Retractable Syringe Plunger with Chamfered Distal Wall
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Solution Overview
Problem
Current retractable needle syringes face challenges in high-volume manufacturing due to complexity and size constraints, particularly in small capacity syringes, which can lead to reliability issues and increased costs, while also needing to prevent inadvertent exposure and reuse.
Innovation Solution
A plunger design with a hollow elongate body and a stopper featuring primary, secondary, and tertiary chamfers, made from thermoplastic and thermoplastic elastomer materials, respectively, that facilitates the retraction of the needle by a cutting sleeve with a sharp edge, minimizing cutting forces and ensuring structural integrity, allowing for efficient manufacturing and use in small capacity syringes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retracting needle syringe is designed with complex retraction mechanisms, then needle safety is improved, but device complexity increases and manufacturing difficulty rises
Solution Approach 1:
The plunger is segmented into a body portion and a stopper as separate functional elements that can be molded together. The stopper includes radial elements that interact with chamfers on the body portion, creating distinct functional zones that simplify the overall retraction mechanism while maintaining safety
Solution Approach 2:
The cutting function is extracted as a separate sharp edge feature on the retraction mechanism, distinct from the plunger body. This allows the cutting action to be performed by a dedicated element rather than requiring the entire plunger structure to be complex
2Force
If the plunger end wall is made thin to reduce cutting forces, then ease of retraction is improved, but structural integrity deteriorates
Solution Approach 1:
The end wall exhibits local quality variation through the chamfer structure. The chamfer creates a localized thin region at its apex that reduces cutting forces, while the rest of the end wall maintains sufficient thickness for structural integrity. The radial elements on the stopper are positioned to engage specifically with the chamfer region, concentrating the cutting action where the material is thinnest
3Reliability
If small capacity syringes are equipped with retraction features, then safety is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The stopper is merged with the plunger body portion through co-molding, creating an integral structure that simplifies assembly. The radial elements on the stopper and chamfers on the body portion are formed as integrated features, eliminating the need for separate parts and reducing manufacturing steps while maintaining the retraction function in small capacity syringes
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 plunger design enhances the reliability and ease of use of retractable needle syringes by reducing the force required for needle retraction, ensuring structural integrity, and enabling high-volume manufacturing of small capacity syringes without compromising usability or safety.
Implementation Method 1
The hub further includes a biasing spring operatively connected to a hollow cutting sleeve
Implementation Method 2
a hollow cutting sleeve having a proximally facing sharp edge capable of cutting through the hub and the plunger
Data Source
AI summary
A plunger for a retracting needle syringe includes a hollow elongate body portion having a proximal end, a distal end, and a side wall therebetween defining a cavity. The distal end includes a distal wall having an inside surface and an outside surface. A stopper, at the distal end of the body portion, includes a peripheral portion performing a seal with the inside surface of a syringe barrel and at least one radial element extending from about a center of the outside surface of the distal wall to the peripheral portion. The distal end of the body portion includes at least one primary chamfer in the cavity at an intersection of the inside surface of the distal wall and the side wall. The chamfer is positioned under the at least one radial element for supporting the distal wall and the radial element when a hollow sleeve in the syringe barrel cuts through the end wall plunger. A secondary, smaller chamfer on each side of the primary chamfer is also provided.