the device consists of three layers made from pdms prepolymer and curing agent ( sylgard 184 , dow corning co. , midland , mi ) at a 10:1 ratio . the top and bottom layers are molded against a master mold made by standard photolithography using the negative - photoresist su-8 ( su-8 , microchem co. , newton , ma ) . the master molds were silanized in a desiccator for 2 hours ( united chemical tech . , the height of all top layer and bottom layer features is 100 m except for those in the top layer of figure 3 which is 30 m . the pdms molds of the top and bottom layers were cured in a 120c oven for over 2 hours . the middle - layer membrane was made by spin - coating a 30 m pdms layer on a silanized silicon - wafer at 1500rpm for 90 seconds and then curing in a 120c oven for 30min . all layers were bonded together using oxygen plasma treatment ( spi plasma - prep ii , structure probe , inc . , west chester , pa ) for 30 seconds . the three layers of the device are bonded together using oxygen plasma for 30 seconds . in the first step , the thin pdms membrane , while still on the silicon wafer ( or any flat substrate ) , is bonded to either the top or bottom layer and then the two bonded layers are detached from the wafer . holes are punched into the bonded middle layer , using a 350 m biopsy punch ( ted pella inc . , redding , ca ) , for the check - valve and switch - valve components for all figures except figure 3e which used a 29 gauge insulin syringe . for check - valve components , a hole is punched in the downstream region of the cavity directly after the gap . switch - valves have holes punched to interface access channels of the top and bottom layers . to ensure efficacy of the components , the circular shape of the biopsy punch can be molded into either or both the bottom layer and top layer so the hole is accurately punched every time ( as shown in figure 4a ) . for the second step , the top layer and the bonded middle and bottom layers are bonded . the gap regions of the components are rendered unable to permanently bond to the middle membrane by placing a pdms stamp which has extruding features that correspond to the gap regions negating exposure to oxygen plasma . finally in step three , all layers are aligned and bonded together ; the device is incubated at 60c for 1 minute to enhance the bond strength . the device should not be used directly after being placed in a vacuum since it can cause some components to open ; in which case waiting about 30 minutes allows air to penetrate back in . the dependence of threshold pressure on the geometry of a component was characterized for three lengths of both l1 and w ( as shown in fig . the threshold pressure was determined by continuously measuring the differential pressure across the component with a differential pressure transducer ( model px139 - 005d4v , omega eng . inc . , stamford , ct ) as a syringe pump continuously pressurized the microchannel with a flow - rate of 6ml / hr . the pressure transducers were connected to access microchannels that were located directly before and after the component for quicker response timing and more accurate readings . the threshold pressure for a given trial was determined by the peak pressure in the pressure histogram as measured by the transducer as the component pressurized to a critical limit and opened . the average of three trials was plotted to give the relationship between the threshold pressure and the component dimension . threshold pressures for components with a constant w of 1 mm with l1 values of 800 m , 400 m , and 200 m as well as for a constant l1 of 800 m with w values of 1000 m , 500 m , and 250 m are provided in si . the oscillator pressure measurements were performed by measuring the gauge pressure of both inlets simultaneously using two pressure transducers ( model px26 - 015dv , omega eng . measurements were taken every 100ms and the graphs are the moving time - average of 50 minus the measured zero value for each sensor . the device consists of three layers made from pdms prepolymer and curing agent ( sylgard 184 , dow corning co. , midland , mi ) at a 10:1 ratio . the top and bottom layers are molded against a master mold made by standard photolithography using the negative - photoresist su-8 ( su-8 , microchem co. , newton , ma ) . the master molds were silanized in a desiccator for 2 hours ( united chemical tech . , the height of all top layer and bottom layer features is 100 m except for those in the top layer of figure 3 which is 30 m . the pdms molds of the top and bottom layers were cured in a 120c oven for over 2 hours . the middle - layer membrane was made by spin - coating a 30 m pdms layer on a silanized silicon - wafer at 1500rpm for 90 seconds and then curing in a 120c oven for 30min . all layers were bonded together using oxygen plasma treatment ( spi plasma - prep ii , structure probe , inc . , west chester , pa ) for 30 seconds . the three layers of the device are bonded together using oxygen plasma for 30 seconds . in the first step , the thin pdms membrane , while still on the silicon wafer ( or any flat substrate ) , is bonded to either the top or bottom layer and then the two bonded layers are detached from the wafer . holes are punched into the bonded middle layer , using a 350 m biopsy punch ( ted pella inc . , redding , ca ) , for the check - valve and switch - valve components for all figures except figure 3e which used a 29 gauge insulin syringe . for check - valve components , a hole is punched in the downstream region of the cavity directly after the gap . switch - valves have holes punched to interface access channels of the top and bottom layers . to ensure efficacy of the components , the circular shape of the biopsy punch can be molded into either or both the bottom layer and top layer so the hole is accurately punched every time ( as shown in figure 4a ) . for the second step , the top layer and the bonded middle and bottom layers are bonded . the gap regions of the components are rendered unable to permanently bond to the middle membrane by placing a pdms stamp which has extruding features that correspond to the gap regions negating exposure to oxygen plasma . finally in step three , all layers are aligned and bonded together ; the device is incubated at 60c for 1 minute to enhance the bond strength . the device should not be used directly after being placed in a vacuum since it can cause some components to open ; in which case waiting about 30 minutes allows air to penetrate back in . the dependence of threshold pressure on the geometry of a component was characterized for three lengths of both l1 and w ( as shown in fig . the threshold pressure was determined by continuously measuring the differential pressure across the component with a differential pressure transducer ( model px139 - 005d4v , omega eng . inc . , stamford , ct ) as a syringe pump continuously pressurized the microchannel with a flow - rate of 6ml / hr . the pressure transducers were connected to access microchannels that were located directly before and after the component for quicker response timing and more accurate readings . the threshold pressure for a given trial was determined by the peak pressure in the pressure histogram as measured by the transducer as the component pressurized to a critical limit and opened . the average of three trials was plotted to give the relationship between the threshold pressure and the component dimension . threshold pressures for components with a constant w of 1 mm with l1 values of 800 m , 400 m , and 200 m as well as for a constant l1 of 800 m with w values of 1000 m , 500 m , and 250 m are provided in si . for all components , the oscillator pressure measurements were performed by measuring the gauge pressure of both inlets simultaneously using two pressure transducers ( model px26 - 015dv , omega eng . measurements were taken every 100ms and the graphs are the moving time - average of 50 minus the measured zero value for each sensor .