Syringe Plunger Assembly for Low-Force, Rotation-Controlled Insertion
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Solution Overview
Problem
Existing syringes face issues with plunger rotation and translation during insertion, which can breach the sterile barrier and require silicone oil for rod insertion, posing risks for drug formulations and biologics.
Innovation Solution
A plunger assembly with a stopper having a non-threaded inner cavity and a plunger rod with a threaded member that allows for a non-rotatable, interference fit engagement, eliminating the need for high insertion forces and silicone oil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a male and female thread insertion method is used to insert the plunger rod into the stopper, then the plunger rod can be inserted, but plunger rotation occurs within the barrel when the plunger rod reaches the termination of the thread section
Solution Approach 1:
The plunger rod is segmented into two functional parts: a threaded portion for initial engagement and insertion, and a smooth cylindrical portion that extends beyond the threads. This segmentation allows the threaded part to guide insertion while the smooth part prevents rotation, resolving the contradiction between ease of insertion and prevention of harmful rotation.
Solution Approach 2:
The threaded portion acts as an intermediary element during insertion. It facilitates the insertion process by providing thread engagement with the stopper, then transitions to allow the smooth cylindrical portion to make contact with the stopper's inner cavity wall, which prevents rotation. The intermediary threaded section enables controlled insertion without direct rotational transfer to the plunger rod.
2Ease of operation
If a push-in method is used to insert the plunger rod into the stopper, then insertion can be achieved, but high insertion forces are required which may cause plunger translation within the barrel
Solution Approach 1:
The plunger rod is divided into a threaded insertion portion and a smooth operational portion. The threaded portion is designed to engage with the stopper's internal threads, distributing the insertion force over a larger surface area and reducing peak forces required. This segmentation eliminates the need for high-force push-in methods while preventing plunger translation through controlled thread engagement.
Solution Approach 2:
The invention replaces the direct push-in mechanical system with a threaded engagement system. Instead of relying on axial compression force to force the plunger rod into the stopper, the threaded portion converts rotational motion into axial motion, allowing insertion with significantly reduced force requirements while maintaining control over the insertion process.
3Ease of operation
If silicone oil is used to facilitate rod insertion into the plunger, then insertion ease is improved, but silicone oil may leech or migrate to the drug product
Solution Approach 1:
The invention replaces the reliance on silicone oil lubrication with a threaded mechanical engagement system. The threaded portion of the plunger rod engages with corresponding threads in the stopper, providing a controlled insertion mechanism that does not require silicone oil. This substitution eliminates the source of potential contamination while maintaining ease of insertion through the self-threading action.
Solution Approach 2:
The invention extracts and eliminates the silicone oil component from the insertion system. By designing a threaded engagement mechanism, the patent removes the need for any lubricating substances, thereby eliminating the harmful effect of silicone oil migration or leaching into the drug product while preserving the functionality of smooth insertion.
Data Source
Figure 1
Figure 2A~3A
Figure 3B
AI summary
A syringe for storing and delivering a fluid that includes (1) a stopper and (2) a plunger rod assembly is provided. The plunger rod assembly includes a plunger rod and a threaded member at a plunger-engaging end. The stopper may be formed of an elastomeric material. The stopper has an exterior surface and an inner cavity. The inner cavity of the stopper may have a generally frustoconical shape with at least one engagement surface. The threaded member contacts at least one engagement surface in the inner cavity of the stopper to support the plunger rod assembly in an integrated, non-threaded engagement with the stopper. In some embodiments, the threaded member is freely rotatabie within the inner cavity.