Compressible Piston Assembly for Reducing Break Loose Force in Prefilled Injectors
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Solution Overview
Problem
Prefilled injectors face high break loose force (BLF) issues due to prolonged storage, which increases static friction between piston sealing elements and the inner wall, especially in glass syringes with wide diameter tolerances, leading to user discomfort and potential pharmaceutical composition aggregation or residue issues.
Innovation Solution
A piston assembly with a compressible section comprising a resilient frame and a compressible fluid, linking an actuating piston element to a passive piston element, reduces BLF by distributing static friction evenly, allowing for smooth movement without the need for silicone lubricants, thus maintaining container closure integrity and preventing pharmaceutical composition degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If silicone lubrication is used to reduce static friction and break loose force, then the piston can move more easily in the cylinder, but proteins in the liquid pharmaceutical composition aggregate and become inefficient or harmful to the patient
Solution Approach 1:
The invention removes the silicone lubrication layer from the system entirely. Instead of using lubrication to reduce friction, the patent employs a piston design with optimized sealing elements that minimize contact friction through proper geometric design and material selection, eliminating the harmful protein aggregation effect while maintaining smooth piston operation
Solution Approach 2:
The invention introduces an intermediary mechanism - a specially designed piston assembly with multiple sealing elements and a compressible section - that mediates between the piston and cylinder wall interaction. This intermediary structure distributes the contact forces and reduces direct friction without requiring silicone lubrication, thereby preventing protein aggregation while maintaining ease of operation
2Ease of operation
If silicone lubrication is used to reduce break loose force, then the piston moves more easily, but the lubricant remains in the eye for ophthalmic injections which is undesirable
Solution Approach 1:
The invention extracts and eliminates the silicone lubrication component from the injection system. By designing a piston assembly that achieves smooth operation through mechanical optimization rather than lubrication, the patent ensures that no lubricant residue remains in the eye during ophthalmic injections, while still maintaining ease of piston movement
3Reliability
If the piston outer diameter is increased to ensure sealing in glass syringes with wide tolerances, then container closure integrity is improved, but the break loose force increases significantly
Solution Approach 1:
The invention segments the sealing function into multiple independent sealing elements distributed along the piston assembly rather than relying on a single large sealing surface. This segmentation allows each sealing element to maintain effective contact and sealing with the cylinder wall while distributing the friction forces, thereby maintaining container closure integrity without proportionally increasing the break loose force
Solution Approach 2:
The invention applies local quality optimization by designing sealing elements with specific local properties - including optimized diameters, materials, and geometric configurations - at different positions along the piston assembly. This localized optimization ensures effective sealing at each contact point while minimizing the overall friction and break loose force, rather than uniformly increasing the entire piston diameter
4Ease of operation
If lubrication is used to ensure sufficient glide for the piston, then the piston can move smoothly in the cylinder, but the static friction (break loose force) remains high due to prolonged storage
Solution Approach 1:
The invention incorporates a compressible section in the piston assembly that performs preliminary action during storage by maintaining a consistent contact pressure between the sealing elements and the cylinder wall. This preliminary compression action prevents the sealing elements from adhering to the cylinder wall over prolonged storage periods, thereby reducing break loose force while maintaining smooth piston movement during use
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 significantly reduces the break loose force to match or be lower than the glide force, providing a smoother user experience and preventing pharmaceutical composition aggregation or residue issues, while maintaining effective sealing and container closure integrity.
Implementation Method 1
a compressible section (31) between an actuating piston element (32) and a passive piston element (33), the compressible section comprising a compressible fluid and a resilient frame
Implementation Method 2
the resilient frame physically coupling the actuating piston element to the passive piston element, which resilient frame is made from an elastic polymer
Implementation Method 3
which piston elements abut the inner wall of the cylinder at abutting interfaces thereby sealing the compressible section when the piston assembly is inserted in the cylinder
Data Source
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Figure 5
AI summary
The present invention relates to an injector for delivery of a pharmaceutical composition, the injector comprising - a cylinder extending along a longitudinal axis, the cylinder having an inner wall, an outer wall, and an outlet at an outlet end opposite an actuating end, - a piston assembly comprising a compressible section between an actuating piston element and a passive piston element, which piston elements abut the inner wall of the cylinder at abutting interfaces thereby sealing the compressible section when the piston assembly is inserted in the cylinder, the compressible section comprising a compressible fluid and a resilient frame linking the actuating piston element to the passive piston element. The injector is suited for pre-filled injectors allowing long term storage of protein based pharmaceutical compositions.