Variable Pitch Screw Dose Control for Syringe Accuracy
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Solution Overview
Problem
Conventional drug delivery syringes face challenges in accurately dispensing microliter doses due to difficulties in reading and controlling plunger travel, leading to inconsistencies in dosage delivery, especially with high dose volume to axial translation ratios, which can result in excessive drug delivery and safety risks.
Innovation Solution
The development of a dose control mechanism featuring a plunger with a coarse pitch screw and a housing with a corresponding coarse pitch guide, along with a fine pitch screw and nut, allowing for precise axial movement and tactile feedback, enabling accurate dosage control and priming of syringes to minimize air bubbles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional syringes are used for microliter dose delivery, then the syringe structure is simple, but the dosing accuracy deteriorates due to high dose volume to axial translation ratio
Solution Approach 1:
The syringe is divided into two functional parts: a standard barrel for drug storage and a specialized control mechanism for precise plunger movement. The control mechanism includes a threaded plunger rod that engages with a threaded bore in the hub, separating the simple storage function from the complex dosing control function.
Solution Approach 2:
A hub component acts as an intermediary between the plunger rod and the barrel. The hub contains a threaded bore that engages with the threaded plunger rod, and also contains a stopper that seals the barrel. This intermediary structure enables precise control of plunger travel while maintaining a simple overall syringe design.
2Measurement precision
If mechanical travel limits are employed to control plunger depression, then dosing accuracy may improve, but the difficulty of detecting and measuring plunger position increases
Solution Approach 1:
The threaded engagement between the plunger rod and hub provides mechanical feedback through tactile resistance. As the plunger rod is rotated, the threads engage with the hub's threaded bore, providing audible clicks and tactile feedback that indicate precise angular and axial positions, enabling the user to detect and control plunger position accurately.
Solution Approach 2:
The patent incorporates visual indicators including a window in the hub that displays colored segments corresponding to different dose volumes, and dose markings on the plunger rod that align with reference markings on the hub. These visual cues enable easy detection and measurement of plunger position and delivered dose.
3Ease of operation
If the plunger seal is allowed to depress freely at end of delivery, then ease of operation improves, but dosing accuracy deteriorates due to variability in seal depression
Solution Approach 1:
A stop mechanism is built into the hub that prevents the plunger rod from rotating beyond a predetermined angle corresponding to the desired dose volume. This preliminary constraint stops the plunger seal from over-depressing, eliminating variability in seal depression while requiring minimal additional force from the user to reach the endpoint.
Solution Approach 2:
The hub's threaded bore and stop mechanism are pre-configured during manufacturing to provide exact control over plunger travel distance. The threading geometry and stop position are predetermined to deliver precise dose volumes, eliminating the need for the user to judge when to stop plunger depression.
4Measurement precision
If reference markings are placed on the syringe barrel, then dosing accuracy may improve, but the ease of manufacture deteriorates due to additional manufacturing steps
Solution Approach 1:
The reference markings are integrated directly into the hub structure during the same manufacturing process that forms the hub's threaded bore and stop mechanism. The markings are molded or etched onto the hub's outer surface, combining the dosing reference function with the structural hub component, eliminating separate manufacturing steps for adding markings.
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 allows for safe, accurate, and ergonomic delivery of microliter volumes, reducing the risk of excessive drug delivery and ensuring precise dosing without altering the user's administration technique, while also facilitating the mixing of medications by ensuring accurate volume control.
Implementation Method 1
a plunger having a coarse pitch screw on an exterior surface of the plunger, a housing having a corresponding coarse pitch guide along an interior surface of the housing, a screw having a fine pitch screw which interfaces with a fine pitch nut of an adapter
Implementation Method 2
A pitch ratio between the coarse pitch screw and the fine pitch screw is from approximately 1:1 to approximately 20:1
Data Source
AI summary
A dose control mechanism for a syringe includes an engaging screw thread arrangement between an exterior surface of a plunger and a longitudinally extending channel of a housing. The engaging screw thread arrangement includes at least one thread segment and a pitch guide including a variable pitch thread. At least a portion of the longitudinally extending channel of the housing including one of the pitch guide and the at least one thread segment, and the plunger includes the other of the pitch guide and the at least one thread segment. The plunger resides at least partially within the housing with the at least one thread segment engaged with the pitch guide. An accurate dose drug delivery syringe includes such a dose control mechanism, a barrel, a plunger seal, and a barrel adapter assembly having a barrel tip and a needle. The syringe may be a fill-at-time-of-use syringe, a pre-filled syringe, or a safety syringe having integrated needle retraction or needle sheathing safety features, or a combination thereof. Methods of assembly, manufacturing, and operation are similarly disclosed.