Deflecting Arm Plunger Rod for Pre-filled Syringe Reflux Control
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Solution Overview
Problem
Pre-filled syringes experience reflux due to the spring-back of stoppers, leading to fluid reversal and potential clogging of catheters, and existing plunger rod designs are difficult to insert into sterilized syringes with minimal force and may become dislodged during use.
Innovation Solution
A plunger rod with deflecting arms that radially deflect inward for easy insertion and lock into the stopper, combined with a self-centering stopper design that forms an active seal with the syringe barrel, reducing reflux by storing potential energy for positive displacement of fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing plunger rod designs are used, then the syringe can be filled and sterilized, but the plunger rod requires significant force for insertion and may become dislodged during use
Solution Approach 1:
The plunger rod incorporates flexible deflecting arms that dynamically change their rigidity based on insertion force. During insertion, the arms deflect elastically to accommodate misalignment and reduce insertion force. Once inserted, the arms return to their original position to provide locking engagement with the stopper, ensuring secure attachment during use.
Solution Approach 2:
The plunger rod is segmented into multiple functional components: an elongated member, deflecting arms, stop members, and a head member. This segmentation allows each component to perform its specific function - the deflecting arms for easy insertion and secure attachment, the stop members for limiting deflection, and the head member for forming seals.
2Reliability
If traditional stopper designs with constant diameter seals are used, then fluid leakage is prevented under high pressure, but static and dynamic frictional forces increase
Solution Approach 1:
The stopper features variable diameter seals with different interference fits at different locations. The front seal has a first interference fit optimized for sealing against the barrel wall, while the rear seal has a second interference fit optimized for engaging the plunger rod. This local differentiation allows each seal to perform its specific function with minimal friction while maintaining reliable sealing.
3Reliability
If non self-centering tip designs are used, then manufacturing is simpler, but positive seal formation with luer taper fails under axial forces
Solution Approach 1:
The stopper tip incorporates a spherical or curved surface that naturally self-centers when subjected to axial forces. This curvature allows the tip to automatically align with the luer taper opening, ensuring positive seal formation without requiring complex alignment mechanisms or precise manufacturing tolerances.
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 effectively reduces reflux by ensuring a secure seal and efficient fluid displacement, while allowing for easy and secure attachment of the plunger rod to the stopper, even in pre-filled and sterilized syringes, with reduced material usage and manufacturing costs.
Implementation Method 1
the deflecting arm is capable of deflecting radially inward upon insertion of the plunger rod into the stopper and deflecting radially outward after insertion into the stopper to lock the plunger rod within the stopper
Implementation Method 2
the increased pressure within the air pocket causes any trapped fluid to be pushed through the luer and any attached catheter
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A plunger rod adapted for attachment with a stopper for use with a syringe barrel is disclosed. The plunger rod includes an elongated member having a front end and a back end, the plunger rod extending along a longitudinal axis. The plunger rod includes at least one deflecting arm associated with the front end of the elongated member. The deflecting arm is capable of deflecting radially inward during insertion of the plunger rod into a stopper, and deflecting outward into contact with an inner surface of the stopper after insertion to lock the plunger rod within the stopper.