Low-pressure bonding of monolithic SU-8 microfluidic devices

Crosslinked SU-8 is a promising material for microfluidic and bio-MEMs applications because of its excellent optical properties, chemical stability, biocompatibility and low absorption of analytes. Thus, devices made out of SU-8 are very well suited for specialized applications such as live cell imaging. However, the design of monolithic SU-8 devices is often limited because the bonding of SU-8 layers usually requires a special bonding apparatus. Here, we present a reliable and user-friendly bonding method for SU-8 layers, which eases the fabrication of 3D SU-8 microfluidic devices. The top layer and the main layer of an SU-8 channel were bonded at pressures of 1, 2, 3, 4 and 8 kPa. The resulting bonding was free of voids in all cases, and the maximum bond strength was 6.5 +/- 1.9 MPa, which is sufficient for most microfluidic applications. All the devices exhibited excellent stability under flow conditions. The device bonded at the lowest applied pressure (1 kPa) was tested for 24h under a flow shear stress of 280 dynes cm(-2) and showed no sign of leakage. Thus, the presented low-pressure bonding is a promising technique to fabricate SU-8 microfluidic devices.