Injection Device Needle Shield Pressure Equalization
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Solution Overview
Problem
Existing pre-filled injection devices face challenges with overpressure in the liquid system, leading to inconsistent dose sizes due to pressure differences, especially caused by temperature changes, which can result in larger ejected volumes than set by the user.
Innovation Solution
The injection device includes a movable needle shield assembly that rotates to expose the needle cannula tip outside the cleaning chamber, allowing equalization of pressure with the surroundings, ensuring accurate dose delivery by venting any overpressure before injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cleaning chamber is filled with preservative containing liquid drug from the cartridge, then the cleaning function is improved, but overpressure is built up inside the liquid system
Solution Approach 1:
A pressure equalization channel is introduced as an intermediary pathway between the cleaning chamber and the cartridge. This channel allows pressure to equalize without requiring direct communication between the cleaning chamber and the liquid drug reservoir, thus enabling the cleaning function while preventing overpressure buildup in the main liquid system.
2Stress or pressure
If the needle shield assembly is made movable and rotatable, then pressure equalization is improved, but device complexity increases
Solution Approach 1:
The needle shield assembly is designed to perform multiple functions: it protects the needle cannula, contains the cleaning chamber, and acts as a pressure equalization mechanism through its movable and rotatable characteristics. By making the shield assembly multi-functional, the patent avoids adding separate components for each function, thus limiting the increase in device complexity.
Solution Approach 2:
The needle shield assembly is made dynamic with movable and rotatable characteristics, allowing it to adapt its position and orientation to perform different functions including pressure equalization. This dynamic design enables the same component to serve multiple purposes rather than requiring fixed, dedicated structures for each function.
3Temperature
If temperature changes occur during storage, then overpressure is built up in the liquid system, but dose accuracy deteriorates
Solution Approach 1:
The pressure equalization channel is designed to allow pressure equalization to occur before the injection process begins. This preliminary action prevents temperature-induced overpressure from affecting the dose accuracy during actual injection, as the pressure has already been equalized in advance through the dedicated channel.
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 solution effectively equalizes pressure within the device, ensuring that the intended dose size is consistently expelled, independent of temperature-induced pressure changes, thereby maintaining dose accuracy.
Implementation Method 1
allowing equalization of pressure with the surroundings, ensuring accurate dose delivery by venting any overpressure before injection
Data Source
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AI summary
The invention relates to an injection device for injecting a liquid drug. The injection device comprises a housing assembly supporting a non-removable cartridge having an interior chamber containing the liquid drug to be injected and a reusable needle cannula connected to the cartridge. A needle shield assembly provided with a cleaning chamber containing a volume of a cleaning agent for cleaning at least the distal tip of the needle cannula between subsequent injections is further provided. The needle shield assembly is axially movable in a proximal direction in relation to the housing assembly from a first position to a second position upon rotation of at least a part of the needle shield assembly, wherein the first position is a position in which the distal tip of the needle cannula is located inside the cleaning chamber thereby cleansing the distal tip of the needle cannula, and the second position is a position in which the distal tip of the needle cannula is located outside and distal to the cleaning chamber for equalizing the pressure in the cartridge.