WO2002070031A1

WO2002070031A1 - Bone replacement material and method for the production of a bone replacement implant

Info

Publication number: WO2002070031A1
Application number: PCT/EP2001/012867
Authority: WO
Inventors: Katja Tangermann; Jochen Bauer
Original assignee: BLZ Bayerisches Laserzentrum Gemeinnützige Forschungsgesellschaft mbH
Priority date: 2000-11-09
Filing date: 2001-11-07
Publication date: 2002-09-12
Also published as: DE10055465A1

Abstract

The invention relates to a bone replacement material, especially for the treatment of bone defects after surgical intervention, consisting of the following main components: a matrix material (2) made of a biocompatible, laser-sinterable polymer material, especially a thermoplastic polymer material, and filling material particles (3) made of inorganic, non-metal materials, especially bioinert or bioactive materials, which are at least partly embedded in the matrix material (2).

Description

Bone replacement material and method for producing a bone replacement implant

The invention relates to a bone replacement material, in particular for the care of bone defects after surgical interventions, a method for producing a bone replacement implant from such a bone replacement material and a bone implant itself.

The present invention is in the field of implant medicine related to bone defects such as e.g. after tumor resection, trauma treatment or in the reconstruction of congenital malformations. The main areas of application are defects in the skull and orbital roof and all other bone defects that require reconstructive or functional interventions on the patient. This results in the following development goals for the development of so-called "Taylored Implants":

Development of prostheses and implants that do not interfere with imaging diagnostics

Development of prostheses with a modulus of elasticity adapted to the bone and sufficient strength in the event of stress, - Optimal fixation and positioning of the prostheses and implants in / on the bone,

Possibility of tracking the postoperative course through imaging diagnostics,

Individual implant geometry adapted to the patient for aesthetic reasons,

BESTATIGUNGSKOPIE Checking the accuracy of fit of the implants on anatomical facsimiles and

Low patient burden.

With regard to the background of the invention and the prior art, reference is made to the following:

The body's own (autogenous) and foreign (alloplastic) materials are used in the reconstruction and care of bony defects.

The use of the body's own bone or cartilage has the disadvantage that a second operation at a further point of the patient is necessary to remove the autogenous material. This can usually affect the donor region of the fibula, rib or iliac crest. There is an additional burden on the patient. Another limitation is the amount of graft material available. A disadvantage also lies in the unpredictable process of remodeling and dismantling transplanted bones, which after a few years leads to renewed surgical interventions on the patient if the transplant is completely dismantled.

The treatment of bone defects using alloplastic materials focuses on the use of methyl methacrylates and titanium. The great advantage of extraneous materials lies in the unlimited availability. Biologically compatible alloplastic materials (plastic, ceramic, metal) are already being used successfully and without complications in a wide variety of areas of modern medicine as implants. Accordingly, these materials do not require an additional bone removal site and are generally not subject to any reconstruction or degradation processes in the human body. The use of polymethyl methacrylates leads to various complications due to the hardening of the plastic mass during the operation. In particular, the development of heat during the polymerization and the monomer release after an incomplete reaction can lead to inflammation reactions. Furthermore, the implant must be preformed in the plastic state and then hardened. One consequence is that the complete hardening causes a change in shape, which makes reworking necessary.

In addition to aesthetic adaptation, the decisive factor in the care of bone defects is primarily the accuracy of fit to the defect edges. The surgical field, which is restricted by the sterile cover, does not allow a comprehensive assessment of the contour during the operation. The exact individual adjustment is therefore limited.

Implant forms that are specifically adapted to the patient are therefore desirable. Computed tomography (CT) can be used to precisely measure bony structures and the resulting 3D data can be used for implant production. Based on these data sets, individual hip endoprostheses and cranioplasties are already made from titanium using computer aided design and manufacturing (CAD / CAM).

The disadvantage of these metallic implants are complications or artefacts that arise in imaging diagnostics using X-rays, computed tomography (CT) or magnetic resonance imaging (MRI). These artifacts have a particularly disadvantageous effect on the precise assessment of the postoperative healing process and in particular in younger patients, which, due to another medical indication, depend exactly on such imaging diagnostics in the area of the implant.

The release of metal ions and their effect on the organism is also critically discussed in the specialist literature for long-term use of metals. Furthermore, due to the strongly varying modulus of elasticity of metal implant and bone tissue (Ti: 110 GPa, bone: cancellous 0.5-3 GPa, cortical 10-25 GPa), bone degradation can occur as a result of the so-called "stress shielding" effect , Another disadvantage of using metals is that they belong to the group of inert materials, so that, as a rule, no non-positive connection between the implant and the recipient tissue can form. The metal implant is therefore fixed to the bone using screws and plates.

In view of these known solutions and their disadvantages and limitations, the object of the present invention is to provide a bone replacement material which enables a non-positive connection to the bone, the modulus of elasticity of which is adapted to that of the bone, and which is achieved by a quick and simple method individually shaped, patient-specific endoprostheses must be processed.

This object is achieved by the features specified in the characterizing part of claims 1, 6 and 10, respectively. The core of the invention is the selection of the materials involved in the bone substitute material according to the invention, which represent an optimal compromise in view of the very different tasks. The starting point is a mixture of a biocompatible, laser-sinterable polymer material as the matrix material and filler particles made of inorganic, non-metallic materials such. B. ceramic powder. A polymer / ceramic compound in powder form is also possible. The inorganic fillers are at least bioinert or preferably bioactive, such as. B. osteoinductive or osteoconductive.

With regard to the choice of materials for the biocompatible polymer materials, a variety of plastics are available, such as. B. polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, polyamide, polyurethane, polysulfone, polysiloxane or polytetrafluoroethylene. The material polyether ether ketone (PEEK), which belongs to the group of high-temperature thermoplastics, is particularly preferred. Further explanations on this can be found in the discussion of the exemplary embodiment.

Suitable for the filler particles include Calcium phosphates, biocompatible glass particles, as are commercially available under the "Bioglas" brand, or carbon particles. These particles can be in the form of fibers, spheres, whiskers or platelets. Their particle size is preferably in the range from 0.1 to 200 μm, which also applies to the particle size of the powdery raw material in the production of a bone replacement implant according to the invention.

The filler particles preferably have a weight fraction of 5 to 80% based on the total amount of material.

The method according to claim 6 for producing a bone replacement implant from the bone replacement material according to the invention is based on the method of laser beam sintering known in connection with the so-called "rapid prototyping". The laser beam sintering is a generative process that can be used to produce components directly from a 3D data set. Using laser beam sintering, complex component structures including undercuts can be produced at short notice. In contrast to cutting processes, the workpiece is created by applying a material. The decisive advantage of laser beam sintering of plastics is the high flexibility with which complex and individually shaped component structures can be manufactured within a very short time. In this respect, this method is also excellently suited for the production of a bone replacement implant, since such workpieces must always be individually manufactured.

Finally, it is provided according to the invention to embed the filler particles in the matrix material made of the biocompatible polymer material in such a way that these filler particles are only partially embedded in the matrix material on the implant surface. In particular when using bioactive fillers, such as calcium phosphates or the aforementioned biocompatible glass particles, no permanent anchoring is necessary by means of fixing agents, since the filler particles lying there achieve a positive connection between the bone and the implant attached to it. Further functions of the filler particles are that the mechanical properties of the bone substitute material, such as elastic modulus, strength and creep behavior, can be adapted to the surrounding bone tissue due to their proportion in the matrix material. Furthermore, such inorganic fillers are advantageous for making the polymeric implant visible on X-ray images, but the imaging diagnostics are not disturbed by these fillers. Finally, the inorganic filler particles have a positive effect on the shrinkage behavior of the matrix material, in which a ch shrinkage is largely prevented. The implants made from the bone substitute material therefore have a high degree of dimensional accuracy.

Further features, details and advantages of the invention result from the following description, in which an embodiment of the subject matter of the invention is explained in more detail. Show it:

1 is a perspective, partially enlarged schematic representation of a bone replacement implant,

Fig. 2 is a schematic, extremely enlarged partial section through the interface between the bone replacement implant and the surrounding bone tissue, and

3 shows a basic illustration of a laser sintering system for producing a bone replacement implant.

As is clear from FIG. 1, a laser-sintered bone replacement implant 1 consists of a matrix material 2 and filler particles 3 embedded therein. The matrix material is polyethene ether ketone (PEEK), the property profile of which is outstandingly designed for use as a matrix material. PEEK is characterized by excellent mechanical properties, high chemical resistance and thus long-term resistance as well as high radiation and wear resistance. In this respect, this material is well suited for use in an aggressive body environment. Another advantage of this material, which is not very sensitive to external influences, lies in its easy sterilizability. The suitability of this material for the medical field is also documented by the existing FDA (American Food and Drug Association) approval.

There are two points to consider when using PEEK as a bone substitute:

- PEEK, like all plastics, is assigned to the group of bio-inert materials, i.e. that the implant cannot make any connection with the bone tissue. - The modulus of elasticity from PEEK with 3.7 GPa is in the lower modulus of elasticity of the human bone (cancellous bone: 0.5-3 GPa; Compacta: 10-25 GPa), with an elastic modulus adapted to the bone in load-bearing endoprostheses must be set.

The problems associated with this are solved by the filler particles 3. Bioactive fillers based on calcium phosphates have emerged as particularly suitable. The calcium phosphate group includes, for example, the osteoinductive hydroxyapatite (Ca ₁₀ (PO) ₆ (OH)) and the osteoconductive, fully absorbable tricalcium phosphate (Ca ₃ (P0 ₄ ) ₂ ). Both materials are already used in medicine as synthetic bone material in mostly granular form for the filling of bone defects. Hydroxyapatite is the inorganic mineral phase in the tooth (98% by weight) and bone (60-70% by weight). Due to their low strength, hydroxyapatite implants are only suitable for non-load-bearing applications with small bone defects. By adding such filler particles, on the one hand the modulus of elasticity and thus the strength of the material are adapted and adjusted to the particular application. The modulus of elasticity stated above increases from pure PEEK to 30 GPa of the mixture when 30% technical glass is added. With the addition of 30% carbon, a modulus of elasticity of 20 GPa is achieved.

Furthermore, the only partial embedding of the filler particles 3 in the area S of the implant 1 creates a point of contact for the ingrowth of bone tissue 4. This growth of the bone tissue 4 to the filler particles 3 creates a non-positive connection between the implant 1 and the bone tissue 4, as is shown in FIG. 2 by the scliraffur lines extending from the bone tissue 4 into the filler particles 3.

The bone replacement implant 1 is produced by means of a laser sintering system shown schematically in FIG. 3. Its core is a C0 ₂ laser 5 with a wavelength λ = 10.64 μm, the beam of which is designated 6. Powdery starting material 8, consisting of the powdery matrix material 2 and the filler particles 3, is applied in a layer thickness 9 to a building platform 10 via an application container 7. Above this construction platform 10 is the installation space 11 for the implant. The construction platform 10 can be moved in the vertical direction via a schematically indicated height drive 12.

To prepare for the manufacture of an implant 1, the three-dimensional geometry data for the implant 1 are determined by suitable measurement methods, such as, for example, computer tomography, and in a corresponding CAD / CAM system 13 entered. The corresponding data are read in and processed in a suitable manner so that the entire sintering process can be controlled fully automatically. In accordance with the desired component geometry, the laser beam is now guided over a scanner mirror 14 controlled by the CAD / CAM system 13 and a corresponding focusing lens 15 over the top layer of the powder 8. In the scanned area, the matrix material 2 and the filler particles 3 are sintered together by melting and glued. The building platform 10 is then moved downward by the layer thickness 9, which can be 10-250 μm depending on the powder grain size, and a new layer of powder material 8 is applied from the application container 7. Again, a certain area of this layer is scanned by the laser 5 in accordance with the CAD data of the implant 1 and the polymer material and the filler particles are sintered together. There is also a firm connection with the previously sintered layer. This process is repeated successively until the entire implant 1 is completed.

When choosing the laser 5, it should also be ensured that the thermoplastic material used for the matrix material has good absorption in the wavelength range of the laser 5 so that the amount of energy required to melt the materials can be absorbed. Furthermore, for optimal processing of the plastic powder, the heating of the material in the application container 7 and in the installation space 11 is necessary to just below the glass transition temperature Tg or, in the case of partially crystalline powders, to just above the crystallite melting temperature Tm. Examples of these temperatures for the material PEEK are Tg = 143 ° C and Tm = 334 ° C. For polyamide, the corresponding values are Tg = 78 ° C and Tm = 260 ° C.

By processing a bone substitute material made of biocompatible thermoplastic materials 2, such as Polyetheretherketon, and functional filling or reinforcing components 3, such as In summary, hydroxyapatite over laser beam sintering has several advantages:

Adaptation of the modulus of elasticity of the implant 1 to that of the bone 4 by varying the filler content, direct non-positive growth of the implant 1 with the bone tissue 4 by means of calcium phosphate 3 embedded therein, the structured surface of the laser-sintered implant 1 has a stimulating effect on a positive connection with the surrounding area Bone tissue 4, in contrast to metallic implants, there are no complications or artifacts in the imaging diagnosis via X-ray, CT or MW, quick and direct implant creation from a 3D data record (CT data), patient-specific, individual endoprosthesis geometry, shortening the operating time and the burden on the patient.

Claims

claims

1. Bone replacement material, especially for the treatment of bone defects after surgery, characterized by the following main components:

- A matrix material (2) made of a biocompatible, laser sinterable, in particular thermoplastic polymer material, and

- In the matrix material (2) at least partially embedded filler particles (3) made of inorganic, non-metallic, especially bio-inert or bioactive materials.

2. Bone replacement material according to claim 1, characterized in that as biocompatible polymer materials preferably polyether ether ketone (PEEK) or polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyamide (PA), polyurethane (PUR) ), Polysulfone (PSU), polysiloxane or polytetrafluoroethylene (PTFE) can be used.

3. Bone replacement material according to claim 1 or 2, characterized in that the filler particles (3) consist of calcium phosphates, biocompatible glass particles or carbon particles.

4. Bone replacement material according to one of claims 1 to 3, characterized in that the filler particles (3) are present in the form of fibers, balls, whiskers or platelets.

5. Bone replacement material according to one of claims 1 to 4, characterized in that the filler particles (3) have a particle size in Have range from 0.1 to 200 microns.

6. A method for producing a bone replacement implant from the bone replacement material according to one of claims 1 to 5, characterized by the following method steps:

- Providing a starting material (8) as a powdery mixture or compound material made of biocompatible, laser-sinterable, in particular thermoplastic matrix polymer material (2) and filler particles (3) made of inorganic, non-metallic, in particular bio-inert or bioactive materials,

- arranging the starting material (8) in layers in a powder layer (9),

- Laser sintering of a position of the implant (1) according to predetermined data of the implant geometry while solidifying the matrix polymer material (2) and at least partially embedding the filler particles (3), and

- successively repeating the two above steps by connecting a sintered layer with the previously sintered layer until the implant (1) is finished.

7. The method according to claim 6, characterized in that the laser sintering is carried out such that filler particles (3) on the surface (S) of the implant (1) are exposed.

8. The method according to claim 6 or 7, characterized in that the particle size of the powdery matrix polymer material (2) is between 0, 1 and 200 microns.

, Method according to one of claims 6 to 8, characterized in that the starting material (8) is heated depending on the material to a temperature just below the glass transition temperature or, in the case of partially crystalline materials, just above the crystallite melting temperature, depending on the material.

10. Bone implant consisting of a bone replacement material according to one of claims 1 to 5, characterized in that the filler particles (3) on the implant surface (S) are only partially embedded in the matrix material (2).