Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1996-11-22
2000-09-12
Milano, Michael J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 233, 623 2356, 623 2376, A61F 228
Patent
active
061171727
DESCRIPTION:
BRIEF SUMMARY
This material 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.sub.10 (PO.sub.4).sub.6 (OH).sub.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 in
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Kirkbride Anthony Nigel
Ripamonti Ugo
Frommer William S.
Implico B.V.
Koh Choon P.
Milano Michael J.
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