Researchers at Singapore University of Technology & Design (SUTD) along with collaborators at Georgia Tech, have made a breakthrough in the development of 4D printing.
According to researcher Martin Dunn, who spoke with Design News from Singapore, “4D printing essentially involves printing something in three dimensions, then subjecting it to some kind of environmental stimulus, like heat, or moisture that transforms it into a new shape. It could also be looked at as printing with smart materials and then activating those smart materials in some way.”
They key to this new process is the use of a two-component composite material consisting of an elastomeric hydrogel and a glassy thermoset shape-memory polymer.
This was not the first demonstration of 4D printing utilizing shape-memory polymers, but previous iterations required a training step where, according to Dunn, “you had to train them, usually by heating them, then physically deforming them into their desired shapes.”
This new process utilizes computational models to control the way that the two materials, a stiff and a soft material, are printed into a composite architecture in a way that builds in a certain level of compressive strain. This eliminates the training process. It comes out of the printer ready to use, as soon as it has been exposed to the conditions that initiate the transformation into the desired shape.
Says Dunn, “We control the final shape by both the process conditions to which the printed object is subjected, and its internal architecture.” The softer, elastomeric material is what contains the pre-stress, which relaxes when heated, changing the shape of the structure as it achieves equilibrium.
According to the paper, which appeared in Science Advances, “Upon heating, the shape memory polymer softens, releases the constraint on the strained elastomer, and allows the object to transform into a new permanent shape, which can then be reprogrammed into multiple subsequent shapes.”
Applications for 4D-printing materials could include things like patient-specific implantable devices, customized instruments, products that are shipped in a flattened or compressed state, or even UAV designed to change the aerodynamic profile on demand.
Working at what he calls, “the intersection of innovative materials, fabrication methods, and design tools,” Dunn’s team uses modeling and simulation to produce design optimization algorithms to formulate how to create these changeable 3D structures. The models are used to “control and design how to lay out the material,” such that the object will take on the desired dimensions when the elastomeric material relaxes, allowing the more rigid thermoset material to release its internal stress and take on the intended configuration. Mechanical properties such as the amount of pre-load remaining after heating can also be controlled. One example is a flat web-like structure that releases when heated into a dome.
Moving forward, Dunn says they are now using their design tools to produce pencil-sized rods that can self-assemble into complex three-dimensional shapes when heated.