Method for coating a substrate with calcium phosphate

Translation of description of equivalent WO 03052164 A2

A process for coating a substrate with calcium phosphate

The invention relates to a process for coating a substrate with a calcium phosphate layer.

For coating substrates, in particular with a bioactive calcium phosphate layer, for example hydroxyapatite, the plasma spray method is used. However, this method is not suitable when the substrate consists of small particles or is not heat-resistant. The electrochemical deposition of calcium phosphate is also not applicable to particles even when the particles are electrically conductive.

In U.S. Patent 6,153,266 a process for producing a calcium phosphate layer is described in which in a first step the substrate is dipped in a phosphate-containing bath containing no calcium. Subsequently, the substrate of the solution is removed, dried and immersed in a second solution that has a pH value of 8 and contains calcium. In this solution, formed on the surface of the substrate calcium phosphate. A disadvantage of this method is first of all that the coating is performed with two steps. A further disadvantage is that it is not possible with the 2-step method of making the film thickness to the desired extent. For dictated ke layers thus provides the known method is another step wherein the substrate provided with the calcium phosphate layer is immersed in a solution Calciumphosphatlö-.

The invention has the object to eliminate the drawbacks of the known processes and produce a calcium phosphate layer in a simple process, having a desired film thickness.

According to the invention this object is achieved in accordance with claim 1 characterized in that the substrate is introduced into a calcium phosphate gel which is dried coated substrate with the gel and separated from calcium phosphate particles. By "gel" is understood in a pasty state a liquid.

According to the invention, it is according to claim 2 also possible to apply the calcium phosphate layer directly on the surface of the substrate by placing the substrate in a calcium introduced umphosphathaltiges colloid of silica and then a crack-free coating film is formed by the removal of the solvent.

Advantageous embodiments of the invention are described in the subclaims.

The advantage of the method is that it is possible to provide a substrate in one step with a calcium phosphate layer. Since the layer thickness depends on the concentration of the calcium phosphate gel and the colloidal solution, a desired layer thickness can be produced by adjusting the concentration. The process is suitable for coating large-area substrates, and particles. It is independent of the material of which the substrate is.

The adhesive strength of the layer on the substrate can be increased, that located at the substrate gas (air) is removed by applying a vacuum. This method is particularly advantageous if the substrate has pores. There is then the air removed from the pores and the calcium phosphate gel is able to penetrate into the pores. A further advantage is the fact that it is possible to produce by an appropriate composition of the gel layer from the various calcium phosphate modifications. This is particularly of importance for a bioactive layer. It is known that the degree of bioactivity of a layer grows with its instability in a physiological environment. Calcium umphosphate with a compared to hydroxyapatite much higher solubility as brushite and Mpnetit have specifically for healing in the bone a special meaning. If the coated particles are used with the aim to improve the bonding of the substrate with bone tissue, is the gel of brushite and / or Monetit or from a mixture of brushite and / or Monetit and hydroxyapatite. The gel may also consist of a mixture of silica gel and calcium phosphate. It may further contain fillers such as calcium sulfate or factors acting knocheninduzierend. It is also possible to introduce inflammatory agent in the drug layer such as antibiotics, growth of the bone accelerating or degradation of the bone, for example by being mixed into the gel.

The coated with the inventive substrates are particularly useful as a bone substitute material for filling bone defects or for filling a gap between an implant and a bone into which the implant used were de. For this purpose preferably coated substrate particles are used that are biocompatible. The particles can also serve to anchor the implant in the bone.

The invention is explained in more detail below with reference to examples, without being limited thereto.

Example 1 :

In a solution of calcium hydroxide, a phosphate acid solution is added with constant stirring. The forming fine precipitate is concentrated by centrifugation and separated from it clear supernatant solution. In the resulting calcium phosphate gel, a titanium granules, which were previously degreased and cleaned, introduced and thoroughly mixed. This mixture is placed in a vacuum chamber. When applying a suitable negative pressure, the air is removed from the pores of the titanium granulate. During the subsequent aeration, the calcium phosphate gel penetrates the pores. The coated granules are dried, particles separated and isolated by screening of fallen calcium phosphate. The thickness of the calcium phosphate is variable and can on - set concentration of the gel produced.

Example 2:

Any calcium phosphate powder is mixed with a silica gel. In this gel a degreased and cleaned titanium pellets are introduced and thoroughly mixed. As in Example 1, the air is removed from the pores of the titanium granules to allow the penetration of the calcium phosphate-silica gel in the pores in aeration. The coated granules are dried, separated and isolated by means of an air stream of precipitated calcium phosphate-silica particles. The thickness of the calcium phosphate-silicate can be adjusted via the concentration of the gel.

Example 3:

In a hydrophilic colloid of the hydrolysis product of an alkoxysilane (for example TEOS) any calcium phosphate powder is introduced and distributed uniformly by stirring. a titanium powder or granule of any particle size in this colloid solution is then introduced and started after thorough mixing, thus, distill gently with continuous movement of the solvent while continuing to stir. The coating end is characterized in that the Schüttfahigkeit the titanium particles is reached, and thereby directly to the substrate surface forms a crack-free film. The coated substrate is finally annealed in multiple stages to 150 ° C.