While the fourth industrial revolution promises automation and data exchange in manufacturing technologies, it leaves behind a prudent technology. Along with the cyber-physical systems, Industry 4.0 still clings on to a technology that was devised back in the early 1990s – 3D Printing. Even though 3D Printing remains one of the best manufacturing practices, researchers may have found something that is worthy of replacing it in the near future. Although they are not ambitious enough to boast its flexibility over 3D Printing, it turns out that this technology could be a potential predecessor for it. As mentioned in the title, this technology is called 4D Printing
What is 4D Printing?
4D printing is akin to the 3D printing technology but with an added dimension. This added dimension is time. Not to confuse with JIT Manufacturing, here the intent is to transform a 3D Printing object into a different structure over time, under the influence of an external factor. Hence, to be specific, the fourth dimension is this transformation over time. To put it into perspective, it is almost like robotics without any wires or motors.
For this to happen, we need a different material for manufacturing. Unlike 3D Printing that uses Nylon, 4D Printing technology would require certain smart materials. Therefore, we can represent 4D Printing technology as a combination of 3D Printing, Smart Materials and Preprogrammed design for the required transformation. To clarify, a 3D Printer can be used to design such transforming shapes. Given, they use Smart materials as raw materials.
Raw Material for 4D Printing: Smart Materials
Like mentioned before, it is important for a 4D Printing technology to have smart materials as raw materials. In layman terms, smart materials are those which can change its shape when exposed to a particular environment. A simple example of this would be ferromagnetic fluid(or ferrofluids). Ferrofluids are responsive to magnetic fields. Hence if they are exposed to a magnetic field, they bend, curl and exhibit all sorts of changes with respect to the applied field. For 4D Printing, we use a bit more complex materials. Some examples would be:
Hydrogel: Responsive to moisture/water. It readily absorbs water, hence transforming over time.
Shape Memory Polymers(SMP): SMP is a polymeric material that is capable of returning to its original shape when deformed. It is almost like a boomerang. These materials have a higher scope for production as compared to other smart materials. The reason for this is that it is cheap and has a low density.
Liquid Crystalline Elastomer(LCE): LCE is an anisotropic material that is capable of undergoing a transformation when subjected to external stimuli. This is generally not preferred because of its low response. In addition to that, LCE is only available at a temperature higher than the ambient temperature. Hence making the handling of such materials difficult.
Why does this transformation occur?
Now that it is clear as to how 4D printed structures transform, it is important to note why these occur. In the sense, why is that a material subjected to light changing its shape? To answer this question, it is important to understand the intrinsic properties of such materials.
As far as the Shape Memory Polymers are concerned, the transformation has something to do with its inner crystalline structure. It exhibits a property called a solid-state phase change. It might sound a bit complex. But the crux of what it pertains to is that molecules of SMP are rearranging themselves in a completely reversible way. Thereby allowing the material to spring back to its original shape. Moreover, this reversible transformation wouldn’t be possible if it wasn’t for the material’s closely packed crystalline structure.
Similarly, Hydrogel and LCE would have their internal structure changed, under the influence of external stimuli. For hydrogels, it is the chemical or physical cross-linking of individual polymer chains. LCE, on the other hand, is a bit complex subject. Its transformation heavily depends on the mesogen orientation, which is a subject beyond the scope of this article.
How is 4D Printing different from 3D Printing?
With the inclusion of another dimension, 4D Printing is different from 3D Printing in certain aspects. Firstly, the materials. 3D Printing materials support a wide variety of raw materials. These materials include Nylon, PLA, Plastic, Epoxy Resins and even Silver. 4D printing is limited to smart materials.
The process differs on either of these technologies. In 3D Printing technology, a 2D structure is printed layer-by-layer from top to bottom. This will continue until a 3D volume is achieved. However, in 4D Printing, the product takes its shape after the transformation of a primary design.
For instance, let us assume you’re in need of a cube. If you’re to use a 3D Printer, you’ll need to print the entire folded cube. However, using 4D Printing you’ll only need to print a flat object. This object would then undergo changes when subjected to external stimuli, folding by itself.
Applications of 4D Printing
Even though 4D printing technology is still at its infant stage, there are a lot of researchers working towards implementing it. This implementation would potentially replace all the existing machinery that industry uses.
1. Self-repairing piping system
This is a prominent field of application for 4D Printing technology. Piping systems are tedious to design and maintain. If only these pipes are designed using 4D Printing technology, it would change its diameter in response to the change in flow rate. In addition to that, these pipes will heal themselves in response to the environment. Thereby eliminating the chances of developing cracks.
2. Self-assembling furniture
Although furniture could be easily designed using a 3D Printer, oftentimes its size is limited. This is due to the size of the 3D Printer. To avoid this limitation, 4D Printing technology could be used. For this, a flat surface is printed using smart materials, so that it could transform itself into a chair or table.
4D Printing is a promising technology to develop preventive medicine. It can create drug capsules that release medicine at the first sign of an infection. A medical researcher said: “If we can design these polymers properly, we may be able to form a drug delivery device that will only release medicine at the sign of a fever.”
4. Extreme environments
This is a field that scientists are heavily banking on! 4D Printing technology is capable of manufacturing intricate structures at Extreme environments, or in specific, Space. Scientists have already sent a 3D Printer to Space. As soon as they start using Smart Materials and preprogram it to exhibit certain transformations, 4D Printing technology is within reach.
5. Energy Sector
Shape changing photovoltaic cells is the next big thing in the energy sector. These cells track sunlight, just like how sunflowers face sunlight. This would increase the overall efficiency of the Solar System. Using shape-memory materials as an actuation mechanism would help in tuning the inclination angle of the solar cell. Ultimately, trapping more sunlight, hence more energy!