Nitinol Stent Loading via Martensitic Phase Control
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Solution Overview
Problem
Self-expanding stents made from shape memory materials like Nitinol often recoil during the loading process due to phase transformations, causing friction and potential buckling or collapse, especially in longer stents, which complicates their insertion into delivery systems.
Innovation Solution
A method involving controlled temperature and force application to maintain a stent in a compressed configuration by cooling it below the martensite finish temperature, applying a force within specific temperature ranges to achieve a stable delivery configuration, and then loading it into a delivery system, minimizing recoil and friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the stent is cooled to a temperature below the austenite start temperature to prevent phase transformation during loading, then the stent can be compressed to a low profile configuration, but the stent may still recoil when compressive stress is removed, causing buckling or collapse during loading
Solution Approach 1:
The patent applies parameter changes by controlling the temperature of the shape memory material during loading to remain below the austenite start temperature, preventing phase transformation. Additionally, a restraining force is applied during loading to counteract recoil, and the temperature is maintained below the martensite finish temperature during the restraining phase to ensure the material remains in the martensitic phase and does not expand
Solution Approach 2:
The patent applies preliminary action by pre-cooling the shape memory material to a temperature below the austenite start temperature before applying compressive stress. This preliminary cooling ensures the material is in the martensitic phase and will not undergo unwanted phase transformation during subsequent loading operations
2Ease of operation
If the stent is maintained at a low temperature to prevent recoiling, then the stent can be loaded into the delivery system, but the loading process becomes more complex due to temperature control requirements
Solution Approach 1:
The patent utilizes phase transitions of the shape memory material by controlling temperature to maintain the material in the martensitic phase during loading. The temperature is controlled to be below the martensite finish temperature during the restraining phase, ensuring complete martensitic transformation and prevention of spontaneous expansion
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
Enables the loading of stents with minimal frictional forces and prevents damage during insertion, particularly benefiting longer stents by maintaining the compressed configuration during loading, thus improving the efficiency of the stent deployment process.
Implementation Method 1
A shape memory material may undergo a reversible phase transformation that allows it to 'remember' and return to a previous shape or configuration. For example, a Nitinol stent may transform from a low-profile compressed configuration during delivery in a vessel to an expanded configuration at a treatment site by transforming from a lower temperature martensitic phase to a higher temperature austenitic phase. The phase transformation may be driven by a change in stress (superelastic effect) or temperature (shape memory effect).
Implementation Method 2
The phase transformation may be driven by a change in stress (superelastic effect) or temperature (shape memory effect).
Implementation Method 3
the stent is cooled to a temperature at or below a martensite finish temperature of the shape memory material
Implementation Method 4
the stent is warmed from the initial temperature to a first temperature at or above an R'-phase start temperature and below an austenite start temperature of the shape memory material
Data Source
AI summary
A process to load a medical device comprising a shape memory material into a delivery system is described herein. According to one aspect, the method includes applying a force to the medical device to obtain a delivery configuration thereof, where the device is at a first temperature within an R-phase temperature range of the shape memory material during application of the force. The medical device is cooled in the delivery configuration to a second temperature at or below a martensite finish temperature of the shape memory material. The force is then removed from the medical device, and the device is loaded into a delivery system. Preferably, the medical device substantially maintains the delivery configuration during the loading process.