Medical implants having desired surface features and methods of manufacturing
In embodiments of the invention, an implant that anchors into bone may have a bone-facing region that comprises a plurality of interconnected struts. The interconnected struts may define local features such as engagement ridges, fins, crests, a macroscopic surface-interrupting feature, a divertor structure, and sawteeth in any combination. Such features may help resist translation or rotation of the implant, and may be conducive to bone ingrowth. Parameters such as local empty volume fraction and local average strut length can be varied, even within the features, by the design of the network of struts. Struts may be tapered. Cantilever struts may also be provided, which may point in a desired direction. The pattern of struts may be specified to the level of dimensions and location of individual struts. The implant may be manufactured by additive manufacturing methods. The mesh of struts may be generated by an algorithm using Voronoi tessellation.
1. An implantable device, comprising:
a first region that is substantially solid; and
a second region, adjacent to said first region, said second region comprising a plurality of interconnected struts, some of said struts joining said first region, said struts having an average strut length, said struts defining openings between said struts through which bone can grow,
wherein said second region comprises struts that are connected at both of their ends to other struts and are outermost struts and define an exterior having a bone-facing enveloping surface,
wherein said second region further comprises a plurality of cantilevers that extend outward from vertices at or near said local enveloping surface and extend beyond said bone-facing enveloping surface,
wherein each of said cantilevers has a respective lengthwise cantilever direction, and at each of said cantilevers there is a respective local normal vector that is normal to said local enveloping surface of said implantable device at a location of said cantilever, and said cantilever direction points more towards a rear of said implantable device than does said local normal vector, and
wherein said implantable device has an external shape that is at least approximately a hemisphere having an equator and a pole, and for each of said cantilevers, said cantilever direction points more toward said equator than does said local normal vector that is normal to said external shape, and said cantilevers exist at or near said equator of said implantable device but a region closer to said pole of said implantable device is free of said cantilevers.
2. The implantable device of claim 1 , wherein at least one of said cantilevers has a cantilever length that is shorter than said average strut length.
3. The implantable device of claim 1 , wherein at least one of said cantilevers is at least approximately straight.
4. The implantable device of claim 1 , wherein at least some of said cantilevers are bent or curved.
5. The implantable device of claim 1 , wherein said first region has an overall density that is at least 90% of a solid density of a material from which said first region is made.