Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-10-01
2004-03-09
Shaver, Kevin (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06702855
ABSTRACT:
The present invention relates to osteophilic implants which can be inserted into bones and which have considerably improved osteointegration characteristics, and to processes for their production.
Implants which can be inserted into bones, for example artificial hip or knee joints or pins to be screwed into the jaw for constructing artificial teeth, are known per se.
Such implants preferably consist of titanium or titanium-based alloys, e.g. titanium/zirconium alloys, which can also contain niobium, tantalum or other tissue-compatible metal additives. A key characteristic of such implants is their osteo-integration time, i.e. the time taken by the bony substance to bond, or integrate, permanently and sufficiently strongly with the implant surface.
How strongly the implant is anchored in the bone can be determined by mechanical measurements, namely by measuring the force (as traction, pressure, shear or torque) which are necessary to pull or twist the implant anchored in the bone out of its anchorage, i.e. to break the adhesion between the surface of the implant and the bony substance bonded thereto. Such methods of measurement are known per se and are described for example in Brunski, Clinical Materials, vol. 10, 1992, pp. 153-201. Measurements have shown that titanium implants with a smooth surface structure do not anchor satisfactorily in the bone, whereas implants with a roughened surface produce a notable improvement in the bone-implant bond in terms of the tensile strength.
EP 0 388 575 therefore proposes firstly to create a macro-roughness on the implant surface by sandblasting and then to cover this with a micro-roughness by treatment in an acid bath. Thus the implant surface can be roughened by sandblasting and then treated with an etching reagent, e.g. hydrofluoric acid or a hydrochloric acid/sulfuiric acid mixture. The surface thus provided with a defined roughness is then washed with water and solvents and subjected to a sterilization treatment.
EP 0 606 566 proposes to treat the implant surface under vacuum firstly with an inert plasma gas, in order to clean the surface, and then with an oxidizing plasma gas or by thermal oxidation and with any other relevant process steps, after which the implant is sealed in glass ampoules and sterilized. All these steps are preferably carried out under vacuum. Said process causes a surface oxide to grow.
Although clean, this surface is immediately contaminated or extensively chemically inactivated in the air.
The chemical state of the surface of titanium and titanium-based alloys is complex. It is assumed that the surface of titanium metal oxidizes spontaneously in air and water and that a reaction then takes place with water on the surface, i.e. in the outermost atomic layer, to form hydroxyl groups. This surface containing hydroxyl groups is referred to in the literature as a “hydroxylated” surface; cf. H. P. Boehm, Acidic and Basic Properties of Hydroxylated Metal Oxide Surfaces, Discussions Faraday Society, vol. 52, 1971, pp. 264-275. A metal surface whose hydroxyl groups are not freely available, e.g. because of chemical modification, is not a “hydroxylated” surface in terms of the present invention.
In terms of the present invention, the metal implant surface is referred to as “hydrophilic” if it is freely accessible to the body fluid and not covered with foreign substances, for example substances with a hydrophobic action. Thus various readily volatile hydrocarbons are conventionally present in non-purified air. These are rapidly adsorbed in a thin layer by hydroxylated and hydrophilic titanium metal surfaces, whereby such surfaces are no longer hydrophilic. Likewise, such a hydroxylated and hydrophilic surface can become hydrophobic if the hydroxyl groups present on the surface associate or react chemically e.g. with carbon dioxide present in the air or with organic solvents, such as methanol or acetone, introduced via the cleaning process.
It has now been found that a hydroxylated and hydrophilic surface of titanium or a titanium alloy has biological properties or is biologically active. This surface can also be referred to as pseudo-biologically active. The expression “biologically active” will be used hereafter. It has been found, surprisingly, that such a biologically active surface, e.g. in the form of an implant, knits with the bony substance to form a strong bond considerably faster than an equivalent surface which is not hydroxylated and/or not hydrophilic. It has further been found that the biological activity of such a metal surface is very quickly lost in the presence of carbon dioxide or volatile hydrocarbons, i.e. in contact with normal air, for example in the drying process, or on cleaning with alcohol. It has also been found that the biological activity of said hydroxylated and hydrophilic surface can be maintained extensively unchanged if this surface is treated according to the present invention, as described below. In this way the biological activity of the implant surface is maintained up to the point of implantation.
The present invention is defined in the Claims. The present invention relates in particular to an osteophilic implant with improved osteointegration characteristics or with improved osteointegration, said implant consisting of titanium or a titanium alloy and being suitable for implantation in bones, characterized in that the implant has a roughened, hydroxylated and hydrophilic surface and hence a biologically active surface.
This surface is preferably sealed in a gas-tight and liquid-tight covering, the interior of the covering being devoid of any compounds capable of impairing the biological activity of the implant surface.
Preferably, the interior of the covering is at least partially filled with pure water optionally containing additives, the amount of water present being at least sufficient to ensure moisturization or wetting of the roughened implant surface. The remaining volume inside the covering can be filled with gases inert towards the implant surface, e.g. oxygen, nitrogen, noble gases or a mixture of such gases.
The present invention further relates to a process for the production of the implants according to the invention.
The implants according to the invention preferably consist of a titanium alloy, particularly preferably a titanium/zirconium alloy, which can also contain niobium, tantalum or other tissue-compatible metal additives. These implants are preferably used as artificial hip or knee joints or as pins to be screwed into the jaw for constructing artificial teeth. Such implants, their nature and the metal materials used to produce them are known per se and are described for example in J. Black, G. Hastings, Handbook of Biomaterials Properties, pages 135-200, published by Chapman & Hall, London, 1998.
The structural and functional anchorage of e.g. a dental implant in the bone is normally achieved by applying a macro-roughness, such as a screw thread or depressions in the surface, and/or optionally a micro-roughness as well, the micro-roughness being applied either in an additive process by plasma technology or in a subtractive process by chemical etching on the surface. How strongly the implant is anchored in the bone can be determined by mechanical measurements, as already described at the outset in this text. Numerous studies have shown that adequate anchorage of an implant in the bone depends to a large degree on the nature of the implant surface, especially the roughness. It is notable that the use of a biologically active implant surface according to the present invention is extensively independent of the physical nature of the implant surface. According to the present invention the biological action of the hydroxylated and hydrophilic surface is added synergistically to the substantially physical action of the surface roughness, resulting in a considerable improvement in the osteointegration. According to the present invention, the two effects are interlinked inasmuch as a physically larger surface also increases the availability of biologically active surf
Simpson James
Steinemann Samuel G.
Institut Straumann AG
McCarter & English LLP
Priddy Michael B.
Shaver Kevin
LandOfFree
Osteophilic implants does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Osteophilic implants, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Osteophilic implants will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3264953