An arrangement is provided including an electrode extending to an electrode tip for contacting a workpiece. The pressure-regulating chamber includes: an inlet port connected to the ink reservoir via a supply conduit; an outlet port connected to the upstream ink conduit; a vent open to atmosphere; and a float valve for maintaining a set level of ink in the pressure-regulating chamber. Polymers may include compositional gradients allowing attached ligands to be presented as continuous gradients across a surface.