Injection Needle Sizing Shaft Flow Path
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Solution Overview
Problem
Medical injection needles exhibit variability in flow rates and injection duration due to inconsistencies in the inner lumen size, particularly between different batches of extruded needle shaft material, affecting the precision and predictability of fluid delivery.
Innovation Solution
Incorporating a sizing shaft within the needle shaft's lumen, which is axially extended and has a smaller cross-sectional size than the lumen, to create a precision fluid flow path, allowing for adjustments in the sizing shaft's size and position to achieve a consistent flow rate and duration by flowing fluid at selected pressures and comparing the results to desired rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard extrusion process is used to manufacture needle shafts, then manufacturing simplicity is maintained, but lumen size variability increases significantly between batches
Solution Approach 1:
The needle assembly is segmented into two independent components: the needle shaft (extruded) and the sizing shaft (separately manufactured). This segmentation allows each component to be optimized independently—the shaft for ease of manufacture and the sizing shaft for precision—together achieving both manufacturing simplicity and lumen size consistency.
Solution Approach 2:
The sizing shaft acts as an intermediary element inserted into the lumen to define the precise fluid flow path. It mediates between the extruded shaft (which has variable lumen dimensions) and the requirement for consistent flow rates, compensating for shaft manufacturing variations.
2Device complexity
If lumen size is allowed to vary for ease of manufacturing, then production cost and complexity are reduced, but flow rate variability increases due to Poiseuille's Law
Solution Approach 1:
The sizing shaft serves as a flow control intermediary that standardizes the fluid passage dimensions regardless of variations in the needle shaft lumen. This ensures predictable flow rates while allowing the shaft itself to be manufactured with simpler, less precise tolerances.
Solution Approach 2:
The invention changes the critical flow-control parameter from the shaft lumen dimensions (which are difficult to control precisely) to the sizing shaft dimensions (which can be manufactured with high precision), thereby improving flow rate reliability without significantly increasing overall device complexity.
3Manufacturing precision
If a sizing shaft is added to define precision flow path, then flow rate accuracy improves within 5-10% tolerance, but device complexity increases
Solution Approach 1:
By segmenting the flow control function into a separate sizing shaft component, the invention achieves precise flow rate control (within 5-10% tolerance) while keeping each individual component relatively simple. The sizing shaft is a straightforward cylindrical element that can be manufactured using standard precision machining processes.
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 approach reduces variability in injection flow rates and duration, providing a predictable fluid flow path that is within 5-10% of the desired rate, enhancing the accuracy and reliability of medical fluid delivery.
Implementation Method 1
Poiseuille's law indicates that volume flow rate through a lumen is proportional to lumen radius taken to the fourth power (or R4), so small variations in the lumen size can make a large difference in flow rates at a given pressure and lumen length.
Data Source
AI summary
A fluid injection needle has a relatively precision fluid flow path. The needle comprises a needle shaft and a sizing shaft axially extending within the needle shaft lumen a selected distance distal of a fluid entry port into the lumen. The sizing shaft has a cross-sectional size smaller than the lumen to define a fluid flow path between the sizing shaft and the needle shaft. An injection device employing such an injection needle and a method of making such a needle are also disclosed.