The development of a printing operation that exploits molecular gates must address two major issues: (1) inking the tool bit surface, and (2) transferring this liquid from the toolbit on to a substrate. The first step is accomplished by the use of molecular gates. The toolbit is in essence a network of microfluidic channels that supply a set of addressable molecular gates that in turn draw the liquid out the surface. The transfer of liquid on to the substrate is modulated by carefully controlling the surface properties of the toolbit. Printing proceeds in the following steps:

1. The microfluidic channels are pressure filled.
2. A potential is applied across a membrane containing molecular gates, mediating between two micro channels. The lower micro channel is charged up.
3. The application of a small voltage on a buried electrode of the toolbit surface electro-osmotically draws fluid to a well on the toolbit surface, thus “inking” the toolbit.
4. Ink is then transferred from the toolbit surface to the substrate.

To modulate the transfer of liquids from the toolbit to a substrate, surface properties are controlled by geometrical patterning and chemical modification. Click chemistries provide a facile method to achieve this. Research in the Moore and Shannon groups has demonstrated precise control over surface properties, e.g., Zeta potential.

The Kenis and Shannon research groups have demonstrated control of the liquid fraction transfer between surfaces by geometric modulation of the toolbit surface. Shown below are results for pico-liter transfer of liquid onto a substrate by micromachined posts on the surface of the toolbit.