Plunger Assembly Axial Protrusion Reduces Break Loose Force
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Solution Overview
Problem
Pre-filled syringes face challenges in optimizing plunger force to ensure easy drug delivery while maintaining adequate container closure integrity, as the tight fit required for integrity increases the force needed to advance the plunger, making it difficult for users to dispense small and precise amounts, especially in auto-injection systems.
Innovation Solution
A plunger assembly with a distal end featuring an axial protrusion that reduces radial compression against the barrel wall, allowing for easier advancement while maintaining a liquid-tight seal, combined with a lubricity coating and a thermoplastic elastomer material for reduced friction, and a design that minimizes insertion force during assembly and prevents detachment during use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the plunger is made with a tight fit against the barrel wall to maintain container closure integrity, then the seal quality is improved, but the force required to advance the plunger increases
Solution Approach 1:
The plunger is designed with a constricted portion that changes the radial dimension parameter, creating a tighter sealing surface against the barrel wall. This localized parameter change improves container closure integrity while the overall plunger geometry is optimized to control the normal force distribution, balancing seal quality with acceptable advancement force.
Solution Approach 2:
The plunger features a constricted portion with enhanced sealing properties at the critical sealing zone, while other portions of the plunger maintain different dimensional characteristics. This local quality enhancement ensures adequate container closure integrity at the seal interface without requiring uniformly tight fit throughout the entire plunger, thereby reducing overall friction and advancement force.
2Reliability
If the plunger diameter is increased to improve sealing, then the seal quality is improved, but the force required to overcome the pressing force increases
Solution Approach 1:
Instead of uniformly increasing the plunger diameter, the invention applies a constricted portion that locally increases the diameter at the sealing zone. This ensures adequate seal quality at the critical interface while keeping the overall plunger diameter optimized to minimize normal force and friction during advancement.
Solution Approach 2:
The plunger is segmented into different portions with different diameters: a constricted portion for sealing and other portions for optimal mechanical performance. This segmentation allows the sealing portion to have increased diameter for better seal quality while the rest of the plunger maintains dimensions that reduce overall friction and advancement force.
3Reliability
If the fit between plunger and barrel is tightened to maintain CCI, then container closure integrity is improved, but the ease of operation deteriorates
Solution Approach 1:
The constricted portion changes the radial dimension parameter locally at the sealing zone, providing tight fit for container closure integrity. The overall plunger geometry and material selection are optimized to control friction coefficients, ensuring that the tightened fit does not excessively increase advancement force, thereby maintaining ease of operation.
Solution Approach 2:
The tight fit is applied locally at the constricted portion where sealing is critical, rather than uniformly throughout the entire plunger. This localized quality enhancement ensures container closure integrity at the seal interface while minimizing the overall friction and normal force, preserving ease of plunger advancement and operation.
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 reduces the break loose force to below 15 N and maintains a low glide force, ensuring precise and comfortable drug administration while maintaining container closure integrity and shelf life, suitable for gas sterilization and automated assembly.
Implementation Method 1
combined with a lubricity coating and a thermoplastic elastomer material for reduced friction
Implementation Method 2
combined with a lubricity coating and a thermoplastic elastomer material for reduced friction
Data Source
AI summary
Plunger assemblies (20) including a plunger sleeve (34), a plunger rod (22), and an axial protrusion (30) disposed within an inner cavity (40) of the plunger sleeve. Application of a distal force onto the plunger via the plunger rod causes the axial protrusion to contact and apply pressure to an engagement surface (50) in the inner cavity. The engagement surface is configured to receive distal force from the end of the axial protrusion. This causes the plunger to elongate and slightly constrict, thus reducing break loose force and facilitating transition from storage mode to dispensing mode of the plunger.