Multi-Layer Nitinol Spring for Bone Stabilization Fatigue Life
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Solution Overview
Problem
Existing bone and joint stabilization devices face challenges in achieving higher ultimate strength and longer cyclic fatigue life, which are essential for maintaining effective compression and range of motion in orthopedic surgeries.
Innovation Solution
The use of a multi-layer spring member made from Nitinol alloy with a plurality of beams arranged in pairs, connected by medial connectors, and anchored by a tooth mechanism within an anchoring head, providing improved fatigue life and strength by allowing individual layers to fail without compromising the device's functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a one-piece spring member is used, then the device structure is simple, but the cyclic fatigue life and ultimate strength are insufficient
Solution Approach 1:
The spring member is divided into multiple layers (first layer, second layer, third layer) instead of using a one-piece structure. Each layer can be independently anchored by teeth, creating modular units that can fail independently without compromising the entire device. This segmentation directly addresses the fatigue life issue by distributing stress and failure points across multiple layers.
Solution Approach 2:
The patent uses a composite construction where multiple spring member layers are combined with anchoring teeth and bone anchors to create a multi-component system. This composite approach allows each component to be optimized for its specific function while working together to achieve superior overall performance in terms of strength and fatigue resistance.
2Strength
If the spring member thickness is increased, then the ultimate strength is improved, but the device flexibility and range of motion are reduced
Solution Approach 1:
By dividing the spring member into multiple thinner layers rather than using a single thick piece, the device achieves the required strength through the combined effect of multiple layers working together. Each thin layer maintains flexibility while the stack of layers collectively provides the necessary ultimate strength, resolving the contradiction between strength and flexibility.
Solution Approach 2:
The patent transitions from a single-dimensional (one-piece) spring member to a multi-dimensional layered structure. By adding the vertical stacking dimension, the device achieves enhanced strength through layer multiplication while each individual layer remains thin enough to maintain flexibility and accommodate anatomical range of motion.
3Device complexity
If a single layer spring member is used, then the device complexity is low, but the reliability upon layer failure is compromised
Solution Approach 1:
The spring member system is segmented into multiple independent layers, each capable of being anchored separately. This creates a redundant system where if one layer fails, the other layers remain anchored and continue to provide structural support, ensuring device functionality is maintained despite partial failure.
Solution Approach 2:
The multi-layer design inherently provides a cushioning effect against complete device failure. By distributing the load and anchoring points across multiple layers, the system is prepared in advance to withstand the failure of individual layers without catastrophic loss of functionality, much like a safety buffer.
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
This configuration significantly enhances the cyclic fatigue life and ultimate strength of the devices, enabling them to maintain compression and allow for full anatomical range of motion while reducing the impact of layer failure, thus improving the durability and effectiveness of bone and joint stabilization systems.
Implementation Method 1
a Nitinol (generally, a NiTi alloy that is superelastic (SE) at human body temperature, i.e., having an Af below about 37° C.) spring member having a plurality of layers of limited thickness
Data Source
AI summary
Bone and joint stabilization devices or systems are described that include multiple-layer bodies. The approach offers dramatically improved fatigue life as compared to one-piece spring members that are otherwise similar or comparable. Coordinated improved-strength anchor embodiments, anchor loading tools and methods of use are also described.