Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating using specified waveform other than...
Patent
1996-12-02
1998-03-03
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating using specified waveform other than...
205318, 623901, C25D 904, A61L 2700
Patent
active
057230382
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/DE96/00197, filed Feb. 6, 1996.
The invention refers to a process for producing a gradient coating containing calcium phosphate phases and metal oxide phases on metallic implants, especially on titanium or titanium alloys, for use as dental, maxillofacial or joint implants.
It is well known that the time of ingrowth of an metallic implant until the full mechanical loadability is achieved can be reduced if the metallic implants have been coated with calcium phosphate phases especially with hydroxyapatite, a calcium phosphate phase similiar to bone.
The connection between metal implant and calcium phosphate can be realized in different ways. According to EP-A 0006544, spherical calcium phosphate particles arc molded into a model together with the implant material, In U.S. Pat. No. 4,145,764 a process is described, in which ceramic particles are thermically sprayed on an implant. However, these techniques are very energy intensive, expensive and time consuming. Furthermore, from EP 0232791 and EP 0237053 processes are known, in which a resorbable calcium phosphate ceramic is deposited on titanium by means of an anodic oxidation under spark discharge in an aqueous electrolyte solution. However, the so produced coating does not consist of hydroxyapatite or fluorapatite but of oxides and strongly resorbable calcium phosphate phases. With a complete resorption of the calcium phosphate phases also the bioactive character of the implant is lost.
DE 43 03 575 C1 describes a process for producing a patite coatings on metal implants by inducing a plasma-chemical reaction by means of alternating current in aqueous solutions. An electrolyte solution is used made from the salts of alkali or alkaline earth metals, in which hydroxyapatite and/or fluorapatite is dispersed with a defined grainsize and concentration. The plasma-chemical process leads to coatings, which consist of pure hydroxyapatite or fluorapatite to an extent of up to 95%.
Disadvantages of this process are especially the large thickness of the coating (up to 250 .mu.m) as well as the come graining of the coating (up to 100 .mu.m). Furthermore, the interface strength between the coatings and implants are not optimal.
WO 92/13984 describes a process of deposition of bioactive coatings on conductive substrates. An electrolyte cell contains an inert anode and an electrolyte consisting of a aqueous solution of ions of the ceramic, having a pH value of less than 8. The activated conductive substrate is dipped into the electrolyte solution and the potential between the anode and the conductive substrate is chosen such that a ceramic layer is deposited on the conductive substrate based on the pH rise at the boundary between electrolyte and conductive substrate.
A disadvantage of this solution is that the deposition of the layer proceeds only on the surface of the substrate. This means on the one hand that there is no connection that can be mechanically loaded. On the other hand, the coating can be completely resorbed biologically. Furthermore, the coating always consists of three components, .alpha.- and .beta.-tricalcium phosphate and components of the chemical formula Ca.sub.5 (PO.sub.4).sub.3-x (CO.sub.3).sub.x (OH).sub.1+x with X=0.2 or less. This means, that the coating is a mixture of these components unlike the composition of bone.
The object of the invention is the coating of metallic implants, preferably of titanium implants or implants made of titanium alloys, with a gradient layer made of calcium phosphate phases and metal oxide phases. Thus, beside the effect of an accellerated ingrowth a permanent improvement of the interaction between implant surface and the biological system can be gained. Moreover, it should be possible to control the composition of the calcium phosphate phases via the process parameters, so that hydroxyapatite, octacalcium phosphate or brushite as well as defined combinations of these phases can be produced alternatively.
According to the invention, the object is realised via an electroch
REFERENCES:
patent: 4478689 (1984-10-01), Loch
patent: 4666567 (1987-05-01), Loch
patent: 5310464 (1994-05-01), Redepenning
patent: 5354390 (1994-10-01), Haszmann et al.
Bersch Henrike
Hofinger Jurgen
Kranz Curt
Pompe Wolfgang
Scharnweber Dieter
Gorgos Kathryn L.
Hofinger Jurgen
Leader William T.
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