manuf_pdms

manuf_pdms - Harvard-MIT Division of Health Sciences and...

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Manufacturing a PDMS microfluidic device via a Silicon Wafer Master Eric Lam, Tri Ngo Abstract This document describes the manufacturing process for a general microfluidic device which uses either pipette tips, O-Ring or non O-Ring syringe reservoirs as a fluid delivery mechanism. The manufacturing process does not involve much labor but requires a lot of waiting. The entire process takes a minimum of 5 hours but optimally the process takes 9 hours. First the PDMS is mixed and degassed for approximate 1 hour. Then the activated PDMS is poured onto the master and baked in an oven. After a minimum of 4 hours of baking, the PDMS is unmolded from the master and processed further. Next a glass slide is cleaned and the PDMS layer containing the microfluidic features are bonded to the glass slide. Finally the device is completed by attaching either pipette tips or pre-cut syringe tubes. Mixing the PDMS In preparation for this stage obtain a some unpowdered disposable gloves, a disposable plastic knife and a disposable plastic cup. PDMS should be mixed in a 1:10 ratio of curing agent and PDMS monomers. The PDMS monomers are much more viscous than the curing agents. For this example implementation, we will be using a mixture which consists of 7g of curing agent and 70g of monomer. Harvard-MIT Division of Health Sciences and Technology HST.410J: Projects in Microscale Engineering for the Life Sciences, Spring 2007 Course Directors: Prof. Dennis Freeman, Prof. Martha Gray, and Prof. Alexander Aranyosi
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The PDMS can be mixed in a disposable plastic cup, not unlike the cups found near water coolers. Wider cups may be better because they expose a larger surface of the contained fluid to air, which will aid in degassing the PDMS later. While PDMS is very safe, it is a sticky and messy substance to work with. You should put on some disposable gloves before touching the containers or tools which come into contact with uncured PDMS. Use unpowered gloves to prevent contaminating the PDMS. At this stage, you should not be too concerned with dust or other particles falling into the PDMS, they will be absorbed into the bulk of the device and will usually not affect the channels. However, powdered gloves should not be used the unmolding and bonding stages of fabrication. Turn on the electronic scale and adjust the device so that it reads the correct units, in this case we adjust it to read in grams. Place the cup on the scale, and press the "Tare" button to rezero the scale.
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Slowly pour 70g of PDMS (base) monomer into the cup. Press the Tare button to rezero the scale. Then pour approximately 1/10 the amount of PDMS curing agent into the cup (7g), for a total mass of 77g for the entire mixture. You will not notice any immediate visible reactions when these two fluids come in contact. In actuality, the order in which the curing agent and PDMS base is added to the cup is not important since they will thoroughly be mixed anyway. Take the cup off the scale and begin to stir the PDMS mixture using the disposable
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This note was uploaded on 01/24/2010 for the course HST. 410J / taught by Professor Alexanderaranyosi during the Spring '07 term at MIT.

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manuf_pdms - Harvard-MIT Division of Health Sciences and...

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