Wave Spring Spinal Implant Using Shape Memory Alloy
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Solution Overview
Problem
Current spinal implant technologies face challenges such as polymer degradation under compressive loads, device migration, and subsidence, leading to pain, inflammation, and potential failure, particularly in disc replacement surgeries.
Innovation Solution
A spinal implant featuring a wave spring made from shape memory materials like Nitinol, which surrounds an artificial nucleus to provide controlled stiffness, shock absorption, and maintain natural spinal motion, while being designed to match the modulus of bone and resist stress shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polymer nucleus is used in the spinal implant, then the implant can be inserted through a small annulotomy and fill the disc space, but the polymer degrades under compressive loads over time leading to device failure
Solution Approach 1:
The patent combines a polymer nucleus with a metal wave spring annulus to create a composite spinal implant. The polymer provides ease of insertion and disc space filling, while the metal wave spring provides structural support and resistance to compressive loads, preventing the degradation issues that would occur with polymer alone.
Solution Approach 2:
The implant is divided into two functional segments: an inner polymer nucleus for shock absorption and disc space filling, and an outer metal wave spring annulus for structural support and load bearing. This segmentation allows each material to perform its optimal function without the weaknesses of the other.
2Stability of the object's composition
If spinal fusion is performed to eliminate motion between vertebrae, then stability is improved, but persistent stress on un-fused areas causes future problems
Solution Approach 1:
Instead of eliminating motion through fusion, the patent uses a dynamic wave spring annulus that allows controlled physiological motion between vertebrae while providing support. The wave spring structure can deform and recover, maintaining stability while permitting natural spinal movement and distributing stress across the implant and adjacent segments.
Solution Approach 2:
The wave spring annulus changes its mechanical parameters (stiffness, damping) based on the applied load and temperature, providing soft support under normal conditions and increased stability under higher loads, thereby reducing stress on adjacent un-fused segments while maintaining overall spinal stability.
3Strength
If the spring is made stiffer to support compressive loads, then load bearing capacity is improved, but the implant creates stress shielding and loses natural spinal motion
Solution Approach 1:
The wave spring annulus is designed to change its effective stiffness based on operating conditions - it provides higher support under compressive loads while remaining more compliant under tensile and shear loads. This parameter change allows the implant to bear necessary loads without creating stress shielding that would eliminate natural spinal motion.
Solution Approach 2:
The dynamic wave spring structure adapts its mechanical response to different loading conditions, providing appropriate support while maintaining natural spinal kinematics. The spring can deform in multiple directions and modes, allowing physiological motion while distributing stresses naturally across the implant-vertebra interface.
4Reliability
If the wave spring is made from shape memory material like Nitinol, then temperature-dependent elasticity and constant force provision are improved, but device complexity increases
Solution Approach 1:
The wave spring is made from shape memory material (Nitinol) that utilizes phase transitions between martensite and austenite phases in response to temperature changes. This provides temperature-dependent elasticity and the ability to maintain constant force over a range of deformations, improving reliability without requiring complex control systems.
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 wave spring implant offers long-term stability, maintains natural spinal motion, reduces stress on adjacent segments, and minimizes the risk of device failure by providing a constant force and temperature-dependent elasticity, thus addressing the limitations of existing technologies.
Implementation Method 1
A spinal implant featuring a wave spring made from shape memory materials like Nitinol
Implementation Method 2
providing a constant force and temperature-dependent elasticity
Implementation Method 3
provide controlled stiffness, shock absorption, and maintain natural spinal motion
Data Source
AI summary
A spinal implant includes a wave spring configured to surround a nucleus. The spring may be formed from a shape memory material. The implant may further include an artificial nucleus configured to simulate a disc nucleus.