Syringe Stopper Trim Geometry for Lower Gliding Force
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Solution Overview
Problem
Existing injection devices face challenges with high variability in breakloose and gliding forces due to stress concentration at the trim member of the stopper, leading to unpredictable injection times and potential adverse effects from lubricants.
Innovation Solution
A stopper design with controlled geometry and diameters for the trim member, including specific dimensions and profiles for the proximal, intermediate, and distal portions, optimized using a cutting tool to reduce gliding forces and improve consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional stopper with uniform trim member diameter is used, then the manufacturing is simple, but the gliding force is high and injection time is unpredictable due to stress concentration at the trim member
Solution Approach 1:
The trim member is designed with non-uniform diameter along its length, featuring a first portion with diameter D1 and a second portion with diameter D2, where the diameters differ by at least 0.05mm. This local variation in geometry redistributes the stress distribution during stopper movement, reducing stress concentration at the trim member-syringe interface and thereby reducing gliding force while maintaining manufacturing feasibility.
2Force
If lubricant is applied to reduce gliding force, then the stopper moves more easily, but the lubricant may have deleterious effects on biotech drugs
Solution Approach 1:
Instead of using lubricant to reduce friction, the invention converts the geometric design of the trim member itself into the solution. The non-uniform diameter profile (D1 and D2 portions) creates optimal contact conditions with the syringe that naturally reduce gliding force through improved stress distribution, eliminating the need for lubricant and thereby preventing drug contamination while achieving smooth stopper movement.
3Force
If the trim member diameter is reduced to lower gliding force, then the stopper glides more smoothly, but the seal formation with the syringe barrel may be compromised
Solution Approach 1:
The trim member employs different diameters at different locations: a first portion with diameter D1 and a second portion with diameter D2, where the diameter difference is at least 0.05mm. This local geometric variation allows one portion to optimize for seal formation while the other optimizes for reduced gliding force, achieving both seal integrity and smooth movement simultaneously without compromising either function.
Data Source
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AI summary
A stopper (10) adapted for use within a syringe barrel, the stopper including a main body (12) defining a proximal end (14), a distal end (16), and a cylindrical sidewall (20) extending between the proximal end and the distal end, wherein the main body defines a first diameter; at least one rib (22) extending radially outward around a perimeter of the main body configured to form a seal with the syringe barrel; and a trim member (24) extending radially outward around a perimeter of the main body, the trim member including a distal portion (28) defining a second diameter, a proximal portion (26) defining a third diameter, and an intermediate portion (30) between the distal portion and the proximal portion, the intermediate portion defining a fourth diameter at least 1% smaller than the second diameter and at least 0.5% smaller than the third diameter.