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Experiment Platforms Microfluidic Chambers Establishing Fluid Flow Microscope Measuring Flow Rates Camscope Taking Measurements Using Multiple Data Sets to Organize Your Measurements Saving Your Results Analyzing Results Laboratory Equipment and SuppliesExperiment Platforms The experiment platforms for the microfluidics laboratory consist of a microfluidic chamber and a video microscope that is controlled via a computer. Microfluidic Chambers We will be using a variety of chamber designs throughout the course of the term; you might even design one of your own for your project. One example design is a long (approximately 30 cm) slender (250 micrometers wide, 75 micrometers high) channel that runs between five reservoirs that can be filled with test solutions and cells. The Harvard-MIT Division of Health Sciences and TechnologyHST.410J: Projects in Microscale Engineering for the Life Sciences, Spring 2007Course Directors: Prof. Dennis Freeman, Prof. Martha Gray, and Prof. Alexander Aranyosiimage below illustrates the topology of this design; the actual layout may differ somewhat. If the two-reservoir end is used as the input, then the solutions in those reservoirs will flow side-by-side as they enter the central channel. Such flow is said to be "laminar" because the fluids seem to be in layers. As the fluid progresses down the channel, the fluids will gradually mix by diffusion. Such mixing is illustrated in the following photograph. Alternatively, the three-reservoir end can be used as input, in which case the flow will be "tri-laminar." This configuration can be useful for mixing cells contained in the central reservoir into a test solution contained in the other two reservoirs.Establishing Fluid Flow A variety of methods have been used to push fluids through microchambers, including macroscopic pumps (e.g., syringe pumps, peristaltic pumps, etc.) and electrically driven flows (e.g., electro-osmosis or electrophoresis). In this lab, we recommend that you use gravity flow. With typical designs, a few millimeter difference in fluid level is sufficient to drive flow rates on the order of micrometers per second, which are satisfactory for most experiment designs. Input and output ports connect the microfluidic channels to macroscopic fluid reservoirs, as shown in the following photograph. A variety of reservoir designs are possible. Before running experiments, the device should be completely filled with fluid. In most cases, this can be accomplished by adding fluid to one reservoir and allowing capillary action to pull fluid through the rest of the device. As the fluid reaches other reservoirs, additional fluid can be added to those reservoirs to help fill the rest of the device more quickly. Be careful not to introduce air bubbles with adding fluid. Alternatively, you can attempt to fill stubborn devices by applying suction to one reservoir. If you need to do this, we recommend speaking to an instructor before proceeding. You should avoid applying positive pressure (pushing), since doing so could rupture the bond between the PDMS and glass, ruining your device. Before leaving the lab, please flush your chamber with deionized water and store the chamber with all reserviors filled with dionized water. This simplifies starting the flow when the chamber is next used. Microscope The microfluidics chambers can be held in place on the stage of the microscope using magnets. The stage has x and y control knobs plus a calibrated focus control knob for z. The microscope illumination system can be turned on with a toggle switch on the back of the microscope. The intensity of the illumination can be adjusted with a control on theright side of the base of the microscope. The microscope has 3 objectives: 4X, 10X, and 20X, which focus an image of the chamber onto a video camera. Measuring Flow Rates Quantitative interpretation of data from microfluidic systems often requires knowledge of the flow rates. Although flow rates can in principle be determined by measuring the time it takes for some known volume of fluid to flow through system, it is often more convenient to measure flow rates by tracking microscopic particles that are suspended in the fluid. Microscopic polystyrene beads with diameters on the order of 1 micrometer are available for this purpose. Because of fluid viscosity, the flow profile across the channel is approximately parabolic, with faster flow near the center than near the channel walls. For that reason, we use beads that are neutrally bouyant in water (by virtue of a tiny air bubble in each bead!). If used in solutions with high concentrations of solutes, these beads can float to the top of the channel (where the fluid moves much less quickly). Camscope A computer running Linux is attached to the video camera via FireWire. You will use a program called camscope to collect and analyze data from this camera. What follows are some instructions to get you started. This program was designed for this lab, and has many important features that are not described below. To take full advantage of everything this program offers, we recommend you read further information on camscope. Here are a few of the things you an do with camscope: • Capture images from the camera • Capture sequences of images (movies) • Play back previously recorded images and movies • Measure distances • Measure velocities • Measure brightnesses • Measure cell sizes To start, log in to the computer using the username camscope and the password camscope. Once you log in, there should be a console (a window with a command prompt) visible. If not, click on the icon that looks like a monitor to open one. Since multiple groups will be using each computer, you will need to use directories to keep your data separate. You can name this directory anything you want, as long as the name is unique. To make a directory and enter it, type commands like the ones below into the console. > cd > mkdir I_Love_Camscope > cd I_Love_CamscopeOnce you are in your own directory, type > camscope to activate the main program. When camscope starts, it will look like the image below. This is the entire interface: no menus, no pop-up windows, no miraculously appearing or disappearing buttons, no monkeys to punch. There are a few controls that don't have visible buttons, but not many. These are documented at the link provided above. The main part of the screen is taken up by the image. This image is


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MIT HST 410J - Experiment Platforms

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