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 are limited by low mechanical advantage and radial force capability due to the use of small pins, ball bearings, and cam-following mechanisms, which restrict the application of sufficient radial force for crimping 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, enabling higher radial forces to be applied without damaging the mechanism, and is designed for disposable, low-cost construction.
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 dies serves as an intermediary element to transmit actuation force. The string distributes force uniformly across multiple contact points on the dies, eliminating the localized stress concentration at pin/slot interfaces and enabling higher radial forces to be applied without damaging the mechanism.
2Ease of manufacture
If hinged dies with small pins are used to transmit forces, then the device construction is 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 forces uniformly across the outer perimeters of multiple dies simultaneously. This eliminates the concentrated stress at small pin interfaces while maintaining the simple injection-molded construction suitable for disposable devices.
3Device complexity
If the handle moves through a small distance of about 45 mm during crimping, then the device structure is compact, but the mechanical advantage is very low resulting in inadequate radial force
Solution Approach 1:
The mechanism transitions from linear handle motion to rotational die closure by wrapping the string around the dies. This dimensional change allows a longer string path to be achieved within a compact handle travel distance, significantly improving mechanical advantage while maintaining structural compactness.
Solution Approach 2:
The string wrapped around the dies serves as an intermediary that converts small linear handle movements into large rotational forces on the dies. The string's path around the dies multiplies the mechanical advantage, enabling adequate radial force to be generated within a compact structure.
4Stress or pressure
If radial force is applied to large-diameter devices like prosthetic heart valves, then the crimping pressure is sufficient for permanent deformation, but the required radial force is six times greater than for coronary stents
Solution Approach 1:
The string wrapped around multiple dies serves as an intermediary force distribution system. It transmits actuation force uniformly across all dies simultaneously, enabling the application of high radial forces required for large-diameter devices like prosthetic heart valves without overloading any single mechanical interface.
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 mechanism effectively imparts high radial forces to medical devices, overcoming the limitations of prior art by providing a more uniform and increased force application, suitable for compressing large stents and prosthetic heart valves, facilitating less invasive implantation procedures.
Implementation Method 1
A first type of prior art device includes a radial compression mechanism wherein several similar wedge-shaped dies with planar surfaces are arranged to form an approximately cylindrical central cavity, the wedges being hinged and driven in unison to change the diameter of the cavity... The handle moves through only a small distance of about 45 mm as the opening reduces from about 30 mm to about 6 mm, resulting in a very low mechanical advantage
Implementation Method 2
A spring may be configured to force the compression dies open and provide some back-tension to the string
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.