A master template was prepared using soft lithography (Fig. 1d) on a four-inch silicon wafer (University Wafer, Boston, MA) in a manner similar to Taylor et al.15, 25 A first layer of photoresist defined 10 μm wide and 100, 200 or 500 μm long axonal extension microchannels (Fig. 1e,f). SU-8 2002 (Microchem, Woburn, MA) was spun onto the wafer at 1,000 rpm to give a 3 μm layer. The layer was exposed to UV using a photomask on an EVG620 (EV Group, Tempe, AZ) mask aligner. The wafer was then developed for approximately 60 seconds in SU-8 developer (Microchem, Woburn, MA) and subsequently hard-baked at 150°C for 30 minutes.
