Patent ID: 8101037

Claim:
A method for forming capillaries in a substrate for a microfluidic device comprising: providing a substrate of a polymeric material; forming microchannels in a surface of the substrate; reversibly sealing a cover layer on the substrate surface over the microchannels enclosing the microchannels by the cover layer and the substrate; filling the enclosed microchannels with a liquid sacrificial material which becomes solid after the filling; removing the reversibly sealed cover layer from the substrate and microchannels filled with the solid sacrificial material; affixing a top cover over the filled microchannel by forming a semi-permeable membrane material in situ over the microchannels to form the top cover comprising a membrane of the membrane material; removing the sacrificial material from the microchannels to form microcapillaries free of the sacrificial material, the sacrificial material essentially non-reactive and non-soluble with the material of the substrate to the extent it does not bond with the material of the substrate, and the sacrificial material non-reactive with the semi-permeable membrane material and the substrate material to the extent it does not bond with or materially degrade the properties of or bonding of the membrane material, and the substrate.