DE3036520A1 - COMPOSITE MATERIAL FOR PROSTHESES - Google Patents

Description

Description:

The invention relates to a composite material consisting of a metallic substrate and a metal wire carried by the latter built-up porous layer, a method for producing such a composite material and a prosthesis that is made using such a composite material.

A composite material of the type discussed above can be in the Use medicine for implants: the porous layer comes into direct contact with the bone tissue surrounding the implant, so that the bone tissue grows into the porous upper layer can. In this way, the prosthesis is firmly anchored.

Prostheses are known to be used to wholly or partially joints or bone segments of the human or animal Replace skeleton. Most often the prostheses are implanted in a remaining part of the skeleton. this leads to to various problems, including an undesirably heavy wear and tear and thus a short service life and that too Problem of permanent attachment of the prosthesis to the remaining hard bone parts. To make a prosthesis permanent fasten, various methods are currently used, e.g. mechanical plague clamping of the prosthesis, for which purpose one The stem of the prosthesis strikes into the medullary canal of the bone; the fixation of the prosthesis using screws; and Fixing the prosthesis using bone cement, which polymerized in situ. The latter method will

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often carried out using methyl methacrylate as cement. The last-mentioned and the other methods have the disadvantage that the prosthesis is often removed from the bone remnant dissolves, as the surrounding bone tissue is destroyed or resorbed.

More recently, other methods of permanently securing prostheses have been proposed that use the Utilizes the ability of the adjacent bone tissue to connect and grow. Examples of such methods are: The use of notches, ribs or roughened areas on the surface of the prosthesis over which the bone tissue grows can; the use of biologically active materials that can react with the bone tissue and so on be able to establish a stable connection; and the use of porous layers or porous elements in which the Bone tissue can penetrate and with which the bone tissue can grow together, so that one is stable in this way Anchoring of the prosthesis.

The present invention particularly relates to the latter method.

For prostheses that have a porous layer or a porous egg ' have ment, various embodiments have already been proposed been. It has been shown that a prosthesis has a porous top layer supported by a substrate is more advantageous than a prosthesis that is completely porous, since the mechanical properties of such a prosthesis,

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For example, the tensile strength and the mechanical durability without fatigue fractures are better. Such properties must be met by a prosthesis. It is also known that in the case of prostheses exposed to high mechanical loads, metals are more suitable as material for the porous layer than ceramic materials and polymers, since the metals have better mechanical properties such as tensile strength and ductility. An upper porous layer of metal wires is also better than an upper porous layer of metal powder, there is obtained an open pore structure with metal wires, ^ie in the cJ middle · pore size is larger and which has improved at the same porosity, mechanical strength and ductility.

In US-PS 3,906,550 an implantable prosthesis is described, which has a metallic rod which represents the part of the prosthesis that absorbs the mechanical load and is surrounded by a porous layer consisting of thin metallic wires sintered together. The porous Layer has an open-pored structure, so that the bone tissue in the manner described above into the pores can grow into it and thus a firm anchorage of the prosthesis to the bone is obtained.

In this known prosthesis, the porous layer is made by having very thin wires made of stainless steel or a similar material, cuts them into pieces and presses the cut pieces into one in a shape three-dimensional network of mechanically mutually attached to each other established fibers, whereupon this network is then sintered

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becomes> metallic at the contact points between the fibers Create bonds.

The porous layer obtained in this way can then be attached to the fasten the metal rod of the prosthesis by sintering it on or otherwise attaching it to the rod.

As a result of the chosen method of manufacture, the metallic wires are randomly oriented in the porous layer the well-known prosthesis. So there you have an open-pored structure, the shape and dimensions of the pores and also the However, the degree of porosity of the porous layer changes in a very considerable manner from one point to the other point of the layer. In addition, the pores must not be chosen too large, as this would reduce the mechanical strength of the material too much would. Finally, the porous layer has a relatively large specific surface area compared to its volume the prosthesis, and thereby; a lot of metal ions are released in the living body .. After all, this is solid Applying the porous layer to the metal rod, which must be done in a separate manufacturing step, pose a significant problem.

The present invention is intended to overcome these disadvantages and a composite material consisting of a metallic substrate and a porous coating carried by these be created, which meets high requirements and. for use in prostheses of those described above

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Kind is suitable. In addition, the present invention a manufacturing process for such a composite material specified, which is simpler than the now known process and is suitable for large scale manufacturing.

The present invention provides a composite material for this purpose consisting of a metallic substrate and a porous layer carried by this and made up of metal wires created, which is characterized in that the porous layer consists of at least one layer of metallic wire mesh, in which the wires are firmly connected to each other and to the substrate by metallic bonds at the points of contact are.

In addition, the invention provides a method of manufacturing specified such a composite material, which is characterized in that at least one layer of metallic Wire mesh is placed on a metal substrate and the wires of the wire mesh at the points of contact with each other and with the substrate connects via metallic bonds.

In this way, the above-mentioned object can be achieved. Since a metallic wire mesh is used according to the invention, one obtains a uniform and easily adjustable pore size, and one can also achieve a uniform porosity of that of the substrate Ensure worn coating. Any pore size and porosity of the coating can also be achieved, In particular, pores with larger dimensions can also be realized without affecting the mechanical strength or the

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Cohesion of the porous layer endangered. In addition, one can have a smaller ratio between the specific surface area and the volume of the material to be implanted, and this reduces the release of metal ions in vivo. One by the manufacturing method according to the invention Another "advantage obtained is that the production of the porous layer, the fixing of the metallic Wires to each other and the attachment of the metallic wires to the substrate can now be done in a single work step. This results in a considerable simplification of manufacture, and such composite material can be produced in large quantities Generate quantities.

In the following the invention will be described with reference to the enclosed Drawing explained in more detail. In this, the only figure in the upper half shows a section through a composite material, which is suitable for use in implantable prostheses, and in the lower half a top view of this Composite material.

As the drawing shows, the composite material consists of a metallic substrate 1, which is a layer of metallic Wire mesh material 2 carries. The wire mesh 2 is a metallic cloth in the form of a flat fabric, which warp wires 3 and Has weft wires 4. It is clearly visible that the warp wires 3 and the weft wires 4 are attached by metallic bonds the contact points are connected to one another and to the substrate 1, so that load-bearing connections are obtained. Remain between the warp wires 3 and the weft wires 4

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Pores 5 and 6, which are uniform in shape and size, because a fabric of the type described above is used.

In the embodiment shown in the drawing, only one layer of wire mesh material is provided. It goes without saying that you can also use a larger number of layers of wire mesh material, the wires then again under each other and are connected to the wires of the underlying layer by metallic bonds.

The substrate 1 consists of one compatible with living tissue Metal, e.g. made of stainless steel, titanium, a titanium alloy, a Co-Cr alloy, tantalum, a tantalum alloy, Niobium, a niobium alloy or zirconium. Metal becomes ceramic ·. =: Materials or polymer materials are preferred as the substrate when using the composite material in prostheses is normally represents the element exhibiting the mechanical loads. Therefore, the substrate must have good mechanical strength and. have good ductility. The substrate can have any shape suitable for the particular purpose, e.g., shape a flat plate, a round rod or the like. Have. It is not absolutely necessary that the substrate already be has the shape required for the prosthesis; it can also be brought into this form for a later time.

The wires of the wire mesh 2 are also made of biocompatible Metal, a metal that is well absorbed by living tissue. In principle one can use the same metals as for the substrate. Although the porous layer made of wire mesh

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is not intended directly as the mechanical load-absorbing part of the composite material, it must be a very resilient Ensure connection with the bone tissue. As a result, the strength of the internal bonds of the composite material should be greater than the strength of the bond between the porous layer and the bone tissue. For this reason too metals are preferred over other materials.

The wire mesh 2 ensures a porous layer with almost absolutely uniform mechanical properties, in particular Pores 5 of uniform size. The wire mesh can either be woven or knitted, with a woven wire mesh still has better properties. It is also important that the wires of the wire mesh cross each other at many points, because in this way the very important pores 6 are obtained, which are particularly important with regard to the penetration of the bone tissue are favorable and thus for a particularly resilient mechanical connection between the porous layer of the prosthesis and care for the bone.

The diameter of the wires and the density of the wires, xi.h. the The number of wires per unit length can vary within wide limits in the network, depending on the pore size and porosity one wishes. One can use metal wires with a diameter between 0.025 and 1.25 mm, while the number of Wires per inch in any direction can be between 400 and 6 (equivalent to 158 and 2.3 per cm). If you keep these limits one, one should still make sure that the mesh size or pore size in the wire mesh is always larger than that

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minimal penetration of the desired bone tissue into the pores.
It is not necessary for the wire mesh to have the shape and dimensions desired for the prosthesis at this point of manufacture; rather, the shape and the dimensions of the wire mesh have to be adapted to a certain extent to those of the substrate used.

One can choose between using a single or a plurality Choose from layers of wire mesh ^ material, depending on how the thickness of the porous layer on the substrate should be large. If several layers of wire mesh material are used, these are usually placed one on top of the other, offset from one another, in order to improve the connection between the various layers to ensure. But you can also use a plurality of layers Use wire mesh material with the same mesh size, which are laid directly on top of each other.

In the production of the above-described Verbundraateric.Isr one or more layers of wire mesh material are placed on the metallic substrate. After that, the wires of the wire mesh metallurgically bonded to one another and to the substrate.

The metallurgical bonds are preferably made by sintering or, even better, by sintering with simultaneous application of pressure manufactured. Although in principle a similar bond can also be made by spot welding, this will be Manufacturing process preferred as it is practical, in particular in the case of curved substrate surfaces, it is very difficult to obtain a

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to weld a large number of metallic wires at their points of contact with one another and at the same time with a substrate. By sintering and in particular by sintering with simultaneous application of pressure, a good connection is obtained between the various metallic wires and between the wires and the substrate. As a result, this is the method of manufacture of the composite material by far the cheapest.

In FR-PS 2 215 927 a perforated film is considered to be porous Layer of composite material is used, and this sheet is attached to the substrate by spot welds. Against this is a wire mesh is used in the manufacture of the composite material described above, and in the manufacture of the metallic connection takes place by sintering with simultaneous application of pressure.

A first advantage of pressure sintering compared to normal sintering is that the wires of the wire mesh are sintered pressed firmly against the substrate. In this way you get a good contact and a resilient sintered one Wire mesh. Pressure sintering also has the advantage that the sintering temperature can be selected to be lower.

The one for making the wires of the wire mesh and for making them Metals used in the substrate are usually sintered at temperatures above 1100.degree. Used like that high temperatures, the mechanical properties of the substrate (tensile strength, ductility, long-term load capacity without Fatigue fractures) deteriorates significantly, and this sets

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Problem in the manufacture of composite materials for prostheses when pressure sintering, on the other hand, the sintering temperature can be somewhat Select 200 - 500 C lower, which eliminates this problem completely or at least considerably mitigates it.

The pressure sintering used to obtain a layer with a porous structure represents a significant port step over the known processes. Pressure sintering is usually used in metallurgy to produce compact sintered objects produce which have the greatest possible density. Often even the theoretical material density applicable to the solid material is used achieved. If you were to pressure-sinter a mass of statistically oriented metal wires, you would get one significant increase in material density. On the other hand, since the present invention uses a wire mesh, one can use a Perform sintering with simultaneous application of pressure without having such a high density of the porous layer and a Loss of porosity must be accepted.

Pressure sintering can be done using devices which are commercially available and which exert the necessary pressure and at the same time heat up to the required level Ensure temperature in a suitable atmosphere.

The size of the selected temperature and the applied pressure as well as the duration of the sintering process depend heavily on the respective type of metal used. These factors also depend on one another, since there is an increase in the sintering pressure or an increase in the sintering time automatically cause that

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the sintering temperature is reduced. In general one can say that one in pressure sintering for the purposes of the present invention good results are obtained when working at temperatures of 600-1000 ° C and pressures of 1 to 150 MPa and one

ι selects the sintering time between 5 minutes and 8 hours. Within these general limits, the more precise working conditions will be chosen with regard to the particular metal used. For stainless steel, for example, to a temperature of 850 selected when pressure sintering - 950 ° C, while a temperature at about 650 one for titanium - 700 ° C and for titanium alloys · a temperature at about 850 selects to 950 ⁰ C. The pressure to be set together with these temperatures and the sintering time can easily be determined experimentally.

The favorable properties obtained by pressure sintering can be improved by the fact that the wire mesh before sintering in a separate process step against the sub ~ strat presses. At the beginning of the sintering process there is already; a touch area instead of touch points or lines of contact, and this is with a view to achieving a good one metallic bond of great advantage. Pressures of 10-600 MPa are used for this precompacting, with the The pressure to be applied in the individual case, the type of metal from which the wire mesh and the substrate are made, and the mechanical Properties and the weaving characteristics of the wire mesh takes into account.

If more than one layer of wire mesh material is used, it can Manufacturing process can be carried out without modification. The Ver-

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different wire mesh layers are placed on top of each other at the desired Place placed on the substrate. The layer structure obtained in this way is then used as a whole, optionally after precompacting pressure sintered. Although the phenomena now occurring are a little more complicated because there are now metallic bonds between the crossing wires of each layer, between the crossing wires of two consecutive ones Wire mesh layers and must also be made between the wires of the lowermost wire mesh layer and the substrate pressure sintering can still be carried out simultaneously in a single sintering step.

The manufacturing process described above is very simple and can be carried out at low cost; therefore even can mass production can be carried out.

The composite material according to the invention and that according to that described above The composite material produced according to the invention has a dense metallic substrate, which carries a porous coating of sintered wire mesh. As in the production with relatively low sintering temperatures the substrate has optimal mechanical properties. Since the sintering under simultaneous pressure takes place, a good, resilient connection between the wire mesh and the substrate is obtained in a single work step as well as between all crossed wires in the wirefibz among themselves. The porous layer has pores of uniform size which are uniformly distributed over the layer. Man can be any pore size, in particular also the ratio

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produce moderately large pores.

The composite material according to the invention is particularly suitable for Use in implantable prostheses, as the porous layer carried by the substrate is ideal for penetration of the bone tissue allows, so that you get a permanent attachment of the prosthesis to the bone. The composite material according to the invention can be used in various orthopedic prostheses can be used, e.g. hip and knee prostheses as well as other joint prostheses. You can also use non-metallic parts of such prostheses in the porous Include coating-bearing metallic substrate. The composite material can also be used in dental prostheses e.g. for jaw bridges. In all applications, with regard to the penetration of the bone tissue into the porous layer and excellent results in terms of permanent attachment of the prosthesis to the skeleton.

The following are two more in no way limiting examples of the practice of the present invention given:

Example I:

On a flat metal substrate made of stainless steel AISI 316L a layer of wire mesh made of the same material is laid.

The wire mesh is a flat fabric, the diameter of which is wire 0.375 mm, the wire density 7.9 / cm in each direction.

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The wire mesh is pre-compacted at room temperature pressed against the substrate by 150 MPa. After that will be the wires of the wire mesh with each other and with the substrate using a normal sintering press by pressure sintering tied together. The sintering temperature is 875 ° C / the sintering pressure 10 MPa, the sintering time one hour. A composite material consisting of a metallic substrate and a porous one is obtained Surface layer made of metallic wire mesh. The mechanical connection between the coating and the substrate is excellent, the coating has uniform porosity with uniform pore size.

Example II:

The procedure is the same as in Example I, the only difference being is that the sintering time is now 2 hours, the sintering temperature is 900 ° C and the sintering pressure 10 MPa. A composite material is obtained which has properties similar to those of Example I.

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Claims (16)

Claims Composite material consisting of a metallic substrate (1) and one carried by the latter and constructed from metal wires (3, 4) porous layer, characterized in that the porous layer consists of at least one layer of metallic wire mesh (2). consists in which the wires (3, 4) with each other and with the substrate (1) by lying at the points of contact metallic bonds are firmly connected. 2. Composite material according to claim 1, characterized in that the metallic wires (3, 4) of the wire mesh (2) made of stainless Steel, titanium, a titanium alloy, a cobalt alloy, tantalum, a tantalum alloy, niobium, a jliobium alloy or zircon. 3. Composite material according to claim 1 or 2, marked dadurph 130020/0617 -2- 3035520- net that the wire mesh (2) is a fabric. 4. Composite material according to one of claims 1 to 3, characterized in that the wires (3, 4) of the wire mesh (2) have a diameter of 0.025 to 1.25 mm and that in each direction of the wire mesh (2) 1 ^f 8 - 2.3 wires per cm are arranged. 5. Composite material according to one of claims 1 to 3, characterized in that more than one layer on the substrate (1) Wire mesh (2) is attached. 6 »Method for producing a composite material, consisting from a metallic substrate (1) and one carried by this, Porous layer made up of metal wires (3, 4), characterized in that at least one layer of wire mesh (2) is arranged on the metallic substrate (1), and the wires (3, 4) of the wire mesh (2) are metallic at their points of contact are connected to one another and to the substrate O). 7. The method according to claim 6, characterized in that the Wires (3, 4) of the wire mesh (2) made of stainless steel, titanium, a titanium alloy, a cobalt alloy, tantalum, a Tantalum alloy, niobium, a niobium alloy or zircon are made. 130020/0617 8. The method according to claim 6 or 7, characterized in that a wire mesh is used as the wire mesh (2). 9. The method according to any one of claims 6 to 8, characterized in that that the wires (3, 4) of the wire mesh (2) have a diameter of 0.025 - 1.25 mm and the wires (3/4) are arranged in each direction of the wire mesh (2) at a density of 158-2.3 wires per cm. 10. The method according to any one of claims 6 - 9 _f, characterized in that more than one layer of wire mesh (2) on the substrate (1) is arranged and is connected to this. 11. The method according to any one of claims 6- 10, characterized in, that the production of the metallic bond takes place by sintering with simultaneous application of pressure. 12. The method according to claim 11, characterized in that the sintering temperature is between 600 ° C and 1000 ° C, that the sintering pressure is between 1 and 150 MPa and the sintering time is between 5 minutes and 8 hours. 13. The method according to claim 11 or 12, characterized in that that precompacting takes place before sintering and simultaneous application of pressure. 14. The method according to claim 13, characterized in that the Pre-compacting takes place at a pressure of 10 to 600 MPa. 130020/0617 15. Composite material, characterized in that it is produced according to the method according to any one of claims 6 to 14. 16. Prosthesis, characterized in that it is made of a composite material as indicated in one of claims 1 to 5 or welc ^v äs according to one of claims 6 to 14 is made. Ι 30020/0617 ORIGINAL INSPECTED