Engineers from Saarland University’s Human Computer Interaction department have designed a soft circuit printing process that can be created by using a conventional inkjet printer. Typically, making soft stretchable circuits is a complicated and time-consuming process that’s limited in the types of materials that can be used. The team has developed a process that allows the printing of circuits that are ultra-thin, stretchable, high resolution, and can be integrated into a myriad of materials for rapid prototyping.
The process is known as multi-ink functional printing, which uses a desktop Epson WF-2010 inkjet printer that supports multi-layer printing of circuits using several different conductive inks, including conductive silver nanoparticle ink, intrinsically stretchable conductive polymer ink, and an electrically isolating ink alongside graphical inks. The different inks are filled into the same cartridges used with the WF-2010 printer, which can be swapped out depending on the desired circuit or stored together inside the printer. It also enables circuits to be printed using a separate top layer with only the necessary parts that require access exposed.
As mentioned earlier, the circuits can be printed onto any number of substrates, including stretchable TPUs (Thermoplastic Urethane Foils), temporary tattoo paper, textile transfer film, and re-shapeable thermoplastic material that can transition from a soft to a rigid state. To demonstrate their printing technique, the researchers designed several devices, including a stretchable input platform, an iron-on t-shirt LED display with artwork, an electronic skin tattoo, and an LED bracelet.
Depending on the application, printing the circuits can be done in minutes rather than hours, which is beneficial for rapid prototyping. The LED bracelet, for example, took 5-minutes to print, 3-minutes to cure, and 2-minutes for assembly. The engineers feel their circuit-printing inkjet printer could benefit makers, researchers, and the DIY community, and would allow users to print personalized interfaces, wearables, and interactive tattoos.