Metal sponge-like structure and method for making the same

p0001The invention relates to a Metallspongiosa of titanium or tantalum or alloys thereof and a method for their preparation. The Metallspongiosaherstellung found in medical applications. The Metallspongiosa be used as a bone substitute in human medicine.

p0002Known are metallic permanent implants of bioinert pure metals or their alloys, which are used for example in the form of joint prostheses in surgery applies and their firm contact with the bone by means of bone cement.

p0003Due to the gradual structural changes of the bone cement it comes to loosening and the time spent shortening of the implant. For this reason, cementless implant-bone connections are desired. Known for this purpose, the surfaces of the metal implants should be structured in a suitable manner or to coat with latticed elements (AT-P 383268); whereby a form-fitting interlocking with bone tissue is to be made possible. Particularly strong implant-bone composites are formed when irregular open cell spongiosaähnliche implants or implant surfaces apply, allow a trabecular ingrowth or volunteers of bone into the implant.

p0004After Henßge (Focus MHL 2 (1985) 4, 1-8) are Metallspongiosa castings of cobalt base alloys that have been developed as a solitary implants to stabilize to Fusion purposes or for structuring the surface for joint replacement implants. It is known that in the use of cobalt-based alloys bindegewebsloser no contact with the bone is achieved and it can be rejection reactions. Moreover, the production of Metallspongiosa-casting technically complex and the surface cleanliness is insufficient.

p0005There are a number of methods known to produce porous or sponge-like metallic body. For this purpose, either liquid heterogeneous systems to be created, such as mixture of gases, or salts and the molten metal, which is allowed to solidify, and then the non-metallic phase removed. An overview of the known methods are Fritsch, G. (Physik in unserer Zeit 15 (1984) 5).

p0006So 658 987, for example, processes for producing bone substitute are in the CH-P 660 122 and CH-P describes the starting manufacture a core model of natural or artificial open-cell models via complex operations whose cavities are eventually filled by casting or spinning with metal and then the core material is removed. This procedure has besides the great effort in the core model making and many process steps in particular the disadvantage that in the production of large-volume implants completeness of removal of the core material can not be guaranteed or poorly controlled and that in Titanium or tantalum or alloys thereof because of high melting points and the reactivity of the liquid metal with the mold materials additional complications.

p0007The invention is based on the object, a high-strength heavy metal-free or low in heavy metals Metallspongiosa, the microstructured over the entire surface and is bioactive and bindegewebsloses waxing or growing through the bone tissue promotes and to provide a method for producing Metallspongiosa excluding core mold material.

p0008According to the invention the object is achieved that the Metallspongiosa in the required shape from point-and cohesively interconnected at regular intervals, as well as irregular form-fitting verschlauften together highly cold-formed wires is of square or rectangular cross-section of Titanium or Titanium alloys, tantalum and tantalum alloys, so that a scaffold of the density of 50 to 90% of the density of the substrate material having irregularly structured cells is present. The cells have miteinder connection, so that the entire implant body has an irregular broken cavity on all sides by irregularly shaped channels the ingrowing bone tissue accessible. The wires have a cross-section mm² up. 3 Instead of wires made of pure metal can also biocompatible alloys, bsw. Tl6Al4V find use.

p0009The entire inner and outer Metallspongiosaoberfläche is provided with an up to 10 .mu.m thick bioactive layer consisting of metal each pure oxide of the substrate material and increasing amounts contains in the direction of the cavity or to the environment of calcium phosphate up to a surface concentration of 12%. The bioactive layer is also microstructured such that> 1 microns and a maximum pore depth of 2/3 of Bioaktivischichtstärke to have a pore diameter present per square millimeter at least 10⁴ pores.

p0010The outward-leading channels or the entire cavity of Metallspongiosa may additionally be filled completely or partially with resorbable biomaterials.

p0011The object of the production is achieved in that a rhombic perforated kaltverstrecktes sheet, preferably made of titanium, tantalum, or alloys thereof, bsw. is rolled into the shape of a known expanded metal wire mesh in tight packing according to the desired outer shape of the implant, wound and / or folded and this pack is first compressed by means of a mold in a press to> 30% in the direction of the main extension of the diamonds, which in other Kaltumformvorgängen the final external implant shaping is.

p0012Another feature of the invention is that the density of the Metallspongiosa having 50% to 90% of the density of the Titaniums or the titanium alloy or tantalum or the tantalum alloy, not only by the compression molding, but also by use of a different perforated metal sheet and / or a differentiated position density is achieved. The perforated sheet is coated bioactive or bioinert before forming.

p0013The advantages of the inventive solution are that a Metallspongiosa created with quasi-isotropic metal wire mesh structure which is opposite to the cast metal grilles Titanium or tantalum is characterized by higher strength and greatly reduced creep.

p0014If differentiated position densities or different perforations are used, formed correspondingly differentiated density distributions in the Metallspongiosa, for example, lead to rand stabilized shaped implants and are very similar to natural bone. Moreover, it is not only possible to produce before the molding presses bioactive or bioinert layers on the metal substrate, but also resorbable biomaterials in loose form with shall be included, which are anchored by the molding presses form-fitting with and as required, completely after pressing or partially can be removed again.

p0015In the following the invention is described using two embodiments. Figure 1 illustrates the structure of a Metallspongiosa.

Embodiment 1

p0016A rotationally symmetrical shaped Metallspongiosa implant body for defect bridging of a long bone has a total length of 42 mm and is divided into three cylindrical sections of which the average 30 mm long portion having a diameter of 18 mm, while the two 6 mm long ends in diameter each have 6 mm. The implant body consists of a supporting frame of wires 1 from Reinsttitanium with a rectangular cross section of 0.5 mm by 1 mm, which are each connected via a length of 1 mm at a distance of 2 mm in alternation with two other wires 1 materially integral manner, so that two adjacent wires 1 are all 5 mm respectively and no cohesively unbound wires 1 occur.

p0017The each 2 mm long not cohesively connected wire sections are formed in an irregular manner and each looped, so that an open-cell wire mesh structure is present with irregularly shaped cavity which is accessible through channels 2 different shape and size. The density of the implant body, whose shape is achieved by multiple cold reductions, is 56% of the density of the pure Titaniums. The entire inner and outer surface of the implant body carries a 5 micron thick Titaniumoxidschicht which contains on the surface 7% calcium phosphate. Scanning electron microscope studies of the surface point to an area of ​​1 mm² 2 · 10⁴ pores with a minimum diameter of 1 micron. The compressive strength of the implant body is> 300 N / mm².

Embodiment 2

p0018To prepare a Metallspongiosaimplantatkörpers for defect bridging of a long bone is a rhombic perforated sheet in the form of expanded metal from EMO-Titan 110 with the following dimensions: width 25 mm (measured along the main stretch of diamonds), length 46 mm (measured along the short diagonal of diamonds), a mesh length of 6 mm (distance from the center hub to center node in the direction of the long diagonal), a mesh width of 4 mm (distance from the center hub to center hub toward the short diagonal), a web width of 1 mm and a web thickness of 0.5 mm in a supersaturated Kalziumdihydrogenphosphat aqueous electrolyte by means of anodic oxidation under spark discharge, with increasing voltage up to 250 V, coated. The carefully rinsed with distilled water and dried blank is then rolled into a 8 mm thick and 25 mm long cylinder and compressed in one coated with titanium nitride mold in the direction of the main extension of the diamonds to a 10 mm long Metallspongiosaimplantatkörper 8mm diameter. Subsequently, the implant body is again recoated in the same electrolyte. The density of the Metallspongiosa thus produced is 2.6 g / cc, corresponding to a void of 42%. The compressive strength> 300 N / mm².