Implant made of a fiber composite material

Abstract

The invention relates to an implant and a set for producing an implant and their uses. Furthermore, the invention describes a method of making an implant as per the invention. An implant for producing bone implants with improved mechanical characteristics, especially with adjustable mechanical characteristics, is provided via the invention. The implant as per the invention made up of a fiber composite material contains resorbable mineral bone cement as the matrix material, to which reinforcing, long metal fibers and/or endless metallic fibers with an aspect ratio of at least 100:1 are added in the form of at least one fiber structure that provides a framework and that preforms the contour of the implant.

Claims

1. Implant made of a fiber composite material, containing: a) resorbable mineral bone cement as a matrix material, b) reinforcing, long metallic fibers and/or endless metallic fibers with an aspect ratio of at least 100:1 in the form of at least one fiber structure with a three-dimensional design providing a framework that preforms the contour of the implant, wherein said reinforcing, long metallic fibers and/or endless metallic fibers are arranged longitudinally with respect to the direction of stress to be applied to the implant and wherein stressed areas of the implant have a quantity of reinforcing, long metallic fibers and/or endless metallic fibers greater than the average quantity in the implant.

2. Implant according to claim 1, characterized in that the fiber structures providing a framework are concentrated in the outer area of the implant.

3. Implant according to claim 1, characterized in that the fiber structures providing a framework exist in the form of multifilaments and/or in the form of a fiber preform made of at least one layer.

4. Implant according to claim 3, characterized in that the fiber structures contain pores with a size of 100-2500 m between the metallic fibers.

5. Implant according to claim 1, characterized in that more than 80% by weight of the metallic fibers are located in a range of 0.1-5 mm measured from the outside of the implant.

6. Implant according to claim 1, characterized in that the long metallic fibers and/or endless metallic fibers are made of a non-resorbable metal.

7. Implant according to claim 1, characterized in that the long metallic fibers and/or endless metallic fibers are made of a resorbable metal.

8. Implant according to claim 1, characterized in that the implant has a compressive strength of >50 MPa and/or a bending strength of >10 MPa.

9. Implant according to claim 1, characterized in that the mineral bone cement contains silicates, phosphates, sulfates, carbonates, oxides and/or hydroxides in combination with calcium ions, magnesium ions and/or strontium ions.

10. Implant according to claim 1, characterized in that the resorbable mineral bone cement exists in the form of a water-free, pasty preparation, wherein mineral bone cement powder is dispersed in a carrier fluid in the water-free, pasty preparation.

11. Implant according to claim 10, characterized in that the proportion of the carrier fluid with reference to the overall mass of the water-free, pasty preparation is 5 to 25% by weight.

12. Implant according to claim 10, characterized in that the water-free, pasty preparation contains surfactants and/or a setting accelerator and/or water-soluble fillers.

13. Implant according to claim 1, characterized in that the implant is reinforced with filler yarn.

14. Method for producing an implant in accordance with claim 1, comprising the provision of the fiber composite material with the steps: a) provision of a pasty preparation containing i. resorbable mineral bone cement powder, ii. that is dispersed in a liquid, b) impregnation of several long metallic fibers and/or endless metallic fibers with an aspect ratio of at least 100:1 in the form of fiber structures with the pasty preparation providing a framework.

15. Set for producing an implant according to claim 1, comprising the components: a) several long metallic fibers and/or endless fibers with an aspect ratio of at least 100:1 in the form of fiber structures providing a framework, b) at least one bone cement preparation, comprising resorbable mineral bone cement powder.

16. Use of a set according to claim 15 for producing a bone implant.

17. Implant according to claim 1, characterized in that the fiber structures are aligned in specific three-dimensional directions so as to provide greater reinforcement at points on the contour of the implant with greater stress from the defective area to be repaired.

18. Implant according to claim 1, characterized in that the reinforcing, long metallic fibers and/or endless metallic fibers have a minimum length of 30 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is to be explained in more detail below with the aid of the following figures and examples without limiting the invention to them.

(2) FIG. 1 Force-path diagram, pulling a titanium wire out of hardened magnesium-calcium phosphate cement

(3) FIG. 2 Force-path diagram, 4-point bending, implant as per the invention (pure titanium fiber scrim and magnesium-calcium phosphate cement) and reference sample (non-reinforced magnesium-calcium phosphate cement)

(4) FIG. 3 Deformation curves of reference material and 2 braid+filler-yarn-reinforced plates during bending

(5) FIG. 4 (A) shows an untreated titanium braid that, in combination with a magnesium-calcium phosphate cement, represents fiber composite material (B) as per the invention; the braid containing metal is included in the magnesium-calcium phosphate cement.

(6) FIG. 5 Schematic portrayal of augmentation material for the tibial plateau for a knee revision.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Example 1

Bond Strength of a Composite Material of Magnesium-Calcium Phosphate Cement with a Titanium Wire

(7) Magnesium-calcium phosphate cement with the composition Mg.sub.2.5Cao.sub.0.5(PO.sub.4).sub.2 is obtained via sintering (5 h at 1050 C.) and a subsequent grinding of calcium and magnesium phosphates and carbonates in a molar ratio to the end composition. The Following components were used: 0.33 mol CaHPO.sub.4, 0.17 mol CaCO.sub.3, 1.67 mol MgHPO.sub.4*3 H.sub.2O and 0.83 mol Mg(OH).sub.2. The bone cement powder that was obtained in this way was mixed with an aqueous 3.5 mol/1 ammonium phosphate solution in a ratio of 0.5 (mass of the liquid to the mass of the bone cement powder). A titanium wire of the alloy Ti6Al4V with a diameter of 0.5 mm and a length of 5 mm was cemented into the hardening compound. After 72 hours of incubation in a physiological salt solution at 37 C., the wire was pulled out of the cement body with a universal testing machine.

(8) FIG. 1 shows the force-path diagram when the wire is pulled out of the cement matrix. The course of the force initially experienced a phase with a high loading to a maximum value of up to 150 N. A residual force of approx. 40 N to 20 N remained over a further pull-out path of 2 mm when the maximum load was exceeded, which shows that a catastrophic failure of a composite material as per the invention is not to be expected even when loads are exceeded; instead there is considerable fracture resistance. It is expected that this behavior will be more pronounced the more fibers there are in parallel with the direction of stress. The absolute value for the pull-out force of the wire out of the cement matrix shows an unexpectedly high adhesive strength of the titanium wire in the cement matrix, both with regard to the adhesive friction and the sliding friction.

Example 2

Bending Strength of an Implant as Per the Invention with Magnesium-Calcium Phosphate Cement and a Braid Made of Stainless Steel Wires in the Form of a Fiber Composite Material

(9) A braid of endless fibers made of stainless steel (fiber diameter 0.2 mm) was impregnated with magnesium-calcium phosphate cement of the composition in accordance with example 1. The proportion of the metallic braid vis-a-vis the fiber composite material was 3% by weight.

(10) An increase in the tensile strength to 320% and an increase in the bending strength to 180% were already achieved with this small proportion. The best values were achieved with the variants reinforced with filler yarn.

(11) TABLE-US-00001 Tensile strength Bending strength [MPa] [MPa] Magnesium-calcium 3.13 5.9 phosphate cement Implant with Magnesium- 10.1 10.8 calcium phosphate cement and stainless steel braid Implant with magnesium- 13.5 8.37 calcium phosphate cement and 1x-stainless steel braid with filler yarn

(12) The tensile strength were determined according to DIN EN ISO 527 Parts 1 and 5. The 4-point bending strength was according to DIN EN ISO 14125.

Example 3

Mechanical Characteristics of an Implant as Per the Invention with Calcium Phosphate Cement and Individual Fiber Filaments Made of Stainless Steel in the Form of a Fiber Composite Material During Hardening Under Normal Pressure

(13) Calcium phosphate cement of the composition 60% by weight of tricalcium phosphate, 26% by weight of dicalcium phosphate anhydrite, 10% by weight of CaCO.sub.3 and 4% by weight of hydroxyapatite was kneaded together with a 1% by weight aqueous Na.sub.2HPO.sub.4 solution in the ratio of 0.4 ml solution to each gram of cement in the form of a water-free preparation; 30% by weight (with reference to the overall mass of the preparation) of stainless steel fibers (90 m diameter, 100 mm length) were mixed in. The compound that was obtained in that was hardened in a silicone mold with the dimensions 66100 mm.sup.3. After removal from the mold, the hardened molded part was incubated for 100 h at 37 C. in simulated body fluid and subsequently subjected to testing.

(14) The compressive strength of the molded part is increased to 140% because of the fiber reinforcement.

(15) TABLE-US-00002 Compressive strength [MPa] Calcium phosphate cement 17.7 Implant with calcium phosphate 24.9 cement and stainless steel fibers

(16) The compressive strength was determined in accordance with DIN EN ISO 5833.

Example 4

Mechanical Characteristics of an Implant as Per the Invention with Calcium Phosphate Cement and Individual Fiber Filaments Made of Stainless Steel in the Form of a Fiber Composite Material During Hardening Under a Pressure of 100 MPa

(17) Stainless steel fibers and calcium phosphate cement were mixed into a pasty mass, analogously to Example 3, and put into silicone molds. After that, pressurization took place with the aid of a ram so that a pressure of 100 MPa was set. After one hour, the hardened molded part was removed from the mold, incubated for 100 h at 37 C. in simulated body fluid and subsequently subjected to testing.

(18) The bending strength of the molded part that was obtained was significantly increase vis-a-vis the molded part that was hardened under normal pressure. A massive increase in the compressive strength to 200 MPa was noted in the molded part that was obtained.

Example 5

Mechanical Characteristics of an Implant as Per the Invention with Calcium Phosphate Cement and Individual Fiber Filaments Made of Stainless Steel in the Form of a Fiber Composite Material, Providing the Bone Cement in the Form of a Water-Free Preparation

(19) A water-free preparation made up of 84% by weight of the calcium phosphate cement, as described in Example 3, and 16% by weight of a mixture of Miglyol 812 (a saturated, partially synthetic, medium-chain triglyceride) and Tween 80 (97% by weight of Miglyol and 3% by weight of Tween 80) was created.

(20) Stainless steel fibers, as described in Example 3, were added to the compound. The proportion of metal fibers to the preparation was 30% by weight.

(21) A cord with a diameter of 8 mm was created in which the stainless steel fibers were largely arranged in parallel along the cord. The cord was pressed into an oblong mold with a cross-section of 66 mm and subsequently hardened by being laid in water. After the hardening, there was an incubation in simulated body fluid at 37 C. for 100 h.

(22) Subsequently, the material was subjected to mechanical testing:

(23) The mechanical testing shows a significantly greater bending strength for the reinforced material than was the case for the non-reinforced material.

Example 6

Mechanical Characteristics of an Implant as Per the Invention with Magnesium-Calcium Phosphate Cement and a Cylindrical Braid of Stainless-Steel Fibers in the Form of a Fiber Composite Material

(24) Magnesium-calcium phosphate cement is provided as described in Example 1 and mixed with an aqueous ammonium phosphate solution. The hardened cement paste was put into a cylinder whose wall was formed from a braid of stainless steel fibers (diameter of a fiber 0.2 mm). The cylinder had a diameter of 10 mm and a length of 100 mm.

(25) The cylinder was completely filled with the cement paste until the cement paste escaped from the pores of the stainless-steel braid. The fiber composite material that was obtained in this way was hardened at 37 C. in simulated body fluid for 100 h.

(26) The implant as per the invention had a 4-point bending strength of 50 MPa. A molded part with the same dimensions made of non-reinforced magnesium-calcium phosphate cement had a bending strength of <15 MPa. The unfilled cylinder of the metal braid had no bending strength. The 4-point bending strength was determined according to DIN EN ISO 5833.

Example 7

Mechanical Characteristics of an Implant as Per the Invention with Magnesium-Calcium Phosphate Cement and a Scrim Made of Titanium Wire in the Form of a Fiber Composite Material

(27) Magnesium-calcium phosphate cement is provided as described in Example 1 and mixed with an aqueous ammonium phosphate solution. The hardened cement paste was put into a scrim made of pure titanium fibers (fiber diameter 0.3 mm). Molded parts with the dimensions 80106 mm.sup.3 were created from that. The proportion of metal in the molded parts was 1% by volume (corresponding to a proportion of 2% by weight). The molded parts were put into a physiological salt solution at 37 C. for 72 hours for hardening. The hardened molded parts were investigated in a universal testing machine for 4-point bending strength.

(28) Compared to a non-reinforced molded part with the same dimensions made of magnesium-calcium phosphate cement, 20% more bending strength was found in the implant as per the invention at the point of cement failure (1st drop in stress).

(29) The non-reinforced molded part with the same dimensions made of magnesium-calcium phosphate cement (reference sample) completely fails when there is a low level of deformation. The implant as per the invention only shows a low drop in force, in contrast, and a continuous increase in force with further deformation (FIG. 2).

Example 8

Mechanical Characteristics of an Implant as Per the Invention with Magnesium-Calcium Phosphate Cement and a 2 Braid Made of Titanium Wire with Filler Yarn in the Form of a Fiber Composite Material

(30) Magnesium-calcium phosphate cement is provided as described in Example 1 and mixed with an aqueous ammonium phosphate solution. The hardened cement paste was put into a 2 braid made of pure titanium fibers (fiber diameter 0.3 mm). Molded parts with the dimensions 80174 mm.sup.3 were created from that (the proportion of metal in the molded parts was 12% by weight). The molded parts were put into a physiological salt solution at 37 C. for 72 hours for hardening. The hardened molded parts were investigated in a universal testing machine for 4-point bending strength.

(31) Compared to a non-reinforced molded part with the same dimensions made of magnesium-calcium phosphate cement (<20 MPa), bending strength that was more than 4 times higher was found in the implant as per the invention with an inserted 2 braid made of titanium wire with filler yarn (90 MPa). The implant as per the invention simultaneously shows a continuous increase in forced with sustained deformation (FIG. 3).

(32) FIG. 3 shows the course of the deformation curve under bending stress. It can clearly be seen here that a significantly greater amount of work is required to bring about deformation or failure of the composite samples than is the case with the brittle fracture of the reference.

Example 9

Comparison of the Bending Strength of an Implant as Per the Invention in the Form of Fiber Composite Materials Containing Magnesium-Calcium Phosphate Cement Combined with a Varying Number of Braids Made of Titanium

(33) The mechanical behavior of the composite materials was determined under the principal kind of stress, bending. Magnesium-calcium phosphate cement was provided for this, as described in Example 1, and mixed with an aqueous ammonium phosphate solution. The hardening cement paste was put into a scrim made of pure titanium fibers (fiber diameter 0.3 mm); the scrims have varying numbers of braids. Cylindrical molded parts with the dimensions I=100 mm, d=8 mm were created from that. The proportion of metal in the molded parts was 6 to 12% by weight, depending on the number of titanium braids. The molded parts were put into a physiological salt solution at 37 C. for 72 hours for hardening. The hardened molded parts were investigated in a universal testing machine for 4-point bending strength.

(34) A significantly more positive influence of added filler yarn on the strength was shown in the bending tests of the cylindrical composite samples.

(35) The tests (cf. the following table) show that the bending strength of magnesium-calcium phosphate cement can be increased by including titanium braids. The bending strength vis-a-vis a non-reinforced magnesium-calcium phosphate cement increases in the process with the number of included titanium braids of a 1, 2 up to a 3 and 4 braid. The use of a 4 braid did not show an additional reinforcement effect here in comparison with a 3 braid.

(36) TABLE-US-00003 Bending Sample strength [N] Implant comprised of magnesium-calcium phosphate 55.78 cement (reference) Implant comprised of magnesium-calcium phosphate 212.00 cement containing a 1x titanium braid Implant comprised of magnesium-calcium phosphate 251.75 cement containing a 2x titanium braid Implant comprised of magnesium-calcium phosphate 375.33 cement containing a 3x titanium braid Implant comprised of magnesium-calcium phosphate 376.75 cement containing a 4x titanium braid

Example 10

Comparison of the Bending Strength of Implants as Per the Invention with a Braid Made of Titanium Wires and/or Filler Yarn in Combination with Different Cement Compositions of Magnesium-Calcium Phosphate Cement in the Form of a Fiber Composite Material

(37) Magnesium-calcium phosphate cement is provided as described in Example 1 and mixed with an aqueous ammonium phosphate solution. The hardening cement paste was put into a scrim made of pure titanium fibers (fiber diameter 0.3 mm); the scrims have varying numbers of braids and/or additional filler yarn. Molded parts with the dimensions 80106 mm.sup.3 were created from that (the proportion of metal in the molded parts was 6-12% by weight, depending on the type of scrim that was used). The molded parts were put into a physiological salt solution at 37 C. for 72 hours for hardening. The hardened molded parts were investigated in a universal testing machine for 4-point bending strength.

(38) The bending strength increased to four times the amount because of the use of filler yarn in a 1 braid compared to braid material without filler yarn. The stress-strain diagrams of the bending tests show significant differences between a non-reinforced and a reinforced sample in the work required up to the failure of the materials.

(39) Furthermore, the bending strengths were analogously determined vis-a-vis non-reinforced implants for selected scrim configurations with which an ideal strength increase was to be achieved with minimal wire content. The reinforcement effect of a 2 braid with filler yarn was compared with a 3 braid, in order to specifically investigate the influence of the material content and additionally contributed filler yarn on the mechanical characteristics of the composite material.

(40) TABLE-US-00004 Bending Sample strength [N] Implant comprised of magnesium-calcium phosphate 72.88 cement (reference) Implant comprised of magnesium-calcium phosphate 339.25 cement containing a 2x titanium braid and filler yarn Implant comprised of magnesium-calcium phosphate 332.00 cement containing a 3x titanium braid Implant comprised of a polymer PMMA cement 190.00

(41) The first fracture events in the cement occurred at around one-third of the maximum force; the further force effect was absorbed by the wire reinforcement until the samples completely failed. Maximum bending strengths of approx. 85-95 MPa were achieved with the two braid types; the mean values for the two reinforcement types are on a comparable level.

Example 11

Production of Molded Parts in the Form of Cylindrical and Plate-Shaped Components Containing Magnesium-Calcium Phosphate Cement

(42) A metal sample mold was prepared for the production of the cylindrical molded parts. It is comprised of two parts that are milled out in a half-round way and that can be firmly put together. The Ti braid that is used is firmly anchored to the ends and can be put under tension if necessary. Cylindrical molded parts with the dimensions L=200 mm, d=10 mm were produced in this sample mold.

(43) The samples were prepared by means of an injection unit and cannula on a vibrator in the cylindrical form. Two-layer braids with filler yarn as the wire reinforcement were used. The diameter of the titanium-wire braid was chosen in an appropriate way for the shape (d=10 mm); in addition, the braid was dilated in the mold such that it made lateral contact with the wall. The cement filling took place from one open end by means of an injection unit and a long cannula with vibration.

(44) After hardening over 4 days at 37 C., the ends of the sample were straightened out and burrs running lengthwise on both sides were ground off. The cement mixture was spread out very well over the entire length of 200 mm because of the vibration; very small air bubbles could merely be seen in the sample.

(45) Plates with the dimensions 2.51280 mm.sup.3 made of composite material were produced as a further mold. Braids with a diameter of approx. 10 mm can be pressed to a size of approx. 80122.5 mm.sup.3 (LWH). The composite samples were produced from a two-layer braid+filler yarn. During the preparation, the Ti-wire braids were filled with MgCPC in a silicone hose with mechanical movement on a vibrator and subsequently pressed to form a flat sample by means of a hydraulic press. The sample production in a transparent hose material permits inspection of the cement distribution during the filling process. The samples were hardened over 4 days at 37 C.

(46) Characteristic mechanical values of these osteosynthesis-plate components were determined by means of static and dynamic bending tests. All of the samples, which are reinforced with a 2 titanium braid and filler yarn, show an increase in the bending strength by around 400-500% compared with the non-reinforced references (cf. the following table).

(47) TABLE-US-00005 Bending strength [MPa] Non-reinforced Implant comprised of reference comprised magnesium-calcium of magnesium- phosphate cement calcium phosphate containing a 2x titanium Sample cement braid and filler yarn MgCPC-110523I/P 0.6 48 189 cylinder MgCPC-120613I/P 23 128 cylinder MgCPC-120613I/P plate 16 81 MgCPC-120123C-04A 15 78 plate