4D printing potential combines smart materials and additive manufacturing

Chameleons can change colour to attract mates, regulate body temperature or warn off intruders. Similarly, the development of smart materials that can change or react to specific environmental stimuli is being combined with additive manufacturing to allow scientists to design objects that can not only change colour, but also change shape, in response to stimuli. Here, John Young, APAC sales director for automation parts supplier EU Automation, looks at what this futuristic technology has to offer to the world of manufacturing.

Most manufacturing processes are subtractive. Whether it is milling, laser cutting or carving, this involves cutting out, removing or subtracting material. Additive manufacturing, or 3D printing, involves adding material layer upon layer.

Originally used primarily for prototyping, 3D printing is beginning to have a profound impact on many manufacturing industries by allowing for more complex designs and reducing waste in the manufacturing process. It has also laid the groundwork for a further technological evolution: 4D printing.

4D printing was coined by MIT architect and computer scientist Skylar Tibbit in 2013. The term is a bit of a misnomer, as 4D printing relies on 3D printing. Rather than adding another dimension, 4D printing offers ‘functionalisation over time’. By combining smart materials with 4D printing, scientists and engineers can 3D print materials that change or modify in response to environmental stimuli. These stimuli might include, for example, temperature, humidity, light or moisture.

From med tech to defence

Objects that have this functionality programmed into them would have enormous benefits and a wide range of potentially transformative applications. Tibbit has stressed the potential of self-assembly, structures that could autonomously assemble themselves under certain conditions. In theory, this would make it possible to erect structures or even entire buildings in places that are usually hazardous or difficult to reach.

Self-adaptability is the next key function that 4D printing promises. Imagine objects or structures that respond to weather conditions for example, by changing shape. This could help reduce costs as fewer parts would be involved in the assembly.

A related function is reversibility. For example, scientists from the Singapore University of Technology have recently made it possible to develop this characteristic without either human intervention or the need for hydrogel. Until very recently, hydrogel was necessary to achieve this outcome, but this lacks mechanical strength and is therefore not suited to load bearing applications.

The final possibility is that of self-repair or self-healing. Imagine implants that can self-heal and thereby limit the need for more invasive surgical procedures, or a leaking pipe on a battlefield that could repair itself without detection or intervention from human beings. The range of possible applications is exciting.

Healthcare is an obvious starting point, with the ability to produce implants or stints that modify in response to certain conditions a fantastic opportunity for medtech. For example, a tracheal stent ─ a tube placed inside a patient to enable breathing ─ could be manufactured with a seal that responds to a certain amount of pressure or water to help keep a patient safe.

Military, aerospace and space applications are also possible. NASA has been developing woven metal fabrics that change shape and are foldable. This could be used for shielding spacecraft or erecting antennae in space. Airbus has been investigating how 4D components could reduce the weight and improve the performance of aircraft.

4D in manufacturing

So, is 4D printing about to revolutionise manufacturing? The short answer is no. We can debate the extent of its potential, but as things currently stand it is a long way from being available in most commercial applications. According to Mordor Intelligence, the 4D printing market was valued at a mere US$62.2 million in 2020.

That market is expected to grow to a more sizeable $488 million by 2026, but there are many obstacles to overcome before 4D printing begins to make a mark on manufacturing in any tangible way.

One obstacle is the limits of smart materials. These are usually made from a limited range of polymers and therefore restricted to specific environmental conditions. It is also difficult to control the speed of transformation with the level of precision required for certain applications. Programming an object to transform is one thing, getting it to transform at the exact right speed is more complicated.

Programming each part and component in a structure is a complex and time-consuming manufacturing process. Furthermore, many of the 3D printers currently available are limited because they can only print 4D structures out of a single material, which further constrains design choices.

According to Tibbit, 4D printing ‘might be the manufacturing technique that allows us to produce more adaptive infrastructure in the future’. For the time being though, the technology is mostly confined to R&D labs and niche innovations in healthcare and defence. So, while manufacturing techniques that produce objects and structures with Chameleon-like qualities are not exclusive to science fiction, manufacturers will have to wait a bit longer before this future tech is widely available for commercial use.