Device Design: Stage 2 (Modified Microchannel Design) Device Objective –To test the viability of a two-level passive micro-fluidic device Modifications from Stage 1 –Moved reservoir positions to fit existing packaging –Created discrete flow paths to test flow on individual layers and between layers –Increased all dimensions to facilitate fabrication and testing Device Logic –Five distinct fluid paths –11 I/O –Two distinct channel levels –One interconnect level –One top cover level Reservoir (I/O) Interconnect

Device Design: Stage 2 (Modified Microchannel Design) Device Geometry –Chosen for process compatibility –Rectangular micro- channels –Square interconnects –Circular reservoirs Materials –SU-8 used as a mold for the PDMS layers –All PDMS layers stacked on a Silicon substrate Critical DimensionValue PDMS Layer Height 100  m Micro-channel Width 500  m Interconnect Width 1000  m Interconnect Depth 1000  m Reservoir Diameter 0.4 cm

Device Design: Stage 2 (Modified Microchannel Design) Process Sequence 1.Begin with four polished Si wafers 2.Spin SU-8 (negative photoresist) on the Si wafers and pre-bake at 95°C 3.Align each of the four wafers with one of four masks and expose the SU-8 to ultraviolet light, then post-bake at 95°C 4.Develop the SU8 so that the unexposed areas are removed –Results in four distinct SU8 molds 5. Spin PDMS on the SU8 molds less than the vertical dimension of the SU-8 protrusions –Mix PDMS (Sylgard 184, Dow-Corning) 10:1 with curing agent –Spin on PDMS –Dip the Si wafer in a sodium dodecyl sulfate(SDS) adhesion barrier and allow it to dry naturally –Bake in box furnace for 2 hours at 70°C

Device Design: Stage 2 (Modified Microchannel Design) 6. Delaminate and stack all four PDMS layers in the following order: Micro-channel Layer 1, Interconnect Layer, Micro-channel layer 2, Top Cover Layer

Device Design: Stage 3 (Pressure Actuated Valve Design) Fluid Flow Modeling –Assumed fluid flow rate based on fluid velocity Based on literature search: 1500 cm/minute = 2.5 E5 μm/sec Fluid flow rate: 1.25 E 10 μm 3 /sec = cm 3 /sec –Used the fluid flow rate calculated to determine the following properties for the fluid flow path: Fluidic resistance and pressure gradient: R = ΔP/Q [(N*s)/m 5 ] Reynolds number: R e = (  vD h )/μ Velocity: v = Q/A Cycle time t = Length/v

Device Design: Stage 3 (Pressure Actuated Valve Design) Fluid Flow Modeling Results –R (circular cross section) = 8μL/(πr 4 ) μ = fluid viscosity= 0.01 g/sec*cm L = Length of channel r = Radius of channel –R (rectangular cross section) ~ 12μL/(wh 3 ) w = Width of the channel h = Height of the Channel –Total Fluidic Resistance = R R + R M + R I + R V R R + R M + R I + R V R Total