SU-8 microfluidic channels with porous sidewalls for biological applications

Microfluidic devices are currently being utilized in many types of BioMEMS and medical applications. In these systems, the interaction between the surface and the biological specimen depends critically on surface properties. The surface roughness and chemistry as well as the surface area to which the biomolecules or cells are exposed affect this interaction. Modification of the surface of microfluidic channels can improve the operation of the device by influencing the behavior of the biological specimens that are flowing through it. SU-8 is an epoxy-based, negative photoresist that has been previously used to create covered channels. Once cured, it is both chemically and thermally stable. It is also optically transparent above 360 nm, which allows optical measurements, including fluorescence imaging, to be taken inside the channel. SU-8 microchannels have been fabricated with a porous layer on the sidewalls by the photo-lithographic process, which is reproducible with precisely controlled channel dimensions. In order to attain these porous sidewalls, no additional fabrication steps are required outside the standard photo-lithographic process. The porosity of the sidewalls is a result of incomplete cross-linking of the polymer. The obtained porous surfaces can be specially treated to provide conditions preferable for biological interactions. The porous layer increases the internal surface area available on the sidewalls, which make these microfluidic channels preferable for biological applications. This paper describes the details of the fabrication process and the experiments that verify the benefit of using SU-8 microchannels with porous sidewalls.