DE19728131A1 - Versatile sliding surface for joint prostheses - Google Patents

Abstract

An implant layer serving as a sliding surface for a second (eg metal or ceramic) part of a human joint prosthesis comprises 60-99 wt.% of a base polymer with the remainder being of one or more finely-divided fillers which (i) are of very small size with breadth : height : length ratio 1 : 1 : 1 - 1 : 4 : 400; and (ii) are such as to influence at least one of the following properties : abrasion reduction; cold-flow reduction; lubrication improvement; strength increase; age cracking reduction; or increase in wetting of the composite.

Description

The invention relates to an implant bearing for artificial joint replacement in men .

Artificial joints of this type have been around in the recent history of human medicine 40 years of rapid development. Such implants are now for practically all joints available. A large part of it take artificial hip and knee joints. The number of corresponding operations is increasing steadily. There are many reasons. For one thing, life expectancy increases, so that more and more people in old age are experiencing joint problems. On the on the other hand, overeating and a lack of exercise play a triggering role. In addition, in the developed industrialized nations there is a high level of thinking, medicine technically feasible to ask for and not with physical limitations to be satisfied.

To date, the required implants are subject to constant further development, whereby the different experiences flow into the development work. goal of Efforts are as long as possible, so that the patient Revi surgery operations at an older age are spared. In the meantime you are at the named goal thanks to improved surgical methods on the one hand and optimized implants approached on the other side.

The weak point of such artificial joints is still the pairing of the materials involved. The most widespread in this regard is the com be a combination between metal and polyethylene. Of this, the polyethylene is in the middle point of discussion moved. Although this material is in principle physiologically unbe is conceivable, then the polyethylene abrasion and the granule initiated by it Lomation responsible for the loosening of prostheses.  

After e.g. B. was attempted in relation to artificial hip joints, by means of a pairing Ceramics / polyethylene to reduce the abrasion rate, there are currently a number of Akti vities to completely eliminate the risk of polyethylene wear. Some manufacturers offer joint components in ceramic / ceramic sliding pairing, others are pure Metal / metal pairings passed. The metal / metal pairings still exist a certain range of variation through the use of suitable coatings z. B. with Titanium nitride, titanium carbide, titanium oxynitrite, diamond-like carbon and the like. The These different solutions generally make the implant more expensive components and also have disadvantages, e.g. B. due to risk of breakage, Sensitivity to damage, lack of cushioning, or the occurrence of Metal abrasion. Since corresponding products have only recently been on the market and also are not widespread, so far no connection can be made about long-term behavior statement can be made.

There was therefore the task of creating appropriate implant bearings, which the inexpensive availability, unproblematic handling and damping properties of the polyethylene should have without its abrasion behavior.

The described object is achieved according to the invention by the provision a special implant bearing made of a certain composite material. Here In principle, this composite material consists of a base polymer and at least a filler with abrasion and / or low friction properties.

Generally, it is in general mechanical engineering and in the field of precision engineering known to use plain bearings made of special particle composites to the Reduce bearing abrasion. However, the requirements go in other directions than in the field of medical technology. Such be as a composite or compound drawn composites are then z. B. on the action of certain tempe instruments, aggressive chemicals, or abrasive contaminants and the like Chen tailored. In addition, the biocompatibility of the individual ingredients does not matter Role.

With the invention, the basic idea known in principle is to be created specifically adapted composite materials made available for the field of medical technology become. It is suggested at least in a body-compatible base polymer a body-compatible filler made from very small particles or short fibers with abrasion and / or friction value reducing properties this special composite material for at least one bearing side as counter-rotating partner to use in artificial joints. Pre-designed as an implant site Impacted composite material, the properties of the individual components advantageously combined with one another in such a way that a higher-value sum result in my property. The compressive forces with which the implant bearing is loaded by the polymeric base material. This is based in the Contact area on the counterpart and ensures that the embedded Fillers do not come under excessive pressure. On the other hand, fillers now work  Short fibers reinforce the mechanical strength of the composite secures over long periods and prevents the formation of aging cracks. Doing so At the same time the annoying cold flow for some base polymers (e.g. polyethylene) is reduced. The interaction between the base occurs in the composite material formed polymer and abrasion-reducing fillers such. B. in the form of microscopic particles special meaning too. Such fillers are able to abrasion the base to reduce polymers drastically while embedding them in the base polymer are protected from breaking out. Fillers with solid properties lubricants support the achievement of low sliding friction coefficients of the Ver material, but are not in all cases indispensable for the function of the Implant bearing, because e.g. B. polyethylene as a base material is already a very low Has sliding friction coefficient, especially when lubricated with the body's own Lymphatic fluid. In addition, the possibility is offered by means of suitable Fillers improve the wettability of the composite material, so as to improve the training ensure that the lymph in the artificial joint is as complete as possible.

For the practical implementation of the invention, a polymer or a Blended or copolymer with tolerable properties, e.g. B. polyethylene (PE), especially ultra high molecular weight polyethylene (PE-UHMW), polyether ketone (PEK), poly ether ether ketone (PEEK), or other polyaryl ether ketones, polyacetal (POM), polyether sulfon (PES), polysulfone (PSU), etc. and with an appropriate amount of e.g. B. between 1 and 40% of at least one body-compatible filler with at least one of the properties lowering abrasion, lowering sliding friction, increasing strength, Improvement in wettability, reduction of cold flow, or age crack inhibition from particles and / or short fibers to mix, then z. B. by means of sintering, pressing, extrusion dieren, injection molding or the like to produce either semi-finished or finished parts. Implant bearings according to the invention are then directly as finished parts or after machining Processing from semi-finished products available.

As a particularly recommended first stage of a practical implementation of the invention proposed ultra-high molecular poly for the implant bearing as the base polymer Ethylene and with a filler in particle form made of aramide or para To provide aramid and / or polyphenylene sulfone. There is a choice one of the fillers mentioned alone or in combination with the other clog. While the filler aramid or para-aramid both in long and short fiber version, as well as in the form of fine powder from particles with a globular shape is available, the filler polyphenylene sulfone has so far only been offered as a powder. For the intended application is preferred to the powder version anyway, because the Short fibers in the case of the aramid or para-aramid due to static charge on the Mixing is difficult to separate and therefore not completely combined are enclosed in the polymer. There is then a risk of using Removing individual fibers and their vagabondation with the body fluid. in the If short fibers are used, a more complex one must be used from the outset Mixing process can be scheduled.  

Fibers from the aramide group are currently used by three different people worldwide Offered to manufacturers. DU PONT is on the market with the product KEVLAR, while AKZO NOBEL sells under the trade name TWARON. As a kind of secondary or waste product from fiber production, powders with different par result Item shape and size, alongside fibers of different lengths and thicknesses. So z. B. A powder is available from AKZO NOBEL under the type designation TWARON 5011, which has an average particle size of 55 microns. Experiments have shown that this filler in combination z. B. with polyamide to a significant reduction in Wear rate leads to more than 60%. Afterwards, the values were even better to achieve powder type 5010. During short cut fibers of the type TWARON 1088 with a length of 0.25 mm gave similar values as the powder type 5011, could the abrasion rate with fiber lengths of 1.5 mm compared to the pure output polymer can be reduced by over 94%. Since the powder types mentioned are already available as Food additive has been approved is in principle of a physical tolerance go out so that with a combination z. B. made of polyethylene and aramid powder for use as an implant site no complications are expected.

With the filler polyphenylene sulfone, trade name CERAMER from HOECHST AG a relatively new material is available, which is either alone with the base polymer or in combination with other fillers to a very abrasion-resistant composite fabric leads. Corresponding powders of particles with globular shape and are currently available average grain sizes of approx. 20 µm are available. Polyphenylene sulfone has very high thermal stability and excellent chemical resistance on. A solvent for this material is not known. Its effect as an abrasion modifier kator is drastic: Try z. B. with PTFE as the base polymer and a weight CERAMER's share of 20% showed a 99% decrease in wear. At the same time, the tendency of the base polymer to creep was significantly reduced. He The surprisingly good tolerability of polyphenylene also seems astonishing to be sulfone. However, this point of view would still have to be put into practice be supported by clinical studies.

Another step in the implementation of the invention is a base polymer for the Use as an implant site with body-compatible short fibers (e.g. carbon fibers) reinforce and in the matrix thus formed also a filler made of body-compatible particles. Here is the sum of the fibrous and particulate type partly between 1 and 40% definable. In such a network z. B. the fiber shaped portion in the essence of strength, cold flow reduction and serve to prevent the formation of aging cracks, while z. B. the particulate to is then largely responsible for reducing abrasion.

The implant bearing according to the invention is for all artificial joints in humans applicable, especially z. B. in the form of cementable hip cups, inlays for press Fit, spread and screw pans for hip joints, as a meniscus for knee joints, as well as for other body joints such as elbow, shoulder, wrist and ankle joints etc.  

The invention provides a corresponding implant site, in which the abrasion is reduced so drastically that the risk of granuloma education is very likely excluded. Because of the extremely low Due to wear and tear, revision operations in this regard become superfluous. Because of the good physical tolerance, complications are not to be expected. The implant site has similarly good damping properties as the pure poly used up to now ethylene, but not its disadvantageous cold flow. In addition, it is as before Radiation can be sterilized. The implant bearing according to the invention is in contrast to ceramic or metallic components easier to handle because of it is less sensitive to knocks, bumps or scratches. A big advantage is the ver Availability of the composite material at an extremely low price and the high flexibility lity, which results from the possibility of using various implementation designs a machining process from a corresponding semi-finished product. The above Advantages make a significant contribution to the improvement of previous articulations represents.

Claims (7)

1. Implant bearing for artificial joint replacement in human medicine as a sliding partner for a second joint component z. B. made of metal or ceramic, characterized in that it is composed with a proportion between 60 and 99% of a body-compatible base polymer and with respect to the remaining amount of at least one body-compatible filler in fine distribution, the filler consisting of very small particles a width / height / length ratio between 1: 1: 1 and 1: 4: 400 is selected and causes at least one of the properties abrasion reduction, cold flow reduction, sliding friction improvement, strength increase, lowering the age cracking or increasing the wettability of the composite material. 2. Implant bearing according to claim 1, characterized in that the base polymer at least two different fillers are mixed. 3. Implant bearing according to claim 2, characterized in that the one filler a compact shape, e.g. B. globular, granular or the like with a Width / height / length ratio up to 1: 4: 10, and the other filler fibrous Has shape. 4. implant bearing according to claim 3, characterized in that the filler with a compact shape of the particles predominantly abrasion-reducing properties, and the fibrous filler predominantly strengthening, cold flow reducing and / or aging crack-inhibiting properties of the composite material. 5. implant bearing according to one or more of the preceding claims, characterized characterized in that the base polymer from at least one of the polymers polyethylene (PE), in particular ultra high molecular weight polyethylene (PE-UHMW), polyether ketone (PEK), Polyether ether ketone (PEEK), another polyaryl ether ketone, polyether sulfone (PES), Polysulfone (PSU) and polyacetal (POM) is selected.   6. Implant bearing according to one or more of the preceding claims, characterized characterized in that the filler consists of at least one of the substances aramid or para Aramid, polyphenylene sulfone and carbon fiber is selected. 7. implant site according to one or more of claims 1, 2 and 5, characterized characterized in that the filler consists of aluminum oxide and / or zirconium oxide.