Figure 2

Negative mold fabrication by three alternative methods: (1) Aluminum pre-mold is machined from a solid block of aluminum and immersed in PDMS within a petri dish then removed leaving a PDMS negative mold. (2) Agarose pre-mold is cast in a plastic template, where the template is machined from a rod using a lathe and drill press. The plastic template is filled with agarose solution that is cured to form a hydrogel that is removed and immersed in PDMS within a petri dish. After the PDMS is cured the agarose gel is removed leaving a PDMS negative mold. (3) A plastic mold can be used directly as the negative mold when the through holes are sealed by pressing a PDMS film over the bottom of the mold and securing with tape (Supplemental Video 2).