Coated Composite Spinal Fixation Rod for MRI-Safe Rigidity
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Solution Overview
Problem
Conventional metal fixture rods for spinal fixation face issues such as image disturbance in MRI due to magnetization, low rigidity, and safety concerns due to exposed fibers during breakage.
Innovation Solution
A fixture rod composed of a fiber-reinforced resin core with a coating resin layer, featuring a fiber volume content of 50-70% near the surface, alternating layers of reinforcing fibers, and a coating resin layer with 30% elongation and 0.05-0.4 mm thickness, using thermoplastic resins like PEEK for integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal is used for the fixture rod, then fixing force and strength are improved, but magnetization causes image disturbance in MRI
Solution Approach 1:
The harmful magnetic properties of metal are extracted/removed from the fixture rod by replacing the metal material with a non-magnetic fiber-reinforced resin composite material, while maintaining the structural function of the rod
Solution Approach 2:
The fixture rod is constructed using composite materials (fiber-reinforced resin) that combine the strength benefits of fibers with the non-magnetic properties of resin, eliminating MRI interference while maintaining mechanical performance
2Object-affected harmful factors
If fiber density is reduced to eliminate metal, then MRI compatibility is improved, but rigidity and strength deteriorate
Solution Approach 1:
A fiber-reinforced resin composite structure is employed where high-strength fibers (carbon, glass, boron, SiC, or aramid) provide rigidity and strength, while the resin matrix provides non-magnetic properties for MRI compatibility
Solution Approach 2:
The fiber volume content is optimized locally at 50-70% in the vicinity of the surface layer to achieve the desired balance between rigidity, strength, and non-magnetic properties
3Object-affected harmful factors
If fiber-reinforced resin is used without proper coating, then MRI compatibility is improved, but fiber exposure occurs at breakage causing safety issues
Solution Approach 1:
A coating resin layer is applied in advance on the surface of the core member to prevent fiber exposure and potential tissue damage in the event of rod breakage, acting as a protective barrier before failure occurs
Solution Approach 2:
A flexible coating resin layer with elongation of 30% or more is applied on the core member surface, providing a protective barrier that can deform without cracking and prevent fiber exposure during breakage
4Reliability
If coating resin layer thickness is increased to prevent fiber exposure, then safety is improved, but rod flexibility and implantation ease deteriorate
Solution Approach 1:
The coating resin layer thickness is optimized within the range of 0.05-0.4 mm to achieve the desired balance between safety (preventing fiber exposure) and ease of implantation (maintaining flexibility)
Solution Approach 2:
A flexible coating resin layer with elongation of 30% or more is applied on the core member surface, providing a protective barrier that can deform without cracking and prevent fiber exposure during breakage
Data Source
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AI summary
An object is to provide an intraspinal fixture rod that reduces damage at the time of fixing with a screw, has high rigidity and high durability against a deformation load, and significantly reduces a risk of damage to a human body even at the time of breaking. A fixture rod according to one embodiment of the present invention comprises a core member containing a fiber-reinforced resin, and a coating resin layer coating the core member, and the coating resin layer has an elongation of 30% or more and has a thickness in a range of 0.05 mm to 0.4 mm.