3D printing has been around for nearly three decades and it captured the imagination of millions of people. Industry, government, and public awareness have reached a “tipping point,” and now recognize 3D printing’s current impact and future potential. Now a new disruptive technology is on the horizon that may take 3D printing to an entirely new level of capability with profound implications for society, the economy, and the global operating environment of government, business, and the public.
4D printing (4DP), has the economic, environmental, geopolitical, and strategic implications of 3D printing while providing new and unprecedented capabilities in transforming digital information of the virtual world into physical objects of the material world. The fourth dimension in 4D printing refers to the ability for material objects to change form and function after they are produced, thereby providing additional capabilities and performance-driven applications.
4-D printing could change our entire idea of manufacturing. Shelters, machines and tools, virtually anything could be printed, then flat-packed and shipped wherever they are needed — disaster areas, perhaps, or prepare them for hostile environments like space or the ocean floor. There, environmental conditions harmful to humans might actually power the object’s changes in shape and properties — not just once, but repeatedly.
Consider how your hair changes shape as a storm rolls in, a simple matter of airborne water causing keratin proteins to form an unusually high proportion of hydrogen bonds, which cause them fold back instead of stretch out. Or think of how a flat inflatable chair assumes a predictable shape as it takes in air because its sections have different properties. Four-dimensional devices do not require the humans hand to build them, nor are they robots that require microchips, servos and armatures to work. Their sole “programming” involves the geometry, physics and chemistry embedded in their structures.
At its core, 4-D printing is a combination of 3-D printing and another cutting-edge field, self-assembly.
“Self-assembly” was originally defined in molecular systems as a process in which molecules or parts of molecules spontaneously form ordered aggregates, usually by non-covalent interactions; examples range from formation of crystals and micelles to formation of complex organic and organometallic molecules by design. Self-assembly is the spontaneous ordering of pieces into a larger, functional whole. Self-assembly already happens at the nanoscale and provides the driving force behind processes ranging from protein folding to crystal formation. We can’t build a molecule-sized machine using the usual mechanical tools. It needs to make do on its own.
In 4D printing, you need some stimuli or trigger to start the transformation. These include water, heat, light, electrical currents. There are other forms of triggers, some of which have to be explored in depth through research. Of course, you need special materials that are able to react to these triggers. Most importantly, you need special materials that are able to react to these triggers. It’s making the objects “programmable” and execute their 3d printed “genetic code” whenever you want to have it triggered.
A major challenge in any 4D printed system is how to design structures that can transform from one arbitrary shape into any another. On the hardware side, this requires complex material programmability, precise multi-material printing and a variety of highly specific joint designs for folding, curling, twisting, linear expansion/ shrinkage etc. On the software front, the challenge is even greater, requiring sophisticated simulation and topology transformation to include the fabrication and material constraints and in the near future, material optimization for efficient structures. Universal transformation is the ultimate goal and the following examples provide systematic advances for a wide variety of applications across products, architecture, infrastructure, biomedical and other industry scenarios.
An example of 4D printed objects that were preprogrammed to respond to a stimulus—water— and change into other shapes is shown in the figure. The figure demonstrates a 1D object morphed into a 2D object— when inserted into water, the snake-like object forms the letters “MIT.”
This figure demonstrate a single strand that self-transforms from the letters “MIT” into the letters “SAL,” a flat surface that self-folds into a truncated octahedron, and a flat disc that self-folds into a curved-crease origami structure.
These experiments were conducted by Skylar Tibbits of the MIT Self-Assembly Lab along with Stratasys, Ltd. and Autodesk, Inc. using Stratasys’ Connex multimaterial printer and a new polymer developed to expand 150 percent when submerged in water. A new application was embedded into the Autodesk software, Project Cyborg, to simulate the dynamics of 4D printed objects and their material optimization.
Another 4D printing technology involves embedding wiring or conducting parts into special compliant components during the 3D printing job. After the object is printed, the parts can be activated by an external signal to trigger full assembly actuation.
This approach has potential implications for areas such as robotics, furniture, and building construction.
Other 4D printing approaches include composite materials that can morph into several different, complicated shapes based on a different physical mechanism and heat activation. Also, demonstrations have been made of materials that self-fold due to light exposure.
4D printing beckons a future where physical and tangibly dynamic structures can be used to understand existing dynamic phenomena. Researchers can utilize self-evolving structures and dynamic models as a test bed for experimenting and discovering new material properties and functional behaviors.
Exciting applications of self-transforming structures can be seen across industries such as; medical devices, sportswear/equipment, aerospace, automotive, marine, defense, construction materials and infrastructure sectors. At extremely large-scales and complex environments, manufacturing and construction can be made easier. Raw materials will be printed on small-volume machines and then self-transform into extremely large functional structures, for eg., space antennae, solar arrays or other non-human constructed space architecture. Building materials may soon be able to adapt to fluctuating environments and dynamically mediate moisture control, sound and temperature with varying thicknesses and active surface treatments.
Although 4D printing is in the early stages of research and development, the possibility of rigid shapes completely transforming themselves into a completely different yet stable structure brings many exciting possibilities. The world is surely not going to be the same when it encounters the full powers of this technology and it is upto us to keep our eyes open so that we benefit from it.