Cartridge Holder Retaining Struts Prevent Septum Expansion
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Solution Overview
Problem
Cartridge holder assemblies in drug delivery devices suffer from issues such as droplet formation and reduced dosage accuracy due to septum expansion and axial displacement during dose dispensing, caused by manufacturing and assembly tolerances, leading to post-dispensing fluid pressure and potential medicinal fluid loss.
Innovation Solution
The design of cartridge holders without a radially inwardly directed flange portion, featuring a distal end with an inner diameter matching the cartridge neck, and incorporating retaining means like radially inwardly protruding struts or ribs to secure the cartridge in place, preventing axial expansion and displacement, thus maintaining dosing accuracy and preventing droplet formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a radially inwardly directed flange portion is used to secure the cartridge, then the cartridge can be retained in position, but it causes axial expansion of the septum and displacement of the cartridge during dose dispensing
Solution Approach 1:
The invention removes the radially inwardly directed flange portion from the cartridge holder design. By extracting this problematic structural element, the patent eliminates the source of septum expansion and cartridge displacement while maintaining cartridge retention through alternative means such as a distal end stop and proper dimensional matching between the cartridge neck and holder inner diameter.
Solution Approach 2:
Instead of using a radially inwardly directed flange portion to secure the cartridge, the invention inverts the approach by using a distal end stop configuration where the cartridge is secured by its distal end butting against the bottom portion of the needle mount, combined with a cartridge holder inner diameter that matches the cartridge neck outer diameter.
2Ease of manufacture
If manufacturing and assembly tolerances are present, then the device can be manufactured cost-effectively, but axial gap variation causes septum expansion and droplet formation
Solution Approach 1:
The invention performs preliminary action by designing the cartridge holder with a distal end inner diameter that precisely matches the cartridge neck outer diameter, and by positioning the distal end stop at a predetermined location. This preliminary dimensional matching and positioning compensates for manufacturing and assembly tolerances, preventing excessive axial gap variation that would otherwise cause septum expansion and droplet formation.
3Power
If the septum is allowed to expand during dose dispensing, then fluid pressure can be built-up for dose delivery, but post-dispensing fluid pressure causes medicinal fluid loss
Solution Approach 1:
The invention extracts the radially inwardly directed flange portion that causes harmful septum expansion. By removing this element, the patent allows the septum to expand only to the extent necessary for dose delivery without excessive expansion that would create post-dispensing fluid pressure and medicinal fluid loss.
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 configuration effectively prevents septum expansion and axial displacement, ensuring accurate dosing and minimizing post-dispensing fluid loss, thereby enhancing the stability and reliability of drug delivery devices.
Implementation Method 1
Due to the elasticity of the septum 18, may lead to a respective axial expansion of the septum 18. Due to its elastic properties, the septum 18 also stores elastic energy during dose dispensing.
Data Source
Figure 1
Figure 2~4
AI summary
The present invention relates to a cartridge holder for a drug delivery device and to a corresponding drug delivery device, wherein the cartridge holder comprises: a proximal portion (36) for receiving a cartridge (12) filled with a medicinal fluid to be dispensed by the drug delivery device, a distal portion (34) comprising a mount for a piercing assembly (24, 25, 30), wherein the piercing assembly is adapted to provide a fluid-transferring connection with the inner volume of the cartridge (12) by way of a piercing element (30) pointing in distal direction with a pointed free end section; and retaining means (40; 42; 44) adapted to substantially prevent the cartridge (12) from displacing in proximal direction with respect to the proximal portion (36) and/or distal portion (34).