The team at CityU call the technique 4D printing, adding a time dimension to 3D printing.
Ceramic materials have a high melting point which is why they are used in power designs, but it is difficult to use conventional 3D laser printing to make components with complex shapes. So the CityU team has developed a "ceramic ink" that is a mixture of polymers and ceramic nanoparticles. The 3D-printed ceramic precursors printed with this novel ink are soft and can be stretched to three times their initial length. These ceramic precursors allow complex shapes, such as origami folding, to be built as the elastomers relax. When these structures are heated, the nanomaterials combine to form robust ceramic components with complex shapes.
"The whole process sounds simple, but it's not," said Professor Professor Lu Jian, Vice-President (Research and Technology) and Chair Professor of Mechanical Engineering. "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."
It took more than two and a half years for the team to overcome the limitations of the existing materials and to develop the whole 4D ceramic printing system. The resultant elastomer-derived ceramics are mechanically robust with a high compressive strength-to-density ratio (547 MPa on 1.6 g/cm 3 microlattice), and they can come in large sizes with high strength compared to other printed ceramics.
In the first shaping method, a 3D printed ceramic precursor and substrate were first printed with the novel ink. The substrate was stretched using a biaxial stretching device, and joints for connecting the precursor were printed on it. The precursor was then placed on the stretched substrate. With the computer-programmed control of time and the release of the stretched substrate, the materials