String-Wrapped Radial Compression Dies for High-Force Crimping
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Solution Overview
Problem
Existing radial compression mechanisms for medical devices like stents and prosthetic heart valves face limitations in applying sufficient radial force due to mechanical stress concentration and small contact areas, resulting in inadequate crimping capabilities, especially for large-diameter devices.
Innovation Solution
A radial compression mechanism utilizing a string wrapped around a plurality of compression dies, coupled with a string tension mechanism, allows for increased mechanical advantage by distributing force evenly across the dies' surface, enabling higher radial forces to be applied without mechanical stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a camming plate with pin/slot engagement is used to drive radially-movable dies, then the mechanical advantage is improved compared to hinged dies, but the radial force capability is still limited by the small contact area between slots and pins
Solution Approach 1:
A string wrapped around the outer perimeter of the compression dies serves as an intermediary element to transmit actuation force. The string distributes force evenly across multiple contact points around the dies' perimeter, converting linear pull force into radial compression force on the medical device without requiring high-stress pin/slot contact areas.
Solution Approach 2:
The patent replaces the traditional camming plate with pin/slot engagement (a mechanical linkage system) with a string-based tension system. This substitution eliminates the need for high-stress concentrated contact areas while maintaining or improving mechanical advantage through the string's ability to wrap around and evenly distribute force across all compression dies.
2Ease of manufacture
If hinged dies with small pins are used to transmit forces, then the device construction remains simple and low-cost, but the concentrated mechanical stress reduces the radial force capability
Solution Approach 1:
The string acts as a mediator that distributes actuation force around the entire perimeter of the compression dies, eliminating the need for high-stress pin connections. This maintains the simplicity of hinged die construction while dramatically improving radial force capability through distributed force transmission.
Solution Approach 2:
The string functions as a flexible element that can wrap around the compression dies and distribute force uniformly. This flexible force transmission method replaces rigid pin connections, reducing stress concentration while maintaining structural simplicity and ease of manufacture.
3Length of moving object
If the handle moves through a small distance of about 45 mm during crimping, then the device structure remains compact, but the very low mechanical advantage results in inadequate radial force applied to the stent or heart valve
Solution Approach 1:
The string wrapped around the compression dies creates a mechanical advantage through its wrapping configuration. Even with limited handle travel distance, the string's path around the dies multiplies the applied force, converting small linear displacement into significant radial compression force on the medical device.
Solution Approach 2:
The string transitions the force application from a single-point linear push (handle to dies) to a distributed circular path around the dies' perimeter. This dimensional change in force transmission path increases mechanical advantage without requiring increased handle travel distance or device size.
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 solution enables the application of higher radial forces to medical devices, improving crimping efficiency and reducing the size of implants, making procedures less invasive and more effective.
Implementation Method 1
a string wrapped around a plurality of compression dies to move the dies inward
Implementation Method 2
A spring may be configured to force the compression dies open and provide some back-tension to the string
Implementation Method 3
A plurality of springs may be configured between the plurality of compression dies
Data Source
AI summary
A radial compression mechanism utilizes a string wrapped around a plurality of compression dies to move the dies inward and close a central cylindrical cavity defined by the working surfaces of the dies. The string may be coupled to a string tension mechanism that enables a user to applied a desired tension to the string and thereby compress an article within the central cylindrical cavity. The compression dies may be coupled to a base and move along die-guiding slots from an open position to a closed position. A spring may be configured to force the compression dies open and provide some back-tension to the string. The string may extend around a pully on an opposing side of the compression mechanism and both ends of the string may be coupled to the string tension mechanism.