What would happen if manufactured three-dimensional objects were capable of behaving like living organisms, detecting external stimuli such as light, temperature, humidity, and electromagnetic fields, and then reacting and adapting to their surroundings? What would happen if they were able to bend, assemble and repair themselves, or even disintegrate on their own just by changing shape, size, colour, or function? And what if they could then also return to their original state? All of these hypotheses might seem like something out of a science fiction novel, but they are already a reality.
By combining developments in 3D technology with the use of so-called smart materials and then applying a mathematical model that can program and predict their behaviour, all of the above is possible. The best labs and research teams in the world have been working on this superior version of digital printing with the goal of creating self-reliant, three-dimensional objects that are wire- and circuit-free.
Imagine an article of clothing that changes colour depending on its surroundings. Or trainers that transform and adapt to your foot depending on movement and impact. What about a flat piece of furniture that can fold away and open up on its own to save space? Or a car with self-repairing tyres? Or pipes that expand and contract depending on the amount of water flowing through them? Don’t forget about implants that can adapt to the body of a child that is still growing and that will dissolve when they are no longer needed. And then there is the special type of mesh fabric that reflects light on one side and absorbs it on the other, can be folded in many different ways, and that is perfect for astronaut suits, building space antennae, or acting as a shield that protects spacecraft and satellites from the impact of meteorites.
All that and more is what 4D printing is all about. It’s the next big challenge for industrial design, signifying a radical change in our understanding of structures and a revolution that just keeps on evolving. “This is the dawning of a new era and it’s got a lot of potential, but it’s still quite early days,” says Carlos Sánchez Somolinos, researcher at the CSIC (Superior Council of Scientific Research) at INMA (the Nanoscience and Materials Institute of Aragón) where he is head of the Advanced Manufacturing Lab and a member of the CSIC’s Interdisciplinary Subject Platform for the Development of Additive Manufacturing. When it comes to 4D structures, Sánchez Somolinos is one of the most knowledgeable scientists in Spain. He and his team are working on some very promising projects in fields such as biomedicine and soft robotics. Here’s just one example:
The origins of 4D printing
Let’s take a look at how this fascinating story began. Not too long ago, the word ‘printing’ brought to mind pieces of paper with some ink on them being spat out of a somewhat noisy machine. Then, towards the end of the 1970s, 3D printing came on the scene. It was one of the most innovative and disruptive technologies in modern manufacturing. But what is it exactly? Well, it’s a technique that allows for the creation of three-dimensional objects using filaments instead of ink and by adding one layer at a time. This means that the pieces are neither moulded nor held together by screws. Rather, the material being used, be it plastic, ceramic, metal, resin, or even a biomaterial, is deposited in successive layers until the desired object has been created.
Even though 3D technology has come a long way, we are nowhere near having a 3D printer in every home around the world any time soon. Nevertheless, the technique is used quite often in robotics, medicine, and aerospace science, as it allows for unique and very personalised structures to be created. Houses have been built using 3D printing and there are plans to manufacture entire neighbourhoods using this technique. NASA has designed several houses with the hopes of one day building them on Mars. Several artworks, furniture pieces, and toys have been created using this technology. There are even 3D printers with pieces created by other 3D printers.
The time factor
Let’s circle back to 4D printing. Its foundation is digital manufacturing technology, without which it would not be possible. But now there’s a new element that’s been added to the equation: time. With this new dimension (i.e., the fourth ‘D’), three-dimensional objects can be transformed in a dynamic way, without any human intervention. It’s simply a revolutionary concept.
The pioneer of this new and innovative technology is Skylar Tibbits, an American architect, computer scientist, and the founder and coordinator of the Self-Assembly Lab at MIT. He presented it to the world in February 2013 during his TED talk in California, revolutionising the 3D printing market in the process. Tibbits debuted a prototype that added something new to the existing technology, allowing for the printing of objects that were self-assembling and that changed shape over time all on their own.
One of the first things that Skylar Tibbits considered when he was working on this new technique was if it could be used to make smart pipes. Making them in 4D would allow them to change their shape and size depending on the volume of water flowing through them. They would also self-repair whenever there was a leak, meaning you wouldn’t have to go through the much slower and more expensive process of digging them up and changing them. The Lab came up with more ideas, too, some of which were presented at Design Miami in 2017. One of them was Liquid Printed Light, a silicone rubber structure that, as Tibbits explains, is printed in small scale and the is stretched around a light (i.e., the stimulus) to create a much bigger surface, cutting down on both time and materials:
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There was also Liquid Printed Bag, which was made using the same technique and material:
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It’s all in the materials
While the foundation of 4D technology is the process itself, its huge potential is thanks to the materials used to manufacture the objects. Remember that all 3D-printed pieces have one thing in common: once they have been printed, they can’t be changed. They are passive, rigid, and final. “3D objects are very pretty, but they are inanimate, just like plastic, metal, and ceramic,” says Sánchez Somolinos.
But of course, that’s all changing. 4D structures are made from so-called smart materials that contain functional or reactive elements that have been mathematically designed and programmed to respond to specific external stimuli, meaning they can inflate, shrink, fold, move, change shape, and even change colour. They are the definition of adaptable and dynamic objects. Bastien E. Rapp, the director of Neptunlab, a process technology lab at the University of Freiburg, summed it up when he said “4D printing is the functional form of 3D printing. Instead of printing only physical structures, we can now print functions. It’s like embedding a piece of code in a material – once triggered, it does what you programmed it to do”. Sánchez Somolinos agrees. “Yes, in a way it’s as if the objects are alive”.
What materials are available in the world of 4D? Well, there are already quite a few. Some are thermosensitive, while others react to stimuli such as humidity, light, electric currents, and magnetic fields. There still aren’t quite as many as those used for 3D printing, but there are three standouts:
- Shape Memory Polymers (SMPs) can memorise a macroscopic shape, maintain it for a certain period of time, and return to their original shape under heat, without any residual deformation. Electromagnetic fields and water immersion can also produce these transformations.
- Liquid Crystalline Elastomers (LCE) contain heat-sensitive liquid crystals. By controlling their alignment, the desired shape can be programmed: depending on its temperature, the material will relax and transform depending on the programmed code. You can see it in action in the below example from AML:
- Hydrogels are polymer chains made mainly of water. They react when they come into contact with water or humidity and can increase in size by up to 200%. Because of their biocompatibility, they are frequently used in medicine.
What about timber? Is it also a smart material?
Actually, it is. Some 4D printing processes use timber-based compounds to which polymers or hydrogels have been added.
Wood-derived cellulose fibrils derived are also being used. At Harvard University’s Wyss Institute, a team of researchers led by American scientist and materials engineer Jennifer Lewis is using ink made from receptive cellulose hydrogel to create programmable architecture inspired by plants that changes shape when submerged in water, resulting in complex three-dimensional morphologies. These fibres are similar to the microstructures that allow flowers to change shape.
Looking to and replicating nature
This is another key aspect of this new technology and smart materials in general: replicating biology. 4D printing is inspired by plant life. This is called biomimetics, i.e., using nature as a model, measure, and guide to create printed works of shape-shifting architecture that imitate the natural movements of plants. As Sánchez Somolinos notes, “Leaves [and] wood have a series of fibres that aren’t just randomly placed. Rather, they have been perfectly and strategically positioned by nature over millions of years of evolution. I have a small vegetable garden and, in the afternoon, when it’s very hot, the leaves on all my plants shrink in the same direction and, if they’re watered, they stretch out again”. Think about sunflowers and Cornish mallows, who move to follow the sun’s path throughout the day and turn to face the dawn despite the fact that they lack a central nervous system.
Similarly, materials scientist and communicator Anna Ploszajski has explained how pinecones are an example of a natural smart material. They have two rigid fibre layers that run in opposite directions and allow for the cone to open and close. When the weather conditions are right for germination (i.e., when it’s hot and dry), the pinecones open and release seeds; they are ‘programmed’ to do so. However, when it is very humid, they remain closed to protect their seeds:
On the horizon: challenges and opportunities
The experts are saying that the future is 4D. Some research projects are further ahead than others, like the European PRIME project led by Sánchez Somolinos himself. It’s received almost 3 million euros in financing for the development of the next generation of active microfluidic devices using LCEs. These devices will be able to manage small amounts of fluids to carry out biochemical analyses in a simple and faster manner. Pregnancy and rapid antigen COVID-19 tests are the most popular examples of this technology, but there are many other medical, environmental, food, and biotech applications, as well as some in veterinary practice and safety. The ALM team is also involved in another Europe-wide project called STORM-BOTS, which consists of creating smart materials designed for soft robotics that have different potential uses, such as grabbing, moving, and removing. These would be very useful for minimally invasive surgery which would be performed “without cutting into any of the patient’s tissue, allowing for a much safer type of interaction,” says Sánchez Somolinos.
Nevertheless, the majority of the potential applications of 4D printing are still just possibilities. They are yet to be tested outside the lab and continue to be in the experimental phase of research and development. This is one of the biggest challenges facing this innovative technology. “There still isn’t anything commercially available that’s being manufactured and sold on Amazon,” says Sánchez Somolinos.
We know all about the advantages of manufacturing using this technology: the objects are capable of ‘remembering’ their shape; they can change their size after being printed, meaning that larger objects can be printed using smaller printers; and because this method doesn’t generate any waste and uses natural and recycled materials, it’s sustainable. But in order for it to find a place in the market and in large-scale manufacturing (i.e., putting it within reach of the average Joe), it must overcome many technological obstacles. For example, it needs more and cheaper printers that can print multiple materials, as well as more types of smart materials with the right properties that offer appropriate solutions, and are less expensive. Another issue with development is knowing whether or not we can trust these printed objects in the long-term.
Nevertheless, there’s hope that 4D printing will reach new heights in the next few years. It will take a little while for it to achieve technological maturity, but we already know that its potential is unprecedented and, for that reason alone, it’s likely that it will form a part of our daily lives in ways that we can’t even imagine. “We are just starting to get more materials, which are the tools [we need], and to give them morphology and functionality, but there’s still a long way to go in terms of real-life applications. The future is bright,” says Sánchez Somolinos.
What do you think? Will 4D design and 4D-printed structures have an impact on our day-to-day lives in the near future? Share your thoughts with us on social media using #ConnectionsByFinsa.