Segmented Piston Rod Prevents Medication Reabsorption
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Solution Overview
Problem
Existing injection devices face issues with accidental needle pricks due to unreliable automatic protection mechanisms, premature activation of needle protection, and reabsorption of injected medication, leading to incomplete dosing and safety concerns.
Innovation Solution
An injection device with a piston rod comprising two portions that can switch between locked and unlocked positions, allowing controlled activation of needle protection and preventing piston retraction, ensuring complete dosing and user safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If automatic protection means are activated by spring deployment when the piston rod reaches a predetermined position, then needle protection is provided, but the piston rod may rise again in the proximal direction causing product reabsorption and incorrect dosing
Solution Approach 1:
The piston rod is divided into two separate portions: a first portion that remains fixed to the syringe body and a second portion that can move independently. This segmentation allows the second portion to be pushed back by the spring during protection activation without causing the first portion (and thus the piston) to move, preventing product reabsorption while maintaining reliable needle protection.
Solution Approach 2:
A detachable connection mechanism serves as an intermediary between the first and second portions of the piston rod. This intermediary allows controlled relative movement between the two portions during protection activation, mediating the force from the spring to prevent it from transmitting to the main piston, thereby eliminating the harmful effect of product reabsorption.
2Extent of automation
If the sleeve is held in a sheath by elastically flexible lateral lugs that are deflected by the piston rod head, then automatic protection activation is achieved, but the intermediate lugs return to their undeflected position causing the piston to rise again
Solution Approach 1:
The piston rod is segmented into two portions, allowing the second portion to absorb the return movement of the flexible lugs without causing the first portion (connected to the piston) to move. This maintains automated protection activation while preventing the harmful piston return movement.
Solution Approach 2:
The harmful return movement of the flexible lugs is extracted and isolated to only affect the second portion of the piston rod through the detachable connection. The first portion remains unaffected, ensuring that the automated protection mechanism functions without causing product reabsorption.
3Device complexity
If the piston rod is designed as a single solid piece, then the structure is simple, but the protection means cannot be activated without causing piston retraction
Solution Approach 1:
The piston rod is divided into two portions with a detachable connection, enabling reliable protection activation by allowing the second portion to move independently during sleeve deployment while the first portion remains stationary, preventing product reabsorption.
Solution Approach 2:
The piston rod transitions from a static, unified structure to a dynamic, segmented structure where the connection between the two portions can detach and reattach. This dynamic capability enables the rod to adapt its configuration during protection activation, ensuring reliable operation without compromising structural integrity during normal injection.
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 device prevents piston retraction after injection, ensuring complete medication delivery and user safety by allowing controlled activation of needle protection, simplifying manufacturing and user reassurance.
Implementation Method 1
a spring arranged to push said second portion in the proximal direction when said sleeve presses against said injection site
Implementation Method 2
The protection means comprise a sleeve held in a sheath by elastically flexible lateral lugs designed to be deflected by the head of the piston rod when the latter arrives at the end of travel
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
The present invention relates to an injection device (1) comprising: - a body (3) receiving a product, having a needle (7) and a piston (5) attached to a piston rod (8) movable between a storage position and an end-of-injection position, - a sleeve (6) for protecting the needle (7), movable between an initial position, where the needle (7) is uncovered, and a final position, where the needle (7) is covered, - biasing means (26) for moving said sleeve (6) from its initial position to its final position, - immobilization means (16, 31) for keeping said sleeve (6) in its initial position, characterized in that: - said piston rod (8) comprises a first portion (9) and a second portion (10), said second portion (10) being able to switch between a locked position, in which said second portion (10) is fixed to said first portion (9) and an unlocked position, in which said second portion (10) is movable with respect to said first portion on a predetermined distance along the longitudinal axis of said piston rod (8).