Auto-Injector Single-Spring Mechanism for Dose Delivery and Needle Retraction
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Solution Overview
Problem
Existing auto-injectors face challenges such as user discomfort due to injection force and hand shaking, risk of incomplete doses, and complexity in operation, particularly for elderly or dexterity-impaired individuals, as well as issues with needle visibility and unintentional triggering.
Innovation Solution
An auto-injector design utilizing a single compression spring for needle insertion, dose delivery, and retraction, with a simplified trigger mechanism and safety features to prevent accidental operation, ensuring complete dose delivery and safe needle retraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a manual device with button/plunger is used, then the user can control the injection process, but the user must continuously press the button during injection which causes high injection forces and hand shaking
Solution Approach 1:
The device uses a spring-loaded mechanism that automatically performs the injection action without requiring continuous user pressing. The spring is compressed during the loading phase and automatically expands to deliver the injection, making the system self-acting and eliminating the need for continuous manual force application during the injection process
Solution Approach 2:
The injection process is divided into distinct phases: a loading phase where the spring is compressed and stored, and an injection phase where the spring automatically expands to deliver the medicament. This periodic action separates the user's control function from the force application function, reducing hand shaking and discomfort
2Reliability
If the button/plunger is extended fully to ensure complete dose, then the injection can be completed, but the extension is too great causing inconvenience for the user to reach
Solution Approach 1:
The spring-loaded mechanism automatically retracts the needle and plunger after injection without requiring the user to manually pull back. The spring's stored energy is released to return all components to their initial positions, ensuring complete dose delivery while eliminating the need for the user to reach for a fully extended button
Solution Approach 2:
The spring is pre-compressed during the loading phase to store the necessary energy for both the injection and the subsequent retraction. This preliminary action ensures that both the injection and retraction operations can be performed automatically without requiring excessive user effort or reach
3Ease of operation
If a simple trigger mechanism is used, then the device is easier to operate, but unintentional triggering may occur
Solution Approach 1:
The trigger mechanism is designed with a specific mechanical configuration where the trigger button must be pressed with sufficient force and in a specific direction to overcome the spring's holding force. This dynamic design ensures that accidental presses are unlikely while still maintaining ease of operation for intentional use
Solution Approach 2:
The spring mechanism is designed to require a threshold amount of force to activate, providing a built-in safety margin that prevents accidental triggering from minor bumps or unintended contact. The spring's stored energy creates a buffer that must be overcome deliberately to initiate injection
4Reliability
If multiple springs are used for needle insertion and retraction, then the functions are reliable, but the device complexity increases
Solution Approach 1:
A single spring element is designed to perform multiple functions: it is compressed during the loading phase to store energy for both needle insertion and subsequent retraction. This multi-functional spring eliminates the need for separate springs for insertion and retraction, reducing device complexity while maintaining reliable dual-function operation
Solution Approach 2:
The spring mechanism is designed to combine the insertion and retraction functions into a single integrated system. The same spring that drives needle insertion also drives needle retraction, merging what would traditionally require separate mechanisms into one unified component that reduces 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
The design provides a reliable, user-friendly, and cost-effective auto-injector that minimizes discomfort, ensures complete dose delivery, and reduces the risk of accidental needle exposure, while being suitable for various medicaments including peptides and proteins.
Implementation Method 1
spring means capable of, upon activation: pushing the needle from a covered position inside the housing into an advanced position
Implementation Method 2
retracting the syringe with the needle into the covered position after delivering the medicament
Data Source
AI summary
An auto-injector for administering a dose of a liquid medicament includes an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end with an orifice intended to be applied against an injection site. The syringe is slidably arranged with respect to the housing. A spring 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 (P), operating the syringe to supply the dose of medicament (M), and retracting the syringe with the needle into the covered position. After delivering the medicament, an activator arranged to lock the spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring for injection.