Superelastic Nitinol Fatigue Life via Pre-Straining
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Solution Overview
Problem
Intraluminal medical devices made of superelastic nickel-titanium alloys face fatigue failure due to high stresses and cyclic loading, limiting their reliability in vivo applications.
Innovation Solution
Applying compressive and tensile stresses exceeding 9% strain amplitude to fatigue critical locations of the devices, inducing residual strain, which enhances the fatigue properties of the materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If superelastic nickel-titanium alloy is used for intraluminal medical devices, then the device can deploy from small-diameter delivery configuration to deployed configuration in body vessel, but the device is subjected to high stresses and high cyclic loading leading to fatigue failure
Solution Approach 1:
The patent applies preliminary plastic deformation (pre-straining) to the Nitinol alloy before the device is deployed in the body. This pre-straining process permanently deforms the material to create a more favorable stress state for fatigue resistance, improving the device's reliability before it encounters cyclic loading in vivo.
Solution Approach 2:
The patent changes the material parameters by permanently altering the crystal structure of the Nitinol alloy through controlled plastic deformation. This transforms the material from its original superelastic state to a pre-strained state with improved fatigue properties, changing key mechanical parameters such as yield strength and fatigue limit.
2Reliability
If pre-straining of Nitinol devices in tension is applied, then fatigue life is improved, but additional processing steps are required
Solution Approach 1:
The patent combines the pre-straining process with the existing device manufacturing and deployment sequence. By integrating the plastic deformation step into the overall device preparation process (either before delivery or as part of the deployment mechanism), the additional processing is consolidated with existing operations rather than adding completely separate steps.
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 significantly increases the fatigue endurance limit of the medical devices by over 115% compared to untreated devices, improving their reliability and performance in vivo.
Implementation Method 1
A compressive stress is applied to a fatigue critical location of a medical device. The compressive stress induces a compressive strain of greater than 9% in the fatigue critical location. A tensile stress is applied to the fatigue critical location of the medical device, where the tensile stress induces a tensile strain of greater than 9% in the fatigue critical location. After application and release of each of the compressive stress and the tensile stress, the fatigue critical location includes a non-zero amount of residual strain
Implementation Method 2
a medical device comprising a superelastic nickel-titanium alloy
Data Source
AI summary
A method of improving the fatigue life of a superelastic medical device includes applying a compressive stress to a fatigue critical location of a medical device comprising a superelastic nickel-titanium alloy, where the compressive stress induces a compressive strain of greater than 9% in the fatigue critical location. After inducing the compressive strain, the compressive stress is released. A tensile stress is applied to the fatigue critical location of the medical device, where the tensile stress induces a tensile strain of greater than 9% in the fatigue critical location. After inducing the tensile strain, the tensile stress is released. After application and release of each of the compressive stress and the tensile stress, the fatigue critical location includes a non-zero amount of residual strain, and the medical device may exhibit improved fatigue properties.