Core and shell coupling of a composite material bone implant
Fiber-reinforced polymer matrix composite material bone screws having threads surfaced with a metallic layer are described. In some embodiments, the metallic layer comprises a plurality of anchors placed to engage with the composite material and resist shearing when the bone screw is inserted or removed.
1. A bone screw having screw threads for rotating insertion to a bone, the bone screw comprising:
a body formed from composite material comprising a fiber-reinforced polymer matrix; and
a metallic layer surfacing the body with at least one metallic ply covering at least a region of the screw threads;
wherein a plurality of anchor structures having a thickness dimension at least 50% of the thickness of the metallic ply are formed out of the material of the at least one metallic ply to engage with the composite material and resist a shearing force applied to the metallic layer and directed along the screw threads when the screw is rotated within the bone.
2. The bone screw of claim 1 , wherein the metallic layer comprises at least one from among the group comprising titanium and a titanium alloy.
3. The bone screw of claim 2 , wherein the titanium or titanium alloy is anodized.
4. The bone screw of claim 1 , wherein a plurality of the anchor structures are formed in the at least one metallic ply as openings filled with the composite material.
5. The bone screw of claim 4 , wherein the openings are formed as convolutions of an edge of the at least one metallic ply.
6. The bone screw of claim 4 , wherein the openings are formed as apertures in the at least one metallic ply.
7. The bone screw of claim 1 , wherein a plurality of the anchor structures are formed by indentation of an outer surface off the at least one metallic ply.
8. The bone screw of claim 7 , wherein the indented anchor is within a recessed region between two turns of the screw thread.
9. The bone screw of claim 7 , wherein the indented anchor protrudes by at least 50% of the thickness of the at least one metallic ply into the composite material, relative to the non-indented surrounding inner surface of the metallic ply.
10. The bone screw of claim 1 , wherein the anchor structures are formed in a repeating pattern along the metallic ply.
11. The bone screw of claim 1 , wherein the screw is cannulated.
12. The bone screw of claim 1 , wherein the at least one ply comprises a strip wound around the body.
13. The bone screw of claim 12 , wherein a first portion of the strip overlies and is welded to a second portion of the strip.
14. The bone screw of claim 13 , wherein a free edge of the first portion of the strip lies in a recess between two turns of the screw thread.
15. The bone screw of claim 1 , wherein the at least one ply comprises a tube compressed onto the body.
16. The bone screw of claim 15 , wherein the tube is welded to another ply of the metallic layer.
17. A bone screw having screw threads for rotating insertion to a bone, the bone screw comprising:
a body formed from composite material comprising a fiber-reinforced polymer matrix; and
a metallic layer surfacing the body with at least one metallic ply covering at least a region of the screw threads;
wherein a plurality of anchor structures are attached to the inner surface of the metallic ply, each anchor structure comprising a thickening by at least 50% of the thickness of the metallic ply, to engage with the composite material for anchoring the metallic ply thereto.