Artefact suitable for use as a bone implant

Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone

Reexamination Certificate

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Reexamination Certificate

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06280478

ABSTRACT:

This invention relates to an artefact suitable for use as a bone implant by implantation thereof into a subject at a body site where bone growth is required. It relates also to a method of making such artefact.
According to a first aspect of the invention, there is provided an artefact suitable for use as a bone implant by implantation thereof into a subject at a body site where bone growth is required, the artefact comprising a three-dimensional lattice structure having a plurality of laths or bars of bioactive material crossing each other in a plurality of zones and interconnected in said zones, with interstices thus being provided between adjacent laths or bars, these interstices defining a plurality of interconnected pores or channels in the lattice structure.
The porous three-dimensional lattice structure thus, in use, permits bone growth into its porous spaces, thereby to secure its incorporation into and osteointegration with the surrounding viable bone at the margins of a bone defect at the site where the artefact is implanted. The lattice structure may thus be osteoconductive, ie permitting bone growth into its porous spaces when it is in direct contact with viable bone, and/or it may be osteoinductive, ie permitting bone growth at its porous spaced independently of the presence of viable bone in contact with the artefact.
The interconnected pores or channels should, for enhanced osteoinductive or osteoconductive compatibility, comprise from 30% to 80% of the total volume of the artefact.
The external surfaces of the laths, bars or rods making up the lattice structure may be smooth. Instead, however, the external surfaces of at least some of the bars or rods may be provided with surface features, such as indentations therein. The indentations, when present, may be of hemispherical, concave or irregular shape.
The bioactive material of the bars or rods may be a sintered ceramic or glass material having low or no porosity. In particular it may be a calcium phosphate-based ceramic material such as hydroxylapatite or tricalcium phosphate.
The porous lattice structure may comprise an extrudate of the bioactive material, with the bars or rods having been formed from extruded strands of the bioactive material, which strands are thus arranged or stacked and consolidated into at least part of the intimately bound three-dimensional open or porous lattice structure.
Thus, according to a second aspect of the invention, there is provided a method of making an artefact suitable for use as a bone implant by implantation thereof into a subject at a body site where bone growth is required, the method comprising
extruding an extrudable mixture of a bioactive material in particulate form and an organic base, into a three-dimensional lattice structure having a plurality of laths or bars formed from extruded strands of the mixture, the laths or bars crossing each other in a plurality of zones, so that interstices are provided between adjacent laths or bars and these interstices define a plurality of interconnected pores or channels in the lattice structure;
removing the organic base, to form a green artefact; and
heating the green artefact to a temperature sufficient to sinter the bioactive material and to fuse the bars or laths in said zones where they cross.
It will be appreciated that the extrusion of the mixture into the three-dimensional lattice structure need not necessarily be effected in one step or operation but can instead be effected in a number of steps or stages. Thus, for example, the extrudable mixture can initially be extruded onto filaments which can thereafter be arranged into the lattice structure.
The method may include, if desired, forming surface features such as indentations in or on the external surfaces of the bars or laths prior to sintering the green artefact eg as the lattice structure is formed.
The extrusion of the extrudable mixture and the formation of the lattice structure can be effected using known apparatus such as known apparatus for injection moulding of particulate materials, known apparatus for solid free form manufacture by means of fused deposition moulding of ceramics, known apparatus for three-dimensional printing of ceramics, known apparatus for multiphase jet solidification of ceramics, and/or known apparatus for stero lithography.
The bioactive material may be in powdered form initially eg may be powdered hydroxylapatite. The organic base is a binder which serves as a temporary vehicle to allow processing of the hydroxylapatite powder. The base may be a single component substance, or may be made up of multiple components and additives. The base or binder can thus be selected so that it influences the flow characteristics of the extrudable mixture, permits interaction and/or agglomeration of the powder, influences the rheology of the mixture, influences the moulding capabilities of the mixture, and permits ready removal or debonding thereof. The binder may thus comprise a mixture of two or more of the following: a lubricant, a polymer, an elastomer, a wax and a tacktifier.
The removal of the organic base may be by solvent extraction and/or by a thermal process.
According to a third aspect of the invention, there is provided a method of making an artefact suitable for use as a bone implant by implantation thereof into a subject at a body site where bone growth is required, the method comprising
extruding an extrudable mixture of a bioactive material in particulate form and an organic base, into a lattice component having a plurality of laths or bars formed from extruded strands of the mixture, with spaces or interstices provided between adjacent laths or bars;
removing the organic base;
either before or after removal of the organic base arranging a plurality of the lattice components into a three-dimensional lattice structure wherein the spaces or interstices of the lattice components define a plurality of interconnected pores or channels in the lattice structure; and
heating the resultant green artefact to a temperature sufficient to sinter the bioactive material and to fuse the bars or laths in zones where they cross.
As described hereinbefore, the extrusion of the mixture into the lattice components need not necessarily be effected in one step or operation but can instead be effected in a number of steps or stages. Thus, the extrudable mixture can initially be extruded into filaments, which can thereafter be arranged into the lattice components. Each lattice component can then, for example, comprise a single or continuous filament arranged in a plurality of the bars or laths. Instead, however, each lattice component can comprise a plurality of filaments each defining one or more of the bars or laths.
The bars or laths in each lattice component may extend parallel to one another.


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patent: 2427315 (1979-12-01), None

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