Porous Strut Geometry for Implant Fatigue and Bone Ingrowth
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Solution Overview
Problem
Current additive layer manufacturing (ALM) techniques for producing three-dimensional porous structures result in low fatigue strength due to rough surfaces, which can lead to increased risk of fracture, and attempting to avoid porous surfaces in high-stress regions compromises bone ingrowth and implant fixation.
Innovation Solution
A method involving the creation of three-dimensional porous structures with specific geometries and struts, where additional struts define additional faces partially confronting a first layer, with nodes repositioned along the boundary to maintain connectivity and allow even abrasive fluid flow, enhancing fatigue strength without sacrificing surface area for bone ingrowth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If porous layers are formed by current ALM techniques to increase surface area for bone in-growth, then bone in-growth capability is improved, but fatigue strength decreases due to rough surfaces acting as stress risers
Solution Approach 1:
The patent applies preliminary action by performing abrasive flow machining polishing on the porous structure before implantation. The abrasive fluid is forced through the porous structure to smooth the internal surfaces in advance, eliminating stress risers while preserving the porous geometry needed for bone in-growth. This pre-polishing step resolves the contradiction by preparing the surface optimally before the structure is subjected to mechanical loads during implantation.
Solution Approach 2:
The patent applies local quality by selectively polishing only the internal porous surfaces that contact bone tissue, while leaving the external load-bearing surfaces with different properties. The abrasive flow machining targets specific regions within the porous structure, smoothing internal interfaces where bone in-growth occurs without compromising the overall structural integrity or external surface characteristics needed for mechanical strength.
2Strength
If polishing is performed to increase fatigue strength, then fatigue strength is improved, but uneven abrasive fluid flow through irregular pore shapes and sizes reduces polishing effectiveness
Solution Approach 1:
The patent applies parameter changes by modifying the pore structure geometry to have uniform pore shapes and sizes, specifically using regular tetrahedral or octahedral unit cells with consistent strut dimensions. This standardization of geometric parameters ensures uniform flow characteristics throughout the porous structure, allowing abrasive fluid to evenly polish all internal surfaces. The controlled pore parameters eliminate preferential flow paths while maintaining high surface area for bone in-growth.
3Adaptability or versatility
If randomization techniques are used to create porous structures, then pore shape and size variety is improved, but abrasive fluid flow becomes uneven leading to preferential polishing paths
Solution Approach 1:
The patent applies inversion by reversing the conventional approach: instead of using randomization techniques to create porous structures and then attempting to polish them, the invention uses highly regular, uniform pore geometries from the outset. This inverted strategy eliminates the polishing uniformity problem at its source by ensuring even abrasive fluid flow through consistent pore dimensions, while still achieving the desired bone in-growth capability through the controlled porosity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method increases the fatigue strength of the structures by ensuring even polishing and maintaining surface area for bone ingrowth, thereby improving the fixation and durability of medical implants.
Implementation Method 1
a first layer of metal powder is deposited and scanned with a high energy beam to melt or sinter the metal powder to form a solid first layer
Implementation Method 2
Successive layers of metal powder are then deposited and scanned with the high energy beam to melt or sinter the metal powder to form porous geometries
Implementation Method 3
The abrasive fluid flows through the interstices of the subject device and smooths its rough surfaces
Data Source
Figure 1
Figure 2A~3B
Figure 4A~4B
AI summary
A porous apparatus (210) includes a first layer (220) and a second layer (230). The second layer has a plurality of struts (240, 245). At least some of the struts define porous geometries (255) defining a plurality of faces (295), at least one of the plurality of the faces at least partially confronting the first layer. Each of the faces is bounded by intersecting struts at vertices. Less than all of the vertices of each face of the porous geometry at least partially confronting the first layer are connected by a strut to the first layer. A process of producing the at least partially porous structure includes depositing and scanning metal powder layers. At least some of the scanned metal powder layers form either one or both of a portion of a first section of the structure and a portion of a second section of the structure formed by at least the struts defining the porous geometry.