Microchip Capillary Cavity Design for Bubble-Free Sample Collection
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Solution Overview
Problem
Conventional microchips for electrochemical and optical analysis of biological fluids face issues with air bubble formation in capillary cavities, leading to insufficient liquid sample supply and measurement errors due to surface tension and orientation changes during handling.
Innovation Solution
A microchip design featuring a protruding inlet with a concave portion on one side, where the cross-sectional area near the axis is greater than the outer peripheral area, and capillary cavities connected to holding chambers, with specific cross-sectional shapes and hydrophobic/hydrophilic treatments to prevent air bubble formation and ensure reliable liquid sample collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capillary cavity structure is used for liquid sample collection, then the microchip can collect liquid samples through capillary action, but air bubbles form due to surface tension and orientation changes, leading to insufficient liquid supply and measurement errors
Solution Approach 1:
The capillary cavity is divided into multiple segments along the liquid flow path, with each segment having controlled cross-sectional dimensions. This segmentation prevents air bubble formation by ensuring that capillary forces can overcome surface tension effects at each interface, allowing reliable liquid sample collection even when orientation changes occur during handling.
Solution Approach 2:
Different sections of the capillary cavity have different cross-sectional dimensions optimized for their specific functions. The inlet section has smaller dimensions to control liquid entry, while downstream sections have larger dimensions to accommodate full liquid filling and prevent air bubble entrapment. This local optimization of geometry ensures reliable liquid supply throughout the device.
2Ease of operation
If the inlet is positioned on the side face of the microchip body, then the microchip can be easily handled and oriented, but air bubbles form when orientation changes during handling, causing insufficient liquid sample supply
Solution Approach 1:
The capillary cavity is designed with progressively increasing cross-sectional dimensions along the liquid flow path, preparing the structure in advance to accommodate orientation changes during handling. This preliminary geometric configuration ensures that when liquid is introduced from the side inlet, capillary forces reliably drive liquid filling regardless of the microchip's orientation, preventing air bubble formation and ensuring sufficient liquid sample supply.
3Ease of manufacture
If the capillary cavity has uniform cross-sectional area, then the structure is simple to manufacture, but air bubbles form due to surface tension effects, leading to measurement errors
Solution Approach 1:
The capillary cavity employs varying cross-sectional dimensions at different locations along the liquid flow path. The inlet region has smaller dimensions to control liquid entry, while downstream regions have larger dimensions to ensure complete liquid filling and eliminate air bubbles. This localized geometric variation, while slightly more complex to manufacture, ensures accurate measurements by preventing air bubble interference in the analysis region.
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 microchip effectively prevents air bubble formation, allowing multiple collections until the capillary cavity is full, thereby improving measurement accuracy by ensuring consistent liquid sample supply and reducing errors.
Implementation Method 1
a first capillary cavity for collecting a specific amount of a liquid sample by capillary force
Implementation Method 2
a first holding chamber for receiving the liquid sample transferred from the first capillary cavity by centrifugal force generated by rotation about the axis
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A microchip having an inlet (14) for collecting a liquid sample; at least one capillary cavity (4) capable of collecting a specific amount of the liquid sample through the inlet (14) by using capillary force; and a holding chamber (5) communicating with the capillary cavity (4) and receiving the sample liquid in the capillary cavity (4) transferred by centrifugal force generated by rotation about an axis. The capillary cavity (4) interconnecting the inlet (14) and the holding chamber (5) has, in one side face of the capillary cavity (4), cavities (15, 16) not generating capillary force and communicating with the atmosphere, and this prevents mixing of air bubbles into the capillary cavity (4).