Moveable Plunger Seal Enables Low-Force Retractable Needle Retraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional medical devices with retractable needles require excessive thumb force for needle retraction, making it difficult for clinicians, especially those with small hands, and can lead to accidental needle stick injuries and contamination due to abrupt motion during retraction.
Innovation Solution
A medical device featuring an elastomeric retainer ring and a plunger seal with an axially moveable annular body and a transverse elastomeric web that reduces the required thumb force by allowing smooth retraction without premature rupture of the web, using a compressed spring to propel the needle holder into a retraction cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plug or rigid barrier is used to block the retraction cavity opening, then the sealing effect is improved, but the thumb force required to dislodge or fracture the barrier increases
Solution Approach 1:
The patent employs a flexible membrane instead of a rigid barrier to seal the retraction cavity opening. This membrane can be dislodged with minimal force while maintaining an effective seal during normal operation, thus resolving the contradiction between sealing reliability and ease of dislodgement.
Solution Approach 2:
The patent changes the mechanical properties of the sealing element from rigid to flexible, altering its force-displacement characteristics. The membrane is designed to require minimal force to dislodge while maintaining seal integrity under normal operating conditions.
2Reliability
If an axially fixed plunger seal with a rubbery portion is used to cover the opening, then the sealing is improved, but additional structural elements like detents and cutters are required, increasing device complexity and thumb force
Solution Approach 1:
The patent removes the complex detent and cutter mechanisms from the plunger structure. Instead, it uses a simple flexible membrane that can be dislodged by direct axial force, significantly simplifying the overall device structure while maintaining effective sealing.
Solution Approach 2:
The flexible membrane is designed to be dislodged directly by the user's axial force without requiring additional cutting or detent-release mechanisms. The membrane itself serves both as the seal and as the element to be displaced, eliminating the need for separate release mechanisms.
3Ease of operation
If a cutter is positioned behind the transverse web to sever the covering portion, then the sealing can be broken for retraction, but there is a risk of premature rupture during injection
Solution Approach 1:
The patent transitions from a static cutter-behind-web design to a dynamic membrane-dislodgement design. The flexible membrane responds dynamically to applied force, allowing controlled dislodgement during retraction while maintaining integrity during injection through its elastic properties.
Solution Approach 2:
The flexible membrane provides a cushioning effect during the injection process, absorbing pressure fluctuations and preventing premature rupture. During retraction, the membrane can be deliberately dislodged to initiate the retraction sequence.
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 significantly reduces the thumb force needed for needle retraction, minimizing motion of the needle tip during retraction and lowering the incidence of needle stick injuries and contamination by providing a smoother operation.
Implementation Method 1
using a compressed spring to propel the needle holder into a retraction cavity
Implementation Method 2
an elastomeric retainer ring and a plunger seal with an axially moveable annular body and a transverse elastomeric web
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A medical device having a barrel, a retractable needle, a needle retraction assembly and a plunger, the needle retraction assembly including and being held inside the barrel prior to retraction at least in part by a retainer member contacting the barrel, the plunger comprising a plunger seal with an body having at least a portion that is rearwardly moveable relative to the plunger and an elastomeric web that seals a retraction cavity inside the plunger prior to retraction of the needle, the retainer member and the plunger seal each cooperating with an inside wall of the barrel to provide a sealed liquid containment chamber inside the device.