Low-pressure bonding of monolithic SU-8 microfluidic devices

Abstract

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 24 h 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.