Micro-pillar Arrays with Capillary Stop Valves for Controlled Fluid Filling
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Solution Overview
Problem
Existing micro-fluidic capillary systems face a trade-off between high capillary pressure and low flow resistance, with irregular and uncontrolled filling leading to air bubbles and shortcut paths, which reduces the effective volume and reliability of fluid propagation.
Innovation Solution
A micro-fluidic device with a substrate and micro-pillar columns featuring sharp corners and notches that function as capillary stop valves, guiding fluid samples through a serpentine propagation path while preventing undesired directions, achieved through semiconductor fabrication techniques like photolithography and deep reactive ion etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If smaller channel dimensions are used, then capillary pressure is increased, but flow resistance increases due to viscous forces
Solution Approach 1:
The capillary pump channel is segmented into multiple parallel channels, allowing the system to maintain small channel dimensions for high capillary pressure while reducing overall flow resistance through parallel flow paths. The channel is divided into multiple segments that operate simultaneously, distributing the total flow across several low-resistance paths.
Solution Approach 2:
The invention transitions from a single-channel design to a multi-channel parallel architecture, adding spatial dimensionality to the system. By creating multiple channels side-by-side, the system achieves reduced flow resistance without compromising the small dimension requirements for high capillary pressure in each individual channel.
2Stress or pressure
If conventional capillary pump designs are used, then high capillary pressure and low flow resistance are achieved, but filling is irregular and uncontrolled creating shortcut paths and air bubbles
Solution Approach 1:
Capillary stop valves are pre-positioned at strategic locations within the channel before fluid introduction. These valves create predetermined stopping points that guide the filling sequence, ensuring complete and controlled channel filling before fluid can bypass through shortcuts or create air bubbles in the pump chamber.
Solution Approach 2:
The capillary stop valves act as intermediary elements that mediate between the fluid source and the pump chamber. These valves control the fluid propagation by creating temporary barriers at specific locations, ensuring systematic filling of the capillary network before allowing fluid to enter the pump chamber, thereby preventing shortcuts and air bubble formation.
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 device ensures reliable, controlled filling and complete volume utilization with high capillary pressure and low flow resistance, eliminating air bubbles and shortcut paths, and facilitating desired fluid propagation patterns.
Implementation Method 1
The micro-pillars columns are configured to create a capillary action when a fluid sample is provided in the cavity
Implementation Method 2
The capillary pressure is represented by ΔP cap = 2γ/R, wherein γ is the liquid-vapor surface tension and R is the radius of curvature of the liquid-vapor interface
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
The embodiments of the present invention disclose a micro-fluidic device comprising a substrate, a cavity in the substrate and a plurality of micro-pillar columns located inside the cavity. The micro-pillars columns are configured to create a capillary action when a fluid sample is provided in the cavity. A micro-fluidic channel is present between two walls of any two adjacent micro-pillars in a same micro-pillar column. Each of the two walls comprises a sharp corner along the direction of a propagation path of the fluid sample in the micro-fluidic channel thereby forming a capillary stop valve. A notch provided in a sidewall of the cavity acts as a capillary stop valve.