Dual function magnetic PDMS microsphere-based microfluidic valve and mixer

To control flow and enhance mixing in microfluidic chips, we have developed a dual function magnetic poly(dimethylsiloxane) (PDMS) microsphere-based microfluidic valve and mixer. T-shape microchannels were formed by soft lithography in PDMS. A crosslinked PDMS magnetic microsphere was placed at the channel intersection, and manipulated by an external magnetic field. The microsphere was controlled to block or open selected microchannel orifice and functioned as a valve. Vibration of this microsphere was induced by a rotating magnetic field, could disturb laminar flows and enhance fluid mixing. Elastomeric PDMS magnetic microspheres, with diameters ranging from 100 to 500mum and containing 5-15 wt% ferromagnetic nanoparticle content, were synthesized by an oil-in-water (O/W) solvent-evaporation microencapsulation technique. A new ethylenediaminetetraacetic acid (EDTA) titration method was developed and validated to measure magnetite content in the resulting microspheres. Preliminary results suggest this device has a fast response time of less than 1 second and enhance mixing in several hundred micrometers.