Plunger Rod Retention Force Measurement in Drug Delivery
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Solution Overview
Problem
Existing drug delivery device testing systems fail to accurately measure the forces experienced by plunger rods during sterilization, leading to inaccurate assessments of retention features and potential device performance issues.
Innovation Solution
A testing system that includes a frame member, a driving member, a surrogate syringe barrel, and a plunger rod with a projecting interface feature, which simulates the forces experienced during sterilization by applying a maximum urging force in the axial direction, measuring the retention force between the plunger rod and the flange extender to ensure the plunger rod remains in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing testing systems are used to measure plunger rod retention force, then the testing process can be completed, but the measurement accuracy is insufficient and does not reflect actual sterilization conditions
Solution Approach 1:
The patent creates a surrogate syringe barrel that replicates the critical geometric and mechanical features of the actual syringe barrel without containing real drug. This copy allows testing of the plunger rod retention mechanism under simulated sterilization conditions, achieving accurate measurement of retention forces while avoiding the complexities and risks of testing with actual medicinal products
Solution Approach 2:
The patent modifies the testing approach by changing the physical parameters being measured - specifically focusing on the urging force applied to the plunger rod during sterilization simulation. The testing system measures the force required to move the plunger rod relative to the syringe barrel, providing quantitative data on retention feature performance under controlled conditions that reflect actual sterilization scenarios
2Reliability
If vacuum is applied during sterilization to maximize sterilant contact, then sterilization effectiveness is improved, but the air bubble expansion causes undesired plunger stopper movement
Solution Approach 1:
The patent designs retention features (such as engagement protrusions and receptacles) that preemptively counteract the forces generated during sterilization. These features are engineered to resist the outward urging force caused by air bubble expansion under vacuum, preventing plunger stopper movement before it can compromise sterilization or device integrity
Solution Approach 2:
The patent implements retention features that are pre-configured in the device assembly before sterilization. These features proactively establish mechanical constraints on the plunger rod and stopper, ensuring they remain in predetermined positions during the sterilization process even when subjected to vacuum-induced pressure differentials
3Stability of the object's composition
If retention features are designed to prevent plunger stopper movement during sterilization, then component stability is improved, but device complexity increases
Solution Approach 1:
The patent divides the retention function into separate, modular components - such as engagement protrusions on the plunger rod, corresponding receptacles in the syringe barrel, and flange extender features. This segmentation allows each component to be independently designed, manufactured, and validated, simplifying the overall implementation while achieving stable component positioning during sterilization
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 system accurately measures the maximum retention force, ensuring the plunger rod does not move undesirably during sterilization, thereby maintaining the integrity of the drug container's sterile barrier and preventing component disassembly.
Implementation Method 1
The driving member measures a maximum urging force exerted on the plunger rod when moving in the axial direction towards the second end of the frame member
Implementation Method 2
When the vacuum is applied, the resulting pressure differential between the interior and the exterior of the PFS causes an air bubble within the PFS to expand
Data Source
AI summary
A testing system for a drug delivery device includes a frame member having first and second ends, a driving member positioned near the frame member, a surrogate syringe barrel operably coupled with the frame member, a flange extender adapted to couple with a portion of the surrogate syringe barrel, and a plunger rod adapted to couple with the flange extender and be at least partially disposed within the surrogate syringe barrel while being movable therein. The driving member is movable in an axial direction between the first end and the second end of the frame member. The plunger rod includes first and second ends and a longitudinal length therebetween, the first end being positioned near a portion of the driving member. The driving member measures a maximum urging force exerted on the plunger rod when moving in the axial direction towards the second end of the frame member.