Capillary Metering Channels for Precise Passive Sample Volume Control
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Solution Overview
Problem
Existing capillary-driven microfluidic systems face challenges in precisely metering a predetermined volume of sample fluid due to the inability to shut off fluid streams once they have started, leading to inaccurate extraction of the required sample volume.
Innovation Solution
The proposed arrangement in a capillary-driven fluid system involves a sample reservoir, capillary channels, and a buffer reservoir, utilizing capillary forces and control circuits to fill and empty specific channels, allowing for precise metering of sample fluid by using a buffer fluid to replace the sample fluid in the channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If capillary forces are used to draw sample fluid through channels, then fluid movement is achieved without active control, but the system cannot shut off fluid streams once started, leading to inaccurate volume metering
Solution Approach 1:
The system divides the fluid path into separate functional channels: a sample channel for introducing sample fluid, a buffer channel for introducing buffer fluid, and a mixing channel where the two fluids combine. This segmentation allows independent control of each fluid stream and enables precise metering by controlling which channels are active at each stage of the process.
Solution Approach 2:
The system pre-fills the buffer channel with buffer fluid before the sample fluid is introduced. This preliminary action ensures that when both fluids are introduced simultaneously, the buffer fluid is already in position to mix with the sample fluid at the predetermined mixing point, enabling accurate volume control without requiring active shut-off mechanisms.
2Device complexity
If a single channel is used for both sample and buffer fluid, then device complexity is reduced, but the ability to precisely meter predetermined volumes is compromised
Solution Approach 1:
The system uses separate channels for sample fluid and buffer fluid to maintain precise control over each fluid's path and volume. The sample channel and buffer channel are distinct, allowing independent metering and control of each fluid stream, which is essential for accurate sample volume measurement even though this increases device complexity.
Solution Approach 2:
The mixing channel acts as an intermediary between the sample channel and buffer channel. It provides a controlled environment where the two fluids combine at a predetermined point, ensuring that the mixing process does not interfere with the precise volume measurement while still allowing the benefits of separate channel control.
3Quantity of substance
If capillary pump is used to empty sample reservoir, then complete sample extraction is achieved, but flow rate control becomes more complex
Solution Approach 1:
The system uses a capillary pump that operates based on pressure differential and capillary forces to empty the sample reservoir. This hydraulic approach allows complete sample extraction without complex electronic flow rate control mechanisms, as the pump's operation is driven by the natural pressure gradient created when the reservoir is emptied.
Solution Approach 2:
The capillary pump is designed to automatically empty the sample reservoir without requiring external control mechanisms. The pump utilizes capillary forces and pressure differentials to self-regulate the emptying process, achieving complete sample extraction while minimizing the complexity of flow rate control.
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 enables precise metering of a predetermined volume of sample fluid without active control, simplifying the system and allowing it to be used in handheld devices, while ensuring accurate measurement and processing of the sample fluid.
Implementation Method 1
the first channel is arranged to draw sample fluid from the sample reservoir by use of capillary forces to fill the second and the third channel with the predetermined volume of sample fluid
Implementation Method 2
the fourth channel being arranged to draw buffer fluid from the buffer reservoir by use of capillary forces, and to open the second capillary trigger valve as buffer fluid in the fourth channel reaches the second capillary trigger valve
Implementation Method 3
a capillary pump being fluidically connected to the sample reservoir via a first flow resistor
Implementation Method 4
the sample fluid and/or the buffer fluid at least partly is in gaseous communication with surroundings of the arrangement such as to allow gas mixed within the sample fluid and/or buffer fluid to escape from the arrangement, wherein the gaseous communication with surroundings occurs through a gas permeable sheet
Data Source
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AI summary
The disclosure relates to an arrangement (100) in a capillary driven fluid system for metering a predetermined volume of sample fluid. The arrangement comprises a sample reservoir (SR) arranged to receive a sample fluid, a first channel (C1) which is in fluid communication with the sample reservoir (SR) and which branches off into a second channel (C2) ending at a first valve (V1) and a third channel (C3) ending at a second valve (V2). The second channel (C2) and the third channel (C3) together have a predetermined volume, and the first channel (C1) is arranged to draw sample fluid from the sample reservoir (SR) by use of capillary forces to fill the second channel (C2) and the third channel (C3) with the predetermined volume of sample fluid. By selectively opening the first valve (V1) and the second valve (V2), a capillary driven flow may be formed, thereby causing the predetermined volume of sample fluid to flow out through the first valve (V1).