SE468502B - POROEST IMPLANT - Google Patents

Description

CA Q 10 15 20 25 30 35 (J1 CD {\) where Y is a geometric position and shape factor, of constitutes the breaking strength and c indicates the largest permissible defect.

For known materials for implant applications, such as alumina and hydroxylapatite with fracture toughness values of 3.0 and 1.0 MPaml / 2, for example, a 200 μm pore entails a maximum strength level of about 150 and 40 MPa, respectively, which makes both these implant materials doubtful for mechanically high stress applications. There is also a risk of slow crack growth, especially for hydroxylapatite, which means that tolerable stresses are easily below the stated values.

New construction ceramics, for example based on silicon nitride or zirconia, are more suitable for such high pressure applications. A ceramic material that has been shown to maintain a relatively high strength despite the presence of a large amount of pores is reaction-bonded silicon nitride, Si3N4 (RBSN). However, even with these structural ceramics, as well as with other conceivable implant materials, such as steel, titanium and other metals, polymers as well as with other oxidic or non-oxidic ceramics, a balance must be struck between the porosity and the nature of the pores and the requirement for strength.

BRIEF SUMMARY OF THE INVENTION The object of the invention is to offer an implant of the type stated in the preamble which in itself combines a high strength with high demands on a favorable situation for both bone ingrowth and for tissue ingrowth with integrated soft and hard tissue cooperation and the ability to provide reservoirs. in the material depositable substances with specific functions. These and other objects can be achieved according to the invention in that communicating pores with a pore size in the range 0.1-10 μm occupy 10-80% of the total pore volume in said at least a portion of the material, that pores with a pore size in the range 10-50 μm um occupies a maximum of 5% of the total pore volume in said portion of the material, and that 5-40% of the surface of said at least a portion of the implant is covered by substantially evenly distributed pores with a pore size in the range of 50-500 μm. Preferably, said communicating pores having a pore size in the range 0.1-10 μm occupy 25-75%, preferably 40-60% of the total pore volume in said at least a portion of the implant material.

Preferably, the major part, by volume, of the above-mentioned communicating pores has a pore size in the range 0.3-8 μm, suitably in the range 0.5-5 μm.

Preferably, a 10-30%, preferably 15-25% of the surface within said at least a portion of the implant is covered by the substantially evenly distributed pores with a pore size in the range of 50-500 μm.

The majority of the large pores in the surface layer preferably have a size in the range 75-400 μm, more preferably the size 100-300 μm and most expediently in the range 150-250 μm.

According to one embodiment, the large pores occur only in a surface layer of the implant, by which is meant a surface layer which is 3 mm, preferably 2 mm and preferably 0.3 mm thick.

Because the material substantially lacks - or at least contains a smaller proportion of - pores in the range 10-50 μm, with moderate requirements for strength according to another embodiment of the invention, large pores can still occur in the interior of the material. According to this aspect of the invention, 10-80% of the total pore volume of the larger pores is occupied by a pore size in the range of 50-500 μm, preferably in the range of 75-400 μm, more preferably in the range of 100-300 μm and most preferably in the range of 150-250 μm. .

By pore size is meant, in the case of pores with pore sizes less than or equal to 50 μm, sizes determined by traditional Hg porosimetry, where the relationship between pore diameter (2 r) is obtained from the expression _ 2 s cosF, p where I * 10 15 20 25 30 35 (_71 -cø m: p = pressure s = Hg's surface tension at current temperature F = meniscus angle (edge angle) (ref LC Ritter and RL Drake, Ind. Eng. Chem. Lz 782 (1945)) For pore sizes exceeding 50 μm, of course sizes obtained by optical determination in a light microscope on a cross section of the samples at a section taken at a depth of 0.1 [mu] m and in a section perpendicular to the sample surface, respectively, the term "total pore volume in the material" means the pore volume measured by water penetration.

The invention is thus characterized by complex pore size distributions, which provides the possibility of optimal combinations of strength and training of soft tissue as well as favorable bone growth.

In general, it can be said that the large pores are favorable for bone growth, while the small pores are favorable for the formation of soft tissue, at the same time as they can function as reservoirs for soluble substances deposited in the material with specific medical / biological functions. In order to allow favorable bone ingrowth and soft tissue formation, respectively, both the large and the small pores must be present in the surface of the implant, at least in a portion of the surface where it is desired that said functions be effective. The whole material also contains the small pores in a communicating pore system in order to act as the said reservoirs for deposited substances, such as substances which contain calcium and / or PO 4, preferably in the form of calcium phosphate material, for example hydroxylapatite, bone growth stimulating hormone, anti-inflammatory substances. etc.

The implant is prepared according to the invention from powders which are consolidated into a porous body, which can be carried out according to any technique known per se, for example conventional sintering, cold pressing followed by hetisostatic pressing, or by nitriding or the like.

Thus, for example, a material of silicon nitride is preferably prepared by nitriding silicon grains so as to obtain so-called reaction-bonded silicon nitride (RBSN), Si3 N4. The material may also contain substances other than Si3N4, but when selecting this material at least 80% by weight should be Si3N4. Other possible materials include calcium phosphate materials, for example hydroxylapatite, Al 2 O 3, titanium, SiC, ZrO 2, chromium, cobalt steel, high alloy stainless steels, and certain polymers. The implant may consist entirely of any of these materials, or of mixtures of two or more of these materials, or consist essentially of any of these materials in combination with any additional material not mentioned herein. It should further be mentioned that the implant may have different composition in different parts, one part may be porous according to the present invention, while another part may consist of a more conventional material and be substantially pore-free. Combinations of batches of different composition, but each porous according to the principles of the invention, are also conceivable.

The porosity and pore size distribution of the material can be controlled via any of the following techniques: 1) by selecting the original grain size of the raw material 2) by regulating process parameters, pressure, temperature and time during consolidation (densification) 3) by additions in gas or in the raw material 4) by post-processing Thus, the finer pore fraction is obtained by controlling 1) and 2) above. For example, in the case of an RBSN material, the size of the original Si grains determines the pore size of the fine pore fraction and the distribution of formed reactive silicon nitride (RBSN), while the larger pores in the surface are preferably obtained by finishing according to 4) above. If, instead or in combination with larger pores produced by finishing the surface, larger pores in the main part of the material are also desired, this can be achieved by adding to the raw material fibers, for example polymer, ceramic or metal, which are burned or leached away before or after the material dering. Glass fibers can also be added, which can be used as sintering agents or removed before or after consolidation. For the production of the larger pores in the surface layer, laser and / or ultrasonic processing or water jet cutting can be used in particular.

In this way pores can be provided with a particularly favorable pore profile, which limits the stress concentrations at the pores. Through such a technique, i.e. selection of not only pore size and depth, but also of pore profile, the implant material can be loaded even higher than otherwise by the Y-value in the basic mechanical expression 1/2 K: YUC lC of the order of 1.2-1.4. , is lowered from the theoretical maximum value of 1.98 to For materials produced by consolidating powders of different metals or very solid ceramic materials, combinations of fine porosity and coarse (macro) porosity can be obtained by any sintering process which is not driven to fullness followed by a surface treatment, e.g. using any of the techniques described above, to obtain macroytic porosity. Relevant materials here can be Co-Cr steel, Ti alloys and ceramics, primarily oxides of aluminum and zircon as well as non-oxidic materials of silicon nitride and SiAlON type.

Further features and aspects of the invention appear from the following examples as well as from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the following description reference will be made to the accompanying drawing figures, of which Fig. 1 shows a shoulder prosthesis, with a portion consisting of a porous material according to the invention, Figs. Fig. 2 shows a hip joint prosthesis, where also a portion consists of a porous material according to the invention, Fig. 3 shows a dental implant for anchoring teeth in bone, which implant also has a porous portion according to the invention, Figs. 4-7 show schematically how in the surface macroporphs present in the material may look like, and. Fig. 8 is a diagram showing the required shear force for ejection of an implant as a function of the growth time.

DESCRIPTION OF EMBODIMENTS Example 1 Fibers in the form of 1-2 mm long pieces of a 0.2 mm diameter nylon line are added to a powder mixture consisting of zirconia containing 3% by volume of yttrium oxide. The fiber content amounts to 12% by volume.

The mixture is tumbled for 2 hours in a roller ball mill with polymer container and spherical grinding bodies of zirconia. Crude bodies are produced by cold pressing at a pressure of 250 MPa. The blank presses are heat treated to drive off the organic component, ie the nylon fibers. During stripping, the temperature is raised 5 ° C / h up to 500 ° C. The relatively brittle crude body obtained is sintered at 150 ° C for 3 hours. Hg porosimetry indicates pores with a size of about 1 μm. Optical examination in light microscope of a cross section shows the presence of large pores of the order of about 170 μm.

Example 2 Alumina powder of a grade with the designation AKP30 with a specific surface area (BET) of about 20 mg / g, corresponding to a grain size <0.1 μm, is pressed into a cubic test body measuring 10 x 10 x 10 mm. The body, encapsulated in glass, is densified by means of hot isostatic pressing, so-called HIP-ning. The densification (consolidation) is carried out at 150 ° C for 20 minutes. The maximum pressure at the peak temperature is 160 MPa.

The porosity is measured by water penetration to 14.5% by volume.

Hg porosimetry shows that the majority, i.e.> 90% of the pores are in the range 0.4-0.7 μm with an average pore size of 0.6 μm, while <3% of the total pore volume is in the range 10-50 μm.

Example 3 Methyl alcohol is added to a silicon raw material consisting of silicon powder of type Sicomill 4D. After light tumbling, grains larger than 5 μm are separated by sedimentation. The remaining silicon raw material thus consists of powder with grain sizes <5 pm. A crude compact with the dimensions 10 x 5 x 30 mm Cï \ GO 10 15 20 25 30 35 .ÄÃJ is produced by cold isostatic pressing with 3 vol% polyethylene glycol as a pressing aid. Evaporation of PEG takes place by heating approx. 10 ° C / h up to 400 ° C. Thereafter, the crucible is nitrided with a nitrogen-containing atmosphere in two steps at 160 ° C for 5 hours and at 140 ° C for 15 hours; to give a reaction-bonded silicon nitride, Si3N4 (RBSN). The nitrided body has 22% by volume of open (communicating) porosity measured by vacuum suction and water penetration.

Hg porosimetry shows a very narrow pore size distribution with> 90% of the total pore volume in the range 0.2-1.0 μm and with <3% in the range 10-50 μm. Of the pores in the range 0.2-1.0 μm, the main part is more specifically in the range 0.2-0.4 μm.

Example 4 10% by volume of glass fibers of CaAl silicates glued to a diameter of 150 μm and with a length of 1-2 mm, a silicon nitride raw material designated UBE E10 is added. The mixture is homogenized and crude bodies are prepared in the same manner as in Example 1. Samples are prepared by sintering the crude bodies at 1800 ° C for 2 hours in a nitrogen atmosphere in a powder bed of coarse silicon nitride. The total porosity of the specimens is measured by water penetration to 11% by volume. Optical evaluation in light microscope shows a coarse fraction of pores of the order of 150 μm.

Example 5 From test strips of completely dense silicon nitride containing 2% yttrium oxide and with a density of 3.22 g / mmm produced by hetisostatic pressing at 1750 ° C, 160 MPa, lh, 20 test rods with the dimensions 3.5 x 4.5 x 40 mm are manufactured for strength testing by cutting and edge refraction (45 °). Half of the test rods are provided with macropores on one side by computer-assisted laser cutting which gives a schematic pore profile according to Fig. 5. Strength measurements show that with 200 μm deep pores and with profile according to Fig. 5 a reduction of the average strength is determined by 4-point bending test from 680 MPa (without macropores) to 350 MPa. The mean value 350 indicates that the Y value in equation (1) is low.

With a measured fracture toughness value of 5.0 Maml / 2, it corresponds to a Y-value of approx. 1.2. Example 15 Raw press bodies from Example 3 are provided with surface macropores of the order of 200 μm by treating the surface with a stamp with tightly distributed, protruding "nail mat" type needles. The needles with a center distance of 400 μm make an impression with a depth of 200 μm. The profile of the impressions is shown in Fig. 7. Thereafter, the samples are nitrided in the same manner as in Example 3.

The average strength of the surface macroporous material prepared by Example 3, determined by 4-point bending test, is 290 MPa.

A material with surface macropores prepared by Example 1 has a strength of 150 MPa determined according to the same 4-point bending test.

Example 7 This example relates to a method of manufacturing the material according to the invention. Samples consisting of sintered zirconia with 3% by volume of yttrium oxide and with a density of 6.07 g / cm: surface-treated with ultrasound, using a boron carbide slurry with a grain size of about 30 μm. Ultrasonic tools with different topography corresponding to pore configurations according to Figs. 4 and 6 were used.

Example 8 This example relates to some possible applications of the invention.

Computer-controlled laser cutting can be used for applying surface macropores to three implant components in areas which are mechanically low-stressed when the implant is used. The material in these areas consists of porous materials according to the invention and has been estimated in Figs. 1-3. These components consist of - a shoulder joint component, Fig. 1 - a hip joint component (stem), Fig. 2, and - a dental implant, Fig. 3. Other parts of the implants, ie the non-shaded, more stressed parts, can consist of materials such as are more conventional implant materials or per se other unconventional 'materials that meet the specific requirements of these parts of the respective implants.

CT * (10 CD, l 10 Example 9 From materials with surface macropores described in examples 3, 5, 6 and 7, cylinders with a diameter of 2.8 mm and a length of 7 mm are manufactured.

The cylinders are implanted in the femora of the rabbit. After three months, the animals are sacrificed and the required shear forces for ejection of the cylinders are determined with a so-called push-out test. The results are summarized in Table 1.

'N Table 1' Material Shear force (MPa) Note RBSN (Example 3) 2 Without surface macropores RBSN (Example 6) ll With surface macropores Zirconia (Example 7, pore appearance, Fig. 4) 12 With surface macropores Silicon nitride (Example 5) 10 With surface macropores Silicon nitride (reference material) 2 Without surface macropores Example 10 Cylinders with a diameter of 2.8 mm and a length of 7 mm of material according to Example 2, i.e. consisting of fine porous alumina, are surface treated by laser processing according to Example 5 to create complex pore size distributions, namely a microporous fraction in the whole material obtained in the manufacture of the cylinders and a macroporous surface fraction. The configuration of the surface macropores corresponds to Fig. 5. In the open fine pore structure, Ca-phosphate precipitates by reaction between calcium hydroxide and ammonium hydrogen phosphate. Similarly, other bone growth stimulating agents may be added to the fine pore structure, for example bonegrowth factor or anti-inflammatory agents by, for example, lyophilization. The cylinders thus produced and treated are implanted in femora in rabbit. The animals are sacrificed after 2, 5 and 8 weeks. Reference material without deposition of Ca-phosphate. Shear forces between implants and newly formed bone are determined by push-out testing. The results are shown in Fig. 8, which shows the shear force as a function of the growth time (weeks).

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Claims (10)

10 15 20 25 30 35 468 502 ll PATENT REQUIREMENTS Implants of porous non-toxic material with a total open porosity exceeding 5% by volume but not exceeding 80% by volume within at least one portion of the implant, characterized by - communicating pores with a pore size in the range 0.1-10 pm occupies 10-80% of the total pore volume in said at least one portion of the implant, - that pores with a pore size in the range 10-50 μm occupy a maximum of 5% of the total pore volume in said at least one portion of the implant, and - that 5-40% of at least a portion of the surface of the implant is covered by substantially evenly distributed pores with a pore size in the range so-soo pm. Implant according to claim 1, characterized in that said communicating pores with a pore size in the range 0.1-10 μm occupy 25-75%, preferably 40-60% of the total pore volume in said at least a portion of the implant material. Implant according to claim 1 or 2, characterized in that said communicating pores have a pore size in the range 0.3-8 μm, suitably in the range 0.5-5 μm. Implant according to claim 1, characterized in that 10-30%, preferably 15-25% of the surface within said at least a portion of the implant is covered by the pores with a pore size in the range 50-500 μm, which pores are substantially evenly distributed over the surface of said portion. Implant according to claim 1 or 4, characterized in that the main part of the large pores in the surface layer has a size in the range 75-400 μm, preferably in the range 100-300 μm and preferably in the range 150-250 μm. Implant according to one of Claims 1, 4 and 5, characterized in that the large pores only occur in a surface layer which is 3 mm, preferably 2 mm and preferably 0.3 mm thick. -P> () \ Of) 10 15 20 25 30 35 KID ßâ 12 Implant according to any one of claims 1-6, characterized in that 10-80% of the total pore volume is occupied by the larger pores with a pore size in the range 50-500 μm. Implant according to any one of claims 1-7, characterized in that said at least a portion of the implant consists mainly of reaction-bonded silicon nitride. An implant according to any one of claims 1 to 7, characterized in that said at least a portion of the implant consists essentially of a plurality of calcium phosphate materials, titanium, SiC, CrO 2, chromium, cobalt steel, high alloy stainless steel and polymer. Implant according to one of Claims 1 to 9, characterized in that the communicating pores with the smaller pore size contain deposited substances with desirable medical and / or biological functions.