Segmented Plunger Rod for Syringe Safety Activation
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Solution Overview
Problem
Existing safety devices for prefilled syringes are often automatically triggered at the end of the piston stroke, which can lead to incomplete delivery of the liquid, especially in cases of extemporaneous injection or when injecting small volumes, and can result in accidental needle exposure due to premature activation.
Innovation Solution
A safety device with a plunger rod that includes a distal part and a proximal triggering part, where the proximal part can move relative to the distal part after the distal part reaches the end of its stroke, allowing the user to choose when to activate the safety mechanism, featuring complementary anti-rotational means and deformable elements to control the activation force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the safety device is automatically triggered at the end of the piston stroke, then the needle is covered to prevent accidental pricks, but the liquid delivery may be incomplete especially in extemporaneous injection or small volume cases
Solution Approach 1:
The plunger rod is segmented into a distal plunger part that remains fixed and a proximal triggering part that can move independently. This segmentation allows the triggering mechanism to be separated from the liquid delivery mechanism, enabling the safety device to be activated only after complete liquid delivery without compromising the delivery completeness.
Solution Approach 2:
The proximal triggering part is designed to move dynamically relative to the distal plunger part only after the distal part reaches the end of its stroke. This dynamic behavior allows the system to adapt to different injection scenarios (complete delivery vs. extemporaneous injection) by enabling or disabling the safety activation based on the actual injection status.
2Reliability
If the safety device activates near the end of the plunger stroke, then the needle is protected, but the ability to inject very small volumes is compromised due to premature activation
Solution Approach 1:
The distal plunger part reaches the end of its stroke first as a preliminary action, which sets the condition for the proximal triggering part to potentially move. This preliminary action ensures that the liquid delivery is complete before the safety activation becomes possible, thereby protecting small volume injections from premature safety activation.
Solution Approach 2:
The proximal triggering part acts as an intermediary between the piston movement and the safety activation. It mediates the transmission of force and motion, allowing the system to distinguish between normal piston movement and the condition that warrants safety activation, thus enabling precise control for small volume injections.
3Quantity of substance
If the proximal plunger part moves relative to the distal plunger part to trigger safety, then complete liquid delivery is enabled, but the device complexity increases with additional moving parts
Solution Approach 1:
The proximal triggering part serves multiple functions: it transmits the triggering force to activate the safety device, it indicates the completion of liquid delivery, and it can be designed to snap back to its initial position to reset the system. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
Solution Approach 2:
The proximal triggering part is designed to snap back automatically to its initial position after triggering the safety device, without requiring manual intervention or additional resetting mechanisms. This self-service feature simplifies the overall device structure by eliminating the need for complex resetting systems.
Data Source
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AI summary
The invention relates to a safety device (12) for an injection syringe (14), the injection syringe comprising a body (16) having an injection needle (18) fitted thereon, the device (12) comprising a plunger rod (22, 28) including a distal plunger part (28D) slidably movable in the body (16) of the syringe, and a proximal triggering part (28P), configured to trigger the displacement of a protection sheath (24), from an injection position, wherein the needle (18) is uncovered, towards a safety position, wherein the needle (18) is covered by the sheath (24). The proximal triggering part (28P) is able to move relative to the distal plunger part (28D) once the distal plunger part is at the distal end of its stroke, to trigger the displacement of the protection sheath (24).