Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1996-11-22
2001-10-16
Milano, Michael J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023300, C623S023560, C623S023760
Reexamination Certificate
active
06302913
ABSTRACT:
This invention relates to a biomaterial useful in bone repair and replacement, and to implants for craniofacial, orthopaedic, and especially dental applications.
Successful osteointegration of implants for dental, craniofacial and orthopaedic applications is a problem central to oral and skeletal rehabilitation.
Conventional treatment of bone defects require the use of either organic (bone derived) or inorganic (man made) biomaterials for successful restoration of form and function, preferably biomaterials with interconnected porous spaces across the substratum of the biomaterial. This allows bone growth into the porous spaces of the biomaterial, securing its incorporation and osteointegration with the surrounding viable bone at the margins of the bone defect. Porous biomaterials which allow bone growth thus into their porous spaces are defined as osteoconductive biomaterials.
The necessity of having viable bone in direct contact with the porous biomaterial to ensure adequate bone ingrowth via osteoconduction is, however, a limiting factor particularly in large bony defects, since the depth of bone penetration within the porous spaces may be confined to the peripheral regions of the implant only. Furthermore, a perfect fit of an implant, designed for orthopaedic and dental applications either for bone repair or replacement, within a bone defect is often technically difficult to achieve, since it is not always possible to prepare the bone margins precisely so as to provide a perfect fit to the implants. Thus, in spite of technological advances in implant design and fabrication, osteointegration often doe not occur or is not maintained along the entire implant surface.
Thus for several applications, it would be preferred for bone to grow more rapidly into the porous spaces and, further, for bone to form independently of the surrounding viable bone, within the biomaterial. The formation of bone within a porous biomaterial independent of the presence of viable bone (when for example the biomaterial is implanted in extraskeletal sites) is defined as osteoinduction. One approach for preparing an osteoinductive material is to adsorb onto its surfaces exogenous growth and morphogenetic factors which are capable of inducing differentiation of bone within the porous spaces of the biomaterial. These molecular initiators of bone formation are collectively named bone morphogenetic proteins (BMPs).
This, however, requires the complexing, onto the biomaterial, of either native BMPs (isolated and purified from organic bone matrix—in particular bovine bone) or recombinant human BMPs, with the accompanying disadvantages of a limited shelf life and possible adverse systemic effects. A preferred alternative would be a biomaterial which is capable of spontaneously initiating bone formation within the porous spaces independent of the presence of viable bone at its interfaces.
The Applicant is aware of previous studies involving the calcium phosphate ceramic called hydroxyapatite [Ca
10
(PO
4
)
6
(OH)
2
] obtained after hydrothermal chemical exchange with phosphate converting the original calcium carbonate exoskeletal microstructure of the scleractinian reef-building coral of the genus Goniopora [1] into an inorganic replica of hydroxyapatite [2-4]. Conversion to hydroxyapatite is monitored by X-ray diffraction pattern, showing that hydroxyapatite replicas consist of ±90% hydroxyapatite and 10% tricalcium phosphate. Previous studies by one of the inventors, Dr Ripamonti, using coral-derived hydroxyapatite introduced the concept that the shape and configuration (hereinafter referred to as “the geometry”) of the hydroxyapatite implant regulate the initiation of bone formation in vivo [6]. These studies showed that in extraskeletal sites of rodents, bone did not form in implants of granular hydroxyapatite, even when pre-treated with bone morphogenetic proteins (BMPs) (which initiate bone differentiation in vivo), while bone formation was observed in porous blocks of hydroxyapatite [5-8]. As part of the research into the subject of spontaneous bone growth and, in particular, the optimum conditions for initiating bone growth, extraskeletal implantation of different forms of hydroxyapatite into primates indicated that the geometry of the hydroxyapatite indeed is important and indeed might even be critical for bone induction to occur [5,7,8]. When implanted intramuscularly in baboons, granular hydroxyapatite implants did not induce the differentiation of bone, while reproducible bone differentiation was observed in porous blocks of hydroxyapatite with identical surface characteristics [5,7,8].
Thus it appeared from said inventor's studies that a critical difference between geometries is the presence of convexities in granular hydroxyapatite and, conversely, the presence of concavities (of the porous space) in the blocks of hydroxyapatite.
Accordingly it is an object of this invention to provide implants for bone repair and bone replacement having a defined macrostructure and especially a defined geometric configuration of the implant surface, i.e. implants with geometric osteoinductive configurations.
It is another object of this invention to provide a biomaterial for bone replacement which is capable of spontaneous initiation of bone formation, i.e. a biomaterial with intrinsic osteoinductive activity.
It is another object of this invention to provide sintered porous ceramic biomaterials and methods for their manufacture derived from synthetic hydroxyapatite particles as starting material.
It is a further object of this invention to provide sintered ceramic biomaterials capable of osteoconduction when implanted into a bone defect.
It is a further object of this invention to provide sintered porous ceramic biomaterials for bone replacement having a defined porous macrostructure and especially a defined geometric configuration of the porous structure (osteoinductive configuration).
It is a further object of this invention to enhance the extent of bone formation and/or bone growth by pre-treatment of the porous sintered hydroxyapatite with liquid etchants.
It is yet a further object of this invention to provide porous sintered ceramic biomaterials which provide an optimal substratum for adsorption of growth and morphogenetic factors, including, but not limited to BMPs.
It is a still further object of this invention to provide a composite of porous ceramic and native or recombinant human BMPs for the rapid initiation of bone formation within the porous spaces of the implant.
A further, important object of this invention is to provide a bone implant for orthopaedic, craniofacial, and particularly dental applications.
How the objectives of this invention are achieved will become apparent in the light of the following disclosure.
Whilst restoration of bone defects may be sought by insertion at the site of the bone defect of porous osteoconductive biomaterials or implants, in several instance treatment requires the insertion of solid prostheses that substitute for a part of the skeleton, as commonly done for femoral and knee replacement (for example, hip and knee prosthesis).
Similarly, dental implants (usually of titanium with or without hydroxyapatite coating) are used as surrogates of tooth roots after implantation in edentulous jaws. Both porous biomaterial implants and solid prosthetic implants for orthopaedic, craniofacial and dental applications need to integrate with the host viable bone for successful osteointegration. It is common knowledge that osteointegration may not occur or is not maintained along the entire surface of solid prosthetic implants for orthopaedic, craniofacial and dental applications. Excluding failures attributable to implant micromotion and infection, lack of optimal osteointegration along solid prosthetic implants may be due to inadequate consideration of the geometric configuration of the implant surface.
Thus, the importance of geometry of an implant for bone repair and replacement may not be limit
Kirkbride Anthony Nigel
Ripamonti Ugo
Frommer William S.
Frommer Lawrence & Haug LLP.
Implico B.V.
Koh Choon P.
Milano Michael J.
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