Methods of designing three-dimensional lattice structures for implants
Inventors
Laine, Christopher • Helmar, Ian • Diehl, Lucas • Tinley, Jason • Chappuis, Kevin D. • Sullivan, John F.
Assignees
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Publication Number
US-11648124-B2
Publication Date
2023-05-16
Expiration Date
Abstract
The methods disclosed herein of generating three-dimensional lattice structures and reducing stress shielding have applications including use in medical implants. One method of generating a three-dimensional lattice structure can be used to generate a structure lattice and/or a lattice scaffold to support bone or tissue growth. One method of reducing stress shielding includes generating a structural lattice to provide sole mechanical spacing across an area for desired bone or tissue growth. Some examples can use a repeating modified rhombic dodecahedron or radial dodeca-rhombus unit cell. Some methods are also capable of providing a lattice structure with anisotropic properties to better suit the lattice for its intended purpose.
Core Innovation
The disclosed invention concerns a method for manufacturing an implant having reduced stress shielding. The method fabricates an implant body that includes a lattice structure comprising a plurality of repeating unit cells, and identifies a principal axis of the lattice structure. A loading axis is defined within 90 degrees of the principal axis, and the implant is fabricated so that, once implanted between two areas of tissue, the implant body defines an implant space between the two areas of tissue.
The implant space provides sole mechanical spacing between the two areas of tissue in at least one plane that intersects the loading axis. The disclosure relates the lattice architecture to directional mechanical response by providing anisotropic properties through fabrication in which elastic modulus along the loading axis is lower than elastic modulus along a second loading axis. The approach maintains stiffness in other directions while reducing elastic modulus along a targeted loading axis to address stress shielding.
The lattice structure is described in terms of repeating unit-cell geometries including modified rhombic dodecahedron and radial dodeca-rhombus, with unit cells defined by nodes and struts and indexed by strut-angle concepts. The disclosure also describes lattice design considerations such as void and interconnection sizing to establish openings configured for tissue and bone ingrowth, and it includes material and surface treatment options for implantable metals and bioactive coatings.
Claims Coverage
The independent claim is clm-00001. The related dependent claims specify five additional inventive features: directional elastic-modulus contrast, quantitative elastic modulus ranges, specific repeating unit cell geometry, and bone-growth-oriented lattice openings and interconnections.
Lattice implant with principal and loading axes
A method for manufacturing an implant having reduced stress shielding by fabricating a lattice structure comprising a plurality of repeating unit cells, identifying a principal axis, and defining a loading axis within 90 degrees of the principal axis.
Sole mechanical spacing plane intersecting loading axis
Fabricating the implant so that once implanted between two areas of tissue, the implant body defines an implant space between the two areas of tissue, and the implant space provides sole mechanical spacing in at least one plane intersecting the loading axis.
Directional elastic modulus reduction relative to a second loading axis
Identifying a second loading axis within an offset relative to the loading axis and fabricating the implant such that the elastic modulus along the loading axis is less than the elastic modulus along the second loading axis.
Elastic modulus range along the loading axis
The elastic modulus along the loading axis comprises a range between and including 0.3 GPa and 12 GPa.
Elastic modulus range along the second loading axis
The elastic modulus of the implant along the second loading axis comprises a range between and including 2 GPa and 25 GPa.
Rhombic dodecahedron repeating unit cell
The repeating unit cell has a rhombic dodecahedron structure.
Openings and interconnections configured to allow bone growth
Fabricating the lattice structure as comprising a plurality of openings and a plurality of interconnections configured to allow bone growth.
Across the independent and dependent claim set, the core coverage is an implant with reduced stress shielding formed from a repeating-unit lattice whose directional response is controlled using a principal axis and a loading axis, combined with sole mechanical spacing between tissue areas in a plane intersecting the loading axis. Further claim coverage specifies directional elastic-modulus contrast with ranges, includes a rhombic dodecahedron unit cell structure, and requires openings and interconnections configured to allow bone growth.
Stated Advantages
Reduced stress shielding.
Documented Applications
Spinal fusion interbody implants using sole mechanical spacing between adjacent tissue areas to promote physiologic loading.
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