Auto-Injector Spring Separation for High-Viscosity Dose Delivery
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Solution Overview
Problem
Existing auto-injectors face challenges such as high injection forces, discomfort due to hand shaking, and the risk of incomplete doses, especially when administering high viscosity medicaments, and often require complex mechanisms for needle insertion and retraction.
Innovation Solution
An auto-injector design with separate control and drive springs, where the control spring manages needle insertion and retraction, allowing for a weaker spring to be used, reducing user impact and ensuring consistent injection depth, and featuring a sequence of operations to prevent accidental needle retraction or incomplete doses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a strong drive spring is used to expel high viscosity medicaments, then the injection force is sufficient, but the impact felt by the user during needle insertion and triggering becomes too high
Solution Approach 1:
The patent divides the spring system into two separate springs: a control spring that manages needle insertion and retraction, and a drive spring that propels the medicament. This segmentation allows the drive spring to be optimized for high force output without transmitting that force to the user during triggering, while the control spring handles user-interaction forces separately.
Solution Approach 2:
The control spring acts as an intermediary between the user's triggering action and the drive spring. When the user triggers the device, they compress the control spring, which then releases to advance the carrier and needle. This intermediary mechanism decouples the user's triggering force from the drive spring's high-force medicament expulsion, preventing direct transmission of harmful forces to the user.
2Device complexity
If manual button pressing is used to deliver medicament, then device complexity is reduced, but the user must continuously press the button which may result in incomplete doses
Solution Approach 1:
The auto-injector performs the injection function automatically once triggered. The drive spring self-propels the plunger to expel the medicament without requiring continuous user intervention. The control spring automatically retracts the needle after injection completion. This self-service mechanism ensures complete dose delivery while maintaining relatively simple device structure.
3Reliability
If the button/plunger extension is made long to ensure full injection, then complete dosing is achieved, but hand shaking and discomfort increase
Solution Approach 1:
The patent extracts the long-button-pressing function from the user interface and replaces it with an automatic spring-driven mechanism. The control spring handles the needle insertion and retraction movements that would otherwise require extended manual manipulation, eliminating the need for users to maintain prolonged button pressure that causes hand shaking.
4Device complexity
If a single spring is used for both needle insertion and medicament expulsion, then device complexity is reduced, but the spring must be strong enough for medicament expulsion causing high impact during triggering
Solution Approach 1:
The patent segments the spring system into two independent springs with distinct functions: the control spring for needle manipulation and the drive spring for medicament expulsion. This allows each spring to be optimized for its specific task, with the drive spring being strong enough for high-viscosity medicaments without requiring the user to directly trigger its release, thereby eliminating high impact during user interaction.
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 design provides a safe, reliable, and user-friendly injection experience with reduced discomfort and improved reliability for administering high viscosity medicaments, ensuring consistent injection depth and preventing wet injections.
Implementation Method 1
a control spring arranged around the carrier for translating the carrier in a proximal direction for insertion of the needle through the chassis into an injection site
Implementation Method 2
The control spring is arranged to bias the case against the chassis in a distal direction so as to extend the chassis out of a proximal end of the case
Implementation Method 3
a drive spring and a plunger for forwarding load of the drive spring to a stopper of the syringe
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament (M) is present having a tubular chassis telescopable in a tubular case, a carrier subassembly comprising a tubular carrier slidably arranged relative to the chassis inside the case, where the carrier is adapted to contain a syringe with a hollow injection needle. The injector also has a drive spring and a plunger for forwarding load of the drive spring to a stopper of the syringe, wherein the syringe is lockable for joint axial translation with the carrier. A control spring is arranged around the carrier for translating the carrier in a proximal direction (P) for insertion of the needle through the chassis into an injection site.