BS in Materials Engineering
Materials Engineering Department
A microfluidic device was synthesized out of polydimethyl siloxane (PDMS) to simulate the structure of the alveolar-capillary interface of the human lung. Soft lithography techniques were used to build a mold structure out of SU-8 epoxy at heights ranging from 30µm to 110 µm on a silicon substrate, with the 70 µm structure working the best. A mixture of 10:1 Sylgard 184 elastomer was then cast using the mold, and cured at a temperature of 80oC. For the porous membrane, the PDMS was spun on at 6000rpm for 30 seconds using a spin coater to produce a membrane 10µm thick with pores 10µm in diameter. The three layers were then plasma treated, aligned under an optical microscope with a float layer of methanol and set back in the furnace for 15 minutes. Various methods of bonding were attempted, including partially uncured PDMS bonding, a sandwich technique which used weights on both sides of the device while it cured, and placing the device under a vacuum before curing. Fluid was pushed through the channels to check for leaks, with the plasma treating and methanol float layer method attaining the most complete bond. To simulate the motion of a human lung, the outer channel was alternately pressurized and depressurized to bend the walls of the center channel, which caused the porous membrane to stretch and compress as in a real lung. The devices did not have a complete bond between the channel layers and did not seal in the liquid flowing through the channels. It is recommended that the PDMS to PDMS bonding techniques used are further investigated or replaced by better methods.