Inkjet printing is familiar as a method for printing ink on absorbent paper. In principle the method can be used to print multilayer devices, but we will then need to be able to control the structure of material deposited onto hard surfaces and to overprint different materials on one another. This paper deals addresses the approaches available to form materials by reaction between successive ink layers. The short diffusion distances allow uniform structures to form instead of interfacial barriers or precipitates that would result on a larger scale. Many aspects of these processes can be compared to those that occur during growth of biological tissues. Thus, biology may be a fruitful source of ideas on how to exploit this technology.
Amine-epoxy based gel actuators have been made since this chemistry allows the small volume gels to be made easily and is expected to provide enough strength for practical use with highly crosslinked networks. In this study, a small drop of cationic polyelectrolyte gel was prepared by crosslinking of trifunctional polyetheramines with ethylene glycol diglycidyl ether. The response of these materials to electrical stimuli, pH and metal ions is controlled by the crosslink density and ionic strength of medium. When the gels contact a platinum anode, positive charges are generated on the amine groups and the ionic repulsion causes the swelling. Reversing current neutralizes amines and the hydrogen bonding interaction causes a volume collapse. These gels show large and rapid swelling in response to an electrical and chemical input on a sub-millimeter scale.