MCG3143‐ Microfluidic , Dr Fenech MCG3143 INTRODUCTION TO MICROFLUIDICS LAB MANUAL (V1.2) SAFETY Personal Protection Equipment: o o o o o o Glove Safety glasses Lab coat Long pants Closed shoes Hair tied University of Ottawa, Mechanical Engineering Manual prepared by Dr Fenech with the participation of N. Ahmadi, O Gliah, J. Morse. (2012) 1/6 MCG3143‐ Microfluidic , Dr Fenech A‐ Enjoy the presentation of the introduction of microfluidic (PPT presentation) B‐ The objectives The objectives are to demonstrate key concepts in the applications of microfluidics. Fundamental concepts in microfluidics include principles of separation, diffusion, and flow regimes. In this lab, we will run a simple set up to display how to fabricate the chips themselves, and to display fundamental properties of fluid flow in microchannels. B‐ Introduction: Microfluidics deals with the behavior, precise control and manipulation of fluids that are geometrically constrained to a small, typically sub‐millimeter. Microfluidics enables processes such as purification, chemical reactions, and biological assays to be integrated into LOC technology. A lab‐on‐a‐chip (LOC) is a device that integrates one or several laboratory functions on a single chip of only a few square centimeters in size. A lab‐on a‐ chip (LOC) technology has experienced a rapid growth within the past decade. In particular in biomedical field for the miniaturisation of point of care analysis, cell sorting in cancer detection, stem cell culture plate, DNA separation, or immunoassay almost other. The basis for most LOC fabrication processes is photolithography. Initially most processes were in silicon, but because of demands for e.g. specific optical characteristics, bio‐ or chemical compatibility, lower production costs and faster prototyping, new processes have been developed such as glass, ceramics and metal etching, deposition and bonding, PDMS processing (e.g., soft lithography). Poly_dimethylsiloxane (PDMS) introduced in the 1998, by utilizing the soft lithographic method of molding and patterning structural features with PDMS, microfluidic devices can be easily fabricated in academic institutions, thus facilitating the growth of academic research in LOC technology. C‐ Calculation: Reynolds number: is a dimensionless number which essentially defines the ratio of inertial force to viscous force for a given flow condition, and is defined as Re =ρLvav/μ 2/6 MCG3143‐ Microfluidic , Dr Fenech Where: ρ is the fluid density, L is the characteristic length scale, vav is the average velocity of the fluid, and μ is the viscosity. The Reynolds number in microfluidic devices is typically <1 and thereforethe flow within the microchannels is laminar flow. Stokes number: describes the interaction of the particle to its surrounding flow field and is given by the ratio of the particle relaxation time to the characteristic time of the fluid. Particles with Stokes number Sk <<1 can be assumed to be always in steady‐state Stokes number is defined as St =τr /τf Where:τris the particle relaxation time and τfis the characteristic time, and τrand τfcan be respectively defined as τr=ρd2/18μ,τf=L/vav where ρ is the particle density, d is the particle diameter, μ the fluid viscosity, Lthe characteristic length scale, and vav is the average velocity of the fluid. D‐ Fabrication 1. Verify the content of your microfluid box, note your names and the number of your box in the lab book. In addition you will need ‐ One bottle of distilled water ‐ Tube support ‐ One transparency ‐ Two glace slides per chip ‐ Three 1.5 tubes ‐ Few pipette tips ‐ Aluminum foil ‐ Skink film During the lab you will fabric your own chip, using a premade wafer for the mixer chip and making your own wafer in a simplest way for the capillarity chip. 2. An array of microfluidic designs was drafted in AUTOCAD drafting software, although simpler software may be used, as shown in figure (1). 3/6 MCG3143‐ Microfluidic , Dr Fenech Figure 1 : Exemple of microfluidic designs 3. Tape a piece of polyolefin shrink film (packing film) onto a transparency slide with the green tape. Place this in the printer so that the ink will be deposited onto the shrink film, not the transparency. as shown in figure (2), put it in the lower drawer with model facing down.. 4. Once printed, remove the transparency from the shrink film. Cut the contour where the tape was in place. Place the shrink film onto in the oven set at 180oC, this should take a few seconds until the shrink film has stopped shrinking. Remove it from the oven. Rapidly flatten it. 5. Cut out the desired shape from the shrunken film. Carefully tape the shape (regular tape) to a glass slide, making sure none of the design is covered with tape and giving enough room to remove it later. 6. Prepare the PDMS (with the TA). PDMS comes in two parts, the polymer and a curing agent. For this we will use 10:1 ratio of polymer to curing agent respectively. Place the designated dish on the scale and weigh it. Zero the scale. Pour in the polymer. Note the weight added. Next, using another dish, follow the same procedure for the curing agent except at 1/10 the amount of curing agent to a separate dish as you did the polymer. Combine the two parts into one and mix. Make sure it is well stirred. 4/6 MCG3143‐ Microfluidic , Dr Fenech 7. In order to degas the silicon, place the container in the vacuum chamber. Seal the chamber and turn on the device. Let it run for approximately 10 minutes. Let it run until all of the bubbles have been removed. *Note* you may need to remove the tube a few times to allow some of the developed foam on top of the PDMS to disappear. 8. Create an aluminum foil "boat" around the wafer. Pour the settled and bubble free PDMS over your design. 9. Set the hotplate temperature to 150ºC. Once at 150ºC, cure the PDMS for 10 minutes. 10. Take the mold off the hot plate. Careful it is hot. Let it cool. 11. Once cool, take the PDMS out of the silicon mold. This may take some effort. Peel the PDMS off the shrink film design. Cut out your mold from the PDMS, leaving some room around it on all sides. Make sure you are aware which side has the features. 12. Clean the PDMS side that has the features with tape (apply and peel off). Punch out the ends, making sure you are punching from the side with features through to the other side. 13. Seal the bottom of the channel with double face tape on a glass slide. This gives the channel 4 solid walls. 5/6 MCG3143‐ Microfluidic , Dr Fenech 14. Inserted pipette tip filled of food colors at the inlet of the device. Let the capillary effect pumps the fluids through. Note the color as it flows along the branched channels. 15. Verify the content of your microfluid box. Give back ‐ The bottle of distilled water ‐ Tube support ‐ The transparency ‐ 1.5 tubes E‐ Analysis 1. How are the channels formed in the microfluidic device? Describe the process. Look in the literature a more accurate way to do it with precise dimensions. 2. What is high‐aspect ratio and why is it important for microfluidics? 3. What are the reasons why microfluidic devices are advantageous over other techniques? 4. What mechanical function causes the fluid to flow? 5. Compute an estimate of the flowrate using the pipette tip volume. 6. Compute an estimate of the Reynolds numbers of the flow 7. Compute an estimate of the Stokes numbers for a red blood cell (7 um) 8. Why does the fluid become a gradient, and not just a single homogeneous liquid? 9. What mechanical function causes the mixing of colors? 10. What possible use could a gradient generator have for biomicrofluidics? (look for example in the literature) 11. How could you achieve a more efficient mixing? Bibliography 1. Diep Nguyen, Jolie McLane, Valerie Lew, Jonathan Pegan, and Michelle Khine. Shrink‐film microfluidic education modules: Complete devices within minutes. Biomicrofluidics. 2011, Vol. 5. 2. D Junker, M Nannini, S Ricoult, R Safavieh. Hands‐on Interdisciplinary Course on Micro‐ and Nano‐biotechnologies. 2011. 3. Collectif, editor F. A Gomez, wiley‐intersience .Biological application of microfluidics. 6/6