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.