Auto-Injector Plunger Coupling for Wet Injection Prevention
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Solution Overview
Problem
Conventional auto-injectors often experience 'wet injections' due to resistance forces during needle penetration, causing liquid medicament to leak out before the needle is fully inserted, which can lead to incomplete doses and inefficiencies in drug delivery.
Innovation Solution
An auto-injector design that couples a plunger to either a syringe or a stopper, utilizing a syringe holder with resilient arms and a compression spring to manage the force transfer, ensuring the load is not directly applied to the stopper until the needle is inserted, thus preventing liquid leakage during needle insertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If force is applied to the stopper to advance the syringe for needle insertion, then the syringe and needle are forwarded for insertion, but the stopper may move in the syringe causing liquid medicament to leak out (wet injection)
Solution Approach 1:
The syringe assembly is segmented into two separate load-bearing paths: one for the syringe body/needle and another for the stopper. The resilient arms transfer load selectively, allowing the syringe to be advanced without necessarily advancing the stopper, thus preventing wet injection while enabling needle insertion.
Solution Approach 2:
The resilient arms act as an intermediary mechanism between the plunger and the syringe/stopper assembly. They selectively transfer mechanical load based on their deflection characteristics, mediating the force distribution to advance the syringe while keeping the stopper stationary when needed.
2Force
If the plunger is directly coupled to the stopper, then force is efficiently transmitted to expel medicament, but the stopper moves during needle insertion causing wet injection
Solution Approach 1:
The direct coupling between plunger and stopper is segmented by introducing resilient arms as an intermediate element. This segmentation allows force to be transmitted to the syringe for insertion while decoupling the stopper movement, preventing medicament leakage during the insertion phase.
Solution Approach 2:
The coupling between plunger and stopper is made dynamic through the resilient arms, which can deflect and engage/disengage based on the operational phase. During insertion, the arms deflect to allow syringe movement without stopper movement; during injection, they transmit force efficiently to expel medicament.
3Reliability
If resilient arms are added to decouple plunger from stopper, then wet injection is prevented, but device complexity increases
Solution Approach 1:
The resilient arms are implemented as flexible, thin-walled structural elements that can deflect under load. This flexible design achieves the decoupling function with minimal material and structural complexity, avoiding the need for complex mechanical linkages or multiple discrete components.
Solution Approach 2:
The resilient arms are integrated into the syringe holder structure, merging the load-transfer function with the existing structural components. This consolidation achieves the desired decoupling effect while minimizing the addition of separate parts, thereby reducing overall device complexity.
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
This design effectively prevents 'wet injections' by ensuring the medicament is only expelled after the needle is fully inserted, ensuring accurate and complete dosing, with a reduced part count and manufacturing costs, and enhanced user safety features.
Implementation Method 1
A resilient syringe holder arm arranged distally. The syringe holder arm has an inclined surface for bearing against a shoulder, which is arranged at the plunger. The syringe holder arm is supportable by an inner surface of the housing in order to prevent it from being flexed outward
Implementation Method 2
spring means, capable of, upon activation: pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end via a plunger
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention refers to an arrangement for coupling a plunger (9) to either a syringe (3) or a stopper (6) arranged in the syringe (3), the arrangement comprising a syringe holder (22) which is slidably arranged in a housing (2), wherein the syringe holder (22) is provided with at least one resilient syringe holder arm (23) arranged distally, the syringe holder arm (23) having an inclined surface for bearing against a shoulder (24), which is arranged at the plunger (9), wherein the syringe holder arm (23) is supportable by an inner surface of the housing (2) in order to prevent it from being flexed outward in a first position and wherein a widened portion (2.1) is provided in the housing (2) for allowing the syringe holder arm (23) to flex outwards and disconnect from the plunger (9) when in a more proximal position so as to switch load of the plunger (9) from the syringe (3) to the stopper (6).