Electrolysis: processes – compositions used therein – and methods – Product produced by electrolysis involving electrolytic...
Patent
1997-03-07
1998-06-02
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Product produced by electrolysis involving electrolytic...
204486, 204487, 204108, 204188, 204189, 204318, 623 16, 623901, C25D 908
Patent
active
057593760
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT EP95/03499, filed on Sep. 6, 1995.
The invention relates to a method for electrodepositing hydroxyapatite layers of the general composition Ca.sub.x+9 (PO.sub.4).sub.x+5 (HPO.sub.4).sub.1-x (OH).sub.x+1, in which x represents a value between zero and 1, on metal surfaces and ceramic surfaces. Materials, coated in this manner, are used in the form of biocompatible implants in human and veterinary medicine, which are distinguished by particularly high growing-in rates. Various methods have already been described for producing hydroxyapatite and other calcium phosphate coatings. However, all of them are afflicted with certain deficiencies.
The already established methods include plasma spraying of hydroxyapatite.sup.1. Although this method is comparatively expensive, it has not been possible, because of the line-by-line or the side-by-side application, to produce coatings, which are uniform in relation to the thickness, adhesion and homogeneity of the layer if substrate geometries are somewhat complicated. Hydroxyapatite coatings with consistently lower adhesion can be prepared by drying.sup.2, conventional sintering.sup.3 or microwave-sintering.sup.4 of hydroxyapatite, produced by methods involving wet chemistry or deposited from suspensions. Expensive (vacuum) sintering processes for producing uniform coatings are also characteristic of the sol-gel.sup.5 and the electrophoresis.sup.6 methods. On the other hand, a high technical effort for the actual coating process characterizes methods, which are based on the sputtering technique.sup.7 and the pulsed laser deposition process.sup.8. An electrochemical method.sup.9, which is suitable for coating mechanically pretreated surfaces of titanium (alloy) substrates with calcium phosphate, can be realized more easily technologically. A more uniform layer growth is said to be achieved by using pulsed direct current.sup.10,11 (20 sec on-off cycle; direct current as in the original method. However, the adhesion of the calcium phosphate layer to the titanium substrate is not increased significantly by these means.
It is an object of the present invention to develop a method for depositing hydroxyapatite on metal, alloy and ceramic surfaces, which is distinguished by a uniform, well adhering coating of optimum thickness and by a low proportion of amorphous materials, while the expenditure for equipment, energy, time and material is relatively small.
Pursuant to the invention, this objective is accomplished owing to the fact that the actual electrochemical coating process, using an electrolyte containing calcium phosphate and calcium hydrogen phosphate and a pulsed direct current of suitable frequency, is preceded by a preliminary coating process using a sol-gel technique. The sol-gel couting is a mutual approximation of the chemical composition of the substrate and of the hydroxyapatite layer because the solution used for the sol-gel coating has elements of the chemical composition of the substrate and/or the hydroxyapatite layer. As a result of the solution used for the sol-gel coating including elements of the substrate and/or the hydroxyapatite coating layer, there is a significant increase in the adhesion of the hydroapatite coating layer. The increase in adhesion is achieved by the number as well as the type of solutions used. With respect to the areas of application of the invention, the substrates themselves, which are to be coated, should have sufficient biocompatibility. This concerns, in the case of the metals, for example, titanium and platinum, in the case of alloys, various iron and nonferrous metal alloys, particularly high-grade steels, CoCr28Mo and TiA16V4, and, in the case of ceramic materials, predominantly oxides, nitrides, oxynitrides and carbonitrides, which contain, in their composition, one or more metals from the and groups 4 and 5 of the periodic system of the chemical elements. The substrates to be coated consist either completely or partly of the materials given above or these materials, in the form o
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patent: 5211833 (1993-05-01), Shirkhanzadeh
patent: 5310464 (1994-05-01), Redepenning
patent: 5470668 (1995-11-01), Wu et al.
patent: 5643447 (1997-07-01), Lev et al.
Neumann H. Georg
Teller Joachim
Dot Dunnschicht- Und Oberflaechen-technologie GmbH
Gorgos Kathryn L.
Leader William T..
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