Other conductive materials can be used to fill the channels. One option that is more biocompatible than EGaIn is ionic liquid, though gradual evaporation of water from the device poses a problem as it affects the ion concentration and conductivity of the liquid.
The Lewis group at Harvard has created a method to directly 3D print conductive circuits into a soft elastomer matrix, using a novel carbon grease-based ink. This enables much more rapid fabrication of complex circuits (Muth et al. 2014).