Microdevice fabrication

Soft lithography was used to fabricate microfluidic devices for cell culture. Briefly, the upper layer of the microfluidic device was produced by casting poly(dimethylsiloxane) (PDMS) against a photolithographically-prepared master that contained a positive relief pattern of a microchannel made of photoresist (SU-8, MicroChem). PDMS pre-polymer (Sylgard 184 Silicone elastomer kit, Dow Corning, Midland, MI) was thoroughly mixed with a curing agent at a weight ratio of 10:1 (PDMS:curing agent) and poured onto the microfabricated master. After curing at 65 °C overnight, the channel slab was removed from the master. The cross-sectional dimensions of the channel were 100 μm (width) by 50 μm (height). The bottom layer of the device was prepared by pouring a mixture of PDMS pre-polymer and curing agent into a 15 mm Petri dish and curing it at 65 °C overnight. For bonding, PDMS pre-polymer was mixed with curing agent at a weight ratio of 10:3 and spin-coated on a 100 mm Petri dish at 9000 rpm for 5 minutes. Subsequently, the channel layer was gently placed on the dish to form a thin film of uncured PDMS on the surface of the PDMS slab. The channel slab was then bonded to the bottom substrate to create an enclosed microchannel. The assembled device was incubated at 65 °C overnight to ensure complete bonding.