A fluid circuit includes a membrane having a first side, a second side
opposite the first side, and a pore extending from the first side to the
second side. The circuit also includes a first channel containing fluid
extending along the first side of the membrane and a second channel
containing fluid extending along the second side of the membrane and
crossing the first channel. The circuit also includes an electrical
source in electrical communication with at least one of the first fluid
and second fluid for selectively developing an electrical potential
between fluid in the first channel and fluid in the second channel. This
causes at least one component of fluid to pass through the pore in the
membrane from one of the first channel and the second channel to the
other of the first channel and the second channel.