Films of the PDMS used to make MN casting molds were cast at a thickness of 2 to 3 mm on a glass dish and cured at 37°C for 2 days and then at 60°C for 4 hours under vacuum. Circular discs with a radius of 1.25 cm were then punched from the silicone film. A minimum of three discs were used for each solvent test. The discs were individually weighed, placed in a vial, and covered with 50 ml of the solvent to be tested. The container was sealed and the discs were allowed to soak for 2 hours. After soaking, each disc was removed from the solvent, lightly blotted onto absorbant paper (Kimwipes, Kimberly Clark, Irving, TX), and then quickly weighed to minimize evaporation of solvent. The percent swelling was determined as the difference between the weight of the disc before and after soaking, and dividing by the initial disc weight.