Microparticle switching devices for use in implantable reservoirs

A switching device for use with a voltage source effective to generate a voltage having a selected polarity, comprising

• a polymer-matrix microparticle composed of a matrix of crosslinked polyionic polymer filaments and defining a surface,
• a first chamber containing an electrolyte medium that is in contact with an interior surface region of said surface,
• a second chamber containing an electrolyte medium that is in contact with an exterior surface region of said surface,
• said first chamber and said second chamber being configured such that said interior surface region is substantially less than said exterior surface region, and
• electrical connections adapted to connect the electrolyte medium to such a voltage source, for applying across said first chamber and said second chamber, a voltage having a selected voltage level and polarity,
• whereby the device allows electric current flow between the first chamber and the second chamber when the voltage has one of two possible polarities, and substantially blocks current flow between the first chamber and the second chamber the other of two possible polarities.