Asymmetric Fluid Well for Microfluidic Loading
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Solution Overview
Problem
Existing microfluidic devices, particularly Active Matrix Electro-wetting on Dielectric (AM-EWOD) devices, face challenges in efficiently loading and controlling the volume of fluid due to hydrophobic surfaces and the energetic unfavorability of aqueous fluids filling by capillary action, lacking effective methods for introducing discrete droplets and measuring inputted volumes.
Innovation Solution
A pre-filled fluid loading cassette with asymmetrically designed wells and a method where the cassette is aligned with the device's ports, allowing filler fluid to sweep assay fluid into the device, ensuring controlled and directional loading, even for fluids with surfactants, using a pre-loaded cassette that simplifies the fluid loading process and reduces user input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If hydrophobic internal surfaces are used in EWOD devices, then droplet manipulation is enabled, but aqueous fluids cannot fill into the device by capillary action alone
Solution Approach 1:
A filler fluid (typically oil) is introduced as an intermediary substance that enables the hydrophobic surfaces to function. The filler fluid displaces air from the device channels, allowing assay fluid droplets to be manipulated on its surface via electro-wetting, while the hydrophobic surfaces prevent the filler fluid from adhering to the channel walls.
Solution Approach 2:
The invention changes the physical state of the fluid loading process by transitioning from direct aqueous fluid introduction to introducing a non-polar filler fluid first, then adding assay fluid droplets on top. This parameter change (from aqueous to non-polar fluid introduction) enables capillary filling of the device channels.
2Productivity
If conventional fluid loading methods are used, then fluid can be introduced into the device, but precise volume control and metering are not achieved
Solution Approach 1:
The device is pre-filled with a controlled volume of filler fluid before use. This preliminary action establishes a known baseline volume, and subsequent addition of assay fluid droplets can be precisely metered by counting individual droplets or controlling their deposition, enabling accurate total volume calculation.
3Device complexity
If capillary filling is attempted with aqueous fluids, then filling process is simple, but filling is energetically unfavourable due to hydrophobic surfaces
Solution Approach 1:
The invention changes the chemical parameter of the introduced fluid from aqueous (polar) to non-polar (oil-based filler fluid). This parameter change transforms the capillary interaction from energetically unfavourable (positive capillary pressure required) to energetically favourable (negative capillary pressure enables spontaneous filling).
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
The solution enables efficient, controlled, and accurate loading of assay fluids into microfluidic devices, improving the ease of use and reducing the risk of overloading, while ensuring the correct volume is introduced for precise biochemical assays.
Implementation Method 1
it is energetically unfavourable for aqueous fluids to fill into such a device from outside by capillary action alone
Implementation Method 2
this technology employs the use of hydrophobic internal surfaces
Implementation Method 3
working particularly well with fluids containing surfactants which reduce the surface tension at the liquid-solid interface
Data Source
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AI summary
A fluid loader (18) is provided for loading fluid into a microfluidic device (10), the microfluidic device having upper and lower spaced apart substrates (17,16) defining a fluid chamber (12) therebetween and an aperture (14) for receiving fluid into the fluid chamber. The fluid loader comprises a fluid well communicating with a fluid exit provided in a base of the fluid loader. The base of the fluid loader is shaped, in use, to locate the fluid loader (18) relative to the aperture (14), and to direct fluid leaving the fluid loader via the fluid exit preferentially in a first direction in the fluid chamber (12) of the microfluidic device. In one embodiment the base of the fluid loader comprises a protruding portion (23) having at least first and second legs (23a,23b), the first leg being shorter than the second leg. In use, the fluid loader is positioned such that the first leg of the fluid loader is between a fluid loading area (32) associated with the aperture (14) and an operating area (33) of the device.