Auto-injector Single Spring Needle Retraction Mechanism
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current auto-injectors face challenges such as the risk of inadvertent triggering, incomplete dose delivery due to manufacturing tolerances, and residual medicament issues, particularly in reliably retracting the needle after injection.
Innovation Solution
An auto-injector design utilizing a single drive spring for both needle insertion and retraction, with an interlock sleeve mechanism requiring two user actions for activation, ensuring the needle remains covered unless intentionally triggered for injection, and automatic retraction upon removal from the injection site.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single drive spring is used for both needle insertion and retraction, then device complexity is reduced, but the risk of inadvertent triggering increases
Solution Approach 1:
The drive spring's function is segmented into two distinct phases: insertion phase (pushing needle forward) and retraction phase (pulling needle backward). This is achieved by having the spring grounded at different ends at different times during the injection cycle, allowing one spring to reliably perform both functions without causing inadvertent activation.
Solution Approach 2:
The grounding position of the drive spring is made dynamic rather than static. The spring transitions from being grounded at its distal end during insertion to being grounded at its proximal end during retraction. This dynamic reconfiguration allows the same spring to provide controlled force in both directions without risk of unintended activation.
2Ease of manufacture
If manufacturing tolerances are not strictly controlled, then manufacturing cost decreases, but incomplete dose delivery occurs
Solution Approach 1:
The drive spring is pre-loaded to a specific compression position before injection begins. This preliminary positioning ensures that the spring has sufficient stored energy to complete the full injection cycle, compensating for variations in syringe friction and medicament viscosity that would otherwise require tight manufacturing tolerances.
Solution Approach 2:
The system uses the drive spring's own stored energy to automatically complete the injection process without requiring additional power sources or complex control systems. The spring's mechanical energy is sufficient to overcome friction and deliver the complete dose, making the system self-sufficient and less sensitive to manufacturing variations.
3Device complexity
If the needle retraction mechanism is simplified, then device complexity decreases, but residual medicament remains in the syringe
Solution Approach 1:
The drive spring maintains continuous useful action throughout the entire injection cycle, including during retraction. By grounding the spring at its proximal end during retraction, the system ensures the spring continues to exert controlled force to pull the syringe and needle back, maximizing medicament delivery even during the return stroke.
Solution Approach 2:
The system changes the operational parameters of the drive spring during different phases. During insertion, the spring is compressed and grounded at the distal end; during retraction, the grounding shifts to the proximal end, changing the direction of force application. This parameter change allows efficient retraction without requiring additional mechanisms.
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 reduces the risk of inadvertent operation, ensures complete dose delivery, and reliable needle retraction, minimizing residual medicament and improving user safety and efficacy.
Implementation Method 1
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, operating the syringe to supply the dose of medicament, and retracting the syringe with the needle into the covered position after delivering the medicament
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
The invention relates to an auto-injector (1) for administering a dose of a liquid medicament (M), comprising: - an elongate housing (2) arranged to contain a syringe (3) with a hollow needle (4) and a stopper (6) for sealing the syringe (3) and displacing the medicament (M), the housing (2) having a distal end (D) and a proximal end (P) with an orifice intended to be applied against an injection site, wherein the syringe (3) is slidably arranged with respect to the housing (2), - spring means (8) capable of, upon activation: - pushing the needle (4) from a covered position inside the housing (2) into an advanced position through the orifice and past the proximal end (P), - operating the syringe (3) to supply the dose of medicament (M), and - retracting the syringe (3) with the needle (4) into the covered position after delivering the medicament (M), - activating means (20) arranged to lock the spring means (8) in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring means (8) for injection. The spring means (8) is a single drive spring (8) arranged to be grounded at a distal end (8.1) in the housing (2) for advancing the needle (4) and for injecting the dose of medicament (M) via a plunger (9) and wherein the drive spring (8) is arranged to have its ground in the housing (2) switched to its proximal end (8.2) for retracting the syringe (3). An interlock sleeve (25) is telescoped in the proximal (P) end of the housing (2), the interlock sleeve (25) translatable in longitudinal direction between a proximal position and a distal position, wherein in its proximal position the interlock sleeve (25) is arranged to be coupled to the syringe (3) in the syringe's retracted position and wherein the interlock sleeve (25) in its distal position is arranged to allow decoupling of the syringe (3).