1.5 mm biopsy punch

Microfluidic channels of dimensions 200 × 75 μm² (width by height) were designed using CleWin software, and PDMS microfluidic devices were fabricated from molds created using standard photolithography. In brief, the chrome mask design was patterned onto a 4 in. Si wafer coated with SU-8 2075 photoresist. When the Si-wafer molds were ready, PDMS mixture from combining Sylgard 184 base to curing agent at a 10:1 ratio was poured onto the Si wafer and baked at 70 °C for ~20 min. The PDMS replicas were then bonded to glass slides via oxygen plasma treatment in a plasma cleaner (PDC-32G, Harrick Plasma). Cube-shaped PDMS blocks (0.5 × 0.5 × 0.5 cm³) were used as microfluidic connectors for attachment of PTFE tubing to the microfluidic devices. The connectors were perforated with a 1.5 mm biopsy punch (Integra Life Sciences, Mansfield, MA) and attached to the PDMS-glass devices using freshly degassed PDMS. The microfluidic devices were then left to bake in an oven at ~80 °C for 30 min, and the microchannels were later treated with Aquapel, flushed with nitrogen, and baked at ~80 °C for 30 min.