Stretchable Bushing Reduces Anvil Approximation Force
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Solution Overview
Problem
Circular surgical stapling instruments face challenges with high frictional forces between the anvil and anvil retainer, requiring increased force to approximate the anvil towards the shell assembly, which can lead to disengagement.
Innovation Solution
A stretchable bushing with a rigid distal and proximal portion and an expandable section that transitions from an initial to a stretched configuration, reducing the retraction force needed by allowing the bushing to stretch instead of relying on frictional forces to prevent disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bushing is provided to prevent disengagement of the coupling between the anvil and anvil retainer, then the reliability of the coupling is improved, but the force required to approximate the anvil towards the shell assembly is increased due to frictional forces
Solution Approach 1:
The bushing transitions from a static rigid structure to a dynamic structure that can change its mechanical properties during operation. The expandable portion allows the bushing to deform elastically, changing its internal diameter and contact pressure with the anvil retainer during approximation, thus reducing frictional forces while maintaining coupling stability.
Solution Approach 2:
The bushing's physical parameters (specifically its length and internal diameter) change during the approximation process. The expandable portion undergoes elastic deformation, increasing the bushing's length and adjusting its internal diameter, which modifies the frictional characteristics and reduces the force required for approximation while preventing disengagement.
2Reliability
If frictional forces between the bushing and anvil retainer are increased to prevent disengagement, then the coupling reliability is improved, but the ease of operation is worsened due to increased force requirements
Solution Approach 1:
The bushing provides dynamic friction control rather than static high friction. During approximation, the expandable portion deforms to reduce contact pressure and frictional forces, making operation easier. Once approximation is complete, the bushing maintains sufficient friction to prevent disengagement, thus improving ease of operation while preserving coupling stability.
Solution Approach 2:
The expandable portion acts as a mechanical intermediary that mediates between the need for high friction (to prevent disengagement) and the need for low friction (to ease operation). It dynamically adjusts the frictional interface between the bushing and anvil retainer based on the operational state, reducing friction during approximation while maintaining it for retention.
3Manufacturing precision
If a rigid bushing is used to prevent disengagement, then the manufacturing precision is improved, but the device complexity is increased due to the need for expandable structures
Solution Approach 1:
The bushing is segmented into distinct functional portions: rigid distal and proximal portions for precise positioning and engagement, and an expandable intermediate portion for dynamic adjustment. This segmentation allows each portion to be optimized for its specific function while simplifying the overall design and manufacturing process compared to a fully complex expandable structure.
Solution Approach 2:
The bushing incorporates minimal dynamic complexity only where needed (the expandable portion), while maintaining rigid, precisely manufacturable sections for engagement. This selective application of dynamic behavior reduces overall device complexity compared to fully dynamic designs, while still achieving the required functionality of preventing disengagement with reduced force requirements.
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 solution reduces the retraction force required to approximate the anvil and shell assembly, preventing disengagement while maintaining effective tissue clamping, thereby enhancing the operational efficiency of circular stapling instruments.
Implementation Method 1
The hollow bushing also includes an expandable portion that connects the distal and proximal portions. The hollow bushing has an initial configuration wherein the hollow bushing defines a first length along the longitudinal axis and a stretched configuration wherein the hollow bushing defines a second length along the longitudinal axis that is greater than the first length.
Data Source
AI summary
A shell assembly includes a housing, a cartridge, and a hollow bushing. The housing defines a longitudinal axis and a cavity. The cartridge is supported on the housing and includes a plurality of staples. The hollow bushing is positioned within the cavity of the housing. The hollow bushing includes a distal portion and a proximal portion formed of a rigid material, and an expandable portion that connects the distal and proximal portions. The hollow bushing has an initial configuration where the hollow bushing defines a first length along the longitudinal axis and a stretched configuration where the hollow bushing defines a second length along the longitudinal axis which is greater than the first length.