Nitinol Stent Loading via Inert Atmosphere Cooling
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Solution Overview
Problem
The challenge lies in loading a coated, self-expanding nitinol stent into a delivery catheter while minimizing condensation and sublimation effects, which complicates the compression process and interferes with the stent's insertion due to the formation of water or ice crystals and other contaminants during cooling.
Innovation Solution
A method involving a loading chamber where contaminants like water vapor and carbon dioxide gas are purged, and the temperature is lowered slowly to below the martensitic start temperature of nitinol, allowing the stent to be compressed and loaded into a transfer tube or delivery catheter without forming contaminants on the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the nitinol stent is cooled below the martensitic start temperature to enable compression and loading, then the stent becomes pliable and ductile for easy compression, but water or ice crystals and other condensates form on the stent surface, interfering with the loading process
Solution Approach 1:
The patent applies an inert atmosphere principle by purging the cooling chamber with nitrogen gas to remove water vapor and carbon dioxide before cooling the stent. This prevents condensation and sublimation of contaminants on the stent surface while maintaining the low temperature required for martensitic transformation and compressibility.
Solution Approach 2:
The patent implements preliminary action by purging the cooling chamber with nitrogen gas to remove water vapor and carbon dioxide before the cooling process begins. This pre-cleaning of the atmospheric environment prevents contaminant deposition on the stent during subsequent cooling and compression operations.
2Volume of moving object
If the stent is compressed to a small diameter for loading into the delivery catheter, then the stent can be inserted through the patient's vasculature, but the compression process becomes difficult when contaminants are present on the stent surface
Solution Approach 1:
The inert nitrogen atmosphere prevents contaminant formation on the stent surface during cooling, ensuring that the compression and loading processes proceed smoothly without interference from ice crystals or condensates that would otherwise increase friction and loading difficulty.
Solution Approach 2:
The patent extracts harmful water vapor and carbon dioxide from the cooling chamber atmosphere through nitrogen purging before cooling occurs. This removal of contaminants eliminates the source of condensation and sublimation problems that would complicate the compression and loading operations.
3Temperature
If the cooling chamber contains water vapor and carbon dioxide, then the atmospheric conditions are normal, but condensation and sublimation occur on the cooled stent, forming additional thickness on the surface
Solution Approach 1:
The patent replaces the normal atmospheric composition (containing water vapor and carbon dioxide) with an inert nitrogen atmosphere in the cooling chamber. This prevents condensation and sublimation on the stent surface during cooling, maintaining surface integrity and dimensional precision while still achieving the required low temperatures for martensitic transformation.
Solution Approach 2:
The patent extracts water vapor and carbon dioxide from the cooling chamber atmosphere through nitrogen purging before cooling. This removal of condensable gases prevents their deposition on the stent surface, preserving the stent's surface integrity and preventing additional unwanted thickness during the cooling process.
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 method ensures the stent is compressed and loaded into the catheter without interference from condensates, facilitating a smooth insertion by maintaining the stent's pliability and preventing additional thickness from forming on the surface, thus enhancing the loading process.
Implementation Method 1
the temperature is lowered to a temperature at least below the transition temperature of the device such as the martensitic start temperature or more preferably the martensitic finish temperature of the nitinol
Implementation Method 2
water or ice as well as other condensates or sublimates, often form on the compression apparatus as well as the coated nitinol stent
Implementation Method 3
water or ice crystals formed from water vapor or crystals formed from the sublimation of carbon dioxide gas
Data Source
AI summary
A method (112) of loading an expandable medical device in a low vapor environment. The method includes placing the device in a loading chamber (114) at, for example, room temperature and removing (116) from the chamber any undesirable contaminants such as water vapor that can form condensation on the device when the device is cooled for compression into a transfer tube or delivery catheter. The temperature in the chamber is lowered (118) to a temperature below the transition temperature (martensitic finish) of the device. The device is compressed (120) below its' transition temperature and loaded (122) into a delivery or transfer device.