A new ceramic ink has made it possible to print complex, 4D ceramic shapes.

Researchers from the City University of Hong Kong (CityU) have created the first ever 4D printing method for ceramics, which are mechanically robust, feature complex shapes and have a high melting point that makes it difficult to print with conventional laser printers or 3D printers.

Four-dimensional printing is conventional 3D printing combined with the additional element of time as the fourth dimension. With 4D printing, objects can reshape or self-assemble themselves over time with external stimuli like mechanical force, temperature or a magnetic field.

The new ink is a mixture of polymers and ceramic nanoparticles and the 3D printed precursors printed with the ceramic ink are soft and can be stretched three times beyond their initial length, allowing complex shapes like origami folding with proper heat treatment.

The researchers used the elastic energy stored in stretched precursors for shape morphing, so that when the precursors are released they undergo self-reshaping. Heat treatment then turns the precursors into ceramics that are mechanically robust with a high compressive strength to density ratio—547 MPa on 1.6 g cm-3 microlattice.

The new method also allows larger ceramics to maintain high strength.

“The whole process sounds simple, but it's not,” professor Lu Jian, the vice-president of Research and Technology and Chair Professor of Mechanical Engineering, said in a statement. “From making the ink to developing the printing system, we tried many times and different methods. Like squeezing icing on a cake, there are a lot of factors that can affect the outcome, ranging from the type of cream and the size of the nozzle, to the speed and force of squeezing, and the temperature.”

The new printing process could be particularly useful in manufacturing electronic devices, where ceramic materials show better performance in transmitting electromagnetic signals than metallic materials. The ability to create complex ceramic materials also enable consumers to tailor individually designed ceramic mobile phone back plates. 

The new technology might also be a boon for the aerospace industry.

“Since ceramic is a mechanically robust material that can tolerate high temperatures, the 4D-printed ceramic has high potential to be used as a propulsion component in the aerospace field,” Lu said.

Next, the researchers would like to enhance the mechanical properties of the material, including reducing its brittleness.