A micro fluidics system includes a closed, expandable volume for mixing a fluid, and a flexible membrane for allowing mixing in the closed, expandable volume. The system further includes a surface having at least one channel for fluidically coupling a first side of the surface to the closed, expandable volume on a second side of the surface. The channel includes a first channel opening fluidically coupling the first side of the surface to the channel and a second channel opening fluidically coupling the channel to the closed, expandable volume. The expandable volume is defined by the flexible membrane closing the second channel opening when there is no fluid in the expandable volume.