Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-01-23
2001-04-24
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06221111
ABSTRACT:
The invention relates to a surface layer for metal bone implants as defined in the preamble of claim
1
. Metal bone implants and in particular those used as permanent implants are frequently coated with a bioactive layer to achieve permanent and stable anchoring in or on the bone. Alloplastic materials are considered bioactive if they chemically combine in firmly adhering manner to the vital bone tissue. Presently known surface layers are produced predominantly by plasma coating and incur various drawbacks; these include low adhesion to the substrate, unreliability in composition (crystal phase), no or few ways to vary the construction and composition of the layer, and especially the high cost of methods and production equipment.
Mixtures of metal oxide (MeO) and calcium phosphate (CaP) are already known in the state of the art, though specific medical applications have not yet been disclosed for them. In particular concrete data are lacking concerning the manufacture of such mixtures and their application as surface layers for surgical implants.
The objective of the invention is remedy. It aims to create a bioactive surface for bone implants on a metal substrate in such manner as to preclude separation between layer and substrate.
This problem is solved by the invention by a surface layer with the features of claim
1
.
The surface layers of the invention are to be produced from mixtures of metal oxides and calcium compounds. Appropriate materials for coating bone implants on metal substrates are substances known as being bioactive or bio-inert The substances denoted in the description below as metal oxides and calcium compounds are meant generically. Illustratively the bioactive surface layer may consist of titanium oxide and calcium hydroxyl apatite. The surface layers of the invention are free of layer/substrate separation between the metallic (substrate) phase and the ceramic phase (layer of oxide+calcium compound), and as a result abrasion or spalling of this ceramic surface layer in the event of non-uniform loading are precluded. The invention is especially significant for screw-shaped implants, whether for temporary implants (for instance Schanz screws) or for permanent anchoring (for instance oral implants). Furthermore these layers also may be impermeable or porous.
The anchoring of the implant fitted with a surface layer of the invention depending on configuration not only is locking in geometric manner but also is predominantly frictionally locking. This feature is caused by the chemical bonding between the bioactive surface layer and the abutting bone tissue resulting from the phase of one or more calcium compounds integrated into the surface layer.
Such surface layers may be prepared by wet-chemical procedures (for instance sol/gel technique; precipitation), thereby assuring good reproducibility and defined quality parameters. Moreover such procedures are comparatively simple and economical over the heretofore known methods (CVD, PVD or plasma spraying).
A preferred further development in making the surface layers of the invention allows different ways of constructing the layer. These osteo-conductive and bioactive surface layers may be impermeable or may be matched to a specific application using a freely selected porosity. Moreover the composition, for instance the MeO/CaP ratio, may be arbitrarily changed over the entire layer thickness to secure optimal bioactivity.
The invention and its further developments are elucidated below by a general description and two illustrative embodiments.
GENERAL DESCRIPTION
The materials used to prepare this bioactive surface layer are one or more metal oxides (MeO), for instance of titanium, chromium, niobium, tantalum and the like or alloys of same in amorphous and/or crystalline form as well as one or more calcium compounds (CaX) composed of portions of calcium phosphates (CaP) and/or calcium apatites (CaAp) and/or calcium carbonate (CaCO
3
) in crystalline form. The expression herein of “calcium phosphates” (CaP) denotes calcium hydroxyl apatite (hydroxyl apatite, HA), Ca
5
(PO
4
)
3
OH and/or &bgr;-tri-calcium phosphate (&bgr;-TCP), Ca
3
(PO
4
)
2
or similar. The expression “calcium apatite” herein denotes carbonate apatite (CO
3
Ap), Ca
10
(PO
4
)
6
CO
3
and/or fluoroapatite (Fap), Ca
10
(PO
4
)
6
F
2
and/or chloroapatite (ClAp), Ca
10
(PO
4
)
6
Cl
2
and/or oxyapatite (Oap), Ca
10
(PO
4
)
6
O. The described mixture is used to coat a preferably metal substrate which may or may not be oxidized. The concentration ratio of MeO to CaX can be selected to be variable or constant across the entire layer thickness. Preferably a variable MeO/CaX ratio will be selected, with a higher value near the metal substrate. The layer thickness may be between 0.01 &mgr; and 5 mm.
Furthermore impermeable or porous layers may be made. A thickness between 0.01 &mgr; and 50 &mgr; was found optimal for impermeable layers; on the other hand, a thickness between 10 &mgr; and 3 mm was found optimal for porous ones. Preferably the thickness of impermeable layers shall be between 0.5 and 20 &mgr; and for porous ones between 100 &mgr; and 1 mm. Appropriately the magnitude of the CaX grains is between 2 nm and 4 mm.
REFERENCES:
patent: 34 12 915 (1984-10-01), None
patent: 211 676 (1987-02-01), None
patent: 232 791 (1987-08-01), None
patent: 264 917 (1988-04-01), None
patent: WO 94/25637 (1994-11-01), None
patent: WO 24391 (1996-08-01), None
Gasser Beat
Piveteau Laurent Dominique
Schlapbach Louis
Dr. H. C. Robert Mathys Stiftung
Isabella David J.
Rankin, Hill Porter & Clark LLP
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