The GeSiM hydrogel valves are small silicon chambers filled with hydrogel particles of defined size that dramatically shrink upon heating to more than 34°C, therefore opening the normally closed microvalves. Different valve designs are available, the standard PV6 valve being vertically flown through by the liquid. By mounting it inside a standard UNF fitting, a microfludic injector is obtained that controls an inlet channel of a branched (e.g. T/Y-shaped) MicCell fluid system. In an alternative design, the hydrogel valve is connected to a reservoir via a tube. The valve is controlled by an electronic module in the Fluid Processor.