Name: analyzing mixing inhomogeneity in a microfluidic device by microscale schlieren technique
Uploaded: 2015-06-12T14:00:00.000+00:00
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Bu eser Hibe Sayısı 101-2221-E-002-064-My3 altında Bilim ve Tayvan Teknoloji Bakanlığı tarafından desteklenmiştir.

Mikroakışkan Aygıt 1. Fabrikasyon <ol><li> T-mikrokanalın anahatlarını çizmek için bir grafik düzen yazılımı (örneğin, AutoCAD) kullanın. T-mikrokanalın için, iki besleme kanalı 90 mikron genişliğinde ve 2.500 mikron uzunluğunda olup, izdiham kanal uzunluğunda 180 mm genişliğinde ve 3000 mm. 1,100 um arasında bir çapa sahip tek bir çevreye her kanalın ucunu. </li><li> Mark &#39;net&#39; ve sırasıyla maruz kalma ve kapalı alanlar için &#39;karanlık&#39;. Negatif fotorezist için (örneğin, SU-8), T-mikrokanalın şekli &#39;açık&#39; ve çevresindeki olan &#39;karanlık.&#39; </li><li> Bir krom-on-cam photomask üzerine, T-mikrokanalın desen transfer 442 nm&#39;lik bir dalga boyunda ve 2 um arasında en az bir özellik boyutu bir lazer desen üreticisi kullanın. </li><li> Photomask, bir substrat (örneğin, tek taraflı cilalı silikon gofret) ve kalıcı bir epoksi ışığa kullanın (örneğin., SU-8) standart litografi süreci boyunca bir kalıp yapmak için. Fotorezist tabakası 55.2 mikron kalınlığındadır. Genel olarak, paslanmaz çeliğin kalınlığı objektif lens 17-19 korelasyon derinliğinden daha ince olması gerekmektedir. </li><li> T mikrokanalı 20 imal etmek için bir kalıp ve polidimetilsiloksan (PDMS) gibi saydam bir malzeme kullanarak. </li><li> Akışkan bağlantısı için, zımba dış çapı 2 mm bir paslanmaz çelik boru kullanarak geçiş delikleri PDMS dairesel şekillere hizalanır. </li><li> PDMS ve 30 saniye süreyle 60 W oksijen plazma bir cam slayt yüzeylerin muamele. Cam slayt PDMS takın. iki malzemenin oksitlenmiş yüzeyleri güçlü bir bağ oluşturur. 120 ° C &#39;de 5 dakika süre ile bir sıcak plaka üzerinde bağlanmış PDMS yapısı yerleştirin. </li><li> Akışkan bağlantı için delinmiş deliklere teflon tüpler yerleştirin. </li></ol> 2. Deneysel Kurulum <ol><li> Bir Hoffma gelen mikro schlieren sistemini Constructkondenserin ön odak düzlemi yarık plakasını kaldırılması ve 5X hedefi 3 arka odak düzlemi içinde bir bıçak kenarı ile modülatörün değiştirerek n modülasyon kontrast mikroskop. amacı, 17-19 sayısal açıklık bağlıdır korelasyon derinliği, mikroakışkan cihazın kapsayacak şekilde, yeterli olmalıdır. bıçak kenar yüzeyi kendi yansıtıcılığını azaltmak için anodik alüminyum oksit ile kararmış. </li><li> Bir C-mount adaptörü üzerinden mikroskop trinoküler tüp yüksek hızlı kamera monte edin. Kamera ışın ayırıcı üzerinden mikroskop optik yolunu yüz var. Bir Ethernet kablosu ile masaüstü bilgisayarınıza bağlayın. Gri tonlama okuma giriş parlaklık orantılı olacak şekilde kamera için 1 gama düzeltmesi ayarlayın. </li><li> Işık kaynağı açın. Aşırı ısı önlemek için, LED (ışık yayan diyot) aydınlatma kullanın. </li><li> Örneğin, &lt;(bir görüntü işleme yazılımı kullanın/ Em&gt; MATLAB fonksiyon imread) edinilmiş bir görüntünün gri tonlama değerlerini elde etmek. , Bıçak kenar Kaldır görüntünün ortalama gri tonlama okuma maksimum değerden yaklaşık% 10 daha az olacak şekilde aydınlatma, diyafram ve pozlama süresini ayarlayın. Bu% 0 kesme arka plan yoğunluğunu gösterir ve biz bir 8-bit görüntü için 230 değerini kullanın. </li><li> Tamamen olay ışığı engellemek için bıçak kenar yerleştirin. Görüntünün ortalama gri tonlama okunmasını kaydedin. Bu, bir% 100 kesme için arka plan yoğunluğu temsil eder ve değeri yaklaşık 15, 8-bitlik bir görüntü içindir. </li><li> Bıçak kenar konumunu ayarlayın şekilde elde edilen görüntünün ortalama gri tonlama okuma% 0 ve% 100 kesme değerleri ortasında yatıyor. Şimdi kesme derecesi% 50 olarak ayarlanır. </li><li> Kurucu maddeler olarak birbirleri ile tamamen karıştırılabilir olduğu bilinen kırılma indeksleri 21 ile iki adet saydam sıvılar hazırlayın. Refraktif ind bağımlılığını değerlendirmekkarışımın konsantrasyonuna eski, edebiyat 21 çek veya Gladstone-Dale denklemini 22 kullanın. Eğri tüm aralığında doğrusal olmayan ise, diğer sıvı bileşenler seçin. Daha sonra, çözeltinin kırılma endeksi konsantrasyonu ile doğrusal olarak değişmektedir aşağıda belirlenen bir bileşim seçin. Örneğin, çalışma sıvıları olarak kitlesel 0.05 fraksiyonu ve su ile sulu etanol seyreltik kullanımı. </li><li> Örnek sahnede T-mikrokanalı koyun. Bıçak kenarına konfluan kanal paralel böylece (Şekil 1) T-mikrokanalı düzenleyin. </li><li> Şırınga bir başvuru sıvı (su) olarak görev yapan çalışma sıvısı ile doldurulur, ve şırınga oda diğer çalışma akışkanı (sulu etanol seyreltik) ile doldurulur: iki aynı şırınga hazırlayın. şırınga boyutu arzu edilen akış hızı Q ve şırınga pompasına özelliklerine bağlıdır: Q = πd d Syr iç çapı 2 V / 4,inge ve V, pistonun hızıdır. Akış nabız, genellikle V 23 geliştirmek için küçük bir şırınga seçerek önlenebilir. </li><li> Bir beher T-mikrokanalın gelen çıkış sıvısını toplayın. Emin teflon çıkış borusu behere duvarına sabitlenir ve son damlacık kopmasına neden olacağı titreşim önlemek için beher sıvı seviyesinin altındadır. </li></ol> 3. Kalibrasyon <ol><li> Karıştırma iki akışkan ve referans görüntüleri görüntüleri edinin. <ol><li> Belirli bir Reynolds sayısı Re, enjektör pompalarının akış hızını ayarlamak, Q. Q = μ (B + D) Re / 4ρ, μ ve ρ viskozitesi ve çalışma sıvısının yoğunluğunun olduğu ve W ile hesaplanır ve D, sırasıyla t-mikrokanalın izdiham kanalının genişliği ve derinliği vardır. </li><li> Yük tek şırınga A ile pompa ve sy ile diğer pomparinge B. Bağlan T-mikrokanalın iki girişlerinin teflon tüp aracılığıyla A ve B şırınga şırınga etmek. Özdeş hacim akış hızlarında T-mikrokanalın içine çalışan sıvıları teslim şırınga pompaları başlatın. </li><li> Sürekli akış kurar kadar bekleyin. sürekli akış koşulu sabit schlieren desen ortaya çıkması ile tanımlanır. </li><li> 30 fps kare hızında akışkan karıştırma yirmi kare kaydetmek için kamera kontrollü yazılımını kullanın. </li><li> Sadece sabit hızda T-mikrokanalın izdiham kanalı içine tek girişten referans sıvısı (su) pompa enjektör B ile yüklenir pompayı durdurun. </li><li> Sürekli akış koşulu ulaşıldığında ve hiçbir schlieren model görülmektedir kadar bekleyin. </li><li> Optik homojen olmama T-mikrokanalda mevcut olduğunda referans görüntü almak için kamera kontrollü yazılımını kullanın. 30 fps kare hızında yirmi kare kaydedin. </li><li> Farklı Reynolds numaralı 3.1.7 3.1.1 tekrarlayın: = 1 Re, 5, 10, 20 ve 50, böylece karmaşık bir akış yapısı T-mikrokanal 24 kesişme bölgesi ortaya çıkar. </li></ol></li><li> I ve j piksel endeksleri olan referans görüntü I 0 (i, j) 25 tarafından satın görüntüyü (i, j) bölmek için bir görüntü işleme yazılımı kullanın. </li><li> T-mikrokanalda belirlenen sıvıların karıştırılması simüle etmek için bir CFD (Computational Fluid Dynamics) paketi çalıştırmak. <ol><li> T-mikrokanalın geometrisi için üç boyutlu bir model oluşturun. Yapılandırılmış ızgaraları içine akış alanını ayrıklaştırılabilir. , Doğruluğunu artırmak izdiham ve T-mikrokanalın merkezi bölgesinde ince örgü istihdam etmek. </li><li> Akışkanların fiziksel özelliklerini atayın ve akış etki sınır koşulları kurmak. Çözme sürecinde, son elde edilen konsantrasyon konsantrasyon-bağımlı difüzyon katsayısı belirlemekYerel konsantrasyonunu güncellemek için yineleme 26. </li><li> Izgara çalışması 27 yaparak bilgisayarlı sonuçların hassasiyetlerini inceleyin. </li></ol></li><li> Her düğüm için (x i, i y) xy -Plane üzerine, trapez kuralı ile kanal derinliği karşısında konsantrasyon alanının ortalama değerleri almak için CFD post-processing aracı istihdam: w (x i, y j) = {Σ k [w (x i, y j, z k) w + (x i, y j, z k +1)] ∙ (z k +1 - z k) / 2} / D 28, D nerede kanal derinliği. Deriva hesaplamak için merkezi farkı şemasını kullanarakçapraz-akış yönüne göre konsantrasyon tive (∂ ağırlık / ∂ y) i, j = [(X, Y, j + 1) w - a (x, Y&#39;nin j-1)] / (y j 1 - Y j-1). </li><li> Pozitif ve negatif geçişlerini hem de, gri tonlama değerleri I / I 0 (3.2 elde) ve kütle fraksiyonun gradyan ∂ w / ∂ y böyle y = 0 (merkez olarak belirtilen yerlerde (3.4 elde edilen), akım içerisinde oranı ayıklamak yönü) ya da çeşitli Verilen x (çapraz akım yönü). </li><li> Sonuçları arsa ve benim aramda / I 0 ilişkiyi belirlemek ve ∂ ∂ / y, I / I 0 w </sulineer regresyon ile / y ∂ + C 2 (C 1 ve C 2 sabitler) w b&gt; = C 1 ∂. </li></ol> 4. kantitasyonu <ol><li> Tekrarlayın 3.1 Hedef mikroakışkan cihaz karıştırmak için 3.2 adımları. Hedef mikroakışkan cihaz derinliği aynı veya T-mikrokanalın buna yakın olmalıdır. Kararsız fenomen bekleniyorsa, bunun yerine adım 3.1.4 Bir video klibi (görüntülerin dizisi) kazanır. pozlama süresi 2.4, 2.5, 3.1.4 ve 3.1.7&#39;de kullanılan değerle aynı olmalıdır iken kare hızı, açıkça geçici akış dinamikleri çözmek için yeterince yüksek olmalıdır. </li><li> Hedef mikroakışkan cihaz kitle fraksiyonun degrade gri tonlama değerleri oranını dönüştürmek için adım 3.6 &#39;de elde edilen ilişki kullanın. </li></ol>

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Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscale+schlieren+visualization+of+near-bubble+mass+transport+during+boiling+of+2-propanol/water+mixtures+in+a+square+capillary.">Microscale schlieren visualization of near-bubble mass transport during boiling of 2-propanol/water mixtures in a square capillary.</a> Experiments in Fluids. 55 (7), 1778 (2014).</li><li>Panigrahi, P. K., Muralidhar, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Schlieren and Shadowgraph Methods in Heat and Mass Transfer. , (2012).</li></ol>

Yazarlar ifşa hiçbir şey yok.

Bir mikroakışkan cihaz akışkan karıştırma için, mikro schlieren tekniği ışık yoğunluğundaki değişim miktarının yoluyla konsantrasyon gradyanı büyüklüğünü ölçebilir. Bu tekniğin prensibi ışık yayılımı ardalanmasından tespit dayandığından, çalışma sıvıları ve mikroakışkan cihaz olayı ışığa şeffaf olmak zorunda. Buna ek olarak, iletişim kuralı kırılma çözeltisi endeksi ve çalışma sıvılarının ön değerlendirmesi gerekli olduğu şekilde bileşime arasında do...

Sıvı karışım, birçok endüstriyel işlemlerde ve biyolojik sistemlerde bulunan önemli bir konudur. Mikroakiskan ortaya çıkması ile, microscale karıştırma nedeniyle toplu taşıma mekanizmaları arasında difüzyon hakimiyeti onun meydan çok önem getirdi. Etkili bir Micromixer gerekli sayısal doğrulama tasarımı yana, birkaç ölçme yöntemleri 5-7 geliştirilmiştir. Bununla birlikte, genel olarak etkin micromixers 5 bulunan, üç boyutlu yapı, yaygın ölçüm teknikleri sunmak için başarısız konsantrasyon alanında daha doğru bir temsilini talep eder. Nedeniyle açısı 8 veya reaksiyon kinetiği 6 görüntüleme sınırı, yukarıda belirtilen yöntemler doğru karışımın homojenliği hesap yok yanıltıcı sonuçlar doğurabilir. Optik olarak transparan mikro karıştırma optik olarak transparan akışkanlar, mikro schlieren teknik 3,9-14 için </sup&gt; homojen olmayan karıştırma analiz için cazip bir alternatif sunuyor. Geçmişte, mikro schlieren tekniği çoğunlukla sıkıştırılabilir akış 9-13, 15 ya da 16 fazını degrade görselleştirmek için kullanılır olmuştur. Mikro schlieren tekniği, basit bir optik düzen ve yüksek hassasiyet hem yararları ve optik rahatsızlık neden ama karıştırma değerlendirilmesinde kullanılmak için uygundur belirli akış özelliği non-invaziv soruşturma sadece sağlar. Bu yazıda, bir mikroskop objektif arka odak düzlemi içinde bir bıçak kenar takarak mikro schlieren sistemini inşa, kantitatif analiz gerçekleştirmek için bir kalibrasyon prosedürü tarif ve mikroakışkan osilatör 4 bir doğrulama ölçümü rapor. Ölçümlerini gerçekleştirmek için, çalışma sıvıları uygun karma bir sıvı kırılma indeksi bileşimi ile doğrusal olarak farklılaştığı şekilde seçilir, ve hedef mikroakışkan cihaz kalınlığı ile aynıdır edilire kalibrasyonunda kullanılan. Türlerin konsantrasyonu yanı sıra, mikro schlieren tekniği doğrusal örneğin sıcaklık veya tuzluluk kırılma indeksi, korelasyon diğer skalar miktar gradyanı ölçmek için genişletilebilir.

<table><tbody><tr><td>Permanent Epoxy Negative Photoresist</td><td>MicroChem</td><td>SU-8 2150</td><td></td></tr><tr><td>single side polished silicon wafer</td><td>Light Technology</td><td>S4W1PP5SABUP1</td><td>p-type, &lt;br /&gt;diameter: 100&amp;plusmn;0.5 mm, thickness: 525&amp;plusmn;25 mm, orientation: (1 0 0)</td></tr><tr><td>syringe pump</td><td>kdScientific</td><td>kds210</td><td></td></tr><tr><td>syringe, &lt;em&gt;i.e.&lt;/em&gt; 10 ml</td><td>Terumo</td><td>SS-10L2138</td><td></td></tr><tr><td>Hoffman modulation contrast microscope</td><td>Leica Microsystems</td><td>DM IL LED</td><td></td></tr><tr><td>5X objective lens</td><td>Leica Microsystems</td><td>N PLAN</td><td>NA = 0.12</td></tr><tr><td>knife-edge</td><td></td><td></td><td>custom made part</td></tr><tr><td>camera, &lt;em&gt;i.e.&lt;/em&gt; high speed</td><td>Integrated Design Tools</td><td>NX7-S1</td><td></td></tr><tr><td>C-mount adapter HC 0.63x</td><td>Leica Microsystems</td><td>541537</td><td></td></tr><tr><td>camera operating software</td><td>Integrated Design Tools</td><td>MotionPro X Studio 2.02.01</td><td></td></tr><tr><td>polydimethylsiloxane (PDMS)</td><td>Dow Corning</td><td>Sylgard-184 silicone elastomer kit</td><td></td></tr><tr><td>Teflon tubing, &lt;em&gt;i.e.&lt;/em&gt; O.D. x I.D. 1/16 in. x 0.031 in.</td><td>Supelco</td><td>58700-U</td><td></td></tr><tr><td>micro glass slide</td><td>Matsunami Glass</td><td>S2215</td><td></td></tr><tr><td>hot plate</td><td>Yeong-Shin</td><td>HP-303DN</td><td></td></tr><tr><td>distilled water, &lt;em&gt;i.e.&lt;/em&gt; HPLC grade</td><td>Alps Chemicals</td><td></td><td></td></tr><tr><td>ethyl alcohol, &lt;em&gt;i.e.&lt;/em&gt; reagent grade</td><td>Nihon Shiyaku Reagent</td><td>EA448652</td><td></td></tr><tr><td>image processing software</td><td>Mathworks</td><td>MATLAB R2009a</td><td></td></tr><tr><td>computational fluid dynamics package</td><td>ESI group</td><td>CFD-ACE+ 2008</td><td></td></tr></tbody></table>

analyzing mixing inhomogeneity in a microfluidic device by microscale schlieren technique

Bu yazıda bir mikroakışkan cihaz homojen olmayan karıştırma ölçmek için mikro schlieren tekniğinin kullanımını tanıtmak. mikro schlieren sistemi, yarık plakasını kaldırarak ve bir bıçak kenarı ile modülatörün değiştirerek objektif lens arka odak düzlemi kolay erişim sağlayan bir Hoffman modülasyon kontrast mikroskop, inşa edilmiştir. mikro schlieren tekniğin çalışma prensibi kırılma indisi 1-3 değişimi nedeniyle ışık sapmasını tespit dayanır. seken ışık kaçar ya da sırasıyla, bir aydınlık veya karanlık bir bant üretmek için bıçak kenarı tarafından tıkalı ya. Karışımın kırılma indisi olan bileşim ile doğrusal olarak değişmektedir, görüntü düzleminde ışık yoğunluğundaki yerel değişiklik optik eksene normal bir konsantrasyon gradyanı ile orantılıdır. Mikro schlieren resim, üç boyutludur homojen tarafından üretilen bozulmuş ışık iki boyutlu bir projeksiyon vermektedir. Kantitatif analiz gerçekleştirmek için, bir T-mikrokanalda iki sıvıları karıştıran bir kalibrasyon prosedürü açıklar. Biz gelen mikro-schlieren görüntü ile yakından ilişkilidir T-mikrokanalda konsantrasyon gradyanı elde etmek için sayısal simülasyonu yürütmek. Buna karşılık, mikro-schlieren görüntünün gri tonlama okumalar ve bir mikroakışkan cihaz sunulan konsantrasyon geçişlerini arasında bir ilişki kurulmaktadır. Bu ilişkiyi kullanarak, bir mikroakışkan osilatör 4 ölçümleri ile mikro schlieren tekniğinin yeteneği ortak mikro schlieren görüntüden karıştırma homojen olmayan durumlar analiz ve göstermek mümkün bulunmaktadır. Optik olarak transparan akışkanlar için, mikro schlieren tekniği karıştırma işlemi üç boyutlu özelliklerini korur anlık tam saha bilgileri sağlamak için cazip bir tanı aracıdır.

gri tonlama oranı I / kütle oranı olumlu ve olumsuz geçişlerini hem de farklı Reynolds numarası altında ben 0 T-mikrokanalın ortasında görünen bir simetrik bant ile (Şekil 2) gösterilmektedir. Düşük Reynolds sayısı anda, schlieren bant kuyruğu nedeniyle karıştırma arabirimi üzerinden dağılım genişletilmiş ve bulanık. Reynolds sayısı arttıkça, difüzyon uzunluğu daha dar bir bant lider kısaltır. Farklı aşağı yerlerde, yoğunluk değiş...

Watch this Scientific Journal Video about Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique at JoVE.com

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image.

Mikro Schlieren Tekniği ile bir mikroakışkan Aygıt karıştırma homojen Analizi

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren ...

analyzing-mixing-inhomogeneity-microfluidic-device-microscale

Research

JoVE Journal

Bioengineering

8.9K Görüntüleme.  National Taiwan University. Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image. 

Video: Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

Yüzey-akustik dalga odaklı Akustik-ters akışlı Mikroakiskan Fabrikasyon, İşletme ve Akış Görselleştirme

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

Mühendislik

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

Kuşatılmış Quiescent ve akan Koloidno polimer Karışımlarının Eşodaklı Görüntüleme

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

Kimya

Microfluidic Chips Controlled with Elastomeric Microvalve Arrays

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays. Robust flow control and precise fluidic volumes are two critical requirements for these applications. We have developed microfluidic chips featuring elastomeric polydimethylsiloxane (PDMS) microvalve arrays that: 1) need no extra energy source to close the fluidic path, hence the loaded device is highly portable; and 2) allow for microfabricating deep (up to 1 mm) channels with vertical sidewalls and resulting in very precise features.

The PDMS microvalves-based devices consist of three layers: a fluidic layer containing fluidic paths and microchambers of various sizes, a control layer containing the microchannels necessary to actuate the fluidic path with microvalves, and a middle thin PDMS membrane that is bound to the control layer. Fluidic layer and control layers are made by replica molding of PDMS from SU-8 photoresist masters, and the thin PDMS membrane is made by spinning PDMS at specified heights. The control layer is bonded to the thin PDMS membrane after oxygen activation of both, and then assembled with the fluidic layer. The microvalves are closed at rest and can be opened by applying negative pressure (e.g., house vacuum). Microvalve closure and opening are automated via solenoid valves controlled by computer software.

Here, we demonstrate two microvalve-based microfluidic chips for two different applications. The first chip allows for storing and mixing precise sub-nanoliter volumes of aqueous solutions at various mixing ratios. The second chip allows for computer-controlled perfusion of microfluidic cell cultures.

The devices are easy to fabricate and simple to control. Due to the biocompatibility of PDMS, these microchips could have broad applications in miniaturized diagnostic assays as well as basic cell biology studies.

We demonstrate protocols for manufacturing and automating elastomeric polydimethylsiloxane (PDMS)-based microvalve arrays that need no extra energy to close and feature photolithographically defined precise volumes. A parallel subnanoliter-volume mixer and an integrated microfluidic perfusion system are presented.

Elastomerik Mikrovalf Diziler Kontrollü mikroakışkan Chips

Miniaturized microfluidic systems provide simple and effective solutions for low-cost point-of-care diagnostics and high-throughput biomedical assays.  ...

Biyoloji

Microfluidic Mixers for Studying Protein Folding

The process by which a protein folds into its native conformation is highly relevant to biology and human health yet still poorly understood. One reason for this is that folding takes place over a wide range of timescales, from nanoseconds to seconds or longer, depending on the protein1. Conventional stopped-flow mixers have allowed measurement of folding kinetics starting at about 1 ms. We have recently developed a microfluidic mixer that dilutes denaturant ~100-fold in ~8 &mu;s2. Unlike a stopped-flow mixer, this mixer operates in the laminar flow regime in which turbulence does not occur. The absence of turbulence allows precise numeric simulation of all flows within the mixer with excellent agreement to experiment3-4.
Laminar flow is achieved for Reynolds numbers Re &le;100. For aqueous solutions, this requires micron scale geometries. We use a hard substrate, such as silicon or fused silica, to make channels 5-10 &mu;m wide and 10 &mu;m deep (See Figure 1). The smallest dimensions, at the entrance to the mixing region, are on the order of 1 &mu;m in size. The chip is sealed with a thin glass or fused silica coverslip for optical access. Typical total linear flow rates are ~1 m/s, yielding Re~10, but the protein consumption is only ~0.5 nL/s or 1.8 &mu;L/hr. Protein concentration depends on the detection method: For tryptophan fluorescence the typical concentration is 100 &mu;M (for 1 Trp/protein) and for FRET the typical concentration is ~100 nM.
The folding process is initiated by rapid dilution of denaturant from 6 M to 0.06 M guanidine hydrochloride. The protein in high denaturant flows down a central channel and is met on either side at the mixing region by buffer without denaturant moving ~100 times faster (see Figure 2). This geometry causes rapid constriction of the protein flow into a narrow jet ~100 nm wide. Diffusion of the light denaturant molecules is very rapid, while diffusion of the heavy protein molecules is much slower, diffusing less than 1 &mu;m in 1 ms. The difference in diffusion constant of the denaturant and the protein results in rapid dilution of the denaturant from the protein stream, reducing the effective concentration of the denaturant around the protein. The protein jet flows at a constant rate down the observation channel and fluorescence of the protein during folding can be observed using a scanning confocal microscope5.

In this work we explain the fabrication and use of a microfluidic mixer capable of mixing two solutions in ~8 &mu;s. We also demonstrate the use of these mixers with spectroscopic detection using UV fluorescence and fluorescence resonance energy transfer (FRET).

Protein Katlama Öğrenmenin mikroakışkan Mikserler

The process by which a protein folds into its native conformation is highly relevant to biology and human health yet still poorly understood. One reason ...

Biyomühendislik

A Microfluidic Device for Studying Multiple Distinct Strains

The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a comparative manner. Multiwell plates are routinely used to compare many different strains or cell lines, but allow limited control over the environment dynamics. Microfluidic devices, on the other hand, allow exquisite dynamic control over the surrounding conditions, but it is challenging to image and distinguish more than a few strains in them. Here we describe a method to easily and rapidly manufacture a microfluidic device capable of applying dynamically changing conditions to multiple distinct yeast strains in one channel. The device is designed and manufactured by simple means without the need for soft lithography. It is composed of a Y-shaped flow channel attached to a second layer harboring microwells. The strains are placed in separate microwells, and imaged under the exact same dynamic conditions. We demonstrate the use of the device for measuring protein localization responses to pulses of nutrient changes in different yeast strains.

We present a simple method to produce microfluidic devices capable of applying similar dynamic conditions to multiple distinct strains, without the need for a clean room or soft lithography.

Birden Farklı Suşlarının incelenmesi için bir mikroakışkan Cihazı

The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a ...

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement during previous phase changes and applied shear. To determine the extent of these changes, we have developed a microfluidic device that enables repeated phase transitions induced by exchange of the surrounding fluid and microrheological characterization while limiting shear on the sample. This technique is &#181;2rheology, the combination of microfluidics and microrheology. The microfluidic device is a two-layer design with symmetric inlet streams entering a sample chamber that traps the gel sample in place during fluid exchange. Suction can be applied far away from the sample chamber to pull fluids into the sample chamber. Material rheological properties are characterized using multiple particle tracking microrheology (MPT). In MPT, fluorescent probe particles are embedded into the material and the Brownian motion of the probes is recorded using video microscopy. The movement of the particles is tracked and the mean-squared displacement (MSD) is calculated. The MSD is related to macroscopic rheological properties, using the Generalized Stokes-Einstein Relation. The phase of the material is identified by comparison to the critical relaxation exponent, determined using time-cure superposition. Measurements of a fibrous colloidal gel illustrate the utility of the technique. This gel has a delicate structure that can be irreversibly changed when shear is applied. &#181;2rheology data shows that the material repeatedly equilibrates to the same rheological properties after each phase transition, indicating that phase transitions do not play a role in microstructural changes. To determine the role of shear, samples can be sheared prior to injection into our microfluidic device. &#181;2rheology is a widely applicable technique for the characterization of soft matter enabling the determination of rheological properties of delicate microstructures in a single sample during phase transitions in response to repeated changes in the surrounding environmental conditions.

We demonstrate the fabrication and use of a microfluidic device that enables multiple particle tracking microrheology measurements to study the rheological effects of repeated phase transitions on soft matter.

Havacilik ve Microrheology tekrarlanan faz geçişleri sırasında yumuşak madde Rheological özellikleri belirlemek için birleştirme

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement ...

One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. Customized channel layout designs are necessary for specific functions and integrated performance of microfluidic devices in numerous biomedical and chemical applications (e.g., cell culture, biosensing, chemical synthesis, and liquid handling). Owing to the nature of molding approaches using silicon wafers with photoresist layers patterned by photolithography as master molds, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights. Typically, channels with multiple heights or different geometric sections are designed to possess particular functions and to perform in various microfluidic applications (e.g., hydrophoresis is used for sorting particles and in continuous flows for separating blood cells6,7,8,9). Therefore, a great deal of effort has been made in constructing channels with various sections through multiple-step approaches like photolithography using several photoresist layers and assembly of different PDMS thin sheets. Nevertheless, such multiple-step approaches usually involve tedious procedures and extensive instrumentation. Furthermore, the fabricated devices may not perform consistently and the resulted experimental data may be unpredictable. Here, a one-step approach is developed for the straightforward fabrication of microfluidic channels with different geometric cross sections through PDMS sequential wet etching processes, that introduces etchant into channels of planned single-layer layouts embedded in PDMS materials. Compared to the existing methods for manufacturing PDMS microfluidic channels with different geometries, the developed one-step approach can significantly simplify the process to fabricate channels with non-rectangular sections or various heights. Consequently, the technique is a way of constructing complex microfluidic channels, which provides a fabrication solution for the advancement of innovative microfluidic systems.

Several methods are available for the fabrication of channels of non-rectangular sections embedded in polydimethylsiloxane microfluidic devices. Most of them involve multistep manufacturing and extensive alignment. In this paper, a one-step approach is reported for fabricating microfluidic channels of different geometric cross sections by polydimethylsiloxane sequential wet etching.

Polydimethylsiloxane mikrosıvısal kanalları sıralı ıslak gravür işlemler tarafından farklı geometrik bölümlerin imalatı tek adımlı yaklaşım

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. ...

A Microfluidic Platform for Precision Small-volume Sample Processing and Its Use to Size Separate Biological Particles with an Acoustic Microdevice

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. However, to achieve robust sample manipulation it is necessary to address device integration with the macroscale environment. To realize repeatable, sensitive particle separation with microfluidic devices, this protocol presents a complete automated and integrated microfluidic platform that enables precise processing of 0.15&#8211;1.5 ml samples using microfluidic devices. Important aspects of this system include modular device layout and robust fixtures resulting in reliable and flexible world to chip connections, and fully-automated fluid handling which accomplishes closed-loop sample collection, system cleaning and priming steps to ensure repeatable operation. Different microfluidic devices can be used interchangeably with this architecture. Here we incorporate an acoustofluidic device, detail its characterization, performance optimization, and demonstrate its use for size-separation of biological samples. By using real-time feedback during separation experiments, sample collection is optimized to conserve and concentrate sample. Although requiring the integration of multiple pieces of equipment, advantages of this architecture include the ability to process unknown samples with no additional system optimization, ease of device replacement, and precise, robust sample processing.

This protocol describes a system architecture for performing automated small volume (0.15&#8211;1.5 ml) particle separations using a microfluidic device, and discusses methods to optimize acoustofluidic device performance and operation.

Bir mikroakışkan Hassas Küçük hacimli Numune İşleme Platformu ve Akustik mikrocihazda Ayrı Biyolojik Parçacıklar Boyutu Kullanımı

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. ...

Window on a Microworld: Simple Microfluidic Systems for Studying Microbial Transport in Porous Media

Microbial growth and transport in porous media have important implications for the quality of groundwater and surface water, the recycling of nutrients in the environment, as well as directly for the transmission of pathogens to drinking water supplies. Natural porous media is composed of an intricate physical topology, varied surface chemistries, dynamic gradients of nutrients and electron acceptors, and a patchy distribution of microbes. These features vary substantially over a length scale of microns, making the results of macro-scale investigations of microbial transport difficult to interpret, and the validation of mechanistic models challenging. Here we demonstrate how simple microfluidic devices can be used to visualize microbial interactions with micro-structured habitats, to identify key processes influencing the observed phenomena, and to systematically validate predictive models. Simple, easy-to-use flow cells were constructed out of the transparent, biocompatible and oxygen-permeable material poly(dimethyl siloxane). Standard methods of photolithography were used to make micro-structured masters, and replica molding was used to cast micro-structured flow cells from the masters. The physical design of the flow cell chamber is adaptable to the experimental requirements: microchannels can vary from simple linear connections to complex topologies with feature sizes as small as 2 &mu;m. Our modular EcoChip flow cell array features dozens of identical chambers and flow control by a gravity-driven flow module. We demonstrate that through use of EcoChip devices, physical structures and pressure heads can be held constant or varied systematically while the influence of surface chemistry, fluid properties, or the characteristics of the microbial population is investigated. Through transport experiments using a non-pathogenic, green fluorescent protein-expressing Vibrio bacterial strain, we illustrate the importance of habitat structure, flow conditions, and inoculums size on fundamental transport phenomena, and with real-time particle-scale observations, demonstrate that microfluidics offer a compelling view of a hidden world.

Microfluidic devices can be used to visualize complex natural processes in real time and at the appropriate physical scales. We have developed a simple microfluidic device that mimics key features of natural porous media for studying growth and transport of bacteria in the subsurface.

Gözenekli Ortam Mikrobiyal Ulaştırma incelenmesi için basit mikroakışkan Sistemleri: Mikrodünya Pencere

Microbial growth and transport in porous media have important implications for the quality of groundwater and surface water, the recycling of nutrients in ...

Polydimethylsiloxane-polycarbonate Microfluidic Devices for Cell Migration Studies Under Perpendicular Chemical and Oxygen Gradients

This paper reports a microfluidic device made of polydimethylsiloxane (PDMS) with an embedded polycarbonate (PC) thin film to study cell migration under combinations of chemical and oxygen gradients. Both chemical and oxygen gradients can greatly affect cell migration in vivo; however, due to technical limitations, very little research has been performed to investigate their effects in vitro. The device developed in this research takes advantage of a series of serpentine-shaped channels to generate the desired chemical gradients and exploits a spatially confined chemical reaction method for oxygen gradient generation. The directions of the chemical and oxygen gradients are perpendicular to each other to enable straightforward migration result interpretation. In order to efficiently generate the oxygen gradients with minimal chemical consumption, the embedded PC thin film is utilized as a gas diffusion barrier. The developed microfluidic device can be actuated by syringe pumps and placed into a conventional cell incubator during cell migration experiments to allow for setup simplification and optimized cell culture conditions. In cell experiments, we used the device to study migrations of adenocarcinomic human alveolar basal epithelial cells, A549, under combinations of chemokine (stromal cell-derived factor, SDF-1&#945;) and oxygen gradients. The experimental results show that the device can stably generate perpendicular chemokine and oxygen gradients and is compatible with cells. The migration study results indicate that oxygen gradients may play an essential role in guiding cell migration, and cellular behavior under combinations of gradients cannot be predicted from those under single gradients. The device provides a powerful and practical tool for researchers to study interactions between chemical and oxygen gradients in cell culture, which can promote better cell migration studies in more in vivo-like microenvironments.

The control of chemical and oxygen gradients is essential for cell cultures. This paper reports a polydimethylsiloxane-polycarbonate (PDMS-PC) microfluidic device capable of reliably generating combinations of chemical and oxygen gradients for cell migration studies, which can be practically utilized in biological labs without sophisticated instrumentation.

Hücre Göç Çalışmaları altında Dik Kimya ve Oksijen Gradyanların için polidimetilsiloksan-polikarbonat mikroakışkan Cihazlar

This paper reports a microfluidic device made of polydimethylsiloxane (PDMS) with an embedded polycarbonate (PC) thin film to study cell migration under ...