http://www.digitaljournal.com/tech-and-science/science/4d-printed-materials-as-stiff-as-wood-or-soft-as-sponge/article/546137

4D-printed materials created as stiff as wood or soft as sponge

Posted Mar 25, 2019 by Tim Sandle
Scientists from Rutgers University have engineered new smart materials that can change shape as temperatures change. The potential for materials that can alter shape and texture is considerable.
A molecular Gordian Knot  based on a strand of 192 atoms coiled around a triple loop which crosses i...
A molecular Gordian Knot, based on a strand of 192 atoms coiled around a triple loop which crosses itself eight times. It’s the most complex molecular knot ever created and might usher in a new class of super-strong materials.
University of Manchester
3D printing (additive manufacturing) is well established for creating a range of customizable and flexible materials. The drawback is that the materials are generally lightweight. A more robust process, in early development, is 4D printing which promises to create materials that are tougher, and which have good shock absorption. Such materials may be better suited for the wings of drones or for robotics, and with biomedical devices.
The 4D printing process uses a digital micro 3D printing process with the addition of a shape memory polymer. The output is a material that can undergo reversible changes in relation to its stiffness, geometry, and function. The researchers are terming this output a ‘metamaterial’. This is with reference to materials with more than one property and the fact that the materials are artificial – with ‘meta’ representing ‘beyond nature’.
The objects produced with the material are capable of altering their shape with environmental conditions, such as variations with temperature. The reason that ‘4D’ has been used is with reference to time, with time being the fourth dimension. This is with reference to the materials changing shape over time.
The new technology is a development beyond previous processes where stronger types of 3D printed materials have been created and ones that can morph into different shapes. However, these previous designs were not reversible.
With the new ‘plastic-like’ metamaterials, these can be built so that they remain rigid when struck or alter so they become soft as a sponge to absorb an applied shock. In terms of a practical example, the material could be used to develop a structure that is collapsible for a space launch and which can then be reformed in space to build a bigger structure, such as a solar panel.
The following video shows the development of the material in greater detail:
According to lead researcher, Professor Howon Lee: “We believe this unprecedented interplay of materials science, mechanics and 3D printing will create a new pathway to a wide range of exciting applications.”
He further adds that the material will herald a number of technological improvements to “technology, health, safety and quality of life.”
The new research has been published in the journal Materials Horizons. The research paper is titled “4D Printing Reconfigurable, Deployable and Mechanically Tunable Metamaterials.”