Development Of A Cell Sorting Device Based On The Integration Of Porous Poly(Dimethylsiloxane) (PDMS) Membranes Into Layered Microfluidic Devices

Abstract

Layered microfluidic devices integrated with semi-porous membranes have been widely used for mass transport control, immunoassays, and blood cell sorting. The placement of a semi-porous membrane at the interface of two channel layers is crucial to minimize unwanted crossover of fluid flows between microchannels while allowing diffusive mixing of reagents. Several methods have been reported to seal off the crevices inevitably generated because of the thickness of the membrane. For example, the application of PDMS pre-polymer as a mortar layer could prevent the leakage along the membrane. This method provides robust and reliable bonding between two PDMS layers. However, in the case of thicker membranes and/or narrower channels, the mortar layer can clog the channels easily. We introduce an alternative strategy of directly using PDMS as a porous membrane itself to fabricate monolithic microfluidic devices. In this case, the integration of a porous PDMS membrane can be completed without clogging microchannels. To prepare porous PDMS membranes, a photoresist is utilized as posts on a silicon wafer. Therefore, a thin film of porous PDMS can be prepared by spin coated on the wafer. This method allows varying sizes of pores on a single membrane, compared to commercially available porous membranes with a fixed pore size. In addition, the wafer can be repeatedly used to create porous membranes. We demonstrate the use of this method to fabricate a cell sorter where a porous PDMS membrane between two layers of microchannel. This porous membrane has two porous regions: 10 μm and 20 μm regions. Thus, a cell sample (lymphocytes) loaded from the top microchannel can be filtered into small or lager size of cells through the porous membrane, and collected from the bottom microchannels.