Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Implant or insert
Patent
1994-12-07
1997-03-18
Page, Thurman K.
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Implant or insert
424 93, 424 94, A61F 1300
Patent
active
056120494
DESCRIPTION:
BRIEF SUMMARY
This invention relates to novel bone-bonding gel-derived titania-based coatings. The invention also includes processes for the preparation of such coatings and their uses as surgical implants.
Titanium and its alloys are extensively used in reconstruction surgery as dental and orthopaedic implants because of their excellent biocompatibility with bone tissue (P. I. Br.ang.nemark, J. Prosthetic Dent. 50:399-410, 1983; D. I. Bardos, D. Williams (ed), Concise Encyclopedia of Medical & Dental Materials, Pergamon Press, Oxford 1990, pp 360-365; R. van Noort, J. Mater. Sci. 22:3801-3811, 1987). This can be explained by the unique characteristics of titanium-bone interface. The extremely slow growth of titanium oxide was observed during the implantation. The TiOH groups within the hydrated oxide layer were considered to be involved in the events leading to osseointegration of the titanium implants (P. Tengwall & I. Lundstr om, Clinical Materials 9:115-134, 1992). The calcium and phosphorous groups were identified in the few nanometer thick oxide layer (D. Mcqueen et al, Clinical application of Biomaterials, John Wiley & Sons, Chichester, 1982, pp. 167-177). Although titanium implants could be fixed in bone bed through osseointegration by using appropriate surgical techniques, the fixation proceeds slowly and depends largely on surgery (L. Sennerby, PhD thesis, University of Gotenburg, Gotenburg, Sweden, 1991). To enhance the bonding process and improve the bonding strength, the plasma-sprayed coatings of apatite, more particularly hydroxyapatite, were developed and approved for clinical application (K. de Groot, J. Ceram. Soc. Japan 99:943-953, 1991). However, from a technical point of view, plasma spraying is cumbersome and essentially complex, because apatite powder is chemically unstable at elevated temperatures.
Implants can chemically bond to bone through apatite because bone mineral is hydroxyapatite. These bone-bonding implants could be wholly apatite ceramic or coated with apatite using specific techniques such as plasma spray coating process. Furthermore, apatite can also be used as a bioactive phase in some composites to make them bond to bone (K. Verheyen, Resorbable materials with bone bonding ability, PhD thesis, Leiden University, Holland, 1993). In contrast to those apatite-based materials, bioactive glasses and glass-ceramics develop apatite layer onto their surfaces after implantation within bone tissue (L. L. Hench, Bioceramics: from concept to clinics, J. Am. Ceram. Soc. 74:1487-510, 1991; T. Kokubo, Bioactive glass ceramics: properties and application, Biomaterials 12:155-163, 1991). This kind of apatite gives the glasses and glass-ceramics a bone-bonding strength stronger than apatite ceramics (T. Kokubo, Bioactivity of glasses and glass-ceramics, in Bone-bonding Biomaterials, P. Ducheyne, T. Kokubo and C. A. van Blitterswijk (eds), Reed Health-care Communication, Holland, 1992, pp. 31-46). This bone-like apatite formation results from the interaction of these bioactive glasses and glass-ceramics with the surrounding biological tissue and especially with body fluid.
The potential for apatite formation can be evaluated for materials by using a metastable calcium phosphate solution, called a simulated body fluid (SBF, Na.sup.+ 142, K.sup.30 5.0, Mg.sup.2+ 1.5, CA.sup.2+ 2.5, Cl.sup.- 148, HCO.sub.3.sup.- 4.2, HPO.sub.4.sup.2- 1.0 and SO.sub.4.sup.2- 0.5 in mM). The fluid has been used in in vitro studies to provide information about the process of bone-like apatite formation on these bioactive glasses and glass ceramics because of its ion concentrations nearly equal to those of human blood plasma (T. Kokubo et al, J. Biomed. Mater. Res. 24, 721-734, 1990). Moreover, it does help a great deal to assess the possibility of bone-bonding for materials before their in vivo study. Those materials which can induce apatite formation on their surfaces in SBF can be placed in the list of candidates for bone-bonding materials. Recent research showed that besides bioactive glass and glass-ceramics, also pure
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Kangasniemi Ilkka
Li Panjian
Axidental Oy
Benston, Jr. William E.
Kubovcik Ronald J.
Page Thurman K.
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