A microfluidic device comprising an array of fluidically interconnected unit cells, wherein each unit cell comprises: a) a first microfluidic flow path in fluid communication with a first microfluidic bus line that is in fluid communication with a first source reservoir; b) a reaction chamber directly connected to the first flow path, wherein at least a portion of one wall of the chamber is permeable to gas and not to liquid; c) a first valve and a second valve situated in said first microfluidic flow path so as to form a defined segment of the first microfluidic flow path between the two valves (V1 and V2); d) a second microfluidic flow path in fluidic communication with: 1) said first microfluidic flow path at a junction between said first and second valves, and 2) a second microfluidic bus line in fluid connection with a second source reservoir e) a third valve situated 1) in said second microfluidic flow path, or 2) in said second microfluidic bus line positioned between the second microfluidic flow path of said unit cell and the second microfluidic flow path of an adjacent unit cell; wherein the defined segment of the first flow path has a defined volume that is less than the volume of the reaction chamber, and at least a portion of one side of the segment is permeable to gases and not to liquid; wherein the reaction chamber is configured for blind filling through a flow channel connected directly thereto, wherein the flow channel comprises the defined segment of the first flow path and is the only flow channel directly connected to the reaction chamber; and wherein the unit cells are configured such that the defined segment of the first flow path can be filled with a fluid from the second source reservoir with the first valve and the second valve closed; and then upon opening the first and second valves, a fluid from the first source reservoir can displace the defined volume of fluid from the defined segment, follow, and mix with the defined volume of fluid in the reaction chamber. a) a first microfluidic flow path in fluid communication with a first microfluidic bus line that is in fluid communication with a first source reservoir; b) a reaction chamber directly connected to the first flow path, wherein at least a portion of one wall of the chamber is permeable to gas and not to liquid; c) a first valve and a second valve situated in said first microfluidic flow path so as to form a defined segment of the first microfluidic flow path between the two valves (V1 and V2); d) a second microfluidic flow path in fluidic communication with: 1) said first microfluidic flow path at a junction between said first and second valves, and 2) a second microfluidic bus line in fluid connection with a second source reservoir 1) said first microfluidic flow path at a junction between said first and second valves, and 2) a second microfluidic bus line in fluid connection with a second source reservoir e) a third valve situated 1) in said second microfluidic flow path, or 2) in said second microfluidic bus line positioned between the second microfluidic flow path of said unit cell and the second microfluidic flow path of an adjacent unit cell; 1) in said second microfluidic flow path, or 2) in said second microfluidic bus line positioned between the second microfluidic flow path of said unit cell and the second microfluidic flow path of an adjacent unit cell;