微營養鹽濃度梯度元件之設計

Designing a Microfluidic Device with Nutrient Gradient

林泓毅(Hung-Yi Lin)

指導教授 ： 孫珍理

國立臺灣大學/工學院/機械工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601252

摘要

本研究目的為針對探討濃度對浮游生物影響的研究，設計一能操控濃度梯度之微流元件。所設計的微流元件為一三層結構，皆以PDMS構成，其中包含上層的濃度梯度供給流道、中層的多孔薄膜與下層的微孔穴流道。本三層構造之目的為分離上層流道與下層流道內之流場，並藉由中層之多孔薄膜層在孔穴中產生濃度梯度。下層為一孔穴觀察區，連接截面為矩形之主流道，上層之濃度梯度供給流道為對稱的雙流道設計，各別通入高濃度與低濃度之流體，以在下層之孔穴內產生濃度梯度，藉由設計多孔薄膜之孔隙數量與孔徑大小，改變濃度梯度的分布型態。
實驗結果顯示，微孔穴流道之流場最容易影響微孔穴內之濃度場，微孔穴流道之Reynolds number增加時，孔穴內平均濃度會明顯降低，但分布差異不大。此外，濃度梯度供給流道的對齊方向可以明顯改變濃度梯度的分布，若與微孔穴流道的主流道平行，濃度在y軸方向的變化較為劇烈，靠近 +y方向之濃度較高；若與微孔穴流道的主流道垂直，濃度在x軸方向的變化較為劇烈，靠近 -x方向之濃度較高。因此若要改變微孔穴內之濃度梯度場，改變濃度梯度供給流道之對齊方向的效果是最好的。此外，在濃度梯度供給流道內的流向為反向流時，孔穴內濃度場較不易受濃度梯度供給流道之Reynolds number影響。薄膜的孔隙過多時會造成孔隙率過大，使微孔穴流道之流場影響濃度梯度供給流道，染劑不易通過孔隙，因此不宜選用孔隙率過大之薄膜。然而，使用較大孔隙之薄膜時，產生之濃度梯度場較為集中，峰值可達到1500 m-1。本研究所得之結果可協助我們得知，藉由改變濃度梯度供給流道與微孔穴流道之流場，可改變孔穴內之濃度場變化，且孔隙率較低之薄膜可降低兩層流道間流場之影響，以利未來進行浮游生物同時受流場與濃度場改變之趨化性研究。

關鍵字

微流元件 ； 濃度梯度 ； 多孔PDMS薄膜 ； 聚乙烯醇薄膜 ； 可調控之微生態環境 ； 趨化性

並列摘要

This study focuses on designing a microfluidic device to generate nutrient gradient for the study of plankton in chemotaxis in the future. The PDMS microfluidic platform is consisted of three layers: the gradient channel, the porous membrane, and the microcavity channel. The 3 layer structure is aimed at generating concentration variation in the microcavity by reducing the influence from the flow field of the gradient channel. The micro cavity channel has a circular pocket connected to a straight channel. The gradient channel has two symmetrical channels, one for water and the other for the dye solution. By transport through the perforated membrane, concentration gradient is formed in the microcavity. The alignment of the gradient channel and the microcavity channel of the bottom layer can be changed to alter the concentration gradient is formed in the microcavity. In addition, we design membrane with different pore size and pitch to study their effect on the concentration distribution in the microcavity.
The result shows that varying the flow velocity of the microcavity channel is the easiest way to change the concentration field. When velocity increases, the average concentration in the microcavity decreases, without significant change of its distribution. In addition, The direction of the concentration gradient can be easily change by the orientation between the gradient and the microcavity channels. When the gradient channel is aligned parallelly to the straight channel of the microcavity layer, higher concentration is found in the bottom of the pocket. When the gradient channel is aligned perpendicularly to the straight channel of the microcavity layer, higher concentration is found near the left edge of the microcavity. For the counterflow configuration in the gradient channel, the concentration is not affected by the flow in the microcavity channel. When the membrane has more pores, porosity too large such that the flow in the microcavity channel may interfere the flow in the gradient channel, which makes the dye more difficult to pass through the pores. Therefore, membrane with large porosity is not recommended. Yet, lager pore size lead to higher concentration gradient in the cavity and the pick value can reach as higher as 1500 m-1.
In this study, we successfully manipulate the concentration field in the microcavity by varying the flow field in the gradient channel and the microcavity channel. To reduce the effect of flow field on the concentration distribution, membrane with lower porosity is preferred.

並列關鍵字

microfluidic device ； concentration gradient ； porous PDMS membrane ； PVA membrane ； manipulative microhabitat ； chemotaxis

參考文獻

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