between 1 and 150 MPa and the sintering time is between 5 minutes and 8 hours. 13. A method according to claim 6, characterized in that a further pre-compaction takes place prior to the pressure sintering. 14. Method according to claim 13, characterized in that the pre-compacting takes place under a pressure of 10-400 M? A. Composite material obtained by the method of claims 6-14. A prosthesis made from the composite material of claims 1-15. 7907231